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QUANTITATIVE
AGRICULTURAL ANALYSIS

EDWARD G. MAHIN, Ph.D.

PROFESSOR OF ANALYTICAL CHEMISTRY IN PURDUE UNIVERSITY

AND

RALPH H. CARR, Ph.D.

PROFESSOR OF AGRICULTURAL CHEMISTRY IN PURDUE UNIVERSITY

First Edition

McGRAW-HILL BOOK COMPANY, Inc.
NEW YORK: 370 SEVENTH AVENUE

LONDON: 6 & 8 BOUVEB.IE ST., E, C. 4

1923

vAD

2338

PRINTED IN THE UNITED STATES OF AMERICA

THE MAPLE PRESS - YORK PA

PREFACE

The time is, happily, past when “ Chemistry for Medical
Students,” “ Quantitative Analysis for Engineers” and similar
titles, indicating treatises on the spoon-feeding of special dishes
of easy chemical cookery to the classes of persons indicated, met
any very general demand on the part of teachers. Even in our
highly specialized chemical science of today and in its enormously
diversified applications to industrial and economic problems, we
recognize the futility of attempting to train students for technical
or professional careers by teaching them only the mechanical
notions and processes of chemistry without the scientific develop¬
ment of fundamentals.

The authors have tried to keep this idea in view in the compila¬
tion of this book. The discussion of special methods (largely
“official,” wherever applicable) for the analysis of materials
of prime importance to chemical students of agricultural mate¬
rials and of agricultural problems forms an important portion of
the book; but we subscribe very heartily to the belief that one
of the things most needed by scientific agriculture today is an
increasing body of agricultural chemists who understand the
importance of desiring to know why matters are thus and so.

The introductory course in general quantitative analysis, in
Part I, deals with a select list of such analytical processes as may
be considered useful for impressing upon the mind of the student
the principles of analytical work, as well as the importance of
exercising intelligence and care in all work of the laboratory.
Bearing in mind the fact that in most college curricula this first
course must necessarily be brief, the typical classes of methods
for a given determination have been treated together. This, in
turn, has involved a preliminary discussion of materials and
methods of both gravimetric and volumetric analysis.

Part II, dealing with certain special measurements, has been
included in recognition of the fact that the highly important

PREFACE

instruments and methods there discussed are too seldom under¬
stood by the chemists who use them in industrial work. In our
own classes we have found lectures upon the theoretical principles
underlying the construction and use of these forms of apparatus
to be of very great value.

In Part III is included a treatment of the six classes of materials
most often considered in courses in agricultural analysis, and
probably of interest to the greatest number of agricultural
chemists. The significance of the results of the analyses, in
connection with agricultural problems, has been given as much
attention as was thought possible, without going outside the
proper scope of a book of this. character. This, it is believed,
will add an interest to the laboratory work and supply a certain
motivation, otherwise largely lacking.

In certain parts of the book we have drawn rather freely upon
portions of another text by one of us. 1 This is particularly true
in the discussion of materials and general operations, of the
analysis of oils, fertilizers and dairy products and of the deter¬
mination of nitrogen. Certain cuts have been borrowed from
the same source, while others are from original drawings, made
by G. B. Wilson.

Problems in analytical calculations have not been included.
Several good problem texts are now available and the authors
believe that a systematic course with one of these, as an
accompaniment to the laboratory work and lectures, is the best
method of impressing this phase of the subject upon the mind
of the student.

E. G. Mahin,

R. H. Carr.

Purdue University,

September , 1922.

1 Mahin, “Quantitative Analysis.”

CONTENTS

Page

Preface. V

Introduction .xiii

PART I

GENERAL ANALYSIS

CHAPTER I

Theory and General Principles. I

Gravimetric analysis—Factors—Factor weights—Temperature
systems.

Volumetric analysis—Adjustment of sample weight—Normal
system—Volumetric factor weights—Decimal system—Stand¬
ardization.

Indicators—“Neutrality” indicators—Hydrogen ion concentra¬
tion—Phenolphthalein—Methyl orange—Methyl red.

CHAPTER II

General Operations. 17

Preparation of samples—Mixing and dividing—Quartering—
Maximum size of particles—The riffle—Sampling liquids—
Dissolving the sample—Fusion—Fluxes—Precipitation—Filtra¬
tion—Washing—Drying—Ignition—Crucibles—Care of plati¬
num—Platinum substitutes—Burners.

Weighing—The balance—Weights—The rider—The chain rider—
Differential weighing—Determination of zero point—Weighing
by the single deflection method—Calibration of weights.

Volumetric apparatus—Specifications—Calibration—C leaning
solution—Calibration of flasks—Of burettes—Of pipettes.

CHAPTER III

Quantitative Determinations.48

Comparative usefulness of different methods—Scope of the .
laboratory work.

Chlorides—Gravimetric by weighing silver chloride—Volumetric
by titration with silver nitrate—Use of a correction factor—
Volumetric by titration with sodium carbonate—Volumetric by
titration with potassium hydroxide.

CONTENTS

viii

Page

Sulphates—Solubility—Crystallization—Change of weight of
barium sulphate—Gravimetric determination—Volumetric by
titration with standard base or carbonate.

Calcium—Gravimetric by weighing calcium oxide—Solubility—
Purity of precipitate—Volumetric by titration with permanga¬
nate—Apparent valence.

Iron—Volumetric by titration with permanganate—Volumetric by
titration with dichromate.

Aluminium—Solubility—Gravimetric determination.

Carbonates—Gravimetric method—Volumetric by use of barium
hydroxide—Alkalinity of carbonates—Alkalinity of limestone.

Phosphates—Gravimetric by weighing magnesium pyrophosphate
—Insoluble phosphates—Volumetric by titration of ammonium
phosp ho molybdate.

PART II

SPECIAL MEASUREMENTS

CHAPTER IV

Density and Specific Gravity. 04

Density—Specific gravity—Baum6 system—Methods for deter¬
mining specific gravity—The hydrometer—The lactometer—

The Westphal balance—Use of the Westphal plummet on an
analytical balance—Applications.

CHAPTER V

Heat of Combustion (Calorimetry). 103

Units of measurement—Apparatus—Emerson fuel calorimeter—
Ignition wire—Formation of nitric acid—Radiation corrections
—Time-temperature curves—Calculation—Determinations.

CHAPTER VI

Index of Refraction.113

Theory—Apparatus—Abb6 refractometer—Dispersion—Butyro-
refractometer—Dipping refractometer—Pulfrich refractometer
—Determinations.

CHAPTER VII

Optical Rotation (Polarimetry;.121

Theory—Specific rotation—The polarimeter—Making a reading—?
Polarizer and analyzer—The Nicol prism—Method of making
observations—Light sources—Quartz wedge compensation and

CONTENTS

Page

the saccharimeter—Light filters—Sugar scale—The Yentzke
scale and the normal weight—The International scale—The
Laurent scale.

The common sugars—Cane sugar—Commercial syrups—Correc¬
tion for volume of precipitate—Direct polarization—Invert
polarization—Beet products—Commercial glucose—Detection
of invert sugar—Determination of commercial glucose in
syrups containing invert sugar.

CHAPTER VIII

Hydrogen Ion Concentration. 138

Methods—The potentiometer method—The indicator method—
Table of indicators—Applications.

PART III

ANALYSIS OF AGRICULTURAL MATERIALS

CHAPTER IX

Feeds ..142

Composition of common feeds—Sampling—Moisture—Ash—
Mineral analysis—Crude fat—Crude fiber—Crude protein—
Nitrogen—Kjeldahl method—Gunning method—Kjeldahl-Gun-
ning-Arnold method—Non-protein nitrogen.

Carbohydrates—Reducing sugars—Determination of reduced
cuprous oxide—Gravimetric method—Approximate volumetric
method—Iodide method—Sucrose—Starch—Diastase method—
Direct acid hydrolysis—Arabin, xylan and pentosans—Galactans.

CHAPTER X

Saponifiable Oils, Fats and Waxes.170

Composition—Separation and identification—Specific gravity—
Index of refraction—Melting point of fats—Iodine absorption
number—Acid value—Saponification number—Soluble and
insoluble acids—Reichert-Meissl number—Butter and substi¬
tutes—Polenske value—Acetyl value—Maumend number and
specific temperature reaction.

Qualitative reactions—Resin oil—Cotton-seed oil—Sesame oil—
Arachis oil—Soybean oil—Marine animal oils—Color reactions.

CHAPTER XI

Dairy Products. 199

Milk—Sampling—Specific gravity—Added water—Use of dipping
refractometer—Acidity—Total solids—Ash—Fat—Paper-coil

CONTENTS

Page

method—Rose-Gottlieb method—Babcock method—Protein
and total nitrogen—Formal titration for proteins—Casein—
Official method—Hart method—Albumin—Lactose—Reduction
methods—Optical methods—Microscopic examination—Borates
—Heated milk—Condensed milk—Sucrose—Powdered milk.

Cream—Fat—Solids—Ash—Nitrogen—Lactose.

Ice cream—Fat.

Butter and substitutes—Adulteration—Sampling—Moisture—Fat
—Casein—Salt—Oleomargerine—“ Nut ” butters.

Cheese—Manufacture—Water—Ash and salt—Fat—Total nitro¬
gen—Acidity—Coloring matter.

CHAPTER XII

Soils.230

Total and acid-soluble matter—Soil constituents—Classification of
plant foods—Value of soil analyses—The report—Potential
plant food—Available plant food—Sampling—Moisture—Opti¬
mum moisture—Total nitrogen—Nitrate nitrogen—Ammonia
nitrogen—Nitrification—Denitrification—Phosphorus—Potas¬
sium—Chlorplatinate method—Perchlorate method—Recovery
of platinum from waste—Organic matter—Carbonate carbon—
Total carbon—Humus—Acid-soluble material.

Other inorganic constituents—Silica—Aluminium—Iron—Calcium
—Magnesium—Manganese—Sulphur—Lime requirements—
Veitch method—Truog method—Thiocyanate method—Hop¬
kins method—Flocculation and deflocculation of clay.

CHAPTER XIII

Fertilizers. 270

Availability—Composition—Compatibility—Sampling—Mechan¬
ical analysis—Moisture—Phosphorus—Availability—W ater-sol-
uble phosphorus—Citrate-insoluble phosphorus—Nitrogen—
Ammonia nitrogen—Nitrate nitrogen—Availability of nitrogen
—Neutral and basic permanganate methods—Potassium—
Chlorplatinate method—Perchlorate method—Centrifugal
method—Pot and field cultures.

CHAPTER XIV

Insecticides and Fungicides. 292

Character as related to insect anatomy—Contact insecticides—
Preparation of insecticides—Compatibility.

Paris green—Total arsenic—Water-soluble arsenous oxide.

CONTENTS

Page

Lead arsenate—Moisture—Lead oxide—Total arsenic—Water-
soluble arsenic oxide—Total arsenous oxide.

Calcium arsenate—Total arsenic.

Lime-sulphur solutions—Total sulphur—Sulphide sulphur—Total
calcium.

Nicotine insecticides—Determination of nicotine.

Bordeaux mixture—Moisture—Carbon dioxide—Copper.

Soap emulsions—Moisture in soap.

Chlor picrin and the poison gases.

Table of Logarithms and Antilogarithms.310

Table of Atomic Weights .Inside back cover.

Index .317

INTRODUCTION

For the most part the operations of analytical chemistry
fall naturally into quantitative lines. This is particularly
true of analysis as applied to agricultural problems because
the qualitative composition of most agricultural materials is
usually fairly accurately known from the nature and proposed
use of the materials themselves.

The qualitative method for the detection of a given element
or compound frequently involves the use of the same reactions
as those that are fundamental to the quantitative determina¬
tion of the same materials and in these cases, especially, it is
most convenient to modify the details of the experiment so as to
make a quantitative determination possible in the beginning,
rather than to repeat the work in this manner after the com¬
pletion of a qualitative analysis. This is not universally true
and there will be occasional instances in which the complete
qualitative analysis will save the labor of quantitative deter¬
mination of elements not present in any significant quantity.

As the name implies, quantitative analysis has for its object
the determination of the quantity (usually, though not always,
expressed as per cent) of the various constituents of a material
under investigation. The constituents determined may be
elements or radicals of a compound, mixture or solution. The
particular method to be used for a given material will be chosen
according to circumstances and, to some extent, according to
individual preference or available equipment. It will necessarily
be modified if interfering substances are present. On this
account it is desirable first to learn a few methods for the quan¬
titative determination of some common elements in pure com¬
pounds and later to apply these and other methods to a more
extended analysis of more complicated materials.

QUANTITATIVE
AGRICULTURAL ANALYSIS

PART I

GENERAL ANALYSIS

CHAPTER I

THEORY AND GENERAL PRINCIPLES

Gravimetric Analysis. —When the quantitative composition
of a material is learned through the direct application of the
analytical balance the method is known as a “gravimetric” one.
In principle the method is comparatively simple. A certain
quantity of the well mixed sample is weighed accurately. It
is then subjected to a series of operations, as a result of which a
certain element or radical is finally separated from other con¬
stituents, either in its simple form or, as is more often the case,
that of a pure compound of known formula. The latter is then
weighed accurately. The two weights thus obtained and the
known composition of the pure compound provide the necessary
data for the calculations.

The determination of phosphorus in a phosphate rock may be
taken as an example. The rock may contain ordinary tricalcium
phosphate, Ca 3 (P0 4 )2, as its chief constituent but it will also
contain varying quantities of other materials, such as clay,
quartz sand, limestone and iron oxide, so that the formula as
given above cannot be assumed to be a correct representation
of the composition of the material. The latter is therefore care¬
fully sampled and a small portion is accurately weighed. It is
then treated with an acid and the insoluble silica and silicates
are removed by filtration. All of the phosphorus is then pre¬
cipitated as ammonium phosphomolybdate, a complex substance
represented by the formula (NH 4 ) 3 P 04 . 12 Mo 03 . This is filtered
out, washed, redissolved and finally precipitated as magnesium

QUANTITATIVE AGRICULTURAL ANALYSIS

ammonium phosphate, MgNB^PO*, which is washed and Mien
changed to magnesium pyrophosphate, Mg 2 P 20 7 , by heating
strongly in a previously weighed crucible. From the weight of
the crucible, with and without the pyrophosphate, the weight of
the latter is found.

Factors. —The formula for magnesium pyrophosphate shows

that it contains 27.87 per cent of phosphorus ( =

Multiplying this figure by the weight of pyrophosphate found
and dividing the product by the weight of sample gives the per¬
cent of phosphorus in the phosphate rock. Stated as a formula:

2 X 31.04 X 100 W
222.72 S

per cent P in sample,

0 )

where W = grams of magnesium pyrophosphate found and
S = grams of sample taken. No matter how many different
samples' of rock or other material might be subjected to this
experimental process, the calculation would always follow the
lines indicated in Eq. (1) and, since the only variables in this
equation are the weights of sample and of pyrophosphate, the
constants may be collected :

2 X 31.04 X 100
222.72

= 27.87 = F.

( 2 )

The quantity F is called a “gravimetric factor” and, since the
procedure for phosphorus as already outlined is an illustration of
the procedure for all gravimetric determinations, this factor may
be calculated once for all for each type of determination and
recorded, together with its logarithm, in a convenient place.
Equation (1) is then a special application of the more general
equation:

F always indicating the per cent of the determined element, or
combination of elements in the weighed pvecipitate , as calcu¬
lated from the chemical formula, and x representing the per cent
of the same entity in the sample analyzed.

As indicated in the preceding paragraph, a combination
of elements (as an oxide or radical) may be calculated. For
example the factor for phosphorus pentoxide would be

100 PsO* = W 208 _ _ Q
Mg 2 P 2 0 7 222.72 63-79 ‘

THEORY AND GENERAL PRINCIPLES

r s

I-

)

Factor Weights. —In Eq. (3) F is a constant for all determina¬
tions of the particular element or group of elements for which
it has been calculated. It is possible to choose the weight of the
sample taken so as to simplify the calculation of this equation.
For instance, by taking a sample weight equal in grams to the
F

value of the factor, ^ = 1 and Eq. (3) becomes:

W=x. (4)

In such a case the weight of precipitate, expressed in grams or frac¬
tions, becomes per cent, or fractions, of the constituent determined.

A weight of sample equal in grams to the value of the factor
is usually too large a quantity to be handled readily and a definite
fraction of this weight (as 0.5, 0.2, 0.1, etc.) may be used instead.
Any such weight is called a “ factor weight/’ which may be
defined as a quantity equal in weight units to the value of the
gravimetric factor, or to some simple fraction of this factor.

Continuing the illustration given above, the factor weight of
sample actually taken would be, for the sake of convenience,
0.6379 gm, in which case the per cent of phosphorus in the sample
would be one hundred times the weight, in grams, of magnesium
pyrophosphate found.

When a Factor Weight Should be Used. —In considering the
actual practice of the operations with the balance it will be
found that the manipulation of the sample to obtain any pre¬
viously specified quantity requires considerable time, if the
weighing is to be done accurately. One cannot judge quantities
accurately by means of the eye and it becomes necessary to
adjust the sample while it is on the balance pan, very carefully by
removing or replacing very minute quantities. On the other
hand, it is a comparatively simple matter to take approximately
the required quantity and to weigh this accurately, using the
figure thus found in later calculations. It may then easily
be seen that all of the convenience and time-saving element
that is involved in the calculations where factor weights (or,
in fact, any other definitely prescribed weights) have been used,
may be more than lost in the time and trouble required for
adjusting the sample weight to this exact value.

For the reason just mentioned it is inadvisable to use factor
weights except in cases where relatively large amounts of sample

QUANTITATIVE AGRICULTURAL ANALYSIS

?nay be used or where no great accuracy is required. In such cases
the sample weight may be accurately and quickly adjusted to
the second or third decimal and the remaining uncertainty will
be relatively insignificant. For example, if a 10-gm sample of
soil is to be used for a nitrogen determination, an uncertainty
of 1 mg in weighing will involve only 0.01 per cent of the total
nitrogen found. But if a 0.5-gm sample of limestone were to be
used for a determination of calcium, this same uncertainty
would amount tO o.2 per cent.

Temperature Systems.—In nearly all scientific work the
Centigrade system is used exclusively for indicating tempera¬
tures and in this book all temperatures mentioned are in Centi¬
grade unless otherwise designated. In some instances the special
agricultural analyst will have to use the Fahrenheit system in
order to conform to established usage. When this is done in the
following pages, the letter “F” will follow the figures indicating
the temperature.

Volumetric Analysis.—The final determination of per cent
by volumetric methods is not made by means of weighing a pre¬
cipitate. The balance is generally used, as in gravimetric
methods, for weighing the sample. The solution of the latter
is then brought into definite reaction with another solution of an
appropriate reagent (a standard solution) until the reaction is
exactly completed. The concentration of the standard solution
is accurately known as a result of a previous analysis (a stand¬
ardization) and the volume required is measured accurately by
means of a graduated burette. The product of the required
volume of the standard solution and its concentration, giving
the weight of the dissolved reacting material, serves as a measure
of the determined constituent of the sample, just as the weight
of the precipitate does in gravimetric analysis, the only difference
in principle being the use of the weight of a reacting body instead
of that of a containing body as a measure of the thing to be
determined. With this exception the calculations will be
similar to those of gravimetric analysis, a titration serving
instead of a weighing.

As an illustration, the determination of sodium hydroxide
in an impure sample may be cited. A weighed quantity of the
material is dissolved and titrated by a standard solution of

THEORY AND GENERAL PRINCIPLES

hydrochloric acid, a drop or two of an appropriate indicator,
as methyl orange or methyl red, being added to show the end
point of the reaction.

If V = cubic centimeters of standard solution required, C —
concentration of standard solution (gm of HC1 per cc), S = gm of
sample used, Eq HCl — equivalent weight (see page 7) of hydro¬
chloric acid (36.468), and Eq KaOH = equivalent weight of sodium
hydroxide (40.008), then

VC— gm HC1 used,
V C Eq,

Eq KC \

100 V C Eq N&OH
S Eq nC [

= gm NaOH in sample used,
= per cent NaOH in sample.

( 1 )

( 2 )

( 3 )

Of course this derivation is based upon the assumption that
sodium hydroxide is the only basic substance present in the
sample.

As in gravimetric analysis it is convenient to collect all of the
constants of the final expression. For all determinations of
sodium hydroxide that are made by means of this particular
standard solution of hydrochloric acid, V and S are the only
variables. The quantity:

C Eq Na oh = 40 .008 C
Eq HC } 36.468

may be called the “base factor” of the acid. This can then be
simplified and recorded upon the label of the bottle. Let this
be designated by F B . Thereafter, so long as this solution is used
for the determination of sodium hydroxide in other samples, the
calculation of the results of titrations will be made by means of
the equation:

--=per cent NaOH. (4)

If the same standard solution is to be used for the determination
of any other base it will be necessary to recalculate the value for
F b for this substance and to use the new value in an equation
similar to Eq. (4). If a new standard solution of a different
concentration is prepared, or if the concentration of the original
standard has changed, a new value for F B is calculated.

t.» ijf A \ Ti 7.1 77 \ K Adh'K I LTI UAL AXALYS1S

Adjustment of Sample Weight. —The volumetric caleul^^ 0]QS

already explained have been made upon the assumption ths^
sample weight was not adjusted to any particular value although
it was. *.if course, accurately determined. In Eq. (4) F& lS a
constant for this particular standard solution in this parti oU-l ar
determination. Therefore if some care is exercised in adjusting
the sample weight. S. so that it will bear some simple relation to
F f; . the calculations will be materially simplified. For exaiXt]pl e >
if „S is made to equal 100 F*, Eq. (4) will become:

r = per cent NaOH. (5)

That is, each cubic centimeter of standard solution used irt
titration represents a weight of sodium hydroxide which is 1
per cent of the sample weight, so that the burette reading becomes
a percentage reading. From this the rule follows:

To make the burette reading a direct percentage reading , tt&& cl
sample weight equal to 100 F s .

In practice it often happens that such an adjustment calls for
a too small weight of sample and it does not then provide for
sufficient accuracy. Ten or one hundred times this weight is
often taken, making 1 cc of standard solution indicate tenths
or hundredths of 1 per cent.

Use of Aliquot Parts.—If the adjustment of sample weight
must be made with a high degree of accuracy it may be that the
extra time involved in the adjustment will not be compensated
by time saved in calculations, in which case such adjustment
will not be desirable. But if relatively large samples may' be
used for the analysis an error in weighing becomes of proportion¬
ately less importance and adjustment may be made more rapidly
and less carefully. These considerations apply as in gravimetric
analysis (page 4).

The use of large samples is rendered practicable by the use of
the principle of aliquot parts. Some simple multiple of the
required weight is taken and the solution is diluted to a definite
volume in a volumetric flask and well mixed. A definite fraction
of this solution is taken for the analysis and the proper factor to
correct for this is used in the calculation of results. For example,
if a degree of accuracy carried to the fourth decimal place is
required in weighing 0.3943 gm for a single analysis, ten times

THEORY AND GENERAL PRINCIPLES

this weight, or 3.943 gm may be weighed to only the third deci¬
mal place, the same number of significant figures being determined
in the two eases. This sample may be weighed much more rapidly
than the first. One solution of sample thus serves for several
different titrations.

The principle of aliquot parts is of service also in the analysis
of materials that are not homogeneous and that cannot be mixed
readily, the larger quantity being more nearly representative
than the smaller one and the mixing being accomplished after
the weighed sample has been dissolved.

Normal System.—In case it is possible to apply a given stand¬
ard solution to the titration of a number of different substances
(as a standard acid for various bases or a standard base for various
acids), there is a certain convenience to be derived from adjusting
the concentration of the standard so as to make F B equal to one-
thousandth of the equivalent weight of the substance determined,
or to some other simple fraction of the equivalent weight, as
0.002, 0.0001, 0.0005, etc.

The “ equivalent weight” of any element or group of elements
is the number of weight units of this entity that is chemically
equivalent to eight weight units of oxygen. In the case of elements
this is the combining weight. In all cases the equivalent weights
compose a series of relative weights of the various chemical
entities, chemically equivalent to each other in reacting power.
From this definition it is obvious that if F B is to be made
equal in grams to one-thousandth of the equivalent weight of
the substance determined (or 1 milligram-equivalent), 1 cc of
the standard solution must contain 1 milligram-equivalent of the
active constituent. A solution of this concentration is a normal
solution and the following relations are consequences of the defini¬
tions discussed above:

(а) One cubic centimeter of any normal solution is equivalent
to 1 milligram-equivalent of any substance.

(б) One cubic centimeter of any normal solution is equivalent
to 1 cc of any other normal solution.

Normal solutions are too concentrated to allow a very high
degree of accuracy in analytical work and it is more often desir¬
able to use half-, fifth-, tenth- or even hundredth-normal solu¬
tions for accurate work. The relations existing between solutions

o' a\ i n a rivi: aokhvltuhal axalyms

of various liunualnies n ill he seen from relations (a) and ( b )
a I»«iv«*.

Volumetric Factor Weights.—If tlie rule given on page 6
for making the burette reading a percentage reading is followed
when u>ing the normal system, the result is the volumetric factor
weight of sample. This, of course, becomes one-tenth of the gram-
pqui valent of the element or compound determined in the sample.

Decimal System.—A further simplification may he made by
adjusting the standard solution until each cubic centimeter is
equivalent to a simple fraction of a gram of the substance to be
titrated, instead* of to a simple fraction of a gram-equivalent
as in the normal system. One cubic centimeter of a standard'
iodine solution might then be equivalent to 0.005, 0.002, 0.001,
etc., gm of sulphur. This results in a very much simplified cal¬
culation and a further saving of time is accomplished by using
a sample weight which bears a simple relation to the equivalence
of the standard. In the case just noted the sulphur sample
might be used in portions of 0.5, 0.2 or 0.1 gm, or of ten times
these weights. Then 1 cc of standard solution would indicate
1 per cent or 0.1 per cent of sulphur.

Such solutions as these are frequently made for technical work
in industrial laboratories, where large quantities of standard
solutions are required for the titration of a single constituent of a
large number of samples. Mention may be made of the use of
potassium permanganate or potassium dichromate solutions for
the titration of iron in ores, of sodium thiosulphate for the titra¬
tion of copper in ores or available chlorine in bleaching powder
and of potassium ferrocyanide for the determination of zinc.
In fact any standard solution may be made in this system and it
should be so made if its use is to be limited to the determination of
one substance.

Standardization.— Thus far we have dealt only with the calcu¬
lation of the results of volumetric analysis, assuming that the
standard solution was ready for use in the experiment. The
determination of the exact concentration of the standard solution
is called “standardization.” The details of the experimental
work will be treated later and will be mentioned here only so
far as they may serve to illustrate the methods used in the
calculations.

THEORY AND GENERAL PRINCIPLES

Standardization may be accomplished h^gne br y

general methods: A ^

Direct Weighing.—The active substance ^of^th^solution is^
accurately weighed and dissolved so as to make a^e%^^yol5p%;
of solution. The method is applicable to only subh^^pances
as may be obtained in a pure state or in a state of uniform and
accurately known composition. Most of such materials are
crystallized salts or acids, or soluble gases.

Weighing a Substance Produced by a Measured Volume of
the Solution.—Sulphuric acid solution may be standardized by
adding an excess of barium chloride to a measured volume of
the solution. From the weight of barium sulphate found the
weight of sulphuric acid may be calculated. Similarly hydro¬
chloric acid solution may be standardized by adding silver
nitrate to a known volume of solution and weighing the silver
chloride produced.

Measuring the Volume of Solution Required to React with
a Known Weight of a Substance of Known Purity.—An acid may
be allowed to react with a pure carbonate and the required
volume noted. Sodium thiosulphate may likewise be titrated
against a weighed quantity of iodine or (indirectly) against
a weighed quantity of arsenic trioxide.

Titration against Another Solution Which Has Already Been
Standardized.—This method is very much used in the laboratory.

Primary Standards.—It will be noticed that in each of these
cases there is some substance of known composition which is
measured or weighed and the solution is somehow compared
with this for standardization. This substance of known com¬
position is called the “primary standard,” whether it be the
substance dissolved in the solution, something produced by the
solution or something reacting with the solution.

The following examples will illustrate the methods of calcula¬
tion in each of the cases discussed.

1. The method of calculation for the first method of stand¬

ardization is self-evident. The normality is equal to the ratio
of the number of grams dissolved in 1000 cc to the number of
grams in 1000 cc of a normal solution. That is,

normality =

gm per 1000 cc
equivalent weight

JO v r -l-Y 777.1 7717: AGRICULTURAL AXALYSIR

2. A solution of hydrochloric acid was 8tandardi^ ed

precipitating The chlorine from 40 cc as silver chloride- e

weiglit of silver chloride found was 0.6327 gm. Requir eC *’ e
normality of the solution.

1 cc acid solution c= gm silver chloride.

1 cc normal acid solution c= 0.1433 gm silver chloride.

, ... 0.6327; 0.6327 1 t o7N.

Therefore normality = —— 0.1433 - 40~X 0.1433 U '

To make the solution decinormal 1000 cc would be diluted to

1107 cc.

3. A similar solution was standardized by titration of pure
sodium carbonate in presence of methyl orange, the following
reaction being completed:

Na«C'0 3 + 2HC1 —»2NaCl + H»C0 3 .

It was found that 32.2 cc acid = 0.1638 gm of the primary
standard, sodium carbonate. Required the normality.

1 cc acid = gm sodium carbonate and

1 cc normal acid = 0 = 0.053 gm sodium carbonate.

Therefore normality = 32-2 'xf 0 f>3 = °‘ 9598

4. Another acid solution was standardized by titration against
a measured volume of standard potassium hydroxide solution
in presence of methyl orange according to the equation:

HC1 -f KOH —» KC1 + H 2 0.

One cubic centimeter of the primary standard contained 0.00468
gm of potassium hydroxide. It was found from the titration
that 50 cc of potassium hydroxide solution c= 43.5 cc of
hydrochloric acid solution.

The weight of potassium hydroxide in 50 cc of solution =
50 X 0.00468 gm. Since this weight was equivalent to 43.5
cc of acid, the potassium hydroxide equivalent to 1 cc acid =

50 X 0.00468

"43.5- gm

50 X 0.00468

tion =

43.5 X 0.0561

The normality of the hydrochloric acid, solu-
= 0.095 N.

THEORY AND GENERAL PRINCIPLES

In case the primary standard is a solution already standard¬
ized in the normal system the normalities of the solutions
are inversely as the respective volumes that are equivalent to
each other.

5. Thirty cubic centimeters of ^ sodium thiosulphate solu¬
tion is found by titration to be equivalent to 29.8 cc of iodine
solution. The normality of the latter is required.

Thi 3 is Sl'H- 1007 W

If solutions are to be standardized in the decimal system
the calculations involve nothing more than finding the weight of
the substance in terms of which the standardization is to be ex¬
pressed, equivalent to 1 cc of the solution which is being stand¬
ardized, always using as the starting point the known weight of
the primary standard.

In many cases the standardization is to be expressed in
terms of the primary standard itself. For example, iodine solu¬
tion is to he standardized against pure arsenic trioxide and
expressed in terms of the same substance. Here we have the
very simple method of weighing a- suitable amount of arsenic
trioxide, then dissolving and titrating by the iodine solution.

Then

1 cc iodine solution o —

cc I-solution

Other familiar examples of this class of methods are the
standardization of permanganate solutions against oxalates or
against elementary iron or antimony for obtaining the weights
of these elements equivalent to 1 cc of the solution.

The following example will serve to illustrate the first case
just discussed:

6. A solution of potassium permanganate was standardized
against sodium oxalate as follows: 2.5340 gm of sodium oxalate
was dissolved and the solution was diluted to 1000 cc. Twenty-
five-cubic centimeter portions were titrated and gave an average
of 24.25 cc of potassium permanganate solution equivalent to
the oxalate solution used. Required the weight of iron and of
calcium equivalent to 1 cc of permanganate solution.

’2 t^'AMITATIVK AGRlcriTURAL AXALYSIS

Twenty-five cubic centimeters of the oxalate solution contained

0.025 X 2,5340 gm and 1 cc of permanganate solution is

. , 0.025X2.5340 , ,. ^ Th -

equivalent to-- gm of sodium oxalate, xms

1A.10

weight, multiplied by the ratio of the equivalent weight of iron
or of calcium to that of sodium oxalate, will give the weights
of these substances that are equivalent to 1 cc of the standard

solution. Then

0.025 X 2.5340 XJ35.88
24.25 X 67.005

0.025 X 2.5340 X 20.035

1 cc solution --

= 0.00218 gm Fe

X 07.005-"- * °- 00078 *“

Indicators.—Any substance that is used to show the end
point of a definite reaction is an “indicator.” The indicator
may do this by a change of color in solution or by the appearance
of a precipitate. In some cases the standard solution itself or
the substance titrated may act as indicator. A familiar example
of this is the oxidation of iron by potassium permanganate. As
long as any ferrous iron is present the intensely colored per¬
manganate is reduced to practically colorless manganese salts
but the least drop of permanganate in excess colors the solution
and indicates the complete oxidation of all iron present. In
this ease, as with other color changes and precipitations of in¬
organic compounds, the reaction at the end is definite and well
understood.

Neutrality” Indicators.—The indicators that are used to show
neutrality points in reactions of acids and bases with each other
are usually organic and their color changes are reversible as the
point of neutrality is passed in either direction. The color
change is due to a change in molecular structure which, in turn,
is in equilibrium with hydrogen or hydroxyl ions present in the
solution.

Hydrogen Ion Concentration.—The volumetric titration of
acids with bases, or conversely, is a process of neutralization.

I his is the production of a condition where neither hydrogen nor
hydroxyl ions are present in more than very slight and negligible
excess. Neither of these ions can be absolutely eliminated from
any aqueous solution. Both must be present and in such propor-

THEORY AND GENERAL PRINCIPLES

tion that the p'oduct of their concentrations is a constant, 10“ 14
gram-ions per liter. This product is a very small quantity and
it is obvious that an acid solution (essentially a hydrion solu¬
tion) must contain extremely minute quantities of hydroxylion,
while basic solutions contain considerable concentrations of
hydroxylion and correspondingly little of hydrion. At the
Cl neutral point” the ion concentrations are equal, so tha t each
of these two ions is present to the extent of 10“ 7 (=\/l0” 14 )
gram-ions per liter. This is the relation for pure water also and
it is expressed as follows:

[H 4- ] = [OH"] =10“ 7 , (1)

[H + ]X[OH~] =K^= 10 -14 . (2)

Since Eq. (2) expresses a condition existing in all aqueous
solutions of electrolytes, it will be seen that the concentrations
of the essential ions of acids and bases cannot be independent but
that they must vary inversely, so that both “acid” and “ basic”
conditions might be represented in terms of either one of these
ions. Following the suggestion of Sorensen the expression
—log [H + ] is used for this purpose and the symbol P H * is used
to indicate this quantity. This symbol has been variously
modified to pH or P H . So long as ion concentrations are ex¬
pressed as powers of 10, as above, P H will be the same as the
negative exponents of 10. Reference to Eq. (1) shows that the
neutral condition will he expressed by the statement

P H = 7 (strictly, 7.03 at 20°). (3)

For acid solutions P s is always less than 7 and for basic solutions
it is always greater than 7.

Et has already been remarked that indicators are themselves
acids or bases, as in solution they yield hydrion or hydroxylion,
or both (amphoteric indicators) and the concentrations of these
ions are definitely related to the equilibrium concentrations of
the tautomeric forms of the indicator, finally responsible for the
color changes. Therefore the color changes of the indicator will
follow the change in the value of P H as neutralization of the
solution is approached.

The use of indicators for the determination of actual hydrogen
ion concentration has been highly developed and this use finds a
wide application in many fields of applied chemistry. This

qvastjta nvi: m;uhtlti'i:al a.xalysls

*>f tin* i> briefly treated on pages 13S to 140. How'-

ever. we should m»te here that in making titrations in analytical
chemistry we arc usually not concerned with existing ion con -
ft-titrations, but rather with total ionizable or tit ratable hydrogen
<j r hydroxyl. In other words, we seek complete calculated
neutrality, with chemically equivalent quantities of titrated and
titrating substances present, rather than what might be called
electrolytic neutrality, where P H equals 7.

0 10 20 30 40 50 60 TO SO SO W0 110 120 130
%-eq. of base (or ac5d ) added b 100 m^.-eq.ofaci’d (or base)

titratioa curves. Indicator ranges are: 1-Thymol blue* 2-

MJsmsxs **- «««*—

The curves shown in Fig. 1 illustrate the variation of P u
values as titration proceeds, in a few typical eases. As the
t.trating standard is added to a definite quantity of the titrated
substance, the value for P B changes with regularity. Two essen¬
tial conditions must obtain, in order that a sharp end point may
!*> observed. These are (a) that the neutralization curve must
show a steep inclination at the point of equivalent neutrality

idd; lr r L Sllght m f 6aSe ^ the am0Unt of sta *dard solution
added shall produce a relatively large change in hydrion concen-

rahon at this point) and (6) that the range of P* over which the

THEORY AND GENERAL PRINCIPLES

indicator changes color must include some portion of this steep
part of the curve and no other portion. The curves shown in
the figure for the “strong ” acids conform to condition (a).

In the curve for the neutralization of carbonic acid there is a
comparatively sudden break near the point of half neutraliza¬
tion. This corresponds to the formation of sodium bicarbonate:

HoC0 3 + NaOH -> NaHC0 3 + H 2 0.

Any indicator whose color change covers only this portion of the
curve will make a titration possible. Phenolphthalein, with a
Ph range of 8.3 to 10, will serve for this purpose if the first appear¬
ance of pink (at the P H value of 8.3) is taken as the end point.
This point is, of course, not as sharp as could be desired. No
indicator can be found that will give a sharp change with equiva¬
lent quantities of carbonic acid and a base, because of the gradual
slope of the neutralization curve at this point.

Examination of the curves for boric and phosphoric (weakly
ionized, polybasic) acids will show why these acids cannot be
accurately titrated. The curve for boric acid shows a faint
inflection at the point representing neutralization of the first of
the three hydrogen atoms, but this would involve only a very
gradual change in color of any indicator that would cover this
range of P H values. The case is quite similar for phosphoric acid.

Only a few of the common indicators are necessary for ordinary
titrations in analytical work and three of these will be described
briefly.

Phenolphthalein.— This compound is a white crystalline
powder, almost insoluble in water but soluble in alcohol. For
use in volumetric analysis a solution of 5 gm in 1000 cc of 50-
per cent alcohol is suitable. One drop of this solution is sufficient
for 100 cc of solution being titrated. The range of color change
is P H = 8.3 to 10.0.

Phenolphthalein is a derivative of phthalic anhydride and the
solution contains two forms in equilibrium:

CO COO

C 6 H 4 <^):0 C 6 H 4 / +H

C = (C 0 H 4 OH) 2

c=c 0 h 4 =o

\c«h 4 oh

QUANTITATIVE AGRICULTURAL ANALYSIS

The second form predominates in basic solutions and the group
[ = CeH 4 =] is in some way responsible for the red color. The first
form is colorless and predominates in acid solutions.

Methyl Red. —This dye is p-dimethylaminoazobenzene-o-
carboxylic acid:

(CH 3 ) 2 N - C 6 H 4 -N=N - C 6 H 4 C0 2 H.

The indicator solution is prepared by dissolving 1 gm of the solid
in 100 cc of 95-per cent alcohol. The solution is pale yellow iq
basic solutions and violet red with acids. It is especially good
for the titration of ammonium hydroxide and the alkaloids, all
being weak bases. It cannot be used if much carbonic acid is
present, hence is useless for the titration of carbonates. The
color range includes P H = 4.4 to 6.0.

Methyl Orange. —The methyl orange of commerce is the
sodium salt of a sulphonic acid:

(CH 3 ) 2 N-C 6 H 4 -N=N-C 6 H 4 S 03 Na.

This is a yellow substance which forms a yellow solution in
water. In presence of acids the salt is decomposed and a red
form, previously existing in equilibrium, now predominates. The
color range includes P u = 2.9 to 4.0.

A water solution containing 0.5 gm in 1000 cc is used as
indicator in volumetric analysis. A single drop is usually
sufficient to give a perceptible color to 1000 cc of solution.

The three indicators described above practically cover the
range of hydrogen ion exponents from 2.9 to 10, with the excep¬
tion of a gap between 6.0 and 8.3. This fact makes unnecessary
the employment of indicators other than these three for the
great majority of volumetric analyses, even when quite weakly
ionized acids or bases are being titrated. It is nearly always
possible to choose a strong electrolyte for the standard solution
and one of these indicators will then generally serve to cover the
portion of the curve that represents equivalent neutrality. The
number of indicators that have been proposed and used for
analytical purposes is very large. Many of these are useful for
the determination of existing hydrogen ion concentration and
these will be mentioned in a later chapter (page 139). 1

1 For an exhaustive discussion of the whole subject of indicators see
Prideaux: “The Theory and Use of Indicators.”

CHAPTER II

GENERAL OPERATIONS

Preparation of Samples. —The object of all preliminary work
with samples is to make it possible to obtain, for the actual analy¬
sis, a portion that shall truly represent the average composition
of the entire material at hand. This matter is likely to be treated
lightly by the beginner, but proper sampling is often one of the
most difficult problems of quantitative analysis. It is often
necessary to use a quantity of 1 gm or less and if the substance
is not homogeneous this small quantity may have an average com¬
position that is very different from the average composition of
the entire material being investigated. No matter how carefully
an analysis may be performed or how accurate the results ob¬
tained, if the substance used does not represent the average of
the substance originally at hand the results become nearly or en¬
tirely valueless. If the substance is practically homogeneous the
operation of sampling involves nothing more difficult than grind¬
ing down to a degree of fineness required for the work. This is
the case when the substance is an approximately pure chemical
compound, such as will be used for the earlier exercises.

The gross sample, as the analyst receives it, may be in the
form of lumps, as is frequently the case with minerals, or it may
be in the form of small pieces, crystals, powder, or solution. In
any case except that of liquid samples, the object is to reduce the
size of pieces to that required for the analysis (usually a rather
fine powder) and at the same time to select from the total mass
such a quantity as is required for the experimental work. The
original sample is often quite large. It is obviously unnecessary
and practically impossible to grind the entire amount into a fine
powder. The operation then resolves itself into a thorough mix¬
ing and progressive grinding and dividing. Many forms of
both hand and power grinders are in common use. For the first
exercises nothing more complicated than a porcelain mortar and
pestle will be required.

QUANTITATIVE AGRICULTURAL ANALYSIS

Mixing and Dividing.—The mixing and dividing is best carried
out by using a sheet of oilcloth or paper and a spatula. In many
laboratories it is customary to use oilcloth, particularly for mixing
minerals. This is convenient but offers the possibility of con¬
tamination (“salting”) of one sample by the remnant of one that
has preceded it. It is better to use a large sheet of tough, flexible
paper, which can be discarded after using. The sample, after
having been broken down to the proper maximum size of pieces,
is placed on the paper and thoroughly mixed by rolling diagonally
across the paper and alternating the direction of rolling as illus¬
trated in Fig. 2. The proper rapid manipulation of the paper is

Fig. 2.—Manipulation of paper for mixing samples.

attained only after considerable practice. One precaution is
essential: the corner of the paper that is lifted must be drawn
across, low down , in such a manner that the pile of material is not
caused to slide along the paper but is turned over upon itself so
that the bottom is brought entirely to the top. In this way only
can a segregation of larger and smaller particles be prevented.
Since the larger and smaller particles usually have different com¬
position it is essential that they should be thoroughly mixed.
The number of times that the sample is rolled before dividing will
depend upon the degree of homogeneity and the accuracy
required in the analysis. In the assaying of gold and silver ores
it is not unusual to require one hundred times.

GENERAL OPERATIONS

Quartering.—When the first mixing is finished the pile is
made approximately circular and it is then divided, by means of a
spatula, into quarters. Opposite quarters are carefully scraped
to another sheet of paper, ground finer if necessary, remixed and
quartered as before. This process of grinding, rolling, and quar¬
tering is continued until a sample is finally obtained, small
enough in quantity and fine enough in texture to serve the pur¬
pose of the final weighing and analysis.

Maximum Size of Particles.—The maximum size of particles
to be allowed in any particular mixing and quartering will depend
upon the total quantity of material being handled in this opera¬
tion. No particle should be so large that its inclusion in any
quarter would cause the average composition of this quarter to be
appreciably different from the average composition of the entire
pile. This means that the ratio of the size of the largest particle
to the size of the quarter should not be greater than a certain
maximum value. What this maximum value shall be must be
arbitrarily determined by the nature of the sample and the degree
of accuracy required in the analysis. It is obvious that the part
can perfectly represent, in composition, the whole only when
the largest particle is infinitesimal. It is equally obvious that
this limit is impossible and unnecessary in practice and we may
say that, in general, the ratio of the largest particle to the portion
that includes it should not be greater than 0.01 per cent. If this
condition is met, then, after thorough mixing of the sample, the
chance inclusion or exclusion of any given particle cannot modify
the results of the analysis to any appreciable extent.

Other Considerations.—The maximum size of the particles to
be obtained in the final portion that is to be weighed and used in
the analysis must be determined, not only from the above con¬
siderations, but also by the nature of the operation to follow the
weighing. This is usually solution or fusion. If the substance
is considered to be almost absolutely homogeneous and if it is
easily soluble (as, for example, a crystal of cupric sulphate) then
the grinding need be carried no farther than is necessary to per¬
mit the easy adjustment, between fairly narrow limits, of the
weight taken for analysis. In such a case, if a sample of 0.3 to
0.5 gm is required, then no particle should weigh more than
about 0.1 gm. If, however, the process of solution or fusion is a

QUANTITATIVE AGRICULTURAL ANALYSIS

difficult one to accomplish or if the material is far from being
homogeneous, the grinding is carried much farther, in order to
provide a very large surface of contact between the particle and
the solution or flux, or in order to conform to the rule of maxi¬
mum size of particles, stated above. In many cases, as with
minerals, the maximum size of particles is fixed by causing the
sample to pass through a sieve having meshes of stated dimen¬
sions. A gold ore may be ground to pass a sieve having 100 or

200 meshes to the linear inch. In such a case one should not
make the mistake of grinding and sifting a portion until a suffi¬
cient quantity is passed, discarding the remainder. This would
cause an error because the particles that resist grinding longest
are less brittle and have a composition different from that of the
particles which pulverize easily.

(1 EX Kit A I, OPERA TIOXS

* to
.lihI
ixi-
f ith
the
en-
) or

ict

ffi-

ild

Effect of Quartering.—The reason for dividing into quarters
after each mixing and for selecting opposite quarters will he
understood from the following: ('lose examination of the pile,
of uninixed material will reveal the fact, that, oven after the most
thorough and careful mixing, it is not entirely homogeneous.
Around the circumference of the base the particles are courser
and they may be gathered toward one side. Around the apex of
the conical pile there is a
collection of coarsen* parti¬
cles. If we simply dig in
at random for the portion
to be removed the lack of
homogeneity will alter the
character of this portion.

Figure 3 shows how the
opposite quarters, no mat¬
ter in what direction the
cuts be made, will obtain
the average of a non-
homogeneous pile, while a
cut into halves will do so
only in case the cut is made
in the direction ah. In
these* diagrams the condi¬
tions are purposely exag¬
gerated.

The Riffle. Various
forms of semi-automatic
sampling devices arc* in use, designed to carry out. the* mixing
and dividing process without laborious hand work. The riffle
is one of these. As shown in Fig. 4 this consists of a hopper,
at the bottom of which are placed several narrow chutes, so
arranged as to transfer alternating adjacent portions of the
crushed material to opposite sides and into separate pans (not
show'n in the illustration). This will have* approximately the
same effect as would cutting the pile of material into vertical,
narrow sections, alternate portions being united so that, the pile
is finally halved. The riffle* may be made* of any convenient size,
to handle large* or small samples.

QUANTITATIVE AGRICULTURAL ANALYSIS

Sampling of Liquids—In case the substance to be analyzed
is a liquid the operation of sampling is usually a simple one.
consisting of thorough mixing before the removal of the proper-
quantity for analysis.

Dissolving the Sample.—After the sain phi of substance
has been properly selected and weighed the next operation is
usually one of solution. What the solvent shall be is determined
by the nature of the sample and by the character of the opera¬
tions subsequently to be performed. Water may be used,
or concentrated or dilute solutions of acids, bases or salts,
organic solvents or solid substances used as fluxes by beating
to high temperatures. In case gravimetric methods an* to be
employed it is desirable to use a relatively small quantity of the
solvent, not only because it must finally be entirely removed,
but also because all precipitates dissolve to some extent and it is
only by keeping the amount of solvent down to the least (plant it y
that is workable that the loss of precipitate is reduced to tin*
minimum.

Fusion.—For the purpose of quantitative analysis the fusion
of materials is almost always accomplished with the end in view of
producing more soluble substances through the interaction of
an added agent, called a flux, and the refractory material.
For instance, most of the natural silicates are practically insoluble
in water and all ordinary reagents and therefore they cannot
be analyzed by ordinary methods. By a preliminary heating
to a high temperature in contact with a basic substance like
sodium carbonate, a fusible mixture of new compounds is formed
and these will, for the most part, be soluble in water and hydro¬
chloric acid so that the solution may be submitted to precipita¬
tion and filtration processes for the separation and determination
of the elements. Similarly, refractory and insoluble metallic
oxides may be heated with sodium pyrosulphate with the forma¬
tion of a fused mass consisting of soluble sulphates of the metals.

The necessary qualities of any useful flux are (1) that it must
be of such a nature as to be capable of reacting wit h the refract ory
body when heated with it and (2) that the resulting compounds
shall fuse at the prevailing temperature. To those the analyst
adds a third requisite: (3) that the resulting compounds shall
be soluble in water or in the laboratory reagents. The first

OENERAL OPERATIONS

ion is mot by choosing as the flux a substance of-opposite
t o that of the refractory sample. That is, if the latter is
iel<l nature (as silica and poly silicates) the flux should be
and conversely.

bility. No general statement can be made with regard
relative fusibility of various compounds, as based upon
emioal composition of these compounds. It may be noted
efractory silicates arc usually made more readily fusible
uoing the ratio of silica to metal oxide through the intro cluc-
: more metals, particularly of the alkali metals. Both of
>oints are made by using alkali metal carbonates as fluxes,
‘ho not result of the reaction at high temperatures is to
■arbon dioxide and to combine the alkali metal oxide with
Fraetory silicate. This will explain why these carbonates
nost always chosen as fluxes for silicates. A reaction such
following may occur when orthoclasc is fused with sodium
nito:

lSi»<) 8 4-. r )Na 8 C0 3 -^K,Si0,+5Na a Ri() 8 +2NaA10 a +6C02,

n or less complicated mixture of aluminates and silicates
alkali metals being formed.

ic Fluxes. —Sodium carbonate, potassium carbonate and
u-potassium carbonate are the most important of the basic
that are used for analytical purposes. These are used
' for fusion with silica and the refractory silicates. Such
as calcium oxide, used for fluxing silicates in the blast
e for iron, are of little use for analytical purposes, partly
«e the resulting compounds are not soluble and partly
-to metals that are to be determined in the sample are
need by the use of such materials.

I Fluxes. -Fluxes of an acid nature are valuable chiefly
ming fusible, soluble compounds when heated with metallic
or salts that are over-saturated with metallic oxides. The
isof ill of such fluxes are the pyrosulphates and the biborates
ium and potassium.

1 sulphates are often used instead of pyrosulphates. When
iner are heated they give off water and they arc completely
rted into pyrosulphates by heating to higher temperatures:

2NaHS0 4 -> Na 2 S 2 () 7 + II 2 0.

Q UA NT IT A TIVJH AGR1CVLTURA L A NA L VS/S

Because of the excess of sulphur trioxide in the pyrosulphate,
this readily reacts with metallic oxides when heated with the
latter:

Fe 2 0 3 + 3Na 2 S 2 0 7 -> 3Na 2 S0 4 + Fo 2 (S< ><):<•

The biborates likewise combine with metallic oxides because
of their excess of boric anhydride.

Fe 2 0 3 + 3Na 2 B 4 0 7 —* 2Fc(B0 2 )a + GNaBO.,.

Precipitation. —The process of precipitation is usually a
chemical reaction between substances in solution, the result being
the production of another substance of relatively small solubility.
The actual precipitation is always preceded by a condition of
supersaturation (with respect to the precipitating substance)
and this breaks down at different rates with different precipitates.
In some cases equilibrium between the precipitate and the satu¬
rated solution of the same substance is attained only after the
lapse of considerable time, while in other cases such equilibrium
results very quickly. An example of the first class of precipitates
is found in magnesium ammonium phosphate. In order to
obtain the greatest possible amount by precipitation the solution
must be allowed to stand for some hours in contact with the
crystals that have already been precipitated. Stirring usually
serves to hasten the attainment of equilibrium by promoting
contact of solid with the supersaturated solution.

It is important to note that there is no definite relation between
the degree of persistence of supermturnlion and the degree of
solubility at final equilibrium .

Solubility Product. —In order to diminish the solubility of the
precipitate to the lowest possible figure, use is made of the* princi¬
ple that in any saturated solution the product of the concentra¬
tions of the constituent ions is a constant (the “solubility
product”) which cannot be exceeded without reproducing the
abnormal condition of supersaturation. By adding an excess
of the precipitating reagent (and therefore of one of the ions of
the substance precipitating) the concentration of this ion is
largely increased. There must then be a corresponding decrease
in the concentration of the ion that is being determined and this
results from increased precipitation.

GENERAL OPERATIONS

Colloidal precipitates, such as aluminium hydroxide, manganese
sulphide, etc., do not obey the law of solubilities referred to above.

Size of Crystals of Precipitates. —Other conditions being
unchanged, it may be said in general that slow precipitation
results in the formation of relatively large crystals and conversely.
The rule that the precipitating reagent should be added slowly
and with continued stirring is a consequence of this fact. But
if it has been found impossible to pro¬
duce a precipitate of sufficient coarse¬
ness to permit retention by the filter
paper this fault may usually be reme¬
died by warming the solution and
precipitate for some time. The actual
result is the resolution of small crystals
and the reprecipitation of their sub¬
stance upon the larger ones. This
is due to the fact that very small
particles have a slightly greater solu¬
bility than larger ones. The process of
heating a solution with its precipitate
in this manner is called" digestion/’

Filtration. —After a precipitate has
been separated by filtration and
washed, it is either dried to constant
weight or strongly heated ("ignited ”)
in a crucible, in order to bring about
some definite change in its composi¬
tion before weighing. In the former
case it is practically necessary to use
a filter of inorganic material because fig. 5.—Gooch or alundum

paper cannot be dried to any constant c \ ruc \ hle Wlt }* rubber filtering
. i .. TJ? , . ring in funnel. (In section.)

degree of hydration. If strong ignition

is to be employed, either paper or inorganic materials may be used
unless burning organic matter exerts a reducing action upon the
precipitate, in which case the use of paper filters is again excluded.

Filter Paper. —For quantitative purposes a paper of very
high grade is required. The texture must be close and uniform
and the material as free as possible from inorganic matter

QUANTITATIVE AGRICULTURAL ANALYSIS

which would be left as an ash on burning. To obtain the
latter condition, paper is subjected to a preliminary extrac¬
tion with hydrochloric and hydrofluoric acids, thus dissolving
all but a small trace of ordinary ash-forming matt er. Such paper
is usually called “ashless.”

Inorganic Filters. —To avoid the reducing action of the
filter either an alundum crucible or a Caldwell crucible may
be used. Alundum is a porous form of aluminium oxide, partly
fused together with a binder. A crucible of this mat (‘rial may
be placed in a rubber holder placed in a funnel, as shown in Fig. o,

and the liquid drawn
through by suction. The
precipitate is then washed
and ignited directly in the
crucible.

The Caldwell crucible
(usually known as a
“Gooch") is a tall crucible
of porcelain whose bottom
is perforated by small holes.
This is used in a manner
similar to t hat described for
the alundum crucible, with
the exception that a pad
of asbestos (see piW 158)
is formed over the bottom

i’lu. o. —Common form of wu«h bottle. this provides (ho neces¬

sary filtering surface. For
high temperatures the platinum form is better. This is tint
original Gooch crucible.

Washing. Wash bottles like Fig. 6 should be provided. A
fine stream of water, hot or cold, may be blown on to the filter,
the precipitate and filter being thus washed free from soluble
impurities. To avoid unpleasant effects due to blowing back
of steam from the hot water bottle, or of volatile liquids when
these are used for washing in special cases, a pressure bulb and
vent may be provided.

Great care must be used to avoid mechanical loss of precipitate.
It is well to remember also that the most efficient washing is

CES E UAL on Hit A TWXS

accomplished by using several small portions of wash wafer,
rather than fewer and larger portions.

Drying. If a precipitate is to be* subjected to strong ignition
it is not usually necessary to carry out any preliminary drying,
other than such as may la* performed in tin* crucible over a low
flame. But some precipitates an* to lx* weighed, after drying
at a definite ternperat tire, in which cases a drying oven ha ving a
fairly close* temporal lire regulation must be* provided. For this
purjMhse* the* use* of eloetrieally heated ovens having automatic
temperature regulation is now
almost universal. Any oven
must have* provision for ron-
tinuouselisplaeeinerit of humidi¬
fied air by drier air. Passing t la*
entering air through a drying
agemt, sueh as ealcitun ohlnrido
or sulphuric acid, will facilitate*
the drying operation but this is
done only in special cases.

In order to understand the*
principle of drying it is well to
recall the* law that any moist
substance* will continue to lose*
moisture* by evaporation until
a certain definite pressure* of

Fee.

wafer vapor (“arjueous tension’*) is established in
ing space, the* value of this pressure depending

Small ili^sji rnfnr

the surround-
upon on the

nature* of the* moist substance and (h) the* temfwrature. If the
pressure* of the* surrounding vapor is reduced by extraneous
means, evaporation proceeds until equilibrium is again i^fale
lishe*el. Thus by continuing to reduce the external vapor pie-,
sun*, evaporation rimy be* continued. However, if is important
to note* that tin* vapor pressure to be* considered is not the total
pressure batch as that of the atmosphere) but the partial pressure
of the vapor of water. As the* latter pressure is directly propm
tiomil to the concentration of wafer vapor in tin* surrounding
space, the same result will finally lx* produced b/j by tedueuig
the* total pressure* by means of u pump. 1 1n by euntinuondv dr
placing the moist air by means of some* other dried gu *»* < f, v

28 QUANTITATIVE AGRICULTURAL ANALYSIS

confining the moist substance in a space which contains some
hygroscopic material.

Certain types of ovens make use of methods (a) or (/>), above.
In such ovens an air-tight chamber is provided and a dried gas is
passed through this or the chamber is exhausted by means of an
air pump.

Desiccators.—Method (c) is employed in the various types of
desiccators, used at ordinary temperatures. Figure 7 illustrates

a small desiccator suitable
for carrying about, the
laboratory. In Fig. «X is
shown a desiccator in which
are used the principles of
methods (a) and (c). This
is what is known as a
“vacuum desiccator.” In
both illustrated forms of
apparatus thedryingngent,
which may be calcium chlo¬
ride, sulphuric acid, or, in
certain special cases, phos¬
phorus pentoxide, is placed
in a layer on the bed tom.

Ignition of Precipitates.
The term “ignition” is
used in this connection in
a sense somewhat beyond
its ordinarily accepted
meaning, since it is applied to the heating to high temperatures of
substances that are entirely incombustible. The* purposes of
ignition are to destroy the filter, if paper has been used, to ex|x*I
the last traces of moisture and volatile impurities that have not
been removed by washing and to cause the precipitate to change
in a definite manner, if a change is to be made. If a pajter filter
has been used it is carefully removed from the* funnel by slipping
up the side. It is then folded as indicated in Fig. 9, the object
being so to enclose the precipitate that loss is impossible. If
it is to be dried and removed it is then placed in the oven on a
cover glass. .

CCD

Fig. 8.—“Vacuum" desiccator.

(r'h'XEli. I/. nVEU \TI(f.\S

Oxidation in the Crucible. The crucible is almost invariably
healed by means of a naked flame, being supported on a tri¬
angle by ni( k ans of some kind of stand. \\ laat the object is to

oxidize the paper or precipitate the crucible is placed on its side
and the rover leaned against it as shown in big. 10. The hunter
is placed under the bottom of the crucible, in such a position that
the gaseous produets of the
burner cannot enter the* cruci¬
ble. The uprising current of
warm air strikes the cover
and is deflected info th<* cruci¬
ble, thus providing an oxidiz¬
ing atmosphere about the
paper. If the flame from the
burner is applied only enough
to keep the* paper burning
the desired condition is
attained. No harm results
if the volatilized combustible
material from the* paper
burns with a flaunt above
the crucible. After tin* jmjxa*
is thoroughly charred tin*
temperature is gradually
raised to complete? the com¬
bustion.

The proper position of the?
crucible on the triangle is shown In Fig. II.

Fig. 12 the crucible is liable to fall back and if may even
times fall through and cause a failure of the determinaii»>n

Vu*. to.

>4 « I *»• iM*

fat MXtUufH*?)

e * jfi*

If placed

‘ >

QUANTITATIVE AGIlH'Vl.TUIt\l. A\ M-) >/>

Even in cases where the burning paper has im ^during art mu
upon the precipitate it is still desirable to complete tli.* com-
bustion of the paper at a comparatively low tein]M*r:»lure. This
is a matter that is too often ignored hg tin . hnh u\.^ < iv>-

talline precipitates that are ordinarily regarded a.- mtudble will
often undergo softening at the sharp corners of tie crystals.
This causes a certain sticking together which result:* in the enclo¬
sure of a small amount of carbon in such a wav a> to make it*
oxidation extremely difficult. If the paper etintaining the

Fig. 11.—Correct, position Xzi» » *i r«-*o pmifinn

of crucible for oxidation. rmriLle f>>t

precipitate is heated to a high temperature at the wry beginning
it is often almost impossible to make* it white. t )n«* of the }*est
examples of this action is in the ignition of magnesium nmmo-
nium phosphate to convert if into magnesium j»y ropier phate.
Premature heating of this substance to very high fejupejaf ures
will frequently result in a black or gray material that cannot 1 m?
whitened by long ignition.

Decomposition in the Crucible. After oxidation of the jmjier
is completed the temperature is rain'd in order to volatilize
completely any volatile? impurities that, may remain and to c ause
whatever decomposition is desired. Since oxidation i no longer
an object the crucible is placed in art upright portion and the
cover is placed over the top. This given an opportunity for
the flame to bear directly on the bottom of the Humble where
the precipitate lies. The cover also largely prevent?* Iokh of
heat due to convection currents of air within the crucible.

Crucibles. —-Porcelain crucibles of high grade mav be med for
most work, in cases where the precipitate h not to be frned.
Alundum already has been mentioned in connection with filtering
crucibles. When any compound or mixture i* to be fused,

CHS EH. t E OPE HA TIOSS

«>

porcelain is usually unsuitable because the fused material will
combine with the glaze, or even with the porcelain itself. For
such work platinum or one? of the newer substitutes, palau or
rhotaniurn, is essential.

Marking Crucibles.- -Metal crucibles should have permanent
identification numbers stamped upon them by means ol small
dies. These numbers form a part of the analytical record arid
they serve to prevent accidental transposition of weight records.

Porcelain crucibles may best be marked by means of a pen
and ink, the marks being inconspicuous figures or small dots.
When the crucible is strongly heated the iron of tin* ink forms
the red oxide, which burns into the glaze and forms a permanent
identification mark, (('ertain common inks do not contain iron,
so that they arc* unsuitable* for this purpose.)

Some manufacturers of chemical porcelain now furnish cruci¬
bles and dishes serially numbered with permanent marks. 'This
is a great convenience to the analyst.

Care of Platinum. Platinum ware will deteriorate rapidly
unless the following precautions arc* taken in its use* and cure.

1. Handle* carefully to avoid bending. Pse dean crucible
tongs and do not allow the* tongs to conn* into contact with fused
materials within the* crucibles or dishes.

2. For cleaning apply the* appropriate* solvent, according to
the nature* of the* material to be removed, ('bromic arid is
suitable* for removing organic matter, and hydrochloric or nitric
acids for insoluble carbonates or metallic oxides; fusing with
sodium carbonate* is suitable* for removing silica or silicate's, or
with sodium pyrosulphate ha* such metals or metallic oxide;* as
resist the* action of acids.

3. Do not he*at platinum in contact with tin* inner cone of the*
laboratory burner, as brittleness results from such exposure.

4. Do not heat compounds of lead, tin, bismuth, arsenic,
antimony or zinc in contact with platinum. Keduetion may
occur, the* reelueod metal alloying with the platinum.

5. Do not attempt to remove* fusions from platinum crucibles
or dishes by means of files, glass rods or either hard toed *, re¬
solvents or a mbbc*r-tip|K*d rod.

0. Dull surfaces should he* polished lightly with wet emery
slime or fine carborundum.

QUANTITATIVE AG ItICl LTl 'HAL ANALYSIS

• 32

Platinum Substitutes. —The increasing .scarcity of platinum
has made the introduction of substitutes a practical necessity.
While it is true that pure platinum {assesses certain prop¬
erties that cannot be duplicated by any other metal or
alloy, yet certain alloys have been found to be suitable for
making into crucibles and dishes that will serve for many
of the operations of the analytical laboratory, in place
of the platinum that has been in use. Two of these will
be mentioned.

“Palau” is a trade name for an alloy containing about M)
per cent gold and 20 per cent palladium. Its melting point is
about 1370°.

“Rhotanium” is a name given to a scries of gold-palladium
alloys whose melting points range from IIoO to I-lotf. Hot It
palau and rhotanium may be used in place of platinum except,
where much oxidation is to be expected or where very high tem¬
peratures are employed.

Unfortunately the manufacturers discourage the use of these
substitutes by maintaining the price of manufactured articles so
close to that of platinum ware that the purchaser will usually
pay the difference in order to obtain the more *utisfnrtnrv
platinum.

Burners —The burner that is to be used by the analyst may l*e
anything from the cheapest and simplest burner of the Bunsen
type to the most expensive and complicated burner obtainable.
The puichaser has his choice and probably certain advantages
are possessed by each burner. The only feature that is really
essential is independent regulation of air and gas supply. The
requirements are quite different in different cases and the analyst
must have at his disposal all kinds of flume, from the yellow illumi¬
nating flame to the most intensely hot and oxidizing flame, and
he requires very small and very large flames of each class.’ In
order to obtain this variety of flame there must be some method of
legulating the gas supply without changing the pressure
gas valve, since this also changes the amount of air drawn in at
the mixer. The simplest form of Bunsen burner does not
this gas regulation without unscrewing the upper f iil*> and chang¬
ing the gas jet by the use of pliers. Such regulation is not pm-
sible m practice.

GENERAL OPERATIONS

In the Teclu burner (Fig. 13) the gas is controlled by the
screw on the side of the base while the disc at the bottom of the
cone controls the air supply.

In this burner the regulation of gas flow is not accomplished
by altering the pressure under which it is delivered but by chang¬
ing the size of the orifice in the burner. The maximum pressure
is thus used at all times and the result is a better mixture of gas
with air than is obtainable by
regulating the gas cock of the
supply line.

A very common error on the part
of students lies in carelessness with
regard to the regulation of flames.

If a relatively cool flame is re¬
quired and if a deposit of carbon
is not objectionable the air should
be excluded from the mixer. If,
on the other hand, the highest
efficiency of the burner is desired,
careful regulation of the air and
gas is necessary. The inner blue
cone should be well defined and it
should not show a yellow tip. If
more air is admitted than that
required to burn the gas com¬
pletely with production of a blue
flame, the result is a roaring and Fig. 13.—Section of Teclu burner,
fluttering flame. This means that

more air is being admitted than can be used and this air, in being
heated by the flame, lowers the temperature of the latter.

Meker Burner. —A somewhat radical departure from the older
types is found in the M6ker burner. This is shown in section
in Fig. 14. The air is drawn in through several holes in the base
of the tube. The delivery of the gas under pressure into the
inverted cone which forms the burner tube causes a greater
reduction of pressure within the tube than is the case with
burners having cylindrical tubes. The result is a greater inflow
of air, making possible the combustion of a greater amount of gas
in a given space, and also more complete mixing of gas and air.

34 Q U AN TIT A TIVE AGRICULT URA L A NA L )

The nickel grid through which the mixture flows at the top of
the burner causes the gas to bum exactly as though each mesh
were a small individual burner. The tip of the inner reducing
cone of each small flame is usually about one millimeter above
the top of the burner and, as all of the small flames unite to form

one large one, the result is a
highly concentrated flame,
every part of which is oxidiz¬
ing in character except a zone
of about one millimeter in
depth, immediately above the
top of the burner. This is a
distinct advantage, especially
in heating platinum articles,
since platinum is easily dam¬
aged by heating in a reduc¬
ing flame.

A number of imitations
and modifications of the
Mdker burner are offered for
use at this time. Most of
these use the same combus¬
tion principle, the burners
differing only in mechanical
features.

Blast Lamp. —In order to
produce a higher temperature
a burner may be constructed
so as to consume a larger

Fia. 14.— Section of M6ker humor, quantity of gas, depending

for its complete combustion
upon admission of air under pressure. A burner so con¬
structed is called a “blast lamp.” Many forms of such burners
are in use.

The flame of the M6ker burner is nearly as hot as that of the
ordinary blast lamp using the same gas and it may be substi¬
tuted for the blast lamp in many cases. There is also a M4ker
blast lamp, similar in construction to the one already described
but using air under pressure.

GENERAL OPERATIONS

Weighing. —From all of the foregoing discussion it will be seen
that every analytical determination involves, at some point,
obtaining an accurate estimation of weights. Even the volumet¬
ric process requires weighing the sample and a weight is usually
involved, directly or indirectly,, in the standardization of the
solutions used for the titrations. It is obvious from this that an
accurately constructed weighing apparatus is a necessary part of
the equipment of the analytical laboratory.

Methods of Weighing. —Any method that depends upon the
attainment of equilibrium between the force of gravity and the

mmtmm

I mm r' ■■■ . ■

[H HHH

Pig. 15.—Essential parts of the balance.

resistance to distortion of a spring is necessarily subject to
considerable and variable errors. These are chiefly due to varia¬
tions in (a) elasticity of the spring and ( b ) the value of gravity
for different altitudes. The only method that is free from these
errors is weighing on a balance, a standard mass being compared
with the object to be weighed and the former being varied until
equilibrium is attained.

The Balance. —The analytical balance should be so constructed
as to provide means for accurate weighing to one ten-thousandth

QUANTITATIVE AGRICULTURAL ANALYSIS

of a gram. In order that such weighing may be performed the
balance must be constructed with mathematical accuracy. The
three bearings are commonly of agate, ground to a very fine
“knife” edge and each resting upon a smooth block of the same
material. They must be so placed as to lie in the same plane
while weighing (the central bearing is usually slightly below the
plane of the end bearings, to allow for distortion of the beam
when loaded) and absolutely parallel. The moving parts are as
light as is consistent with the strength required to bear the rated
load and they are provided with a mechanism for arresting their
motion and for lifting the knife edges from their bearings. The
entire balance is enclosed in a glass case, which is kept closed
during the final adjustment of weights, so as to avoid inter¬
ference of air currents.

These points will be made clearer by reference to Fig. 15, which
shows only the skeleton of the balance.

Weights.—Practically all weighing operations of analytical
chemistry are carried out by means of metric weights. A balance
is rated for a certain maximum load and the largest piece of the
set of weights should not be heavier than half this rated load.
A balance rated to carry 100 gm in each pan will thus require
a set of weights having a 50-gm piece as the largest piece of the
set. The smaller pieces will then be, in grams, as follows: one
20, two 10’s, one 5, one 2 and three l’s. These will total 100 gm.
The fractional pieces (milligram pieces) are then apportioned as
follows: one 500, one 200, two 100’s, one 50, one 20 and two
10’s, with a movable “rider” on the right arm of the balance
beam to make another 10 mg, the beam being graduated so that
by shifting the rider, 0.1 mg fractions may be made. It will be
seen that these milligram pieces total 1 gm.

The Rider. —The reason for using a rider on the beam instead
of the very small weight pieces on the pan is largely one of
convenience. The rider may be adjusted with the balance
case closed and this facilitates the final adjustment. This
method also dispenses with the use of a large number of very
small weights.

The actual weight of a rider to be used on a given balance
will depend upon the manner in which the beam is graduated.
These graduations are to indicate a certain number of milli-

GENERAL OPERATIONS

:\7

grams and fractions. The generally approved method is to have
the space between the central knife edge and the pan support
marked in ten principal divisions, each with ten subdivisions.
The number over the central pivot will then be 0 and that directly
over the pan will be 10. If the
rider is placed over the pan it
will have the same value as if it
were in the pan. Hence it should
weigh, in milligrams , whatever is
indicated by this number. Various
balances have, instead of 10, the
figures 5, 6 or 12 over the right
pan. They will then require
riders having these indicated
values, in milligrams.

The Chain Rider. — The

u Chainomatic” balance entirely

dispenses with a separate rider.

One end of a small gold chain is

permanently attached to the

balance beam. The other end

of this chain is fastened to a

hook which may be moved up

and down a scale (Fig. 16),

this action being controlled by

a knob outside the balance case.

Movement of the hook on the

scale varies in a definite manner

the length of side of the loop

Which is Supported by the beam Fig. 10.— Chain riclor rind part

and this may be adjusted while °* as U,S0( ^ t*ho “chainonm-
• i i . . tic ' balance.

the beam is m motion. This

is a distinct advance in balance design, although this improve¬
ment adds considerably to the cost of the balance.

Use of the Balance.— It, has already been stated that the
process of weighing involves the adjustment of weights upon
one pan until they are in equilibrium with the material on
the other pan. This is not done by noting when the balance
beam fails to swing but by the more accurate method of causing

QUANTITATIVE AGRICULTURAL ASAIA SIS

it to swing several times in both directions, noting when a pointer
attached to the beam swings equal distances on either side of a
“zero point” on a fixed scale. The balance should be adjusted
so that without load it swings about the true zero of the scale
but thermal changes, settling of buildings, etc., will cause this to
change and the zero point must be determined occasionally and
the adjustment changed, if found necessary.

Differential Weighing. —Where the desired weights are found
by a differential process it is not necessary that the adjustment
of zero point should be made, or even that the zero point should
be known. It is sufficient to assume the zero point to be t he same
as that of the scale. Although this may involve an error in
weighing, this error will be the same for both weights obtained
and the subtraction will eliminate it entirely. For example, a
crucible is being weighed empty and again containing a pre¬
cipitate of barium sulphate, in order to find the actual weight of
the latter. A plus or minus error may have been made in the*
recorded weight, due to an incorrect assumption of zero point,
but this will be the same for both weighings and when the
observed weight of the empty crucible is subtracted from the
observed weight of the crucible and barium sulphate, this error
disappears.

To Determine the Zero Point.—(-lose the balance case and carefully
lower the pan rests in such a manner as to stop any lateral swinging of the
pans, then lower the beam rests and set the beam in motion by allowing
the rider to rest momentarily on the beam, then raising it. This should
cause the pointer to swing five to ten divisions on either side of the zero
of the scale. Take at least three readings on one side ami two on the other.
Subtract the less average from the greater and divide the remainder by two.
This gives the zero point if the proper direct ion is noted.

The zero point may be determined with sufficient accuracy for most
work by simple observations without computations , by notiny that
the amplitude of vibration of the pointer diminishes regularly with
each successive swing.

Weighing by the Single Deflection Method.- 'This rapid
method has been described by Brinton. 1

The pan rests must first be adjusted so that when released t hey
shall give no swinging impulse to the system. That is, if the

1 /. Am. ('hem. Soc 41, 1151 (][) 19).

CHS RUM, nrhlUM'lOSS

loads are in equilibrium thorn must bo no swinging of the pointer
at release of the pans, the beam rests bring down. Kquilibrium
is then destroyed by adjusting one of ( ho snrws on f in* end,

so that at release the pointer will swing 2 to 7 scale divisions
in one direction. The point on tin* scale which t hr pointer
reaches on its first excursion is taken as the “zero point,” the
pans having first boon stoadied to stop latoral swinging.

In weighing, the weights an* adjusted as by any other method,
the rider finally being placed so that when the pans are released
the pointer will reach tlie* same “ zero point, ” on its first, excursion,
that was first determined.

Although this method would seem, at first, to he* essentially
incorrect in principle, it. is capable of giving accurate results in
the hands of a careful analyst, with the following limitations:

1. It. cannot be used with balances having a single control,
releasing beam and pans at one operation.

2. The pan rests are cleaned, if necessary, with alcohol to
prevent sticking to tin* pans, as otherwise a swinging impulse
would be given by release of the hitter.

2. Most balances show a variation of .sensibility with variation
of load. Tin* “zero point” must then be determined at the
approximate load that is to ho weighed, if a single weighing is to
he made, or at both loads in ease of differential weighing, unless
the single load or the difference between flat two loads is quite
small. One* of these two conditions is met in most analytical
work. Sample weights or weights of precipitates are loss than
one* gram, in the majority of cases. If a sample is to be weighed
on counterpoised glasses it. is sufficient to determine the point
reached on the* first swing, with the empty glasses. If it is
to be weighed from a weighing lad Me, or if the precipitate is
to be weighed in a crucible, the point reached when the tilled
weighing bottle or the empty crucible, res{x*ctivelv, in bring
weighed, is taken as the zero point for that particular pair of
weighings.

4. It is obvious that a single observation gives no check upon
chance causes of variation, such as vibration or air currents
within the balance ease*.

The method is useful, (‘specially for rapid work, if proper care
and consideration are exercised. In any event the balance mmd

Q l >A X 77 7VI77 V K t 67*/f 7 7//7 7M /, A X AL) \s (S

bo carefully tested at the hegilining, to give a,-surnnce that if
can safely be used for this method of procedure.

Calibration of Weights.— Expensive sets of weights an* usually
adjusted with sufficient accuracy for most analytical work, but
with weights of the grade ordinarily available a calibration
should be made. Weights that are found to be in error may then
be either adjusted to accurate values or used with corrections.

This is a matter that is given serious attention in jar too few
laboratories , college or industrial. Commercial freights frequently
are in error to the extent of two or three per rent and even larger
errors may be found, after the weights have been in use for a year or
more. To ignore such errors as these , white, insisting upon a high
degree of accuracy in the other phases of the laboratory mark, is
nothing less than gross inconsistency.

Calibration may be accomplished most conveniently and
with accuracy by comparison of each piece of tin* set with the
corresponding pieces of a standard set., whose* corrections are
known. Also, if the arms of the balance* are known to be of the*

same length to within a negligible error^ 1 t not more than

0.00001^ the comparisons may be made by placing the pieces
on opposite pans of the balance and noting whether the rider
must be used to obtain equilibrium and, if so, its necessary
position on the beam. This gives, directly, the* value of the
experimental piece in terms of the standard piece. Since this is
a direct comparison, the zero point of the balance* must be known.

If an entire set of standard pieces is not available a single
standard piece, as a gram, may be used, when (la* ealrulafions
become more complicated and the calibration less accurate.
Also if the balance arms are not sufficiently near the same lengt h
(found by weighing an object and then exchanging object and
weights, and reweighing) or if nothing is known regarding this
point, a different method of comparison must be employed.
This is known as the “method of substitution.” In the exercise
that follows it will be assumed that an entire standard set is at hand
and that the method of substitution is to be used. This method is
safest in any case and it makes unnecessary a determination of
the relative length of the arms or of the zero point of the unloaded
balance.

(rh:\KU.\L nmatArmss

Calibration. Besides tin* set to lx* ejilibnitcd then* must be provided a
stain lard set, also a third set to lx* used as counterpoise. 'Phis hit I it '■•rl
mav lx* of any cheap weights as the actual values of the pieces do not eitfri
into tin* calculations.

Begin with one of tin* l-gm pieces. Place a 1-^m counterpoise on the
left pan and the corresponding st andard piece on I he right pan. < 'arelullv
lower th<* beam rests, and then the pan rests, and start tin* balance swinging
by lowering the rider momentarily to the beam. Note the zero point and
adjust the rider so that the pointer swings about the true zero of t lie lower
,s<*ale. Now, without moving the rider, raise the pan rest - at the moment
when the pointer is passing zero, then the beam rests.

Remove the standard piece and substitute tin* piece
of the set. to be calibrated. Repeat t lie def ermine ■*
lion of zero point. If the latter has not been j

changed by the substitution of weights, tIn* standard
piece and tin* experimental piece have the same
value, irrespective of the value of the counterpoise.

If the zero point has changed, shift- tin* rider to
restore equilibrium. The amount of diift given the
numerical difference between the two pieces. If
the shift of the rider is to the riyhl the experi¬
mental piece is liyhttT than the standard piece and
if to the lift it is Inurin'. Apply tin* indicated
correct ion.

Repeat the process just described, comparing
each piece of the entire .*>et with the corresponding
piece of the standard set, finally tabulating the
corrections. The*e should be recorded on a card,
which may he placed in the balance case for future
reference.

If an accurately standardized complete vet of
weights is not available, the set may be calibrated
to a single standard piece, or simply relative values
of the various pieces may be estublr lied. H ung the
method of Richards. :

r a n «•

I »«♦ IV \ppi«c/« d

•:hajM- -*ud ifi-.ci ij#f »i*i»
Jo* * otuoief \ O flii-di

Volumetric Apparatus. It has already been shown that the
balance is concerned, directly or indirectly, in all detenniunfion
made by volume!rie processes. Hut the work is e* enf billy
different, from gravimetric analysis in that no final weighing of
preei pi tales is made. Instead of this a measurement i : made of
the volume of a standard solution required to complete a definite
renet ion with the substance under investigation.

1 ./. Am. ('him. Kw. t 22 , tit f HMKb; Mamin, '*( LMi.mht at i o
2nd ed., fin <10.

\u »1 } ■/“

QUANTITATIVE AGRICULTURAL ANALYSIS

The apparatus necessary for this class of
work will include accurately standardized
volumetric flasks, burettes and pipettes. I he
first are for making solutions of definite con¬
centrations and occasionally for measuring
aliquot parts of such solutions. Pipettes are
for measuring definite portions of solutions
and burettes are for measuring the necessary
volume of standard solution as the titration
is being made. Because of the fact that tin*
required volume of standard solution varies in
n different titrations and that it is

[1 unknown until the experiment is
finished, the burette must hour
graduations for small subdivi¬
sions, from zero to full capacity.

Figures 17, 18 and 19 illustrate
the three types of apparatus just
~=° described.

li Because of the fact that no
/ \ t glass apparatus can bo made to

y | deliver all of its contained solu-

I 3 tion upon emptying, it is neees-

\ / s&ry to specify whether a given

|- piece of apparatus is graduated

t 5 “to contain” or “to deliver 1 ’

ffi the stated amount. Also if the*

fj measurement of the delivered

I- solution is to be at all accurate

1 the apparatus must, be eon-

fs structed scientifically and used

Ij with many precautions. Much

inaccurate work of the chemical
laboratory may be traced to
I \ poorly constructed volumetric*

li ^ apparatus or to carelessness
Fig. is.— («) with regard to its use. The
^>) a 11 nioasuring Bureau of Standards has under-

pipottes.

Yu*. I si, -Showing
p niiU gmuhiutirmn

a special study of this improved for hurotte*.

GKXURAL Ork'ItA VIOXS

\\\

matter and has prescribed 1 rules for the construction and use o!
all volumetric apparatus. Some of the more important features
of these specifications are given below. Kvery good laboratory
should prescribe that apparatus shall conform to these spend-
cations wherever possible and upon receipt of t he various pieces
they should be calibrated, in order to establish any necessary
corrections in the* graduations.

Specifications. --The unit of volume is the true liter. This is
defined as the volume occupied by one kilogram of pure water at
4°. The standard working temperature is 20".

Inscriptions.- .JOvery instrument must bear a legend indicating

the capacity in liters or milliliters (the latter is almost, identical
with cubic centimeters), the, temperature at which it is to be used
and whether to contain or to deliver the stated amount. Buret trs
and pipettes must bear a statement as to tin* time required for
unrestricted outflow of tin* full quantity of water.

Special dimensions ant given for each class of instrument.

The time of outflow is specified as follows: Pipettes having a
single graduation (“transfer” pipettes) must have the tip of
such size that the time of free* outflow is not more than 1 minute
nor less than the following, according to the size of the pipette:

Capacity (in cr) tip to nod including. 5 Hi 50

Minimum outflow firm* fin «et\ j .... to 20 50

Burettes must empty in not more than A minutes nor less
than as indicated below.

Taiii.k I. Rati; op Octfi.ow k>h Beiumnu

length

Minimum time

length

Minimum fiiur

graduated, cm

of outflow, HCI\

l graduated, rut

of outflow. UVi\

| 4o :

:ir>

120

! ao

105

*25

oo !

'20

45 |

H0 |

;to

1 V. S, Purenu of Standard*, Cirr. 9.

QUANTITATIVE AGRICULTURAL ANALY&I*

Calibration.—The standard working temperature
At this temperature 1 liter of distilled water, free from
gases and weighed in air with brass weights, has an
weight of 997.18 gm. The simplest and most accurate ]
calibrating is based upon this relation. Flasks or othc
tus, rated to contain any stated volume, are marked at
reached by the meniscus of water, taken at the rate c
gm for each cubic centimeter at 20°.

If the temperature of the balance room is not 20° a
weight of water must be taken. Bearing in mind that
ratus actually has different volumetric capacities for
temperatures it will be seen that the calculated weight
to be used for calibrating at temperatures other than
include corrections for (a) expansion or contraction of
change in density of water and ( c ) change in density of
air. All of these corrections are used in compiling the
table.

Table II.—Temperature Corrections

Temperature, deg.

i Weight of water, in grai
taken for ealibrati

997.93

997.80

997.66

997.51

997.36

997.18

996.99

996.81

996.61

996.39

996.16

In calibrating burettes or pipettes the water is delivei
these into a weighing bottle, which is then stoppered
weighed. The marking on a burette is too complicated
it practicable to remark the instrument. Therefore t,h

GENERAL OPERA TIONS

45 -

oapacities between stated markings is calculated and a correction
is applied, if necessary.

Cleaning Solution.—Prepare a cleaning solution by dissolving 5 gm
of powdered commercial sodium dichromate in 500 cc of commercial
sulphuric acid. The solution may be kept in a bottle having a wide mouth,
such as those in which dry chemicals are purchased. Burettes may be
inverted and left standing in the bottle, the solution then being drawn up by
suction and held in the burette by closing the cock. For cleaning flasks
the solution may be allowed to remain in the flask for some time or a small
amount may be warmed and the flask rinsed with it. The chromic acid
produced by the interaction of sulphuric acid and sodium dichromate
oxidizes all organic matter and leaves the glass thoroughly free from it:

Na 2 Cr 2 0 7 + H 2 S0 4 + H 2 0 Na 2 S0 4 4* 2H 2 Cr0 4 ,

4H 2 Cr0 4 + 3C + 6H 2 S0 4 2Cr 2 (S0 4 ) 3 + 3C0 2 + 10H 2 O.

Disappearance of the red chromate ion and the appearance of a green color,
due to the positive chromium ion of chromic sulphate, indicate exhaustion
of the solution.

Have the flask clean and quite dry. Place on a balance of capacity
sufficiently great to carry the filled flask. Counterpoise, then add
weights to the right pan at the rate of 997.18 gm for each liter.
Remove the flask from the balance and fill with recently boiled distilled
water at 20°, nearly to the point where it is thought that the mark will be
placed. Remove drops from the inside of the neck, above the level of the
water, using a roll of filter paper. Replace the flask upon the balance pan,
then carefully drop in water from a pipette until the balance is in equilibrium.

To mark the flask cut a strip of gummed label, long enough to reach
around the neck and about 5 mm wide. Carefully paste this with the
original straight edge at the level of the meniscus, where the mark is to
be made. Melt a small quantity of paraffin and brush a thin layer over
the label and over a space of about 3 cm on either side of it. Using the
point of a knife or of a sharpened piece of wood trace the straight edge
of the label around the neck of the flask, making a mark sufficiently wide
to be easily visible. The label here merely serves as a guide, making a
regular line possible. Using a small feather as a brush apply a few drops
of hydrofluoric acid and allow this to remain on the flask for two or three
minutes, after which the acid may be washed off and the paraffin removed
by warming.

In case the flask already has a graduation and the calibration shows
this mark to be incorrectly placed it is desirable to indicate the new mark
by making a small, well-defined arrow with the point resting exactly upon
the new mark. The operator’s initials may be placed beside the arrow and
if this is done carefully, no interference will result.

If the flask contains no inscription etch the side in a manner similar to
that shown in Fig. 17, page 41.

QUANT IT A TIYK AGRICULT t > It A L . 1 X A L YSIS

Calibration of Burettes.—The marking of a burette is too complex to In*
easily changed and the calibration will therefore consist of finding wind, if
any, corrections must be applied to the existing graduations.

First inspect the burette to determine whether it conforms to specifi¬
cations, especially with respect to outflow time. If not, make what altera¬
tions are possible. A burette whose outflow time is too short will give
erratic measurements. Clean the burette with chinning solut ion, followed
by distilled water. Fill with distilled water at 20°. Weigh accurately a
25 cc weighing bottle to the third decimal then measure 5 cc of water into
it from the burette, and reweigh. Add another 5 cc and weigh, continuing
until the bottle is full. Empty the bottle, reweigh and continue tin* process
until the water from the entire graduated portion of the burette has been
weighed. Repeat the process in order to have a cheek upon the work.
Calculate the true capacity of each of the ten portions, using the weight
0.99718 gm for 1 cc of water. Record im follows, the capacities in t he last
two columns being recorded only as far as the second decimal place.

Mark

Weight of water.

True capacity, each

each interval

interval

True total capacity, zero to rwi
of interval

Construct a curve showing the true reading at till points. In case any
marked irregularity is observed at any part of the burette so flint correct ions
taken from the curve would be inaccurate, recalibrate this portion, using
1 cc at a time.

Calibration of Transfer Pipettes.—Determine whether tin* time of
outflow conforms to the requirements as set forth on page 48. If not, alter
the tip of the pipette before calibrating. Provide a weighing hot tie having
a capacity of 10 cc, also a larger one having a capacity equal to that of the
pipette. Cut a strip of paper about 2 mm wide and 5 cm long and carefully
rule this in divisions of centimeters, marking from 0 to 5, and subdivisions
of millimeters, using fine lines. Strips cut from coordinate* paper are
suitable for this purpose. Determine the approximate location of the
capacity mark on the pipette by a rough experiment., unless the pipette
is already marked. Paste the paper strip on the stem of the pipette with the
division 2.5 at the supposed place for the capacity mark and with the zero
toward the point of the pipette. Having cleaned the pipette with chromic,
acid solution it is drawn full of distilled water which is at a temperature of
20°, and the water is allowed to flow out until the zero mark is exactly
reached. The pipette must be held in a vertical position and the eye must
be in the same horizontal plane as is the meniscus. The pipette tip is now
touched against the side of the beaker to remove* the last drop. The
finger is then removed from the top of the pipette and the water is allowed
to flow, at full speed, into the larger weighing bottle, which has already been
weighed. The tip is immediately touched to the side of the weighing bottle
to remove the hanging drop. The weighing bottle is then stoppered and

GENERAL OPERATIONS

weighed. Calculate the volume of the water from the observed weight and
record this as the capacity af the pipette to the zero mark.

Using the small weighing bottle determine in a similar manner the
capacity of the pipette stem between 0 and 5. Divide this capacity by 50
in order to obtain the value of the smaller subdivisions.

From the capacities so determined calculate the number of stem divisions
to be added to the zero in order to obtain the rated capacity of the pipette.
Mark the point so determined, using the method directed for marking
flasks.

CHAPTER III

QUANTITATIVE DETERMINATIONS

Comparative Usefulness of Different Methods.- In a amoral
way it may be stated that gravimetric methods permit greater
accuracy in determinations, while volumetric processes make
for rapidity in routine work with large numbers of samples. This
is due to the fact that one standardization of a solution forms the
basis for many determinations, provided that a sufficient quan¬
tity of standard is made. Experience shows that, for a single
determination, the time required to make and standardize a
solution, added to that required to make a determination by
means of this solution, often leaves the advantage in favor of the
gravimetric method.

Whether the method used is gravimetric or volumetric, if
precipitation is an essential part of the process it must be remem¬
bered that solubility is of the highest importance. No substance
has zero solubility and, since the substance that is precipitating
leaves a solution that is saturated with itself, the part in solution
is necessarily not determined.

In the industrial laboratory methods are chosen, to a consid¬
erable extent, upon the basis of time saving. However it. some¬
times happens that for a given element or compound the known
convenient and, at the same time, accurate methods fall in one
class only. As an example of this may be mentioned the deter¬
mination of the sulphate radical, which is almost universally
carried out by precipitating and weighing barium sulphate.

Scope of the Laboratory Work. —The time that is available
for the college laboratory course is, necessarily, inadequate
to the gaining of the skill that comes from extensive* experience.
The entire field cannot be covered. The greater stress is there¬
fore laid upon the learning of principle.H of correct manipulalion
as well as of chemical processes. The laboratory exercises that
are described in Part I of this book are selected largely with this

ST IT A 77 I A* / tKTKHMI XAT K>\ S

end in view. .Most of the methods (inscribed arc typical and
illustrate* the different kinds of work that will lx* of importance
in Uic future* activities of flu* agricultural chemist. In Part III
these and many other methods will he applied to tlie analysis of
materials that arc* of great importance to agrieult ure and, direct ly
or indirectly, to the economic life* of all of our people.

Certain conventional modes of expression an* common and
will be* used in the* following pages. Most of these arc familiar to
the student but the* following should be especially nofed:

(a) Water always means distilled wafer, unless otherwise
stated.

(h) Accurate./if iniyhnl sa at files are* always understood, even
when “about 2 gm,” or a similar expression, is used, unless
the* use* of an approximate weight is specifically directed.

(e) 7 etaperaturvs are* always centigrade unless otherwise
specified.

CHLORIDES

Gravimetric, by Weighing Silver Chloride. Silver chloride
is a substance* of very slight solubility in water and its precipita-
tion arid weighing therefore forms the basis for flic determiuafion
of chlorine (of inorganic* chlorides) and of silver. Silver chloride
dissolves in pun* water to the extent- of about 0.001 o gm jier
lite*r. This corresponds to 0.001 1 gm of silver or 0,0001 gm
of chlorine*. As the* total amount of water that is ii rd in the
precipitation and washing processes need not exceed I.Vl re, and
can be* made less than this, it rimy lie* seen that the recoverv of
chlorine* or of silver may be regarded as. practically complete,
for all ordinary purposes.

However, it must be remembered that silver chloride di -olve
emsily in ammonium hydroxide and to an appreciable extent m
concentrated solutions of sodium or potassium chloride, and of
hydrochloric arid. It is decomposed by warming with sodium or
jKtiassimn hydroxide, silver oxide being formed.

In the determination of chlorine in impure chlorides it j-
necessary to guard against the precipitation of other alvei
salts, such as phosphate or carbonate, by having a small excess
of acid present. Nitric acid is suitable for t hi- purpose and

QUANTITATIVE AGRICULTURAL ANALYSIS

this serves also to insure against the objectionable action of
bases, noted above. Silver nitrate being used as reagent, the
following reaction occurs:

AgN0 3 + MCI —> AgOl + MNOa.

The following experiments must be conducted in a room which
is not brightly lighted and they should not be unduly prolonged.

Gravimetric Determination.—Prepare two “Gooch” (Caldwell; filters hy
the following procedure, first marking them I and II as directed on page HI:
Place the crucible in the holder as shown in Fig. 5, page 25. Apply the
suction and pour in prepared asbestos suspended in water until a felt of
sufficient thickness is obtained on the perforated bottom. The* required
thickness will vary according to the condition of the aslwstoH, a compara¬
tively fine material making a compact pad which need not lx- as thick as
one of coarser material. These points must be determined by experiment,
guided by the advice of the instructor. Place a small perforated porcelain
plate on the pad, to prevent injury when solution is poured in.

Finally give the crucible a single rinsing with redistilled alcohol to promote
rapid drying, drawing out as much liquid as possible. Remove the cruci¬
ble, carefully wipe the outside and place in an oven which is maintained at a
temperature between 105 and 110° and dry for at least HO minutes. Place
in the desiccator and weigh after 30 minutes cooling.

If an alundum crucible is to be used instead of the Gooch it is placed in
the holder so that the top is even with the rubber. This is to provide for
thorough washing of the entire body of the crucible, which is porous. So
asbestos is used but a new crucible should be given a preliminary washing
with hot water, followed by alcohol. It should then be dried at 105 to
110° before weighing.

While the filters are drying proceed with the weighing and precipitation
processes. Fill a clean, dry weighing bottle with the powdered and well
mixed chloride sample. Provide two clean, 250-cc beakers of Pyrex or
other resistance glass and mark them 1 and II. If the substance is known
to be unaffected by contact with air it may be poured directly into one of the
counterpoised glasses on the balance, until about 0.2 gm is obtained. (The
glasses should have been brought to balance by means of the rider.) This
sample is then weighed accurately and brushed into one of the beakers by
means of the small pencil brush of camel’s hair. A second sample is weighed
and brushed into the second beaker. The weights are* recorded in the
proper places in the data book.

If the nature of the sample is such that it should not be unnecessarily
exposed to air it must be weighed by difference. Place the filled weighing
bottle on the left pan of the balance, using for this purpose a pair of crucible
tongs having short pieces of clean tubing drawn over the tips, and carefully
weigh. Record this weight in the data book at the top of the space marked

QiwsrnwriYE uktekmisa rmxs

for .sample I. Carefully remove tin* .'topper, holding over l»eakcr I, a ml
pour aixmf. 0.2 to 0.5 gn 1 info tin* beaker. Replace fin* .stopper, u 'iug great
can* that no particles shall fall outside tin* fwaker and lx* Inst, thru rrwrigh
the? l>oftI(* and contents. For these lilies tin* zero point of tin* balance

need not ho known, as explained on page JiS. Horonl tin* last weight tonin'
the* first-ami subtract to obtain tin* weight. of sample used. Re*cord tin-
last. weighing also at tin* top of the .space for samph* II. Remove a neeoml
portion to lx*aker II ami reweigh the bottle, recording un<i<*r t he preceding
weighing. Subtract again for the weight of sample II.

Dissolve each weighed sample in 75 ee of distilled wafer, measure*! with a
fair degree of accuracy in a graduated cylinder, mu! add 1 ee of ’,!() per rent
nitric acid. (Water and acid must he free from chlorides, d eaf by mixing
the quantities mentioned above and adding a few drop** of clear silver
nitrate* solution. ) Heat the chloride solution nearly to boiling then precjpj
fate with clear 5-per cent solution of silver nitrate, adding drop bv drop
from a pipette and stirring continuously, 'fen to 20 cc of solution may l»*
required, according to tin* nature* and purity of the* cample.

(’over the* beaker* and plae*e on the* steam hath or over a low flame* w hirh
shows no yellow. Digest at near the* boiling temperature until flu* preetpi
tate* has been well floeculated, then test for completeness of precipitation bv
adding a drop or two of silver nit rate* aoluf ion to t he clear, supernatant liquid.

During this process of digestion the* crucibles are* to be* r«*ine»ve*d from the
oven and cooled in de mentors for 20 minutes, then weighed accuralelv,
handling only with e'b*;m crucible tongs (not rubber tipped*. Place a
crucible* in the holder and, if a (»ooch i* used, moisten flee* pad with a f‘*w
drops of water from the* wash bottle*. Apply the auction to cither f!»*■*
(lunch or th»* alundurn crucible ami filter, bedding th<* beaker close to fh«*
te>p e»f the crucible and pouring down a glass rod. If a (5«»o«*h crumble is
uscei place* the* real again:-! the perforated plate covering 0m asbestos
Rinse* all loose precipitate into the* filte r, then clean the beaker bv means
of the* policeman hi rubU*r-tipp<*»l glass rod) and wash lioftle and fimdlv
wash the i*ijfir«* precipitate and crucible by pouring in 2 p*-r cent, chloride
fre*c nitre* acid from a beaker until the* washings bow no cloudiness with a
drop or two of dilute* hydrochloric acid, thus showing that all .silver nit fate
has he*i*n removed. In making such a test fir i rinse* the* Hutnult of the* low* t
end of the* funnel tube*, then collect about l re of the* washings from the
silver chloride in a clean tent. tube* containing a elrop of elibite* hvdro* Idoiir
arid. If an alundurn crucible* in used, observe particular care in washing th«*
upper portion, as the porous walla are; filled with a solution containing all
soluble* Halts present.

Finally give* the silver chloride and filter a single rinsing with redistilled
alcohol, wipe* th«* out aide of the* crucible, if a (modi, and dry at the* tempera¬
ture that wan employed for the original filter. After 20 minutes, cool m the
desiccator and weigh. Dry for additional period* of 15 minutes until Up¬
weight does* not vary more* than 0.3 mg, Calculate the per ce*nt of chlorine
in the an triple.

QUANTITATIVE AGRICULTURAL ANALYSIS

Volumetric, by Titration with a Standard Solution of Silver
Nitrate. —Chlorine of inorganic chlorides may be titrated very
accurately by a standard solution of silver nitrate, potassium
chromate serving as indicator. The solubility of silver chloride
is so much less than that of silver chromate (1000 cc of water at
20° dissolves 0.0015 gm of silver chloride and 0.024 gm of silver
chromate) that the latter exists permanently only after the
chlorine has been practically completely precipitated. Its
intensely purple color then serves as an indicator of the end
point of the reaction with chlorides:

AgN0 3 + MCI -> AgCl + MNO s ; (1)

AgNOs + K 2 Cr0 4 Ag 2 Cr0 4 + KN0 3 . (2)

This method may be employed to determine the chlorine of
chloride solutions but the latter must be neutral before the titra¬
tion can be made.

Equation (1), above, shows that the hydrogen equivalent of
silver nitrate is 1 and its equivalent weight is therefore the same
as its molecular weight. A tenth-normal solution (see page 7)
will then contain 16.989 gm of the salt in each liter. Instead of
this the solution may be made in the decimal system (page 8),
each cubic centimeter being equivalent to some simple weight of
chlorine. If n is used to indicate this required weight of chlorine,

each liter of solution must contain

1000X169.89 n
35.46 gm

of silver

nitrate.

Volumetric Determination: Silver Nitrate Method. —Prepare the follow¬
ing solutions:

(a) Silver Nitrate .—Calculate the weight of silver nitrate necessary to
make 1200 cc of a solution, either tenth-normal or of such concentration
that 1 cc is equivalent to 0.005 gm of chlorine, adding 1 per cent for
possible impurities. Weigh to centigrams on counterpoised glasses and dis¬
solve in chloride-free distilled water. Dilute to 1200 cc, mixing the diluted
solution very thoroughly.

(Jb) Sodium Chloride .—Prepare 500 cc of a solution of pure sodium
chloride which has been powdered and dried at 105°. The concentration
should be equivalent to that desired for the silver nitrate solution. The
equivalent weight of sodium chloride being its molecular weight (58.46),
a tenth-normal solution must contain 5.846 gm of the salt in each liter.

Ql AST IT A 77 VK DKTERMISA TIOSS

If instead, 1 ee of the. solution is to contain a simple, definite weight, n

. 1000X58.10 n . .. ..

gin, of chlorine, each liter must contain

rldo. In this ease // may conveniently h<* 0.005 gin. Whatever its vain**, n
is the “chlorine factor*', Fri face page 5) of this solut ion.

Weigh the salt carefully on counterpoised glasses and dissolve in chloride-
frc(‘ water in a calibrated flask, dilute to the mark and mix thoroughly,

(r) VnttiHxium Chromate,' Prepare 50 ee of a 5-per cent solution of pot ns •
sium chromate and drop into it silver nitrate solution until a perceptible
coloration, due to silver chromate, is obtained, thus showing that all chlorides
have* been removed. Allow the precipitate to settle and then decant into a
bottle that can be stoppered.

Standardization. Pipette 25 ee of the sodium chloride solution into a
200-ec casserole, fir into a beaker which is placed over a white surface.
Dilute with 25 ee of chloride-free distilled water, add 1 ee of chromate
{solution and then add the silver nit rats* solution from a burette, stirring
constantly, until the first permanent purple or reddish tint is obtained.

Ah each drop of silver nitraf<* solution is added, a purple precipitate in
produced. Near the beginning of the titration this disappears immediately
after mixing but. toward the finish it persists for a longer time. This
behavior serves as a warning of the approach of t he end point. At th<*
first indication of a faint but permanent color, rinse flown the walls of
the beaker or casserole with distilled water, read the burette and then confirm
the reading by adding another drop of silver nitrate solution, which should
deepen the color. When this has occurred, record the volume first noted aa
the end jaunt. Kirns* tin* casserole and repent the titration with a new
portion of sodium chloride solidion, until agreement is obtained.

If a tenth-normal solution of silver nitrate in desired, the sodium chloride
solution will have been made to this normality. In this case, use is made nf
the following simple relation: That the normalities of two .solutions are
inversely as the volume# found to be equivalent to each other. Suppose
that 25 ee of tenth-normal chloride solution is exactly titrated by 21 15
ee. of silver nitrate solution. 'Hie normality of the .silver solution is then

•> ."j y «>r

and the “dilution ratio” in 7 , ~ 1.055 ffl. 1055 is flat “m*r-

21.1.) 10 21.1 o

inality factor”).

If the decimal system in to be used and if the sodium chloride solution
ha# been made so an to contain 0.125 gm in 25 ee, ns above suggested, the
dilution ratio for the silver nitrate solution is again th<* inverse ratio of
equivalent volumes, exactly as illtiafrated in the preceding paragraph.

In the above example 1 ee of the solution would have to be diluted to
1.055 ee, to make it tenth-normal, 100 to 105.5 ec, f liter to 1055 re, etc,
Upon the assumption that the Mum of original solution and added water
equal# the volume of diluted solution fan assumption nut strict jv accurate,
although practically ho for wdutionH not more concentrated than thene)
55 ee of water should be added to each liter of the standardized solution of
this example.

QUANT IT ATI VE AG UK'VLTV UAL .1 AM L YSIS

The dilution is carried out as follows: Kill a dry 100()-<■<■ voluntcl i if flask
exactly to the mark, add the necessary water from a burette and mix well.
This requires a flask that will hold the required added water uborr the mark.

In case the dilution ratio has been found to lie greater than about. l.OIO,
as in this example, the dilution should he accomplished in two steps. I In-
solution is first diluted, adding 3 or 4 ee of water less than the calculated
amount. The solution is then mixed, restandardized and the final adjust-
ment is made with greater accuracy.

Titration.— Weigh samples of about 0.2 to 0.5 gm of the chloride sample
into 200-cc casseroles or beakers. Refer to the directions given on page
50 for weighing and recording weights. Dissolve the weighed samples in
50 cc of chloride-frce water, add 1 cc of potassium eliminate solution and
titrate as in the standardization of silver nitrate solution. Multiply the
number of cubic centimeters of standard solution required by its value in
terms of chlorine, divide by the sample weight and multiply by 100, to
obtain the per cent of chlorine in the sample.

Use of a Correction Factor.—There is a too common practice
among chemists, and especially among industrial analysts, of
using standardized solutions with a correction factor instead of
diluting them to the desired concentration. In flic* example
illustrated above the solution would be used as a tenth-normal
solution, the factor 1.035 being used in the calculations of titra¬
tions to correct for the over-concentration. Or if a decimal
solution were desired and if, for example, the first standardization
showed the chlorine factor to be 0.005012 gm, instead of 0.005
gm, the calculations corresponding to Eq. (4) of page 5 would
be

100 7^ 100 V X 0.005 X 1.0024

-g- =---- - per emit ( 1.

This common technical error is based upon fallacious reasoning.
In actual practice the standard solution is generally made in
quantity for a considerable number of determinations, economy
of time resulting from using one standardization for nil. In
such a case the solution should he diluted to the* desired con¬
centration; so that simplicity of calculations may result from the
use of the milligram-equivalent (in the normal system) or of the
simple factor of one significant figure, such as 0.005 as in the rase
already considered, for the substance to be calculated. Even if
the solution is to be used for only one or two determinations the

« t. >

(It\\x 77 VM 77 17*: HETEUMt \ATfn\S

llsr <,f the correct ion factor is illogical. In the equation ;i I *c»

0 OOo an< l 1.002*1 arc constants and they should he collected.
In other minis the}/ should never hurt' hern calculated for such
isolated experiments , the oriijiual O.OOoOl'J serviiuj in their place.

The same nasunimj applies to tin' normal si/stem. / he conclusion
is that for a solution to he used for atilt/ one or tiro deter mi na¬
tions, neither the decimal nor the normal si/stem should hr adopted,
unless the, primanj standard is the active material of the sta inlaid
solution , so that it map he uccuruteh/ ireii/fud, as is the ease with
sodium chloride. In such a ease no correction factor will he
ncccssart/.

Volumetric, by Titration against Sodium Carbonate. 11 yd n »gr n
chloride (hydrochloric acid] may he determined volume!rically
by titration with standard base, such as potassium hydroxide,
using methyl orange or methyl red as indicator, or by titra
fjon against a solution containing a weighed amount ot sodium
carbonate. These methods are included in tie* general group
designated by the term “neidimetry.” The following two meth¬
ods are applicable to hydrochloric acid only, as the special rep¬
resentative of the more general group of chlorides.

Hydrochloric acid reacts with sodium carbonate in two stage :

IKI 1 Xad'Oj > Xuiiro, } Xat'l; (1 )

11(1 | XalH *< ht > H *(>, f Na< *1. (2i

This is followed (unless the concent rat ion is small) by deeone
position of the carbonic arid so produced:

11,CO, * HA) 1 CO.,. Cij

For sodium bicarbonate, produced by reaction Hi, and in com
c«uitrations ranging up to about fifth-normal, I*a about -Vd.
This is a nearly neutral solution and phenolpbtbalein, whose color
range is S.d to 10, will indicate this point by the disappearance
of a pink tint but. titration by Use of this indicator jm not satis¬
factory localise of the difficulties attending the prevention of
local action according to Jvp (2q and consequent escape of cm bon
dioxide*. At the completion of the second react ion the solution
may contain any quantity of carbon dioxide* up to the saturation

QUANTITATIVE AGRICULTURAL ANALYSIS

point at the prevailing temperature. A tenth-normal solution
of this gas, has a P H value of about 3.75, from the small amount,
of weakly ionized carbonic acid existing in the solution. More
concentrated solutions, such as might be produced bv temporary
supersaturation, will have somewhat lower U u values but they
will usually fall within the color range of methyl orange, which is
2.9 to 4. It is therefore convenient to titrate a weighed sample
of sodium carbonate, dissolved in water, to an end point with
methyl orange, this representing complete decomposition of tlm
carbonate. In this case the hydrogen equivalent of sodium car¬
bonate is 2, since both univalent sodium atoms are replaced by

hydrogen. Its equivalent weight is therefore 53, while

that of hydrochloric acid is 36.468, as usual.

These points will be made clearer by reference to Fig. I, page*
14.

The determination above discussed is introduced here as an
example of a method for determining the concentration of
any hydrochloric acid solution. The analysis of such a solution
is expressed as grams per cubic centimeter or as per rent hij weight.
However, it should be remembered that the method will apply to
similar determinations of concentration of other strong acids,
such as sulphuric and nitric acids. Also it is a much used
method for standardizing volumetric acid solutions, in which
case the result of the experiment is expressed either in normality
or in terms of the weight of some other element or group of
elements equivalent to 1 cc as explained on page K and as
discussed in connection with standard silver nitrate solution,
above. This method for standardizing hydrochloric acid is
described on page 83, for the analysis of carbonates.

Volumetric Determination: Sodium Carbonate Method . The laboratory
stock of “dilute" acid is suitable for this exercise, or a Humph* muv be
furnished by the instructor. Calculate, the dilution ueriwtary to make the
solution approximately fifth-normal, if anything is known regarding the
approximate concentration of the sample. If there* is no available infor¬
mation on this point determine the specific gravity with a flouting hydrom¬
eter (see page 97) and calculate the approximate concent rut ion from the
following table.

QUANTITATIVE DETERMINATIONS

Table III.— Conversion Tajble for Specific Gravities

Specific

gravity*

Per cent, HC1

Specific

gravity*

Per cent, HCl

1.000

0.16

1.115

22.86

1.005

1.15

1.120

23.82

1.010

2.14

1.125

24.78

1.015

3.12

1.130

25.75

1.020

4.13

1.135

26.70

1.025

5.15

1.140

27.66

1.030

6.15

1.142

28.14

1.035

7.15

1.145

28.61

1.040

8.16

1.150

29.57

1.045

9.16

1.152

29.95

1.050

10.17

1.155

30.55

1.055

11.18

1.160 j

31.52

1.060

12.19

1.163

32.10

1.065

13.19

1.165

32.49

1.070

14.17

1.170

33.46

1.075

15.16

1.171

33.65

1.080

16.15

1.175

34.42

1.085

17.13

1.180

35.49

1.090

18.11

1.185

36.31

1.095

19.06

1.190

37.23

1.100

20.01

1.195

38.16

1.105

20.97

1.200

39.11

1.110

21.92

* At 15°.

In carrying out the dilution the required amount of acid is measured in a
dry volumetric flask. This is then poured into a 1000-cc volumetric flask,
the smaller flask being rinsed several times with distilled water and the
rinsings added to the solution in the larger flask. Dilute to the base of the
neck of the 1000-cc flask and mix; finally dilute to the mark and mix
thoroughly.

Sodium Carbonate .—The sodium carbonate to be used as a standard is
best made from sodium bicarbonate, as this salt can usually be obtained in a
high state of purity, so far as other interfering solids are concerned, the only
impurities being water and normal sodium carbonate. By heating to about
300° the following reaction is produced:

2NaHC0 3 -> Na 2 C0 3 + H 2 0 + C0 2 .

At the same time water of crystallization is expelled and pure dry sodium
carbonate remains.

QUANTITATIVE AGRICULTURAL ANAL VSIS

Heat about 25 gm of high-grade sodium bicarbonate in an electric! oven
to 300° for three to five hours. A platinum dish is best for this purpose.
Cool the product in a desiccator and preserve in a tightly stoppered bottle.
On a counterpoised glass weigh exactly 5.300 gm of the* pun* sodium car¬
bonate. Brush this into a dry funnel which rests in tin* neck of a oOO-co
volumetric flask. Jar most of the salt into the flask and rinse clown the*
remainder with distilled water. Remove the funnel, gently agitate until
the carbonate is dissolved, then dilute to the mark and mix well.

Titration.—Fill two burettes with the respective solutions. Before
proceeding with the titrations, practice reading t he color changes as follows:
Place 100 cc of distilled water in a beaker and add a drop of methyl orange
and 0.5 ce of carbonate solution. Drop in acid until'! he last drop changes
the tint from yellow to pink. Now, drop in carbonate* solution until the
yellow color reappears. Repeat the process until the color change can be
observed when but one drop of cither solution is added. It will aid in the
next process if this solution is preserved and another prepared, flu* two
showing the two colors of methyl orange. These an* sot aside for <•< unparison.

Measure out exactly 25 cc of the sodium carbonate solution into a
beaker or Erlenmcyor flask, placed on a white, surface. Add a drop of
methyl orange and then carefully run in acid solution from the other burette
until one drop changes the color from yellow to pink. Record t he volume of
acid required to do this. In wise the end point has been overstepped,
add 5 cc more of the carbonate solution to that already in the flask and
continue the titration. Finally record the volumes of both carbonate and
acid.

Since the carbonate solution was exactly fifth-normal, 1 <*c is equivalent to
0.007294 gm of hydrochloric acid. The concentration tin grams of IB *1 per

cubic centimeter) of the titrated solution is then when* 1',.

and V a are the volumes of carbonate and acid, respectively, equivalent

to each other, and that of the original sample is ^ w hen* S

is the volume of sample used for the dilution. Grama ptr vuluc nntumttr
may be converted into per cent by weight by dividing by the specific* gravity
of the sample, measured at 20°. The normality of the titrated acid solu¬
tion is obtained, if desired, as in the case of silver nit rate solid ion: ^

normality, F' e being the volume of acid equivalent t.<> ee of t he lift h-uorimil

carbonate. For the original sample, normalit y - 1,KM) y " zr> ■ N ' •TOlHtN

•WF. .ST'.

Volumetric, by Titration with Potassium Hydroxide. In case
the number of determinations of hydrochloric acid to be made i.s
small, no advantage is gained by the use of standard potassium
hydroxide. This is because (he most satisfactory method for
standardization of this solution is by titration against an acid

Of’A X Tl T. 177 VK DETERM l S A TIDES

solution which, in turn, is standardized by tho method used in
\\ i{ > preceding exercise. As that standardization was, in effect,
an analysis of tin* acid solution no further experimental work
should be necessary. Hut because of the fact that potassium
hydroxide and sodium hydroxide solutions have a wider applica¬
bility than do carbonate solutions, serving for the titration ot a
great variety of strong and weak acids as well as ot acid salts,
the bast* solutions are more often kept as standards and, as such,
may be conveniently used for the* determination of hydrochloric
acid in solutions.

Volumetric Determination: I'alnxxium II ydi'nfidr Milhtul, (nlculate tie*
weight of solid potassium hydroxide necessary for 112(H) cr of fifth normal
solution. Add 1 per cent for water and other impurities and dis solve the
calculated quantity in recently boiled and cooled distilled wafer. 'The solid
base* need not he weighed on tin* analytical balance. Dilute the solution to
about 1200 cc, mix and allow to cool to 20 \

Prepare an approximately tiffh-normal solution of hydrochloric acid and
titrate against fifth-normal sodium carbonate, as directed in the preceding
exercise. Am t lie acid is merely an intermediate in the proce. 4 if s normality
need not be calculated. Men (ire out 2a cc of the l»a»<* solution from a
burette, add a drop of methyl orange or methyl red and titrate to a faint
pink color with the acid solution. (Methyl red should not he med if the
haw* contains more than very small quantities of potassium carbonate.)
This is simply an indirect comparison of the normalities of baar and car¬
bonate solutions, and the volume of acid docs not. enter into the final caleu
Iations if equal volume* of base mid carbonate were used, m ia seen from tlm
following:

Let Y„ volume of acid equivalent to 2~» ce of carbonate solution and
P« volume equivalent to 2o ee of base. 'Then the normality of the

. V* N

base y * . ’

Titration. The standard bane just prepared will *erve for the fit rat mu
of hydrochloric aeiri and of other strong and weak acid*', also of umnv seal
salts, such as acid sulphates, 'Die titration r* carried out m in atandardi/mg
the base, except, that phenolpbthalein in used as imlieator for the weaker
acids. In any cum* the wimt- induttfnr must he urnd when titrating the
lm.se against the intermediate acid in standardizing, nine#* the invariable
presence of a small amount of carbonate in the b/mie solution givea a dighflv
different normality, as calculated from titrations in presence of different
indicators,

'Hie titrations may be carried out in either direction, bjme being added f«>
acid or acid to base, provided t hat t he same eojor tint i»taken aa »be end point,
indication in all eases with a given indicator. However it n usually ftue
that it is easier to judge the first upjH'uruure of pink than its fund di-sapp* *r-

60 QUANTITATIVE AGRICULTURAL ANALYSIS

anee. This means that it is usually better to add acid to base in presence of
methyl orange or methyl red, and base to acid in presence of phenolphtlialein.
Methyl orange is the only indicator that can be used sat isfaet orily for car¬
bonate solutions.

SULPHATES

Gravimetric, by Weighing Barium Sulphate.- - 1 he basis for
this method is the following reaction:

BaCl> + M 2 SO 4 -> BaS0 4 + 2MCI.

Solubility. —The solubility of barium sulphates in wafer is
quite low. At 20°, 1000 cc of water will dissolve about 0.002(>
gm of the salt. This contains 0.00153 gm of barium and ().()() 107
gm of the sulphate radical. The precipitation of barium sulphate
is made the basis for the determination of either barium or
sulphates. In either case it is necessary to maintain a slightly
acid solution in order to avoid the possibility of precipitating
other barium salts, such as carbonate, oxalate or phosphate, in
case traces of these salts, or of their acids, are present in the
sample or in the reagents. A slight excess of hydrochloric acid
is used for this purpose.

Crystallization. —Because of the very small solubility of barium
sulphate it precipitates almost instantaneously as the* reagent
(a soluble sulphate or barium chloride) is added. On this
account it usually forms relatively small crystals and these may
be so small as to pass through filters of ordinary density unless
care is given to the precipitation process. 'Flic* best conditions
are provided by keeping the solution hot, adding the reagent
drop-wise and stirring continuously. Tins is followed by a
process of digestion, which serves to enlarge the crystals already
formed, as explained on page 25.

Change of Weight of Barium Sulphate.— ('onsiderable care
must be exercised in burning the paper upon which barium
sulphate has been filtered and in subsequent ignition of the
precipitate to expel traces of moisture. If the temperature is
allowed to rise to too high a point barium sulphate will
gradually decompose, yielding sulphur trioxide and losing
weight thereby:

BaSO* —> BaO + SO*.

(1)

Ql 'A XT/TA 77 YE DETEUMIX A T/nXS

On this account the blast lamp or Mrfkcr burner should never be
used for heating the precipitate and the temperature should not
be allowed to rise above that of dull redness.

On the other hand, errors may occur through partial reduction
of barium sulphate by carbon monoxide or organic gases resulting
from heating of the filter paper. Barium sulphide is thus pro¬
duced and again the material loses weight:

BaS <>4 + K ’() - , BaS + 4( ’O... f2l

In order to avoid this reduction the temperature should be held
at as low a point as will serve to accomplish the combustion of
the paper and a plentiful supply of air must 1m* maintained by
inclining the crucible and rover, as directed cut page* 29. Kven
with these precautions some reduction may occur but if beating
is continued for a few minutes after the carbon has disappeared,
reoxidation will take place:

BaS + 20,. f BuSO*. CJ)

If it should be suspected that either or both of the errors just
discussed has occurred in any given analysis a correction may be
made by adding a drop of dilute sulphuric acid to the precipitate
after the first weighing, then gently reheating to expel the excess
of acid and water, and reweighing. A gain in weight is taken
as evidence that sulphide or oxide of barium was present in the
first case. The second weight is then the correct one.

This addition of arid, with subsequent heating, also serves
to correct any error that may have occurred in the determination
of barium , through the occlusion of barium chloride by the
precipitating barium sulphate but not in the determination of
the Hulphatv. radical, ft will lie seen that such occlusion would
occasion a negative error in the determination of barium, hut a
positive one in the deteiiuinafion of the sulphate radical. Then
in the first ease sulphuric arid converts occluded barium chloride
into barium sulphate and gives a precipitate of correct composi¬
tion. In the* second case barium chloride is an occluded impurity
in the precipitate and its conversion to sulphate merely serves
to increase the error. Therefore*, when barium chloride i* med
as the precipitating reagent for sulphuric acid if is highly
important that the precipitation should be carried out very slowly

QUANTITATIVE AGRICULTURAL ANALYSIS

by adding the reagent drop-wise and stirring vigorously. This
method serves not only to minimize occlusion of the reagent but
also to prevent the formation of a very finely divided precipitate.

Determination of the Sulphate Radical.—Weigh duplicate samples of
0.25 gm of the sulphate into beakers and dissolve in 75 cc of distilled water.
Add 1 cc of dilute hydrochloric acid, heat to boiling and adcl, drop-wise and
with constant stirring, a clear 5-per cent solution of barium chloride until
the sulphate is completely precipitated. Digest on the steam bath until
the precipitate settles and the solution clears, then filter and wash with
hot distilled water, testing the washings finally with dilute sulphuric acid to
insure removal of barium chloride.

While the digestion of the precipitate is proceeding the crucibles should
be prepared. New crucibles generally lose weight slightly during the first
heating. Clean tw;o porcelain crucibles and mark them with small symbols,
I and II (small dots are best), using an ordinary pen and ink. Allow the ink
to dry, then place the covered crucibles over a blast lamp or a No. 4 M6ker
burner and heat with the full flame for 30 minutes. Remove the flames and
allow the crucibles to cool to below redness, then place them in the desic¬
cators and, after 15 minutes standing, weigh accurately, handling only with
the tongs. The rubber tipped tongs are conveniently used for the cold
crucibles.

After the paper and precipitate has been washed free from soluble salts,
drain thoroughly and then slip the paper up the side of the funnel and fold
as shown in Fig. 9. Place-the folded paper in the weighed crucible. The
crucible is then inclined on the triangle, as indicated in Figs. 10 and 11, and
the flame of the ordinary burner is applied, gently at first to avoid loss of
precipitate by spattering. After the paper has become dry the temperature
is raised, the burner being placed under the bottom of the crucible so that
warm air, and not products of combustion, pass through the crucible.
Proceed in this way until all carbon has been oxidized and the precipitate is
white, but without allowing the crucible to become more than a dull red.
When the precipitate is quite white the covered crucible is cooled in the
desiccator for 15 minutes and weighed. The difference between this and
the first weight represents barium sulphate, from which the per cent of
the sulphate radical, of sulphur trioxide or of sulphur is calculated.

In order to confirm the accuracy of the work the covered crucible is
heated for additional periods of 10 minutes and cooled and weighed after
each heating. The weight should not change more than about 0.2 mg after
such heating, unless the temperature has been carried too high. If any
trouble has been experienced in obtaining constant weight it may be well
to add a drop of dilute sulphuric acid to the cooled material, then to evaporate
carefully over a flame, and finally to heat gently and reweigh. This will
correct for the formation of barium sulphide or oxide, as already explained.

Volumetric, by Titration with Standard Base or Carbonate.—

Just as the chloride of hydrogen (hydrochloric acid) may be

QUANTITATIVE DETERMINATIONS

determined by titration with a standard solution of a base or
carbonate, so may the sulphate of hydrogen (sulphuric acid) be
determined. It is obvious that both determinations, as well
as all other acidimetric determinations, are measurements of
ionizable hydrogen alone, and that they can be calculated only to
this hydrogen itself or, if other acids are known to be absent, to
the acid present—in this case sulphuric acid. Such titrations
could not properly be regarded as determinations of the acid
radical, since salts of the essential acid are almost invariably pres¬
ent in small and variable quantities.

Determination of Sulphuric Acid: Potassium Hydroxide Method. —Fifth-
normal potassium hydroxide is prepared and standardized as in the deter¬
mination of hydrochloric acid, page 59. The sample of sulphuric acid,
being non-volatile, may be weighed in a flask or beaker, if an accurate
balance of sufficient capacity is at hand, or it may be measured and the
specific gravity determined, the weight then being calculated. The dilution
and titration are carried out exactly as directed on pages 57 and 59. The
calculation of grams per cubic centimeter, per cent by weight and normality
differ from that for hydrochloric acid only in the equivalent weights used.
Sulphuric acid, being a dibasic acid, has a hydrogen equivalent of 2 and its
equivalent weight is one-half of its molecular weight.

CALCIUM

Gravimetric, by Weighing Calcium Oxide. —If a neutral or
basic solution of a calcium salt is treated with a soluble oxalate,
as ammonium oxalate, a reaction like the following occurs:

CaCl 2 + (NH 4 ) 2 C 2 0 4 -> CaC 2 0 4 + 2NH 4 C1. (1)

After filtering and washing the calcium oxalate this is ignited:

Ca0 2 0 4 -» CaC0 3 + CO; (2)

CaCOa -> CaO + C0 2 . (3)

The calcium oxide is then weighed.

The method is applicable only to soluble calcium salts and to
calcium oxide, hydroxide or carbonate. The last three com¬
pounds dissolve in hydrochloric acid, with formation of water or
carbonic acid as byproducts, and carbonic acid is expelled by
heating. Calcium phosphate must be given a preliminary
treatment to separate phosphoric acid, as otherwise the phos¬
phate will reprecipitate as soon as the solution is made basic.

QUANTITATIVE AGRICULTURAL ANALYSIS

Solubility. —The solubility of calcium oxalate in water at
ordinary temperatures is about 0.0050 gm per liter, expressed
as the anhydrous salt, this containing 0.0016 gm of calcium.
A slight excess of ammonium oxalate diminishes the solubility, as
explained on page 24, so that the recovery is very good. It
is necessary to precipitate from hot solutions in order to avoid the
formation of very fine crystals.

Purity of Precipitate. —Examination of physical data will
show that oxalates of all of the alkaline earth metals and of the
heavy metals have comparatively small solubilities in water.
If any of these metals are present it will therefore be necessary
to effect a preliminary separation before calcium can be pre¬
cipitated and recovered as pure oxalate. This will be given due
attention later in the work but in the following exercises calcium
is assumed to be the only metal present, with possible exceptions
of the alkali metals.

Determination of Calcium: Gravimetric Method .—From a closed weighing
bottle or on counterpoised glasses (according to the nature of the sample)
weigh accurately two portions of about 0.2 to 0.4 gm of the prepared cal¬
cium compound, placing in 200-cc Pyrex beakers. Add 75 cc of water and
5 cc of a 10-per cent solution of ammonium chloride, the latter to prevent
the precipitation of possible traces of magnesium.

If the calcium salt contains carbonate it will not be completely dissolved
in water. In this case do not add ammonium chloride but provide cover
glasses for the beakers and add 10 cc of dilute hydrochloric acid. Calcium
carbonate will dissolve with effervescence. The covered solution is then
boiled for a few minutes to expel carbon dioxide. Now remove the covers
and rinse them and the upper portions of the beakers with a jet of distilled
water, allowing all of the rinsings to run back into the beakers. Dilute to
about 75 cc.

Having obtained a solution by either method add 15 cc of ammonium
hydroxide (5-per cent ammonia). A distinct odor of ammonia should be
perceptible after blowing away the vapors above the liquid. Heat nearly
to boiling and add, from a pipette, a recently prepared saturated solution
of ammonium oxalate, drop by drop and with constant stirring. Ten to
15 cc of solution may be required. Digest on the steam bath until the
precipitate settles and test the solution above by adding another drop of
oxalate solution.

When precipitation has been completed, filter on a paper of medium
density and wash precipitate and paper with hot water until the washings
test free from chlorides, as determined by allowing the washings to fall into
a test tube containing silver nitrate acidified with nitric acid. Finally drain
as well as possible, remove the paper from the funnel and fold as shown in

QtWXriTA 77 YE liKTKHM l \.\ 7 ‘/n\S

r>;>

Fig. 0, page 20. Place in a porcelain or platinum crucible that, has
ignited to constant weight, incline the crucible and burn the paper. When
the precipitate is white place the crucible in an upright position, cover and
beat with the full flame of tin* blast lamp or of the No. t Meker burner until,
after cooling for Id minutes in the desiccator, the weight is constant. If
the former burner is used tin* first weighing may be made after 15 minutes
of heating. If the Mdker burner is used the precipitate .should be heated for
30 minutes before tin* first weighing.

From the weight of calcium oxide found calculate tin* per cent of calcium
in the sample.

Volumetric, by Titration with a Standard Solution of Potas¬
sium Permanganate. Instead of igniting calcium oxalate ami
weighing the oxide fin* purified oxalate may he redissolved in
sulphuric acid and the resulting oxalic acid tit rated with standard
potassium permanganate:

Ca( y>4 i II s S<> 4 - *< uSO* h HmC V >*; (!)

f)H,(y >4 + 2 KMn( >4 + :UI 2 S () 4 - K 2 S< >4 ( 2MnS( > 4 I

Si 1,0 1 moo,. ( 2 )

Although this eonsfitutes a direct titration of oxalic arid it is
indirect, so far as calcium is concerned, and tin* calculation
of the latter can he accurate only M) if the precipitation has
recovered all of the calcium, (2) if the calcium oxalate has been
well purified and (!i) if the oxalic acid resulting from its decom
position by sulphuric* acid has been recovered completely. The
process of washing is then doubly important. If ammonium
oxalate* is left in the precipitate this will later yield oxalic acid
and give* a high result for calcium. On the other hand, if the
paper is not well washed after sulphuric acid has been added, not
all of the oxalic* acid which has been yielded by calcium oxalate
will he titrated, and the result will be low.

Standard Solution. Permanganate solutions for this purfKw
may be made in tIn* decimal system or in the normal system.
If calcium is the only element to be determined the decimal sys¬
tem offers greater convenience, of course. If the solution b to l>e
used also for tin* determination of iron and possibly of other
elements, then the normal system offers advantages. In cither
case it is necessary to know the equivalent weights of calcium
and permanganate and these cannot he calculated as simply as in
eases already considered.

QUANT IT A TIVK AGHIUUl/ITIiM. ASM.) >7 N

Apparent Valence.--In ordinary read ions o! double doromposi-
tion the valences of the elements and radicals which arc being
transposed arc measures of the respective reacting powers of
these entities. This is not true; tor reactions oi oxidation and
reduction. Here the reacting power of a compound is determined
by the extent of change of valence. As an illustration may be
taken the reversible oxidation of hvdriodic acid bv ferric chloride:
2FeCl, + 2III + 211H f I,.

The valence of iron in ferric chloride is 'A but. this compound does
not exchange three atoms of chlorine for an equivalent amount, of
another radical—it simply parts with one atom of chlorine
which oxidizes hydriodic acid. The hydrogen equivalent of
ferric chloride in this reaction is then equal to tin* change in
valence of iron. This is 3 — 2 =■■ 1.

For the purpose of this inspection tin* actual valence of the
elements undergoing the reaction need not be considered as flu’s
depends upon the structural composition of the compounds,
which is not always known. The apparent valence is that which
is indicated by the simplest direct combination of positive and
negative elements and it is therefore a measure of combining
power. In the above reaction iodine is the element that is
oxidized and it is sufficient to regard its apparent valence in
hydriodic acid as 1 and in the form of tin* element as 0. The
hydrogen equivalent of hydriodic acid is the difference lief ween
these two apparent valences, or 1.

The reaction between potassium permanganate and oxalic
acid may be inspected similarly. Omitting the coefficients
given in Eq. (2), page 65 ; the empirical equation is

H2C2O4 + KMn 0 4 + H 2 S 0 4 —► K2SO4 f- MnS< > 4 b 11 A > }• (‘() 2 ,

Obviously, carbon is the element that is oxidised and manganese
is reduced. The apparent valence of an element which is in the
negative radical of an oxyacid or of its salt is found bv subtracting
the total valence of the positive radical from that of the other
elements of the negative radical and dividing the result hv the
number of atoms of the element in question.

In oxalic acid the apparent valence of carbon j* t ben ' * X ~ 2
— 3, while in carbon dioxide it in ■(. The hydrogen equivalent

(jr A ST IT AT IV E UKT EH M ! .V AT f<>\S

(17

of carbon is then i and that, of oxalic acid (containing two atoms
of carbon) is 2. Since one atom of calcium is equivalent to one
molecule of oxalic arid, the hydrogen equivalent of the former

also is 2 and the equivalent weight of calcium is 20.Odd.

The apparent valence of manganese in potassium permanga¬
nate is (1 X 2) — 1 7. In manganese sulphate if is 2. The

hydrogen equivalent of potassium permanganate is then f> and

the equivalent, weight is * 31.000.

Standard Potassium Permanganate Solution. In order to

prepare a stable solution it is necessary that, manganese dioxide

shall be absent and that the container and the distilled water

shall he free from reducing matter. Bottles and flasks are

cleaned by a preliminary treatment with warm chromic acid

chaining solution, followed by a thorough rinsing. A good

distilling process will usually produce sufficiently pure wafer;

manganese dioxide already present, in the permanganate is

removed by filtering the solution through asbestos.

Prom the above discussion of equivalent weights if- will be

seen that a normal solution of potassium permanganate will

contain JU.bOh gm in each liter. A solution, I ce of which is

equivalent, to a given weight of calcium, will contain in each liter:

10(H) X Sl.fiOft n x . , , t .

“gm, where n is the weight of calcium to be

equivalent to each cubic centimeter.

The solution may Ik* standardized against pure sodium oxalate,
ferrous ammonium sulphate, or calcium carbonate* whose
calcium content has been determined gravimetrically. The
equations for the reactions of the first two with permanganate
follow.

r>Xa,r v C> 4 f- 2KMu< U + KH 2 S< V * bXa*S< ) 4 b l0.SO 4 d~

2MnSO t | HU, O; f I )

10FeSO 4 .(XH 4 ) 2 S(> 4 d- 2 KMii 0 4 T HHnSt U *bFe a (S<>*);* f

K a S0 4 d lOfXH^SO* I 2MnSO* j SlMh f2)

(Ammonium sulphate of the double salt is seen to play no
part in the reaction and its formula could be omitted from

QUANTITATIVE AGRICULTURAL ANALYSIS

the equation. However, it must be considered in calculating the
equivalent weight of the salt, since it is weighed along with the
ferrous sulphate. The same is true of water of crystallization.)

For standardizing by calcium carbonate the latter is weighed
and treated according to the principles discussed on page 65,
the value of the permanganate solution being calculated from
the volume of solution found to be equivalent to this weight.

The equivalent weights of all of these substances may be
calculated by the methods illustrated in the preceding discussion.

Preparation of Solution.—Prepare 1200 cc of a solution, either tenth-
normal or of such concentration that 1 cc is equivalent to 0.002 gm of
calcium, as the instructor may direct, as follows: Weigh to centigrams on
counterpoised glasses, 1 per cent more than the calculated amount of the
best grade of potassium permanganate obtainable, brush this into a glass
stoppered bottle and add 1200 cc of water. Agitate until the salt is
thoroughly dissolved and the solution is well mixed. Place the bottle out
of bright light for 24 hours then decant through a Gooch filter or an alundum
crucible into a cleaned flask or bottle, using a pump. The solution must not
be allowed to come into contact with rubber. Rubber stoppers used during
the filtration process should first be well washed to free them from loose
material. Do not attempt to recover the last portions of solution remaining
in the bottle.

Standardization.—Use one of the following methods.

(a) With Sodium Oxalate. —Weigh two or three portions of about 0.2 gm
each of sodium oxalate of known purity (a Bureau of Standards sample
if this is available) into 250-cc Erlenmeyer flasks. Dissolve in 50 cc of
recently boiled and cooled distilled water and add 10 cc of dilute sul¬
phuric acid. Place a thermometer in the flask, warm to 90° and titrate with
permanganate solution, stirring vigorously and continuously. The per¬
manganate must not be added more rapidly than 15 cc per minute and the
last cubic centimeter must be added drop-wise, with particular care to allow
the color from each drop to disappear before the next drop is added. When
a final permanent pink is obtained observe the volume of solution required
and calculate (a) the normality of the permanganate solution and (b)
the weight of calcium equivalent to each cubic centimeter, referring to the
discussion on page 67.

(b) With Ferrous Ammonium Sulphate. —Use accurately weighed portions
of about 1 gm of the pure crystallized salt. Titrate as for sodium oxalate
except that the solution is not to be heated and the titration may be carried
out more rapidly, the reaction being nearly instantaneous. The experiment
must be completed immediately after dissolving the iron salt, as otherwise
oxidation by air will vitiate the results.

(c) With Calcium Carbonate. —Use a dried sample in which calcium has
been determined gravimetrically as directed on page 64. The method to be

(Jt \ t A T IT A 77 YE DETERM l X .1 T/OSS

used for standardizing the permanganate solution is exactly the sumo as
described below for the determination of calcium, and from the results the
normality and the ealcium equivalent of the solution are calculated:

\YP

0.020027 r
u*
v
v

20.027

calcium equivalent of the permanganate, and

normality of permanganate*, where

weight of calcium earl innate,
known proportion of calcium in the carbonate,
volume of permanganate solution used, and
equivalent weight of calcium.

If purr calcium carbonate is used, R the factor for calcium in calcium
carbonate, divided by KM).

Determination of Calcium: Prrmnnganntv Method. Weigh on counter¬
poised glasses two portions of the prepared sample into 250 re Pyre*
beakers, using 0.2001 gm if the standard solution is tenth* normal, or
exactly 0.2000 gm if the solution is in the decimal syutem. (See the discus¬
sion of factor weights, page K. It is not always advisable to use this system
for such small samples. If not, weigh accurately samples of ntmnl 0.2 gm;.
Add 75 rr of water, cover and add 10 re of 10-per cent hydrochloric acid.
After the material has dissolved boil the covered solution gently to expel
carlsiu dioxide, then rinse down the cover glass and the sides of the breaker
with distilled water. Add 15 er of ammonium hydroxide (5-per cent
ammonia*, which should leave the solution distinctly basic but clear.

Heat nearly to boiling and add from a pipette 10 to 15 ee of a recently
prepared saturated solution of ammonium oxalate, drop by drop and with
stirring, (’over and digest on the steam bath until the precipitate nettles,
then test the Hear, supernatant liquid for completion of precipitation by
adding another drop of oxalate solution, Finally filter and wash with
hot water until a few drops of the washings give no turbidity with a basic
l-per rent solution of calcium chloride, showing the complete removal of
ammonium oxalate, fn applying the wash wafer the entire paper must, be
treated, us in cither eases.

Pirns* a 250-rr Krlenmryer flask under the funnel, pierce the point of the
paper and wadi as much as possible of the precipitate into the flask with a
stream of hot water. Dissolve the remaining precipitate with two or three
5-cc portions of hot 25-per cent sulphuric arid. Finally give the* paper a
thorough washing with hot water from the wash bottle. The total volume
of solution in each flask should be 50 to 75 er.

Place a thermometer in the flask and warm the solution to 00'*, then
titrate in the manner described for tie* standardization of permanganate
by sodium oxalate, page* OH. If the sample weight was exactly KM) tune* the
calcium equivalent of the standard solution, the burette will read directly
in per cent of calcium.

Q UA N TITA TI YE A UUl rVUl UAL WAD SIS

IRON

Iron is sometimes determined gravimeiri^aliy by precipitating
ferric hydroxides by ammonium hydroxide, igniting and weighing
this as ferric oxide:

Fcida + SNII4OII -> Fernm, i dNHd 'l: Uj

2Ke(OHh ' Fed >;i T dH,< >. (2)

However ferric hydroxides is a colloidal >ub>tanre which adsorbs
soluble salts with groat tenacity, so that it is difficult *»» purify
any but a small precipitate by washing. Also during ignition
on paper, reduction of the oxide is liable in orrur. tor these
reasons volumetric methods are usually preferable. Standard
solutions of permanganates or of dichromate^ are Mutable for
this purpose.

Volumetric, by Permanganate. In acid solutions, potassium
permanganate oxidizes ferrous salts by the following reactions:

KMn0 4 + < r >Fe( ’I, + SIICI • K( A * Mid 1 •

ol el | * IIJMI; r Ij

2KMn0 4 + IOF0SO4 + KH 2 S<b ‘ K 7 S» b * 2MnS< b *

.MVS* b f s U (). ri )

The equations show that the added acid play a definite part in
the reactions and if an insufficient amount is present the solution
will become basic and a precipitate will Pom, consisting of
hydrated manganese dioxide and basic iron *ah :

3FeCl 2 + KM11O4 + (n 4 2; fid t - :U ef A a Uf f

Mnn mild* f KoH. Cl)

Aside from the trouble* exjierienced in reading the end point,
caused by the appearance of the precipitate, it in seen from
Iiq. (tt), above, that manganese is reduced to the apparent
valence of 4 instead of 2, ho that tie* iron jw-r cent earned Ik*
calculated when both reactions take plan*.

In presence of hydrochloric acid more permanganate than
the theoretical amount may la* used, with liberation of some*
free chlorine. This action may !«* almost enfiiely prevented by
the addition of manganese sulphate to the solution, ftenerally
phosphoric acid also is added to prevent the hydrolvsi* of ferric

QCASrn'A 77 17'/ UKTEUM / AM 77 OSS

chloride, thus avoiding tin* appearance of a ml color which
would mask the* end point, of the titration. 1

Reduction of the Iron Solution.— Iron exists in the feme con¬
dition in most, ores or other minerals. In order to reduce the
solution of ferric, salt cither stannous chloride, zinc, sulphurous
acid or hydrogen sulphide may In* employed. The first, two an*
the only ones now commonly used.

Stannous chloride, in solution, possesses the advantage 1 of
instantaneous action if added to the* hot solut ion of ferric chloride*.
If the* iron is to 1><‘ redu<*ed by stannous ehle>ride an addition of
this salt to the ore during the* process of solution will materially
hasten the* action. For the* final reduction the* stannous chloride
solution may he added from a pipette, the disappearance of the*
red color of basic ferric chloride providing an approximate indica¬
tion of the end-point.

In the analysis of iron ores there is occasionally trouble at this
point unless certain precautions have* been taken. In the first
place*, many iron ores contain appreciable quantities of organic
matter and this serves to produce a yellow color when t he* on* is
dissolved. As color due* to this cause* does not disappear when
the iron has been reduced it is not possible* to determine when the*
correct amount of stannous chloride* has been added. This
trouble* may be* avoided by igniting the* weighed sample- for a
short time in a porcelain crucible, before dissolving.

The se*eon<l cause* e>f irremovable color comes from fusion of
insoluble* residues in platinum crucibles. The* pyrosulphnte
which is use*d as a flux dissolves traces of platinum and this, with
stannous chloride, forms a yellow solution containing a complex
of tin and platinum. This interference is avoided by the sub¬
stitution of porcelain crucibles for those of platinum.

After a slight excess e>f stannous chloride has been adeted the*
solution is cooled and a considerable, etxeess of mercuric chloride*
is added, the* unuse*d stannous chloride being thereby oxidized:

2HgC] 8 + SiiH- —SnfU + 211 gH.

Mercuric chloride will not oxidize ferrous chlorate ami hence* may
be* left in the* solution. If an insufficient e*xcess of mercuric

1 For the explanation of these points see* Maicin, “Qumititstiv** Anuiysis/*
2nd cd., pp. 241 245.

QUANTITATIVE AGRICULTURAL ANALYSIS

chloride is used, or if it is added too slowly, free mercury may be
produced:

HgClo ~f" S11CI2 —* S11CI4 Hg.

The indication of such action is the appearance of a gray precipi¬
tate of mercury instead of the characteristic white silky crystals
of mercurous chloride. If mercury is so produced the deter¬
mination is ruined because this mercury will itself reduce some of
standard oxidizing solution during the process of titration of the
iron.

Standard Solution. —The permanganate solution as used for
calcium is suitable for the iron determination, or a new solution
may be made in the decimal system. In the latter case a con¬
centration such that 1 cc is equivalent to 0.005 gm of iron is
conveniently used. As iron is oxidized from a valence of 2 to a
valence of 3 its equivalent weight is 55.84 and 1 cc of a tenth-
normal solution is equivalent to 0.005584 gm of iron. The
equivalent weight of potassium permanganate is one-fifth of its
molecular weight, as was shown on page 67. The concentra¬
tion of permanganate solution to be equivalent to any specified
weight of iron may be calculated by the methods illustrated on
page 67.

Determination of Iron in an Ore.—Sample the ore and grind the last selec¬
tion to pass the 100-mesh sieve. Weigh three samples of exactly 0.5 gm of
ore on the counterpoised glasses, brushing into each of three porcelain cruci¬
bles. Heat the crucibles without covers for 5 minutes, using the ordinary
desk burner, then allow the crucibles to cool, place in casseroles and add to
each 25 cc of concentrated hydrochloric acid. If method ( b ) is to be used for
reducing the iron add also at this point 0.5 cc of 5-per cent stannous chloride
solution. Cover and warm until solution is complete or until no further
action appears to take place. If the residue is not colored, proceed, without
filtration, as directed below. If the residue is colored it may contain iron.
In this case filter on a small paper and wash the paper free from iron solution
with hot water. Set the filtrate and washings aside and burn the paper at a
low temperature in a porcelain crucible. If the residue is small in amount
and apparently contains little silicious matter it may be decomposed by fus¬
ing with potassium pyrosulphate. Cool and dissolve the mass in hot water,
adding the solution to the former filtrate.

Concentrate the iron solution, if necessary, to about 50 cc and transfer to
a 1000-cc Erlenmeyer flask. While the solution is nearly boiling add, drop
by drop from a pipette, a 5-per cent solution of stannous chloride until the
ferric chloride has just been reduced, this being made evident by the disap-

Q U AN TIT A TIVE DETERM IN A TIONS

pearance of the red color. Add two drops more of stannous chloride solution
then cool quickly by immersing the flask in running water. When cool add,
all at once , 25 cc of a 5-per cent solution of mercuric chloride and mix well
with the solution. The precipitate should be pure white mercurous chloride
without a trace of gray mercury. Dilute to 500 cc with recently boiled
and cooled distilled water and add 50 cc of a solution containing 144
gm of phosphorous pentoxide, 245 gm of sulphuric acid and 67 gm of
crystallized manganous sulphate in each liter of solution. Titrate at once
with standard potassium permanganate solution and calculate the per cent
of iron in the ore.

By Dichromate. —In acid solutions ferrous salts are oxidized
completely by dichromates. Potassium dichromate, a salt
readily purified by crystallization, is generally used as a standard.
The reaction between this salt and ferrous chloride is expressed
by the equation :

6FeCl 2 + K 2 Cr 2 0 7 + 14HCl->6FeCl 3 + 2KC1 + 2CrCl 3 + 7H 2 0.

As in the oxidation of iron by permanganates the acid actually
takes a part in the reaction and if an insufficient amount is
present, a basic condition will result and a precipitate of basic
salts of iron and of chromium will form.

Potassium dichromate possesses several advantages over
potassium permanganate as a standard oxidizing agqnt. It is
relatively more stable and therefore may be obtained in a state
of uniform purity. This makes it possible to standardize solu¬
tions by direct weighing when the degree of purity of the salt
has been established by analysis. The relative stability is the
same with solutions and the standard solution can be kept almost
indefinitely without changing its concentration. Potassium
dichromate may also be used for the titration of iron and other
reducing agents in presence of hydrochloric acid or chlorides,
without oxidation of the latter taking place. This is a very
decided advantage in the determination of iron since it makes
possible the use of stannous chloride as a reducing agent without
the addition of manganous sulphate and phosphoric acid. There
is no indicator that can be added directly to the solution which is
being titrated by potassium dichromate and the color of the
standard solution is not sufficiently intense to be of any use for
this purpose. The indicator that is commonly used is a very
dilute solution of potassium ferricyanide, placed in drops on a

QUANTITATIVE AGltlCL'I/mtAL AXAJ. VSIS

white porcelain “ spot plate.” Drops of t he soluf ion an* removed
from time to time by means of a stirring rod and allowed to touch
the drops of ferricyanide. So long as ferrous iron is present the
blue of ferrous ferricyanide is apparent on the* spot plate. When
the last trace of iron has been oxidized then* is produced on the
plate only the light brown ferric ferricyanide. There being
nothing in the appearance of the solution of the iron salt to
indicate the approach to the end point, the* tit rat ion is necessarily
somewhat tedious unless a system is devised for rapid readings.
Such a system is indicated in the* next exercise.

Standard Solution.—The solution should lx* <>f >wh concent ration that.
1 ce is equivalent to 0.005 gm of iron. Calculate the weight of potassium
dichromate necessary for 1000 cc of such a solution. If the salt is known
to be pure, weigh exactly the calculated weight and omit further standard¬
ization. If it is not pure but its oxidizing power known from previous
determinations, calculate the weight, of impure sample required and me this
weight. If nothing is known of the purity use 1 per cent more than the
weight of pure salt required for 1200 cc of solution and standardize the
solution as directed below. In any case dissolve the weighed salt and dilute
to the proper volume. In case titration for ataudurdi/af ion b to be omitted
and direct weighing is to be made the basis for standardization, HHH) ct*
of the solution should be accurately made and poured into a dry bottle.

Standardization , if this should be necessary, is aceompli died by titra¬
tion against ferrous ammonium sulphate. Write and balanee the equa¬
tion for the oxidation of ferrous sulphate by potasdum dirhroinafe in
presence of sulphuric acid, referring, if necessary, to the equation for the
oxidation of the chloride, page 75. Calculate the weight of crystallized
ferrous ammonium sulphate necessary to reduce 55 rr ,,f the dirhronmte
solution. Weigh four portions of exactly this weight into 2 .Vm*c beakers and
dissolve each, just before titrating, in 50 ccof recently boiled and cooled water.
Prepare a 0.01-per cent solution of potassium ferricyanide and place a drop
in each of the depressions of a white porcelain spot plate. Add to the
solution of ferrous ammonium sulphate 5 cc of dilute sulphuric acid, and
titrate at once, as follows: To the first soluf ion add the diehronmte solution
5 cc at a time, stirring well after each addition, and test by removing a drop
by means of the stirring rod and touching t o n drop $ t f pot aw nun ferri-
cyanide solution on the spot plate. The end point i > reached when a
blue color is no longer produced on the plate, after standing for 1 minute,
(Dust or reducing gases will interfere by reducing trace* of ferric chloride.)
titrate the second solution by adding 5 cc lew than the amount of diehro-
mate solution used in the first, them adding I rr at a time. Titrate the
third solution by adding 1 ee less than the total used in the nerond, then
adding 0.1 cc at a time. Titrate the fourth solution in the ?*nme manner and
take the average of the last two titrations for permanent record. { aleulnt.e

Q UANTTTA TIVE DETERM IN A TIONS

the value of the solution in terms of iron. Dilute to make 1 cc equivalent
to 0.005 gm of iron.

Instead of weighing four portions of ferrous ammonium sulphate a
standard solution may be made by dissolving ten times the required amount,
adding 50 cc of dilute sulphuric acid and diluting to 500 cc with recently
boiled and cooled water. Portions of 50 cc are then measured and titrated.
The solution oxidizes upon exposure to air and it must be kept in a closely
stoppered flask.

Determination of Iron in an Ore.—Prepare a sample of iron ore by grinding
to pass a 100-mesh sieve. Weigh four portions of exactly 0.5 gm each,
using the counterpoised glasses and brushing the ore into porcelain crucibles.
Heat the inclined crucibles for 5 minutes over the desk burner, cool, place
in casseroles and dissolve in hydrochloric acid, with or without the addition
of stannous chloride. Reduce each solution just before titration, following
the directions given for dissolving and reducing by method ( b ) of the per¬
manganate method but do not add the solution of manganous sulphate and
phosphoric and sulphuric acids. Dilute to 100 cc. The titration is carried
out exactly as directed for standardizing potassium dichromate solution.
Calculate the per cent of iron in the ore.

ALUMINIUM

The direct determination of aluminium is made by precipi¬
tating the hydroxide, changing this to oxide by ignition, and
weighing the product:

AlCls + 3NH 4 OH -> Al(OH) a + 3NH 4 C1; (1)

2A1(0H) 3 —» A1 2 0 3 + 3H 2 0. (2)

If iron and aluminium occur together they are precipitated
together and the product of ignition is a mixture of ferric oxide
and aluminium oxide. In such a case the usual procedure is to
weigh the oxide mixture, then dissolve and determine the iron
volumetrically, calculating this to oxide and subtracting from
the weight of mixed oxides to find the weight of aluminium oxide.
Or the aluminium may be determined directly by precipitating
as phosphate, first reducing the iron to the ferrous condition by
sodium thiosulphate; ferrous phosphate is sufficiently soluble to
make a separation possible. This method will be described
later for the determination of aluminium in soils (page 258).

Solubility. —The solubility of aluminium hydroxide in water
is not definite as this substance belongs to the colloid class. The
presence of various salts diminishes the solubility to a low

QUANTITATIVE AURICl 'I,TVHAL .1 A'.-l LVSIR

figure, and especially so if the solution is boiled to cause floccula¬
tion of the colloid. Either acids or bases will dissolve the pre¬
cipitate; acids form soluble aluminium salts and bases form
soluble aluminates:

Al(OH).t + 3IIC1 -» Ain, + :m,<); ( 1 )

Al(OH), + NaOIi -> XuAH h + 2H S <). (2)

The possibility of the second reaction makes necessary the use
of ammonium hydroxide, rather than sodium or potassium
hydroxide, for the precipitation, as the excess ot ammonia may
be removed by boiling the solution.

Determination of Aluminium.—Fill a weighing bottle with the powdered
sample of an aluminium salt. Choose the method to he used in weighing
according to the nature of the substance and weigh two samples of about
1 gin each into Pyrex beakers. Dissolve in 100 ee of water and add
dilute, recently filtered ammonium hydroxide, stirring until the liquid
is distinctly basic, as shown by a drop of methyl red added to the solution.
Boil until the precipitate is coagulated and until the odor of ammonia above
the solution is faint. Boiling after the odor has disappeared will cause some
of the precipitate to return to the .solution:

A1(01I) 8 +3NH 4 < , 1 •••> AlCIt MNH i HMh

Allow the precipitate to settle and then filter through paper, using a
filter pump attached to a hell jar or filter flask and plat ing a supporting
cone of hardened paper or platinum in the funnel. Wash with hot distilled
water containing 1 percent of ammonium nitrate, until the washings uni
free from chlorides, shown by adding a drop of nitric arid and a lew drops
of silver nitrate solution to a small amount of the washings caught in a test
tube; also from sulphates, as shown by adding a drop of dilute hydrochloric
acid and a few drops of barium chloride solution to another portion of the
washings. Suck the precipitate as nearly dry as possible and transfer the
paper and precipitate to a porcelain or platinum crumble which ban been
ignited and weighed, folding the paper in the manner already learned.

Heat very gently in the covered crucible until the momture is volatilized,
then raise the temperature and burn the paper, inclining the crucible and
placing the cover as in the caw* of the ignition of the paper containing cal¬
cium oxalate. When all of the carbon has been burned, cover the crucible
and heat over the blast lamp or the large Mcker burner for *10 minutes.
Cool in the desiccator and weigh. Heat again for 10 minutes, cool and
weigh. If necessary repeat this process until the weight in constant.

Calculate the per cent of aluminium in the salt.

Aluminium oxide absorbs watei from the air, reforming the hydroxide
with a corresponding gain in weight. On this account the crucible and
oxide should be weights! rapidly.

qtaxtita tiye deteeauxat/oxs

CARBONATES

The Carbonate Radical. Tin* determination of the carbonate
radi<*al of solid carbonate** can lx* made* with accuracy only l>v
decomposing th«* carbonate with a .stronger a<*id, tlicn purifying
the resulting carbon dioxide and absorbing it, in some manner
in another reagent. This is the bn,sis for both gravimetric, and
volumetric methods. In the former class of methods (.he carbon
dioxide is absorbed in a basic* substance* (usually potassium
hydroxide* or soda lime*) contained in a small apparatus that, oui
he weighed, the* gain in weight serving as a measure* of the
quantity of gas absorbed. Or it is sometimes absorbed by a
solution of barium hydroxide*, the* barium carbonate* so formed
being removed by filtration, dissolved in hydrochloric acid and
the barium re*precipifated as sulphate*. From the* weight ol
barium sulphate* the corresponding weight of carbon dioxide is
calculated.

In the* volumetric modifications the* absorbing re*ngent is a
standard solution of a lease*, such as barium hydroxide*, a measured
volume* of this being titrated by a standard acid solution after
the absorption is finished. Wither method will give* accurate
results, if can* is used.

Gravimetric Method. The* necessary parts of the* apparatus
are shown in Fig. 20. In this figure*, A represents a generating
flask in which tho weighed sample* of e*arbomife* is placed. It
is a dropping funnel having a capacity of 50 c*c anel having the*
lower end drawn out to a point and turned upward. This part
should extend to the* bottom of the* flask. At. the top of flu*
dropping funnel a elrving tube* (' is connected by menus of a
rubber stopper and a bent glass tube*. The drying tube is filled
with soda lime for the absorption of carbem dioxide* from the* air
that is later to be* drawn through. Following the* generating
flask is a short condenser 1 ) (the lower end of which should la*
be*veleel) and them l -tubes A, P anel ( 7 . I la* first I "tube is
omitted if sulphuric* acid is to be* used for decomposing the* car¬
bonate or it is filled with an absorbent for hydrochloric acid
vapors if this aciei is to be* used. The l -tubes P and (t an* filled
with granular calcium chloride which absorbs moisture* from the*
gas mixture. Following these is the apparatus If in which
potassium hydroxide* is placed for the* absorption of carbon

QUANTITATIVE

AGRicri/rriiM. analysis

dioxide. This apparatus also carries a small tube Idled with
calcium chloride to prevent the removal ut moisture irom the
apparatus, which would occur if the dry entm-mg gases were
allowed to leave the apparatus saturated with moisture. o
provide a means for drawing air through the whole apparatus the
aspirator J is placed at the end of the series, while to prevent
moisture from diffusing backward into the absorption apparatus
the calcium chloride tube / is interposed.

Choice of Acid —The carbonate should He decomposed with
dilute sulphuric acid if insoluble sulphates are not thereby formed.
This point may bo decided by making a preliminary qualitative
test. If this acid cannot be used, hydrochloric arid is taken for
the purpose but it then becomes necessary to introduce into the
apparatus train a tube containing silver sulphate for t he absorp¬
tion of traces of hydrochloric acid that might pass the condenser.

Absorbent for Carbon Dioxide. ~ A water solution of potassium
hydroxide serves best for this purpose. This is made by dissolv¬
ing one part, by weight, of the base in t wo parts of water, thus
making a solution practically 33 per cent by weight. The
containing apparatus, to be weighed before and after the absorp¬
tion, must include a small additional tube which is filled with

Ql .1 XT IT A TlYK DKTKRMIX A T/OXS

calcium chloride. Tin’s prevents loss of moisture from the
weighed apparatus.

Soda lime is sometimes used for the absorption of carbon
dioxide. This is made bv fusing together sodium hydroxide and
lime, the product being granulated during the cooling process.
The chief objection to this use of soda lime is the fact that it, is
somewhat uncertain in its action and the absorption of gas is
liable to be incomplete unless the moisture content is kept
within fairly narrow limits (about 15 per cent).

Determination of the Carbonate ^Radical: <iravimetric Method. Procure
the following parts for assembling:

1 dropping funnel, 50 <•<•, with one-holt* rubber stopper,

1 short, wide flask, 75 e<\ such as is used for fat. extractions, with two-hole
rubber stopper,

• 1 condenser with body not- more than b inches long,

3 P-tubcs with corks to lit,

1 I'-tube with glass stoppers,

1 straight drying tube with one-hole rubber stopper,

I set (lewder “potash bulbs” or bulbs of some other approved form,

1 aspirator bottle, tubulated near bottom, with fine-hole rubber stoppers
to fit,

1 piece glass tubing, about 2 feet, l»v 1 > inch, for supporting apparatus,

2 clam pH,

2 pinch cocks,

1 small screw clump (Hoffman screwu,

2 retort at am la, *

(llnsM and rubber tubing for connections,

Fill and connect the apparatus in the manner previously described.
The drying tubes are filled nearly to the sale arms with a good grade of
granular enleium chloride. A loose plug of cotton is placed on top of the
chloride and then a cork is pressed in until the top in about 2 mm below the
top of the tube. Into the eup thus formed melted paraffin is poured as a
scaling material. If bubbles appear in the paraffin after cooling they are
removed by remelting the surface by a flame.

When filling the absorption bulbs with potassium hydroxide solution
the latter should not be warmer than the air of the room. The bulbs
arc now detacher! from the apparatus and the solution is drawn in through
a tube attached at <t, suction being applied at /#. The solution should
about half fill the bull# r when air is bubbling through. The ground *
glass joint between the drying t ubc /» and t he bulbs should hr* light I v costed
with vaseline and flu 4 tube then twisted on until it fits closely enough that,
there will be nr* danger of loosening during tin* comae of an experiment.
Any surplus vaseline is removed from the outside of the joint.

QUANTITATIVE AGRICULTURAL ANALYSIS

Place the bulbs in position, close the cock of the dropping fimriel an( *
open the pinch cock at e to allow water to flow from the aspirator. J3ubbles
of air will at first pass through the bulbs but this action will finally cease
unless there is a leak in the apparatus, in which case it must be found und
closed. It is important that all glass tubes be brought entirely together
inside the rubber connections since rubber is slightly permeable to gases.

After the apparatus has been shown to be free from leaks the pinch
cock at / is closed, the cock of the separatory funnel is slowly opened and,
after equilibrium is established, the clamp k is so adjusted that when clamp
/ is opened air will pass through the bulbs at a rate not greater than three
bubbles per second. Clamp k is not thereafter changed. This provides
against too rapid flow of gas under any conditions. Clamp/is now closed,
the bulbs are removed, the inlet and outlet tubes are closed by short rubber
tubes containing glass plugs and the bulbs are wiped clean and placed in the
balance case. A short glass tube is inserted to bridge the gap made by
removing the bulbs.

The bulbs should be allowed to stand for 15 minutes before weighing- In
the meantime about 1 gm of the carbonate is weighed and brushed into the
generating flask and a small amount of water is added to moisten the
sample. The stopcock of the funnel B and the clamp E are now opened
and 500 cc of air is drawn through the apparatus, measured by the out¬
flowing water from the aspirator. This frees the apparatus from carbon
dioxide. After the absorption bulbs have stood for 15 minutes the tubes
carrying the plugs are removed and the bulbs are weighed. The plxxgs are
then replaced and left so until the bulbs can be connected in the apparatus.
Fifty cubic centimeters of dilute sulphuric acid or hydrochloric acid is placed
in the dropping funnel, a test having previously been made to determine
whether sulphuric acid will form a clear solution with the carbonate- If
such a solution is not produced, of course hydrochloric acid must be used
and silver sulphate and pumice must be placed in tube E.

Reconnect the apparatus and open all cocks except the stopcock in the
dropping funnel, leaving the clamp k set for the proper rate of gas flow, its
previously determined. Slowly open the cock of the dropping funnel,
allowing acid to drop just fast enough to evolve carbon dioxide at the
prescribed rate. The constant attention of the operator is necessary at this
point, for by causing too rapid evolution of gas some moisture may escape
absorption in the small tube of the absorption bulbs and the experiment
be rendered worthless.

The acid should be allowed to run in until about 1 cc is left above the
stopcock, this acting as a seal during the subsequent boiling. After the
decomposition of the carbonate is complete the solution in the flask is
slowly heated until it boils, always with due regard to the rate at which
the gas is made to flow through the absorption bulbs. The boiling is
continued for one minute, when the flame is withdrawn, the cock of the
dropping funnel being opened at the same time to allow air to enter so
that no back suction occurs, due to the cooling effect. Air is now drawn
through the apparatus until 1000 cc of water has flowed from the aspira-

Qf M A 77 7M 77 I A’ /;A7*A7,M//A. 1 T!<>\S

lor. This amount, of air should !»<• Huflicmnf. hi .sweep nil of fh<* rarlxm
dioxide info flu* absorption bulbs.

The (damp J is now elosni, and the absorption bulbs are removed, plugged
and placed in the balance case. After 1 T> minutes they are weighed without,
the rubber tubes and plugs, the increase in weight being the weight of
carbon dioxide. From this and t he weight of sample tin* per eenf. of cnrlionie
anhydride (combined carbon dioxide i orof the carbonate radical is calculated.

For the duplicate or any subsequent det.cnniimt.inn the generating
flask and the dropping funnel are washed absolutely free from acid, ho
that no decomposition ot the next carbonate sample may occur before
the lmlbs are in place.

if a largo number of determinations arc to be math* with the same appara¬
tus much time will be saved by providing two decomposition flasks and two
absorption bulbs. While one determination is being made another sample
may be weighed into the duplicate flask and the second absorption bulb may
bo weighed. 'I’he next determination may then be started while the first
lmlbs are standing in the balance case, preliminary to the final weighing.
It is also necessary to determine when tin* various absorbents have become
so saturated as to be inefficient for further work. Soda lime in f be t ube (' in
good until the lumps have begun to fall info a powder. Silver sulphate in the
pumice of tube K may become inefficient through absorption of hydrochloric,
acid or through the accumulation of water in the ttiIn*. The solubility of
silver sulphate in wafer is much less than in concent rated sulphuric acid. If
the acid solution ftermites diluted the silver salt crystallizes and will not*
thereafter readily absorb hydrochloric acid. Ah the silver sulphate becomes
saturated with hydrochloric acid it darkens, on account, of the action of
light. When tin* darkening effect bus proceeded as far as the middle of
the tube the material should be replaced. ( alcium chloride must be replaced
when it becomes visibly moist for thjir.it third of any absorbing tube.

Gravimetric by Absorption and Subsequent Precipitation.
Carbon dioxide, evolved by the method just described, is some¬
times absorbed in a somewhat concentrated solution of barium
hydroxide*, the barium carbonate f 1ms formed being; then removed
by filtration, washed, redissolved in hydrochloric acid and the*
barium precipitated as sulphate. The weight of this gives u
measure of carbon dioxide in the sample.

In this method, tubes A\ F and (l of Fig. 20 are omit ted and tin*
Meyer tube, Fig. 21, is substituted for// of Fig. 20.

Volumetric, by Absorption in Barium Hydroxide. Three
different methods of procedure arc* offered: (1 / "Flic* gas is
absorbed in a standard solution of barium hydroxide, tin* unused
excess of the latter being titrated by standard hydrochloric acid
without previous filtration. (2 ) The barium carbonate* is

82 QUANTITATIVE AGRICULTURAL ANALYSIS

removed by filtration‘before titrating the unused base. (3) r -The
barium carbonate is filtered out, washed and dissolved in an
excess of standard acid, the unused acid being then titrated by
standard base. In method (3) a more concentrated solution of
barium hydroxide may be used and it need not be standardized.
Phenolphthalein is used as indicator in all three methods. ]\dethod
(1) will be described.

Apparatus. —Parts A, B, C, D and J (including clamps k
and /) of the apparatus shown in Fig. 20 are used. If hydro¬

chloric acid is used for decomposing the carbonate, tube
E, filled with pumice bearing silver sulphate in concentrated
sulphuric acid, is required also. Drying tubes F and O are
omitted. For the absorption the Meyer tube, shown in Fig- 21,
is suitable.

Barium Hydroxide Solution.—A saturated solution of barium hydroxide
is prepared by warming and stirring the solid base with recently boiled
water, using a ratio of 70 to 100 gm of base to 1000 cc of water, accord¬
ing to the purity of the barium hydroxide. Cool to room tempera¬
ture and siphon into a bottle to be closed with a rubber stopper. I>ilute
550 cc of this solution to 1000 cc with distilled water, mix and. empty
into a bottle which is provided with a siphon or similar outlet, from which
the solution may be drawn, and a guard tube of soda lime to remove carbon
dioxide from the air which is drawn in.

The last diluted solution should be about 0.25 normal. It is not adjusted
to any exact normality because its concentration is subject to change with
time. Instead, the standard acid to be prepared is taken as the primary
standard and “blank” titrations are made frequently.

Sodium Carbonate for Standardizing Acid.—Prepare as directed on page
57.

Hydrochloric Acid.—From the known per cent of hydrochloric acid and
the specific gravity of the concentrated solution in the laboratory, calculate
the volume of solution necessary to make a suitable quantity (1200 cc to
10 liters, according to whether this is to be an individual preparation or

QUANTITATIVE DETERMINATIONS

laboratory stock) of solution, either fourth-normal or of such strength that
1 cc shall be equivalent to 0.005 gm of carbon dioxide, calculating equiva¬
lent weights from the equations:

C0 2 -f H 2 0 — H 2 C0 3 ; (1)

Ba(OH) 2 -f H 2 C0 3 -» BaC0 3 + 2H 2 0; (2)

Ba(OH) 2 + 2HC1 -* BaCl 2 + 2H 2 0. (3)

Measure 2 per cent more than this amount, using a graduated cylinder.
Empty into a bottle of suitable capacity and add the necessary quantity of
water. Stopper and mix thoroughly. Since the solution has been warmed
by the reaction between acid and water it should stand until the tempera¬
ture of the room is attained, before standardizing.

Standardization.—Calculate the weight of sodium carbonate required for
250 cc of a solution of strength equivalent to that of the desired acid.
Weigh this quantity of the prepared pure material on counterpoised glasses
and brush into a funnel which is placed in the neck of a 250-cc volumetric
flask. Rinse down with distilled water, remove the funnel and dilute to the
mark on the flask. Mix thoroughly, best by pouring into a dry beaker or
flask and back several times.

Fill a burette with the solution and another with the acid solution already
made and titrate as directed on page 58. Calculate the normality of the
solution, also the volume of water to be added to each 1000 cc to make
a solution of the exact concentration required. If water to be added is more
than 10 cc add nearly the required amount to each liter of the acid, mix,
and restandardize. If the quantity to be added is less than 10 cc the acid
is diluted as follows: Fill a dry 1000-cc graduated flask to the mark with the
acid solution. This flask should be capable of holding the required amount
of water above the mark. From a burette add the calculated quantity of
water directly to the solution in the flask and mix thoroughly. Pour into a
dry bottle and make more diluted solution in the same manner, having
first rinsed and dried the graduated flask. Check the accuracy of the
dilution by restandardization.

A preliminary titration should be made to determine whether the barium
hydroxide solution is approximately equivalent to the standard acid. Meas¬
ure 25 cc of the base into an Erlenmeyer flask, add a drop of phcnolphthal-
ein and titrate rapidly to the disappearance of the pink color. Twenty-two
to 27 cc of acid should be required, although no special note is made of the
exact quantity, the value of the basic solution being determined accurately
by a blank titration, made at the time the carbonate analysis is carried out.

Water , Free from Carbon Dioxide .—All water that is to be used for dilutions
and for rinsing apparatus must be free from carbon dioxide and it must be
neutral to phenolphthalein. Carbon dioxide is removed by boiling the
water for 10 minutes, cooling and placing in a bottle provided with a guard
tube filled with soda lime. Boiling large quantities of water is often not
conveniently done in the laboratory. An equally satisfactory method is to
provide the bottle with a two-hole stopper through which pass two glass

QUANTITATIVE AGUK A 7/77 ' AM /. .1 .Y.l /, K.S'/.S’

tubes. One of these is for entering air. It i.s:if.t:ielicil tu :i * uln -<>f wxl.-i lime
outside and it extends to the bottom of the bottle. ( I he .-oil.-i lime must be
well co nfin ed by a filter of cotton.) The other tube is connected with an
air pump. The purified air is then drawn flirmigli the water for an hour,
after which the bottle is stoppered.

The three reagents may be placed on a shelf and connected as shown in
Fig. 22, for convenient use.

Fig. 22.—Assembly of reagents for tin* carbon dioxide determination.

Determination of the Carbonate Radical: Valumrtrir 5/Assemble
the apparatus discussed above, the Meyer absorption tube being half filled
with distilled water. Close the cock of funnel // and test for leaks by
opening cocks k , / and e. Water will flow from the aspirator until the
pressure within the apparatus is reduced to equilibrium with the water
column. If an air leak exists at any point between H and the Meyer tube
air will bubble slowly through the tube. Any leak (bus evidenced must be
located and stopped.

The clamp at k is now closed and the rork of the dropping funnel Ji is
opened. With c and / left open k is so ml justed as to allow about three
bubbles of air per second to pass through the Meyer tube. Clamp k is not
thereafter changed and this keeps the gas flow under control. Now Hose/
and remove the flask A. Weigh into this about 0.3 gm of the sample of
carbonate. One-half of the factor weight (pages A ard K» may be used, if
desired. This would be 0.2750 gm for a fourth-normal solution, or 0,2500
gm for the solution of which 1 ce is equivalent to 0,005 gm of carbon dioxide.
(The student should prove this statement.)

Q( 'A XT IT A 77 YE DETEItM 1X A TIOXS

The flank is now replaced in the train and the dropping funnel and cocks
cun df arc opened. Two hundred cubic, centimeters of water is allowed to
flow from the aspirator, to remove carbon dioxide from the apparatus. The
Meyer tube is now removed and emptied and 50 ce of barium hydroxide
solution is measured into this tube from a burette or an automatic pipette,
first discarding the tew drops that are in the outlet of the measuring instru¬
ment. Add to the tube, from a graduated cylinder, enough cold carbon
dioxide-free w at er to tiring t he water to the lower edge of the upper bulb when
gas is flowing. 'Ha* quantity of water necessary should be measured, once
for alb so that it can be added without, delay in subsequent, determinations.

Replace the Meyer tube in the train and add 50 ce. of dilute sulphuric or
hydrochloric acid to the funnel //, the stopcock being closed. Now open
v and / , then admit acid to t lie carbonate at a moderate rate unt il the entire.
50 cr has entered. Finally close the stopcock and beat the acid slowly
to boiling. Hod for 1 minute then remove the flume and open the stopcock.
Pass air through until I liter of water has run from the aspirator, then close r.
Remove the Meyer tube and rinse the contents into a. 5(M)-ce flask, using tint
carbon dioxide-free water but not from (lie ordinary wash bottle which is
operated by blowing. Add a drop of phcnolphlhulciu and titrate rapidly
and with continuous stirring, to the disappearance of color.

While the experiment just described is under way, measure 50 er of
barium hydroxide into another flask, add approximately the same amount of
carbon dioxide-free wafer that was used in diluting the solution for absorp¬
tion and titrate with standard acid. From the volume of acid here required
deduct that used for the base after the absorption of carbon dioxide. The
remainder is the volume of standard acid equivalent, to carbon dioxide
absorbed. < alculafe the per cent of carbon dioxide, or of the carbonate
radical, in the sample of carbonate.

‘‘Alkalinity” of Carbonates. The methods tlmf. have just,
been described furnish a means for determining direetly the
actual carbon dioxide of carbonates. It is sometimes desirable
to determine the power of a carbonate to neutralize acids. 'Phis
can be calculated from the known carbon dioxide content only
upon the assumption that no other basic substance is present.
This assumption is not always correct-. For instance, soda
lime (essentially a mixture of sodium hydroxide and calcium
oxide, but always containing some carbonated has a much
greater power for neutralizing; acids than would be indicated
by tin* carbon dioxide obtained from it. The same is true of
lime that is partly air slaked, or of soda ash, which might contain
hydroxide.

It is also true that the basic strength or “alkalinity ” is often
the figure that is desired and this may be obtained more quickly

QUANTITATIVE AGRICULTURAL ANALYSIS

by a direct titration method. With carbonates that are soluble
in water this is accomplished by dissolving a weighed sample,
adding methyl orange and titrating with standard acid. If the
carbonate is only slightly soluble in water an excess of standard
acid is added. This dissolves the carbonate and the unused
excess of standard acid is then titrated with a standard base.
In this case, if the solution has been boiled to remove carbon
dioxide, phenolphthalein or methyl red may be used as indicator
but the same indicator must have been used when standardizing
the base against the acid.

Soda Ash.—The standard acid that was used in the preceding
exercise is suitable for this determination. The soda ash may
be weighed on a counterpoised glass, if this is done quickly.

Determination of Alkalinity of Soda Ash.—Weigh about 2.5 gm of sample,
dissolve in a small beaker and rinse the solution into a 500-cc volumetric
flask. Dilute to the mark and mix well. By means of a pipette, measure
25 cc of the solution into a 250-cc Erlenmeyer flask or beaker, dilute with
50 cc of water, add a drop of methyl orange and titrate to the color change
with standard acid. Calculate the per cent of sodium carbonate in the
sample. This, of course, is upon the arbitrary assumption that no other
carbonate or basic substance is present. Sometimes the alkalinity is
expressed in terms of sodium oxide, Na 2 0.

Limestone.—Powdered limestone is used for neutralizing the
acidity of soils. If the alkalinity is calculated in terms of calcium
carbonate the result may be greater than 100 per cent in case of
dolomitic limestones, on account of the presence of magnesium
carbonate, a substance of lower equivalent weight than that of
calcium carbonate. Although a figure so obtained would be
fictitious, in one sense, it is after all a practical basis for calculat¬
ing the amount of stone required. If a determination of soil
acidity should indicate n pounds of pure calcium carbonate
required per acre, a sample showing by analysis a calculated per

cent of 105 would be used in the ratio of pounds per acre, no

matter what carbonates were actually present.

Determination of Alkalinity of Limestone.—Prepare a solution of sodium
hydroxide, equivalent to the standard acid already on hand, or use the basic
solution prepared for acidimetry, page 59. This should be made from
material as nearly as possible free from carbonates. Sodium hydroxide

Qi'A XTlTATlYt': DETKUMIX ATKiSS

by alcohol is herd. and the water should first, hr boiled, to <v\j>*•!
carbon dioxide, then moled. Standardize the solution by fil.niting again.:!,
the standard arid, using methyl red or phenulphf hnlein. (See helow.i

The sample should he ground to pass a 100-niesh sieve and it. must, he
well mixed. Weigh 0.5 gin of the sample on counterpoised glasses and
brush into a 250-re Krlenmeyer flask. Moisten with water and then
pipette 75 ee of the standard arid into the flask. After effervescence has
nearly erased connect the flask with a reflux condenser by means of a
rubber stopper. Boil gently for 5 minutes to expel carbon dioxide and to
insure complete solution of all carbonate, then cool. Rinse down tin* con¬
denser, the stopper and the upper part of the flask. Add a drop of methyl
red or of phenolphthalein and titrate the excess of acid by means of standard
sodium hydroxide. (If pbenolphtbnleia is used as indicator, the bast* must
have been standardized by use of the same indicator. Also, in this case
water that, is used for rinsing must be free from carbon dioxide and it. must
not be blown in from the wash bottle.)

Calculate the alkalinity of the limestone in terms of per cent, of calcium
carbonate.

PHOSPHATES

Gravimetric, as Magnesium Pyrophosphate. Any phosphate
that is directly soluble in wafer can contain only metals of fin*
alkali group, as all oilier phosphates have a relatively low degree
of solubility. Solut ions of phosphates or of phosphoric arid may
he precipitated as dimagnesium ammonium phosphate by the
addition of magnesium chloride or sulphate, the solution being
made basic with ammonium hydroxide*:

NanP0 4 + Mg( 'Is } NH 4 (>f 1 “ >MgNH 4 P( > 4 f 2 Na( ’1 f Nat >JI; (l)
N a 2 1 IPO 4 + M g( ’1 a + X H 4 <> 11 >M g NII 4 PO 4 f 2 N a< ’1 1 11,0; ( 2 )

n :j P0 4 + Mgf v+:<MI 4 OII -MgNH 4 P() 4 f 2 NH 4 n ( 211 , 0 . Ci)

The* precipifate always contains a variable amount, of water
of crystallisation and it is therefore not weighed direef ly. Igni¬
tion eon verts it definitely into magnesium pyrophosphate:

2 MgNH 4 PO 4 —>Mg«PoO 7 f2NH;i | 11,0. t h

In practice, the concentration of ammonium hydroxide* ami of
ammonium salts must he regulated within certain limits to pre¬
vent the partial precipitation of certain other phosphates
which cannot be changes! to pyrophosphate* by ignition. For
example, j/w/mmagnesium ammonium phosphate, formed to

QUANTITATIVE AGRICULTURAL ANALYSIS

vsome extent if ammonium salts are present in immoderate
quantities, decomposes at high temperatures into magnesia na
metaphosphate:

Mg[(NH 4 ) 2 P0 4 ] 2 -► Mg(P0 3 )i> 4- 4NH 3 + 2H 2 0. (5)

Also, inmagnesium phosphate, Mg 3 (P0 4 ) 2 , may be precipitated
if the solution contains too much ammonia and this will remain
unchanged by ignition.

Insoluble Phosphates. —Phosphates of other than alkali metalB
are usually soluble in acids but a direct precipitation of magne¬
sium ammonium phosphate cannot be made because phosphates
of the original metals reprecipitate as soon as ammonium hydrox¬
ide is added to neutralize the acid. For example, tricalcium
phosphate, Ca 3 (P0 4 ) 2 , furnishes much of the phosphorus of
fertilizers as the mineral apatite. This is soluble in acids but If
an attempt were made to determine the phosphorus by sl
magnesium precipitation, the precipitate would be a mixture of
phosphates of calcium and magnesium.

In order to prepare such a phosphate for a determination of
phosphorus a preliminary separation of the phosphate radical
is made by the addition of ammonium molybdate to the solution
in nitric acid. This results in the formation of a yellow pre¬
cipitate of ammonium phosphomolybdate:

(NH 4 ) 3 P0 4 + 12(NH 4 ) 2 Mo0 4 + 24HN0 3 ->

(NH 4 ) 3 P0 4 .12Mo0 3 + 24NH 4 N0 3 + 12H 2 0. . (1)

This is filtered out and washed free from the alkaline earth
metals. The precipitate is then dissolved in ammonium hydrox¬
ide, reforming ammonium molybdate and ammonium phos¬
phate, both of which are soluble. This reaction is represented
as follows:

(NH 4 ) 3 P0 4 -12Mo0 3 + 24NH 4 OH (NH 4 ) 3 P0 4 +

12(NH 4 ) 2 Mo0 4 + 24NH 4 N0 3 + 12H 2 0. (2)

The magnesium salt is now added and the precipitation and sub¬
sequent treatment are carried out as described for soluble
phosphates.

Determination of Phosphorus in Soluble Phosphates.—Prepare a solution
of “ magnesia mixture ” as follows: Dissolve 55 gm of crystallized magnesium

QD. 1 A 77 7VI 77 YE DETER MI AM TIONS

chloride* and HO Kin of ammonium chloride in water, add 150 <•<• of ammo¬
nium hydroxide (specific gravity 0.11(0 and dilute to 1000 cc. If this solution
is kept in stock for any considerable time it will acquire a floeculent. precipi¬
tate of hydrated silica, derived from solution of the glass by the base. The
solution must In* dear when used. This condition may be insured by
filtering tin* solution or by preparing only enough of the reagent to last
a short time*.

Weigh duplicate samples of 0.2 to 0.4 gm of the phosphate into beakers
of resistance glass, dissolve ami dilute to 75 or. Add a drop of methyl red
and if a basic reaction is not shown add dilute* ammonium hydroxide until
the solution becomes yellow, avoiding an excess. Add 10 or. of a 10 per
cent-solution of ammonium chloride, mix and then add, very slowly, “mag¬
nesia mixture” suflieient in quantity to precipitate all of the phosphate.
As the preeipitate does not form rapidly in a barely basic solution it. is not
always easy to determine when enough of the reagent has been added.
It is then best to use what is thought to be a good excess and to rely upon
testing the filtrate which is obtained Inter.

Allow to stand for 15 minutes until a considerable part of the precipitate
has appeared, then add concentrated ammonium hydroxide solution (specific,
gravity 0 AH) , in such quantity that the solution shall finally contain ammo¬
nium hydroxide equivalent, to one-ninth of its total volume. Cover and
allow to stand for 5 hours or stir continuously for 50 minutes. A small
stirring machine may be used for this purpose.

Kilter the preeipitate on a filter of extracted paper, in a weighed platinum
Gooch crucible or in an ignited and weighed nlundum crucible, and wash
until free from chlorides with a solution containing 2 per cent of ammonia
or 10 per cent of ammonium nitrate, finally testing a few drops of the wash¬
ings with silver nitrate after acidifying with nitric acid.

Set. the filtrate aside, after adding 5 ec more of magnesia mixture. If
more precipitate forms after standing an hour this must be filtered out,
washed and added to the main portion.

If a Gooch crucible has been used for filtration, place the cap on the bottom
and heat over the burner until dry, then over the blast lamp for 20 minutes.
An nlundum crucible is treated similarly. If a paper filter was used remove
the paper from the funnel, fold and place in a weighed porcelain or platinum
crucible. Incline the crucible with the cover leaned against it and heat
gently over the burner until the paper is completely burned and the pre¬
cipitate is nearly white. After the precipitate is white or light gray the
crucible is heated for 20 minutes over the blast lump, cooled in the desiccator
and weighed. From the weight of magnesium pyrophosphate calculate the
percent of phosphorus, of phosphorus pcntoxidcor of the phosphate radical,
according to the nature of the sample used.

Determination of Phosphorus in Rock Phosphate. -Prepare a sedation of
ammonium motybtlnl* as follows:

Dissolve 100 gm of molvbdic acid in a mixture of 115 ec of concentrated
ammonium hydroxide (specific gravity 0.90) and 270 ec of water, Pour
this solution slowly and with vigorous stirring into a mixture of J90 re of

QUANTITATIVE AGRICULTURAL AN ALYA

concentrated nitric acid (specific gravity 1.42) and 1150 cc of ’
to stand at a temperature of 30 to 40° for several days, the
preserve in glass-stoppered bottles.

The phosphate sample should be finely ground and well m
about 2.5 gm, accurately to milligrams, and brush into a.
Add 30 cc of concentrated nitric acid and 5 cc of concentratec:
acid and warm until solution is complete, or until only inso
matter remains. Cool, rinse into a 250-cc volumetric flask,
mark and mix well. Pour the solution into a dry filter. Difc
10 to 25 cc of filtrate, and receive the remainder in a dry flask -

Pipette 25-cc portions of the clear solution into 250-ec
flasks. Add ammonium hydroxide until a slight precipitate <
of iron, aluminium or other earth metals persists. Clear with t
nitric acid, dilute to about 100 cc and heat to 60 to 65°. Imir:
in water which is at this temperature, a thermometer being ;
flask. Add 75 cc of molybdate solution, mix and maintain at;
ture noted above for 1 hour. Filter and wash v/ell witlx
ammonium nitrate solution. The precipitate that adheres
need not be removed but it must be well washed. Test the filtr*
more molybdate and returning to the water bath. If max’'
forms it must be added to the main body.

Place the flask n which precipitation was made under tin
drop over the paper enough concentrated ammonium hydroxic.l
the precipitate, avoiding unnecessary excess. Wash this solix*
flask below with hot water and, if necessary, add more ammoniu
to dissolve all of the precipitate in the flask. Wash the papo:
with hot water, then rinse the entire solution into a 200-cc be**
to room temperature. Nearly neutralize with hydrochloric acid
solution slightly basic. The formation of yellow precipitate
sequent resolution by ammonia is sufficient indication.

Cool if necessary and add, very slowly and with vigorous B"t
of magnesia mixture. After 15 minutes add concentrated
hydroxide as directed for analysis of soluble phosphates, page ;
ceed from this point as there directed. Calculate in the same w

Volumetric, by Titration of Ammonium Phosphomcx

It has been shown that the precipitation of ammon
phomolybdate from acid solutions of phosphates j
means for separation from metals that would form
phosphates in basic solutions. This precipitation also *
basis for an indirect determination of phosphorus. TT:
already given for the double compound shows that it i*
as a compound of ammonium phosphate and mo
trioxide, the latter being the anhydride of molybdic
therefore capable of neutralizing a base, as was shov

QUANTITATIVE DETERMINATIONS

(2) on page 88. If the base is added as a standard solution in
measured excess and the unused portion is titrated by a standard
acid the phosphorus (or the corresponding phosphoric anhy¬
dride) may be calculated.

Variation in Composition. —It has been found that the ratio
of molybdic anhydride to ammonium phosphate in the precipitate
is somewhat variable unless the conditions of precipitation are
standardized and kept constant. This is probably due to
the coprecipitation of some free molybdic acid. Such varia¬
tions must occasion an error in the volumetric determination,
since it is the molybdic anhydride or acid that furnishes the acid
properties of the compound. If the method is followed as
outlined the composition of the precipitate will be fairly accu¬
rately represented by the formula already given.

Titration. —Sodium hydroxide reacts as follows:

(NH 4 ) 3 P0 4 .12Mo0 3 + 24NaOH (NH 4 ) 3 P0 4 +

12Na 2 Mo0 3 + 12H 2 0. (1)

Upon addition of acid any excess of base is neutralized and if
the acid is added to a color change with phenolphthalein, tri¬
ammonium phosphate will have been changed to diammonium
phosphate, since the normal salt is basic to this indicator. The
net result is therefore to be expressed by the following equation:

2(NH 4 ) 3 P0 4 .12Mo0 3 + 46NaOH -+ 2(NH 4 ) 2 HP0 4 +

23Na 2 Mo0 3 + (NH 4 ) 2 Mo0 4 + 22H 2 0. (2)

It should be noted that it is necessary to have the solution
cold when the excess of base is added and to have present suffi¬
cient water to prevent the escape of ammonia, which would
be produced by reaction of ammonium phosphate with sodium
hydroxide.

Determination of Phosphorus in Rock Phosphate: Volumetric Method .—
The molybdate solution that was used for the gravimetric determination
may be used here also, first adding 5 cc of concentrated nitric acid to each
100 cc of solution. This additional acid serves to prevent the precipitation
of molybdic acid.

Prepare a half-normal solution of hydrochloric acid, standardizing
against .sodium carbonate as directed on page 83, modifying the weights
according to the different normality of this solution. Prepare a half¬
normal solution of sodium hydroxide in boiled and cooled water, standard¬
izing against the acid, using phenolphthalein.

QUANTITATIVE AGRICULTURAL ANALYSIS

Use' 2.5 gm of sample, weighed accurately to milligrams. Dissolve as
directed for the gravimetric determination of phosphorus in rock phos¬
phate, page 90, and dilute the solution to 500 cc in a volumetric flask. Mix
well and pour into a dry filter. Reject the first 25 cc and collect the rest
in a dry flask. Pipette 25-cc portions of this solution into 250-cc flasks.
Add ammonium hydroxide until a slight precipitate persists and clear with a
few drops of nitric acid. Place a thermometer in the flask, immerse in the
water bath and heat to 65°, then add 35 cc of freshly filtered molybdate
solution. Mix and leave the flask in the water bath for 15 minutes, then
filter at once. Wash twice with water by decantation, using 25 cc each
time, pouring the washings into the filter. Transfer the precipitate to the
filter as thoroughly as can be done without the use of a policeman and wash
the flask and filter with cold water until the filtrate from two fillings of the
filter yields a pink color upon the addition of phenolphthalein and one drop
of standard base. (Test the wash water in this manner before using.)

Return the filter and precipitate to the flask in which precipitation was
made and add 50 cc of cold water. Add half-normal base from a burette
until all of the precipitate is dissolved, mixing by gentle rotation. Imme¬
diately add a drop of phenolphthalein and titrate with standard acid. From
the total Volume of base used, deduct that equivalent to the acid required
and from$khe remainder. calculate -the per-cent of phosphorus and of phos¬
phorus pentoxide in the sample.

PART ir

KPK< ’ IA I, M KASl'R KM ENTS

In addition fo the* work of a st.rint.ly analytical nature* the
quantitative* laboratory is usually equipped for certain quanti¬
tative measurements which involve the use of special instru¬
ments, not mentioned or described in the preceding pages. In
this division certain of these* instruments will be* described arid a
brie*f discussion e>f theoretical principles will bet give*n, together
with directions for making the* nmasummemts. The* application
of the* results will lie* discusser! also. Later fin the* work of
Part III) these* instnune*nts will he* useel for te*st.ing agricultural
materials. , .

CHAPTER IV

DENSITY AND SPECIFIC GRAVITY

Density. —The density of a given substance is the mass of
unit volume. When the metric system of weights and measures
is used, as is customary in most scientific work, the density equals
the weight, in grams, of 1 cc of substance.

Specific Gravity. —Specific gravity is the ratio of the density
of a given substance to that of some other arbitrarily chosen
substance. For liquids and solids the substance which is gen¬
erally chosen for reference is water. Since the weight of a
milliliter (which, for all practical purposes, may be taken as a
cubic centimeter) of water at 4° is, by definition, 1 gm, the
density of any substance becomes its specific gravity if the latter
is referred to water* at 4°. This is the preferred method for
expressing specific gravity and the figure so determined is
stated as

t°

specific gravity* 0

for the specific gravity when the substance is at temperature t°.

Most of the laboratory methods for determining specific
gravity involve measuring either (a) the buoyant effect of the
(liquid) substance upon an immersed “float,” ( b ) the com¬
parative weights of equal, but unmeasured, volumes of the
(liquid) substance and water, or (c) the weight of water displaced
by a weighed, but not measured, quantity of the (solid) sub¬
stance. To carry out such experiments at 4° is a problem
offering great experimental difficulties and the work is usually
performed at some more convenient temperature, higher than 4°.
On this account it is customary to express the results as

specific gravity* 0

this quantity being the ratio of the density of the substance
at 1° to that of water at the same temperature. This quantity

t°

can be converted into the specific gravity at by multiplying

ItJ’.'XS/TV AM) SI'ECIFIC UHAY1TY

by the densit v of water at t°. Or it ran hr eon varied into specific,

gravity at ^ « by multiplying by the ratio of the density of water

at to that at t} \ the latter symbol representing any desired
temperature.

It cannot be too strongly emphasized that, both temperatures
represented in these symbols should always be expressed or
understood. Beeause of failure to do this there is much confusion
in the records in scientific* literature.

Baume System. In this system two scales are used, one
being for liquids lighter than water, the other for liquids heavier
than water. The first is applicable, to petroleum products and
to most other oils and fats. The second scale is used for most#
solutions in water.

In the original Baum/ scale for liquids heavier than water
the point to which a hydrometer float sinks in a solution of
sodium chloride, la per cent by weight and at If/* (h, was taken
as ln° Baume (abbreviated B/.j. The corresponding point for
pure water was taken as (T Be. and all other points wen* located
by these two. For liquids lighten’ than water the scale has the
point 10° Be. for pure water and 0° B<h for a 10-per cent, solution
of sodium chloride, the scale lieing extended beyond 10° for lighter
liquids. It will be seen that this is a wholly arbitrary system
and conversion of degrees Baum/' into specific gravity, or vice*
versa, will involve the use of special formulas. Several modifica¬
tions of the original Baum/ scales have come into user and the.
difficulties involved in interpretation have been correspondingly
increased. On account of the complexity of the system and the*
fart that such a system seems quite unnecessary it is unfortunate
that if has become .no generally used in the chemical industries.

No one set of formulas can serve for the conversion of specific
gravity and Baume degrees into one another but as the system
is at present used in many industrial laboratories the following
formulas will la* useful.

For liquids heavier than water:

QUANTITATIVE AGRICULTURAL ANALYSIS

For liquids lighter than water:

and

S =

140

130 + B
140

B = ^ - 130,

where B = degrees Baum6 and S = specific gravity at 15.5° C.

Methods for Determining Specific Gravity. The Picnometer.
The most accurate method for making this determination
depends upon the use of a vessel known as a “picnometer.”

There are various forms of pienomoters but
the instrument is essentially a small flask
which may be weighed, first filled with water
and then with a liquid whose specific gravity

t°

is to be measured. Specific gravity at is

given by the ratio of the two weights, as ex¬
plained above. Two forms of pienomoters
are shown in Figs. 23 and 24.

The picnometer flask has an accurately
ground stopper which is bored longitudinally
as a capillary tube. The dry flask is first
weighed. Filled with distilled water, which
has been boiled recently to expel dissolved
air, it is then nearly immersed in a constant
temperature bath and when t he water has
been brought to the required temperature
the surplus drop is removed from the top of
the stopper. The flask is then removed

,, _ from the bath, wiped dry and weighed. It

Fig. 23.—Picnometer . . ’ ! * ^

bottle, with cap. is necessary that the room temperature shall

be a few degrees lower than that of the bath,
so that the liquid may recede from the tip of the stopper after
removing from the bath.

After the weight of water contained at t° has been determined
the flask is emptied, rinsed with redistilled alcohol and dried.
It is then filled with the liquid whose specific gravity is to be
measured and this is treated in the same way as was the water.

DKXSri'Y AM) Sri'CIFIC UliAVIT)

The weight of this liquid divided by t,he weight, of water gives

the specific gravity at 0 *

A modified Ostwald pienometer is shown in Fig. 24. For
filling, a rubber tube is attached to the larger branch of the
pienometer. By clipping the other end into a liquid and applying
suction to the rubber tube* the pienometer is filled with liquid.
It is them hung in a constant
temperature water bath.

After the liquid has reached
the tenqxTature of the hath
the liquid is carefully blown
out until if stands' at the?
mark on the tube. After
taking ofT the- surplus drop
from the upjier end the* liquid
is allowed to fall back into
the pienometer. The latter
is then removed from the
hath, the rubber tube? is re¬
moved and the instrument is
wiped dry and weighed. The
calculations are the same as
with the flask form of pieno¬
meter.

Hydrometer. ~ The floating
hydrometer (Fig. 25) or
“spindle” is a bulb, weighted
at the iKit.tom and having a
slender upper stem which will
he partly immersed when the?
hydrometer is floating in a liquid. The* depth to which the
instrument will sink depends upon its displacement of liquid
which, with a given instrument, depends in turn upon the
density of the liquid. A scale? upon the? stem provides the
necessary means for making the; observation.

The graduations on t ho hydrometer shun may indicate
either specific gravity or ftauml? degrees. Also there an;
numerous special hydrometers, reading in various scales

QXTANTITATIVE agricultural axalysis

Fig. 25.—Floating hy¬
drometer and cylinder.

ment with the dry

which apply to special industrial uses. Two
of these will be mentioned.

Lactometer.—This is an instrument much
used in dairy laboratories. Queveime’s
lactometer is graduated in degrees from 15
to 40, corresponding to specific gravity
1.015 to 1.040. The New York Hoard of
Health lactometer also is graduated in
arbitrary degrees in such manner that 0°
corresponds to specific gravity 1.000 and
100° to 1.029, the latter figure being con¬
sidered as the average specific gravity of
pure milk. Degrees on this lactometer
would thus roughly indicate the per cent of
whole milk in a milk and water mixt ure.

Other special names, such as “saccharo-
meter,” “alcoholometer,” etc., apply to
hydrometers for sugar solutions, alcohol
and other special uses.

In using hydrometers the temperature at
which the experiment is performed must be
that for which the instrument is calibrated
and care must be taken to remove air bub¬
bles which might cling to the hydrometer
and thus increase the effective displace¬
ment.

The floating hydrometer is much used
for measurements not requiring great ac¬
curacy, as a reading is very quickly made.
The scales found on the stems are fre¬
quently very inaccurate and any hydrom¬
eter should be calibrated by the use of
liquids of known specific gravity.

Westphal Balance.—In effect, this
balance (Fig. 26) weighs the liquid which
is displaced by an immersed plummet
whose displacement of water is known.
The balance is first brought into adjust-
plummet hanging on the beam. A eylin-

DENSITY AND SPECIFIC GRAVITY

der containing the liquid is then brought under the beam in
such a position as to allow the plummet to be totally immersed
in the liquid. Weights are then placed on the beam to bring the
balance again into adjustment. These weights are so related to
the volume of the plummet and to the graduations on the beam

Fig. 26.—Westphal specific gravity balance.

as to give directly the specific gravity at Usually the dis¬
placement of the plummet in pure water at the rated temperature
is 5 gm and the figure on the beam directly over the plummet
is 10. Therefore the largest weight piece should weigh 5 gm.

100

Q UA NT IT A TI YE A GUI ('{' LTV RAl. AN ALYS1S

lu pure water this would he placed at 10 to bring the balance
into equilibrium. This would read 10 tenths, or 1. Three
other denominations of weights are provided, reading to the
second, third and fourth decimal places, respectively.

Calibration. —This instrument, like the floating hydrometer,
must be used at the temperature for which its displacement of
water is known. Any plummet may be calibrated lor use. at
its rated temperature or at any other desired temperature by
weighing it dry, and again suspended in distilled water which
has been boiled to expel dissolved gases, Hum cooled tot he desired
temperature. The difference between these weights represents
the weight of water displaced. If the displacement so found is
not exactly 5 gm, all specific gravity determinations are corrected
to take account of the deviation, thus:

t° t° K

= ,SV° X ,

where S* is the true specific gravity,/S7° the figure found (experi¬
mentally and d the water displacement at t°.

The weights for the Wcstphal balance are calibrated by the
method described for analytical weights, page* *11.

Use of the Westphal Plummet on an Analytical Balance.
The Westphal balance is a convenient and low priced piece of
apparatus for making specific gravity determinations with a fair
degree of accuracy. Determinations may be made with a higher
degree of refinement by using the Westphal plummet with a
good analytical balance. The plummet is cleaned and dried,
then suspended from a hook on the left arm of the balance.
Weights are added to the right pan to counterpoise, then a
cylinder of the liquid to be tested is placed on a bridge* over the
balance pan in such a way as to allow the balance to swing
unimpeded, but supporting the cylinder so that the* plummet is
entirely immersed in the liquid. A counterpoise? is again effected
by removing weights from the right pan. The difference be¬
tween the two weights is the liquid displacement. This divided
by the water displacement, found as already described, gives
t°

the specific gravity at ^ The mechanical arrangement is shown
in Fig. 27.

DENSITY AND SPECIFIC GRAVITY

101

Applications.—For the application of specific gravity deter¬
minations to the quantitative analysis of solutions, two condi¬
tions are necessary: The solution must be a binary one (having
only two components, solvent and solute) and the variation of
specific gravity with concentration must be great enough to
make possible calculations of concentration to a reasonable
degree of accuracy. Accurate tables have been worked out in a
limited number of cases and for these the specific gravity deter-

Fig. 27.—Westphal plummet as used with an analytical balance.

mination frequently offers the most convenient method for the
analysis. Examples of such cases are solutions of ethyl alcohol,
methyl alcohol, various sugars and various acids in water. If it
is known that only one of these compounds is present in a solu¬
tion, the concentration can readily be determined. Of course a
good thermostat is necessary, in order to avoid temperature errors.

Such tables as those mentioned above are found in many of
the standard handbooks. Quite elaborate tables are contained
in “Methods of Analysis/ 7 published by the Association of Official
Agricultural Chemists, and in U. S. Bureau of Standards Circular
19. The latter may be obtained from the Superintendent of
Documents at small cost.

102

QUANTITATIVE AGRICULTURAL ANALYSIS

Determination of Specific Gravity.—Make accurate determinations of
specific gravity of solutions of methyl alcohol, ethyl alcohol, cane sugar, etc.,
as they may be furnished by the instructor, and using the methods described
in the foregoing pages. Report the per cent concentration of the solutions,
found by reference to tables such as those mentioned above. The tempera¬
ture used for the determination must correspond to that for which the table
in question is constructed.

In Chap. X this determination is applied to the identification
of the various oils, fats and waxes and in Chap. XI, dealing with
the analysis of dairy products, the application of specific gravity-
determinations to milk testing is discussed.

CHAPTER V

HEAT OF COMBUSTION (CALORIMETRY)

All chemical reactions involve either evolution or absorption
of heat energy. The measurement of the “heat of reaction”
has proved to be a valuable method for investigation, in both
pure and applied chemistry. We are here particularly concerned
with the amount of heat evolved by the combustion of fuels and
of foods. In the case of fuels this, of course, has a direct bearing
upon the value of the fuel when it is burned for the production
of useful heat, while the heat of combustion of foods and feeding
stuffs is of interest in connection with their relative values as
energy producers in the animal body. However, the student
is cautioned against the fallacy that the “calorific value” (heat
of combustion) of a food is the only criterion as to its value.
Even an elementary study of physiology should convince one
that such matters as balancing of diet, proper proportioning of
rougher and more refined foods, stimulation of appetite, per cent
of contained nitrogen, etc., are of prime importance in this
connection.

Units of Measurement.—In scientific work the accepted unit
of heat is the calorie. As ordinarily used this is the heat that is
absorbed by 1 gm of pure water as its temperature rises 1° C.
(strictly, from 15° to 16°). The specific heat of water is not the
same for all temperatures but the variation is only 0.013 over
a range of 0° to 100°.

In engineering work, for expressing the value of fuels, the
British thermal unit (B.t.u.) is more often used. This is the
heat absorbed by 1 lb of water as its temperature rises 1° F.

The “calorific value,” “fuel value” or “heat units,” as it is

variously expressed, is the number of calories per gram or of

B.t.u. per pound, made available by burning the material. The

following equations represent relative values:

cal per gm X 1.8 = B.t.u. per lb; 1 (1)

B.t.u. per lb , /rkN

-- = cal. per gm. (2)

1 For the derivation of these formulas see Mahin, “Quantitative Analy¬
sis,^ 2nd ed., p. 314.

103

104 QUANTITATIVE AGRICULTURAL ANALYSIS

Apparatus.—A great many forms of calorimeters have beoi
used for measuring heats of combustion but all of the inor<
successful of these are based upon a measurement of the ritAi

in temperature produced by burning a weighed sample in oxygen
at high pressure, in such a way as to have the evolved heat
absorbed by a known quantity of water and by the material of the

HEAT OF COMBUSTION

105

calorimeter itself. The weights of these (and the known specific
heat of the materials of the calorimeter), taken with the weight
of the substance burned and the temperature rise, furnish the
necessary data for the calculation.

Emerson Fuel Calorimeter.—Following is a description of the
Emerson calorimeter and also directions for making the deter¬
mination of fuel value.

Bomb.—The bomb, made of steel, consists of two cups joined
by means of a heavy steel nut. The two cups are machined
at their contact faces with a tongue and groove, the joint being
made tight by means of a lead gasket inserted in the groove. The
lining is of sheet nickel, platinum or gold, spun in to fit. The
bomb is closed by a milled wrench or spanner. The pan holding
the combustible is of platinum or nickel, and the supporting
wire of nickel. (See Fig. 28.)

Calorimeter.—The jacket is a double walled copper tank,
the space between the walls being filled with water. The calo¬
rimeter can is made as light as is possible, of sheet brass, nickel
plated.

Stirring Device.—The stirrer is directly connected to a small
motor and it is enclosed in a tube to facilitate its action in circu¬
lating the water. The stirrer is mounted on a post on the calo¬
rimeter jacket as is also the thermometer holder.

Ignition Wire.—Unless ignition of the fuel requires a very high
temperature a platinum resistance wire is suitable. For ignition
of such substances as are used in determining the water equivalent
of the calorimeter (naphthalene or cane sugar) or of anthracite
coal an iron wire is more certain in its action because it burns
and produces a higher temperature. When iron wire is used a
correction of 1600 calories per gram of wire is subtracted from
the total calories obtained from the fuel combustion. This
is the heat of oxidation of the iron.

Formation of Nitric Acid.—When any nitrogenous organic
matter is burned in air practically all of the nitrogen is liberated
in the elementary form. On account of the high concentration
of oxygen in the calorimeter bomb a considerable portion of the
nitrogen is oxidized and the products dissolve in the water which
is formed by the combustion of hydrogen. A dilute solution of
nitric acid is thereby formed. This gives rise to a positive error

106 QUANTITA TIVE AGRICULTURAL A \'AL YSIti

in the observation of fuel value, the magnitude of the error
depending upon the extent to which nitric acid is formed. As a
rule the error is small and it may be ignored for ordinary fuel test¬
ing but if a correction is to be made the nitric acid is titrated
by standard base, at the end of the experiment.

The heat of formation and solution of nitric acid from elemen¬
tary nitrogen is 230 calories per gram. It is convenient to use a
standard solution of base, 1 cc of which is equivalent to 5 calories.
The normality of such a solution is

"230 X 0.00302

= 0.3450 N.

The number of cubic centimeters of base required to titrate the
nitric acid in the born!) after the combustion is multiplied by 5,
the product being subtracted from the observed calories.

Radiation.—Radiation or absorption of heat by the calorim¬
eter may be avoided by making the calorimeter “adiabatic.”
This may be done in a number of ways, three of which will be
mentioned.

1. The water in the surrounding jacket may be heated by
electrical means, so as to keep pace with the- rise in temperature
of the calorimeter water. This is the most satisfactory method,
although somewhat complicated and expensive apparatus is
required.

2. The water in the jacket may he warmed by chemical
action. By Richards’ method a basic solution is used to fill the
jacket and an acid is run in from a burette at a rate which
depends upon the rate of change in temperature of the calorim¬
eter water and upon the concentration of the acid. The acid
solution may be standardized in terms of the number of calories
liberated by the action of each cubic centimeter upon the* base, in
which case the proper rate of addition is more easily determined.

3. The jacket of the calorimeter may be evacuated, on the
principle of the Dewar flask, the transfer of heat outwardly then
being limited to that which occurs through conductivity of the
glass of the jacket. This would appear to bo the* least trouble¬
some method but it has not worked well in practice.

Radiation Corrections.—If adiabatic conditions cum not be
maintained several methods for making radiation corrections
are available.

UK AT OF COM HOST ION

107

1. The combustion may bo begun as far below atmospheric
temperature as it is to end above it. By this means absorption
of heat in the first half of the experiment would appear to balance
radiation during the last half.

This is the roughest sort of approximation and it would not
serve for ordinarily accurate work.

2. The rate of change of temperature may be observed for a
certain period before firing and for another period after the
calorimeter water has absorbed all of the heat from the bomb.
The ai'crayc of these rates is then considered to bo the mean rate
of absorption or radiation of heat for the entire experiment and
if this is multiplied by the time* (‘lapsing between the firing and
the maximum absorption the. net gain or loss during the entire
observation period is given.

This method is very commonly employed and it gives a very
close approximation to flu* true correction.

?>. Observations an? made? in the same? way as in method (2).
In addition the time, n , required for six-tenths of the? total rise? in
temperature is observed, also the time, for tin? remaining rise.
Instead of averaging the two radiation for absorption) rates the
preliminary rate, It is multiplied by a and the? final rate*, /f 2 ,
by b. The corrected rise* is them

t f n x tt + /<y>,

where total rise, and It i and It* are regarded as positive* for
falling te*mperatures and negative for rising temperatures.

The observatiem of the time, a, is subject te> some? uncertainty
whe*n the* frunpemf ure* is rising rapidly and on this account
the* method is not so easily applied as is method (2). It will
rarely Is* found that the difference between the* corrections
calculated by these* two methods will differ by more* than 0.2
per cent and as this is well within the* permissible? variation,
method (2) is re*e*ommeneie»el for all but the? most refineel work.

4. The Regnault-Pfauridler method approaches theoret ieal
accuracy more nearly than any of the* methods already described.
For a discussion of this method, se*e White, “(las and Fuel Analy¬
sis” (International Chemical Scries) 2nd eel., page* 208.

Time-temperature Curves. -Three types of time-tempera¬
ture curves are* produced, according to whether the experiment is

108

QUANT IT A TJ VJ'I AURIC l 'J/Tl UAL .1A .1 L > SIS

(a) begun and finished below room temperature, (b) begun below
and finished above or (c) begun and finished above. Ihese
types are illustrated in Fig. 29. The relative slopes of the ends

of the curves represent R\ and R>. .

It will be observed that these slopes are easily determined m
curve (b) but that it is especially difficult to decide as to what
temperature should be taken as the maximum produced by the
fuel combustion, in the experiment represented by curve (a).
Conditions represented by curve (6) are to lx* obtained when
possible.

Determination of Heat of Combustion of Fuels, Foods or Feeds.- - Place
the lower half of the bomb in the holder and t he fuel pan in the wire support,
after having wired the fuse wire according to Fig. *2H.

Extend the wire across the pan, allowing it to dip sufficiently to 1st in
contact with the substance, which is later to be placed in the pan. The wire
must in no ease touch the pan. The fuse wire should be placed in series
with two 100-watt lamps in parallel when the 110-volt, power circuit is used
for firing.

The material whose calorific value is to be determined should be ground
to pass a OO-mesh sieve and it should be dried at 100“ before weighing the
sample for combustion. If the material is a liquid, such as milk, or a sub-

HE A T OF COMBUSTION

109

stance containing a large amount of water, 100 gm or more is first weighed
(to centigrams only). It is then evaporated to dryness over the steam
bath and reweighed. The loss of water gives the necessary data for calcu¬
lating the fuel value of the dry material to a basis of the original sample.
Thus, if M represents the per cent of water, c the calorific value of the dry
residue and C that of the original sample,

= (100- M)c

i"oo"'.

As suitable materials for exercises in calorimetry of foods, such substances
as dried egg albumen, starch, sugar and butter fat may be used. Coal,
coke, crude oil, kerosene or gasoline are fuels whose calorific power may be
determined. Volatile liquids, such as the last named two, can be weighed
and burned in a gelatine capsule, such as are used for medical preparations.
Blank determinations must then be run on other similar capsules, so that
corrections may be subtracted. All of the capsules are weighed.

Fill a weighing bottle with the prepared sample and weigh accurately to
0.1 mg. Pour from this into the pan in the bomb, until the pan is approxi¬
mately half full. Weigh the bottle again, the difference between the above
weighings giving the weight of the fuel in the bomb. This weight should be
greater than 0.5 gm and not more than 1.2 gm. For hard coal the charge
should be not greater than 1 gm. Hard coal should not be as finely divided
as soft coal or foods.

The upper half of the bomb is now placed in position and the nut is
screwed down as far as may be by hand, care being taken not to cross
the threads. The shoulder on the upper half of the bomb, over which
the nut makes bearing contact, should be lubricated with oil. Extreme
care should be taken that no oil or grease is deposited on the lead gasket.

The bomb is now ready to be filled with oxygen. The nipple is coupled
to the oxygen piping by means of the attached hand union. In handling
the bomb, care should be taken not to tip or jar it, as fuel may be thrown
from the pan.

The spindle valve on the bomb is opened one turn and then the valve
on the oxygen supply tank is very cautiously opened. The pressure gauge
should be carefully watched and the tank valve so regulated that the pres¬
sure in the system shall rise very gradually. When the pressure reaches 300
lb per square inch, the tank valve is closed and the spindle valve immediately
afterward. The bomb should be immersed in water immediately to detect
any possible leaks. The bomb is now ready for the calorimeter, which is
prepared as follows:

Nineteen hundred grams of distilled water, weighed or measured in a cali¬
brated flask, is placed in the calorimeter can at a temperature about 1.5°
below the jacket temperature (which should be in the proximity of the room
temperature). The bomb is then placed in the calorimeter and the stirrer
and thermometer are lowered into position as indicated by Fig. 28. The
thermometer is immersed about 3 inches in the water. The bulb of the ther¬
mometer should not touch the bomb.

110

QUANTITATIVE AGRICULTURAL AXALYSIS

The terminals of the electric, circuit used lor firing are now attached.
Care should be taken that neither the bomb nor tin* stirrer is
allowed to touch the sides of the can. The stirrer is now started and
allowed to run 3 or 4 minutes to equalize the temperature throughout
the calorimeter.

Readings of the thermometer are now taken for f> minutes (reading
to 0.001° or 0.002° every minute) at the end of which time the switch is
turned on for an instant only, which will i>e found sufficient to tire the
charge. In course of a few seconds the temperature begins to rise rapidly
and approximate readings are taken every minute until tin* rise heroines
slow, more accurate readings then being taken. After a maximum temper¬
ature is reached and the rate of change of temperature is evidently due only
to radiation to or from the calorimeter, the readings are continued for an
additional 5 minutes, reading every minute. These readings, before the
firings and after the maximum temperatures, are necessary in the com¬
putation of the cooling correction. The time elapsed from the time of
firing to the maximum temperature should lie, in no ease, more than (>
minutes.

When through with the run, replace the bomb in the holder and allow
the products of combustion to escape through the valve at the top of the
bomb. Unscrew the large nut and clean the interior of the bomb. The
inside of the nut should be kept greased, also the threaded part at the top
of the lower cup.

Immediately after each run, the lining of flu* bomb should be washed
out with a cloth moistened with a dilute* solution of ammonium hydroxide
and then with water. When the apparatus, after using, is to be left for
several hours or more before making another test, the linings should lie
removed and the inner surface of the bomb slightly coated with oil. This
oil under the linings should be removed when next preparing the bomb for
\ise, as an excess of it may be ignited with a possible resulting injury to the
linings.

Heavy Oils , Coke and Hard Coal.—T\w determination of the heat of
combustion of heavy oils, such as crude petroleum, and also of coke ami
extremely hard coals, is best made by mixing with a ready burning com¬
bustible, such as a high-grade bituminous coal or pure carbon. This
auxiliary combustible facilitates the complete combustion of the whole
mixture in the case of coke and hard coal, and with the heavy oil it acts as
a holder and prevents rapid evaporation of the oil. The auxiliary combus¬
tible should be placed at the bottom of the pan and the coke, coal or oil
sprinkled over it. It should be dried with extreme care and carefully
standardized as to the resulting rise in temperature per gram in the calori¬
meter when completely burned.

Calculation.—First plot a smooth curve, using temperatures
as ordinates and time as abscissas. Use only the st raight por¬
tions of the ends of the graph for calculating Hi and K 2 .

//AM T OF CO Min: XT JON

ill

The* difference ix*t\vc*f*ri flu* temperature at maximum and the.
temperature at firing gives directly the total rise in temperature
in the calorimeter. To this rise a cooling correction must he
applied, which is computed as follows:

The change in temperature during the preliminary H minutes
of reading, divided hy the time (T> minutes) gives tint rate of
change of temperature per minutes dm* to radiation to or from
tlle calorimeter, and also any heating due. to stirring. This
factor is Ah and in like manner the readings taken after the
temperature change has heroine uniform give /{%. The two
rates of change of temperature give (he existing conditions in
lilt* calorimeter at the start and at the finish of the run. The
algebraic signs of Ah and 10* will he (~\ ) for falling temperatures

and ( .) for rising temperatures. Therefore, the algebraic sum

of flic two rates, divided hy 2, will give the* mean rate of change of
temperature due to radiation or absorption, during the entire
experiment. This value, multiplied hy the time in minutes
elapsing between firing and the attainment of maximum tempera¬
ture. gives the total radiation correct ion. This radiation correc¬
tion is thus expressed:

(It t f K'M M v

( 2 ’ W

when*/' radiation correction,

/ time from firing to maximum
and Hi and Ah> have the significance already explained. The
radiation correction may have either a positive or a negative
sign, according to wind her the net effect was actual radiation
or absorption of heat from file surrounding atmosphere.

The quantity (' is applied to the total observed rise to obtain
the corrected rise and the latter, divided hy the weight of material
burned, will give the rise per gram of sample. This rise per gram
is multiplied by f lie weight of water used plus the “ wafer equiva¬
lent" of the calorimeter and tin* product, is calories per gram of
sample. This figure multiplied by l.K gives Ii.l.u. per pound
of sample, if this met find of expression is desired.

Summarizing, if T total observed temperature rise and c
wafer equivalent,

0(1000 T /*>

cal per grn

( 2 )

112 QUANTITATIVE AGRICULTURAL ANALYSIS
Substituting the value of C,

(T + ( gL+^ )( 19 00 + e)

-—_—^ -= cal per gm. (3)

The water equivalent may be calculated from the known
weights and specific heats of all of the parts of the calorimo'tor
but it is better determined experimentally by burning a
substance of known heat of combustion, such as naphthaJono
or cane sugar.

CHAPTER VI

INDEX OF REFRACTION

Theory.—When a ray of light passes from one transparent
medium into another of different density, at the surface of separa¬
tion the ray is always bent from its first course, unless if. strikes
this surface at an angle of 90°. This phenomenon is known ns
optical “refraction.” The angle i, included between the
incident ray and the normal to the separating surface (nee Fig.
30) is the angle of incidence while the angle r, between the

refracted ray and the normal, is the angle of ref raction. The ratio
i .

~ is the index of refraction.

If ^ and .s' represent, respectively, the speed of light in the

medium from -which the light
emerges and in that into which it
passes, then the index of refraction
of the latter medium with respect
to the former is greater than 1 if :t
is greater than and conversely.
In a general way the speed of light
varies inversely with the density
of the medium, although this is not
a strict mathematical relation.

It will thus be seen that the con¬
ception of index of refraction must
involve two substances and that
its value will depend upon the
density of each. Ah ordinarily
used, it is understood that the
light emerges from ordinary air
. into the substance whose index in

being measured and the term “index of refraction" therefore
signifies the ratio of the angle of incidence from air to the
angle of refraction in the substance under consideration
8 113

Fig. 30.—Illustrating refraction
of light.

114

QUANTITATIVE AGRICULTURAL ANALYSIS

Applications.—In a number of instances the measurement of
index of refraction furnishes a means for identifying certain
materials and in some cases a quantitative estimation is made
possible, where the identity of all components in a given mixture
is known. As an example of qualitative testing may be men¬

tioned the measurement of this property in oils and fats. This
is discussed in Chap. X. The quantitative determination of
alcohols and sugars in aqueous solutions and of milk fat in milk
and the detection of added water in milk by the examination of
milk serum are familiar examples of quantitative application of
refractivity measurements. Some of these are given attention in
Chap. XI.

INDEX OF REFRACTION

115

Light of short waves is refracted more than that of longer
waves. Therefore in expressing the index of refraction the
character of light must be indicated. Ordinarily the refraction
for the Z)i sodium line of the spectrum is understood unless some
other light is specified.

Apparatus.—For the determination of
refractivity an instrument must provide

(a) a prism of known index of refraction,
a plane surface of this lying against the
liquid or solid under investigation and

(b) an optical system of lenses for exam¬
ination of the effect of refraction. All
other parts may be regarded as acces¬
sories, for adding convenience of manipu¬
lation or for increasing the accuracy of
observations.

Abbe Refractometer.—This instru¬
ment (Fig. 31) serves very well for
measuring refractive indices of fairly
viscous and non-volatile liquids. The
optical system is represented in section
in Fig. 32. The lower half of the prism
(not shown in the figure) serves merely
as a means for holding a layer of liquid
in contact with the upper half. A

mirror, below, reflects light into the
system and this passes through the lower
prism and the layer of liquid, emerging
from the latter into the upper prism at '

all possible angles. The ray g, g', g", Fio-32—-Path of rays in the

Abb6 refractometer.

grazing the lower surface of the upper

prism, represents the limiting angle of incidence (90° to the
normal) and the angle of refraction of this ray (or of one whose
angle of incidence is infinitesimally less than 90°) forms the
bounding line between a region of light and one of darkness.
This will be seen as the line G in Fig. 32.

If the liquid from which light emerges is exchanged for one of
different index of refraction the angle of refraction of the grazing
ray will be changed. In other words the boundary between

116 QUANTITATIVE AGRICULTURAL ANALYSIS

light and dark in the field of observation will be shifted. It is
the observation of the position of this boundary that constitutes
the determination of index of refraction by means of this instru¬
ment. The relative positions of telescope and prism system can
be altered at will. The prism system is tipped until the bounding
line lies upon the cross hairs of the telescope. The index of
refraction is then read on an outside scale.

Dispersion. —The refractive effect at the surface separating
transparent media varies according to the wave length of the light,

shorten’ waves being most re¬
fracted. The result of using
polychromatic light in a sys¬
tem like that just discussed
will therefore be that the light
and dark fields will be sepa¬
rated by a colored zone of
spectral tints, instead of by a
sharp, uncolored lino. It then
becomes necessary to use
monochromatic light or else
to introduce some device for
correcting the dispersion. In
the Abbtf instrument a “com¬
pensator” provides this cor¬
rection.

The Compensator.— T h e

dispersive effect of different
transparent- media is not a
definite function of the* index
of refraction for monochro¬
matic light. For example, two media might have 1 the same
indices of refraction for yellow light but quite? different indices
for violet light. This principle is utilized in the construction
of the Amici prism. In Fig. 33 the parts a, a' are prisms of
crown glass and 6 is of flint glass. The angles and the dispersive
powers of these prisms are so related that when they are cemented
together the combined effect is to allow the. yellow (D i) ray of
entering polychromatic light to pass through with its direction
unchanged, while rays of all other wave lengths arc? refracted.

Fio. 33.—Single Amici prism, as used in
dispersion compensators.

INDEX OF REFRACTION

117

In other words, the part b has a refractive power which is greater
for red, smaller for violet, and the same for yellow as the cor¬
responding powers of the combination of a and a'.

If this Amici prism is placed in the path of light which has
been refracted (and dispersed) by the prism-fluid system of the
refractometer, it will either add its dispersive effect to that
already produced or oppose the latter, according to the way in
which it is turned about the axis of the instrument but, no matter
what its position, the direction of the yellow ray is unchanged and
the reading for index of refraction is not altered, since this value
is usually stated in terms of yellow light. If the angle between
the planes of dispersion of Amici and refractometer prisms is such
that the dispersion of the latter is exactly neutralized, “compen¬
sation” is effected and the border line between light and dark
fields becomes distinct and without color.

Fig. 34.—Five typical positions of the units of a double compensator, showing
net dispersive effect (D) in the direction ab.

If two Amici prisms are used, as is the case in the Abbd
refractometer, and if they are mounted in such a manner as to
revolve in opposite directions, the dispersive effect of the com¬
bination may be varied between the limiting values of + 2 d and
— 2d, where d is the quantitative effect of one Amici. This
widens the range of possible compensation.

118

QUANTITATIVE AGRICULTURAL ANALYSIS

The diagrams of Fig. 34 illustrate a few of the possible posi¬
tions of the two elements of a double compensator, with the
net effect of the altered system upon dispersion. In explanation
of these diagrams the combined dispersive effect in the direction
ab is represented by D and that of one unit in its own plain* (repre¬
sented by the arrows) by d. It is evident that the component
of dispersion in ab for any given position of a unit varies as the
cosin of the angle, 0, between ab and the plane of dispersion for the*
unit.

Any conceivable value between 2 d and —2 d may be* obtained
and compensation thus effected for any dispersion within this
range.

Butyro-refractometer.—The Zeiss bu tyro-ref ractometor has
an optical system similar to that of the Abbe instrument.
The principal difference is in the fact that the* telescope
and prism system of the former instrument are rigidly con¬
nected so that the divided field cannot be shifted to bring
the line of division upon the central crossing of cross hairs.
Instead, a scale graduated in arbitrary degrees is fixed within
the instrument and the position of the bounding line is read
upon this.

As its name indicates, the butyro-refraetometer is designed for
use in dairy laboratories and its chief function is in the testing
of butter. Therefore, instead of being provided with a com¬
pensator the prisms of the instrument are “achromatized”
for pure butter so that this fat gives no dispersion. This con¬
stitutes the basis for an additional qualitative test for butter,
since other fats used as substitutes will have different dispersive
power and the bounding zone in the field will therefore be
spectrally tinted.

Dipping Refractometer.—From an inspection of Fig. 32 it, will
be seen that the essential parts of the Abb6 refractometer, from
the optical standpoint, arc the upper prism, the objective and an
eyepiece for viewing the field. (The latter is not shown in the
figure.) The thickness of the liquid film is of no particular
moment and the prism might as well be immersed in a quantify
of the fluid. In the dipping refractometer (Fig. 35) this principle
is utilized. The entire instrument is in one rigidly built piece,
the prism being fixed at the lower end. The instrument is hung

INDEX OF REFRACTION

so that the prism is immersed in a, hath of the liquid under
examination and t Ik* index is mad on a scale within.

The compensator for the dipping refraetometer / .^

consists of a single Amid prism (C of Fig. *h r >) rotates 1 V W
by the milled ring Y. The range of compensation is
thus less than that of the double compensator but it
is sufficient for this refraotometer, whoso range for
indices of refraction is comparatively narrow. CO'ulu

In Fig. 3o two points are arbitrarily selected to
represent the entire surface of the prism where light jw J
enters, gg' is the ray of grazing incidence refracted || /{

and focused at (7, which bears the scale. a and <t' If
represent rays entering at any other incident angles a|( W
focused at A. Above is a projection of tin* field. At |J
the right of (} the fiedd is dark because the* crit ical ray, ||
refracted as it enters the prism, can make no greater |( 1,

angle of refraction for the given prism-fluid combina- |( j >1
tion. When the fluid is changed for another having | l|
a different index of refraction that angle of rofrao- jr* ! J
tion for the critical ray is changed and the border line |
within the field is shifted. I /I

Pulfrich Refractometer.—This instrument is espe- M \
cially adapted to use with volatile liquids, although til. .. jJ
it is suitable also for exact determinations of index lui VI "(J
of refraction of any liquid whatever. The optical gil lid I jj
principle is (exactly the same as that of the Abbrt |!'n -i ^
instrument, light; entering the fluid-prism system at • q 7

grazing incidence and the critical angle of total refleo- :y
tion being measured. The liquid is placed in a glass 'f/yj

cup which is cemented to the top of the* refracting [;■/j

prism, and which may be covered to prevent. evapo- yh
ration of the liquid. Monochromatic light is used
and an observation telescope is swung upon an arm j, sa ,
in such a way as to bring the division between light. r»-

and dark fields upon its cross hairs. A circular scale
provides the reading.

On account of the more expensive construct,ion of
the Pulfrich refraotometer, it is not a common part of the
equipment of the technical laboratory. Its more important use*

I > ii r t I y

fuu'tioti.

120

QUANTITATIVE AGRICULTURAL ANALYSIS

is for measurements of refractivifcy in work of the laboratory
of physical chemistry.

Determination of Index of Refraction.—Determine the index of refraction
of solutions of sugars or alcohols, furnished by the instructor, and report the
per cent concentration, found by reference to tables in the A. (). A. C.
“Methods of Analysis” or in other special books, circulars or handlx>oks.
Or use the dipping refractometer for the determination of added water in
adulterated milk. For the latter, see page 202, Part. III.

CHAPTER VII

OPTICAL ROTATION (POLARIMETRY)

Theory..In any ordinary beam of light the wave motion

is regarded as being transverse and in all possible pianos which
can include the axis of propagation. When such a beam pjisscs
through, or is reflected from, certain transparent media these
vibrations are suppressed in all but one plane. The beam of
light is then said to be “plane-polarized.”

a b

Fig. 36.—Diagrammatic ruprowntntion of typical piano* of vibration of (a)
unpolarizod and (h) pIuM*-polurizcd light..

This change is illustrated in Fig. 30, in which a represent* some
of the planes of vibration of unpolarized light and b that of
plane-polarized light. In these diagrams the axis of propagation
of the beam of light is understood to be perpendicular to the
plane of the paper.

121

122

QUANTITATIVE AGRICULTURAL ANALYSIS

Most transparent media permit plane-polarized light to pass
through them unchanged but there are certain crystals and
solutions that possess the remarkable property of rotating the
plane of polarization to the right or left. Further, this is a
quantitative property and the magnitude and direction of the
angle of rotation is a specific property of the substance itself,
a given solvent being understood in the case of solutions. This
property undergoes a definite change of value with definite
changes in temperature and in the case of solutions it varies
directly with the concentration. This last is a very important
consideration and it will be readily seen that if an instrument
can be constructed for measuring the angle of rotation, this will
serve as a means for the quantitative determination of optically
active substances in solution.

Substances that rotate the plane of polarization to the right
are dextro-rotatory while those that rotate to the left are laevo -
rotatory. The angle of rotation varies according to the wave
length of the light that is used and it therefore becomes
necessary to use monochromatic light in order to have a
definite, measurable rotation. Sodium light is generally used
for this purpose.

Specific Rotatory Power .—The angle of rotation which would
he produced by a column of solution 1 dm long and containing 1 gm
of the active substance in each cubic centimeter is known as the
“specific rotatory power 77 or “specific rotation 77 of a given
active substance. This is, in a sense, a hypothetical figure as
few solutions could be made of so great a concentration; however,
the specific rotation can be calculated from the results of measure¬
ments on more dilute solutions. The specific rotation, at 20°
and for the D-line of sodium light, is expressed by the symbol

M 2 f.

For a solution of an active substance in an inactive solvent,
such as water, the angle, a, of rotation is approximately in
proportion to the concentration, which may be expressed as
grams of active substance in 100 cc of solution. This relation
does not hold strictly, on account of changes in electrolytic
dissociation (ionization), molecular association (polymeriza¬
tion), hydrolysis, or hydration, with changes in concentration,
where any of these factors apply to a given solution. In many

OPTICAL ROTATION

123

of the ordinary applications of the polarimeter to analytical
problems the influence of these factors is negligible.

From these considerations the formula:

T 120 ° 100 O? fl”)

[a] » = -jj-

is derived, as representing the specific rotation of an active
substance in solution, where a is the angle of rotation pro¬
duced by a column l dm in length and of concentration c gm
in 100 cc.

A few examples, out of a very large number of optically active
substances, with their specific rotatory powers are given in the
following table, in which the sign (+) indicates dextro-rotation
and ( —) laevo-rotation. The solvent is understood to be water,
unless otherwise stated.

Table IV.— Specific Rotatory Powers

Substance

r -i 20° *

[<*]/>

Dextrose (grapesugar).

4-53.1

Levulose.

-93.3

Sucrose (cane sugar).

4-66.5

Invert sugar.

-20.57

Lactose (milk sugar).

4-52.53

Maltose (malt sugar).

+ 137.5
+ 190.0
+ 12.0
— 164.0

Starch.

Tartaric acid (ordinary).

Nicotine (in benzene).

Cocaine (in chloroform).

— 16.3

Quinine sulphate (in alcohol).

—225.7

Camphor (in benzene).

+41.4
+59 to +67
+96 to +98

Lemon oil (no solvent). .

Orange oil (no solvent).

* These figures represent mean values for ordinary concentrations.
There is nearly always a certain variation with concentration and where
this is large it must be taken into consideration. For example, the Hpe
cific rotation of levulose is —88.13 — 0.2583 c, and of dextrose -4-52.50 *-{
0.0188 c 4- 0.000517 c 2 , c indicating grams of active material per 100 ec.
It must also be noted that a number of substances exhibit “mutarotation,”
that is, the rotation of the freshly prepared solution changes after a. certain
lapse of time into the final, stable value.

124

QUANT IT A VIVE AGRICULTURAL . 1 S ALYSIS

The Polarimeter—Listed in what (perhaps somew:
trarily) may be regarded as the order of relative import?
not in the order in which they are fixed in the inslrun
essential parts of an instrument for measuring optical rot
as follows:

(а) An optical part, P, (Fig. 37) for polarizing
monochromatic light in a definite plane. This is the “ p<

(б) A part, A, similar to the polarizer, which can I
in the path of the light and rotated about the axis of pro
of the beam. This is the “analyzer.” With the
fixed in position there will be a corresponding positio

Flo. 37.—I)iaKrummatie representation of tho r^i-rUinl p;irt
a simple jiolurimctcr.

analyzer which will permit the maximum brightness <
mitted light find another which will cause* total extinct
first representing a coincidence of the planes of poh
of polarizer and analyzer, the second an inclination of
those planes.

(c) A tube, S, to contain the solution under in vestigatif
can be placed in the light path, between tin* analyzer
polarizer. This tube must be of definite 1 length and if rm
plane, transparent ends, placed perpendicularly to flu* <i
of light travel.

(d) A lens, /, for directing parallel light into theinst

(e) A system of lenses, 7\ through which tin* ojjeral
observe the action of the first four parts.

(/) A circular scale upon which is indicated the angle i
which the analyzer is rotated.

The relative positions of these parts are shown in Fig.

Making a Reading.--Briefly stated, the determinu
rotatory power with the most simple instrument possible w
made as follows:

The analyzer is brought into a relation with the p<
such as to permit the maximum transmission or exfine
light. This establishes the zero point of the instrument

OPTICAL ROTATION

125

tube of solution is then placed in position and the analyzer is
turned so that its plane of polarization lies in the new plane,
which has been rotated by the solution from its original position.
The magnitude and direction of the angle, oc, through which the
analyzer has been turned, is noted and from this and from the
length of column and the known concentration of the solution
the specific rotation is calculated.

In the more common case the specific rotation of the substance
is already known and the concentration of the active substance
in the solution is the factor in question. For example, the per
cent of cane sugar in a syrup is to be determined. A definite
weight of the syrup is diluted to a definite volume and the angle
of rotation produced by a column l dm in length is determined.
The specific rotation of sucrose is given as +66.5. We have
then the equation (from Eq. (1), page 123):

66.5

100 a 100a

cl ’ or C ~ 66.5 r

The length, Z, is known and the angle, a, is determined by
observation. The concentration, c, of sugar in the solution,
as well as the concentration of sugar in the original syrup, is then
easily calculated.

Construction of Polarizer and Analyzer.—In the most common
form of this instrument the polarizer and analyzer are of identical
construction. It is a well known fact that when a ray of light
falls perpendicularly upon certain faces of a crystal of Iceland
spar (natural, crystallized calcium carbonate) the light is broken
into two rays which are unequally refracted, so that when any
object is viewed through such a crystal two images are observed.
What is equally important is that these two rays are polarized in
planes perpendicular to each other.

The Nicol Prism.—This is made by cutting a crystal of Iceland
spar into two wedge-shaped pieces and grinding the faces in such
a manner that when these pieces are cemented together one of the
plane-polarized rays may pass through while the other will be
reflected to the side of the prism and there absorbed by a black¬
ened surface. In Fig. 38 the incident ray, W, is double-refracted
and at the dividing surface between the two parts of the
crystal, the “ordinary” ray, o, is reflected to the side of the prism

126

QVANTJTA TIYFj AGRK'VLTUUAL . 1 XAL YS1S

while the “extraordinary” ray, o, passes through. This ray is
polarized in a plane which is perpendicular to the “optical
principal plane” of the prism, a term which need not be defined
here.

This Nicol prism, properly fixed in place in the end of the
polarimeter nearest the light source, forms the polarizer. The
analyzer is another Nicol of similar construction. When this
is turned so that the optical principal plane is parallel to that of
the polarizer, maximum brilliancy of transmitted light is ob¬
served. If these two planes arc perpendicular to each other,

Fig. 38.—Nicol prism.

total extinction results because the extraordinary ray from the
polarizer is now in the plane for the ordinary ray for the analyzer
and it is therefore reflected to the side of the latter and there
absorbed.

Method of Making Observations.—Tn practice it is not easy
to determine when either maximum brightness or maximum
extinction of entering light occurs. Accordingly most polarim-
eters are constructed with an additional device to aid in making
the reading. In “half-shadow” instruments the field is divided
into halves by interposition of a thin plate of quartz which covers
half of the diaphragm of the polarizer. The thickness, method of
grinding and position of this plate arc such as to cause a small
difference between the angles of maximum intensity or extinc¬
tion for the two halves. That, is, as the analyzer is rotated, one
half of the field gains in intensity while the other half diminishes.
The zero of the instrument is the position of the analyzer which
gives a uniformly lighted field.

By use of a somewhat similar principle triple fields may be
produced. The arrangement of the Nicol prisms is different
in instruments using this principle but the effect is such that the
field is divided into three parts. The sides have always like

OPTICAL ROTATION

127

intensities and these brighten as the middle section darkens.
Here again, the field of uniform intensity is seen at the zero
angle.

Light Source. Many of the forms of polarization apparatus
are constructed for monochromatic light of a specified wave
length. White light cannot bo used with such an instrument
because its component rays suffer different rotation of their
polarization planes, according to their wave lengths, the shorter
waves being rotated to the greatest degree. Sodium light is
most commonly used for this purpose as it contains rays from a
very narrow band in the spectrum and it is therefore nearly
homogeneous. A sodium light is easily produced by placing
any suitable sodium compound in a non-luminous flame. So¬
dium carbonate or recently fused sodium chloride is suitable for
this purpose. The salt is placed in a platinum spoon or fused
into a bead in a loop of platinum wire, or some similar device may
be employed.

Quartz Wedge Compensation: The Saccharimeter. It has

been stated in the preceding paragraph that the rotation of the
planes of polarization varies for light of different wave lengths.
If white light is used to illuminate the ordinary polarimeter the
effect of interposing an active substance in the path of the rays
is a dispersion of the various polarization planes. This is
analogous, in a manner, to the dispersion of white light, by
refraction and it was seen in the discussion of the refract,omoter
(page lib) that this dispersion could be corrected by optical
means without altering the refraction of a given ray, such as the
yellow one.

The quartz wedge compensator for the polarimeter makes
possible the use of white (polychromatic) light. Quartz is optic¬
ally active and it occurs in both doxtro- and lacvo-rotatory forms,
the angle of rotation of sodium light at 20° for a plate 1 mm
thick being ±21.72°. If absolutely similar plates of right arid
left rotating quartz should be placed between polarizer and
analyzer, the net effect would be zero rotation. If the thickness
of either one of those could be varied at, will the effect of the
combination could be made either right or left rotating, within
certain limits, and this effect might be made such as to com¬
pensate (neutralize) exactly the rotation of a solution which

128

QUANT IT ATI VE AGRICULTURAL ANALYSIS

is placed in the instrument and whose rotation is to be measured.
In such a case both polarizer and analyzer might be made as
rigid, stationary parts of the instrument, the only adjustable
part being one of the quartz plates. This possibility of adjust¬
ment is accomplished by cutting one of the plates diagonally,
making two wedge-shaped pieces which may be thrust past one
another by means of an appropriate screw, the magnitude of the
effect being noted upon a scale.

Now it happens that the rotation dispersion of quartz for white,
or other polychromatic, light is nearly identical with that of
cane sugar in solution. Since, in using this instrument, the
quartz wedge combination will always be adjusted to be equal in
rotatory power to that of the solution being investigated, but
in the opposite direction , it will also be true that the dispersion of
the sugar solution will be nearly compensated by the opposite,
but otherwise nearly equal, dispersion of the quartz system.
Because of these relations the instrument constructed in this

r\.

. n __

ZS7 r i \

I-P-5-

LI A - J

l - iL

W IT

Fig. 39.—Diagrammatic ivimputation of lh<* ossontial parts of a quartz wedge?
saeoharimetor, having double? rompcn.suting vmlgos.

manner is known as a “saeeharimeter.” If used with other solu¬
tions than those of cane sugar the polarization dispersion could
be compensated only approximately, at best, and readings of the
angle of rotation could not be correct. In such a case it would be
necessary to use sodium light or a selective light filter.

The relations of the optical parts of the quartz wedge saeehari-
meter are shown diagrammatically in Fig. 39.

Light Filter for Use with the Saccharimeter.~”The quartz
wedge system fails to give exact compensation for the rotation
dispersion of sugar solutions and in order to avoid slightly high
readings it is necessary to absorb a part of the. blue and violet
waves from white light, as these suffer the greatest dispersion.
The International Commission for Unifying Methods of Sugar
Analysis adopted the suggestion of Bryan 1 that white light shall
1 J. I ml . Eng. Chcm. f 6 , 107 ( 1913 ).

OPTICAL ROTATION

129

be passed through a solution of potassium dichromate “of such
concentration that the percentage content of the solution
multiplied by the length of the column of solution in centimeters
is equal to nine.”

The Sugar Scale.—The simplest and most generally useful
scale for the polarimeter is the circular scale, divided into angular
degrees, with a vernier for greater accuracy in reading. But in
the practical use of the instrument for analytical purposes there
arises (as is usually the case when scientific instruments are
used for practical testing) a demand for a direct-reading scale
that can be interpreted in terms of the per cent of active sub¬
stance, without calculations other than of the simplest sort. The
largest commercial use of the polarimeter is for sugar testing and
for this purpose there have come into general use three scale
systems: the Ventzke (German), the Laurent (French) and the
International, the latter being a development of the Ventzke
scale. A scale of one of these types is usually placed upon the
instrument, even when angular degrees also arc indicated.

The Ventzke Scale and the Normal Weight.—In this system
a “normal” solution of cane sugar was first defined as one having

a specific gravity of 1.100 at

17.5°

17.5°*

Of course this is an entirely

arbitrary value but it served to fix the basis for the system. The
scale values were fixed by polarizing a solution of this concen¬
tration in a 200-mm tube at 17.5°C., this defining the 100° point
on the scale. Because of the difficulties involved in preparing
solutions having this exact concentration by use of the hydrom¬
eter alone, it became customary to make the normal solution
for fixing the scale points by weighing 26.048 gm of sucrose and
making the solution to 100 cc at 17.5°. This is the same as
Ventzke’s solution. The “normal weight” was then 20.048
gm.

The adoption of the Mohr unit of volume (1 cc “Mohr”
= 1.00234 true cc) brought confusion into the scheme, as instru¬
ment builders for a time used the old normal weight with the now
volume unit. The 100° point on the Ventzke scale was then
fixed 1 “by polarizing in a 200-mm tube a solution containing
26.048 gm of sucrose, weighed in air with brass weights, in 100

1 U. S. Bureau of Standards, Circ. 44, 27, 2nd ed. (1918).

130

QUANT IT A TIYK AGRICULTURAL ANALYSIS

Mohr cc at 17.5°, the temperature of the quartz wedges, as well
as the polarizing temperature, being 17.5°. This confusion
has been still further increased by the more recent readoption
of the true cubic centimeter as a unit for practically all scientific
work (volumetric apparatus now being furnished by the manu¬
facturers, graduated upon this basis) and by the fact that there
is frequently no indication upon the instrument as to what unit
has been used in working out the scale. And it may be well to
remark here that the all too general custom in industrial (and
some college) laboratories of using all commercial volumetric and
other apparatus, and even weights, without calibration leaves the
accuracy of much analytical work in a very questionable light.
The only way by which accuracy can be assured is by calibrating
the flasks, burettes, pipettes and weights to be used in this work
and by checking the saccharimeter scale against quartz plates
that have been tested by the Bureau of Standards or by other
competent standardizing bureaus.

The International Scale.—In 1900 the International Sugar
Commission recommended that, the sugar scale be redefined,
basing the 100° point upon the true cubic centimeter and a
temperature of 20° O. Introducing the correction for the changes
of volume unit, and of the specific rotation of sucrose, the expan¬
sion of the glass polarizing tube, quartz wedges and metal scabs,
between 17.5° and 20°, the normal weight of sucrose becomes
26.000 gm. The International sugar scale is then to be defined
as follows: “The graduation of the median meter ahull he made at
20° C., 26 gm of sucrose dissolved in 'water and the volume made
up to 100 metric cc. All weighings are lo be made in air with
brass weights , the completion of the volume and the polarization
are to be made at 20° C. This will determine the 100° point. 11

In order to determine the per cent of sucrose in a material
of unknown purity is only necessary to weigh 26.000 gm of tins
sample, dissolve and dilute to 100 cc and then “polarize” in
a 200-mm tube. If the material were pure cane sugar the read¬
ing would be 100° International (100° I.). If it were 50 per cent
pure the reading would be 50° I. In general, then, degrees on
this scale indicate per cent of sucrose. Of course it is essential
that no other active substance shall be present in the solution
or that some method for accounting for these shall be available.

OPTICAL ROTATION

i:n

In order to make a simple reading possible it is not necessary
to use the normal weight of sample or to polarize in a 200-mm
tube. Any simple fraction or multiple of these numbers may
be employed and due account taken in the calculation. Polariza¬
tion tubes are provided, varying by even stages from 100 to
400 mm in length.

The sugar scale provides direct readings for other sugars and
for other optically active substances, not sugars, by use of a
properly modified normal weight. Thus for lactose (milk
sugar) [a];"° = 52.53, instead of 66.5 as for sucrose. Therefore

it will require ^^ X 20 = 32.9 gm of lactose in each 100 ec to

give a rotation of 100° on the sugar scale. 32.9 gm is then the
normal weight for lactose and if, for example, 32.9 gm of milk
were treated in such a manner as to obtain the clear serum and
this diluted to 100 ce and then polarized in a 200-mm tube,
degrees International would indicate directly the per cent of
lactose in the milk. This determination is described in the
section on Dairy Products, page 214, Part III.

The Laurent Scale. -This is constructed so that a quartz
plate 1 mm in thickness and cut so that its faces arc perpendicu¬
lar to the optical axis will give a rotation of 100° L. The normal
weight for this scale will then be such that when this quantity
of substance is dissolved in 100 ce and the solution is polarized
in a 200-mm tube it will give the same rotation as a quartz
plate of the above description. Because of small differences in the
specific rotation of quartz specimens there has been some uncer¬
tainty regarding the normal weight. The value now accepted
for sucrose is 10.29 gm, dilution to 100 true ec being understood.
Both Ventzke and Laurent scales are falling into disuse, being
properly replaced by the more rational International scale.

The Common Sugars.—Sucrose, or cane sugar, is the principal
sugar of the juices of sugar cane, sorghum, beets and many
fruits. It may he converted into a mixture of equal parts of
dextrose and lcvuloso by hydrolysis, induced by action of acids:

CiJKmOx, + h 2 o -»<! 6 h«*06 + c!Ji 12 o 6 .

Sufiroeo Dextrous JVvulow*

The difference between the molecules of dextrose and levulose is
a structural one and this has a direct bearing upon the; rotation

132

QUANTITATIVE AGRICULTURAL ANALYSIS

of these sugars. The values for the specific rotation (for 20-per
cent solutions) of sucrose, dextrose and levulose are +00.5,
+53.1 and —93.3, respectively. The mixture of dextrose and
levulose has a specific rotation, for these concentrations, of
— 20.57, which is practically the mean of the separate values for
the two sugars. Because of the change in the direction of rota¬
tion with this conversion of sucrose, the reaction is known as one
of “inversion" and the resulting mixture of sugars is called
“invert sugar/ 7

Cane Sugar.—Sucrose can be determined by a single polar¬
ization only in case no other active substance is present in the
solution. In case either dextrose or invert sugar is present a
polarization before and after the inversion of cane sugar gives the
necessary data for the calculation of sucrose, by the modified
Clerget formula. This formula is derived from the following
considerations:

From the values for [ajjf, given above:

X 26 = 83.9. Therefore 83.9 gm is the normal weight

(International) for invert sugar.

From the equation for inversion: 26 gm of sucrose yields

27.37

27.37 grn of invert sugar and this is ^ ^ = 0.3262 of the normal

weight. (Herzfeld’s value, 0.3266 is now generally used.)

If the normal weight of sample (based upon sucrose*) has been
used for making the solution for the direct polarization (/'), then
each per cent of sucrose in the sample; will give a rotation of
+ 1° (International scale) before the inversionand —0.3260°after
inversion. Therefore the change of rotation (P — J) would be
1.3266° for each per cent of sucrose. If = per cent of sucrose,

P - I
1.3266'

( 1 )

This is for a temperature of 20° and it is found that between 0°
and 20° the left rotation of invert sugar produced from the
sucrose of a normal solution decreases 0.005° for each per cent,
for 1° O. rise in temperature. This is chiefly due to a decrease
in the rotatory power of levulose. At 0° C. the formula would
then read:

(2)

OPTICAL ROTATION

133

and, in general

o = P-I

1.4200 - 0.005 t

This is usually written:

^ 1 ()()(/> - I)

' " 142.()() - 0.5 i

t indicating temperature in degrees (Centigrade.

Recent work 1 at the Bureau of Sta.ndn.rds has shown that the
(-target divisor should be 145.25 instead of 142.00, in presence
of the acid used to cause inversion.

The method is applicable only to materials containing no other
compounds whose activity is changed by treatment with acids.
Molasses from beets and, to some extent, beet sugar contain
certain quantities of raffinose ((a sugar whose specific
rotation is +104.5°. This rotation is diminished by one-half by
warming with dilute acids. (See page 130.)

Commercial syrups of various kinds usually possess a color
which interferes with transmission of light and makes polari-
scopic readings difficult. This color is due to a variety of
colored organic substances and to caramel formed during the
heating processes. It can be removed in most eases by addition
of a basic lead salt, of which basic lead acetate is most suitable,
or of “alumina cream/’ a suspension of colloidal aluminium
hydroxide in water, freshly prepared. In the ease of lead salts
the action is partly chemical and partly physical. Complex
lead salts of organic acids are formed and these, being colloidal
in character, flocculate and carry with them other colloidal
colored compounds. Neutral lead acetate is used in some eases
where a basic reaction is to be avoided.

Correction for Volume of Precipitate.—In the method as
usually followed the clarified solution is diluted to 100 cc before
filtration. This ignores tint volume of the precipitate and an
error is introduced from this source. However, the actual vol¬
ume occupied by this precipitate is much less than the apparent
volume, owing to its colloidal nature. If there is produced a
larger quantity of precipitate than can safely be ignored the
double dilution method of correction is used. In this method
one polarization is made on the clarified solution which has been

»U. S. Bur. Stand. 8<d. Paper, 375 (1920).

(3)

(4)

134

QUANTITATIVE AGRICULTURAL ANALYSIS

diluted to 100 cc, as usual. Another sample of the normal weight
is clarified and diluted to 200 cc and the filtrate is polarized.

Let P = true polarization of a normal solution,

Pi = polarization of the solution in the 100-cc flask,
P 2 = that of the solution in the 200-ce flask and
v = actual volume of solid precipitate.

Then

P'i

PJ\

Pi-Pi

100 P
100 - V

1/ 200P_ \ = 100 P
2\200 - v) 200 - v
(100 P ) 2

(100 — a)(200 - v)'

100 P(200 - v) - 100 P(100 - v)
(100 - v) (200 - if)

( 1 )

( 2 )

( 3 )

(UK) — wj(200 — v) ;

From Eqs. 3 and 4,

p^ = „

pi - Pi

(5)

Therefore the true rotation is the product of the two readings, divided
by their difference.

The Association of Official Agricultural ('hemints has placed
the arbitrary limit of 1 cc of precipitate from 2b gm of sample,
for the solution for which no correction need be made.

Determination of Sucrose in a Commercial Syrup. --Prepare a solution
of basic load acetate by one of the following methods:

(a) Add 215 gm of neutral lead acetate and 05 gm of litharge (PbO)
to 500 cc of distilled water (or a smaller amount using the same proportions)
and boil in a covered dish for 30 minutes. Cool, decant the dear solution
and determine the specific gravity by means of a hydrometer. Dilute until
the specific gravity is 1.25, using recently boiled water.

(5) Make the solution directly from dry basic lead acetate and dilute until
the specific gravity is 1.25.

Direct Polarization.—Weigh a small dish, then drop in and weigh 20.000
gm of the commercial syrup or molasses. Rinse into a 100-cc volumetric
flask with about 50 cc of water and then carefully add basic lead acetate
solution until the sugar solution is decolorized as far as any effect can be
noticed, avoiding an unnecessary excess of the clarifying agent. Dilute to
the mark on the flask, mix thoroughly and filter through a dry filter, rejecting

OPTICAL ROTATION

135

the first 15 ec. Polarize at a temperature of exactly 20°, using a 200-mm
tube unless the solution is still colored enough to make this difficult, other¬
wise use a 100-mm tube and double the reading. This is the quantity P
in the Clerget formula (4) on page 133.

Invert Polarization.—Precipitate the lead from the clarified sugar solution
by adding either powdered anhydrous sodium carbonate or powdered
anhydrous sodium oxalate, very carefully, until a very slight excess is
indicated by failure to produce more precipitate. Filter on a dry filter
to remove the lead salt. Reject the first 15 cc and save the remainder
of the filtrate.

Pipette 50 cc of the clear, lead-free filtrate into a 100-cc flask of ordinary
form. If sodium carbonate has been used for precipitating lead, carefully
neutralize the excess with hydrochloric acid. Invert the sucrose by one of
the following methods:

(а) Add 25 cc of water and then add from a pipette 5 cc of concentrated
hydrochloric acid, dropping the acid slowly and mixing by rotating the
flask. Place the flask in a water bath which is kept at 70°. The tempera¬
ture of the solution should reach 69° in about 3 minutes. After the flask
has been in the bath for 10 minutes remove and cool to 20° in running
water. Rinse into a 100-cc volumetric flask, dilute to the mark and mix.

(б) Add 5 cc of concentrated hydrochloric acid, slowly and mixing well.
Set the flask aside for 24 hours at a temperature of 20 to 25°, or for 10
hours at somewhat above 25°. Dilute to 100 cc and mix.

On account of the considerable variation of the specific rotation of levu-
lose with temperature it is necessary to polarize at a constant, definite
temperature. For this purpose a water jacketed tube is used and water at
20° is circulated.

Since the dilution of the solution was doubled after the direct polarization,
the reading for the invert polarization is multiplied by 2 if a 200-mm tube
is used, or by 4 for a 100-mm tube. Calculate the per cent of sucrose in the
syrup.

For low concentrations of invert sugar the variation of rotation
with concentration is such that formula (4) on page 133 will not
apply. The official method specifies the following formula,
where the concentration of sugar in the invert solution is less
than 12 gm per 100 cc:

= _100( P - 1 ) _

142.66 - | - 0.0065[l42.66 - 1 - (P - I)]

This might be further simplified to

« = _ 100CP - I) _

141.73 - 0.4967 t + 0.0065(P - 1)

(6)

136

QUANTITATIVE AGRICULTURAL ANALYSIS

Iii these formulas the symbols have the significance expressed
in the Clerget formula.

Beet Products.—The interference of raffinose in the calcula¬
tion of sucrose from direct and invert polarizations has already
been noted. If the direct polarization reads more than 1° I.
higher than the sucrose calculated as already described, the
presence of raffinose is indicated. In this case sucrose and
raffinose are calculated by the formula of Herzfeld:

0.5124 P - I
0.839
P - S
1.852 ?

( 7 )

( 8 )

R indicating the per cent of raffinose and the other symbols
having their former significance.

Commercial Glucose.—This substance contains dextrin and
maltose in variable quantities, in addition to the essential
dextrose. The specific rotation of the various dextrines is
usually about +193 and that of maltose is about +138, that of
dextrose being only +53. On this account the specific rotation
of commercial glucose is somewhat variable but it is always
higher than that of dextrose. The investigations of Leach 1
indicate that +175° I. is the average rotation for a solution con¬
taining 26 gm of commercial glucose in 100 cc polarized in a 200-
mm tube. From this is deduced the formula:

„ 100 (a - S )

0 = 175“

( 9 )

a indicating the direct polarization in International degrees, S the
per cent of sucrose, determined as already directed, and G the per
cent of commercial glucose polarizing +175° I. If invert sugar
is present the formula is inapplicable. In this case use is made of
the fact that the left rotation of invert sugar decreases with
rising temperature, becoming zero at 87° C. At this tempera¬
ture the mean rotation of commercial glucose has dropped
to +163° I., so that the calculation is made by the formula:

G =

100 7
163 ’

(10)

where I is the corrected invert reading at 87° C.
1 U . S. De'pt. of Agr. Chem. Bull . 65 , 48 .

OPTICAL ROTATION

137

Detection of Invert Sugar. 1 —Dissolve about 20 gm of sample and dilute
to 100 cc. Clarify, if necessary, before diluting. Filter and add a slight
excess of sodium carbonate. Filter again if not clear. To 50 cc of the
solution in a casserole add two drops of a 1-per cent solution of methyl blue
and boil. If the color disappears after 1 minute, at least 0.01 per cent of
invert sugar is present. If not completely decolorized after boiling for 3
minutes no invert sugar is present.

Determination of Commercial Glucose in Syrups Containing Invert
Sugar.—Prepare and clarify, if necessary, the solution of molasses or syrup,
following the directions already given on page 134. Invert and obtain
the invert reading at a temperature of 87°, using the water jacketed tube for
this purpose. Calculate the per cent of commercial glucose by dividing the
invert reading (corrected for dilutions) by 163 and multiplying by 100, as
indicated in formula (10), page 136.

Leach, “Food Inspection and Analysis,” 4th Ed., 613.

CHAPTER VIII

HYDROGEN ION CONCENTRATION

In the chapter on indicators, in Part I, it was noted that the
color change of the indicator bears a definite relation to the
changing hydrogen ion concentration in the solution, and that
upon this consideration rests the suitability of an indicator
for a given titration. The investigation of hydrogen ion con¬
centration must necessarily precede this quantitative knowledge
of color changes and such investigations may be made with a
high degree of accuracy.

Methods.—A number of methods have been used for the
determination of hydrogen ion concentration. Of these, two
will be mentioned. These are the potentiometer method and the
indicator method. The manipulative details, necessary pre¬
cautions and the sources of error of these determinations lie
outside the scope of this book. The brief discussion here inter¬
posed is provided in order to give the student an idea of the
general principles involved in the laboratory methods and of the
importance of such measurements to the problems of the agri¬
cultural chemist. For a full discussion and detailed directions
for the determinations, refer to the numerous papers in the
journals and to Clark's book, “The Determination of Hydrogen
Ions.” In this book is a tolerably complete bibliography of the
various papers that have appeared on the subject.

The Potentiometer Method.—In principle, this method
depends upon measuring the electromotive force of a system in
which are placed (a) a hydrogen electrode immersed in a solution
of known hydrogen ion concentration, ( b ) a hydrogen electrode
surrounded by the solution whose Pit value is to be measured and
(c) a potentiometer. From the measured e.m.f. of the system
and the known hydrogen ion concentration around the standard
electrode, the ion concentration in the unknown solution is
calculated, using the equation:

e.m.f. -- 0.0i>9 log £ f/ »

where (! and (■' represent the hydrogen ion concentrations in the
two solutions.

HYDROGEN ION CONCENTRATION

139

In practice, corrections must be applied to the above formula
in order to account for certain effects not here discussed. It is
possible also to substitute for the standard hydrogen electrode
certain other well known forms of standard electrodes, such as
the “calomel” electrode, in which case the measured e.m.f. has
to be corrected for the difference between the potentials of the
calomel and the hydrogen electrodes.

The Indicator Method.—This method may be used with
greater convenience and at less expense for equipment than the
potentiometer method, although it should be recognized that the
latter is the fundamental method and that the indicators must
themselves have been standardized, usually by the potentiometer
method. For the test, there must be provided a series of indi¬
cators of which the color corresponding to a given hydrogen ion
concentration is known, and extending over a wide range of
Pji values. A set of “buffer” solutions is prepared, these being
solutions of certain salts or acids whose hydrogen ion concentra¬
tion is definite and known and which are easily reproduced. By
matching the color produced when definite quantities of suitable
indicators are added to the solution under investigation, with
those produced by the same indicators and the various buffer
solutions, the P tt value of the former is determined.

The indicators listed below are the selection of (dark and Tubs
and their preparation and use are described in detail by (dark,
in his work above cited.

Taijlk V.—Indicators

Common name of indicator

j (Jolor change*, i
acid to base

Pit

range

Thymol blue (acid range).

! 1

. . 1 Red-yellow j

1.2

- 2.8

Brom phenol blue.

. . | Yellow-blue !

2.0

* 4.0

Methyl red.

. . | Red-yellow

4. '1

0.0

Brom crenel purple.

. .! Yellow-purple

r >,2

0.8

Brom thymol blue.!. . . .

. . | Yellow-blue !

0.0

7.0

Phenol red.

. . | Yellow-red

r>, h

8 4

Oresol red..

. J Yellow-red

7.2

s.s

Thymol blue (bank range).

. j Yellow-blue

K 0

0.0

Crowd phthulein...

| Colorless-red

K 2

0 0

140

QUANTITATIVE AGRICULTURAL ANALYSIS

The series of buffer solutions suggested by Clark and Lubs
consists of mixtures of hydrochloric acid with potassium chloride
and with potassium acid phthalate, and of sodium hydroxide
with potassium acid phthalate, with monopotassium orthophos¬
phate and with orthoboric acid. By mixing these in stated
proportions and at stated dilutions the Pn range is covered from
values of 1.2 to 10.0, in steps of 0.2.

Gillespie has described 1 a method for dispensing with the use
of buffer solutions.

Applications.—A high degree of importance is attached to the
application of Pn values to problems of agricultural and biological
chemistry. Mention may be made of the bearing of soil acidity
upon productiveness and upon adaptation to different crops; of
acidity of plant juices upon plant health and disease; and of
acidity of milk upon butter and cheese production. Hydrogen
ion concentration is of importance also in t he culture and study
of bacteria, yeasts and molds; in the study of physiological
chemistry, particularly with relation to the digestive system and
the blood. Many other applications might bo noted, of not so
direct interest to the agricultural or biological chemist and many
interesting lines of research have been opened up by the high
degree of development of this line of testing.

1 Soil faience, 9, 115 ( 1920 ); J. Am. Chinn, far., 42, 742 ( 1920 ).

PART III

ANALYSIS OF AGRICULTURAL MATERIALS

The following chapters constitute an introduction to the appli¬
cation of quantitative analysis to the solution of agricultural
problems. The subjects treated are typical phases of the broad
field of agricultural analysis. The student is especially cau¬
tioned that if he is to avoid the common danger of falling into
ways of mere mechanical routine he must, here as elsewhere,
cultivate the habit of looking for the scientific principles under¬
lying his work, as well as for the significance of its results in
connection with scientific agriculture.

141

CHAPTER IX

FEEDS

The raw materials of feeds vary greatly in their composition,
their feeding and commercial values depending upon their con¬
tent of protein, fat, mineral matter, carbohydrates and vitamins
and upon the ease with which food elements are digested and
assimilated. There is much difference in the feeding value
of protein and fat, according to the sources from which they are
derived. The degree of utilization of these products can not
always be measured with exactness by chemical means but it
must be determined from feeding trials with animals. However,
chemical analysis furnishes the best available means for estimat¬
ing approximate feeding values from percentage composition.
This is especially true of commercial ready-mixed feeds, which
are often made up from many different plant and animal sources;
chemical analysis furnishes the only quick method for determin¬
ing their approximate commercial value.

Composition of Some Common Feeds. —If the feed is made
from the whole grain the composition of the groups will be about
as represented in the table below and if made up of grain by¬
products, with the more valuable parts taken out and substituted
with cheaper materials, it is often possible to detect the deception
by analysis.

The analysis of feeds commonly includes the determination
of moisture, ash, crude fat, crude fiber, crude proteins, carbo¬
hydrates and pentosans. The entire carbohydrate group is often
expressed as “ nitrogen-free extract,” which is obtained by
deducting the sum of all other groups from 100.

Most states now have laws which control the manufacture and
sale of feeds. These laws usually require a guarantee of the
per cent of ether extract , crude protein , fiber and ash. The average
composition of the principal cereal grains is tabulated as follows
by Villier and Collin.

142

FEEDS

J 43

Table VI. —Average Composition of Principal Cereals

Wheat

Bur- I

I°.v I

Rye ; Outs

ltfce

(Jorn!

Mil¬

let

Buck-

wlieat

Water.

13.05

i !

i:i.77 ir>.oo;i2.:i7

13. 1 1

13. 12

11 .(id

12.03

Crude protein (Nit.ro-

go no us .sul>-

stances).

12.35

11.14 11.52

10.41

7.85

0.85

10.30

('rude fat.

1 . 75

2. 10

1.70

r, . :v2

0.88

4 . 02

3.50

2.81

Sugar.

1.45 j

1.50

0.05

l.oi

2.40

Gum and dextrin. . .

2 . 38 j

1.70

4.80

1.70

1(3.52

3 . 38

! i

05.05;

r>5. k l

Starch.j

1 04.08

(H 07

(32 00

54 . OS

02.57

Crude fiber.j

2.53 :

5.31

2.01

11 . 10

O.Oli

2.20

7. •«>'

10.43

Ash. 1

1.81 !

2 . 00

1.81

3 . 02

1 .01

1.51

2.72

Method of Sampling.— (Commercial feeds are usually shipped
to the consumer in sacks and it is important that the samples
chosen from them shall be representative of the feed contained
in all parts of the sack. A sampleY*somewhat similar to that
used for fertilizers (Fig. 59, page 273), but larger in diameter than
this, may be forced to the bottom of the sack of feed, the slide
covering the opening in the tube being moved to the side and
tapped so that the tube can fill with feed. The slide is again
closed, the tube is withdrawn from the feed sack, and the con¬
tents of the sampler placed on a sheet of paper and thoroughly
mixed. About a pint of this uniformly mixed feed is saved for
analysis.

Preparation of Sample. —The sample should be ground in a
feed grinder (Fig. 40, suitable for grinding coarse feed materials)
so that it will pass a sieve having openings 1 mm in diameter
(0.04 in). Sometimes it is quite difficult to reduce it to this
degree by grinding, in which case it should be made us fine as
possible by any other available means. A container which
may be tightly stoppered should be provided to hold the sample.
At the start, enough should be prepared and mixed to serve for
the entire analysis. This will require about 200 gm.

Moisture.— -There are several minor factors which tend to
modify the results of moisture determinations. One of these

144

QUANTITATIVE AGRICULTURAL ANALYSIS

is the loss of essential oils and other volatile bodies during the
drying process. Partly compensating this is a possible gain in
weight due to oxidation of fats and sugars, when drying takes
place in the air. As these changes are variable the method of
drying in air at elevated temperatures has been abandoned. If
a temperature of 100° is to be used it is necessary to have avail¬
able an oven for drying at reduced pressure or in an atmosphere
of an indifferent gas, such as hydrogen.

Fig. 40.—One form of grinder for coarse feeds. (Shown disassembled.)

Feeds dried at ordinary temperature under reduced pressure
usually show about 1 per cent less moisture than is found by a
direct heating method. About four to six days is usually required
to obtain constant weight by the reduced pressure method, even
if the sulphuric acid used in the desiccator is changed several
times. The special advantage of the method lies in the thorough
desiccation of the sample without the possibility of chemical
changes brought about by heating and oxidation but the length
of time required for the experiment makes the method imprac¬
ticable for all work except that requiring a high degree of refine¬
ment and accuracy.

Determination of Moisture: At 100°.—Weigh about 2 gm of the feed
in a weighed flat dish or, in case the fat is to be extracted, in a weighed
alundum cup. Place in an oven which can be exhausted or through which
dry hydrogen can be circulated and heat at 100° for at least five hours or

FEEDS

145

until the weight is constant. After the sample has cooled in a desiccator
ifc should be weighed as rapidly as possible in order to avoid undue exposure
to moist air. Preserve the dried sample for the crude fat determination
(page 147), or for the ash determination, described below.

At Room Temperature .—Place 2-gm samples in separate 6-inch vacuum
desiccators (see Fig. 8, page 28) containing 200 cc of fresh concentrated
sulphuric acid and exhaust to a pressure of 1 mm by means of a
pump. It will require about four to six days drying to secure constant
weights. The desiccators should be rotated gently several times a day in
order to mix the lower, more concentrated sulphuric acid and the upper
layers that have become diluted by absorbed moisture. After 24 hours
drying, carefully open the desiccator and weigh the sample. Place in a
desiccator containing fresh sulphuric acid and repeat the process of drying
and weighing until the weight becomes constant. Calculate the total loss
as moisture. Preserve the dried sample for the crude fat determination
(page 147), or for the ash determination, described below.

Ash. —The ash determination requires much patience. The
high carbon contained in oily seeds is very hard to oxidize so as
to secure a white or gray ash but too high a temperature will
cause volatilization of certain ash constituents, such as chlorides
of the alkali metals. The ash should contain the mineral
compounds (such as calcium phosphate, potassium or sodium
chloride and some silicon compounds) of the plant tissues and
sap. Some phosphorus and sulphur may be present as part of
the protein molecule and these may be volatilized but they are
not properly to be considered as part of the ash unless they
are normally left upon burning (as phosphates or sulphates).
This is usually the case in grasses and leaves but not in seeds.

Determination of Ash.—Either the dried sample obtained in the moisture
test or a new undried sample may be used for this determination. Ignite,
cool and weigh a porcelain crucible, brush in the weighed sample and burn
at a low temperature, using a burner, or place the uncovered crucible in
a muffle furnace heated to about 700°. The crucible should be kept at
dull redness until the carbon is all consumed and the ash becomes nearly
white. A gray or black appearance of the residue indicates the presence of
unburned carbon but a red tint may be given by iron oxide normally present.
Cool in a desiccator, weigh and calculate the per cent of ash.

Mineral Analysis. —The solution of the ash in hydrochloric
acid is diluted to 250 cc and the mineral constituents determined
as described under soil analysis, beginning on page 256. This
analysis involves a considerable expenditure of time and it is
rarely useful, except in the solution of certain research problems.

146

QUANTITATIVE AGRICULTURAL ANALYSIS

Crude Fat or Ether Extract.—The nature of the material
obtained by extracting feeds with ether varies according to the
nature of the feed. Grains and other seeds yield nearly pure
fat, while in fibrous materials many compounds, such as waxes,
resins and chlorophyl, also are extracted by the ether.

Fig. 41.—Apparatus for extraction by volatile solvents.

When there is present in the feed a considerable amount of
soluble carbohydrates, such as starch or sugars, and a relatively
small amount of fat, as in wheat and rye, it is best to dissolve
out these substances with water before attempting to extract
the fat. It is quite essential that samples to be extracted be
thoroughly dried and that the ether be free from alcohol and

FEEDS

147

water as otherwise various substances, soluble in water or alcohol
(salts, sugars and amids) would be extracted. Certain other
fat solvents have been used, such as benzol, gasoline and carbon
tetrachloride, but none has been found to be quite as satisfactory
as dry ether.

One form of assembled extraction apparatus is shown in Fig.
41. Any number of separate pieces may be assembled upon one
heater. In. Fig. 41 the third extractor is shown in section.
Ether (or other volatile solvent) is placed in the weighed cup a
where it boils and the condensed vapor from the condenser d
falls to the sample in the porous cup 6. As the solvent fills the
siphon cup c to the level of the siphon bend, the cup automatically
empties into a, below. This process repeats itself indefinitely.

Determination of Crude Fat.—Wash commercial ether by shaking in a
separatory funnel with two or three successive portions of water and drawing
off and discarding the latter. Add solid sodium or potassium hydroxide
and let stand until most of the water has been, abstracted from the ether.
Decant into a dry bottle, add small pieces of cleaned metallic sodium
or sodium wire, freshly extruded from a sodium press, and let stand until
there is no further evolution of hydrogen. Keep the ether, thus dehy¬
drated, over metallic sodium in lightly stoppered bottles.

The sample is thoroughly dried at 100° in an alundum cup or fat-free
paper capsule (or the sample used for the moisture determination is taken),
then placed in an extracting tube and sufficient ether, as above prepared, is
added to the weighed cup a of Fig. 41 (previously cleaned, dried and
weighed) to enable continuous extraction to proceed automatically. The
alundum cup is a porous vessel, cylindrical in shape, and convenient to use
because it is easily cleaned by burning, so that it may be used repeatedly.
It is suitable to use also in fiber filtration, as it permits weighing and burning
of the fiber without removal to another vessel. The porous alundum cup,
grade R. A. 98, permits rapid filtering and washing.

Extract the sample for sixteen hours, saving the residue for the fiber
determination (page 148), then remove the cup a and allow the ether to
evaporate, or place the cup in a special apparatus for distilling and recovering
the ether. Dry at 100° for 30 minutes, cool in a desiccator and weigh.
Repeat the drying fox 30-minute periods until the weight is constant. From
the difference between the weights before and after extraction, calculate the
per cent of crude fat.

Crude Fiber. —The so-called “ crude fiber” is a mixture of
substances which make up the framework of a plant. It is
composed of cellulose, part of the hemicellulose and lignin of the

148

QUANT IT A TIVK AaitlCULTUltM. -I \ A LYSIS

<•.<',11 walls. Lignin also is a collective name applied (o the “in-
crusting substances” formed with cellulose as Ihe plant matures.

Determination of Crude Fiber.—Prepare the following solutions:

(a) Sulphuric Acid , 1.25 per cent (0.255 normal) us determined by
titration against a fifth-normal base.

(b) Sodium Hydroxide , 1.25 per cent (0.5125 normal). This solution

should be practically fret* from sodium ear-
13E3xWoffer bonate. Use sodium hydroxide* sticks that
have been purified by alcohol. Titrate
against a standard acid and adjust,.

Use the residue from the ether extrac¬
tion, page 147, or extract a fresh dry sample
(2 gm) with ether, using the apparatus
already described. Rinse the residue into
a 250-cc wide mouth flask connected with a
return condenser (Fig. 42), then add 2(K)eeof
sulphuric acid («), previously heated to
boiling. Boil gently for 50 minutes. After
this time remove the residue from the flask
and filter the liquid through an alundum
cup, using suction. Wash the cup and
contents until free from acid. Wash the
residue from the cup back into the flask
with 200 cc of boiling sodium hydroxide (b)
and boil for 50 minutes. Kilter through an
alundum cup as before and wash free from
base. The cup is dried at 110 to constant
weight, then the residue* is burned and tin*
per cent, of fiber calculated from the loss in
weight. A linen filter may la* used instead
of an alundum cup, in which ease rinse t he
washed fiber into a flat platinum dish by
means of a stream of water; evaporate to
dryness on a steam bath, dry to constant
weight at 110°, weigh, burn the organic,
matter and weigh again. The loss in weight
is crude fiber. If a weighed paper is used
instead of alundum or linen, weigh in a
weighing bottle. In any ease the crude
fiber after drying to constant weight at 110° must be burned and the loss
of weight determined.

Optional Method . 1 —Proceed as above* until the acid extraction is com¬
pleted. Neutralize the sulphuric acid without filtration, using l()-per cent
sodium hydroxide and phenolphthalcin. Add 200 cc of 2.6-por cent solution

Fm. 42.—Apparatus for crude
fiber determination.

1 Ohio Exp. Sla. Bull, 255 (1015).

FEEDS

149

of boiling sodium hydroxide, make the volume up to 425 cc and boil for
30 minutes. Filter through an alundum cup and wash with hot water
until neutral to phenolphthalein. Dry the residue in an oven for 3 hours at
110°, place in a desiccator, cool and weigh. Ignite as in the ash deter¬
mination, cool and weigh again. The loss in weight represents fiber. Cal¬
culate the per cent of crude fiber in the sample.

Crude Protein.—“Crude protein/ 7 is a conventional term,
embracing all forms of plant nitrogenous bodies except nitrates.
The latter are not usually found in feeding stuffs. There is no
good direct method for determining protein and either pure or
“crude 77 protein is calculated from the per cent of nitrogen.
Since plant proteins contain about 16 per cent of nitrogen, the

nitrogen per cent is multiplied by 6.25 ^ to convert it to

the approximate corresponding per cent of protein. The nitrogen
content varies for proteins of different classes. In the deter¬
mination of milk protein 6.38 is the factor used, but nitrogen
found in grasses and fruits is partly in the form of amids and has a
lower conversion factor because of somewhat higher per cent.

Nitrogen.—From the above discussion it will be seen that the
determination of protein rests upon the nitrogen determination.
The Kjeldahl process for this determination consists in digesting
the organic material with boiling concentrated sulphuric acid
until complete decomposition has been effected. The exact
course of the reactions cannot be traced but the carbon and
hydrogen are completely oxidized and nitrogen is converted into
ammonia, which immediately combines with sulphuric acid and
remains as ammonium sulphate. The completion of decom¬
position is insured by the final addition of a small amount of
potassium permanganate. The solution is then diluted with
water, an excess of sodium hydroxide is added and the resultant
ammonia is distilled into a measured quantity of standard acid
solution, the excess of which is then titrated by a standard base.

Digestion.—The digestion with sulphuric acid is best accom¬
plished in a pear-shaped flask with a long neck, like that shown in
Fig. 43. The concentrated sulphuric acid of commerce boils at
temperatures ranging from 210° to 340°, according to the per
cent of water contained in it. Such a temperature is high enough
above that of the surrounding air to permit condensation of

150 QUANTITATIVE AGRICULTURAL ANALYSIS

nearly all of the vapor without the use of a water condenser, the
long neck of the digestion flask serving for this purpose. It is
convenient to distill from the flask in which digestion is accom¬
plished, in which case the capacity of the flask should be 500 cc.
The digestion must be performed under a hood or some other
provision must be made for carrying away the fumes. An
excellent arrangement for this purpose is a lead pipe, 6 inches in
diameter and with holes in the side so that the necks of a number

of digestion flasks may be inserted with the flask in an inclined
position. The end of the lead pipe leads to a chimney.

Catalytic Agents.—The addition of oxides or salts of mercury,
copper or iron to the mixture of the organic material and sul¬
phuric acid considerably accelerates the reactions that occur
during digestion. The action is of a catalytic nature and depends
upon the capability of the metal of existing in more than one state
of oxidation. The metal is thus alternately reduced by organic
matter and oxidized by sulphuric acid, somewhat as follows:

2HgS0 4 Hg 2 S0 4 + S0 3 + 0. (1)

The nascent oxygen thus formed attacks the organic matter and
mercurous sulphate is immediately reoxidized:

Hg 2 S0 4 + 2H 2 S0 4 2HgS0 4 + 2H 2 0 + S0 2 . (2)

FEEDS

151

Of the three metals named, mercury serves well because its
salts are colorless and they do not obscure the end point of the
oxidation. It is necessary in this case to precipitate the mercury
by the addition of potassium sulphide, before distillation,
in order to prevent the formation of mercurammonium com¬
pounds which later are not readily decomposed by sodium
hydroxide. Copper sulphate as a catalyst is often preferred
because it serves as an indicator when sodium hydroxide is
added, a deep blue solution being formed when the solution
becomes basic.

Prevention of Bumping.—During the distillation of ammonia,
after the addition of excess of sodium hydroxide, there is usually
a tendency toward bumping. In order to prevent this, granular
zinc or pumice stone may be used. An excellent substitute is a
small amount (about 0.5 gm) of crushed porcelain from which
the dust has been removed by sifting.

Blank.—Sulphuric acid nearly always contains a small amount
of ammonium sulphate. Distilled water which has been exposed
to laboratory air also may contain a small quantity of ammonium
hydroxide. In order to make the proper correction for the
ammonia that will be derived from the reagents a “blank”
determination must be made, omitting the sample of feed but
carrying out the operations exactly as in the real determination.
In this case cane sugar is added to reduce possible traces of
nitrates existing in the reagents, as they would be reduced by the
organic matter of the feed.

Determination of Organic Nitrogen (of Crude Protein): Kjeldahl Method .—
Prepare the following reagents:

{a) Hydrochloric or Sulphuric Acid Solution , Fifth-normal. —Standardize
against pure sodium carbonate as directed on page 58, making the necessary
changes in weight of carbonate to account for the different normality of the
acid here used. The standardization of these acids by weighing silver
chloride or barium sulphate (the official methods) is not to be recommended
because chlorides and sulphates, respectively, are nearly always to be
found in the acids. These would give high values for the acid content, so
determined.

(b) Sodium Hydroxide or Potassium Hydroxide Solution, Fifth-normal .—
Standardize by titration against the acid (a), using methyl red as indicator.

(c) Sulphuric Acid. —The concentrated acid of the laboratory, specific
gravity 1.84, as nearly as possible free from nitrates and ammonium salts.

152

QUANT IT A TI YE AGRICULT l 'RAL ,1 SAL YS1S

(d) Metallic Mercury, Mercuric Oxide or Cupric Sulphate. .Mercuric.

oxide should be that prepared in the wet way but not irom mercuric nitrate.

(e) Potassium Sulphide Solution .—Dissolves at the rate of *10 gm lor
each liter of solution. Commercial potassium sulphide is used. This
solution is not required unless mercury or mercuric oxide is to be used as
the catalyzer.

(/) Sodium Hydroxide Solution .—A saturated solution (55 gm per 100
cc of water), free from nitrates and containing as little carbonate as possible.

(g) Methyl Red Solution .—Dissolve 1 gm of methyl red in 100 cc of
95-per cent alcohol. This is the solution ordinarily used in volumetric
analysis. Add very dilute acid or base to make exactly neutral.

If the approximate per cent of nitrogen in the sample is known, calcu¬
late the weight that will yield ammonia equivalent to about 55 cc, of the
standard acid. If nothing is known of the nitrogen content use about
2 gm of sample. (For this method the sample must contain no nitrates,
nitrites, or nitro-compounds. This is ordinarily true with feeds.) Place
two weighed samples in 500-cc Kjeldahl digestion flasks, holding f lie* latter
in a vertical position to prevent the sample from sticking to the sides of the
neck, which should be dry. Weigh 1 gm of sugar into each of two other
flasks and treat the same as the feed sample. Add about 0.7 gm of
mercuric oxide or of mercury, or 0.5 gm of copper sulphate, also 25 cc
of concentrated sulphuric acid. Incline the flask in a hood or with the
neck inserted into a lead-pipe ventilator and heat gently until the violence
of the reactions has moderated, then gradually raise the temperature until
the acid is boiling. The flask may be heated without protection by a
gauze if it is of Pyrex or similar resistance glass and if it is placed over
a hole, in a stand of sheet iron in such a manner that the flame cannot
come into contact with the sides of the flask above the? liquid.

Digest by gently boiling until the solution is nearly colorless (blue if
copper sulphate hits been used). This may occur after a short time or the
digestion may require several hours. Finally remove the flame and at. once
drop into the flask small quantities of powdered potassium permanganate
until the solution acquires a green or purple tint which persists after shaking.
Allow the flask to stand until cool. (Do not and under a tap.) Carefully
add 200 cc of distilled water and mix by rotating the flask. Add about
0.5 gm of crushed porcelain and 25 cc of potassium sulphide solution (e),
shaking as the latter is added. (If cupric sulphate has been used as a cataly¬
zer, omit the potassium sulphide solution.)

Have the connections with a tin condenser ready and have 50 cc of st and¬
ard acid measured into a 250-ce flask into which the delivery tube (of
glass) dips. Most laboratories in which much work of this kind is done will
be equipped with a special form of apparatus for carrying on several distil¬
lations at once. Such an apparatus as is shown in Fig. 44 will be found
convenient for individual work. The flask should be in a vertical position
and some kind of trap should be used to prevent spray from being carried
over by the steam. The delivery tube should be capable of being detached
from the condenser for the purpose of cleaning and rinsing it.. The entire

FEEDS

153

condenser must be thoroughly rinsed before each distillation, to insure
freedom from basic solutions.

Pour 50 cc of saturated sodium hydroxide solution (/) down the inclined
flask in such a way that mixing does not occur. Immediately connect, wit h
the condenser, carefully mix the contents of the flask by shaking gently,
then distill into the standard acid until about 150 cc of distillate has been
collected. It sometimes happens that a considerable excess of sulphuric acid
has been used in order to hasten a difficult digestion, or that the sodium

Fin. 44. Apparatus for ammonia distillations.

hydroxide solution is not saturated. The consequence is that the solution
still contains an excess of acid when ready for distillation. This will not be
the case if the directions have been carefully followed but the addition of a
drop of phenolphthalein to the solution will serve to indicate the fact.
(It should be remembered, however, that a concentrated solution of a base
soon decolorizes phenolphthalein and this action may be mistaken for an
indication of an excess of acid.) If copper sulphate has been used as an
accelerator a deep blue color will indicate the presence of sufficient sodium
hydroxide.

When the distillation is finished lower the* receiving flask until the delivery
tube is above the liquid, then remove* the flume. Disconnect the delivery
tube from the condenser and rinse inside and outside, allowing the rinsings
to run into tin* flask. Add enough methyl red to tint the. solution then
titrate with standard base. Subtract the? excess of acid thus indicated and

154

QUANTITATIVE AGRICULTURAL ANALYSIS

calculate the per cent of nitrogen in the sample, making proper correction
for any nitrogen found in the reagents by the blank determination with
sugar. Multiply the result by 6.25 and express as crude protein.

Gunning Method.—It was observed by Gunning 1 that in the
ordinary Kjeldahl process the water produced by the oxidation
of organic matter dilutes the sulphuric acid and retards its
action. Gunning proposed the addition of potassium sulphate,
thus forming acid sulphates which lose water much more readily
than the hydrates of sulphuric acid so that the solution is easily
concentrated by boiling. The potassium sulphate also raises
the boiling point of the acid and a higher temperature is attained
during the digestion. A mixture of one part of potassium sul¬
phate and two parts of sulphuric acid is heated together and
finally allowed to cool. This mixture is measured into the diges¬
tion flask, where the digestion is performed as in the Kjeldahl
process except that no mercury is added and, consequently, no
potassium sulphide is needed before the distillation. In the
method as now carried out the required amounts of potassium
sulphate and sulphuric acid are added directly to the flask with¬
out preliminary heating. Copper sulphate may be used as an
accelerator.

Determination of Organic Nitrogen: Gunning Method .—Calculate the
weight of sample required, as in the Kjeldahl method, and weigh this
amount into digestion flasks. Add to the sample in the digestion flask 10
gm of powdered potassium sulphate and 15 to 25 cc of concentrated
sulphuric acid. Digest as in the Kjeldahl process except that 0.3 gm of
copper sulphate is used instead of mercury, mercuric oxide or potassium
permanganate. When the solution is clear blue, cool, dilute and conduct the
distillation as in the Kjeldahl process, omitting, however, the potassium
sulphide solution. Make a blank determination as in the Kjeldahl process.
Calculate the per cent of nitrogen in the sample.

Kjeldahl-Gunning-Arnold Method.—This method of digestion
combines the accelerating action of mercury salts, potassium
sulphate and cupric sulphate. Otherwise the method is not
essentially different from those already described. It is not
applicable to materials containing nitrates.

Determination of Nitrogen: KjeldahLGunning-Arnold Method. —Digest
the usual amount of sample with 10 gm of potassium sulphate, 1 gm of
cupric sulphate, 1 gm of mercury or mercuric oxide and 25 cc of concen-

l Z. anal. Chem ., 28, 1S8 (1889).

FEEDS

155

trated sulphuric acid. Heat gently until frothing ceases, then boil the
mixture briskly and continue the digestion until the solution is colorless or
nearly so or until oxidation is complete. Cool, dilute with about 200 ec of
water, and add 50 oe of potassium sulphide solution. Make basic and distill
ass in the Kjeldahl method.

Non-protein (Amid) Nitrogen.—The non-protein forms of
nitrogen compounds are usually soluble in water and they are not
precipitated by copper hydroxide. This fact is utilized in effect¬
ing a separation of the amids from true proteins as the latter
form an insoluble compound with copper hydroxide, which
may be separated from the amid by filtration. The amount of
protein nitrogen in the residue is determined by the Kjeldahl
method. This per cent., subtracted from that of total nitrogen,
gives the amid nitrogen.

Determination of Protein Nitrogen.-—Prepare cupric hydroxide us follows:

Dissolves 100 gin of pure cupric sulphate in 5 liters of water, add 2.5 ec
of glycerol and then l()-per cent sodium hydroxide until the liquid is just
basic. Allow the precipitate of cupric hydroxide, to settle and decant off the
supernatant liquid. Add distilled water containing 5 per cent of glycerol,
decant and continue to wash the precipitate by decantation with this
glycerol solution until the washings are no longer basic to phcnolphthalcin.
Rub the cupric hydroxide precipitate in a mortar with enough water con¬
taining 10 per cent of glycerol to make a uniform gelatinous mass capable
of being measured with a pipette. Calculate the weight of cupric hydroxide
in 1 ce of the mixture.

Place a 1-gm sample of the feed in a beaker and add 100 ec of water.
If the feed is high in alkaline phosphates (as are seeds and oil meals) .‘i cc
of a pure saturated potassium alum solution (free from ammonia) should be
added to avoid any solution of the protein-copper precipitate. Heat slowly
to boiling and add sufficient cupric hydroxide reagent to contain about 1 grn
of cupric hydroxide. Stir thoroughly and filter after the liquid has cooled.
Wash with cold water, place the paper and washed residue in a Kjeldahl
digestion flask and determine the amount of protein nitrogen, as already
directed for nitrogen of crude protein.

Amid Nitrogen.—-Calculate the per cent of amid nitrogen by deducting
the protein nitrogen from the total nitrogen of the sample.

Carbohydrates.—Carbohydrates are found in vegetable foods
in variable quantities. In corn, they range from 70 per cent
in the grain to 16 per cent in the stalks. Their food value
depends to a considerable extent upon the degree of solubility
as a result of mild hydrolysis and enzyme action. The ones
that are immediately soluble in water are the most readily

156

QUANTITATIVE AGRICULTURAL ANALYSIS

digestible. Sugars and dextrins are the most important of these.
Starch is next in importance as it is easily made soluble in
digestive processes by hydrolytic action/ Other groups such as
the hemicelluloses (examples of which are the pentosans, galac-
tans and pectins) are made soluble with more difficulty and they
are therefore less valuable as foods. That portion of the carbo¬
hydrates which does not yield soluble forms on hydrolysis is
practically worthless for feeding purposes. It is chiefly cellulose
and from the analysis it is reported as “crude fiber.”

The pentosans are widely distributed in the vegetable kingdom,
being present in the seeds, roots and leaves of all plants. One
of the most common of the pentosans is gum Arabic, which occurs
intimately associated with the other plant constituents. The
galactans also are widely distributed in plants and they occur
chemically combined with the pentosans in the plant. Agar-agar
is one of the most common of the galactans. It yields galactose
upon hydrolysis, while pentosans yield pentose sugars when
similarly treated.

Analytical Methods.—Carbohydrates in foods and feeds are
determined (a) by direct acid hydrolysis and subsequent deter¬
mination of the reducing sugar thus formed, ( b ) by hydrolysis of
starch by diastase, thus forming dextrins, maltose and glucose,
or (c) by difference, deducting from 100 the sum of the per cents
of crude protein, crude fat, ash, crude fiber and moisture. This
difference is reported as “nitrogen-free extract.”

True starch cannot be determined accurately by direct
hydrolysis with acids because other polysaccharides, such as
gums, pentosans and galactans, are hydrolyzed at the same time,
yielding reducing sugars which are determined along with those
that are derived from starch. The type reaction of hydrolysis is
as represented in the equation:

(CeHioC^n + nK 2 0 —>

A separation from these hydrolyzable materials may be
made by first digesting with the enzyme diastase, from malt
extract, then washing out the soluble carbohydrates and hydrolyz¬
ing them to glucose by boiling with dilute acids. By this pro¬
cedure only the true starches are affected by the enzyme and a
series of compounds of simpler structure are formed. A large

FEEDS

157

number of dextrins are formed as intermediate products. Some
of these (erythrodextrins) give a red color with iodine while
others (acroddextrins) give no color. Under the influence of the
acid these dextrins finally yield maltose, a sugar having the same
molecular weight as sucrose.

Polarimetric methods are not well suited to the determination
of the carbohydrates in feeds, because of the relatively small
amounts usually occurring in such materials. Greater reliance
is placed upon chemical methods, such as those here to be
described.

Reducing Sugars. —■“ Reducing sugars ” are those that have
the power of reducing the copper from an alkaline solution
of copper tartrate to cuprous oxide, Cu 2 0. Dextrose, levulose,
maltose and invert sugar are examples of common reducing
sugars while sucrose is a non-reducing sugar.

It has already been stated that reducing sugars may either
be present in the original material or they may be formed as a
result of hydrolysis of other carbohydrates, such as starch or
sucrose. Therefore the determination of original reducing
sugars may conveniently be combined with that of sucrose.

Calculation of Reducing Sugars from the Weight of Cuprous
Oxide.—When the weight of cuprous oxide is used as a basis
for calculating weights of sugars, the method of reducing and
precipitating must be definitely standardized as the formation
of cuprous oxide does not proceed according to an absolutely
definite and constant reaction, depending not only upon the kinds
and amounts of reducing sugars present but also upon the tem¬
perature and concentration of the solution and upon the length
of time it is heated. Tables have been prepared for different
sugars, giving the amount of cuprous oxide reduced by each
under specified conditions. These are given in Table VII,
pages 160 and 161.

Methods for Determining the Reduced Cuprous Oxide.—A

number of methods are in use for the determination of the
cuprous oxide reduced by the sugars. Three of these will be
described.

In method (a) the solution is filtered through a Gooch crucible,
the cuprous oxide then being dried and weighed as such or
ignited and weighed as cupric oxide. Direct weighing is suitable

158

QUANTITATIVE AGRICULTURAL ANALYSIS

only in the case of solutions of pure sugars. Molasses and
syrups usually contain colloidal organic matter which cannot be
washed out of the precipitate. It is then necessary to ignite in
air, when cuprous oxide is oxidized to cupric oxide and organic
matter is destroyed by oxidation.

Method ( b ) is an approximate volumetric one, differing from
method (a) in that a standard copper sulphate solution is used,
whose sugar equivalent is known.

In method (c) the cuprous oxide is removed and redissolved
and the copper is determined volumetrically by the “iodide”
method. Potassium iodide and acetic acid are added, cuprous
oxide being precipitated and iodine liberated:

2Cu(C 2 H 3 0 2 ) 2 + 4KI 2CuI + 4KC 2 H 3 0 2 + I 2 .

The free iodine is titrated with standard sodium thiosulphate
and the copper equivalent to it calculated.

It is also practicable to dissolve the cuprous oxide and to
determine the copper by electrolysis or by any other standard
gravimetric or volumetric method.

Asbestos.—Since this is to be used as a filtering medium for
strongly basic solutions it must be prepared with special reference
to removing base-soluble materials. The amphibole variety is
required, as serpentine asbestos is too easily soluble.

Determination of Sucrose and Reducing Sugars.—Prepare the following
materials:

(a) Fehling’s Solution (1).—Dissolve 34.639 gm of pure crystals of copper
sulphate in distilled water and dilute to 500 cc. Filter, if not clear, through
asbestos.

( b ) Fehling’s Solution (2).—Dissolve 173 gm of sodium potassium tar¬
trate (“Rochelle salts”) and 50 gm of sodium hydroxide in water and
dilute to 500 cc. Allow the solution to stand for two days and filter through
asbestos, if not clear.

(c) Neutral Lead Acetate. —Prepare a saturated solution of lead acetate
(the normal salt). This is made by warming 50 gm of lead acetate with
100 cc of water until the salt is dissolved, then cooling to room temperature.

(d) Asbestos .—Digest the fiber for three days with dilute hydrochloric acid.
Wash free from acid in a large funnel fitted with a perforated porcelain
plate, then digest for a similar period with 10-per cent sodium hydroxide
solution. Drain away this solution and then treat for two or three hours
with alkaline tartrate solution similar to solution ( [b ), above described.
Wash practically free from base and then digest for several hours with dilute
nitric acid. Finally wash free from acid and shake the material to a pulp

FEEDS

159

with distilled water. The prepared material is now to be used as any other
asbestos for forming Gooch filters.

Extraction of Sugars from the Feed .—Place 12 gm of the material in a
250-cc round flask and, if the substance has an acid reaction, add 2 gm of
calcium carbonate. Add 150 cc of 50-pcr cent alcohol (volume) and
boil on the steam bath for one hour, using a reflux condenser. Cool and
allow the mixture to stand for several hours. Rinse into a 250-cc volumetric
flask with 95-per cent alcohol which is not acid to phenolphthalein and
dilute to the mark with this alcohol. Mix thoroughly, allow to settle,
transfer 200 cc to a beaker with a pipette and evaporate on a steam bath to
a volume of about 20 ee. (Do not evaporate to dryness, a little alcohol
in the residue doing no harm.)

Clarification .—Transfer to a 100-ec graduated flask and rinse the beaker
thoroughly with water, adding the rinsings to the contents of the flask.
Add enough saturated neutral lead acetate solution (c) to produce a
flocculent precipitate, shake thoroughly and allow to stand for 15 minutes.
Dilute to the mark on the flask, mix thoroughly and filter most of the
solution through a dry paper, rejecting the first 5 cc of filtrate. Add
sufficient anhydrous sodium carbonate to the filtrate to precipitate all of the
lead, again filter through a dry paper and test the filtrate with a little more
sodium carbonate, in order to b(5 sure that all of the lead has been removed.

This solution will serve for the determination of both sucrose and reducing
sugars.

Since the insoluble material of grain or cattle food occupies some space
in the flask as originally made up, it is necessary to correct for this volume.
Results of a large number of determinations on various materials have,
shown the average volume of 12 gm of material to b(5 9 cc, and therefore
to obtain the true amount of sugars present all results must be multiplied

by the factor 0.904

/ _ 250 - 9
\ 250

)

If the sample weight was not 12 gm

(±0.5 gm) the factor should 1x5 modified accordingly.

Reducing Sugars.—-Measure 25 cc of the copper sulphate solution (a)
and 25 cc of the alkaline tartrate solution (6) into a 400-cc beaker. Add
25 cc of water and 20 cc of the sugar solution already prepared. Cover the
beakers with watch glasses and heat on an asbestos mat. at such a rate
that boiling begins in 4 minutes. Continue the boiling for exactly 2 min¬
utes. Filter through Gooch crucibles (weighed if method («), below, is to be
followed) immediately after heating and wash thoroughly with hot water
(about (>0°.) From this point proceed by one of the following methods:

(a.) Gravimetric Method .—The Gooch filters must 1x5 dried, ignited, cooled
and weighed before filtration. After filtration dry the crucible and con¬
tents, then place in a muffle furnace which is heated to redness (about 70(f)
and heat for 15 minutes. Cool and weigh and from the weight of cupric
oxide find that of dextrose from Table VII. Multiply by 0.025(- 0.904 X

^20^ ^20()) anc * ca ^‘ u ^ a ^° fhe corresponding per cent of dextrose in the

12-gm feed sample, reporting as **reducing sugars/’

160

QUANTITATIVE AGRICULTURAL ANALYSIS

Table VII. —Munson and Walker's Table for Calculating Dextrose,
Invert Sugar Alone, Invert Sugar in the Presence of Sucrose,
Lactose, and Maltose (All weights are given in milligrams)

FKEDti

1 C> I

Taiilk V11. - (( •( mlinucd )

Cuprous oxide j

Copper

Invert sugar
and sucrose

Lactose

Maltose

Dextrose

Invert sugar

0.4 gm totai
sugar

2 gm total
sugar

Anhy¬

drous

crys¬

talline

Anhy¬

drous

■ crys-
} talline

200

231.0

117.0

121.4

120.1

114.0

109.4

178.3

203.9

214.7

200

205

235.4

120.0

123.9

122.0

110.5

172.8

181.9

207.9

218.8

205

270

239.8

122.5

120.4

125. 1

119.0

170. 1

185.4

21 1.8

223.0

270

275

244.3

124.9

128.9

127.7

121.0

179.5

188.9

215.8

227. 1

275

280

248.7

127.3

131.4

130.2

124.1

182.8

192.4

219.7

231.3

280

285

253.2

129.8

133.9

132.7

120.0

180.2

190.0

223.7

235.5

285

290

257.0

132.3

130.4

135.3

129.2

189.5

199.5

227.0

239.0

290

295

202.0

134.7

138.9

137.8

131 .7

192.9

203.0

231.0

243.8

295

300

200.5

137.2

141.5

140.4

134.2

3 90.2

200.0

235.5

247.9

300

305

270.9

139.7

144.0

142.9

130.8

199.0

210. 1

239.5

252. 1

305

310

275.4

142.2

140.0

145.5

139.4

203.0

213.7

243.5

250.3

310

315

279.8

144.7

149. 1

148. 1

141.9

200.3

217.2

247.4

200.4

315

320

284.2

147.2

151.7

150.7

144.5

209.7

220. 7

251,3

204.0

320

325

288.7

149.7

154.3

153.2

147.1

213. 1

224.3

255.3

208.7

325

330

293.1

152.2

150.8

155.8

149.7

210.4

227.8

259.3

272.9

330

335

297.0

154.7

159.4

158.4

152.3

219.8

231.4

203.2

277.0

335

340

302.0

157.3

102.0

101.0

154.8

223.2

234.9

207. I

281.2

340

345

300.5

159.8

104.0

103.7

157.5

220.5

238. 5

271.1

285.4

345

350

310.9

102.4

107.2

100.3

100. 1

229.9

242.0

275.0

289.5

350

355

315.3

104.9

109.8

108.9

102.7

233.3

245.0

279.0

293.7

355

300

319.8

107.5

172.5

171.5

105.3

230.7

249. 1

282.9

297.8

300

305

324.2

170. 1

175.1

174.2

107.9

240.0

252.7

280.9

302.0

305

370

328.7

172.7

177.7

170.8

170.0

243.4

250. 2

290.8

300. 1

370

375

333.1

175.3

180.4

179.5

173.2

240.8

259.8

294.8

310.3

375

380

337.5

177.9

183.0

182. 1

175.9

250.2

203.4

298.7

314.5

380

385

342.0

180.5

185.7

184.8

178.5

253.0

200.9

302.7

318.0

385

390

340.4

183. 1

188.4

187.5

181.2

250.9

270.5

300.0

322.8

390

395

350.9

185.7

191.0

190.2

183.9

200.3

274.0

310. 0

320.9

395

400

355.3

188.4

193.7

192.9

180.5

203.7

277.0

314.5

331 . 1

400

405

359.7

101.0

: 190.4

195.0

189.2

207.1

281.1

318. 5

335.2

405

410

304.2

193.7 !

199.1

i 198.3

191.9

270.5

284.7

322.4

339.4

410

415

308.0

190.3

201.8

! 201.0

194.0

273.9

288.3

320.3

343.5

4 15

420

373.1

199.0

204.0

203.7

197.3

277.3

291.9

330.3

347.7

420

425

377.5

201.7

! 207.3

200.5

200.0

280.7

295.4

334.2

351 .8

425

430

382.0

204.4

1 210.0

209.2

202.7

284.1

299.0

338.2

350.0

430

435

380.4

207. 1

212.8

212.0

205.5

287.5

302.0

342. 1

300. 1

435

440

390.8

209.8 j

215.5

214.7

208.2

290.9

300.2

340. 1

304.3

440

445

395.3

212.5

218.3

217.5

211.0

294.2

309.7

350.0

308.4

415

450

399.7

215.2

221.1

220.2

213.7

297.0

313,3

353.9

372.0

4 50

455

404.2

218.0

223.9

223.0

210.5

301.1

310.9

357.9

370.7

4 55

400

408.0

220.7

225.8

219.2

304.5

320.5

301 .8

380.9

4 00

405

413.0

223.5

229.5

228.0

222.0

307.9

324.1

305.8

385.0

405

470

417.5

220.2

232.3

231.4

224 . H

311 .3

327.7

309.7

389.2

470

475

421.9

229.0

235.1

234.2

227.0

314.7

331 3

373.7

393.3

475

480

420.4

231.8

237.9

237.1

230.3

318. 1

334.8

377.0

397.5

480

485

430.8

234.0

240.8

239.9

233 2

321 .5

338.4

381.5

401.0

485

490

435.3

237.4

243,0

242.7

230.0

324.9

342.0

385.5

405 8

490

162

QUANTITATIVE AGRICULTURAL ANALYSIS

(b) Iodide Method .—Sodium thiosulphate solution is prepared and
standardized as follows. Dissolve 19 gm of pure crystals of sodium thio¬
sulphate and dilute to 1000 cc with recently boiled and cooled distilled
water. Mix well. One cubic centimeter should then be equivalent to about
0.005 gm of copper. Weigh in duplicate about 0.2 gm of pure copper foil,
place in 250-cc Erlenmeyer flasks and dissolve the copper by adding 10 cc of
a mixture of equal parts of water and concentrated nitric acid. Boil until
red f um es have been expelled, add 40 cc of water and 5 cc of saturated
bromine water, mix and boil until the bromine vapor has disappeared. Add
7 cc of ammonium hydroxide and boil again to expel excess of ammonia,
but not far enough to cause a precipitate. Add 4 cc of glacial acetic acid
(or 40 cc of 10-per cent acid), cool to room temperature and add 10 cc of
30-per cent potassium iodide solution. Immediately titrate with sodium
thiosulphate until the solution bearing the white precipitate shows only a
faint yellow tinge and then add 1 cc of starch indicator. (The starch
indicator is made by mixing 1 gm of starch with 1 cc of cold water, pouring
into this 100 cc of boiling water and boiling for a minute. This solution
should be made fresh each day, as required.) Continue the titration with
sodium thiosulphate until the blue color is discharged. Calculate the weight
of copper equivalent to 1 cc of the solution.

Drop into the Gooch crucible containing the cuprous oxide, 5 cc of warm
nitric acid (1:1) and cover the crucible. Collect the filtrate in a 250-cc
flask. Wash the crucible once or twice with hot water. Pour 5 cc of
bromine water into the crucible, then wash with 50 cc of hot water. Boil
filtrate and washings to expel bromine, then proceed from this point as
directed for standardizing sodium thiosulphate solution. Calculate the
weight of copper present, from which the corresponding weight of dextrose
can be obtained by reference to table VII. Multiply by 6.025 (see page
159) and calculate the per cent of reducing sugars in the feed sample.

Approximate Volumetric Method. —Prepare:

Standard Invert Sugar Solution. 1 —Dissolve 4.75 gm of pure sucrose in
75 cc of water, add 5 cc of concentrated hydrochloric acid and let stand
at a temperature not below 20° for 24 hours, or for 10 hours if the tempera¬
ture is above 25°. The solution should not be heated. Neutralize the
acid with 5-per cent sodium hydroxide solution (using methyl orange),
dilute to 1000 cc in a volumetric flask and mix well. Ten cubic centimeters
of this solution contain 0.050 gm of invert sugar and it should reduce
about 5 cc of the Fehling’s copper solution. Standardize as follows:

Pipette 5 cc of each of Fehling’s solutions (a) and (6) (page 158) into a
small casserole or beaker and add 10 cc of water. Heat to boiling and add,
from a burette, 9 cc of the standard invert sugar solution and boil for 2
minutes. This should reduce nearly all of the copper to cuprous oxide,
removing all but a faint blue color. Continue to add small portions of the
invert sugar solution, boiling after each addition. When the end is nearly
reached and the amount of sugar solution to be added can no longer be

1 For a discussion of the common sugars and of the process of “inversion”
of sucrose, see page 131, Part II.

FEEDS

163

judged by the color of the solution, remove about 1 cc of the liquid and
filter rapidly into a small porcelain crucible or on a test plate; acidify with
10-per cent acetic acid and test for copper with a 5-per cent, potassium
ferrocyanide solution. After the end point has been reached calculate the
invert sugar equivalent of the cupric sulphate solution.

Determine the reducing sugars of the solution containing the extract from
the feed by adding it to the Fehling’s solution in the manner described for
the standard invert sugar solution. In this case the approximate sugar
content is not known and the first trial may show that too much was added.
If so, make another trial, modifying the volume of sugar solution to be added.
Calculate the weight of reducing sugar as dextrose which, of course, has

the same equivalent weight as does invert sugar. Multiply by ~~

^ = 0.964 X |jg X where v — volume of sugar solution used, and

calculate the per cent in the original 12 gm of sample.

Determination of Sucrose.—Pipette 25 cc of the clarified sugar solution
from the feed sample (page 159) into a 100-cc volumetric flask, add a few
drops of methyl orange, neutralize with dilute hydrochloric acid and then
add 5 cc of concentrated hydrochloric acid and allow the inversion to
proceed at 20° for 24 hours. Neutralize with sodium carbonate, then
dilute to the mark with water, filter if necessary and determine reducing
sugars in 50 cc of the solution by any of the methods described for reducing

/ 250 100 100\

sugars. Multiply by 9.64 I =0.964 X 2 qq X ^ X -^q- 1 to obtain the

weight of sugar in the original 12 gm of sample. Calculate the per cent.
Subtract the per cent of reducing sugars before inversion from the percent
of total reducing sugar after inversion, both being calculated as invert sugar,

and multiply the remainder by 0.95 = = 0.95^ to obtain

the per cent of sucrose.

Starch: Diastase Hydrolysis .—When starch is gelatinized
by boiling with water it is possible to convert it to maltose and
dextrin by treating it with either ptyalin or malt diastase, these
enzymes accelerating the hydrolysis:

(C,HxoO,). +|H,0 -»|Ci,H m Ou.

(Taka-diastase, 1 if available, is more convenient to use, no
blank determination being required with malt extract.) The
enzymes thus introduced have no action on other carbohydrates
present. Starches from the different grains are not acted upon
with equal vigor by diastase so it is necessary to test with iodine
solution to determine whether the conversion has been completed.

1 J. Agr. Sci., 11, 9 (1921).

164

QUANTITATIVE AGRICULTURAL ANALYSIS

After hydrolysis of the starch by the enzyme, the resulting
maltose and dextrin may be further hydrolyzed to dextrose
under the influence of acid as follows:

Ci 2 H 22 O n + HoO 2C 6 H 12 0 6 .

Maltose Dextrose

The dextrose so produced is then determined by methods already
described for reducing sugars.

The work should be so planned that the determination can be
carried through without delay. If an interruption is necessary
after the completion of the enzyme action, fermentation should
be prevented by the addition of 0.2 gm of salicylic acid.

Determination of Starch: Diastase Method .—Prepare malt extract as
follows:

Grind about 10 gm of malt and add to it 200 cc of water. Allow it to
digest at the temperature of the room for about three hours, with occasional
shaking. Filter. Determine the weight of reducing sugars in 40 cc of the
extract, after treatment with hydrochloric acid as described below for the
feed.

Extract on a hardened filter 5 gm of the dry material, very finely ground,
with five successive portions of 10 cc of ether. Wash with 150 cc of 10-per
cent alcohol and then with a little 95-per cent alcohol. This removes all
fatty material and sugars. Place the residue in a beaker with 50 cc of
water, immerse the beaker in boiling water and stir constantly for 15 minutes
or until all the starch is gelatinized. Cool to 55°, add 20 cc of malt extract
and maintain at this temperature by placing in a water hath for an hour.
Heat again to boiling for a few minutes, cool to 55°, add 20 cc of malt extract
and maintain at this temperature for an hour or until particles of the residue
treated with iodine show no blue color upon microscopic examination.
Cool, make up directly to 250 cc and filter through a dry paper. Place
200 cc of the filtrate in a flask with 20 cc of 25 per cent hydrochloric acid
(specific gravity 1.125). Connect with a reflux condenser and heat in a boil¬
ing water bath for 2.5 hours. Cool, nearly neutralize with sodium hydroxide
solution, finish the neutralization with sodium carbonate solution (using
methyl orange) and make up to 500 cc in a volumetric flask. Mix the solution
well, pour through a dry filter and determine the dextrose in 50 cc as
directed on page 159. Conduct a blank determination upon 40 cc of the
malt extract by hydrolyzing with acid, with subsequent determination of
copper reduced, and correct the weight of copper reduced by the feed
solution accordingly. The weight of the dextrose obtained multiplied by
0.93 gives the weight of starch. Calculate the per cent.

Direct Acid Hydrolysis.—Members of the starch group com¬
prised in the “ nitrogen free extract ” are often determined by
direct acid hydrolysis. When the mixed feed is boiled with

FEEDS

105

acid, after most of the fat has been removed, the starch and some
of the pentosans are hydrolyzed to reducing sugars. It is due to
the pentosans that these results, considered as starch, are too
high when compared with the amount obtained by the diastase
method just described.

Determination of Starch: Direct Add Hydrolysis .—Stir a quantity of
the sample, representing 2.5 to 3 gm of the dry material, in a beaker with
50 cc of cold water for an hour. Transfer to a filter and wash with 250 cc
of cold water. Heat the insoluble residue with 200 cc of water and 20 cc
of 25-per cent hydrochloric acid (specific gravity 1.125) and boil for 2.5 hours,
in a flask provided with a reflux condenser. Cool, rinse into a 250-cc volumet¬
ric flask and nearly neutralize with sodium hydroxide, using methyl-orange.
Dilute to 250 cc mix and filter, and determine the dextrose in 50 cc of the
filtrate as directed on page 159, omitting the addition of water just before
mixing with Fehling’s solution. The weight of the dextrose obtained
multiplied by 0.93 gives the weight of starch.

The factor 0.90 is the theoretical ratio between starch and glucose but,
according to Noyes and other investigators, 1 the factor 0.93 more nearly
represents the analytical ratio.

Arabin, Xylan and the Pentosans.—These are compounds
of unknown constitution but they all yield pentoses (aldehyde
sugars containing five carbon atoms) upon hydrolysis under the
influence of hydrochloric acid. Arabin and xylan are constitu¬
ents of the plant gums. Arabin may be obtained from gum
Arabic, while xylan is found in many woods, in straw and in corn
cobs. Lignin is one of the most common of the pentosans. It
occurs with cellulose in wood, straw, bran and similar materials.
It will thus be seen that all of these substances will be probable
constituents of the rougher materials of the sort to be found in
animal feeds.

The pentoses which are formed by hydrolysis of the com¬
pounds already mentioned are further converted into the alde¬
hyde furfural, upon distillation with hydrochloric acid. The
type reaction is as follows:

HO H OHH H H

I II I II

H—C— C —C— C —C = O —>•HC = C —C = C —C = O + 3H 2 0.

H OHH OHH I-O-1 H

A pentose Furfural

1 J. Am. Chem. Soc., 26 , 266 (1904).

166

QUANTITATIVE AGRICULTURAL ANALYR/S

In the analytical method, furfural is produced by hydrolysis
and distillation with hydrochloric acid. Phloroglucin, an aro¬
matic alcohol, C c H 3 (OH) 3 , is added and this precipitates furfural
phloroglueide:

C 5 H 4 0 2 + C«H s (OII) 3 -> CJ„H»(>4 + II»0
From the weight of furfural phloroghuu’de the corresponding
weight of pentosans, may be found by referring to Krobor’s
table, found on page 167.

Determination of Pentosans and Allied Substances.—Prepare the follow¬
ing reagents:

Phloroglucin. —Test the purity of the laboratory supply by dissolving
a small amount in a few drops of acetic anhydride, heating almost to boiling
and adding a few drops of concentrated sulphuric acid. If more than a
faint violet color appears the phloroglucin contains diresorcin and it must
then be purified. For this purpose heat 11 gm of phloroglucin with 3(X) c«
of 1‘2-per cent hydrochloric acid (specific gravity 1.0b), adding the phloro¬
glucin very gradually. Continue heating and stirring until solid inn is nearly
complete. Pour the hot solution into 1200 <*c of hydrochloric acid of the
same concentration. Allow to stand for several days, to permit tin* dire¬
sorcin to crystallize. Filter just before using.

Aniline Acetate Paper .—This is prepared by mixing aniline and water in
equal volumes, then adding glacial acetic acid until the mixture is clear.
Moisten filter paper with the solution.

Place 2 to 5 gm of feed in a 250-eo dist illing flask which is fitted with a
separatory funnel and which is connected with a condenser. Add 100 ec
of 12-per cent hydrochloric acid (1.OB specific gravity) and several pieces of
pumice stone, dropped in while hot. Heat over a wire gauze at such a rate
that about .‘10 ec will distill over in 10 minutes, passing tin* distillate through
a small filter paper into a 500-ec volumetric flask. Add 30 ec of 12-per
cent hydrochloric acid to the flask through the separatory funnel. Continue
this process of distilling and replacing the distillate bv hydrochloric acid until
the distillate amounts to about 300 ec and until a few drops give no red or
pink color to aniline acetate paper.

Gradually add to the total distillate an amount of pure phloroglucin about
double the furfural estimated to be present.. (Consult, tin* instructor.)
It will be observed there are several color changes taking place, the solution
becoming yellow, then green and finally an almost black precipitate appears.
The solution is diluted to 400 ec with 12-per cent hydrochloric acid and
allowed to stand for 12 hours. Test the solution with aniline acetate paper
to see if precipitation of furfural has been complete, a red color developing
if any furfural remains in solution. Filter the precipitate through a dried
and weighed Gooch crucible. Wash with 150 cr of water (retaining some
water in the Gooch crucible until the last, during the washing) and dry for
4 hours at 100°. Cover the crucible, cool and weigh rapidly.

FEEDS 167

The weight of pentosans cannot be calculated accurately from that of
phloroglucide by use of a constant factor which has been derived from the
theoretical equation, because of variation in the composition of the furfural
phloroglucide, according to the proportion of furfural present.

Table VIII. —Krober’s Table for Determining Pentoses, Pentosans
and Related Substances

Furfural-

phloro-

glucidc

Furfural

Arabi-

nose

Arabin

Xylose

Xylan

Pentose

Pentosan

0.030

0.0182

0.0391

0.0344

0.0324

0.0285

0.0358

0.0315

0.035

0.0209

0.0446

| 0.0393

0.0370

0.0326

0.0408

0.0359

0.040

0. 0235

0.0501

0. 0441

0.0416

0. 0366

0.0459

0. 0404

0.045

0.0260

0.0556

0.0490

0.0462

0.0406

0.0509

0.0448

0.050

0.0286

0.0611

0.0538

0.0507

0.0446

0.0559

0.0492

0.055

0.0312

0.0666

0.0586

0.0553

0.0486

0.0610

0.0537

0.060

0.0338

0.0721

0.0634

0.0598

0.0526

0.0660

0.0581

0.065

0.0364

0.0776

0.0683

0.0644

0.0567

0.0710

0.0625

0.070

0.0390

0.0831

0.0731

0.0690

0.0607

0.0761

0.0670

0.075

0.0416

0.0886

| 0.0780

0.0736

0.0647

0.0811

0.0714

0.080

0.0442

0.0941

0.0828

0.0781

0.0687

0.0861

0.0758

0.085

0.0468

0.0996

0.0877

0.0827

0.0727

0.0912

0.0803

0.090

0.0494

0.1051

0.0925

0.0872

0.0767

0.0962

0.0847

0.095

0.0520

0.1106

0.0974

0.0918

0.0808

0.1012

0.0891

0.100

0.0546

0.1161

0.1022

0.0964

0.0848

0.1063

0.0935

0.105

0.0572

0.1215

0.1070

0.1010

0.0888

0.1113

0.0979

0.110

0.0598

0.1270

0.111S

0.1055

0.0928

0.1163

0.1023

0.115

0.0624

0.1325

0.1166

0.1101

0.0968

0.1213

0.1067

0.120

0.0650

0.1380

' 0.1214

0.1146

0.1008

0.1263

0.1111

0.125

0.067G

0.1435

0.1263

0.1192

0.1049

0.1314

0.1156

0.130

0.0702

0.1490

0.1311

0.1237

0.1089

0.1364

0.1201

0.135

0.0728

0.1545

0.1360

0.1283

0.1129

0.1414

0.1244

0.140

0.0754

0.1600

0.1408

0.1328

0.1169

0.1464

0.1288

0.145

0.0780

0.1655

0.1457

0.1374

0.1209

0.1515

0.1333

0.150

0.0805

0.1710

0.1505

0.1419

0.1249

0.1565

0.1377

0.155

0.0831

0.1765

0.1554

0.1465

0.1289

0.1615

0.1421

0.160

0.0857

0.1820

0.1602

0.1510

0.1329

0.1665

0.1465

0.165

0.0883

0.1875

0.1650

0.1556

0.1369

0.1716

0.1510

0.170

0.0909

0.1930

0.1698

0.1601

0.1409

1 0.1766

0.1554

0.175

0.0935

0.1985

0.1746

0.1647

0.1449

0.1816

0.1598

0.180

0.0961

0.2039

0.1794

0.1692

0.1489

0.1866

0.1642

0.185

0.0987

0.2093

0,1842

0.1734

0.1529

0.1916

0.1686

0.190

0.1013

0.2147

0.1889

0.1783

0.1569

0.1965

0.1729

0.195

0.1039

0.2201

0.1937

0.1829

0.1609

0.2015

0.1773

0.200

0.1065

0.2255

0.1984

0.1874

0.1649

0.2065

0.1817

0.205

0.1090

0.2309

0.2032

0.1920

0.1689

0.2115

0.1861

0.210

0.1116

0.2363

0.2079

0.1965

0.1729

0.2164

0.1904

0.215

0.1142

0.2417

0.2127

0.2011

0.1770

0.2214

0.1948

0.220

0.1168

0.2471

0.2174

0.2057

0.1810

0.2264

0.1992

0.225

0.1194

0.2525

0.2222

0.2102

0.1850

0.2314

0.2037

0.230

0.1220

0.2579

0.2270

0.2148

0.1890

0.2364

0.2081

0.235

0.1245

0.2633

0.2318

0.2193

0.1930

0.2413

0.2124

0.240

0.1271

0.2687

0.2365

0.2239

0.1970

0.2463

0.2168

0.245

0.1297

0.2741

0.2413

0.2284

0.2010

0.2513

0.2212

0.250

0.1323

0.2795

0.2460

0.2330

0.2050

0.2563

0.2256

0.255

0.1349

0.2849

0.2508

0.2375

0.2090

0.2612

0.2299

0.260

0.1374

0.2903

0.2555

0.2420

0.2130

0.2662

0.2342

0.265

0.1400

0.2957

0.2603

0.2465

0.2170

0.2711

0.2385

*0.270

0.1426

0.3011

0.2650

0.2511

0.2210

0.2761

0.2429

0.275

0.1452

0.3065

0.2698

0.2556

0.2250

0.2811

0.2473

0.280

0.1478

0.3199

0.2745

0.2602

0.2290

0.2681

0.2517

0.285

0.1504

0.3173

0.2793

0.2647

0.2330

0.2910

0.2561

0.290

0.1529

0.3227

0.2840

0.2693

0.2370

0.2960

0.2605

0.295

0.1555

0.3281

0.2887

0.2738

0.2410

0.3010

0.2649

0.300

0.1581

0.3335

0.2935

0.2784

0.2450

0.3060

0.2693

If >8

QUANTITATIVE AGRICULTURAL ANALYSIS

Krobcr’s table, pago 107, gives the weights of furfural, pentoses and pento¬
sans for weights of phloroglucide between 0.03 and 0.30 gin. For weights
less than 0.03 gm, use the following formulas:

Furfural = 0.5170 (a + 0.0052), (1)

Pentoses = 1.0170 (a + 0.0052), (2)

Pentosans — 0.8040 {a -\r 0.0052), (3)

where a = weight of phloroglucide and 0.0052 r(‘presents weight of phloro-

glucidc soluble in the 400 cc of acid solution.

Galactans.—These are substances of unknown constitution
which, like the pentosans, are widely distributed in the vegetable
kingdom. Agar-agar is one of the important, members of this
group. Another is the principal carbohydrate of the soybean.
When the galactans are hydrolyzed by acids they yield galactose,
a sugar having the same empirical formula as dextrose, and nitric
acid further converts this into mucic acid, C 1 4 n 4 ron) 4 (('OOH)^
The galactans are of considerable importance in feeds. They
are said to be utilizable to the extent of 50 per cent by herbivo¬
rous animals, but agar-agar only 8 to 27 per cent by man. 1

Determination of Galactans.—Prepare reagents as follows:

(a) Ammonium Carbonate Eolation. —Dissolve 2 gm of ammonium
carbonate in 38 cc of water and add 2 co of concentrated ammonium
hydroxide.

(ft) Nitric Acid. —Prepare 250 cc of nitric acid, specific gravity 1.15.

Extract an accurately weighed sample of about 2.5 gm on a hardened
paper, with five successive portions of 10 cc each of ether, plaee the insoluble
residue in a beaker, about 5.5 cm in diameter and 7 cm deep, together with
00 cc of nitric acid (ft) and evaporate the solution to exactly one-third of its
initial volume in a water bath whose temperature is 04" to IMP. After
standing for 24 hours add 10 cc of water and allow to stand another 24
hours. The mucic acid has, in the meantime, crystallized but it is mixed
with other material only partly oxidized bv the nitric arid. Filter, wash
with 30 cc of water to remove as much of the* nitric acid as possible and
replace the filter and contents in the beaker. Add 30 cc of ammonium
carbonate solution (a) and heat the mixture on a water hath at HO" for 15
minutes, with constant stirring.

The ammonium carbonate reacts with the mucic acid, forming soluble
ammonium mucate. Wash the filter paper awl contents several times with
hot water by decantation, passing the washings through the filter paper, to
which finally transfer the material arid thoroughly wash. Evaporate the
filtrate to dryness on a water hath, avoiding unnecessary heating (which
causes decomposition), add 5 cc of nitric acid (ft), stir the? mixture thoroughly

1 Saiki, Biol. Chcm ., 2, 251 (1000).

FEEDS

169

and allow to stand for 30 minutes. The nitric acid decomposes ammonium
mucate, precipitating mucic acid; collect this on a weighed Gooch or alundum
crucible, wash, with 10 to 15 cc of water, then with 60 cc of alcohol, and
finally several times with ether. Dry at 100° for 3 hours, cool and weigh.
Multiply the weight of mucic acid by 1.33, which gives galactose, or by
1.197, which gives galactan. Calculate the per cent of galactan in the
feed.

CHAPTER X

SAPONIFIABLE OILS, FATS AND WAXES

Composition.—The chief constituents of animal and vegetable
oils are esters derived from fatty acids and glycerol, a triatomic
alcohol. Of the former the most important are palmitic, stearic
and oleic acids, the first two being saturated, the last an un-
saturated acid. The glycerides of these acids are respectively
known as palmitin, stearin and olein and they have the following
composition:

C ;jH r> ( 0 1 fiH ;u 0 2 ) 3, C 3 IT & (( mhH ;jr>( >i>) 3,

Palmitin Stearin

(■inHn.'iO'i);}*
Olein

In addition to these are esters of higher alcohols other than
glycerine and of other saturated and unsaturated fatty acids,
also in certain cases small amounts of free higher alcohols. The
chief differences in properties of different, oils are caused by varia¬
tions in the proportions of the constituent; esters. Vegetable
oils contain much palmitin while stearin predominates in animal
oils. The more liquid oils contain more olein and esters of acids
having smaller molecular weights.

The animal and vegetable oils and fats are thus in a class quite
distinct from that of mineral oils, the latter being mixtures of
various saturated and unsaturated hydrocarbons, not saponifi¬
able, as distinguished from the saponifiable esters of the former
class.

Waxes.—The true waxes differ chemically from the oils and
fats in that they are not glycerides but arc* esters of mono- or
diatomic; alcohols with the higher fatty acids. These alcohols
are either aliphatic; or aromatic. Following are some examples
of such esters: Octyl palmitate, derived from palmitic acid and
cetyl alcohol, C’V.HaaOII; this is the chief constituent of sperma¬
ceti. Oeryl palmitate*, the chief constituent of opium wax, is
derived from palmitic acid and cervl alcohol, Myri-

170 *

SAPONIFIABLE OILS , FATS AND WAXES

171

cyl palmitate occurs in beeswax. It is an ester of palmitic acid
and myricyl alcohol, C 3 oH 61 OH. Ceryl cerotate is the chief
constituent of Chinese wax. It is an ester of cerotic acid,
C25H51COOH, and ceryl alcohol. The most important aromatic
alcohols occurring in waxes are the isomeric alcohols cholesterol
and phytosterol, C 26 H 43 OH. These are found as esters of
palmitic, stearic and oleic acids.

Separation and Identification.—Notwithstanding the differ¬
ences in composition the task of separating and determining the
per cent of different oils in a mixture is a difficult and sometimes
impossible one, because of the fact that the same general com¬
pounds constitute the greater proportion of all fats and oils.
The chemist must usually be satisfied if he can recognize single
oils or, with the nature of a single oil known, determine the
approximate extent and nature of adulteration. The differences
in molecular weight and degree of saturation, the presence and
per cent of free alcohols or acids and the occasional occurrence
of traces of unusual substances, characteristic of certain oils,
constitute the bases of the tests used in the effort to identify an
oil. The examination becomes therefore not an analysis, in the
usual sense, but a series of tests applied in order to gain informa¬
tion regarding the identity of a pure oil and, so far as is possible,
the composition of a mixture. Certain physical and chemical
“constants” are determined and compared with the constants
obtained from examination of oils of known purity. The chief
obstacle to the use of such figures lies in the fact that, for a given
kind of oil they are actually variable within certain limits. These
limits may be very narrow, but it sometimes happens that the
ranges for two or more oils overlap. Thus olive oil from Italy is
not chemically identical with olive oil from California. The soil,
climate, variety of plant and method of expressing from the
olive have their influence upon the properties of the various
glycerides and other substances present in the oil. It is only
when the ranges of variation for different oils do not overlap that
it is easy to determine the identity of a single oil, although it
usually happens that while overlapping occurs with a single con¬
stant it does not occur with others.

The significance of the various constants and their methods of
determination will be described.

172

QUANTITATIVE AGRICULTURAL ANALYSIS

Specific Gravity.—In a general way the specific gravity of oils
increases with the per cent of ( a ) glycerides of unsaturated acids,
(b) glycerides of soluble acids and (c) free fatty acids. Old
oils also usually have higher specific gravities than the normal,
on account of oxidation. The specific gravity of the waxes
and of solid fats is usually higher than of liquid oils. These
rules do not hold in all cases and the determination of specific
gravity, like that of the other constants of oils, is made for com¬
paring with recorded data for the purpose of identification more
often than for throwing light upon the chemical constitution
of oils of known purity.

The principles underlying the modes of expression and deter¬
mination of specific gravity have been discussed on pages 94 to
102 , Part II. Unfortunately there has been a great lack of
uniformity in selecting conditions and modes of expression for spe¬
cific gravities of oils as they are recorded in the literature. Tem¬
peratures of 15.5°, 17.5°, 20°, 25°, 40°, 60°, 100° and others are
commonly used. In favor of the higher temperatures it may be
said that the fats and waxes are all liquid at these temperatures
so that determinations may readily be made. It has been found 1
that a fair degree of approximation may be made in correcting the
specific gravity to another temperature by using the coefficient
0.0007 as the change for each Centigrade degree. This is the
average value for a considerable number of oils between tem¬
peratures of 15.5° and 98°. Of course this does not remedy the
lack of uniformity of expression, noted above.

For the determination use a picnometer, a Westphal balance or an
accurately calibrated hydrometer. If a Westphal balance is used the
displacement of the plummet in pure boiled water should be accurately
determined at the temperature at which the balance is to be used. The
thermometer in the plummet should be compared with a standard ther¬
mometer. The picnometer method is recommended.

20 °

Determination of Specific Gravity of Oils at ^ 5 —Use a 25-cc specific

gravity bottle (picnometer). Clean with chromic acid, followed by distilled
water,'then rinse with alcohol and dry in an oven at 100°. Cool in the bal¬
ance case (in which the air should be at a temperature not above 20°) and
weigh. Fill with distilled water which has been recently boiled to expel
dissolved gases and cooled to a few degrees below 20°. Insert the stopper
and nearly immerse the stoppered bottle in a bath of distilled water which is

1 Wright, J. Sac. Chew. Inti , 26, 513 (1907).

SAPONIFIABLE OILS, FATS AND WAXES

173

kept at exactly 20°. After 30 minutes take off the drop of water from
the tip of the stopper, remove the bottle and wipe perfectly dry with a
clean towel but without warming the bottle to above 20°. Place in the
balance case and weigh after 15 minutes. Calculate the weight of con¬
tained water.

Empty the bottle and dry inside and out, then fill with oil and ma¬
nipulate as before, calculating the weight of contained oil. This weight
divided by the weight of contained water gives the specific gravity of the
. 20 °
oil at 2 qo*

If the specific gravity has been determined at any other temperature or if
it is desired to calculate the specific gravity at any temperature from the
determination at 20°, use the following formula:

G = G' -f 0.0007 it ' — t), where
G — specific gravity at temperature t,

G' = specific gravity at temperature t'.

20 °

Determination of Specific Gravity at ^r* —Multiply the specific gravity

at 2 qo by 0.99897, which is the density of water at 20°. The product is the
20 °

specific gravity of the oil at-jr* (See page 94.)

Determination at the Temperature of Boiling Water.—Fill a 25-cc
picnometer, dried and weighed as above described, with freshly boiled
hot water. Nearly immerse in a bath of briskly boiling water and leave
for 30 minutes, replacing evaporated water with boiling distilled water.
Insert the stopper, previously heated to 100°, remove the picnometer
from the bath, wipe dry, cool to room temperature and weigh. Cal¬
culate the weight of contained water.

Fill the flask, dried at 100°, with the dry, hot, freshly filtered fat or oil,
which must be entirely free from air bubbles. Keep in the boiling
water bath for 30 minutes then insert the stopper, which has been heated
to 100°, wipe dry, cool to room temperature and weigh. Calculate the
weight of contained oil and from this and the weight of water contained
at boiling temperature calculate the specific gravity of the oil at the temper¬
ature of boiling water.

This determination is necessarily less accurate than the one
at 20°, on account of the difficulty involved in keeping the bath
at any constant temperature. Superheating may easily occur
with distilled water and less pure water may have a boiling
point above 100°. Variation in barometric pressure will also
change the temperature of the bath so that it becomes necessary
to carry out both parts of the experiment at the same atmos¬
pheric pressure. However the determination is sanctioned and
has been made official by the Association of Official Agricultural
Chemists.

174 QUANTITATIVE AGRICULTURAL ANALYSIS

The specific gravity at any temperature other than 20 may be
determined by the method outlined for this temperature or it may
be calculated from the determination at this temperature, using
the formula given above. It should be understood that the figure
desired for purposes of identification is the specific gravity at
the temperature for which data may be found in the literature.

Index of Refraction.—A discussion of the underlying theory
and of the determination of index of refraction is found on pages
113 to 120, Part II.

The measurement of index of refraction is a valuable addition
to the list of tests for oils. While not in all cases characteristic
it will frequently serve to distinguish between certain possi¬
bilities when other tests, are not conclusive. The refractive
index increases with (a) increasing molecular weight of the
combined acids and (b) increasing unsaturation. If free fatty
acids are present in an oil the refractive index will be lower than
the normal value for the oil. In consequence of the latter fact
one may expect to find abnormally low indices for old or rancid
fats or oils.

The selection of standard temperatures for the determination
is highly desirable in order to make comparison data useful.
Temperatures of 20° for oils and 40° or 60° for fats and waxes
are suitable in most cases. For calculating the index of refrac¬
tion at any temperature from experimental results at another
temperature the following formula may be used:

R = R' + 0.000365 it' - t),

where R and R ' indicate indices of refraction at temperatures
t and t respectively. The coefficient 0.000365 is the average
change of index for 1° for a large number of common oils.

The index of refraction of oils is conveniently determined by
use of any of the standard instruments, such as the Abb4,
Pulfrich, Zeiss butyro-refractometer or the immersion refrac-
tometer. Of those named the Abb6 instrument is probably the
most generally useful because it may be used with liquids cover¬
ing a wide range of refractive indices and because it does not
require the use of monochromatic light. The principles under¬
lying the use of this and other instruments are discussed on pages
115 to 120, Part II.

SAPONIFIABLE OILS, FATS AND WAXES

175

Determination of Index of Refraction by Means of the Abbe Refrac-
tometer. —Set up the instrument in front of a window or any artificial light
•source, noting, that monochromatic light is not essential. Connect a
constant temperature apparatus furnished with the instrument and adjust
the flow of water and the height of the flame until the desired temperature
(20° for oils, 40° or higher for fats or waxes) is attained. Open the prism
so that the lower half is in a horizontal position and place two or three
drops of oil or melted fat or wax upon it, using a glass rod or pipette but
avoiding scratching the prisms. Quickly close and lock the system, allow
time for the temperature to become constant and then adjust the com¬
pensator and focus until the line of division of the field is sharply defined and
bring this to the cross hairs. Read the index of refraction upon the scale.

Clean the prisms by applying a mixture of equal volumes of alcohol and
ether, using a tuft of absorbent cotton.

Melting Point of Fats.—From the fact that fats are mixtures
and not pure compounds, it will be seen that they cannot have
definite and sharp melting points. The observation will there¬
fore be a somewhat arbitrary one. The following is Wiley’s
method.

Determination.—Prepare discs of fat as follows: Allow the melted and
filtered fat to fall a distance of about 20 cm, from a dropping tube to a
piece of ice or to the surface of cold mercury. The discs thus formed should
be 1 to 1.5 cm in diameter and they should weigh about 200 mg. Since a
recently melted and solidified fat does not have its normal melting point the
discs should stand two to three hours before testing.

Prepare an alcohol-water mixture of graduated density, as follows: Boil,
separately, water and 95-per cent alcohol for ten minutes to remove dis¬
solved gases. While still hot pour the water into a 20 cm test tube until
it is almost half full. Nearly fill the tube with the hot alcohol, pouring
down the side of the inclined tube, to avoid too much mixing.

Place the test tube containing the alcohol-water mixture in a tall beaker
containing ice water, until cold. Drop the disc of fat into the tube and it
will at once sink to a point where the density of the mixture is exactly equal
to its own. Lower an accurate thermometer, graduated to tenths, into the
test tube until the bulb is just above the disc, stirring very gently. Slowly
heat the water in the beaker, stirring constantly with an air blast or
mechanical stirrer.

When the temperature of the alcohol-water mixture has risen to a point
about 6° below the melting point of the fat the disc will begin to shrivel and
roll into an irregular mass. Now lower the thermometer until the fat particle
is even with the center of the bulb. Rotate the thermometer gently and
regulate the temperature so that about 10 minutes is required for the last
increment of 2°. As soon as the fat becomes a spherical globule read the
thermometer. This serves as a preliminary determination of melting point.

17() quantitative agricultural analysis

Remove the tube from the bath, and place in the latter a second tube of
alcohol and water. 1 he latter, having been cooled in ice water, is sufficiently
low in temperature to cool the bath to the desired point. Add another disc'
of fat and regulate the temperature so as to reach a maximum of 1.5° above
the melting point as already determined. Run a third determination, which
should agree closely with the second.

The disc of fat should not be allowed to touch the side of the tube, in any
determination.

Iodine Absorption Number.—The iodine absorption number
is the per cent of halogen, expressed as iodine, absorbed by
the fat or oil when subjected to the action of a halogen solution
under specified conditions. The absorption takes place because
of the presence of glycerides of unsaturated acids, which contain
double or triple bonded carbon atoms.

This action is analogous to the absorption of oxygen. In the
latter case saturated oxygen compounds are formed, often hard
and resinous in nature. Absorption of oxygen from the air
in this way is known as “drying,” although the term is mis¬
applied, since no real drying occurs. The determination of halo¬
gen absorption number is, in a general way, a measure of drying
properties and it serves as a distinction between the somewhat
arbitrary classes of drying, semi-drying and non-drying oils.

Of the unsaturated acids whose glycerides commonly occur in
fats or oils the following important members may be mentioned:

Oleic Acid , (U 8 H 34 Q- 2 .—The unsaturated character of this
acid is indicated by the formula

CVHa((TI.,) 7 CH = CH(CH 2 ) 7 COOH.

Olein, the triglyceride of this acid, occurs to some extent in all
oils and fats, but especially in the former. The empirical formula
of the triglyceride is

(' 3 II & (C_y 1 8^1 3 3 O 2 ) 3«

Olein is liquid at ordinary temperatures and its presence in oils
is responsible, in a large number of cases, for their liquid character.

Oleic, acid will absorb two atoms of bromine, iodine or chlorine,
or one molecule of iodine; monochloride tor monobromide, the
double bonded carbon atoms thus becoming saturated. Simi¬
larly, either oleic acid or olein might be expected to absorb
oxygen and to give; drying properties to a fat or oil but this

SAPONIFIABLE OILS, FATS AND WAXES 177

action does not take place readily and most of the oils of pro¬
nounced drying properties are found to contain considerable
quantities of simple or mixed glycerides of linolic or linolenic
acids, more highly unsaturated compounds than oleic acid.

Linolic Acid, C 18 H 32 O 2 , contains two pairs of doubly linked
carbon atoms:

CH 3 (CH 2 ) 4 CH = CH*CH 2 -CH = CH(CH 2 ) 7 COOH.

This acid will absorb four atoms of halogen or two atoms of
oxygen. It gives marked drying properties to oils, linolin being
abundant in linseed, soybean and poppy seed oils.

Linolenic Acid, C 18 H 30 O 2 , probably to be represented as

CH 3 -CH 2 -CH = CH-CH 2 *CH = CH-CH 2 -CH = CH* (CHo) yCOOH.

This acid possesses three sets of double bonds and will absorb
six halogen atoms or three oxygen atoms. It occurs as simple
or mixed glycerides in linseed oil and, together with linolic acid,
plays the most important part in the hardening or “drying”
of this oil when it is exposed to the air. An isomer, isolinolenic
acid, also occurs as a constituent of the glycerides of drying oils.

Ricinoleic Acid, C 18 H 34 O 3 , is hydroxyoleic acid and, like oleic
acid itself, contains only one pair of doubly linked carbon atoms.
It will not readily absorb oxygen from the air and it does not
impart drying properties to an oi£ It is, however, an important
constituent of castor oil and will be mentioned later, in the
discussion of acetyl value.

The five acids named above serve to illustrate the principle that
only those unsaturated acids which contain more than one pair
of doubly bonded carbon atoms are important from the stand¬
point of drying. Also an interesting, although perhaps unex¬
pected fact is that trebly linked carbon atoms do not, under
ordinary conditions, absorb halogens or oxygen to the point of
complete saturation, only two atoms of halogen or one of oxygen
adding to each such pair.

Solvent.—Absorption of halogen by oil cannot readily take
place unless there is present some solvent which can dissolve
both oil and halogen. The halogen solution earliest used for
this purpose was of iodine and mercuric chloride in alcohol.
This has been almost entirely replaced by a solution of either
12

178

QUANTITATIVE AGRICULTURAL ANALYSIS

iodine monobromide or iodine monochloride in glacial acetic
acid. The monobromide solution was proposed by Hanus, that
of monochloride by Wijs. As the former is somewhat more
easily prepared its preparation and use will be described.

The following solutions will be required for the determination of iodine
number:

(a) Potassium Dichromate. —A tenth-normal solution, made by dissolving
exactly the calculated weight of a salt of known purity, or standardize as
directed on page 74. Five hundred cubic centimeters of this solution will
be sufficient.

(h) Potassium Iodide. —Prepare 200 ee of a solution containing approxi¬
mately 25 gm of the solid.

(c) Starch. —Moisten 1 gm of potato starch with enough cold water to
make a thick paste. Heat 100 ee of water to boiling and pour it into the
starch paste. Boil gently, with constant stirring, for about a minute.
The solution does not keep well and it should bo made each day, as required.
The addition of preservatives, such as chloroform or zinc chloride, has been
tried but the solution deteriorates, even with such additions.

(d) Sodium Thiosulphate. —Prepare an approximately tenth-normal solu¬
tion, calculating the equivalent weight from the following equation:

2 Na 2 S 2 0 3 + I 2 -> Na 2 S 4 0« + 2NTaI.

In weighing the crystallized salt, calculations must include 10 molecules of
water of crystallization, the formula being Na 2 S 2 () 3 .10H 2 O.

Standardize the thiosulphate solution as follows: Pipette 25 ee. of the
dichromate solution into an Erlenmeyor flask and add 50 ee of potassium
iodide and 10 cc of concentrated hydrochloric acid. Iodine is liberated
according to the equation:

K 2 Cr 2 0 7 + OKI + 14IIC1 -> 8KC1 4- 2CrCl# + 7H 2 G + 31*

Titrate immediately with sodium thiosulphate, adding 1 cc of starch solution
after most, of the iodine 1ms disappeared. If starch is added too soon a
blue precipitate will be produced and the end point will be reached too
early in the titration.

The solution of chromium chloride, formed by the reduction of potassium
dichrornate, is green. The solution has an amber tint as long as free iodine
is present. Upon addition of starch the solution acquires a blue-green color
and the change to emerald green at the end point may be difficult to judge
at first trial. By setting aside for comparison a solution that has been over¬
titrated, the detection of the color change will be made easier.

(c) Iodine Monobramide.— First test the* laboratory stock of glacial
acetic acid to insure the absence of reducing matter. Add a drop of sul¬
phuric acid and two or three drops of potassium dichrornate solution to 10
cc of acetic acid, and warm. The yellow color should x>ersist, without the
appearance of green chromium salts.

SAPONIFIABLE OILS, FATS AND WAX'NS

170

Dissolve 13.6 gin of powdered iodine in S25 co of glacial acetic acid.
The mixing machine shown in Fig. hi, page 236, will lie found useful for
hastening solution. Cool, decant to insure that no particles of iodine
remain undissolved, and mix. Measure from a burette 25 ec of the solution
into a 250-cc Erlcnmeycr flask, add 15 ec of potassium iodide solution
(6) and 100 ec of water, and mix. Titrate at once with tenth-normal
sodium thiosulphate solution.

From a small burette measure 3 cc of bromine into 200 co of glacial
acetic acid. Mix and titrate 5 cc of the solution against sodium thiosul¬
phate solution, adding potassium iodide and water as in the iodine titration.
From those titrations calculate the volume of bromine solution that would
1)0 equivalent to 800 cc of iodine solution. Add this quantity of bromine
solution to the iodine in a glass stoppered bottle and mix well. This should
produce a solution of iodine monobromide, containing only a very slight
excess of either bromine or iodine.

The addition of potassium iodide, both before and after absorption by the
oil, gives a titration which may be calculated as though iodine were the only
halogen present, since this element is titrated at the end, in both eases:

IBr + KI KBr + I*

(Of course the iodine is then present as K1 3 .)

Determination of Iodine Number. —Half fill a 20-ce weighing bottle
with oil, place in it a piece of glass rod and weigh without the stopper.
Carefully pour about 0.25 grn of the oil into a 500-cc bottle or flask having
a ground ghiss stopper, using the glass rod to assist in the transference.
Reweigh and prepare another sample in the same manner.

Dissolve the weighed sample of oil in 10 cc of chloroform then add
25 cc of iodine monobromide solution, measuring from a pipette. Stop¬
per, mix and allow to stand for 30 minutes, shaking occasionally. The
bottle should not be left in strong light.

At the time that the iodine monobromide solution is measured into
the oil solution, measure the same amount of solution into two bottles,
containing the chloroform but no oil. Treat these in exactly the same
manner as the solution containing oil. This is for the “ blank "determination.

At the end of the absorption period add 15 cc of potassium iodide solution
(b). Add 100 ec of water, washing down any iodine that may be on the
stopper. Titrate the unahsorhed iodine with standard sodium thiosulphate,
shaking constantly. When only a faint yellow remains add 1 cc of starch
solution and finish the titration. At the last the bottle should be closed
and shaken until all iodine remaining in the* chloroform has been extracted
by the potassium iodide. The temperature should he kept us nearly con¬
stant as possible throughout the experiment,.

From the volume of sodium thiosulphate required for the iodine solu¬
tion alone subtract that required for the oil and iodine solutions. 'The
remainder is the volume corresponding to the absorbed iodines Calcu¬
late the per cent of iodine absorbed.

180 QUANTITATIVE AGRICULTURAL ANALYSIS

Iodine monobromide is absorbed at a double bond thus:
—C = C + IBr -> —C—C—

I I

I Br

Acid Value.—Fresh oils sometimes contain small amounts of
free fatty acids produced during the process of extraction.
Rancid fats and oils, contain free acids as products of hydroly¬
sis of the glycerides composing them. The acid value is defined
as the number of milligrams of potassium hydroxide required to
neutralize the free fatty acids in 1 gm of oil or fat Acidity is also
sometimes expressed in terms of oleic acid as per cent, or as “acid
degree,” which is cubic centimeters of normal base equivalent to the
free acids in 100 gm of oil or fat. The determination of acid
value is made for the purpose of determining the condition of the
oil and its fitness for a given use, rather than for the purpose of
identifying it, since the acid value is a variable within rather wide
limits for any oil.

Determination of Acid Value.—Weigh 20 gm of oil or fat into a 200-cc
flask and add 50 cc of 95-per cent alcohol which has been made neutral to
phenolphthalein by a dilute solution of sodium hydroxide. Heat to the
boiling-point in a steam bath and agitate thoroughly. Titrate with a tenth-
normal solution of sodium or potassium hydroxide, using phenolphthalein.
Shake vigorously during the titration and add the standard solution until
the pink color persists for a short time. An absolutely permanent color
cannot be obtained because any excess of base will finally saponify the oil
and thereby become neutralized.

Saponification (Kottstorfer) Number.—The saponification
number is the number of milligrams of potassium hydroxide
required to saponify 1 gm of oil or fat. Different oils show differ¬
ent saponification numbers because of variation in the molecular
weight of the esters contained in them, those of relatively low
average molecular weights requiring more base for the saponifica¬
tion of a given weight of oil than those of higher molecular
weights. The variation is, however, not as great as is the case
with iodine absorption numbers and the saponification number
is consequently not as valuable for use in identifying oils as is
the iodine number.

Notable exceptions to this rule are butter and cocoanut fat,
on the one hand, and the true waxes on the other. Of these the

SAPONIFIABLE OILS , FATS AND WAXES

181

first group contains appreciable quantities of the glycerides of
butyric, caproic and caprylic acids, in addition to those of oleic,
palmitic and stearic acids, which make up the bulk of most other
oils and fats. The lower molecular weights of these acids raises
the saponification number of butter to about 227 and that of
cocoanut fat to 255.

The .true waxes are not glycerides but esters of mono- and
di-hydric alcohols, usually of higher molecular weights than that
of glycerol and always of higher equivalent weights. Most
waxes contain also acids of higher molecular weight than that of
stearic acid, as constituents of the essential esters. This gives
lower saponification numbers to waxes, as will be noted from an
inspection of Table XII on page 198.

It will thus be seen that the determination of saponification
number will be useful chiefly in identifying materials of the
classes just named. In most other cases this constant will fall
between the approximate limits of 190 and 210.

Insoluble Acids (Hehner Value) and Soluble Acids.—The
determination of the saponification number may be conveniently
combined with the determination of soluble acids and insoluble
acids. Among the most important of the acids of smaller
molecular weight than oleic acid, combined as glycerides, are
butyric, caproic, caprylic and capric acids, discussed above.
These acids are soluble in water, the solubility decreasing as the
molecular weight increases, so that, while butyric acid is infi¬
nitely soluble, capric acid dissolves only to the extent of 1 part in
1000 parts of boiling water. The next acid in the series, lauric
acid, is almost insoluble while the still higher acids are prac¬
tically insoluble. An approximate separation of the lower
acids from the higher ones may be accomplished by saponifying
the oil, decomposing the resulting soap with sulphuric acid and
washing the fatty acids with water. The per cent of insoluble
acids is called the Hehner value.

An inspection of the formula for a typical triglyceride, as that
of palmitin, C 3 H 5 (Ci 6 H 3 i 0 2 ) 3 , shows that the acid residue
comprises the greater part of the compound. Also since the
variation in the molecular weights of the three acids, palmitic,
stearic and oleic, which make the greater part of the acids of
most oils and fats, is small as compared with the molecular

182

QUANTITATIVE AGRICULTURAL ANALYSIS

weights themselves, it is not to be expected that there would be a
large variation in either the Hehner value or the per cent of
soluble acids. The former has an average value of about 95 and
the latter of considerably less than 1. Therefore these numbers are
without any great significance in most cases and their determina¬
tion will give little assistance in the task of identifying most
oils. A few exceptions to this statement should be noticed.

Butter has already been mentioned as containing unusually
large quantities of butyric, caproic, caprylic and capric acids.
Consequently its Hehner value falls to 88-90 and its per cent of
soluble acids rises to about 5. Other notable exceptions are
cocoanut, palm nut and croton oils. Practically, it is in these
cases only that the determination of soluble and insoluble acids
will be of any great use.

Determination of Saponification Number.—Prepare the following
solutions:

(a) Alcoholic Base. —Purify 2 liters of alcohol by heating on a steam
bath for 3 hours with about 10 gm of sodium hydroxide, using a reflux
condenser. Distill and make 1000 cc of a solution of 40 gm of potassium
hydroxide in the alcohol. The potassium hydroxide should be as nearly
free from carbonate as is possible. Allow the solution to stand until
the small amount of potassium carbonate that is always present has settled
out, then decant into another bottle. The concentration does not remain
constant for long and the solution should not be standardized, except by a
blank determination, made at the time saponification number is determined.

(i b ) Prepare also a half-normal solvtion of hydrochloric add in water.

Select two ordinary flasks of 250-cc capacity having, if possible, necks of
slightly larger diameter at the top than at the bottom, though this feature
is not essential. Clean with alcohol. Weigh into each flask about 5 gm
of oil or fat, using a small bottle and glass rod as in the determination of
iodine number. Add to each flask 50 cc of the alcoholic solution of potas¬
sium hydroxide-from a calibrated pipette or burette, place in the neck of the
flask a funnel having a short stem and warm on the water bath until the
alcohol boils, though it should not be evaporated more than is necessary.
The oil is usually saponified in about 30 minutes. A homogeneous solution
must be produced, so that no separation will occur when boiling is inter¬
rupted. Measure 50 cc of the alcohol solution of potassium hydroxide into
each of two other flasks, for standardization. While saponification of the oil
is proceeding titrate these solutions with the half-normal acid, using phenol-
phthalein. Cool the flasks in which the oil was saponified, add a drop of
phenolphthalein and titrate the excess of base with half-normal acid, deduct
from the volume used for 50 cc of the base in the standardization and calcu¬
late the saponification number.

SAPONIFIABLE OILS , FATS AND WAXES

183

If it is desired to determine insoluble and soluble acids the solution which
has just been used for the determination of saponification number may be
used for this purpose. For detailed directions refer to other works on this
subject. 1

Reichert Number and Reichert-Meissl Number.—There is no
sharp line of division between the fatty acids volatile with steam
and those not volatile and it is not possible to effect more than a
very approximate separation by a method of distillation unless
this is continued for a very long time. On the other hand
fairly constant proportions of acids may be distilled if the method
is rigidly standardized. In this way figures may be obtained
that have a value in identifying certain oils and fats. The
determination is made chiefly in the examination of butter and
its substitutes. Pure butter contains volatile acids to the extent
of nearly 10 per cent of the total fatty acids.

The saturated acids to and including capric acid are the only
ones of the series that may be distilled without decomposition.
They are therefore known as “volatile” acids while the higher
acids (above lauric) decompose when distilled and arc therefore
called “non-volatile.” Lauric acid distills with steam but is
slightly decomposed. Although the volatile acids boil at tem¬
peratures higher than 100° they can be distilled with steam.

The method proposed by Reichert and modified by Meissl has
been extensively adopted. It should be understood that neither
method gives the correct per cent of volatile acids but simply the
proportion that will be distilled under certain stated conditions.
The Reichert Number is the number of cubic centimeters of tenth-
normal base required to titrate the acids obtained from 2.5 gm, of oil
or fat by Reichert's distillation process. The Reichert-Meissl
number is the same as the Reichert number except that 5 gm of
oil or fat is used. The Reichert-Meissl number is not exactly
double the Reichert number.

The Reichert-Meissl number of most oils, fats and waxes is
less than 1 and the determination will be of little service in
identifying these oils. The following oils are exceptional in
this respect.

1 Lewkowitsch, “ Chemical Technology and Analysis of Oils, Fats and
Waxes;” Assoc. Off. Agri. Chemists, “Methods of Analysis;” Mahin,
“Quantitative Analysis.”

QVANTITATI vjs AGRICULTURAL ANALYSIS

Labi/k IX!.— —Reichert-Meissl Numbers

Oil or fat

Iteichert- !

Oil or fat

Reichert-

iYLeissl number j

Meissl number

Butter fat.

28.5

Mocaya.

Cocoanut..

Palmnut.

Croton.

Porpoise.

Butter and Substitutes. —Practically speaking, the deter¬
mination of Reichert-MfeissI number is a test chiefly of value in
the dairy laboratory. Butter substitutes are of two general
classes: (a) Oleomargarines, made chiefly from refined lard and
“oleo oil” (the olein of beef tallow) and ( b ) preparations in
which eocoanut fat is one of the essential constituents. For
members of the first class the Reichert-Meissl number will be
less than 1, while mixtures of the second class will show numbers
ranging up to 7, according to the per cent of eocoanut fat in the
preparation. The number for pure butter is about 28.5, as noted
in the table above.

Applications to butter testing are noted in the chapter on
Dairy Products, page 223.

Spitzer and Epple 1 have constructed the chart shown in Fig.
45 for the application of Jteichert-Meissl and saponification num¬
bers to the approximate calculations of the proportion of oleo
oils, eocoanut fat and butter fat in adulterated butters and butter
substitutes. While no great accuracy is claimed for this pro¬
cedure, it will undoubtedly give useful information in the inter¬
pretation of analytical results.

Determination of Reichert-Meissl Number.—Prepare the following
reagents:

(a) Sodium hydroxide solution in water, 50 per cent by weight.

(b) Alcohol T 05 jxr cc.nl, redistilled from sodium or potassium hydroxide.

(d) Polanxium hydroxide , .approximately tenth-normal*, standardized
against standard acid, using pbenolphthalein as indicator.

If flat sample is either real or imitation butter it will contain water
and curd. Melt and keep at 00° until the fat has separated and, if necessary,
filter the fat through a dry' p^P er placed in a hot-water funnel (Fig.
50, page 220).

l Ind. Exp. Sla. Hull., 254 (1021).

SAPONIFIABLE OILS , FATS AND WAXES

185

Ordinary flasks of 200-cc capacity, are cleaned and dried. The oil
or melted fat is dropped in from a weighed bottle until 5 gm, measured
to within one drop; is obtained. The oil must not be left on the neck of
the flask. Record the exact weight. Add 10 cc of alcohol and 2 cc of 50-
per cent sodium hydroxide solution, connect with a reflux condenser and
heat upon the steam bath until the oil is saponified. Remove the con¬
denser and evaporate the alcohol on the steam bath. Add 135 cc

260 267 266 263 261249 247246 243 241.220 237236 233 231 229 227 226 223221 219217'216 213 211209 207 205 203201199197
Cap.Ho. 268 256 264252260 248-246244 242 240 238236 234 232.230 228 22b 224 222220218210 211 212210 208200204 202200198196 a

% 100 95 90 85 80 75 70 65 60 55 60 45 40 35 30 25 20 15 10 5 0 %

Upper Saponification Numbers
Lower — Percent Cocoanut Fat

Fig. 45. —Spitzer and Epple’s chart for composition of butter substitutes.

of recently boiled water and warm on the water bath until solution
is complete, then cool. Add two or three pieces of pumice stone or
about 1 gm of crushed porcelain to prevent bumping, then add 10 cc
of the diluted sulphuric acid. Again attach the reflux condenser and heat
on the steam bath until the acids form a clear layer. Connect the flask
with a distilling tube (Fig. 46) and a condenser and distill over a flame at
such a rate that 110 cc shall be obtained in approximately 30 minutes.
The distillate is received in a flask which is graduated to contain 110 cc.
Mix the distillate, and filter through a dry filter to remove traces of insoluble

186

QUANT IT AT I YE AGRICULTURAL ANALYSIS

acids carried over by the steam, receiving the filtrate in a flask graduated to
contain 100 ec. Titrate 100 cc of the filtrate with standard potassium
hydroxide. Make the proper correction for the fact that only 100 cc of the
distillate was used, also correct tin* number of cubic (Multimeters of standard
potassium hydroxide used, in case this solution was not exactly tenth-normal
or in case the sample weight was not exactly 5 gin. The result is the
Keichert-Meissl number.

Polenske Value.—One of the very important constituents
of some butter substitutes is coeoanut oil, a pure white vegetable

fat having a pleasant taste and a con¬
sistency which is about the same as
that of butter. Its Keichcut-Meissl
number is lower than that of butter,
as is shown in Table IX, page 184.
The volatile acids obtained from
coeoanut oil in the Keichert-Meissl
distillation contain much larger
quantities of acids insoluble at 15°
than do the volatile acids from butter.
Butyric acid comprises from 60 to 70
per cent of the volatile acids from
butter and this acid is soluble in
water in all proportions. The volatile
acids from coeoanut oil contain larger
quantities of eaproie, cnprylie, cupric
and Iaurie acids, these 1 being almost
insoluble at 15°. The Polenske value
(called by its author the “now butter value”) is the number of
cubic centimeters of tenth-normal base, required to titrate the insoluble
acids obtained in the Reichert-Meisst distillation
The Polenske value for pure butter varies from 1.5 to 3.0,
while that for coeoanut oil varies from 16 to 18.

It is necessary to avoid the use of alcohol in the saponification
of the fat and therefore the determination of Keichert-Meissl
number must be modified if the two determinations are to be
combined. Polenske's modification is essentially as follows:

Determination.— Saponify 5 gm of the fat by heating in n 2f>0-ce round
flask, using a reflux condenser. For the saponification use 20 gm of glyc¬
erol and 2 cc of a 50-per cent solut ion of sodium hydroxide in water. When
saponification is complete dissolve the soap in W> ec of recently boiled

Fig. 40.— Distilling tube.

SAPONIFIABLE -OILS, FATS AND WAXES

187

water and add 25 cc of dilute sulphuric acid (50 cc in 1000 cc of solution)
and a small amount of crushed porcelain or pumice. Connect with a
condenser by means of a distilling'tube (Fig. 46) and distill into a flask
which is graduated at 100 cc and 110 cc; the distillation should proceed
at such a rate that 110 cc passes over in about 20 minutes. When the
distillate reaches the 110-cc mark on the flask replace the latter by a 25-cc
cylinder and stop the distillation. Immerse the flask in water at 15° and
allow to remain for 15 minutes. The level of the water must be above the
110 ~cc mark on the flask. Mix the contents of the flask and pass through
a dry, 8-cm filter and, if desired, determine the Reichert-Meissl number,
using 100 cc of the filtrate. Rinse the 110-cc flask but without removing
any of the insoluble acids adhering to it. Wash the filter three times with
15 cc of water, this water having previously been used for washing the con¬
denser, cylinder and flask. Dissolve the insoluble acids from the con¬
denser, cylinder and filter, using three successive portions of neutral (to
phenolphthalein) 90-per cent alcohol and allowing the solution to run into
the 110-cc flask. Titrate the alcoholic solution with tenth-normal potassium
hydroxide solution, using phenolphthalein, and calculate the Polenske value.

Acetyl Value.—Compounds containing a hydroxyl group will
readily combine with acetic anhydride, acetic acid and an acetyl
compound being produced. This takes place with an oil con¬
taining free higher alcohols or hydroxy-acids, the latter either in
the form of esters or of free acids. For example lanopalmic acid
forms acetolanopalmic acid:

C15H30OHCOOH + (CH 3 C 0) 2 0 -> C 16 H3oOCH 3 COCOOH +

CH3COOH. (1)

After washing out the excess of acetic anhydride the amount
absorbed may be determined by saponifying the oil with an
alcohol solution of potassium hydroxide, evaporating the alcohol,
adding standard sulphuric or hydrochloric acid to liberate the
acetic and fatty acids and either distilling the acetic acid or
washing out with wa,ter, then titrating. The reactions illustrated
by the case of aceto-lanopalmitin are

C 3 Hb(OC 1 5 H S 0 OCH 3 COCO), + 6 KOH -> C 3 H 6 (OH ) 3 +

3C 15 H 30 OHCOOK + 3CH 3 COOK. ( 2 )
2C 15 H 3 oOHCOOK + H 2 S0 4 -> 2C 16 H 30 OHCOOH + K 8 S0 4 , (3)
2 CH 3 COOK + H 2 S0 4 -> CH 3 COOH + K 2 SO 4 . (4)

188

QUANTITATIVE AGRICULTURAL ANALYSIS

Effects of Soluble or Volatile Acids.—It should be noticed that
whether the distillation or the filtration process is employed,
the standard base required finally to titrate the acid will include
that equivalent to acids other than acetic. That is, the distilla¬
tion process will yield a distillate of acetic acid and volatile
organic acids while the filtration process will yield a filtrate con¬
taining acetic acid and soluble organic acids. The close relation
between soluble acids and volatile acids has already been dis¬
cussed (page 183). To correct for the presence of these acids in |

the solution containing the acetic acid one may either subtract
the volume of base used in the determination of soluble (or vola¬
tile) acids, or a different method may be used. As a rule this
correction will be small except with oils showing a high soluble-
acid number or Reichert-Meissl number and in these cases the
acetyl value is nearly zero, so that it is of little use as a means for
identifying the oils.

The “acetyl value” is defined to be the number of milligrams of
potassium hydroxide required to combine with the acetic acid lib¬
erated from 1 gm of acetylated fat or oil. Certain oils are charac¬
terized by unusually high acetyl values and it is only in these
cases that the determination will be of value for oil testing.

Castor oil is the most noteworthy of these, having a value of
about 150. Another class of oils having high acetyl values is
composed of “blown” or “oxidized” oils. By blowing air
through oils at somewhat elevated temperatures (70° to 115°) the
viscosity and specific gravity are considerably increased and they
become suitable for use as lubricating oils. The chemical
changes that take place are not thoroughly understood but j

oxidation is known to occur. This is partly due to combination S

with unsaturated acids (evidenced by a diminished iodine absorp-
tion number) and partly to the formation of hydroxyl radicals j

from hydrogen. The latter change results in an increased |

acetyl value and this may even reach a number as great as that t

for castor oil. J

The large variation in acetyl values recorded in Table X will f

indicate the value of this determination for the identification of 1

certain oils and fats. In other cases the determination will have 1

little value.

KAPOXIFIABLK OILS, FATS AND WAXFS ISO

Table X.— Acetyl Values of Oils

Oil or fat

Acetyl value
(average)

Oil or fat

Acetyl value
(average)

Castor.

150

Fish.

Colza.

1 17

Olive.

: 15

Cotton seed.

i IS

Shark liver. .

■ is

Croton.

20 1

i 1

Abnormal Variation in Acetyl Values.—Certain abnormalities
in acetyl values should be noticed and due allowance made in
specific cases.

Since acetic anhydride is absorbed by the hydroxyl radical
it might be expected that free acids, free alcohols or partly
hydrolyzed glycerides or other esters would show such absorption
and that their occurrence in oils or fats would cause these to
exhibit unusually high acetyl values. This is found to be the ease
and, since the three classes of substances named above are the
direct products of hydrolysis, it follows that rancid oils or fats
will not give normal acetyl values. For example, hydrolysis of
stearin will yield free stearic acid, together with distearin,
monostearin or glycerol, according to the degree of hydrolysis:

C 3 H & ( 0 ( * i sH 3 bO) a + H 8 0->C,H 6 0H(0C5 i «II* 6 0)2 + Ci«H ao O a ,

Stearin Dintenrin Stearic acid

( 1 )

CjH &OH (OC i 8 H 35O) 2 + H 2 0 —C :i II ll (()H),0(),jr,c() +

MonoHloarm

( 2 )

C*H i (OH) 1 OC Ig H,sO + H 2 0 -> C,H f ,(()II) a +

Glycerol

^MHlIgnOa. ( 3 )

Each of these reactions produces a hydroxylated compound,
which is capable of combining with acetic anhydride. The
calculated acetyl values of these substances are as follows:

Table XI.— Acetyl Values of IIyduolyzed (Ilycehides

Compound

Acetyl value

Distcarin.

S4.2

Monostearin.

254.9

Glycerol.

772.0

100

quantitative agricultural analysis

Glycerol and acetoglycerol are easily soluble in water and they
would therefore be removed in the process of washing the
acetylated oil, so that no error would result from this source.
On the other hand both distearin and monostearin, as well as
their acetylated products, are insoluble in water. On this
account the acetyl value of the partly hydrolyzed oil would be
materially increased.

The free acids produced by hydrolysis, themselves containing
a hydroxyl group, will combine with acetic anhydride to a
varying degree and this will still further increase the acetyl value
of such rancid materials.

It is to be noted also that many of the waxes contain certain
quantities of free higher alcohols and free acids. In consequence,
these waxes will show moderately high acetyl values, as will be
noted in table XII, page 198.

It will be obvious from these considerations that acetyl values
cannot be used with safety for identifying oils unless these are
reasonably fresh. This will be indicated by the acid value, which
should be low.

The most important application of this determination is in
the identification of castor oil. This oil is nearly pure ricinolein ,
a glyceride of ricinoleic acid. The latter is hydroxylated oleic
acid,

CH 3 (CH 2 ) 5 CH-OH*CH 2 *CH = CH(CH 2 ) 7 cooh,

and the glyceride, ricinolein, has a theoretical acetyl value of
159.1. Its abundance in castor oil gives the latter an actual
acetyl value of about 150, a value which is far above that of
any other natural oil, only blown oils approaching it in this
respect.

Lastly may be mentioned the occurrence of certain quantities
of free alcohols, especially in the waxes which have, on this
account, appreciable acetyl values. Cholesterol, C 27 H 46 OH, in
fats, oils and waxes of animal origin, and its isomers, the phytos¬
terols, in vegetable oils, are the most important of such alcohols.

Determination of Acetyl Value.—Place about 20 gm, approximately
weighed, of oil or fat in a 100-cc flask, add an equal volume of acetic anhy¬
dride, insert a short-stemmed funnel and boil gently for two hours. Cool
and pour into 500 cc of water contained in a beaker. Pass a current of car-

SAPONIFIABLE OILS, FATS AND WAXES 191

bon dioxide into the beaker through a fine orifice of a glass tube to agitate
the liquid and hasten the washing. Boil for 30 minutes. At the end of this
time siphon out the water layer and repeat the treatment with water and
boiling until the water is no longer acid, as shpwn by a litmus test. Separate
the acetylated oil in a separatory funnel, filter in a drying oven or hot-water
funnel (Fig. 50, page 226) and dry.

Weigh accurately 2 to 4 gm of the acetylated oil into a flask and saponify
according to the method used in determining the saponification number,
measuring the alcohol solution of potassium hydroxide accurately arid
running blank determinations for standardization. Evaporate the alcohol
and dissolve the soap in water. Add standard hydrochloric acid in a
quantity exactly equivalent to the potassium hydroxide added, warm to
melt the fatty acids and filter through a wet paper. Wash with boiling
waiter until the washings are no longer acid, testing with litmus paper by
barely touching a corner to the bottom of the funnel. The combined filtrate
and washings are titrated with tenth-normal base. Calculate the acetyl
value according to the definition of this number.

Maumene Number and Specific Temperature Reaction.—All

oils and fats react with concentrated sulphuric acid, heat being
evolved. The reactions are complex and cannot be expressed
by a simple equation but oxidation occurs to a considerable
degree. The heat evolution varies with different oils and it is, to
some extent, characteristic. The Maumend number is the
number of Centigrade degrees rise in temperature caused by mixing
10 cc of concentrated sulphuric acid with 50 gm of oil .

A small variation in the proportion of water in the acid causes
a considerable variation in the heat evolved and to this extent the
figures recorded by different investigators are not comparable
because “ concentrated sulphuric acid,” as obtained commer¬
cially, is not a substance with any definite per cent of water.

In order partly to eliminate the errors due to variation in water
another determination may be made, using the same amount of
acid but substituting 50 gm of water for the oil. The ratio

Rise in temperat ure with oil
Rise in temperature with water

is known as the “specific temperature reaction.” This number
is not subject to as great variation as is the Maumend number.

These determinations are necessarily very crude* and a con¬
siderable variation may be expected, even under the best of
conditions. Variable radiation is one of the important sources

192

QUANTITATIVE AGRICULTURAL ANALYSIS

of error. These “constants” will be of use chiefly in the detec¬
tion of drying oils, all of which show high values.

Determination of Maumene Number.—Place a beaker, about 5 by 1.5
inches, inside a somewhat larger one and pack the open space between with
wool, asbestos or cotton. Cover the beakers with a piece of cardboard
through which passes a thermometer. Weigh into the inner beaker 50 gm of
oil. Bring concentrated sulphuric acid to the same temperature as that of
the oil, and then add, under a hood, 10 cc of this acid, stirring thoroughly
with the thermometer. When the acid is all in, place the thermometer in the
center of the oil-acid mixture and note the highest point attained by the
mercury. The total rise in temperature is the Maumend number.

Determine also the specific temperature reaction as follows: Clean the
inner beaker and introduce 50 cc of water. Add 10 cc of acid as before
and note the rise in temperature. The Maumend number divided by this
rise is the specific temperature reaction.

The drying oils often develop so much heat that active foaming results.
Such oils should be first diluted with petroleum oils or olive oil and the
proper correction made in the temperature rise.

Qualitative Reactions.—If simple and reliable qualitative
tests were known for all of the oils, it is not likely that the work
outlined in the preceding pages would often be carried out. It
has already been explained that comparatively few such tests
are known because of the similarity in the composition of the
various animal and vegetable oils. Aside from the mere varia¬
tion in the proportion of the various glycerides, free alcohols and
free acids, there are certain constituents of certain oils that will
give color reactions which are characteristic. A few of those
that are reliable will be described. In most cases these tests
should accompany the determination of the analytical constants,
rather than be substituted for them.

Resin Oil.—Polarize the oil in a 200-mm tube. If the oil is too dark
in color for this purpose it may be diluted with petroleum ether and the
proper correction made in the reading. Resin oil has a polarization in
a 200-mm tube of from -{-30° to 40° on the International sugar scale (see
page 130) while other oils read between 4-1° and —1°

Cotton Seed Oil: Halphen Test —Mix carbon disulphide containing about
1 per cent of sulphur in solution, with an equal volume of amyl alcohol. Mix
equal volumes of this reagent and the oil in a test tube and heat in a bath
of boiling, saturated solution of sodium chloride for about an hour. In
the presence of as little as 1 per cent of cotton seed oil a characteristic
red color is produced. Lard and lard oil from animals fed on cotton seed
meal will give a faint reaction for cotton seed oil. The unknown con-

SAPONIFIABLE OILS , FATS AND WAXES

193

stituent which gives the color apparently is assimilated by the animal
without change.

A negative result does not prove the absence of cotton seed oil because
heating the oil for 10 minutes at 250° renders it incapable of giving the color.

Sesame Oil: Baudouin Test. —Dissolve 0.1 gm of finely powdered
sugar in 10 cc of hydrochloric acid (specific gravity 1.20), add 20 cc of the
oil to be tested, shake thoroughly for a minute, and allow to stand. The
aqueous solution separates almost at once. In the presence of even a very
small admixture of sesame oil this is colored crimson. Some olive oils give a
slight pink coloration with this reagent, but they are not hard to distinguish
if comparative tests with sesame oil are made.

Arachis (Peanut) Oil.—The constants of arachis oil are almost
identical with those of olive oil and the difficulties involved in
detecting admixtures of the two are correspondingly great. The
Renard test for arachis oil is based upon the isolation and weigh¬
ing of the small amount (about 5 per cent) of arachidic acid
(C 20 H 40 O 2 ) that occurs as its glyceride in arachis oil. The
method must be carried out with great care or stearic acid
(Ci 8 H 36 0 2 ), whose solubility is not far from that of arachidic acid,
will be obtained and mistaken for the latter. The Renard
method is fully described elsewhere . 1

Soybean Oil.—This oil is increasing very much in importance
as a commercial product, on account of the large increase in
production of soybeans for food products and for feeding to
farm animals. The oil possesses drying properties, having an
iodine absorption number of about 136, which is not far from
that of linseed oil. For this reason soybean oil is used to some
extent as an adulterant of linseed and china-woocl oils. It is
used also very largely in the manufacture of butter substitutes
and of high-grade soaps.

A modification of Settings test 2 has been given by Newhall . 3
This is performed as follows:

Add 5 cc of chloroform to 5 cc of the oil in a test-tube, then add a
few drops of a solution of gum Arabic and 5 cc of a 2-per cent solution
of uranium nitrate or acetate. Shake vigorously to form an emulsion.
Soybean oil will give a characteristic lemon-yellow emulsion, while other
oils will give only faint yellow or brown.

1 Assoc. Off. Agr. Chemists, “ Methods of Analysis,” 253; Mahin, “ Quan¬
titative Analysis,” 2nd Ed., 383.

2 Chem. Abstr ., 7 , 908 (1913). '

3 J. Ind. Eng. Chem., 12 , 1174 (1920).

194

QUANTITATIVE AORH'ULT(‘H U• 1 \ ALYSfS

Newhall states that as little as f> per rent, of soybean oil may
be detected in a mixture, by this test. To the limited extent to
which this test has been used by the auf hors if has been found f o
be reliable but see also a criticism by Hoiinoy and Whifescarvor. 1

Fish and Marine Animal Oils in Mixtures with Vegetable
Oils. —Practically all of these oils have very considerable
“drying” properties, as shown by their iodine absorption
numbers. They are characterized by the presence of glycerides
containing highly unsaturated acids. The peculiar “fishy’’
odor of these oils is probably due to tin* presence of the glycerides
of such acids.

Absorption of bromine by imsaturafed acids or their glycerides
produces bromides of limited solubility and high melting point,
Octobromstearin, obtained from such acids, melts at a higher
temperature (above 200°) and has a lower solubility than hexa-
brom,stearin, obtained by broininating linoleum, and this also
differs in a similar manner from f of rabromsf earin, obtained from
linolin. Therefore the separation of octobromstearin front
brominated fish and blubber oils provides a means for detecting
marine animal oils in the presence of vegetable oils. The test is
performed as follows:

Dissolve in a test-tube about 0 gm of the oil in 111 re uf u mixture of
equal parts of chloroform and glacial acetic acid, Add bromine, drop
by drop, until a slight excess is indicated by the eider, keeping the solution
at about 20°. Allow to stand for 15 minute* or more and (hen phiee the
test-tube in boiling water. If only vegetable oil* are present (be sola firm
will become perfectly clear, while fish oils will remain cloudy or contain a
precipitate of insoluble bromides.

Color Reactions. A large number of qualitative tests, based
upon certain color react ions, have* been proposed and considerably
used in the past for the defection of various oils. Color reactions
produced by adding concentrated nitric or sulphuric acids
may be mentioned. Almost without exception these have l**en
found to be unreliable and they will not tx* described here in
detail.

Hardened Oils. —Under any circumstances the analytical
investigation of oils and fats offers difficulties that are often

1 J- Itul. Eng. Chan., 13, 571 0021).

SAPONIFIABLE OILS , FATS AND WAXES

195

serious. The problems of the analyst are now increased many
fold by the large development of the industry of hydrogenation
of liquid oils.

It has been seen that the most important difference between oils
and fats lies in the larger proportion of olein in the former and of
stearin and palmitin in the latter. Olein differs from stearin
only in that it contains one unsaturated double bond in each
oleic acid residue; the problem of saturating this group by the
insertion of hydrogen, thus forming stearin, is one that has occu¬
pied the attention of chemists for many years. At the present
time the hydrogenation of the cheaper liquid oils ( e.g ., cottonseed,
corn and peanut) to form edible fats is an industry that has at¬
tained large proportions. While this process changes liquid
oils to solid fats, it will also make a corresponding change in any
analytical constants or tests that depend upon the degree of
unsaturation, as well as in the physical properties of the oil.
Linolin, linolenin and glycerides of still less saturated acids will
be changed to stearin. Consequently the halogen absorption
number, drying properties, specific gravity, refractive index and
temperature reactions will be materially altered, as will also the
odor and the general appearance and consistency. It has been
stated that fish oils probably owe their characteristic odor to
glycerides containing highly unsaturated acids, while the some¬
what similar odor of linseed oil is due to glycerides of linolic and
linolenic acids. It is interesting to note that these odors are
entirely lost through hydrogenation and that the fats so produced
are no longer recognizable by tests depending upon unsaturation.
Many special tests for other oils, such as the Halphen reaction
for cottonseed oil and the Renard test for sesame oil, fail in the
hydrogenated product.

From one standpoint it might appear that the determination
of what oils originally formed the raw materials for the a hard¬
ened’ ; product is not a necessary one for the analyst to solve,
since the properties of the finished product are, after all, the ones
that have the chief practical interest for us. Yet it may some¬
times happen that the identity of the original oil or the proof
that a hydrogenating process has been employed may have a
legal or other significance; the development of a series of suitable
tests is therefore very desirable.

Marine animal oils:

198

QUANTITATIVE AGRICULTURAL ANALYSIS

Analytical chemistry has made little progress in this direction.
The application of delicate tests for metals (nickel, palladium,
etc.) that are used as catalyzers in the hardening process, may
sometimes serve to prove that the material is a hardened oil,
rather than a natural fat. Other than this one can say very little.
But the knowledge of the nature of the changes caused by hydro¬
genation should serve to make the analyst more cautious than
he might otherwise be when interpreting the results of his
analytical data on oils or fats of unknown origin.

Interpretation of Analytical Data.—In the discussion of each
so-called “constant,” in the foregoing pages it has been shown
that each determination will be of importance in the identifica¬
tion of a certain limited number of oils, fats or waxes and that
in cases other than these the figures will give only negative
results. The materials for which such figures have proved to be
of significance were given in most of the discussions of these
determinations.

In Table XII the various “constants” for a number of the more
common oils, fats and waxes are collated and the ones that are
of particular value in each case are printed in bold face type.
The iodine number will be of value in practically all cases, since
it is characteristic of classes, even when not of the individuals
of a given class.

Although only one value is given in each case , it should be remem¬
bered that these are merely approximate averages and exact agree¬
ment with experimental results should not be expected. Where
blanks occur in the table this is either because no value is on
record or because the figure is so low as to be practically negligible.

For additional special tests and for a complete description of
the individual oils, consult special treatises on the subject,
such as Lewkowitsch, “Chemical Technology and Analysis of
Oils, Fats and Waxes,” and Fryer and Weston, “Oils, Fats and
Waxes.”

CHAPTER- XI

DAIRY PRODUCTS

The rapid development of the dairy industries in recent years
has made it imperative that dairy products be standardized to a
greater degree than ever before. In most of the states legal
standards have been established for dairy products so that it is
unlawful to offer such food materials for sale unless they conform
to certain rigid requirements as to composition and cleanliness.
The standardizing of dairy products has thus made necessary
the services of many technically trained men, not formerly
required.

MILK

The milk of different mammals varies greatly in composition,
depending to a great extent upon the time required for their
young to reach maturity. This is shown in the following table:

Table XIII.— Average Percentage Composition of Milk of Various

Kinds

Kind of milk

Water

Total

solids

Protein

Fat

Lactose

Ash

Casein

Albumin

Human.

87.6

0.8

1.2

3.7

6.4

0.3

Cow.

87.3

2.9

0.5

3.7

4.9

0.7

Goat.

86.9

2.9

0.9

4.0

4.6

0.8

Sheep.

83.6

4.2

1.0

6.2

4.7

0.9

Buffalo (Indian).

82.2

4.3

0.4

7.5

4.7

0.8

Camel.

87.1

3.5

0.4

2.9

5.4

0.7

Reindeer.

67.2

8.4

1.5

17.0’

2.8

1.4

Horse.

90.6

9 ‘

1.3

0.7

1.1

5.8

0.3

Swine.

84.0

! 7.23

4.5

3.1

1.0

Whale.

48.6

.11

;43.6

0.4

199

200

QUANTITATIVE AGRICULTURAL ANALYSIS

It is thus seen that the milk of most mammals lias been
analyzed and its composition determined but, for practical
purposes, the analyst rarely has to do with any other than cow's
milk and human milk. The analysis of cow’s milk may be made
for purely scientific purposes as, for instance, the determination
of the relation between the composition of milk and the breed
of animal, the season of the year or the rations upon which the
animal is fed, or the determination of the changes that occur in
composition during the period of storage, and other similar
questions. The analysis may also be made for purposes of legal
control to detect sophistication. The analysis of woman’s
milk is usually made for hygienic purposes, in order to provide
a basis for modification of the mother’s diet, in cases where the
infant is not thriving.

The percentage composition of milk varies rather widely
although the same substances are found in practically all milk
from a given species of animal. It is therefore not possible to
fix, by legal enactment, the exact composition of milk that is to
become an article of commerce, but certain minimum figures
are usually established by law and any milk containing a con¬
stituent in quantity below the legal minimum is considered to be
adulterated.

Milk is a very complex fluid, secreted through the alveoli cells
of the udder. The fat is present as a suspension (emulsion) of
very small globules. The milk sugar and inorganic salts are
present in true solution while the proteins, casein, albumin,
globulin and fibrin, are in colloidal solution. According to Bab¬
cock, the composition of cow’s milk is as follows:

DAIRY PRODUCTS

201

x>^ n -+- Glycerides of ]

a mi in insoluble and V3.3

Stearin ...

x , . non-volatile

Myristm ., I

qaiHq J

Fat.3.6 • Butin (trace)

® Utyr | n 1 Glycerides of '

aprom soluble and [0.3 ,

Caprylin (trace) .... .,

. volatile acids

[Caprin (trace)

[Casein. 3.0

Albumin. 0.6 Containing j

Lactoglobulin , nitrogen pro- [ 3.8

Galactin 0.2 teida J

Fibrin (trace)

Lactose. 4.5

Citric acid. 0.1

Milk Potassium oxide. 0.175'

■serum.. 96.4 Sodium oxide. 0.070

Calcium oxide. 0.140

Magnesium oxide. 0.017 . , . _

Ferric oxide. 0.001 ,Afi **** 0

Sulphur trioxide. 0.027

Phosphorus pentoxide.. 0.170

Chlorine. 0.100 .

Water.

Solids not
1 fat.

Ash... 0.7

100.0

Preparation of Sample.—When milk is allowed to stand the fat
rises slowly to the top. Before the analysis is started it is
therefore necessary to mix the milk thoroughly by pouring from
one vessel to another several times, but without shaking vigor¬
ously as air would thus be incorporated with the liquid anid there
would be also a coalescence of fat globules.

The following table will serve to indicate how far each deter¬
mination must be carried before it can be stopped with safety:

Table XIV.— Progress of Determinations

Determination

Stage after which work may be interrupted

Specific gravity.

Cannot be delayed

Acidity.

Cannot be delayed

Total solids.

Evaporation of sample

Ash.

Weighing sample

Total nitrogen.

Addition of sulphuric acid

Casein and albumin....

Filtration of proteins and addition of sulphuric acid

Lactose.

Addition of mercuric iodide or nitrate solution

Fat, paper coil.

Drying milk on paper coil

Rose-Gottlieb.

Extraction of the fat

Babcock.

Addition of sulphuric acid

202

QUANTITATIVE AGRICULTURAL ANALYSIS

It may sometimes be impossible to begin the analysis before
bacterial action begins. In such a case add formaldehyde at
the rate of 1 cc of the 40-per cent solution to 2 liters of milk.

Specific Gravity.—This determination is usually made with a
lactometer, which is a hydrometer of a special form. However,
it can be determined also by a Westphal balance or a picnom-
eter. For a discussion of the use of these instruments, see
pages 96 to 100, Part II.

Added Water.—As a means for detecting adulteration the
specific gravity determination alone is of little value. The spe¬
cific gravity of butter fat is about 0.93 and of milk solids other
than fat is 1.5, while that of whole milk is 1.030 to 1.034. If
water is added the specific gravity is lowered but if milk is
skimmed the specific gravity is raised because the lighter
portion has been removed. Therefore fat could be removed
and water added in such a way as to keep the specific gravity
unchanged.

A more certain method for the detection of added water is in
the examination of milk serum, from which all of the fat and
proteins have been removed.

Determination of Specific Gravity.—A sample of fresh milk is thoroughly
mixed by pouring from one vessel to another several times, avoiding violent
agitation. Determine the specific gravity at 20° within 2 minutes after
mixing.

Detection of Added Water.—The ash and milk sugar are the least variable
constituents of milk and they afford a suitable basis for the detection of
adulteration. A clear serum may be obtained by precipitating the proteins
with acetic acid or copper sulphate or by spontaneous souring, and filtering.
Examine the filtrate for ash, also for other dissolved solids by means of a
dipping refractometer. This instrument is described on page 118, Part II.

Examination of Acetic Serum: (a) Zeiss Dipping (. Immersion) Refractom¬
eter Reading .—To 100 cc of milk at a temperature of 20° add 2 cc of 25-per
cent acetic acid (specific gravity 1.035) in a beaker and heat the mixture,
covered by a watch glass, by immersing in a water bath at 70° for 20 minutes.
Place the beaker in ice water for 10 minutes and separate the curd by filtering
through a 12.5-cm folded filter. Transfer about 35 cc of the serum to one
of the beakers that accompanies the temperature control bath used in
connection with the Zeiss dipping refractometer or fill the metal cup that is
attachable to the instrument; take the refractometer reading at 20°, using
a thermometer graduated to tenths of degrees. A reading below 39 indi¬
cates added water. If the reading is between 39 and 40 the addition of water
is not certain but is to be suspected.

DAIRY PRODUCTS

203

(Jb) Ash. —Transfer 25 cc of the serum to a flat bottomed platinum dish
and evaporate to dryness on a steam bath, then heat over a low flame until
the solids are thoroughly charred. Place the dish in a muffle furnace
and ignite to a white ash at a temperature not higher than 500°, cool and
weigh. Express the results as grams per 100 cc. Multiply by the factor
1.02 to correct for the dilution by addition of acetic acid. The result
is the ash on the undiluted sour serum. An ash content below 0.715 gm
per 100 cc indicates added water.

Examination of Sour Serum: (a) Zeiss Dipping Refractometer Reading .—
Allow the milk to sour spontaneously, filter and determine the dipping
refractometer reading of the clear serum at 20°. A reading below 38.3
indicates added water.

(6) Ash. —Determine the ash in 25 cc of the sour serum, using the method
as directed for ash of acetic serum. Ash lower than 0.730 gm per 100 cc
indicates added water.

Examination of Copper Serum: Zeiss Dipping Refractometer Reading .—
Use a solution of copper sulphate containing 72.5 gm per liter, adjusted if
necessary to read 36 at 20° on the scale of the dipping refractometer. To
one volume of this solution add four volumes of milk. Shake well and filter.
Determine the refractometer reading of the clear serum at 20°. A reading
below 36 indicates added water.

Acidity of Milk.—Acidity of milk is due to acid phosphates
and lactic acid, the latter being produced by bacterial action
upon milk sugar. This is the “souring” of milk.

Determination of Acidity.—Place 20 cc of milk of known specific gravity
in a 100-cc porcelain casserole and add tenth-normal (to phenolphthalein)
sodium hydroxide from a burette, using phenolphthalein as an indicator,
until a pink color appears and remains for 1 minute. Calculate the per cent
of lactic acid, HC 3 H 6 0 3 , in the milk.

Total Solids.—In order to dry the solids rapidly without
decomposing them it is desirable to use a weighed flat porcelain
or aluminium dish in which has been placed enough sand or
asbestos fiber to cover the bottom. The sand or asbestos
increases the drying surface and hinders the formation of a scum,
which would interfere with the evaporation of the liquid beneath.
The solid thus formed should be nearly white except as it may
be colored by sand. If there is any considerable browning or
blackening it is probable that the milk sugar has been partly
caramelized and the resulting loss would therefore not indicate
correctly the evaporated water.

•ji-j ! . • , :;.\i /i i: .u,i:n-fUTiiM. a.\alvsis

Determination cf Total Solids—Use a Hat porcelain or aluminium dish,

.., i, } , ? r , .md :uld 10 to 15 grn of white sand. Heat the dish

... • fjiiht .it 100\ then add about 5 gin of milk, cover and
r , u j-:!k to the weighed ribband sand and calculate the

0 * r ’ - 1 . vitio gravity. Dry at 100° until the weight is constant.

i , < , a; i; d.-.-i-, r and w* -igh rapidly. Calculate the per cent of solids.

Ash.-—'Hr* ash does not represent all of the inorganic constitu-
( f *j;ilk in their original combinations because certain
cJianiro- take place during the burning of the organic matter.
The a^l; Cfiuidd not be heated to a temperature higher than
a* thr -hloride- of sodium and potassium might be vola-
tilizvb a! a higher temperature. Nitric acid may be added to
aid in oxidizing the organic matter.

Determination of Ash.—Weigh accurately a flat platinum or porcelain
ti 'h ! : i i g 25 ?** HO ci*. Add 20 (*c of milk of known specific gravity or
<>M a -ir. H i wtdiihT l*y direct weighing. In the latter case the dish must be
c. >v*Trd Hef. >r** cif-d after adding the milk. Add five drops of concentrated
idtr:.' a ad and fva]n >rate to dryness on the steam hath, then ignite at a
teniP*ratuiv ;ust below redness until white. Cool in a desiccator and
v» ngh. Calculate the per cent of ash.

Fat.— The fat contained in milk is usually given more con¬
sideration than any other constituent, since milk is bought and
sold largely on the basis of its fat content. To some extent this
i> unfortunate as it has tended to underrate the other constitu¬
ents, winch may be of equal or greater value as food.

‘Taper Coil 1 ’ Method.—In this method the milk is absorbed
on porous fat-free paper and dried. In this condition the fat
i> easily ami quickly extracted as most of it is on the surface of
the paper and it is thus somewhat separated from the proteins
present. Ether is generally used to extract the fat. This must
te anhydrous in order to avoid dissolving some of the milk sugar
present. Petroleum ether is sometimes used but it has the
disadvantage of dissolving fats more slowly than ordinary ether.
Iho tat extractor, shown in Fig. 41, page 146, is used for the
determination. If other forms of extractors employing cork
.stoppers are used the corks must be made free from ether-soluble
waxes and resins by previous extraction with ether and they
must tit tightly enough to prevent the escape of any considerable
a mourn of other.

20-5

Determi natl0n

©f Fat: I' •/- f .V- !■' - s
extracting i u = . iV y «.3t.-r p.ipi-r \wtL» H;< r, - r -

pap er as 4 d ;t ; iiii< *i ll; till nmrkc! h'T ?L> t>-.r; - -■■
().5 cm w i % lr ni; Kma. Pim :!.*■ -? 7 *-:p

paper 012 ; i*jr:m surtax* and ny >-f a

pipette d asst ribut* 1 5 iv«»i ?h«- n.iik vwr tin* pap* r.
The weipri^ , ,f tin* sample i> d* 1 * Tinned
specific gi» av jty :ihi { tp,» Ht>11 rh»» pap* r

so that It, will go into tho extractinriMpp.ar.i? a-,
bind with a tine wire and plan* on a u atrh zia»
in an o\-*en. Dry’ at iOtV fur about 2 h^.r-.
Meanwhile the fat tul m* connect oil with tia
extractor of Fig. 4i i> dried and weigh-d. Ti.r
dried an< j milk are placed in the extract;* n

tube (c) and ether is added until it siphons *<\<r
automatically. Heat t hi * apparatus hy steam or
electricity. Continue the extract ion f«»r at lenst
2 hours. Kinaliy disconnect tin* apparatus ju>t
before the ether is ready to siphon over and
remove the extraction tube containing the pap* r.
Evaporatrc* the ether remaining in the lower cup
(a) on tine steam bath, finally coinplet.ini: the dry¬
ing in tile? oven at ICO*. Weigh the fat and cup.
after cooling in a desiccator, and calculate the p« r
cent of frit present. See that no flames are near
when etli*pr is being handled.

* UP

, 2>-v-

! -d * r “
l > „ >r e3tl s

Rose — Gottlieb Method.—This method,
with some slight modifications, is being
widely used at present for the determina¬
tion of fat in whole milk, skim milk, milk
powders, and condensed or evaporated
milk. [Before fat can be separated from
milk it is necessary to get the casein in
solution or semi-solution. This is accom¬
plished in this method by adding ethyl
alcohol and dissolving the casein in ammo¬
nium hydroxide. The method is particu¬
larly applicable to powdered, condensed
and eva, porated milk because it is possible
that is mechanically enclosed in the dried casein.

-• i -_

Frj.

thus

R hrig tube.

to extract fat

I) et enmLirLation of Fat: Rose-Got Hub Method .—Place 10 cc of milk; in sl
Rob rig •fcxx'be (Fig. 47) or other similar tube and add 2 ec (2.5 cc if milk; is
sour) of concentrated ammonium hydroxide. Mix thoroughly by inversion

of the stoppered tube. Add 10 cc of 95-per cent alcohol and mix again.
Add 25 ft* of ethyl ether, stopper the tube and shake vigorously for 30
seconds, then add 25 cc of petroleum ether (distilled below 60°) and stopper
ami shake again for 30 seconds. Let stand until the bubbles of air have
disappeared from the lower layer. Both layers should be clear and free
from suspended particles. Draw off most of the upper layer of ether-fat
solution by opening the stop cock and tipping slightly to make the separation
more complete, but without removing any of the lower layer. The fat
solution is run through a small (about 5 cm), dry filter, into a dried and
weighed fat flask. Repeat the extraction, using 15 cc of each ether as
before. Wash the tip of the outlet tube, the funnel and the filter with a
small amount of the ether mixture, then evaporate the ether from the fat
and ether mixture.

Dry the flask at 100°, cool and weigh. Calculate the per cent of fat in
the sample.

Babcock Method.—This method is rapid and convenient for
general dairy control testing. The test is based upon the fact
that concentrated sulphuric acid will dissolve all proteins in
milk or cream and thus enable the fat to separate when whirled
rapidly in a centrifuge. When the acid is added to the milk,
the casein is first precipitated and then dissolved in the excess of
acid. The solution darkens because of the charring of the milk
sugar, due to the heat of reaction.

It is important that the acid should have a specific gravity
of 1.S2 to 1.83. If the acid is too dilute the fat will have a white
appearance with gray particles beneath it, while if too concen¬
trated the fat will be dark colored with black charred particles
beneath. The temperature of the fat should be about 60°
(140° F.) when the fat reading is made. Appreciable errors will
result from volume changes if the temperature of reading is
allowed to vary more than 10° (18° F.) either way. The fat
should have a clear, golden yellow color and it should be separated
clearly from the chocolate-colored acid solution beneath.

Standard Babcock Test Bottles. 1 —The standard Babcock test
bottles for milk and cream are as follows:

1 . Eight-per cent, 18-gram, 6 -in. Milk Test Bottle .—The total
per cent graduation is 8. The total height of the bottle is 150
to 165 mm. The capacity of the bulb up to the junction with
the neck is not less than 45 cc. The graduated portion of the
neck has a length of not less than 63.5 mm, and the neck i?

1 Assoc. Off. Agr. Chemists, “Methods of Analysis,” 227 (1919).

DAIRY PKUUITT.'

cylindrical for at least 9 nnn below the lowest and above the
highest graduation marks. The graduations represent whole
per cents, halves and tenths of a per cent.

2. Fifty-per cent y 9 -gram, ti-in. Cream 7V>/ Bottle. —The total
per cent graduation is 50. The total height of the bottle is 150

Fig. 4S.—Test bottles for fat in (a) cream, *&» milk and (c) skim-milk.

to 165 mm. The capacity of the bulb up to the junction with the
neck is not less than 45 cc. The graduated portion of the neck
has a length of not less than 63.5 mm and the neck is cylindrical
for at least 9 mm below the lowest and above the highest gradua¬
tion marks. The graduations represent five per cents, whole
per cents and halves of a per cent.

3. Fifty-per cent , 9-gram, 9-in. Cream Text Bottle .—Same as
(2) except that the total height of the bottle is 210 to 225 nnn.

Certain forms of test bottles are illustrated in Fig. 4$.

20 S

QUANTITATIVE AGRICULTURAL ANALYSIS

Standard Babcock Milk Pipette—This pipette is graduated
to deliver 17.6 cc of water at 20° in 5 to 8 seconds.

Calibration— The official method for calibrating Babcock
test bottles is to fill the dry bottle to the zero mark with pure
mercury at 20°, weigh, fill to the highest mark and reweigh, cal¬
culating the bulb and stem capacities on the basis of 13.5471
gm of dry mercury for eadh cubic centimeter at 20°.

It is difficult to see what advantage this possesses over the
method of calibrating by weighing water at 20° especially since
the Babcock bottle filled with mercury must weigh more than
600 gm. Accurate weighing of such a quantity would require a
special balance, as sensitive as the analytical balance and having
large capacity’.

Milk pipettes and graduates are calibrated according to the
official method by measuring in a burette the quantity of water
delivered by the instrument at 20°. Unless care has been exer¬
cised in wetting the inner surface of the burette, using the
standard method by which the burette was calibrated, this
method will be subject to considerable error since all burettes
are graduated for delivery and not for capacity. A better
method for calibrating pipettes is described on page 46.

Determination of Fat: Babcock Method .—Fill a 17.6-cc pipette to the
mark with mixed milk sample and deliver to the graduated test bottle.
Add to this 17.5 cc of sulphuric acid (specific gravity 1.82 to 1.83), pouring
it in slowly so as to form a layer beneath the milk. Prepare an even number
of bottles, up to the capacity of the centrifuge. After the acid has been added
to all the bottles, mix the acid and milk by giving it a gentle rotary motion,
being careful to keep the liquid from collecting on the neck of the bottle.
Place the bottles in the centrifuge in such a way that they will be counter¬
balanced and rotate for 4 minutes at the required speed for the machine
used. This is about 1,000 revolutions per minute for a wheel 10 inches in
diameter or 700 for a 24-inch wheel. Add hot water to each bottle until it is
filled to the neck and whirl 1 minute longer. Again add enough boiling
water to bring the fat column into the graduated portion of the neck and
whirl for another minute. Place the bottles in a glass vessel which is filled
with water at a temperature of 57° to 60°. The water should surround the
neck of the bottle to a point above the fat layer. After 1 minute measure
the fat column from the top of the upper meniscus to the plane of separation
between fat and aqueous solution, using a pair of dividers if considered
desirable.

DAIRY PRODUCTS

209

Proteins and Total Nitrogen. —Of the nitrogenous materials
in milk, the principal protein, casein, makes up about 3 per cent
of the total 3.8 per cent usually present. Globulin, albumin and
fibrin comprise the other 0.8 per cent. Casein and albumin
together are at least 95 per cent of the total protein content and
analysis shows these two proteins to contain slightly less than
15.7 per cent nitrogen. The factor to convert the per cent of
total nitrogen to protein is thus 6.38.

Either the Kjeldahl or the Gunning method may be used for
the nitrogen determination. These are discussed in connection
with the analysis of feeds, page 149.

Determination of Total Nitrogen.—Measure out 5 cc of well mixed milk
of which the specific gravity has been determined, using a pipette and
delivering into a 500-cc Kjeldahl digestion flask. Determine the per cent of
nitrogen by the Kjeldahl or Gunning method, described on pages 151 and
154. Multiply the nitrogen per cent by 6.38 and report as total nitrogenous
material.

Formal Titration for Total Proteins. —Proteins and their
derivatives are related to certain amino acids. This is illus¬
trated by the simple dipeptide, glycylglycine, which is derived
from two molecules of the amino acid glycine, as follows:

2 NH 2 -CH 2 *COOH -+ NH 2 CH 2 -CO-NH*CH 2 COOH + h 2 o.

Glycine Glycylglycine

These substances are amphoteric, possessing basic properties on
account of the amino group (NH 2 ) and acid properties through
the carboxyl. Proteins, as well as their decomposition products,
will react with formaldehyde, forming derivatives of the amino
acids which have lost their basic character through substitution
in the amino group:

NH 2 -CH 2 -CO-NH-CH,-COOH + 2HCHO —>2CH 2 N'CH 2 *COOH

Glycylglycine Formaldehyde

+ h 2 o.

Thus the proteins of milk are neutral to phenolphthalein but upon
addition of formaldehyde they become decidedly acid.

The equations given above are presented merely to show the
supposed general nature of certain changes. Calculations of the
results of titrations cannot be based upon these equations because
the true formulas of the proteins are not known.

210

QUANTITATIVE agricultural analysis

Determination of Total Protein: Formaldehyde MethodA —Weigh out
20 gm of milk and place in a 200-cc beaker. Add 1 cc of phenolphthalein,
then add from a burette twentieth-normal sodium hydroxide (standardized
using phenolphthalein) until a distinct pink color appears. This neutralizes
any lactic acid present in the milk. Next add 10 cc of formaldehyde which
is neutral (a single drop of twentieth-normal base should produce a distinct
pink color in 10 cc) to phenolphthalein. Stir thoroughly and add twentieth-
normal sodium hydroxide until a faint pink color remains after mixing.
Note the total volume of basic solution added after introducing the
formaldehyde and from this calculate the per cent of total protein present.
One cubic centimeter of twentieth-normal base has been found by experiment
to he equivalent to 0.0864 gm of milk proteins.

Casein. —Casein exists in milk in a colloidal condition. When
a dilute acid or an alum solution is added casein is flocculated.
To effect complete separation the acid must be very dilute
because casein and other proteins are somewhat soluble in a
small excess. The separation is most nearly complete at a
temperature of 40°.

Determination of Casein: Acetic Acid Method .—To 10 cc of milk of
known specific gravity, add 90 cc of water at a temperature of 40° to 42°,
stir well, add 1.5 cc of 10-per cent acetic acid and allow to stand until a
fiocculent precipitate settles out and a clear liquid is obtained. This should
not take more than 5 minutes. Filter, wash three times with cold water and
add the washings to the clear filtrate. Save the filtrate and washings for
the albumin determination. Place the paper and precipitate in a Kjeldahl
flask and determine nitrogen by the Kjeldahl or Gunning method as described
for total nitrogen. Use the factor 6.38 to convert the per cent of nitrogen
to that of casein.

Determination of Casein: Alum Method .—To 10 cc of milk add 50 cc of
water at a temperature of 40°. Then add 2 cc of a solution of potassium
alum (saturated by heating 25 gm of crystals with 100 cc of water, until
dissolved, then cooling to 40°) and stir. A fiocculent precipitate forms and
it should settle rapidly. Let the precipitate settle for 5 minutes or more
and then filter and wash with cold w r ater. Save the filtrate and washings
for the albumin determination. The nitrogen is determined in the residue
by the Kjeldahl or the Gunning method and multiplied by 6.38 to obtain the
equivalent of casein.

Casein by Hart’s Method . 2 —The methods described above
are rather long and tedious. The Hart volumetric method is
based upon the fact that the amphoteric casein has properties of

1 Henriques and Sorensen, Z. physiol. Chem. } 64, 120 (1909).

3 Wis. Exp. Sta. Res. Bull , 10 (1910).

i>au;y runwrTs

211

an acid, as explained on page 209, and combines with a l^e i* 1
iairly constant proportions. If an excess of Ium n^vd T °
dissolve the casein, the uneombined base can be determined
titration. It has been found that i ec of tenth-normal poT£3LJ»—
snim Hydroxide is equivalent to 0.10S gin of easein if phenol—
phthalein is used as indicator. Hence, when 10 > gin of milk: is
used, each cubic centimeter of tenth-normal base required wdll
be equivalent to 1 per cent of casein. The specific gravity of
average milk being 1.032, 10.5 cc may be measured with sufficient
accuracy for most work.

I>eterxnination of Casein: Hart's M dhoti —Place 10.5 cc of milk in a
200-ce Erl enm ever flask containing 75 cc of distilled water which has
freed from carbon dioxide by boiling, then cooled to 20'. Add 1,5 ec of
10-per cent acetic acid, warm to about 40" and tiller off the casein throujg'H a
10-cm filter. Wash the paper and precipitate thoroughly, using about
250 cc of cold water. Return the paper and contents to the Erif'nineyer
flask, add 75 cc of carbon dioxide-free water and a drop of phenolpkth aIcin-
To this add 10 cc of tenth-normal potassium hydroxide. Stopper carefully
and shake vigorously. When solution of the protein is complete, titrate to
the disappearance of the red color, using tenth-normal acid. It is necessary
to run. a blank as this will usually require 0.2 ec or more of the tenth-normal
potassium hydroxide. The number of cubic centimeters of base used in the
titration, thus corrected, will express the per cent of easein.

Albxxmin.—Albumin is soluble in the milk serum and is coa,§zrti—
lable by heating to 100°. It is necessary, however, first to
neutralize part of the acetic acid, if this was added to precipitate
casein.

D eterminatioii of Albumin.—Neutralize the filtrate from the casein deter¬
mination (acetic acid method) with tenth-normal sodium hydroxide' or
potassium hydroxide, using phenolphthalein, or use the filtrate from the
alum precipitation, of casein without neutralization. Add 0.3 cc of lO-per
cent acetic acid and heat in a boiling-water bath until the precipitate
becomes settled. Filter, wash with cold water and determine the nitrogen
and albumin as in the casein determination, using the same factor.

A comparison of the results obtained by various methods Tor
determining milk proteins has been made by Spitzer. 1 who
conclizded that where speed and convenience are important the
formal titration is to be preferred.

1 PVoc. Ind. Acad . Sci., p. 173 (1915).

212 QUANTITATIVE AGRICULTURAL ANALYSIS

Lactose. —This sugar is the only carbohydrate occun ins ih
appreciable Quantity in milk. It is not as sweet as cane sugar
and it is not fermentable by yeast. It readily reduces Fehling’s
solution (a basic solution of copper sulphate and a tartrate),
forming cuprous oxide (Cu 2 0) and use is made of this fact in its
quantitative determination. It is optically active and. this
affords another method for its quantitative determination.

It is necessary to remove the proteins and fat from milk
before the lactose can be determined by Fehling’s solution.
This is one of the objections to this method but if the milk can
thus be made reasonably free from other reducing agents the
method is capable of yielding fairly accurate results.

If the cuprous oxide formed were to be weighed directly there
would be an error due to inclusion of organic impurities in the
precipitate. This error can be lessened by heating the cuprous
oxide in a muffle furnace for 20 minutes to a dull redness. This
converts the cuprous oxide to cupric oxide (CuO), which can. be
weighed free from organic impurities, the per cent of sugar being
then calculated. A better way, however, is to dissolve the
cuprous oxide from the filter with dilute nitric acid and to
determine the copper electrolytically or volumetrically. All of
these methods are discussed in connection with feed analysis,
pages 157 and 158.

Determination of Lactose: Reduction Method .—Pipette 25 cc of well
mixed milk into a 500-cc volumetric flask. Add 350 cc of water, 10 cc of
Fehling’s copper sulphate solution (page 158) and 44 cc of tenth-normal
sodium hydroxide or an equivalent volume of a solution of any other nor¬
mality. Colloidal cupric hydroxide flocculates, carrying down fat and pro¬
teins. Copper will be present in very slight excess. Make the volume up to
500 cc and mix thoroughly. Although the apparent volume occupied by the
precipitate is considerable, its actual volume is relatively small and an
approximate correction is made as noted below. Filter through a dry filter
and use 50-cc portions in making the lactose determination. It is necessary
to follow directions carefully as the reactions taking place are modified by
variation in time of heating or in the concentrations of the solutions.

Into a 400-cc Pyrex beaker, pipette 50 cc of the clarified milk serum and
25 cc each of the two Fehling’s solutions prepared as described on page 158.
Heat at such a rate that the boiling begins in about 4 minutes and continues
for exactly 2 minutes. Keep the beaker covered while heating. Filter off
the cuprous oxide through a Gooch crucible. Wash five or six times with
hot water. Dissolve in a warm mixture of 2 cc of concentrated nitric acid

DAIRY DRtJin i JS

and 2 ec of water, wash the solution through with hot water
an< 3- determine copper by any of the methods used in feed
an *dysis, described on pages 159 to 163.

Optical Methods.—The ability of carbohydrates
containing one or more asymmetric carbon atoms to
rotate the plane of polarization, of polarized light
affords the basis for an important method for their
determination. The proteins of milk also are slightly
optically active, hence they must be removed before
lactose can be determined.

Tine subject of polarimetrv is discussed on pages 121

137, Part II. This should be reread before starting
tho determination of lactose. The instrument de¬
signed especially for sugar determinations is called a
sa,echarimeter. Its graduations read directly in per
cent of sugar when a definite specified weight the
“normal weight)” is contained in 100 ec and when
tho polarization is made in a 200-mm tube. The
following determination is based upon the use of an
instrument bearing the International scale. See
page 130, et seq.)

^Protein Precipitation. —By treatment of milk with
an acid solution of mercuric iodide the proteins are
com bined with the mercury and flocculation results.
If the solution is then diluted to a definite volume
without previous filtration the solids present cause a
volume error unless a correction is applied. It has
bee;rx found that a close approximation may be made
by- deducting 2.6 cc for the volume of precipitate
obtained from the sample as specified below, the
dilution being accomplished in a flask graduated
to contain 102.6 cc. If a flask graduated in this
manner is not at hand, prepare one as follows:
Fill a, 100-cc volumetric flask exactly to the mark
with distilled water. From a burette add 2.6 cc
more and mark the position of the bottom of the
meniscus with a strip of label. Mark permanently,
if desired, by the method described on page 45.
Part I.

fcS'

* 81 " “fT'I
/nr .ado®* 1

ae-stru ■

teSzc .

I k.. 49.—
Milk pipette
for laetose
determina¬
tion.

214

QUANTITATIVE AGRICULTURAL ANALYSIS

A still more accurate method involves the double dilution,
discussed on page 133.

The normal weight for lactose, 32.90 gm (see page 131), is too
small a quantity of milk for convenient accurate determinations
and it is customary to use twice this amount or 65.80 gm. In
order that the sample of milk may be measured instead of weighed
the following table may be used and a special pipette like Fig.
49 will be found convenient.

Table XV.—Volume of Milk for Lactose Determination

Specific gravity of milk

Volume of milk (cc) for a lactose
double normal weight (International
scale)

1.024

64.26

1.025

64.20

1.026

64.13

1.027

64.07

1.028

64.01

1.029

63.94

1.030

63.88

1.031

63.82

1.032

63.76

1.033

63.70

1.034

63.64

1.035

63.58

1.036

63.51

Determination of Lactose.—Prepare acid mercuric iodide solution as
follows:

Dissolve 33.2 gm of potassium iodide, 13.5 gm of mercuric chloride and
20 cc of glacial acetic acid in 640 cc of water.

Determine the specific gravity of milk by means of a sensitive hydrometer
or a picnometer. Refer to the table and measure, at the temperature at
which the specific gravity was taken, the quantity of milk indicated in the
table above, the sample having been mixed thoroughly immediately before
making both measurements. The milk is run into a volumetric flask,
graduated at 102.6 cc. Add 30 cc of acid mercuric iodide solution, dilute
to the mark on the flask, mix well and allow the precipitate to settle. Filter
through a dry filter, rejecting the first 25 cc of the filtrate and receiving the
remainder in a dry flask. Polarize in a 200-mm tube, having the solution at
a temperature of 20°. The reading on the sugar scale is to be divided by

h.uin t V

I'M !\\i»v T lit - li.»riii:i! ^*^h‘ ( ’f s..!;jp> o ’ - a •

the pc‘r (LM-nt of lart.*so in tin- milk

^Microscopic Examination of Milk.— H r > - - , * :

variation in the size of fat globulo in U\r milk
cows of the same breed or of different bri-v.N.
between Jersey and Holstein animals. An». paM* u ri :^at:-=n
modifies the size and grouping of fat globules.. Extensive stu<t:v*
w ere tiiade by Woll 1 on the number and size of fat jr o:;E>
modified by the period of lactation, and by the age an-; r<.*eu of
the cow, He found that the period of lactation was the mo- t
important cause of variation — t hat the average mu n ‘ **r * »t gh »! >uies
in 0*0001 cmm for all cows is 13S, at the loginning oi tho lactation
period, and at its end 367. The average “relative diameters*'
(per cent of fat divided hv the number of globules in t.'MWl
cmm) of fat globules was found to be 290, 217 and 177 tor the
Jersey, Guernsey and Shorthorn, respectively.

De -termination of Number of Fat Globules. -—Dilute 10 c? oi a samp.*’
of fresh milk to 500 ce and mix well. Prepart' six capillary tufas i f about
0.1-rrLrrx inside diameter by heating o-mm tubing and pullma it to a thread.
Cut into pieces about 3 cm long. Dip the end of each capillary tub* m?.»
the dL ilia ted milk (recently mixed) and when hik'd seal both ci.ds * I tic
tubes by dipping them into vaseline. Place one of the tubes on a -a C 1
upon which has been placed a drop of glycerine and determine the aurme
inside diameter by placing it in the field of a microscope which contain* a
micrometer eye piece having 0.01-nim divisions. After about. 20 nun lit s
make a count of the number of fat globules contained in a section of the t .*oe
equivalent to 20 or 30 divisions of the scale. Repeat the mea^uren^-Tvs
and. count, using another capillary tube. From the diameter of o.e tuce
and -tine length of the section in which the count was made calculate the
number of fat globules in 1 cubic millimeter of undiluted milk. N te tne
form of the fat globules in this and in a portion of the same sample pasteur¬
ized a/t 140° F.

In. -the experiment just described, the function of the glycerine
is to cover the capillary tube with a fluid medium having neariv
the same index of refraction as that of the glass, thus avoiding
the magnifying effect of the curvature of the tube, as a>
preve rating the apparent distortion of form of fat globule.

Fonoaaldehyde is very efficient as a preservative and when
present in so small an amount as 1 part in 20,000, it will extend
the time of milk preservation at least 24 hours at 15°. Its use

i Exp . Sta . *4nn. Rep. 11 (1S94).

216

QUANTITATIVE AGRICULTURAL ANALYSIS

in commercial milk is usually forbidden, as is that of most other
preservatives.

Test for Formaldehyde. —In a porcelain dish mix 5 cc of milk with 10
cc of concentrated hydrochloric acid, containing 0.2 gm of ferric chloride
per liter. Heat cautiously nearly to boiling and keep near the boiling point
for 1 minute. A violet color indicates the presence of formaldehyde.

Test for Borates. —Make 25 cc of milk slightly basic with lime water and
evaporate to dryness in a porcelain dish over the steam bath. Char the
residue in the dish and when cool add 15 cc of hot water, then boil. Add
hydrochloric acid drop by drop until neutral to litmus, then add an excess
of about ten drops. Filter and evaporate to dryness on a steam bath.
Immerse turmeric paper in the solution while the evaporation is taking
place. If borax or boric acid is present, the turmeric paper will turn cherry
red when dry and it will change to a bluish green when moistened with
ammonium hydroxide.

Cane Sugar. —Cane sugar is occasionally present in milk
which has been thickened with calcium saccharate or which has
been mixed with sweetened condensed milk.

Test for Cane Sugar. —Mix 10 cc of milk in a test-tube with 0.5 gm of
ammonium molybdate and 10 cc of 3-per cent hydrochloric acid. Make
a blank test using milk of known purity. Place the tubes in a water bath
and gradually raise the temperature to 80°. A blue color will develop
in normal milk but if sucrose is present the milk remains unchanged in
color. The test is quite delicate as even 1 gm in a liter may be detected by
the reaction.

Heated Milk.—One method for the detection of heated
milk is based upon the presence in raw milk of an enzyme which,
in the presence of hydrogen peroxide, is capable of producing
color changes with certain organic substances, the enzyme
probably acting as a catalyzer.

Bacteria in normal fresh milk will change methylene blue to a
colorless compound in about 20 minutes. But when milk has
been heated these bacteria are present in greatly diminished
numbers and are no longer capable of decolorizing the solution.
This furnishes another test for heated milk, since by this reaction
one may detect milk which has been pasteurized at 65° and held
at that temperature for 30 minutes, or at 70° for 10 minutes.

Test for Heated Milk. —( a) To 10 cc of milk add about three drops of a
freshly prepared 2-per cent solution of p-phenylenediamine hydrochloride
and a few drops of hydrogen peroxide. Shake well. Milk which has not
been heated will give a blue color.

DAIRY PRODUCTS

217

( b ) Prepare a test solution of methylene blue by mixing 5 cc of saturated
alcoholic solution with 5 cc of 40-per cent formaldehyde and 190 cc of water.
Add 1 cc of this solution to 20 cc of milk in a test-tube, and place the tube
in a water bath at 45°. Cover the liquid with a layer of paraffine oil to
exclude the air. Repeat the test on a heated sample of milk. It will take
about 20 minutes for the unheated milk to decolorize while the heated sample
will require considerably more time.

Condensed Milk.—“Condensed’’ milk is made by evaporating
either whole or skimmed milk under reduced pressure and adding
cane sugar. “Evaporated” milk does not contain cane sugar.
The Federal standard provides that in evaporated milk there
shall be not less than 34.3 per cent solids, including fat, that the
fat content must be at least 7.8 per cent and that it must not be
made up to this minimum by adding butter oil. 1 The composi¬
tion of three commercial brands of evaporated milk is given in the
following table: 2

Table XVI. —Composition op Evaporated Milk

Sample

Water

Fat

Lactose

Protein

Ash

70.75

9.42

9.75

8.44

1.54

70.90

8.35

10.37

7.86

1.62

72.11

8.69

9.66

[ 7.52

1.54

The methods of analysis of condensed and evaporated milk
are similar to those described for raw milk, except in the
determination of cane sugar and of lactose.

Preparation of Sample: (a) Unsweetened .—Dilute 40 gm of the homo¬
geneous sample with 60 gm of water and make the mixture uniform by
pouring from one beaker to another.

(b) Sweetened .—If the can is cold, place it in water at about 35° until
the temperature of the contents becomes uniform. Open, scrape out all the
milk adhering to the interior of the can and mix by transferring the contents
to a dish sufficiently large to permit stirring thoroughly to make the whole
mass homogeneous. Weigh 100 gm into a 500-cc volumetric flask and,
make up to the mark with water. If the milk will not dissolve completely,
weigh out each portion for analysis separately.

1 Food Insp. Decision, 131 (1911).

2 Ind. Exp. Sta . Bull, 134 (1909).

218

QUANTITATIVE AGRICULTURAL ANALYSIS

Determination of Total Solids.—Use 10 cc of the solution just prepared
and dry as directed on page 204, drying on either sand or asbestos fiber.

Determination of Ash.—Evaporate 10 cc of the solution to dryness in a
platinum or porcelain dish on the water bath and ignite the residue as directed
on page 204.

Determination of Protein.—Determine the nitrogen in 10 cc of the
solution using the Ivjeldahl method as described on page 151 and multiply
by 6.38 to obtain the equivalent of protein.

Determination of Pat.—Weigh 4 to 5 gm of the homogeneous sample into
a Rohrig tube or similar apparatus, dilute with water to about 10.5 cc and
proceed as directed on page 205.

Determination of Sucrose in Sweetened Condensed Milk.—Prepare a
reagent for clarification as follows:

To 220 gm of yellow mercuric oxide add 400 cc of water and sufficient
concentrated nitric acid to form a clear solution, being careful to avoid an
excess. Dilute to about 900 cc and add sodium hydroxide solution, slowly
and with constant shaking, until a slight permanent precipitate is obtained.
Dilute to 1000 cc and filter. The solution will become acid in time, due to
hydrolysis and precipitation of basic mercuric nitrate. Dilute base solution
may be added to correct this.

Introduce 50 cc of the milk solution already prepared into a 100-cc
volumetric flask, add 25 cc of water, mix, add 5 cc of mercuric nitrate solu¬
tion and shake. Without delay, and while stirring constantly, add enough
of a 2-per cent sodium hydroxide solution to render the solution neutral to
litmus paper, being careful to avoid a basic reaction. Dilute to the mark on
the flask, mix thoroughly and filter through a dry paper, discarding the
first 10 cc of filtrate.

Polarize the filtrate in a 200-mm tube at 20°, then invert as follows:
Pipette 50 cc of the filtrate into a 100-cc volumetric flask and add 5 cc of
concentrated hydrochloric acid, slowly and mixing well. Set the flask
aside for 24 hours at a temperature of 20° to 25°. Polarize the solution of
invert sugar in a 200-mm tube at 20° and multiply the reading by two, to
correct for the dilution.

Correct both direct and invert readings for the volumes occupied by the
precipitated protein and fat at the time dilution was made, using the per
cents of these substances as already determined and assuming a volume of
0.8 cc and 1.075 cc, for 1 gm of protein and fat, respectively. The volumes
of these substances will be:

V = —-— = 0.08 P + 0.1075P, (1)

and the corrected readings on the saccharimeter:

100 -
100

:)r=(

100 - 0.08 P -0.1075 F

.ioo

>•

where

V — volume of protein and fat precipitate,
P = per cent of protein,

( 2 )

DAIRY PRODUCTS

F =* per cent of fat,

R — corrected reading and
r = observed reading.

219

Ten grams is the weight of the original undiluted sample in the solution as
finally used for polarization.

Calculate the per cent of sucrose by Clerget’s formula, developed on
page 132, Part II. Taking account of the fact that less than the normal
weight of milk sample was used this formula becomes:

2,600 (a — b) .

S = j z A ?T a ~K - r\ ~ x T \ ~ m which

(142.66 — 0.51) iv

S — per cent of sucrose in the sample,

a = corrected direct polarization,

• b = corrected invert polarization,

t = temperature of solution polarized (20°),

v) — weight of sample taken (in this case 10 gm).

Determination of Lactose.—On account of the presence of sucrose in
condensed milk, the lactose cannot be determined directly by polarization.
The copper reduction method is suitable for this purpose, as sucrose does not
reduce Fehling’s solution.

Measure 100 cc of the milk solution already prepared into a 250-cc volu¬
metric flask and dilute to about 200 cc. Add 6 cc of Fehling’s copper sul¬
phate solution (see page 158) and make up to the mark. Mix well, filter
through a dry filter and determine lactose as directed on page 212.

Powdered Milk. —The rapid progress made in recent years in
producing a high grade of powdered milk has greatly stimulated
its use by bakers and confectioners. It also is used in ice cream
to give body and smoothness to the product. The spray process
now used in its manufacture probably owes its success to the
comparatively low temperature at which evaporation and con¬
densation take place. Milk or evaporated milk is dried by forcing
a fine spray into a current of warm air, thus causing the milk
particles to remain in suspension long enough to lose most of
their water before depositing on the sides of the container.

For the analysis, dissolve 10 gm in water, dilute to 100 cc, mix well and
proceed as outlined for condensed milk. To determine moisture, dry about
2 gm to constant weight at 100° and calculate the per cent loss.

CREAM

Commercial cream must contain not less than 18 per cent of
fat according to the Federal standard. The following table gives
some figures on the composition of a typical milk, cream and

220

QUANTITATIVE AGRICULTURAL ANALYSIS

skim milk, the latter obtained by separating the cream with a
centrifugal separator.

Table XVII. —Comparative Compositions of Milk, Cream and Skim

Milk

Fat

Ash

Casein

Lactose

Total

solids

Specific

gravity

Milk.

5.0

0.79

3.50

4.70

14.0

1.032

Cream.

21.9

0.58

2.02 |

3.32

27.0

1.015

Skim milk.

0.2

0.78

3.62 !

5.05

9.6

1.034

Fat.—The Babcock bottle used for testing milk is not suitable
for cream on account of the higher proportion of fat. If the
cream were 25 per cent fat, 18 gm would contain 4.5 gm of pure
fat. Assuming 0.9 as the average specific gravity of butter fat,
it will be seen that 5 cc of space would be required for the fat.
Various forms of bottles are used for this purpose, one of which is
shown in Fig. 48.

Either 9 or 18 gm of cream is weighed into the counterpoised
test bottles. Fat is determined by the Babcock'method as used
for milk, described on page 208, with the exception of the method
for reading the position of the upper end of the fat column. First
determine the value of the upper meniscus (in per cent) between
the extreme upper and lower points of the curve. Add one-third
of this value to the reading of the lowest part of the curve and
consider this the final reading. 1

The fat column may be read more easily by adding a light
mineral oil which has been colored red with a vegetable pigment.
There are several such preparations on the market under trade
names such as “glymol,” “alboline” and “red top.” The use
of a colored mineral oil was suggested after extensive investigation
of various compounds. 2 If such an oil has practically the same
surface tension as that of melted butterfat the surface divid¬
ing the two liquids is approximately plane. While the use of
such a device for making easier readings has become quite

1 Hunziker, Iml. Ex'p. Sta. Bull ., 145 (1910).

2 Ibid .

DAIRY PRODUCTS

221

extensive there seems to be some evidence to the effect that lower
readings are obtained in this way.

Total solids, ash, total nitrogen and lactose are determined as
with whole milk. A somewhat smaller sample (2 to 3 gm) is
used for the total solids determination. The gravimetric
method for lactose is preferred.

ICE CREAM

Determination of Fat: Rose-Gottlieb Method. —Weigh. 4 gm of ice cream
(melted by exposure to air, then thoroughly mixed) in a 50-cc beaker, add
3 cc of water and mix with a glass rod. Pour the mixture into a Rohrig
tube and wash the beaker and rod, using 3 cc of water and adding the wash¬
ings to the tube. Add 2 cc of concentrated ammonium hydroxide and after
mixing thoroughly, heat in a water bath at 60° for 10 minutes. Add 10 cc
of 95-per cent alcohol and continue as directed on page 206 for the deter¬
mination of fat in milk.

BUTTER AND SUBSTITUTES

Butter, according to the Federal standards, is the clean, non-
rancid product made by gathering, in any manner, the fat of
fresh or ripened milk or cream into a mass containing also a small
portion of other milk constituents, with or without salt, and
which contains not less than 82.5 per cent of milk fat. 1 By acts
of Congress, approved Aug. 2, 1886 and May 9, 1902, butter
also may contain added coloring matter.

Adulteration.—Analysis of butter is usually made (a) to
determine whether or not some foreign oil or fat has been partly
or wholly substituted for butter fat, (6) to determine whether an
excessive amount of milk or water has been incorporated or (c)
to identify “ process” butter (butter which has been steamed to
correct rancidity). Adulteration with another fat or steaming
rancid butter changes the microscopical appearance of the
mixture from non-crystalline (as butter fat naturally exists) to
crystalline, the added fat usually having been previously melted.

Preparation of Sample.—Butter is not usually of a homogeneous com¬
position but it can be made approximately so by melting and shaking during
solidification. If large quantities of butter are to be sampled, use a butter
sampler. Place 500 gm or more of the sample in a wide-mouth glass
stoppered bottle and warm gently until the entire mass is melted. Stopper

1 U. S. Dept. Agr. Chem. Bull 64, 37 (1920).

222

QUA NT IT A TlYK AURU'UL'l'l ’HAL A A'.! /. YS/S

and shako vigorously and continue. to nlmki* during cooling, to prevent the
separation of fat and water. Preserve in a cool place.

Moisture.—This is a variable quantity in butter, the moisture
content ranging from 5 to 25 per cent, but it averages about 16
per cent. Most of the states have laws regulating t he maximum
amount allowed. For the determination, dry sand or asbestos
is used in the evaporating dish to increase the effective surface
and thus increase the rate of the drying, unless the dried butter
sample is to be used for the indirect determination of fat, in
which case the sample is placed in the ('lean dish. There is
danger of oxidizing the fat if it is subjected to prolonged heating.

Determination of Moisture.—Place about 2 gm of hi it-ter in a dish having
a flat bottom and containing asbestos fiber or sand, t he dish and contents
having been dried at 100°, cooled and weighed. Weigh accurately, then
dry the fat for one hour at 100°, cool in the desiccator and weigh. Repeat
the drying, cooling and weighing hourly until the weight is constant to the
third decimal. Calculate the per cent of water in the sample. Preserve
the dried sample for the fat determination.

Fat.— The fat may be determined either directly, as in milk
analysis, or indirectly by weighing the solids left after extracting
the fat with ether or petroleum ether.

Determination of Fat: IHreet Method.™- The sample of water-free fat
obtained in the moisture determination is used. Remove the asbestos
fiber or sand containing the fat from the aluminium dish to an alundum cup
or paper capsule for the extraction apparatus of Fig. 11, using anhydrous
ether to rirmo out the last traces of fat. Place in the extraction apparatus
and thoroughly extract with ether, free from alcohol and water. (Sec
page 147 for details of the use of the extractor.) Recover the ether by dis¬
tilling it on a steam bath or electric hot plate, cooling the vapor by means of
a glass condenser. Dry the flask and fat at I00 \ cool, and weigh. Repeat
the drying, weighing each hour until the weight is constant to the third
decimal. Calculate the per cent of fat in the butter.

Indirect Method. -Prepare a Gooch filter, dry at 1(KP and weigh. Use the
sample of butter which was dried without asbestos or sand in the moisture
determination. Dissolve this in anhydrous, alcohol-free ether or anhydrous
petroleum ether and pass through the filter. Wash with the solvent until
free from fat. Dry at 1(X)° and weigh. Calculate the fat by difference.

Casein or Curd. --The amount of curd in good butter varies
from 0.4 to 0.9 per cent. Any considerable amount of butter¬
milk left in the butter causes a rapid development of protein
decomposition products which impair the flavor of the butter.
The casein may be determined by the Kjeldahl or Gunning

DAIRY PRODUCTS

223

method as in milk, using about 5 gm of sample, or by burning the
casein from the residue from the indirect fat determination,
calculating the loss in weight as casein. The temperature is
kept just below redness (to avoid volatilizing salt) until the
residue is white. A muffle furnace, heated to 600°, is suitable
for this ignition.

Salt. —Salt is added to improve the keeping quality and the
taste of butter. The amount added ranges from 2 to 6 per cent.
Salt is determined by adding a standard solution of silver nitrate
to the water extract of the butter, using potassium chromate as
an indicator. (See page 52, Part I.)

Determination of Salt.—In a small counterpoised beaker place about 10
gm of butter, secured from various parts of the prepared sample, and weigh
to the third decimal place. Add about 20 cc of boiling water and when the
butter is melted transfer to a small separatory funnel of about 50-cc capacity.
Shake the mixture thoroughly and allow the fat to come to the top of the
water. Draw off the water layer into a 250-cc volumetric flask, guarding
carefully against the passing of any fat globules. Repeat the extraction
with hot water ten to fifteen times. Cool the washings to 20°, dilute to the
mark on the flask, mix thoroughly and pipette 25 cc of the liquid into a
casserole for the determination of salt. Titrate with twentieth-normal
silver nitrate solution, using 1 cc of neutral 5-per cent potassium chromate
solution as indicator.

Examination of Butter Fat. —The composition of butter fat is
quite different from that of other fats in that it contains a larger
proportion of the glycerides of fatty acids of low molecular
weight, particularly of butyric acid.

In the following table by Brown, 1 the average composition of
butter fat is expressed in terms of the various glycerides, also of
free acids obtainable by hydrolysis.

1 J. Am. Chem. Soc. f 21 , 807 (1899).

224

QIIA N Tl TA 77 I' K . I (IKK 7 7//7 7i\ 1 /. .1 A', 1 L > \S7A?

Table XVIIL-— Average Composition* of Buttek Fat

Acid

(ilyeeride,
i percent

Per rent

Soluble*

1 in water

Volatile
with Hteam

Butyric, O a H 7 OOOII.

0.2.‘5

5.15

}

Caproic, (VH,i<’OOII.

2 22

2 00

Partly

Oaprylie, (blli&OOOH.. ..

0 r>:{

o.-m

.....

Oapric, CoIhoCOOH.

o:u

0.22

H-

Laurie, (J„II„<7><>II.

2.7:5

2 57

...

Partly

Myristic, (LdbrCXX)II. .

10 14

9 so

Palmitic, (LdLA •( )<>!!.. .

torn

as 01

Stearic, (’17barXXXMI.

1 m

1 k:j

Oleic, OitIImC’OOII.

DiliydroxyHtoiiric,

.'52 50

—*

Ci7H il: ,(OIIj,<:OOH.

1 .0-1

l 00

—

Total.

100 00

01 75

* Solubility is at 15°, given in approximate terms.

Butter Substitutes. The oleomargarine of commerce is
usually composed of refinet 1 olein of beef fat (culled “oleo oil”),
churned up with neutral lard, milk and some butter fatthe latter
two imparting a butter flavor to the* product. Other oils often
used are cottonseed, peanut, and eoeoanut oils. Salt is added
and sometimes the oleomargarine is colored to make it more
nearly resemble natural butter. If is to be expected that
the composition of the various oleomargarines would vary greatly
because of the variety of oils and fats used in their manufacture.
Kven the fat from any one source may vary somewhat depending
upon the conditions under which if was produced. The use
of eoeoanut oil in the manufacture of the 44 nut” margarines is
very common practice because eoeoanut 44 oil” is a high grade
edible fat, resembling butter in several ways. The fact that
some of its constants are near to those of butter makes its
detection in butter substitutes more difficult.

(/ocoanut fat, like that of butter, has a fairly high per cent of
volatile fatty acids and it melts at nearly the same* temperature.

DAIRY PRODUCTS

225

It differs from butter fat mainly in the larger proportion of the
volatile fatty acids that are insoluble in water. These differ¬
ences are used in its detection,, especially the volatile insoluble
fatty acids as indicated by the Polenske value (page 186), which
is the number of cubic centimeters of tenth-normal base required
to neutralize the insoluble volatile fatty acids obtained from
5 gm of fat. The Polenske value for butter is 1.5 to 3.0, for
oleo oil 0.5 and for cocoanut fat about 17. The average Reichert-
Meissl number for cocoanut fat is about 7, while that of butter
fat is about 28. This makes it possible to distinguish (a) between
butter and butter substitutes and (Jb) between oleomargarine and
“nut” butters. The fatty acids of the glycerides of cocoanut
fat are as follows: 1

Table XIX.— Fatty Acids of Glycerides of Cocoanut Fat

Acid Per cent

Caproic.
Caprylic
Capric..
Laurie..
Myristic
Stearic..
Oleic
Palmitic

Volatile but largely insoluble

Non-volatile

The particular “constants” that are mentioned in the following
table will be found of greatest value in identifying butter and
butter substitutes. Of these the Reichert-Meissl number, the
Polenske value and the soluble acid number are perhaps of
first importance. Microscopic examination will serve to dis¬
tinguish process butter, by the fact that fat crystals are to be
found only in butter that has been remelted.

Elsdon, Analyst, 38, 8 (1913).

22G QUANTITATIVE AGRICULTURAL ANALYSIS

Table XX.—Constants of Butter and Common Substitutes

Butter fat

: Oleomargarine*

Nut butterf

Iodine absorption number.. .

26-38

52-65

35.72

Soluble acids.

4.5

0.7

Insoluble acids.

87.5

95.5

Reichert-Meissl number.

24-32

0.8-1.0

5-6.5

Polenske value.

1.5-3.0

Less than 1

10-18

Saponification number.

220-233

195

225-250

Index of refraction.

1.454

1.458

Butvro refractometer reading

42.0

48.0

43.5

* A representative oleomargarine made from oleo oil, lard and milk,
f Made from peanut and cocoanut oils.

Fig. 50.—Steam or hot water funnel.

Preparation of Samples of Butter Fat. —Melt the butter at
60° and keep at this temperature for several hours, or until the
curd and water have separated completely. Pour off the clear
fat through a dry filter paper which is placed in a hot water or
steam funnel (Fig. 50).

For the general methods to be used in the examination of
butter fat refer to Chap. X, on fats, oils and waxes.

CHEESE

According to the Federal standard, cheese is the sound, solid
and ripened product made from cream or milk by coagulating the
casein with rennin or lactic acid, with or without the addition of

DAIRY PRODUCTS

227

ripening ferments. It contains, in the water free substance, not
less than 50 per cent of fat.

Manufacture. —The action of the enzyme rennin is to change
the casein, by hydrolysis, into albumoses and peptone and soluble
paracasein. The calcium salts present in solution in the milk
serum unite with the soluble paracasein to form an insoluble
curd. The curd carries down not only the fat but also the greater
part of the microorganisms contained in the milk. If these
organisms are of a desirable kind they will produce a homo¬
geneous curd and good cheese, otherwise a spongy curd and a
cheese of poor consistency will be the result.

The table below gives the average composition of certain
samples of four kinds of cheese.

Table XXL— Composition of Cheese

Kind of cheese

Water

Fat

Ash

Proteins

Primary
products of
ripening

Secondary
products of
ripening

American “Cheddar”

34.2

33.7

3.8

25.2

Roquefort.

31.2

33.2

6.0

27.6

Swiss.

33.0

30.2

5.3

25.4

2.7

3.1

Gervais.

44.8

36.7

2.9

12.7

1.9

0.8

Determination of Water.—Place about 15 gm of clean white sand in a
flat aluminium dish, dry at 100° and weigh. Add about 3 gm of cheese
and reweigh, quickly. More sand is needed if the cheese is very rich in fat.
The mixture is then dried at 100° to constant weight and the per cent loss in
weight calculated as moisture.

Determination of Ash and Salt.—Ignite, cool and weigh a covered porce¬
lain crucible. Add about 15 gm of cheese, cover and reweigh. Uncover the
crucible and drive off most of the moisture and volatile matter by carefully
heating over a small flame. Place the uncovered crucible in a muffle furnace
which is held at about 600° and through which air may circulate. Continue
the heating until all carbon is burned. Cool in a desiccator and weigh.
Calculate the per cent of ash.

After weighing the ash, add water, dilute to 250 cc in a volumetric flask
and mix. Either 50 or 100 cc of this solution is taken for the chlorine
determination as directed on page 223. Calculate as sodium chloride. The
residue insoluble in water may be dissolved in a small amount of dilute
hydrochloric acid, diluted to 250 cc and calcium and phosphorus determined
in aliquot parts of this solution, if desired.

228

Q ( 'A NT IT A Tl 1' K ACM Cl 7 AVI RA L AS MA ’ SIS

Determination of Fat.—Place a mixture of equal parts of anhydrous copper
sulphate (dried at 225°) and pun? dry sand in an alundum cup and fill to a
depth of about 5 cm, packing loosely, (’over the upper surface of material
with a layer of asbestos. Place on this 2 to 5 gm of sample and ex¬
tract with anhydrous ether for 5 hours in a continuous extraction apparatus
(Fig. 41, page 146). Remove the cheese to a mortar and grind it with the
sand to a fine powder, return the mixed cheese and sand to the extraction
tube, wash the mortar with ether, add the washings to the tube and con¬
tinue the extraction for at least 10 hours.

Determination of Total Nitrogen.'-Determine nitrogen as directed on
page 151, using about 2 gm of cheese, and multiply the percent of
nitrogen by 6.58 to obtain the per cent, of protein.

Determination of Acidity.—To 10 gm of finely divided cheese add water
at a temperature of 40° until the volume equals 105 cc. This allows 5 cc
for the volume of the cheese. Shake vigorously and filter. Titrate 25-cc
portions of the filtrate, representing 2.5 gm of sample, with tenth-normal
sodium hydroxide? using phenolphthaleiu us an indicator. Express the result
in terms of lactic acid.

Detection of Coloring Matters in Butter or Cheese: d ) Oil-Mluhlr I);/ch. -
Prepare an alcoholic solution of the oil-soluble dye by one of the following
methods, which is to be applied to the oil or fat obtained by extraction with
ether or gasoline.

(a) Shake the oil or melted fat with an equal volume of IHbper cent
alcohol. The alcohol after separation will contain aniline yellow, “butter
yellow,” aminoazotoluene and auramine, or such of these as may be present.

(/>) Dilute 20 to 200 gm (according to the intensity of colon of the oil or
melted fat with two volumes of gasoline and shake* out successively with
4-percent potassium or sodium hydroxide solution, 15-per cent hydrochloric
acid, and phosphoric-sulphuric acid mixture, prepared by mixing 85-per cent
phosphoric acid with about 20 i>er cent by volume of concentrated sul-
phurie acid.

The dilute base extracts Sudan G and annatto. The dilute hydrochloric
acid extracts aniline yellow, aminoazotoluene and “butter yellow," the
first two forming orange-red, fcho latter cherry-red solutions in this solvent
Tint phosphoric acid mixture is necessary for the extraction of »Sudan i,
Sudan II, Sudan III and Sudan IV. Ikmzenenzn-,Miaphthylamin and
homologues also come in this group, though they readily undergo chemical
changes in the strongly acid mixtures. The procedure is not very suitable in
the presence of auramine but this dye is seldom found in oils.

Neutralize the alkaline and dilute hydrochloric acid solutions. Dilute the
phosphoric acid mixture and partially neutralize, cooling the liquid during the
operation. Extract the dyes from the neutral solutions by shaking with
ether or gasoline.

For the direct dyeing test use the alcoholic solution obtained in (a).
Evaporate to dryness the ether or gasoline solutions, obtained as directed
in (/>), arid dissolve the residue in 10 to 20 cc of 05-per cent alcohol. To the
alcoholic solution add some strands of white silk and a little water and

DAIRY PRODUCTS

229

evaporate on the steam bath until the alcohol has been removed or until the
dye is taken up by the silk. The dyeing test is sometimes unsatisfactory,
and in all cases a small portion of the alcoholic solution should be tested by
treating with an equal volume of hydrochloric acid or stannous chloride
solution. The common oil-soluble coal-tar dyes are rendered more red or
blue by the acid and are decolorized by the reducing agent. Most of the
natural coloring matters become slightly paler with the acid and are little
changed by the stannous chloride solution.

(2) Annatto Coloring Matter .—Pour on a moistened filter a basic solution
of the color obtained by shaking out the oil or melted and filtered fat with
warm, dilute sodium hydroxide solution. If annatto is present the filter
paper will absorb the color so that when washed with a gentle stream of water
it will remain dyed a straw color. Dry the filter and add a drop of stannous
chloride solution. If the color changes to pink the presence of annatto is
confirmed.

CHAPTER XII

SOUS

A soil analysis is made to find out the extent and distribution
of plant food elements and thus to determine which elements are
the limiting factors in crop production. The term ct soil fertility”
is often used to express this relation and this is understood to
mean the crop producing power of any soil under specified
climatic conditions. “ Fertility ” is really an indefinite term as
the property indicated is the resultant of many forces which
are frequently opposed to each other in their action.

Total and Acid-soluble Material.—The analysis of soils with
a view to measuring their fertility and studying their geological
origin has received much attention in recent years. It was
formerly thought, and it is still held to some extent, that the
fertility can best be measured by extracting the soils with strong
acids, thus obtaining an invoice of the total plant food con¬
tained. But by this method there is left some available potas¬
sium and a mass of substances of unknown composition, which
yet need to be determined in order to have complete information
concerning the geological origin of the soil. On this account
the value of many early analyses is being called into question
and at present it is regarded as desirable that the total constitu¬
ents of the soil should be determined. The complete examina¬
tion of a soil involves its study from chemical, physical and
biological points of view. The chemical phases of this subject
will be given most attention here.

Soil Constituents.—Soil has been defined as that portion of
the earth’s surface, climatic conditions being favorable, which
makes possible complete growth and development of plants.
Ordinarily soils are made up of mixtures of organic matter, rock
at various stages of disintegration, water, gases and bacteria.
The great mass of this material is not directly essential to the
growth of plants but aids in holding moisture and making a
medium in which the roots may anchor themselves.

230

Classification, of Plant Food Elements in the Soil.—The

food elements of the soil occur principally as follows:

1* Nitrogen ^ f OUIU j [ n * 0 iis as a constituent of organic matter,
nitrates, anxinonium salt s and amino acids.

2. PhospFxon^ present in organic forms or combined with
calcium, iron or aluminium as phosphate.

3. Potassium j s widely distributed in all soils of granitic
origin. It is combined with silica as silicates in granite, ortho-
clase and mica.

4. Calciuni is found as carbonate and silicate, as sulphate in
gypsum, as constituent of rock phosphate and in organic forms.

5. SulphuLr occurs combined with calcium as gypsum. It is
quite deficient in some soils.

6. Iron and manganese are found as oxides and silicates.

7. Magnesium is associated with calcium as dolomitic lime¬
stone, also ns silicates.

Aluminium, sodium and silicon are probably non-essential to
plant growth.

Value of Soil Analysis.—There has been much discussion
concerning -the adequacy of soil analysis as a means of measuring
soil fertility. Many writers confuse the narrow purpose of
simply determining the plant food immediately available with
the broader one of obtaining an extensive knowledge of the total
plant food supply and a determination of the possible geological
origin of the soil in order to plan better for permanent improve¬
ment. The value of the analysis is expressed by Hopkins 1 as
follows:

“The chief "value of a chemical analysis is to serve as an absolute
foundation upon which methods of soil treatment can safely be based
for the adoption of a system of permanent soil enrichment, not for one
crop or for one year only but for progressive improvement/'’

The Ohio Station has shown 2 how accurately the excesses and
deficiencies may be measured by analysis when good and poor
methods of agriculture have been practiced for a period of fifteen
years. There is no other tool which compares with it for this
purpose and as an aid in unlocking soil secrets. The value of

1 “Soil Fertility and Permanent Agriculture,” p. 568.

2 Ohio Exj> . *Sta . BnU 261 (1913).

232 QTAXTITATI V E AGR1CVLTVRAI. aX-MAS f.S

soil analysis in the determination of geological origin has been
considerably underestimated, although few data are at hand to
aid in such an interpretation.

Soil Classification Based upon Mode of Fonm-^ion.. For con¬
venience in the study of soils they may be divided according
to manner of formation into eight groups 1 as follows: C'urnxdose
soils are chiefly deposits of vegetation in various stages of decay.
Residual soils—unmoved from the rocks from, which they were
formed. Loess —residue deposited as dust carried by wind.
Glacial soils are deposits which have developed from glacial
action. Colluvial soils are deposits which. h.a“ve been moved
downhill by gravity. Alluvial soils consist of re si dues deposited
from flowing water. Marine soils are formed by" deposits carried
into seas. Lacustrine soils are formed by deposits carried into
lakes.

Classification Based upon Composition.—It is to be expected
that soils whose origin is so different as is noted above would
vary greatly in chemical analysis. Ames has made a study
(unpublished work) of the relation between soil hype and compo¬
sition, considering at the same time the geological formation.
The chief differences observed were with respect to the calcium
carbonate, total organic matter and nitrogen content. Tor
example the soils of limestone origin, as compared with those
from sandstone and shales, contained larger amounts of calcium
and magnesium. In many cases these larger amounts of calcium
and magnesium are accompanied by larger amounts of phos¬
phorus, organic matter and nitrogen. It is evident that if only
disintegrating forces had been active the soil particles would be
of the same general composition as the original rock. However,
many agencies tend to change this original material until only
the most resistant minerals remain. 2

The Report.—Determinations of the inorganic constituents of
soil are usually reported in terms of their most stable compounds or
of their oxides although nitrogen is reported astho element- The
determination is usually made on an air-dried sample. Besides
reporting results as per cents on this basis it is sometimes desir¬
able to report the amount per acre (2,000,000 lb. is considered as

1 Trowbridge, /. Geol. , 22, 420 (1911).

2 See also A r . C. Exp. Sta. Tech. Bull., 9 (1914).

the approximate weight of a loam soil, 6^3 in. deer) over an acre
of land, while 1,000,000 lb. is taken as the average weight of a
muck soil over the same area).

Analytical Methods. —The chemical method.- for -tinlying the
soil may be considered under the following heads;

(а) Complete analysis.

(б) Potential plant food.

Complete Analysis. —The inorganic analysis is usually made
by fusing the soil with alkali carbonates, the insoluble silicates
forming alkali silicates which can be dissolved in hydrochloric
acid. From this solution the total inorganic constituents, with
the exception of carbon dioxide, sulphur, sodium and potassium,
may be determined. The latter group, as well as moisture,
nitrogen, phosphorus, and organic matter, are determined in
separate samples.

Potential Plant Food.— This is separated by digesting the
soil in hydrochloric acid of constant boiling point specific
gravity 1.115, containing about 23 per cent of HCT, using the
ratio of 1 part of soil to 10 of acid, thus effecting the solution
or partial decomposition of soil minerals. This was formerly
the official method.

Available Plant Food. —This is the part of the total supply
which is immediately available to plants. There are many
natural agencies tending to make plant food available, such as
bacterial action, plant decay and root acidity, and it is difficult
to determine the part played by any one, especially by dilute
acids. After making an extensive study of the acidity of various
plant roots it was suggested by Dyer in 1894 that solubility in a
1-per cent solution of citric acid most nearly measured the true
availability, as indicated by the ability of growing plants to
absorb material from the soil. Various other solvents have been
tried, such as distilled water, carbonated distilled water, acetic
acid, aspartic acid and fifth-normal hydrochloric and nitric acids.
The latter seems to give more consistent results on many soils
than does citric acid. However, all lalxmatorv results obtained
by the use of weak .solvents are only approximations to the action
of natural solvents in the soil.

234

QUANTITATIVE AGRICULTURAL ANALYSIS

Choosing Samples.—In choosing soil samples it is very important to
secure representative ones. The sampling should be done when tb.e ground
is dry enough to plow. An area should be selected such that tlie soil is
typical with respect to texture and color. Note should be made of any
available information concerning the geology of the area, original timber
of the land, the present productivity, or any peculiarities in location which
may aid in interpreting its analysis. The surface accumulations of such
materials as decaying grass should be removed and the borings for samples
then made with a soil auger or other soil tube. Composite samples are
taken from different depths as follows: (a) surface to 6 in., (b) 6 to 20 in., (c)
20 to 40 in. For each depth ten to fifteen borings are taken and well mixed.
About a pint of soil from each depth should finally be preserved. Sample
(c) need not be mixed with as great care as are samples (a) and (b) since it
is not usually taken for analytical purposes but for obtaining some insight
into the physical nature of the subsoil, drought resistance and drainage
depending to some extent upon the nature of substrata. The borings are
placed in clean cloth sacks in the field and immediately sent to the laboratory.
Here they are dried and later ground for analysis.

Preparation of Samples.—Spread the samples on paper or in shallow pans
in a dry place, in clean air, and allow to remain until apparently dry- Pul¬
verize lumps and divide each sample into two fractions by use of a 4-mesh
sieve. The stone remaining in the sieve is weighed and its per cent of
the total is calculated. Grind the finer soil portion in a porcelain pebble
mill or other pulverizer until it will pass a 40-mesh sieve. Mix thoroughly
and then grind about 100 gm of this sample until it will pass a 100-mesh
sieve. Riffles of different sizes may be used for .sampling, or rolling on
paper or oilcloth may be employed. (See the discussion of sampling,
Part I, pages 17 to 22.) The samples should be placed in stoppered bottles
and carefully labeled.

Moisture.—The proportion of moisture in air-dried soil
depends largely upon the proportion of organic matter. The
water-holding power of soil is of great significance from a, prac¬
tical standpoint.

Determination of Moisture.—Weigh accurately 5 gm of finely pulverized
100-mesh soil into a flat porcelain crucible about 4 cm in diameter and pro¬
vided with a glass cover. Remove the cover and dry the sample at 110°
for five hours. Cover and cool the crucible in a desiccator and then weigh.
Preserve the dried sample for the determination of volatile matter. Calcu¬
late the per cent of moisture in the prepared soil.

Optimum Moisture of Soils. —The water-holding capacity of a
soil depends upon its content of organic matter and its structure.
The amount of water which just permits a soil to crumble is
considered the optimum. This is about one-third of its total
water-holding capacity.

SOILS

235

Approximate Determination of Optimum Moisture Content of Soils.—

Weigh three 25-gm portions of the 40-mesh air-dried soil and place them in
200-cc beakers or wide-mouth bottles. Add to the three portions, 5, 6 and
7 cc of water, respectively. Cover the bottles with watch glasses and
allow to stand for two days. Remove the soil and see if any sample is wet
enough to form balls. If not, repeat the experiment with modified quantities
of water. The optimum moisture should be just a little less than this
amount.

Total Nitrogen.—The relative amount of nitrogen in soils
varies greatly, although it is usually approximately in proportion
to the organic matter. A soil in Manitoba is reported to contain
as high as 20,100 lb. per acre (1.005 per cent) while a sample
from the “ Jack Pine” plains of Michigan is said to contain only
740 lb. per acre of 2,000,000 lb. (0.0037 per cent) of soil.

Nitrogen is one of the most important of all elements in the
soil. It is absolutely essential to plant existence and it cannot
be taken from the abundant supply of the air by the plant
itself. Certain forms of soil bacteria cause the fixation of this
elementary nitrogen in the form of nitrates, which can then be
utilized by the plant. The chief purpose of nitrogen in plant
economy is to provide for the construction of protein by the
plant. The deep green color of plant leaves is often an indica¬
tion of an abundance of available nitrogen.

Determination of Total Nitrogen.—Place 10 gm (5 gm if a muck soil)
of 40-mesh soil and 30 cc of concentrated sulphuric acid in a 500-cc Kjeldahl
flask. Proceed as described on page 151, and following. Calculate the
per cent of nitrogen.

Nitrate Nitrogen. —The amount of nitrate nitrogen present in
a soil depends mainly upon the amount and kind of vegetation,
and upon the degree of compactness, the temperature and the
water content of the soil. The most favorable temperature
seems to be about 35° and the most favorable water content is
one-third of its saturation. These factors largely determine
whether or not a soil is suitable for bacterial development.

The amount of nitrate present in a soil at any one time is
seldom very large, ranging from zero to 1000 lb. per acre (0.05
per cent). It is difficult to find more than a trace of nitrate
nitrogen in soil just under an old sod whereas in some western

236

QL A XT ITA T1VE AGRICULTURAL ART AL YSIS

soils nitrates have accumulated in such amounts as to interfere
with plant growth. 1

The phenoldisulphonic acid method is used for the deter¬
mination of nitrates, the following equations representing the
reactions:

HsSCU + 2KN0 3 2HNO s + K 2 S0 4 ; (1)

C 6 H 3 0H(S0 3 H) 2 -f HN0 3 -~> kQH 2 0H-N0 2 (SO3H)2 +- H 2 0; (2)

Phenoldisulphonic acid \ * NitrophenoIdisulpUonic acid

C 6 H.OH-XOo(SO s H) 2 + 3NH 4 0H->C 6 H 2 O]SrH4(SO 3 NH4) 2 NO 2

+ 3H 2 0. (3)

The ammonium salt of nitrophenoldisulphonic acid, thus
formed, is intensely yellow and the color so produced is compared
with that formed from a standard nitrate solution.

Fig. 51.—Mixing machine.

Determination of titrate Nitrogen.—Prepare the following reagents:

(а) Phenoldisulphonic Add .—Mix 30 gm of pure crystallized phenol with
370 gm of concentrated sulphuric acid. Immerse the flask: in boiling water
for six hours. When cool store in an amber colored bottle. A smaller
quantity of the solution may be made, if desired.

(б) Standard Color Solution .—Prepare a standard solution of potassium
nitrate by dissolving 0.7215 gm of dried pure potassium nitrate in distilled
water and diluting to 1 liter. Each cubic centimeter of this solution will
contain 0.1 mg of nitrogen. Pipette 10 cc of this solution into a dish and
evaporate to dryness over a steam bath. Cool and moisten the dry nitrate
with 2 cc of phenoldisulphonic acid, rubbing together with a glass rod

1 Colo. Exp. Sta . Bull ., 178 (1911).

Fig. 52.—Schreiner color comparator.

Wliifi#!!

238 QUANTITATIVE AGRICULTURAL ANALYSIS

After 5 minutes dissolve and dilute to 1000 cc in a volumetric flask. This
makes a permanent color standard, 1 cc of which will contain 0.001 mg of
nitrate nitrogen.

Place two 100-gm samples of 40-mesh soil and 5 gm of calcium hydroxide
(to aid in securing a clear solution) in salt mouth or shaker bottles and add
400 cc of nitrate-free distilled water (tested as below) to each bottle. Mix
in a machine for 30 minutes and then remove the bottles and let stand over
night. Pipette 10 cc or more of the clear, supernatant solution into a 8-cm
porcelain evaporating dish and evaporate to dryness on a steam bath.
Remove from the steam bath as soon as dry, cool, add 2 cc of phenoldi-
sulphonic acid and mix well with the aid of a glass rod. After the acid
has stood in contact with the residue for 15 minutes add 5 cc of cold dis¬
tilled water, stir and add enough ammonium hydroxide (1 to 1) to produce
a permanent yellow color. The standard (a suitable measured quantity
of which has been made basic with ammonium hydroxide in the same manner
as the unknown) is rinsed into a cylinder for a colorimeter, such as that illus¬
trated in Fig. 52, and diluted to the 100-mm mark. Rinse the unknown
into another tube and dilute to the 100-mm line, provided that the color
qf this solution is not over two-thirds as intense as that of the standard.
Place both tubes in the colorimeter and move the tube containing the more
intense color up or down until the intensities of color in the two are equal.
The nitrogen concentrations are inversely as the lengths of column equiva¬
lent in intensity of color. Take three readings on each sample and from
these calculate the per cent of nitrate nitrogen in the sample.

A mm onia, —The amount of ammonia nitrogen in soils is
usually very small, although in certain swamps it is present in
considerable quantities as ammonium salts. Such plants as
rice, which grow in water, secure considerable nitrogen in the
form of ammonia or of nitrogenous organic decomposition
products- Among these compounds are amino acids, e.g .,
arginine and glycocoll.

The chemistry of a possible mode of ammonia production from
amino acids may be represented by the following equations:

RCHNH 2 COOH + 0 2 RCOOH -f C0 2 + NH 3 ; (1)

Amino acid Patty acid

RCHNH 2 COOH + H 2 0 -» RCHOHCOOH + NH 3 . (2)

Thus an amino acid when oxidized or hydroli^ed produces
ammonia as an end product.

Determination of Ammonia.—Place 25-gm samples of soil, together
with 5 gm of sodium carbonate, in aeration flasks (Fig. 53), add three drops
of light hydrocarbon oil (to prevent frothing) and 100 cc of boiled distilled
water to each flask. Connect the flask with a wash bottle containing 25 cc

ijJ

of tenth-normal sulphur;- and ani n. », , r ... . .. .

lO-per cent sulphurs ; ... ... - , .... .

gas, as shown. Aitmp- \ \ < .• ♦

from the uonnion flask .. -a ,U.. , : _ . . I ‘V

end of this period, titrate the -tar:d tra . , ; . • «. i: . •- .

methyl red as indicator. I->iu.u ihv \t , r .i u : • y

the anitu osiitiobtained f r*. >U: Mfil .'ult' lit t; r* j a. S * f t — ;;

soil sain

j K

-- ^-r.y

Fiu. 5;>,—Aer;iU’>u upparuu«

Nitrification.—A productive soil is. not dimply a dead medium
in wlxicfc the plant can fix itself and from which i? mm g-t food
"by processes of solution ami diffusion; on tie contrary it is
teeming; with living organisms which bring: aUvut changes
difficult to duplicate in the laboratory. By their activity’ much
food wfiich otherwise might not be used is made available to the
plant}. Two important organisms have loen isolated. One,
called. € * nitrosococcus," causes oxidation of ammonia to nit rites
and other, “mtrobacter," causes*oxidation of nitrites to

nitrates, according to the following reactions:

2NH 3 + 30 2 — 2HNOi - 2H A ,1)

2HN0 2 +• 0 a — 2HX0* ;2)

Meastiremeat of Nitrification.— Prepare 430 cr of an approximately
fifth—n.or*mal solution of ammonium sulphate in a SOO-ce volumetric thisk
and add 0.3 gm of dipotassiufci phosphate. 0.3 gm of calcium oar r *_.>!; ate,
and 2.0 gm of afresh sample of a fertile soil. The purpose of
phosplistte is to furnish food for the growth of bacteria. The nitrifying
bacteria- in the soil will convert the ammonia nitrogen to nitrate nitrogen and
the calcium carbonate serves to neutralize the nitric aeai formed. Mix

240

QUANTITATIVE AGRICULTURAL ANALYSIS

thoroughly. Dilute to the mark and determine the per cent of ammonia
nitrogen in 100 cc by placing the solution in a Kjeldahl flask, adding 15 cc of
10-per cent potassium hydroxide and distilling the ammonia into 25 cc of
fifth-normal hydrochloric acid, using a tin condenser.

Place 200 cc (or enough to cover half the sand) of the ammonium sul¬
phate culture solution, prepared as above, on clean white sand in a percolator
(Fig. 54). Cover the percolator with a watch glass. Keep in a dark place

.-. for three or four weeks, then drain out all liquid and rinse

V _ J the sand with about 200 cc of distilled water (ammonia-

free), using about 50 cc portions at a time. Make the solu¬
tion up to 500 cc in a volumetric flask, mix well and deter¬
mine the amount of ammonia nitrogen in an aliquot part
by the distillation method, as above described. The differ¬
ence between the amount present at the beginning and at
the end will represent the amount converted to nitrate.
Calculate the per cent of nitrogen which has been changed
from ammonium sulphate to a nitrate. This gives an
estimate of the activity of nitrifying bacteria in the soil.

Denitrification. —Certain bacteria (, B . denitrifi-
cans alpha , also beta ) have the power, under ap¬
propriate conditions, to reduce ammonia, nitrites
and nitrates to the form of elementary nitrogen.
This is usually brought about in a water-logged
soil or in the presence of an excess of nitrogenous
organic matter. The amount of released element¬
ary nitrogen may be measured and the bacterial
activity noted.

Fig. 54.
Percolator.

Demonstration of Denitrification.—In a 250-ce wide mouth flask or bottle
place 20 gm of horse manure and add 100 cc of water containing 1 gm of
potassium nitrate. Fill the bottle with water and close the mouth with a
rubber stopper connected with a delivery tube. The tube is inserted into a
500-cc graduated cylinder wHicli has been previously filled with a 5-per cent
sodium hydroxide solution and inverted into a 1000-cc beaker containing
about 300 cc of water. The method of assembling the apparatus is shown in
Fig. 55. After standing 24 hours at about 35° a mixture of carbon dioxide
and nitrogen will begin to be produced. The former will be absorbed by the
sodium hydroxide while the latter will be caught in the cylinder and can be
measured. Calculate the per cent of denitrification of the nitrate added.

Phosphorus. —Phosphorus is present in all soils, usually in
small amounts, varying from 300 to 5000 lb. per acre of 2,000,000
lb. of soil (0.015 to 0.25 per cent). The plant demand for
phosphorus is large, as crops remove from 5 to 30 lb. per acre

SOILS

241

annually. It occurs in the soil chiefly as apatite (calcium fhtoro-
phosphate) and, to some extent, in organic forms.

The most pronounced effect of phosphorus upon the plant is
noted in the greatly increased development of lateral and fibrous
roots. This feature is of much importance in clay soils, especially
as it induces the formation of an extensive system of roots, thus
enabling the plant more successfully to withstand drouth. A

deficiency of phosphorus is often shown by late maturity of
crops and, in the case of cereals, in the lack of good grain
development.

Before phosphorus in soil can be determined it is necessary to
remove organic matter, oxidizing phosphorus so held to phos¬
phoric acid, and to bring the phosphorus of both organic and
inorganic matter into solution. The methods now in use for
this purpose are (a) oxidation of organic matter by heating with
sodium peroxide, with subsequent solution of phosphates by
hydrochloric acid, (b) a procedure similar to (a) but substituting
magnesium nitrate for sodium peroxide, and (c) oxidation of

organic matter and solution of phosphates by heating with
16

242

QUANTITATIVE AGRICULTURAL ANALYSIS

concentrated sulphuric acid, with or without the addition of a
catalyzer. From the solution produced by any of these methods
phosphorus is precipitated with a molybdate solution as am¬
monium phosphomolybdate. The precipitate is either dissolved
in standard base and the excess of the latter titrated, or it is
dissolved in ammonium hydroxide and the phosphorus precipi¬
tated as magnesium ammonium phosphate, ignited to magnesium
pyrophosphate and this weighed. The principles of these meth¬
ods are discussed in Part I, pages 88 and 91.

Determination of Phosphorus.—Use one of the following methods for
obtaining the phosphate solution:

(a) Place 10 gm of sodium peroxide in an iron crucible, add 5 gm of the
soil and mix thoroughly by means of a glass rod. If the soil contains only a
small proportion of organic matter add 0.5 gm of starch and mix as before.
The starch will hasten the action. Heat the mixture by applying the flame
of a burner directly upon the surface of the charge and the sides of the
crucible until the action starts. Cover the crucible until the action is
over and continue heating at a temperature of dull redness for 15 minutes.
The residue in the crucible should not be fused. Transfer the charge to a
250-cc beaker with about 150 cc of water; add hydrochloric acid until acid
to methyl red and boil. Cool, rinse into a 250-cc volumetric flask, dilute
to the mark and mix. If the action has taken place properly there should be
no particles of undecomposed soil in the bottom of the flask, although the
solution will usually be turbid from silicic acid.

(b) Place 5 gm of soil in a 50-cc porcelain crucible and moisten with 5 cc
of 50-per cent magnesium nitrate solution. • Evaporate to dryness on the
steam bath and ignite at dull redness. Let the crucible cool and add 5 cc of
water and 10 cc of concentrated hydrochloric acid, then cover and heat on
the steam bath for two hours. Stir several times while digesting. Transfer
the contents of the crucible to a 250-cc volumetric flask, cool to room
temperature, dilute to the mark and mix well.

(c) Place 5 gm of soil in a 500-cc Kjeldahl flask and digest with 30 cc of
concentrated sulphuric acid and 0.5 gm of mercuric oxide until the carbona¬
ceous matter has been oxidized. Cool to room temperature (do not place
the flask in cold water until it has cooled somewhat in air), then add 100 cc
of water, 5 cc of concentrated hydrochloric acid and 2 cc of concentrated
nitric acid. Boil for 5 minutes, cool, dilute to 250 cc in a volumetric flask
and mix well.

Filter the phosphate solution through a dry folded filter until the filtrate
is no longer turbid. By means of a pipette or volumetric flask measure
100 cc of the clear solution and deliver into a 10-cm porcelain dish. Evapo¬
rate on the steam bath to dryness, take up with 5 cc of hydrochloric acid and
an equal amount of water, filter to remove silica and wash. From this point
proceed as directed in Part I, page 90, beginning with “Add ammonium

SOILS

243

u 4o until a slight precipitate of hydroxides. -• \ ’ <>r ;t “

,Ci 92, beginning with “Add ammonium hydroxide u.nt'll a s lg i

'^te persists.”

l Ssiuin and Sodium.—Potassium is essential to plant
^ and it is present in most soils in sufficient amounts to
J he plant needs, but only partly in an available form, it
^ery gradually changed to soluble potassium carbonate by
of carbonic acid upon orthoclase, which is nearly insoluble
not readily available to plants. Sandy soil often con-
•^ss than. 0.1 per cent of acid-soluble potassiuim, sandy
0.1 to 0.3 per cent, loams from 0.3 to 0.45 per cent
^vy clays 0.45 to 0.8 per cent.

^ssinm functions notably in the photosynthesis and
xent of starch within the plant. Lack of starch formation
ovement is one cause of shriveled and sterile grain. An-
-ffoct of a lack of potassium is to make the plant less resis-
> disease. This may be said of a plant suffering from any
:ood deficiency but it seems to be especially true in the
potassium.

um is not of great importance in plant nutrition. It is
d with, delaying potassium starvation but it will not
Y prevent this condition.

method generally used for decomposition of insoluble
Is, preliminary to the determination of potassium and
l, is the J. Lawrence Smith method. It is based upon
ion of calcium chloride (formed from calcium carbonate
imonium chloride) upon complex silicates at texxiperatures
n 800° and 900°. Sodium and potassium chlorides,
a,s silicate of calcium, are formed. The reaction taking
oetween orthoclase, calcium carbonate and ammonium
e may be represented as follows:

| 3 0 8 + 6CaC0 3 + 2NH 4 C1 —> 2KC1 + Al 2 0 3 -b

6CaSi0 3 + H 2 0 + 2NTT 3 -f 6C0 2 .

platinum crucible (Fig. 56) is preferable for the decom-
3 . but an iron or nickel 1 crucible of 50-cc capacity' may be
Such base metal crucibles deteriorate rapidly when used
w ay.

,tcej:r, J . Ind . Eng. Chem ., 11 , 1139 (1919).

244

QUANTITATIVE AGRICULTURAL ANALYSIS

In the solution of salts finally obtained potassium may be
separated from sodium by the chlorplatinate or the perchlorate
method or it may be precipitated as potassium sodium cobalti-
nitrite and a volumetric method used for its determination. The
accuracy of the various methods is in the order named, although
_ the high cost of platinum is a great

Fig. 56.—J. L. Smith crucible.

obstacle to the continued use of the
chlorplatinate method and its re¬
covery from residues involves con¬
siderable expense and loss of metal in
each operation.

Chlorplatinate Method.—This con¬
sists in the precipitation of potassium
chlorplatinate from an alcoholic solu¬
tion by chlorplatinic acid:

2KC1 + H 2 PtCl 6 -+ KoPtClc + 2HC1.

Sodium chlorplatinate is soluble in
alcohol and this fact is used in its
separation from potassium. Ammo¬
nium chlorplatinate, also, is only
slightly soluble in alcohol. It is
therefore necessary that ammonium
salts be expelled by heating, before the
reagent is added, and that the work be
done in a room free from ammonia.

Decomposition of Soil Sample.—Grind in an agate mortar 0.5 gm of soil,
accurately weighed, with 0.5 gm of ammonium chloride. When thoroughly
mixed, add 4 gm of precipitated calcium carbonate and mix well by grinding.
Place about 2 gm of calcium carbonate in the bottom of the crucible then
add the ground mixture from the mortar and rinse the latter with about
0.5 gm of calcium carbonate. Brush the mortar well and add any traces
of material to the charge in the crucible. Settle the mixture well by tapping
gently, place the crucible in a hole in an asbestos board and heat in such a
way that only the lower portion is reddened. After ammonia ceases to
escape, turn on the full heat of the burner to all but the upper portion of
the crucible and continue the heating for 45 minutes. The crucible should
be red hot. The entire heating may be done more conveniently by placing
the asbestos carrying the crucible over the top of a small electric furnace of
crucible type, the lower portion of the crucible being in the furnace. The

SOILS

245

temperature of the latter is gradually raised to SOO-900 0 , as shown bv a
pyrometer.

-^fter the crucible has been cooled transfer the contents to a 300-cc
porcelain dish, add sufficient hot water to cover the semi-fused mass, heat to
boiling and let stand until the whole mass is completely slaked. Some
samples are difficult to slake, due usually to heating to too high a temperature
or to the presence of too little calcium carbonate in the mixture. These
require digesting for some time on a steam bath; or the solution and residue
may be placed in a porcelain dish and ground gently with an agate pestle.
Filter the solution containing the disintegrated mass, collecting the filtrate
in a 400-cc Pyrex beaker. Macerate the residue in a mortar, rinse several
times with boiling water and finally filter and wash with boiling water until
about 350 cc of filtrate has been collected.

To the filtrate add enough ammonium hydroxide to make basic, then
ammonium carbonate to precipitate calcium. Heat to boiling then filter
into a platinum dish, evaporate to dryness on the steam bath and heat to dull
redness to expel most of the ammonium salts. Dissolve the residue in 5 ee
of hot water. If any insoluble residue remains, repeat the addition of
ammonium hydroxide and carbonate, filter through a small paper, wash the
paper with hot water, add 1 cc of dilute hydrochloric acid to the filtrate and
evaporate filtrate and washings in a platinum dish. Heat to dull redness for
a short time to expel ammonium salts. This residue of potassium and
sodium chlorides is ready for the determination of potassium.

Determination of Potassium: Chlorplatinate Method .—(To be performed
in an atmosphere which is free from ammonia.) Dissolve the residue of
potassium and sodium chlorides, obtained as above directed, in 50 cc of hot
water and then add chlorplatinic acid (containing 10 per cent of platinum
or 26.5 per cent of chlorplatinic acid crystals), using about 1 cc more than
the theoretical amount, calculated upon the assumption that the chloride
residue was all potassium chloride. Evaporate on the steam bath to a thick
paste but not to dryness, cool and add 50 cc of SO-per cent alcohol, stir up
the solid matter and allow 7 to stand, covered, for 30 minutes.

If the liquid is not visibly colored too little reagent has been used. In this
case new samples should be taken and the quantity of chlorplatinic acid
increased. Filter and wash the precipitate thoroughly with 80-per cent
alcohol, washing several times after the washings pass through colorless.
The wash bottle should be provided with ground-glass joints so that no rub¬
ber will come into contact with the alcohol. Remove the filtrate and
washings, pouring these into the bottle provided for platinum w 7 aste residues,
and wash the precipitate again, thoroughly, with 80-per cent alcohol, using
particular care in washing the upper part of the paper. Wash until only a
faint turbidity is produced by the addition of a drop of silver nitrate solution
to the last washings.

Drain most of the alcohol from the paper (or see next paragraph), slip the
latter out of the funnel and dry in the oven at 100°. Place a weighed
porcelain crucible upon a piece of glazed paper, remove most of the precipi¬
tate to the crucible, brushing up any particles that may have fallen upon the

24G

QUANTITATIVE AGRICULTURAL ANALYSIS

glazed paper, and then replace the paper in the funnel. Place the crucible
under the funnel and dissolve the remainder of the precipitate in the smallest
amount of nearly boiling water, allowing the solution to run into the crucible.
Evaporate to dryness on the steam bath, carefully wipe the outside of the
crucible with a clean towel and dry for 30 minutes at 105°. Weigh and
calculate the per cent of potassium in the soil.

Use of a Gooch or Alundum Crucible. —Proceed as above until ready to filter
out the potassium chlorplatinate. Prepare two Gooch filters as directed
on page 50, paying attention to the precautions suggested, and using strong
suction in forming the asbestos felt; or wash alundum crucibles with hot
water, using suction. Finally rinse the crucibles with alcohol, remove, wipe
the outside and dry at 100° to 105° for 30 minutes or until the weight is
constant. Weigh and replace in the holder. If Gooch crucibles were used,
moisten the asbestos with one or two drops of alcohol before the suction
pump is again turned on. Start the pump, then filter and wash the precipi¬
tate exactly as above directed. Remove the crucible, dry in the oven and
weigh. Calculate potassium as before.

Recovery of Platinum from Waste and Preparation of Chlorplatinic
Acid. 1 —Place the waste solutions in an evaporating dish having a capacity
of 2 liters for each 100 gm of platinum and evaporate until most of the water
has been expelled. Make basic with sodium hydroxide and add, stirring,
sodium formate, either solid or in concentrated solution. A quantity of
sodium formate equal to about half the weight of platinum to be reduced
will be required. If foaming occurs, add more sodium hydroxide. Heat
on the steam bath for one hour, stirring occasionally, then acidify with
hydrochloric acid (25-per cent solution) stirring during the addition of acid.

Filter off the precipitated platinum on a soft paper, using suction. Wash
twice with hot 2-per cent hydrochloric acid, then with hot water until free
from acid. Separate the platinum from the paper, dry, ignite and weigh.
Pour over the platinum in a porcelain dish five times its weight of 25-per cent
hydrochloric acid, heat on the steam bath and add slowly 50-per cent nitric
acid until no more gas is evolved. About 1 cc of nitric acid will be required
for each gram of platinum.

After the platinum is in solution, add 10 cc of 25-per cent hydrochloric
acid, evaporate to small volume and repeat this process twice. This
reduces and eliminates nitric acid. Dilute with water and evaporate, two or
three times, to expel hydrochloric acid. Finally dilute, cool and filter on a
soft paper whose approximate weight is known. If the filtrate is not per¬
fectly clear, refilter. Wash the paper free from any platinum stain and if
any appreciable residue remains on the paper, dry and weigh it on the filter.
Correct the weight of platinum for this weight of carbon, or other residue,
then make the solution to the desired concentration. For potassium
determinations the solution should contain 10 per cent of the element
platinum.

Delong, Chem. Weekblad , 10, 833 (1914).

SOILS

.247

Perchlorate Method. —Potassium perchlorate is nearly insolu¬
ble in 97-per cent alcohol while sodium perchlorate is quite
soluble. Potassium may be precipitated and separated from
sodium by making use of this difference in solubility. A 60-
per cent solution of perchloric acid is generally used. This
solution does not deteriorate on standing and it is not dangerous
to handle, as is the pure acid. It is necessary to have the solu¬
tion free from ammonium salts since ammonium perchlorate is
only slightly soluble in alcohol.

Determination of Potassium: Perchlorate Method .' 1 —The solution of
potassium and sodium salts, obtained by the Smith method (page 244) is
used for this determination. Evaporate to about 25 cc and add 1 to 2 cc
of 60-per cent perchloric acid solution. Evaporate in a hood until white
fumes of perchloric acid appear, cool and dissolve the residue in a small
amount of hot water. Again add 1 cc of perchloric acid solution and evaporate
until the solution evolves dense white fumes of'perchloric acid. Cool to
room temperature and add 25 cc of a solution made by mixing 1 cc of 60-
per cent perchloric acid with 300 cc of 97 to 98-per cent alcohol. If the
insoluble potassium perchlorate is caked it should be broken with a stirring
rod so that no soluble salts will escape the action of the alcohol.

During the process of evaporation of the various solutions a Gooch filter
should be prepared, the asbestos felt being washed with the perchloric acid-
alcohol mixture. The filter is dried for one hour at 120° to 130°, cooled and
weighed. Filter the solution on this prepared filter, removing every trace
of the precipitate from the beaker by means of a policeman and the prepared
washing solution, and wash four or five times with this solution. Dry for
one hour at 120° to 130°, cool and weigh.

From the weight of potassium perchlorate thus obtained calculate the
per cent of potassium in the sample.

Loss on Ignition. —Loss due to igniting the soil in contact with
air includes that due to the volatilization of ammonium salts
and water of hydration, to combustion of organic matter, and to
decomposition of carbonates and sulphides. This loss may be
reduced, in some instances, by the oxidation of ferrous iron.

Determination of Loss on Ignition.—The samples of dry soil obtained in
the moisture determination are heated slowly to redness in a muffle furnace,
using the same crucibles, until the organic matter is destroyed. The
crucibles are then cooled in a desiccator and weighed and the per cent
of loss is calculated.

'Scholl, J. Am. Chem. Soc., 36 , 2085 (1914).

248

QUANTITATIVE AGRICULTURAL ANALYSIS

Organic Matter. —In a natural soil there is a close relationship
between the proportion of organic matter and the fertility.
The cause of this is partly physical (improving the texture of a
soil increases its absorbing capacity) and partly biological in
that promoting the growth of bacteria, molds and protozoa helps
to release essential elements to further availability. Organic
matter also furnishes plant food directly. Many definite
chemical compounds have been isolated 1 from the complex soil
organic materials.

Methods for Determining Total Organic Matter. —An ap¬
proximate calculation of organic matter may be made from the
per cent of carbon, the average carbon of soil organic matter
being taken as 58 per cent. 2

Loss on ignition, as already determined, is sometimes taken as
an approximate measure of organic matter. The results obtained
by this method usually differ considerably from those obtained
by calculating the organic matter from carbon, for reasons already
explained.

Of the various methods that have been used for the determina¬
tion of carbon, direct combustion and oxidation by a mixture of
chromic and sulphuric acids have been most widely adopted. At
present, due chiefly to the efficiency of the modern electric furnace
and to failure to obtain complete oxidation by other methods, the
direct combustion method has found greatest favor. By any
of these methods, carbon dioxide of carbonates is measured
along with that produced by the oxidation of organic carbon
and this occasions an error in organic matter calculations, unless
carbonate carbon is determined and a correction applied.

The combustion method is similar to that used for the deter¬
mination of carbon in iron and steel. It depends upon the direct
combustion of the soil in a current of oxygen, the carbon dioxide
produced being absorbed in standard barium hydroxide and the
excess of base titrated.

Warrington and Peak illustrate the discrepancies between
the results obtained by calculating organic matter from
loss on ignition and from carbon determinations by the
following table:

1 U. S. Dept . of Agr., Soils , Bull. 74 (1910).

2 See also Read and Riddgell, Soil Sci., 13 , 1 (1922).

SOILS

249

Table XXII.— Organic Matter by Two Methods

Kind of
soil

Per cent loss on ignition after drying at

Organic
matter
calculated
from carbon

100°

120°

150 c

a ^t\ire.

9.27

9.06

8.50

6.12

Pasture.. . .

..| 7.07

6.88

6.55

4 16

s soil.

. .| 5.95

1 5.70

5.61

2.44

subsoil.

! 5.39

4.76

0.65

•rbonate Carbon.—Carbon dioxide of carbonates varies from
to 0.25 per cent in all but limestone soils. It is necessary
now the amount of carbonate carbon in a soil before that
in/fc in organic form can be calculated.

ie method for the determination of carbonate carbon depends
i blie decomposition of the carbonate with dilute hydrochloric
a nd the passing of the gas into standard barium hydroxide,
excess of base being titrated with standard acid. See page
3 art I, for details of the method.

! teinnination of Total Carbon.—The apparatus (Fig. 57) consists of the
ving parts: A steel cylinder, A, containing oxygen under pressure; a
e, J3 } containing 30-per cent potassium hydroxide solution followed by

Fig. 57.—Apparatus for the determination of carbon by combustion.

Dn-fcaining soda lime to remove possible traces of carbon dioxide from the
5 en.. D , an electric tube furnace 30 cm long fitted with a combustion
i, _E7, of fused quartz, vitreous silica or porcelain, 60 cm long and with an
le.diameter of 2.5 cm, to serve for the combustion. To insure complete
ation of carbon monoxide, the last half of the portion of the combustion
5 which is inside the furnace is filled loosely with platinized asbestos,
zIol acts as a catalyzer.

orLnection with the combustion tube is made by means of one-hole rubber
>pers and short glass tubes. The ends of the combustion tube, contain-
th.e rubber stoppers, are cooled by means of cotton wicks which dip into

250

QUANTITATIVE AGRICULTURAL AN A ^ Y * IS

bottles containing distilled water. (Ordinary ground will deposit a

crust of salts in the wick, this finally stopping capillary SL&'bion.)

A small bottle, F , containing granulated zinc, is attached *fco the combustion
tube. This absorbs chlorine and oxides of sulphur fror 11 P r °ducts of

combustion. Connected with this bottle is the set of HVteyer absorption
bulbs, G y containing standard barium hydroxide. The tu.t> e ^ contains soda
lime and this protects the barium hydroxide from the carbon dioxide of the

The furnace should be heated to about 950° (bright red ) ^nd the stopcock
opened so as to permit oxygen to pass through at the rate about 1000 cc in
20 minutes.

Prepare solutions as follows:

(a) Barium Hydroxide. —A saturated solution of the base is first made by
warming and stirring the solid with recently boiled water*, using a ratio of
70 to 100 gm of the base to 1000 cc of water, according to the purity of the
barium hydroxide obtainable. Cool to room temperature and siphon
into a bottle, which is then closed with a rubber stopper. Dilute 550 cc of
this solution to 1000 cc with recently boiled and cooled distilled water, mix
and place in a bottle which is provided with a guard tube of soda lime and
a siphon or similar outlet. (For a method for protecting tliis and the other
solutions, see Fig. 22, page 84.)

( b ) Hydrochloric Acid. —Calculate the dilution such tlr ut 1 cc shall be
equivalent to 0.002 gm of carbon and make the solution from recently
boiled and cooled distilled water. Standardize against sodium carbonate,
using methyl orange. Refer to page 82, Part I.

• (c) Water , Free from Carbon Dioxide. —Boil distilled water for 5 minutes
and then cool rapidly and preserve in bottles provided witlu siphon outlets
and soda lime guard tubes. Instead of boiling, a current of air may be
drawn through the water (best slightly warmed) for one Dour, the air first
passing through soda lime. This water is not to be used in ctn ordinary wash
bottle, from which water is expelled by blowing.

Blanks. —Rinse the Meyer bulbs with water (c), then moixsure into them
from a burette or an automatic pipette attached to the bo'fctle, 50 cc of the
dilute barium hydroxide solution, first discarding the few drops that are in
the outlet of the measuring instrument. Add to the bulbs From a graduated
cylinder enough water (c) to bring the liquid to the lower edge of the upper
bulb when the gas is flowing. The quantity necessary shoirld be determined,
once for all, so that it may be added without delay in subsequent determina¬
tions. With the furnace already heated, connect the bult>s in place while
the oxygen is flowing at the rate of about three bubbles per* second. At the
end of 15 minutes, disconnect the bulbs without stopping the flow of gas and
replace with a second set of bulbs, similarly charged.

Rinse the barium hydroxide solution from the first set into a 500-ce
Erlenmeyer flask, using water (c). Pay no attention to any precipitate
that may remain in the bulbs. Add a drop of phenolphtlrrtlein and titrate
at once with the standard hydrochloric acid. The acid mriHt not he added
too rapidly and the solution must be stirred continuously, ho that no local

SOILS

251

excess of acid may be attained. Note the volume of acid required to dis¬
charge the color. The pink color may return as the solution is allowed to
stand but this is not considered in the reading.

At the end of 15 minutes from the time the second set of bulbs was inserted,
replace the first bulbs, recharged with barium hydroxide. The titration of
the second solution constitutes the second “ blank ” and the average of this
and the first is to be taken as the acid equivalent of the bari um hydroxide
solution.

While one or more blank determinations are running weigh 2 gm of 100-
mesli soil and transfer it to an alundum boat (about 10 cm long and as wide
as the tube will allow) and mix the soil with an equal weight of 20-mesh
alundum. Replace the Meyer absorption tube by another, containing
exactly 50 cc of fifth-normal barium hydroxide solution. Place the boat in
the combustion tube, connect and continue to pass oxygen for 20 minutes.
At the end of this period, disconnect the absorption tube and replace by a
second, containing barium hydroxide as before. Without interfering with
the flow of oxygen, immediately withdraw the boat from the tube and insert
another, containing a sample weight as before. Insert the stopper carrying
the oxygen tube and while combustion is proceeding with the second sample,
rinse the barium hydroxide from the first Meyer tube into a 500-cc Erlen-
meyer flask, using 50 cc of carbon dioxide-free water, and titrate the unused
excess with standard acid, using phenolphthalein as indicator. Calculate
the per cent of total carbon and from this the per cent of organic carbon,
deducting that present in the carbonate form.

Soil Humus.—This is a somewhat indefinite term, used to
designate an intermediate stage of decomposition of the complex
organic residues usually found in the soil. The term “humus” is
arbitrarily used to include that part of the soil organic matter
which has reached a stage of decomposition in which it is soluble
in 4-per cent ammonium hydroxide. Part of this decomposed
organic matter contains certain substances having acid prop¬
erties, which combine with basic materials to form organic
salts called humates. Total humus material is the active avail¬
able organic plant food, while the residual organic matter is
useful in improving the soil texture.

There has been considerable discussion concerning the real
value of the humus determination. While it must be admitted
that the term “humus” does not cover a sharply defined class of
compounds and that the result of the determination is subject
to considerable variation unless the method is rigidly standard¬
ized, it yet appears that some useful information is obtained,
in at least approximately classifying organic matter into easily

252

QUANTITATIVE AGRICULTURAL ANALYSIS

and immediately available forms and those not so available. 1 The
determination is no longer official.

Determination of Humus.—Five-gram samples of air-dried soil, ground
to pass a 60-mesli sieve, are placed in 500-cc wide-mouthed bottles and
washed repeatedly by shaking with a 1-per cent solution of hydrochloric acid
until calcium and magnesium are no longer extracted, as shown by testing a
small quantity of filtered solution with ammonium hydroxide and ammo¬
nium oxalate. The first washings need not be tested. The wash¬
ing can be hurried by manipulating the bottle in a shaking machine for
15 minutes (Fig. 51). After calcium and magnesium have been removed,
filter the solution and wash the soil free from acid by decantation. Return
the filter and its contents to the bottle and add 250 cc of 4-per cent ammo¬
nium hydroxide. Shake in the machine for three hours, or every 30 minutes
by hand for six hours, then place the bottle in a horizontal position for twelve
hours.

Again shake the bottle well and pour the contents upon a 24-cm filter
paper in a funnel. Cover the funnel with a watch glass. The filtrate may
be very turbid for an hour or more. In this case, refilter. When the filtrate
comes through clear, save 100 cc or more of it in a clean flask. Pipette
50 cc of the clear filtrate into an 8-cm evaporating dish. Evaporate to dry¬
ness on a steam bath, dry in the oven for an hour at 100°, cool in a desiccator
and weigh. Burn the carbonaceous matter to an ash in the muffle furnace,
cool, weigh and calculate the difference between the two weights as per cent
of humus.

Extraction of Material Soluble in Strong Acid.—As in the case
of organic matter, the inorganic constituents of the soil are
combined in forms which differ widely in degree of availability.
Calcium may be present either as limestone (calcium carbonate)
which is easily soluble in acids, or as one or more of a variety of
silicates, such as anorthite (calcium aluminium silicate) which is
nearly insoluble. A similar variation exists with potassium,
which may be present as a soluble carbonate or as orthoclase, a
silicate of potassium and aluminium which is highly insoluble.
Extraction of the soil with hydrochloric acid provides an approxi¬
mate distinction between materials of small availability and the
more available ones. The acid extract may be evaporated to
dryness and the extract simply weighed, or the residue may be
subjected to a partial or complete analysis as outlined for the
original soil.

The amount of material dissolved by the acid varies with the
concentration of the latter, the fineness of division of the soil

1 Soil Science, 3, 515 (1017).

SOILS

253

particles and the length of heating. It is therefore obvious that
such an extraction constitutes only a conventional division into
somewhat arbitrary classes of materials.

Other Inorganic Constituents. —The methods outlined in the
following pages may be applied to the analysis of the original
soil or of an acid extract, as explained above. As the soil always
contains a large proportion of materials insoluble in acids the
principal analysis must be preceded by a decomposition such as
will bring the sample into complete solution, with the exception
of silica, which is separated and weighed. Two methods for the
decomposition will be discussed.

Decomposition of Soil Sample : (a) Hydrofluoric Add Method .—
The soil is treated with hydrofluoric acid and a small amount
of sulphuric acid. Silica of silicates is volatilized as silicon
tetrafluoride:

Si0 2 + 4HF SiF 4 + 2H 2 0.

Metals are left as sulphates, which decompose by ignition, leaving
oxides. These are, for the most part, soluble in hydrochloric
acid. This method of soil decomposition is often used where a
determination of silica is not required. It obviates, to some
extent, the difficulties which are encountered when silica is
determined in the same sample with the other constituents but
the residue of oxides is often difficult to dissolve and the fusion
method is to be preferred.

(6) Fusion with Alkali Carbonates .—The decomposition of a
soil by fusing with sodium carbonate is of greatest use when total
silica is to be determined. The silica is usually chiefly com¬
bined with sodium and aluminium in albite (NaAlSi 3 0 8 ), with
potassium and aluminium in orthoclase (KAlSi 3 0 8 ), or with
aluminium in clay (AhS^CVAH^O). When orthoclase, for
example, is fused with sodium carbonate, the reaction which
takes place may be represented as follows:

2KAlSi 3 0 8 + 6Na 2 C0 3 K 2 Si0 3 + 5Na 2 Si0 3 + 2NaA10 2 +

6C0 2 . (1)

The silicates formed in the above reaction may be decomposed
easily by hydrochloric acid, forming soluble alkali chlorides and
silicic acid:

Na 2 Si0 3 + 2HC1 H 2 Si0 3 + 2NaCl.

(2)

254

QUANTITATIVE AGRICULTURAL ANALYSIS

There are also formed soluble chlorides of iron, aluminium,
calcium and such other metals as were present in the soil.

The silica is separated almost completely from the other
compounds by evaporation to dryness and heating to about 120°
to decompose the silicic acid:

H 2 Si0 3 H 2 0 + Si0 2 . (3)

The residue is taken up with water and hydrochloric acid and
the insoluble silica is separated by filtration. However, this
separation is incomplete as there is a tendency to form a hydrosol
of silicic acid. The error thus produced may be avoided by
filtering off the silica formed on first evaporation and repeating
the dehydration of soluble silica by a second evaporation. The
silica finally obtained is not pure but the amount of impurities
may be determined by treating the ignited and weighed pre¬
cipitate with hydrofluoric acid, thus converting the silica into
silicon tetrafluoride. The latter is volatilized by heating, leaving
oxides of iron and aluminium as a residue.

Silica.—The function of silicon in plant growth is not well
understood. There is a considerable amount of this element in
some plants (notably oat and rye straw) and it may serve some
useful purpose, not yet understood.

Aluminium.—Compounds of aluminium are present in normal
soils in rather large quantities.. The per cent of aluminium in
sandy loam is about 1.5, in clay loam, 4.5, and in residual soils
formed from gneiss or limestone about 13. Residual soils
usually contain much more aluminium and iron than do glacial
soils. Salts containing aluminium are present in some acid
soils in sufficient amount to exert a toxic influence on certain
plants; barley and corn are particularly sensitive t'o it. This
effect is probably due to the existence of colloidal basic aluminium
salts which are capable of being absorbed by the plant. The
toxicity may be corrected to a considerable extent by an applica¬
tion of calcium silicate, acid phosphate, or limestone to the soil,
thus causing the aluminium to form a less soluble compound.

Iron. —The iron content of soils is quite variable. In soils
only slightly tinted, from 1.5 to 4 per cent of iron, calculated
as ferric oxide, is found. Ferruginous loams contain from 3.5
to 7 per cent and the red lands from 7 to 14 per cent.

SOILS

255

Iron and aluminium are precipitated together as hydroxides.
If titanium is present in the soil the precipitate will contain also
titanium hydroxide. Phosphorus will be precipitated here as
basic ferric phosphate. The combined precipitate is ignited and
the oxides and phosphate weighed together. Iron is then
determined by dissolving and titrating with a standard per¬
manganate or dichromate solution. Phosphorus is determined
in a separate sample and calculated to.the pentoxide, while
titanium is usually ignored unless it is known to be present in
appreciable quantities, as it has no known biological signifi¬
cance. The sum of the per cents of oxides of iron and phos¬
phorus, subtracted from the per cent of total residue, gives the
per cent of impure aluminium oxide.

Direct Method for Deter minin g Aluminium.—The above
procedure necessarily throws the combined errors of all of these
determinations upon aluminium. If an accurate determination
of the latter is required, a direct determination may be made.
In this case the precipitate of hydroxides is redissolved without
previous ignition and the iron is reduced to the ferrous condition
by sodium thiosulphate:

2Na 2 S 2 0 3 + 2FeCl 3 Na 2 S 4 0 6 + 2FeCl 2 + 2NaCl.

The aluminium is then precipitated as phosphate, ferrous phos¬
phate remaining in solution.

Purification by Double Precipitation. —The precipitates of
iron and aluminium hydroxides, of calcium oxalate and of mag¬
nesium ammonium phosphate are difficult to purify by simple
washing. If accuracy is important, purification is usually
accomplished by dissolving the partly washed precipitate,
redissolving and reprecipitating. In the solution from which the
second precipitation is made the concentration of soluble salts
is only a small fraction of that in the original solution and the
amount now carried down by the precipitate and not removed
by washing is extremely small.

Calcium.—Many soils that are noted for their fertility have a
high calcium carbonate content. Examples of such are the
blue grass soils of Kentucky, the calcareous prairie soils of
Illinois and Indiana and the black prairie soils of Texas and
Mississippi.

256

QUANTITATIVE AGRICULTURAL ANALYSIS

Calcium functions particularly in stimulating root develop-'
ment and it is thought to be connected in some way with the
development of cell wall material. Some crops, such as alfalfa,
clover, and tobacco, require large amounts of calcium for good
growth and development.

For the determination, calcium is precipitated from the
filtrate from iron and aluminium as calcium oxalate. The
calcium may then be determined gravimetrically, as oxide, or
volumetrically by titration with standard potassium perman¬
ganate. These determinations are discussed on pages 63 to
69, Part I.

Magnesium. —This is a plant food element which plays an
important part in seed production as magnesium, like phosphorus,
moves to the seed to a great extent. In this respect it is unlike
potassium and calcium, which remain largely in the stem and
leaf. Magnesium appears also to function in oil and chlorophyll
production.

Magnesium is determined in the filtrate from calcium oxalate
by precipitating as magnesium ammonium phosphate in a solu¬
tion previously made basic with ammonium hydroxide. The
precipitate is ignited and weighed as magnesium pyrophosphate.
The principles underlying this determination have been discussed
in connection with the analysis of phosphate, page 87, Part I.
When magnesium is being determined, a soluble phosphate is
used as the reagent.

Determination of Total Silica.—Weigh accurately about 1 gm of soil into
a platinum crucible, burn off the organic matter and when cool mix with
approximately 10 gm of sodium carbonate. Place the cover on the crucible
slightly to one side so that the contents may be observed. Heat gently at
first, using a small burner. Gradually raise the temperature to that of the
full flame and heat until gas evolution is only slight. Place the crucible over
a blast lamp and heat for at least 15 minutes after the evolution of carbon
dioxide has ceased. While it is still hot, rotate the crucible by manipulating
the triangle, so that the fused mass will spread over the sides as ffc solidifies.
When it has cooled, place the crucible on its side in a casserole and cover
with hot distilled water.

Heat until the fused mass has disintegrated, cover and gradually add 15 ce
of concentrated hydrochloric acid from a pipette through the lip of the cas¬
serole. Place on a steam bath and, after all effervescence has ceased, remove
the crucible and cover, rinsing well. Use a stirring rod for this purpose.
By inserting this in the mouth of the crucible the latter can be raised out of

SOILS

257

the solution and the outside thoroughly rinsed. It can then be taken in
the hand and the interior rinsed. A policeman may have to be used if silicic
a cid adheres to the crucible. Do not use metal crucible tongs for removing
cruczbles from solutions, especially if the latter are acid , as in this case.

Evaporate the liquid to dryness over a steam bath, or keep the casserole
in constant motion over a low flame. Heat for 15 minutes at 120° in an
oven constructed of material that will not be damaged by acid vapors, or to
just below redness over a flame. When cool, add 5 cc of' concentrated
hydrochloric acid and 75 cc of water, heat until soluble salts are dissolved,
filter off the silica and wash the paper and silica with hot water until free
from acid. Repeat the evaporation of the filtrate and washings and treat
ns before, using a different filter paper. Save the filtrates and washings for
the determination of other inorganic constituents.

hurn both filter papers in one platinum crucible (which need not be
weighed previously) then ignite over a blast lamp, cool and weigh. Add a
few drops of sulphuric acid and about 5 cc of hydrofluoric acid (pouring the
latter directly from the bottle) to the material in the platinum crucible and
volatilize the silicon tetrafluoride and acids by evaporation to dryness under
a hood. Ignite the residue and weigh. The loss in weight represents
silica. Calculate the per cent.

The residue in the crucible consists of oxides of iron and aluminium. Add
about 1 gm of potassium pyrosulphate and heat, gradually raising the tem¬
perature to redness, until solution of the oxides is complete. Cool and
dissolve the fusion in hot water. Precipitate the metals as hydroxides, as
directed below, wash and discard the filtrate and washings. Preserve the
precipitate on the paper, so that it may be burned in the same crucible as
the main precipitate of iron and aluminium hydroxides, the total oxides
being weighed together.

I>etermination of Iron and Aluminium: Direct Method for Iron, Indirect
Method for Aluminium .—Dilute the filtrate from the determination of
silica to about 75 cc. Add a drop of methyl red and then add dilute ammo¬
nium hydroxide until the solution is distinctly basic, avoiding an undue excess.
Boil for 5 minutes or until the odor of ammonia is faint, but without
prolonging the boiling until the solution becomes acid in reaction. Filter the
precipitate through an extracted paper and wash with hot water two or three
times. Return the precipitate to the first beaker and dissolve in warm water
containing a small amount of hydrochloric acid. Reprecipitate, filter and
wash the precipitate free from chlorides. Save the filtrate and washings
from both precipitations for the determination of calcium and magnesium.

Burn the paper at a low temperature in a weighed platinum crucible,
inclining the crucible to facilitate oxidation. When most of the carbon has
been removed, add the paper containing the iron and aluminium hydroxides
from the silica determination (see above) and burn this in the same manner.
Finally heat to bright redness, cool in a desiccator and weigh as oxides of iron
(ferric), aluminium, titanium and phosphorus.

Unless the residue of oxides is white, add about 2 gm of potassium
pyrosulphate and heat^gradually raising the temperature to bright redness.

258

quantitative agricultural analysis

solution appears to be complete, cool and place the crucible on its side
in 50 cc of hot water in a beaker or casserole. Warm to hasten solution of
the mass of sulphates. Remove and rinse the crucible, heat to boiling and
add 1 cc of 5-per cent stannous chloride solution to reduce the iron. Cool
rapidly in running water and add, all at once , 50 cc of 5-per cent mercuric
chloride solution. This must produce a precipitate of pure white mercurous
chloride. If no precipitate is produced, not enough stannous chloride was
added. If the precipitate is gray, instead of white, too much stannous
chloride was used.

Titrate at once with standard potassium dichromate, following the
details of the method described on page 74, Part I. Or the determination
may be made with standard potassium permanganate as directed on page
72, Part I. Calculate the per cent of the total oxide and phosphate residue
and of ferric oxide in the soil sample. The latter, together with the per cent
of phosphorus pentoxide (as determined in a separate sample), subtracted
from the per cent of total residue, gives the per cent of aluminium
oxide and titanium oxide. The titanium is usually ignored, as
already stated.

Determination of Aluminium: Direct Method .—Make the double pre¬
cipitation of hydroxides and wash free from chlorides, as directed above,
saving the filtrates and washings for the determination of calcium and
magnesium.

Place a 500-cc beaker under the filter and redissolve the precipitate with
warm dilute hydrochloric acid. Pierce the filter and wash the paper well
with hot water. Dilute the solution to about 400 cc. Add 30 cc of a 10-per
cent solution of ammonium phosphate and then stir and add dilute ammo¬
nium hydroxide until a precipitate appears. Add 1.5 cc of concentrated
hydrochloric acid and 50 cc of a 20-per cent solution of sodium thiosul¬
phate and boil for a few minutes. Now add 15 cc of a 20-per cent solution
of ammonium acetate and 8 cc of 30-per cent acetic acid and boil for 15
minutes. The colloidal aluminium phosphate becomes granular and it is
then easily filtered and washed. Save the filtrate and washings for the
iron determination unless the original precipitate of hydroxides was per¬
fectly white, indicating the presence of no more than a trace of iron.

Redissolve the phosphate on the filter with concentrated hydrochloric
acid, wash through with hot water and reprecipitate aluminium phosphate
exactly as before. Wash with hot water, ignite and weigh as aluminium
phosphate, A1PO*. Calculate the per cent of aluminium oxide in the
sample.

Determination of Calcium. —Evaporate the combined filtrates from.
aluminium and iron hydroxides to about 50 cc, cool, add ammonium sul¬
phide to precipitate the manganese, filter and wash with hot water. Discard
the precipitate. Again evaporate the solution to about 50 cc, make slightly
basic with ammonium hydroxide and add, while still hot, 4-per cent ammo¬
nium oxalate solution, dropwise and with stirring, so long as any precipitate
is produced. Heat to boiling, allow to stand one hour or longer, decant
the clear solution on a filter, pour about 20 cc of hot water on the precipitate

SOILS

259

and again decant the clear solution on the filter. Dissolve the precipitate
in the beaker with a few drops of hydrochloric acid, add 15 cc of water
and reprecipitate by adding ammonium hydroxide and ammonium oxalate
solution as before. Allow to stand for an hour and filter through the
same paper. Wash the beaker and precipitate with hot water until free
from chlorides. Save the filtrate and washings from both precipitations
for the determination of magnesium.

Determine the calcium either gravimetrically or volumetrically.

(a) Gravimetric Method .—Place the paper and calcium oxalate in a weighed
crucible, heat carefully until dry and then ignite in the covered crucible for
30 minutes over a blast lamp or a Mdker burner. Weigh as calcium oxide
and calculate the per cent of this in the sample.

(b ) Volumetric Method .—Dissolve the calcium oxalate and titrate with
potassium permanganate, following the details outlined on page 69, Part I.
Calculate the per cent of calcium oxide in the soil sample.

Determination of Magnesium.—Acidify the filtrate from calcium with
hydrochloric acid and evaporate until ammonium chloride or oxalate begins
to crystallize. Add 10 cc of water and stir until the salts are in solution.
To the filtrate add a drop of methyl red and sufficient ammonium hydroxide
to make the solution barely basic. Now add from a pipette, slowly and with
stirring, 20 cc of a 10-per cent solution of disodium orthophosphate. Let
stand for 20 minutes or until crystallization begins, then stir and add a
quantity of concentrated ammonium hydroxide about equal in volume to
one-ninth of the total. Cover the beaker and let stand for three hours or
over night. Filter on paper, making no effort to remove adhering precipitate
from the beaker. Wash two or three times with dilute ammonium hydroxide
and discard the filtrate and washings. Dissolve the precipitate on the filter
with hydrochloric acid and allow the solution to run into the beaker contain¬
ing some of the precipitate. Wash down the paper thoroughly with hot
water, dilute to about 75 cc and precipitate the magnesium as before. Filter
the precipitate in an ignited and weighed alundum crucible and wash until
free from chlorides with a 2-per cent solution of ammonium hydroxide, test¬
ing the washings finally with silver nitrate solution made acid with nitric
acid. Cover the crucible and heat gently over a burner until dry and finally
heat for 20 minutes, using a blast lamp. Cool in the desiccator and weigh.
From the weight of magnesium pyrophosphate calculate the per cent of
magnesium in the sample.

Manganese. —Manganese is present to some extent in alluvial
clay soils but it is more abundant in volcanic clays. In small
amounts, approximating not more than about 50 lb. of manganese
per acre of soil, 6% in. deep (0.0025 per cent), it seems to have
a stimulating effect on plant growth. Many plant compounds
contain manganese but its biological function is not well
understood.

260 QUAXTITATJVE AGRICULTURAL AX A L Y SIS

The manganese content of a large number of different legumes
(aerial portion) was determined by Jones and Bullis, 1 who found
alsike clover to liave the greatest amount, averaging 0.068 per
cent, while alfalfa had the least, with 0.023 per cent.

Work on tlie effect of manganese has been done also by Kelley, 2
who concluded that manganese is a plant food, w^hen present in
small amounts, but that in larger quantities it becomes toxic.

In some Hawaiian soils the per cent of manganese is so high
as to interfere with the growth of the pineapple, causing a depres¬
sion in iron assimilation. 3

The bismuthate method for the determination of manganese
is one of the best. It is based upon the use of sodium bismuthate
to oxidize bivalent manganese to heptavalent manganese in the
form of permanganic acid. When a solution of manganous
nitrate is treated with sodium bismuthate the reaction proceeds
thus:

2Mn(N0,) s + 5NaBi0 3 + 14HN0 3 2NaMn0 4 + 3NaNO s +

5Bi(N0 3 ) 3 + 7H 2 0.

Sodium permanganate so produced is reduced by means of a
standard reducing agent, the excess of which is then titrated
with standard permanganate solution.

Persulphate Method for Manganese.—Manganese may be
oxidized by ammonium persulphate, in the presence of silver
nitrate, from a bivalent to a heptavalent condition, producing
permanganic acid:

(NHO 2 S 2 O* + 2AgK0 3 -> AgaSsOs + 2KTH 4 N0 3 , (1)

AgoSgOg + 2H s O —>2H 2 S0 4 4- Ag 2 0 2 , (2)

5Ag 2 0 2 -f 2Mh(N0 3 ) 2 + 6HN0 3 ->2HMn0 4 + lOAgNO, +

2H 2 0. (3)

The manganese is determined in an extract from the soil fusion
by comparing the intensity of color produced in this manner with
that of a manganese solution of known concentration, similarly

1 J. Ind. Eng. Chem., 13, 6 (1921). See also McHabgtte, J . Am. Chem.
Soc., 44, 1592 (1922).

2 Hawaii Exp. Sta. Bull. 26 (1912).

2 Johnson, Ibid., 9, 1 (1917).

-yuiLs

-treated, or by titration with a standard reducing asent
ferrous ammonium sulphate „ r .odium argute: '

2HMn0 4 “h oXa.^AsO^ 4- iHvn_- v , \ • o m, v,

k X a A-<) i 4- 2M:i XO

•>H i>

Detenniip^a of Manganese:

ing solutions:

(a) Potassiu/n per /nan gait at *■ , s ’duh^n 1 n*
gin of manganese by the following r i*aetmn:

KM 11 O 4 + 5 Fe(XO ;i ),> - 4 - SHNi > k\< > ..

MlJ N«

Standardize against ferrous ammonium sulphate „r ..lain, „vai it «. ,,
directed on page 68, Part I.

(*) Ferrms ammonium tulphot, edition, the e..«uvntrati.. !1 to U- uh„u<
equivalent to that of the potassium pcnuHcamfr solution and ™r a , BS
50 cc of concentrated sulphuric add in each HAW ce. The .-du- ,.., .
standardized by blank titrations at the time it is used in the determ;rum.V
of manganese.

centrated acid with three volumes of water

(d) Nitric Add, Specific Grant,, 1.015.—Dilute three volumes of the cm-
centrated acid with 100 volumes of water.

Ignite I gni of soil gently in air until all organic matter is burned.
the ignited soil as directed for the silicon determination, page 256. After
the fusion is perfectly fluid place the cooled crucible on its side in a covered
casserole and add nitric acid ; v < until the sodium carbonate is decom postil.
Rinse and remove,the crucible unci evaporate the solution to dryness on the
steam bath. Finally take up with 50 ce of nitric acid c . Heat to aid in
solution but do not evaporate much of the acid. Cool, add about 0.5 grsi
of sodium bisrnuthate and stir. After 10 minutes add 50 cc of nitric acid
(d) and filter the whole through a Gooch filter, using suction. After filter¬
ing? wash the beaker and crucible with <50 ec of the same nitric acid.
From a burette add to the filtered solution 35 ce (more if necessary to
reduce all permanganate) of ferrous ammonium sulphate solution <h: m The
permanganate is reduced and there is an excess of ferrous salt present.
Titrate this excess to a faint pink color with standard potassium perman¬
ganate solution (a).

A blank determination is made, using 50 ce of dilute nitric acid, 50 ce of
nitric acid (d) and 0.25 gm of sodium bisrnuthate. Filter through asbestos
and wash with 50 cc of nitric acid as in the previous determination.
From a burette add 35 cc of ferrous ammonium sulphate solution and
immediately titrate with the standard potassium permanganate. The
difference between the volumes of permanganate required for the blank and
the manganese determination, respectively, is that equivalent to manganese
in the sample of soil. Calculate the per cent of manganese-

262 QUANTITATIVE AGRICULTURAL ANALYSIS

Determination of Manganese: Persvl'phate Method. The standard per¬
manganate solution prepared as for the bismuthate method is used in this
case.

One gram of soil is fused and treated as directed above for the bismuthate
method. Do not add sodium bismuthate but after the residue from evapora¬
tion has been dissolved in nitric acid, add 15 cc of a 0.2-per cent silver nitrate
solution, following immediately by 1 gm of ammonium persulphate. Heat
by placing the beaker or casserole in hot water until the pink color is fully
developed. Cool and rinse into a tube of a color comparator. Place in
another tube enough of the standard permanganate solution (measured
accurately) to make a somewhat greater intensity of color, when viewed from
above, dilute to the mark and mix. Place both tubes in the comparator
(Fig. 52, page 237) and adjust to equality of color. Calculate the per cent
of manganese in the sample.

Sulphur.—The sulphur content of most soils is usually less
than that of phosphorus, while considerable sulphur is needed
by certain plants to produce proteins and flavoring oils. It has
been shown that onions, mustard, and cabbage usually respond
favorably to the addition of either elementary sulphur or sul¬
phates to the soil. The function of sulphur in the plant metab¬
olism is not well understood.

The determination of sulphur in soil is preceded by fusion with
sodium carbonate in the presence of a small amount of an oxidiz¬
ing agent, the latter in order to convert protein sulphur to the
form of sulphates. The sulphate thus formed, together with
sulphates originally present as such, is later precipitated and
weighed as barium sulphate. The heating should be done with
an alcohol burner or in an electrically heated muffle furnace
instead of with a gas flame because of danger of absorption of
sulphur dioxide from the burning gas (which always contains
hydrogen sulphide) by the sodium carbonate.

Determination of Sulphur.—Mix 2 gm of 100-mesh soil with 7 gm of
anhydrous sodium carbonate (free from sulphates) and 0.5 gm of potassium
nitrate in a platinum crucible. Place the covered crucible in an electrically
heated muffle and heat to dull redness until well fused, after which remove
the crucible and tip it in such a manner as to cause the contents to solidify
on the sides. While it is still hot place the crucible in 75 cc of cold water in
a 200-cc beaker (use care). Cover and heat the beaker and contents to
boiling. Stir until all lumps of the fused mass have been disintegrated, then
filter into a 400-cc beaker and wash the residue until the volume is about
200 cc. Reduce any sodium manganate present by boiling with a few drops

°! al ^ohol t add a dmp „f methyl r**d ,-md add :,d;n t ,r,; * r ■

Pipuntil neutral. Xmv add 1 n* of ’.v — C /-i: : , -

acic * (or an equivalent volume of acid «.f uth, r . lb/w* % : *■

au<i a dd, dropwise and with eontmuuiis >*irrirm. a !h_-,. , ,•?

solution of barium chloride to precipitate all -ulph.it*>. IhD-? at ’*,;r/.
boiling until the precipitate settle- readily. Kilter of: the prevented
ftrium sulphate and wash with li**t water until fret* from -rales, i'.m ~
u lly burn the paper in an inclined erueihle, with free access of air. u:;?d
white but do not allow the erueible to become bright red and d- :a*t ia at
onger than is necessary to burn all carbon, tfalculate the per cent v:
sulphur in the soil, expressing as the element and as -ulphur trloxide.

Lime Requirements of Soils. —Lime is added to acid soils for
the purpose of neutralizing their excess of acid but it also changes
the physical texture of the soil. In addition to these effects,
there is a precipitation of iron and aluminium from soluble salts
as hydroxides, in this way lessening their toxicity.

Calcium itself is regarded as one of the necessary elements
in the plant economy’. There is considerable difference with
regard to the need of different plants for calcium and also with
respect to their ability to draw this element from the less available
sources. Alfalfa Is an example of a plant that needs much cal¬
cium in its metabolic processes but having a rather limited feed¬
ing power while, on the other hand, the rye plant needs much
less calcium but possesses ample feeding capacity to secure the
little it requires.

It is generally r considered that many’ soils possess acidity
through the presence of insoluble acid salts of organic and
inorganic acids and a number of methods in use for the deter¬
mination of soil acidity are based upon this assumption. Certain
fertilizers have a tendency’ to cause a soil to become acid. This
is especially true of ammonium sulphate. As nitrogen is taken
from this salt by the plant, sulphuric acid remains as a
residue in the soil. Green manures have been credited also with
producing acid soils, acid being formed during fermentation.
However, much confusion still exists concerning the true nature
of soil acidity’ and consequently’ there is no generally’ accepted
method for its determination. The lime calculated to be
required to neutralize acidity varies, therefore, according to the
method employed for the determination of acidity’.

204 QUANTITATIVE AGRICULTURAL ANALYSIS

Veitch Method . 1 —In the Veitch method for the determination
of soil acidity a measured quantity of lime water solution of
known concentration is evaporated to dryness with a definite
amount of soil. The mass is then extracted with distilled water,
phenolphthalein is added and the solution is concentrated by
boiling. If the quantity of calcium hydroxide added was more
than sufficient to neutralize soil acids, an indication of this will
be given by a pink color from the phenolphthalein. By this
method there is probably some error due to a combination of
calcium hydroxide with organic matter and possibly with carbon
dioxide from the air.

Determination of Lime Requirement of Soil: Veitch Method. —Weigh five
portions of 10 gm each of the soil into 8-cm porcelain evaporating dishes.
Add fiftieth-normal calcium hydroxide solution in such amounts that it will
range from 2 cc below to 2 cc above the probable amount of calcium
hydroxide needed, making a difference of 1 cc in the volume of calcium
hydroxide for each pair of consecutive members of the series. A series
extending over 5 to 10 cc of solution may be used as a beginning. Evapo¬
rate all to dryness over the steam bath and immediately take up the residues
with distilled water and transfer to 300-ec flasks, using 150 cc of water,
previously freed from carbon dioxide by boiling for several minutes in an
open beaker or dish. Shake well, stopper and let stand over night, then
pipette 50 cc of the clear liquid from each flask into Pyrex beakers. Add a
drop of phenolphthalein and heat to boiling, continuing the boiling until
two-thirds of the liquid has been boiled away. Note in what beakers, if
any, the liquid has turned pink. Repeat, using a narrower series whose
limits are indicated by the results on the first series. The least volume of
calcium hydroxide solution required to cause a pink tint is equivalent to the
lime requirement of 10 gm of soil. Calculate the pounds of calcium carbon¬
ate needed on the basis of 2,000,000 lb. of soil per acre.

The Truog Method . 2 —If barium chloride and zinc sulphide are
added to an acid soil, evolution of hydrogen sulphide takes place:

2E.COOH + BaCl 2 —► (RCOO) 2 Ba + 2HC1, (1)

ZnS + 2HC1 -+ H 2 S + ZnCl 2 . (2)

This gas coming in contact with lead acetate paper produces a
degree of blackening somewhat in proportion to the amount of
acid present.

H.S + Pb(C 2 H 3 0 2 ) 2 —»PbS -I- 2HC 2 H 3 0 2 .

1 J. Am. Chem. Soc., 26, 261 (1904).

2 Wis. Exp. Sta. Bull., 249 (1915).

(3)

-'OILS

Potassium Thiocyanate Method.— When ^ a eef e e- -

of calcium or magnesium carbonate in t ^uniimvv and

iron present combine with anv free arid rndmab *o v-m e*
these metals. If an alcohol solution of pota^um thiocyanate
is added to such a soil the solution will acquire a red color. : the
intensity of which has been shown to be approximately propor¬
tional to the acidity of the soli. Also if to thb red elution an
alcoholic solution of logwood be added, a blue color will develop,
the intensity of which is again proportional to the concentration
of both aluminium and acidity in the soil extract.

As an explanation of this color formation, it may be supposed
that, in an acid soil, iron and aluminium exist in the form of
partly hydrolyzed, largely colloidal salts in equilibrium with the
weakly ionized soil acid. These salts are capable of react mg wit h
such salts as potassium thiocyanate, which would not be true of
insoluble oxides or silicates, such as would he present in a neutral
or basic soil. This might be expressed thus:

FeA 3 + HoO «=± FcOH A, + HA, U)

FeOH.Ao + 3KCNS + HA ^ FeiCNSu 4- 3KA 4- HA), (2)

ion u: pom-

.-rum

ti*ioe^> an ate

i will acquin

> a r«

oi color. : the

. to in* appr<

)\im:

itely propor-

Also if to th

i- re?

I solution an

dod, a blue *

a/iur

will develop.

port ion a I To
he >uil extra

the concentration

LCt.

urination. it

may

be supposed

iminium ex:

st in

the form of

1 salts in eqi

lilibr

iuni with the

its are eapab

le of

reacting with

where A represents any acid radical. The ferric thiocyanate
thus produced colors the solution somewhat in proportion to the
amount of acid which made iron available for this reaction.
The addition of a standard solution of a base decomposes the
ferric thiocyanate and destroys the color.

It has been noted in making soil acidity determinations by this
method that certain soils cause the supernatant liquid to assume a
green color, as the red color of the ferric thiocyanate disappears.
Analysis has shown that this color is due to the formation of a
manganese compound, which is produced after the solution has
been made basic. This green color develops if the soil contains
as little as 0.008 per cent of soluble manganese. In most
cases it has been found that it starts to develop as soon as the red
color entirely disappears, but its intensity is increased if 5 ee more
of base be added than that required to titrate to the disappear¬
ance of red. This red color disappears when Ph equals about 5.5
while manganese does not start to precipitate as hydroxide until

* Com her J. Ayr. AW., 10, -420 11920 .

266

QUANTITATIVE AGRICULTURAL ANALYSIS

Ph equals about 7.2, this being completed at about 7.9. It is
evident that with such a soil a large amount of limestone would
have to be applied to precipitate all of the manganese, and in
some instances this cost would be prohibitive.

Determination of Soil Acidity: Potassium Thiocyanate Method . 1 —Prepare
the following reagents:

(a) Potassium Thiocyanate Solution .—Prepare a 5-per cent solution in
95-per cent ethyl or methyl alcohol. This solution should become slightly
pink (Pu = 5.4) upon the addition of methyl red. If neces¬
sary, add very dilute potassium hydroxide or hydrochloric
acid, drop by drop, until this color is obtained with a few
drops added to methyl red on a test plate.

(b) Alcoholic Solution of Potassium Hydroxide .—Prepare
a tenth-normal alcoholic solution of potassium hydroxide
by dissolving the base in 95-per cent ethyl or methyl alcohol.
Titrate against (c), using methyl red.

(c) Alcoholic Solution of Hydrochloric Add .—Prepare a
tenth-normal alcoholic solution of hydrochloric acid by
diluting concentrated acid with 100 volumes of 95-per cent
ethyl or methyl alcohol. Standardize against sodium car¬
bonate, first dissolving the weighed salt in a small amount
of water. See page 83.

Place 50 gm (25 gm of muck) of 10-mesh air-dried soil in
a 100-cc glass-stoppered cylinder or in the lower chamber of
the specially designed glass tube shown in Fig. 58. Add 30
cc (50 cc for muck) of potassium thiocyanate solution.
Stopper the cylinder and agitate for two minutes. Place
in an upright position, allow to settle for several minutes and
note the color of the supernatant liquid. If the solution is
pink or red, add from the upper burette a few tenths
of a cubic centimeter at a time (depending upon the
color) of tenth-normal alcoholic solution of potassium
hydroxide. Shake well after each addition and allow several
minutes to settle. Continue the addition until the red or
pink color has just disappeared. Let stand fifteen hours
and add more base, if necessary, to remove any pink which
may have developed. If too much base has been added
titrate back to a faint pink color using tenth-normal alco¬
holic acid. Note the volume of tenth-normal base required
and calculate the pounds of calcium carbonate required
to correct the acidity of the soil, on a basis of 2,000,000 lb. of
ordinary soil or 1,000,000 lb. of muck soil per acre.

The time required for complete development of color in the thiocyanate
solution may be shortened by use of the mixing machine.

1 Carr, J. I rid. Eng. (■hem., 13, 931 (1921).

I50cc

Fig. 58.—Soil
acidity
burette.

SOILS

267

If no red color has developed in the extract, the soil is already basic.
In this case, add from a burette tenth-normal alcoholic solution of hydro¬
chloric acid until a pink color develops after standing several minutes, agitat¬
ing after each addition and then allowing the soil to settle. From the
volume of acid used calculate the calcium carbonate equivalent of the soil.
If there is any indication of a green color developing after the disappearance
of red and after standing over night, add 5 cc more of base. If a green color
should develop, it would require from 40 to 50 cc (corresponding to 4 to 5
tons of limestone) of base, in addition to that added to remove the red color.

Hopkins Method. —The acids of the soil (existing in equilib¬
rium with partly hydrolyzed salts, as shown in equation
(1), page 265) are not easily extracted with water. If a solution
of potassium nitrate is added, such a reaction as the following
may occur:

H A + KNOa *=> K A + HN0 3

Equilibrium is established with the weakly ionized acid pre¬
dominating but if the solution is removed and replaced by
more potassium nitrate solution, the reaction will proceed still
farther. By repeating this process several times, a result is
finally obtained, approximating complete extraction of the acid.
It has been found by working with a number of different soils
that the sum of the acid of such a series of extracts is about two
and one-half times that of the first extract. In the Hopkins
method the assumption is made that the value of the first titra¬
tion may be multiplied by 2.5 to give total acidity. The method
seems to be more reliable with clay and loam than with muck
soils.

Determination of Acidity of Soil : Hopkins Method .—Place 100 gm of soil
and 250 cc of normal potassium nitrate solution in a 400-cc wide mouthed
bottle, stopper and shake continuously in a machine (Fig. 51) for three hours,
or every half hour for three hours by hand. Allow to stand for fifteen hours.
Draw off 125 cc of the clear solution, using a pipette, boil for 10 minutes to
expel carbon dioxide, cool and titrate with tenth-normal sodium or potassium
hydroxide, using phenolphthalein as indicator. Multiply the figure so
obtained by 2.5 and calculate the number of pounds of calcium carbonate
required per acre of 2,000,000 lb. of soil.

The titrations of duplicate samples should not differ by more than 0.8 cc
for soil samples requiring less than 100 cc of sodium hydroxide.

Active Plant Food. —The amount of nitrogen, phosphorus and
potassium that may be made available in a soil during a given

268

QUANTITATIVE AGRICULTURAL ANALYSIS

year is of interest and importance. Various weak acids, which
imitate the action of the plant roots, have been used for extract¬
ing available plant food. Dyer 1 has shown that root acidity
(expressed as citric acid) varies from 0.34 to 3.4 per cent of the
weight of the plant. He found the average acidity of one
hundred plants (root and top) to be about equal to that of 1-
per cent citric acid and so used this acid for soil extraction.
Fifth-normal nitric and oxalic acids are other solutions that have
been used for this purpose. Fifth-normal nitric acid has given
best results 2 in field tests and this has been quite widely adopted.

The amount of acid capable of being neutralized by materials
already present in the soil also is a factor of importance in
fertility work. This is estimated by titrating the solution after
the extraction has been completed. The amount of acid con¬
sumed depends considerably upon whether the soil is calcareous,
it being much greater in this case.

Flocculation and Deflocculation of Clay.—When “silt” soil
is suspended in water it may be easily flocculated by a calcium
salt, such as calcium nitrate. However, if calcium hydroxide is
added so that the solution becomes basic, flocculation is more
difficult. A clay responds in just the opposite manner, being
easily precipitated from suspension by a basic solution.

Determination of Comparative Degree of Flocculation and Defloccula¬
tion.—Place about 3 gm (not accurately weighed) of a clay soil in a mortar
and add sufficient water to make a thin paste when rubbed, then dilute to
one liter and mix. Repeat this process, using a “silt” soil. Pipette 25 cc
of each turbid liquid into each of nine test tubes and add each of the following
solutions in order to test its power to flocculate or deflocculate clay and silt
soils. The solutions should have approximately the concentrations indi¬
cated but they need not be accurately standardized.

(1) Use as a control—water and soil suspension only.

(2) 5 cc of tenth-normal sodium chloride.

(3) 5 cc of tenth-normal monosodium phosphate.

(4) 5 cc of tenth-normal sodium hydroxide.

(5) 5 cc of tenth-normal hydrochloric acid.

(6) 5 cc of tenth-normal ammonium sulphate.

(7) 5 cc of tenth-normal monocalcium phosphate.

(8) 10 cc of twentieth-normal calcium hydroxide.

(9) 5 cc of tenth-normal calcium nitrate.

1 J. Chem. Soc., 65, 115 (1894).

2 Ohio Exp. Sta. Bull., 261 (1913).

the reagents have all been added, shako. each tube ton times and
pc time and the* order in which the turbidity of tho liquid disappears,
j the shaking until the* time of clearing is established for each coin-
added. Xoto what ion or ions appear to be the most effective in
^ flocculat ion of the soil particles in both types of soils.

CHAPTER XIII

FERTILIZERS

Fertilizers, or manures, are those materials which either
increase the supply of elements in the soil, needed for the growth
of plants, or exert a corrective action in making conditions more
favorable for the plant’s best development. Farm manures
are usually mixtures of the excrement and urine of farm animals
with stable litter.

A distinction is sometimes made between materials which
furnish plant food directly, such as nitrates, phosphates and
potassium and ammonium salts, and indirect fertilizers like
calcium carbonate, which neutralize soil acid as well as serve as
plant foods. There are also those which furnish plant food and
aid in loosening hard clay, as is ‘the case with manures. The
direct fertilizers containing nitrogen, phosphorus and potassium
furnish the elements that are most frequently lacking in soils.

Availability.—The value of a fertilizer is usually determined
by the per cents of the fertilizing elements and by the solubility
of the compounds containing these elements in water or soil
acids, also by absence of injurious salts, such as those containing
boron or aluminium. Solubility is ail obvious measure of avail¬
ability to plants. The most commonly used, easily available
water-soluble salts containing nitrogen are sodium nitrate,
ammonium sulphate and calcium cyanamid. Materials in
which the nitrogen is available more slowly are manures, legumes
in green manuring, stubble and dead roots of plants. In these,
nitrogenous organic matter is gradually broken down into
simpler, soluble compounds, by bacterial action. Examples of
nitrogenous materials in which the nitrogen is practically
unavailable are hair, hoof, horn and leather. These are rich in
nitrogen but they are insoluble and decompose very slowly in the
soil. The phosphate fertilizers also present considerable variation
in solubility. This subject is discussed more fully on page 275.

270

FERTILIZERS

271

It is therefore a matter of great importance to the analyst that
he should know the origin of the constituents of a fertilizer
because the methods of analysis and the interpretation of results
differ according to the nature of the material present.

The composition of some of the more common fertilizers is
indicated in the following table:

Table XXIII. —Approximate Composition of Certain Commercial
Samples of Fertilizers with Respect to Three Essential

Elements

Name of material

Pounds of element per ton of
fertilizer

| Nitrogen

Phosphorus

Potassium

Fresh farm manure.

Dried blood.

Sodium nitrate (com.).

Ammonium nitrate (com.)
Acid phosphate (com.)... .

Acidulated bone meal.

Steamed bone meal.

Raw bone meal.

Raw rock phosphate.

Basic slag.

Potassium sulphate (com.)
Potassium chloride (com.).
Wood ashes.

280

310

400

125

140

250

180

250

160

850

100

Compatibility. —When artificial manures are to be mixed it is
important to know what ones can be combined without loss of
fertilizing value. Losses may be caused by reactions that release
combined nitrogen, usually in the form of ammonia, or that
make a phosphate less available to the plant by producing less
soluble compounds.

When an acid phosphate, for example, is mixed with sodium
nitrate or calcium nitrate free nitric acid is produced and this may
be partly lost:

Ca(H 2 P0 4 ) a + 4NaN0 3 -> CaNaPQ 4 + Na 8 P<> 4 + 4HNO a .

QUANTITATIVE AGRICULTURAL ANALYSIS

Table XXIV.— Fertilizer Compatibility

Fertilizer

“Superphosphate,"

Ca(H 2 P0 4 )2

kainit

potassium salts

Ammonium sulphate

Calcium cyanamid
CaXCX

Potassium salts

Sodium nitrate

Bone meal
Kainit,

MgS0 4 ’KCF3H 2 0.
Basic calcium nitrate

Should not be mixed ; Mixed just before using
with ; with

lime

Thomas slag
calcium cyanamid
sodium nitrate
basic calcium nitrate
superphosphate
ammonium sulphate
bone meal
barnyard manure
guano
lime

calcium cyanam id
basic calcium nitrate
Thomas slag
ammonium sulphate
superphosphate
barnyard manure
guano

Thomas slag

ammonium sulphate potassium salts

superphosphate ; sodium nitrate

barnyard manure ■ kainit

guano basic calcium nitrate

Thomas slag j calcium cyanamid

j lime

1 basic calcium nitrate
calcium superphosphate : calcium cyanamid

basic calcium nitrate

lime

Thomas slag I calcium c} r anamid

calcium c} r anamid
lime

basic calcium nitrate
Basic calcium nitrate ; ammonium sulphate calcium cyanam id

superphosphate potassium salts

barnyard manure : sodium nitrate

_I guano _ kainit _

Barnyard manure and j lime

guano calcium cyanamid

basic calcium nitrate
Basic slag (“ Thomas kainit

slag”) potassium salts j

ammonium sulphate
superphosphate i

Any of the above fertilizers may be mixed, at any time, except as noted
otherwise.

A similar rouetion i> hr* m^h; .u*c;t *a];*>x }i ..; « , .

mixed with kainit nr ,. rUl ir ' b Y‘ ;. r? , ■■

case hydrochloric arid b u>nnvd A>uh ! *b- < ;*.

detected with I>1 up litmu- pa]**ix Amm* -ii;usi ■■*.■;[* - t .;■ * -
l>e mixed with such had** cumjiojini- hi d r;*Vsi l.n.r ,.• »• i ...i'.
slag since a loss of nitrogen in the form of aiumoioa w ill r^u-h

2]STH 4 X0, 4- Ca;.OH 2 ~*<aX(i ; : — 2XH - ll*K 2

These basic compounds should not te nu\e <i with farm manure.

for the same reason.

If hydrated lime, or any other bade compound wen* m:\ed
with calcium acid phosphate, the nearly insoluble :p ?rina]

phate would be produced:

Ca(H 2 P0 4 ) j + 2Ca(0Hb — Cay P<V: - 4Hph 3

In some cases it is not desirable even to mix fertilizers which
do not react with each other -e.y\, sodium nit rate and i\u.-.,v das
because the large difference in the densities of the t wo comp mm is
makes it difficult to secure thorough mixing. The slag, being
much heavier, settles to the bottom of the container as a roult
of agitation in handling.

Table XXIV shows which fertilizers may l*o mixed without
danger of loss of fertilizing value, which ones should :;<■? he
mixed until just before applying, and which combinations da mid
never be used.

Pin. 39.—Sumplor f»>r fV*rt iSizi'r**

Choice and Preparation of a Sample of Commercial Fertilizer
for Analysis.— The sample of fertilizer is obtained tnnu the sack
or bin by means of a sampler, one form ot which is shown in
Fig. 59. This should secure a representative portion from the
whole mass.

Mechanical Analysis. — Mix the sample well and transfer about 100 gin
of it to a sieve having circular openings 0.5 mm m diameter- Break up the
soft lumps with a pestle, then sift.. Weigh the coarse portion remain-

274

QCAXTITA T1YE AGRICULTURAL ANALYSIS

nig on the sieve. Th<‘ percentage of the fine portion is determined by
difference.

Preparation of Sample.—Refer to the discussion of sampling, pages 17 to
21. Reduce the remainder of the gross sample, by quartering or by use of
a riffle, to an amount sufficient for analytical purposes (25 to 50 gm), transfer
this to a sieve with 1-nim openings and sift, breaking the lumps with a
pestle. Grind the part remaining on the sieve in a mortar until the
particles will pass through, mix thoroughly and preserve in tightly stoppered
bottles. Carry out these operations as rapidly as possible to avoid loss or
gain of moisture during the operation.

Moisture. —Loss of weight on drying may be.due to escaped
hygroscopic water, chemically combined water or ammonia or,
to some extent in certain cases, to oxidation of organic matter.
For this reason “moisture” as usually reported, is not a strictly
accurate term.

Determination of Moisture.—Weigh 2 gm of the sample into wide
crucibles or small dishes and heat for five hours at 100°. In the case of
potassium salts, sodium nitrate and ammonium sulphate, heat at about 130°
to constant weight. Calculate the loss as percent of moisture.

Phosphorus.—Phosphorus is deficient in soils more often
than are the other necessary elements. The mineral phosphates
form the chief commercial source of phosphorus, although
a considerable amount is obtained from bone, Thomas slag
(from the basic Bessemer steel furnace), tankage and fish scrap.
Calcium orthophosphate, Ca 3 (P0 4 )2 5 is the chief constituent of
“raw” rock phosphate. Its solubility in water is very small,
in absence of acids, and therefore it is advisable to use it only
in a soil where there is considerable decaying organic matter to
furnish carbonic acid, as otherwise its availability is small. 1

Large amounts of rock phosphate are now commercially
made into acid phosphates by treating the finely ground stone
with sulphuric acid, thus converting the normal phosphate to a
soluble form, suitable for use as a fertilizer. The character
of the result of this treatment depends upon the concentration
of acid and upon the relative amounts of rock phosphate and
acid employed in the treatment. Dicalcium or monocalcium
phosphate, or even phosphoric acid itself, may be formed, accord-

1 See also Hopkins, III. Exp. Sta. Circ., 167 (1913) and Stewabt, Ibid
245 (1920).

ing to whether one, two or three atoms of hydrogen are sub¬
stituted for calcium. The last t w named phosphates are easily
soluble in water, w hereas diealeium phosphate is nearly insoluble
(0.130 gm in lOOO gm of water at 20°) but soluble in soil acids.
In practice the reaction is never allowed to proceed as far as the
formation of phosphoric acid.

The possible reactions involved in the commercial process are
indicated as follows:

ViirS. P< Uh + H 2 S0 4 — CaSC>4 + 2CaHP0 4 , (1)

Dioalcium phosphate

Ca 3 (P0 4 ) s + 2H a S0 4 — 2CaS0 4 + Ca(H 3 P0 4 ) 2 , (2)

» Monocalcium phosphate
C*S uperpbosphate”)

Ca 3 (P0 4 V. 4- 3 HsS 0 4 — 30aS0 4 4- 2H*PO«. (3)

Phosphoric acid

Sulphuric acid of 00-per cent concentration is most suitable
for making acid phosphates because this produces the maximum
quantity of monocalcium phosphate, the water-soluble form.
“Reversion'’ may occur during storage if unchanged tricalcium
phosphate remains in the mixture. This is due to the inter¬
action of monocalcium phosphate with tricalcium phosphate, the
dicalcium salt being produced:

Ca.-ii P(> 4 h ~t~ Oa( H JH ) 4 ).j—*40aHP04.

Measure of Availability.— Dicalcium phosphate is soluble in
salt solutions, such as ammonium citrate, as well as in salt or
acid soil solutions. Hence both citrate-soluble and water-soluble
phosphorus are rated as available to plants. The phosphate
found in bone is in t he form of the tricalcium phosphate but in
this case it is in a more porous condition and it is also inter¬
mingled with organic matter. It is soluble to the extent of 30
to 40 per cent in ammonium citrate solution and it is somewhat
soluble in soil acids and salts.

The principles involved in the determination of phosphorus in
phosphates are discussed on pages 87 to 92, Part I. This should
be reread before beginning the following determinations.

Determination of Total Phosphorus.—The choice of method for dissolving
the sample will depend upon the nature of the latter.

276

QUANTITATIVE AGRICULTURAL ANALYSIS

Preparation of Solution.—Treat 2.5 gm of the sample by one of the
following methods:

(a) Ignite in a crucible until organic matter is removed (the residue will
not necessarily be white), then dissolve in hydrochloric acid.

(b) Evaporate with 5 cc of magnesium nitrate solution, made as follows:
Dissolve 320 gm of calcined magnesium oxide in nitric acid, avoiding an
excess of the latter; add a little calcined magnesium oxide in excess, boil,
filter from the residue and dilute to 2000 cc.

After evaporating the fertilizer and magnesium nitrate solution, ignite
until organic matter is removed and dissolve in hydrochloric acid.

(c) Boil with 20 or 30 cc of concentrated sulphuric acid in a Kjeldahl
flask, adding 2 to 4 gm of sodium nitrate at the beginning of the digestion
and a small quantity after the solution has become nearly colorless, or adding
the nitrate in small portions from time to time during the digestion. After
the solution is colorless add 150 cc of water and boil for a few minutes.

(d) Digest in a Kjeldahl flask with concentrated sulphuric acid and such
other reagents as are used in either the plain or modified Kjeldahl or Gunning
method for the determination of nitrogen (page 152). Do not add any
potassium permanganate but, after the solution has become colorless, add
about 100 cc of water and boil for a few minutes.

(e) Dissolve in 30 cc of concentrated nitric acid and 5 cc of concentrated
hydrochloric acid and boil until organic matter is destroyed.

(f) Add 30 cc of concentrated hydrochloric acid, heat and add cautiously,
in small quantities at a time, about 0.5 gm of finely pulverized potassium
or sodium chlorate to destroy organic matter.

(g) Dissolve in 15 to 30 cc of concentrated hydrochloric acid and 3 to
10 cc of concentrated nitric acid. This method is recommended for fertil¬
izers containing much ferric or aluminium phosphate.

After the sample of fertilizer has been brought into solution by any of the
methods described above, cool, dilute to 250 cc, mix and pour into a dry
filter, discarding the first 10 cc of the filtrate and allowing the remainder to
run into a dry flask which can be stoppered.

Gravimetric Determination.—Prepare solutions of “magnesia mixture”
and ammonium molybdate as directed on pages 88 and 89, Part I. Prepare
also:

(a) Ammonium Hydroxide. —Dilute the concentrated solution ten times.

(5) A mmonium Nitrate. —A 10-per cent solution.

Measure 25, 50 or 100 cc of the fertilizer solution, according to the
probable per cent of phosphorus, using a pipette or volumetric flask. Trans¬
fer to a 250-cc flask of resistance glass, neutralize with ammonium hydroxide
and clear with a few drops of nitric acid, thus dissolving the small amount
of precipitated hydroxides of iron and aluminium. In case hydrochloric
or sulphuric acid has been used as a solvent for the fertilizer material add
also 15 gm of dry ammonium nitrate.

To the hot solution add ammonium molybdate solution, about 70 cc for
each decigram of phosphorus pentoxide thought to be present. Immerse in
water and digest at 65° for an hour and determine whether the phosphorus

FERTILIZERS

completely precipitated, by adding more molybdate solution to the
supernatant liquid. If more precipitate forms continue the digestion,
ky testing as before. Filter on paper and wash with cold water or
nitrate solution ib . During the washing the precipitate that
es the flask need not be completely removed bu it. must ♦** washed.
co the flask in which precipitation was made under the filter and
the precipitate on the filter in concentrated ammonium hydroxide
? as little as possible) followed by hot water, allowing the solution to
n.t>o the flask, thus dissolving the adhering precipitate. Wash the
Ver y thoroughly with hot water. Transfer the entire solution and
to a 250-cc beaker of resistance glass. The total volume of the
011 should not be greater than 1(H) ce. Nearly neutralize with hydro-
c ^cid, the reformation of the yellow precipitate serving as indicator.
;s °l Ve the precipitate that finally forms by the addition of a few drops
u t-e ammonium hydroxide. Cool and add. very slowly and with vig-
stiirring, 25 ce of magnesia mixture. After 15 minutes add ammonium
}>cide (specific gravity 0.90) equal to one-ninth of the total volume of
D ^- 1 - 1 'fcion, stirring as this is added. Cover and allow to stand for tw o
Filter and wash with dilute ammonium hydroxide 'a until prae-
y Free from chlorides, as shown by acidifying the washings with nitric
a-nci adding silver nitrate solution. Dry the filter and precipitate and
^ er the latter to a porcelain crucible, previously ignited and weighed.
e -fche filter separately and transfer its ash, when white, to the crucible
lining the main precipitate. Ignite to whiteness or grayish white over
•last lamp or Meker burner, weigh and calculate the per cent of pkos-
lls pentoxide.

l^ixnetric Determination.—Have the following solutions ready:

) Ammonium Molybdate. —To each 100 cc of the molybdate solution
was prepared for the gravimetric determination of phosphorus add 5 cc
>ncentrated nitric acid. The solution should be filtered immediately
re using.

) ^Standard potassium hydroxide solution , 1 cc of which is equivalent to
of phosphorus. (Refer to equation (2) on page 91. Part I.) This should
\ nearly free from carbonates as possible and is made as follows: Dissolve
r cent more than the calculated quantity for 1000 cc, dilute to 100 ce
acid 1 cc of a saturated solution of barium hydroxide. Stopper the
. and allow to stand until the precipitate of barium carbonate has settled,
mt and dilute to 1000 cc. Standardize by titration against solution
using phenolphthalein. Adjust so that 1 cc is equivalent to 0.1 mg of
sphorus.

) JStandard Hydrochloric or Nitric Acid .—This solution should be
valent in strength to the standard base. It should he made from
ioxisly boiled and cooled water and it should be standardized by titration
nst the basie solution, using phenolphthalein as indicator.

Ho fertilizer is dissolved by either of methods (b), (t ), (f) or (pb page 27tb
-Hod (e) is to be preferred if the material will yield to this treatment,
solution is to be diluted and filtered as already directed.

278

QUANTITATIVE AGRICULTURAL ANALYSIS

In the case of fertilizers containing less than 5 per cent of phosphorus
pentoxide, use an. aliquot corresponding to 0.4 gm of substance. If the
percentage is between 5 and 20 use an aliquot corresponding to 0.1 gm of
substance.

Add 5 to 10 cc of concentrated nitric acid, the amount depending upon
whether this acid has been used in making the solution; or add ammonium
nitrate equivalent to this amount of nitric acid. Nearly neutralize with
ammonium hydroxide, precipitation of hydroxide of iron or aluminum
serving as indicator. Clear with a drop of nitric acid, dilute to about 100 cc
and heat by immersing in water at 60° to 65°. For phosphorus pentoxide
per cents below 5 add 25 cc of freshly filtered molybdate solution; for
percentages between 5 and 20 add 35 cc of molybdate solution. For
percentages greater than 20 add sufficient molybdate solution to insure
complete precipitation of the phosphorus. Stir, allow to stand in the bath
for 15 minutes and filter at once. Wash twice with water by decantation,
using 25 to 30 cc each time and agitating and settling each time before
decanting. Transfer the precipitate to the filter as thoroughly as can be
done without the use of a policeman and wash the flask, paper and precipi¬
tate with cold, recently boiled water until the filtrate from two fillings of the
filter yields a pink color upon the addition of phenolphthalein and one drop
of the standard base. Remember that a trace of acid left in any of these
materials will vitiate the results of the titration.

Return the filter paper and precipitate to the flask in which precipitation
was made. Add a measured, small excess of the standard base to dissolve
the yellow precipitate, then add a few drops of phenolphthalein and titrate
the unused excess of base with standard acid. Calculate the per cent of
phosphorus pentoxide in the sample.

The following changes in the method just described are made optional:

(a) Heat the solution to only 45° to 50° and allow to stand in the bath,
after the addition of the molybdate solution, for 30 minutes.

(5) Cool to room temperature before adding the molybdate solution.
Add the latter at the rate of 75 cc for each decigram of phosphorus pentoxide
present, place the stoppered flask containing the solution in a mixing appa¬
ratus (Fig. 51) and mix for 30 minutes at room temperature. Filter at once
and proceed as already directed.

Determination of Water-soluble Phosphorus: Gravimetric Method .—
Place an accurately weighed 2-gm sample on a filter and wash with small
portions of cold water until about 250 cc of washings has been obtained.
Allow each portion of water to run through before adding another. Keep
the residue for the determination of citrate-insoluble phosphorus. Dilute
the filtrate to exactly 500 cc and mix.

Place 50-cc aliquots in flasks, add 10 cc of concentrated nitric acid
and then ammonium hydroxide until a slight permanent precipitate is
formed. Clear with a few drops of nitric acid, dilute to about 100 cc
and determine the water-soluble phosphorus gravimetrically as in the
case of total phosphorus. Report as phosphorus pentoxide of water-
soluble compounds.

fei:t/uzem

279

Volumetric Determination. --Vuish 2 gm of the sample as directid aU<»w
for the gravimetric method. Measure the aliquot of the filtrate, and
neutralize as there directed. Dilute to C>0 cc and precipitate the phosphorus
as directed for the volumetric determination of total phosphorus. Calculate
the per cent of phosphorus pentoxide of water-soluble compounds.

Citrate-insoluble Phosphorus.—The value of a fertilizer is
frequently rated upon the degree of solubility or the availability
of its constituents to plants, as already explained. For this
purpose it is desirable to imitate the solvent action of solutions
found in soils. The use of ammonium citrate solution provides
an approximate distinction between available and non-available
phosphates, although it should be noted that there is still con¬
siderable disagreement among agricultural chemis s as to the
true availability of the different compounds of phosphorus.
The solvent action of this solution upon calcium phosphate is
largely due to the presence of free citric acid or of acid citrates,
caused by the hydrolysis of the ammonium citrate (i.e., to the
fact that chemically equivalent quantities of ammonium hydrox¬
ide and citric acid in solution yield an acid condition, Ph being
less than 7).

(NH 4 ) 3 C 6 H 5 0 7 + H 2 0-> (NH^HCeHsCb + NH 4 0H ( 1 )
(NH 4 ) 3 C 6 H 5 0 7 + 2H*0 -> NH 4 H 0 C 6 H 5 O 7 + 2 NH 4 OH, (2)
(NH 4 ) 3 C 6 H 5 0 7 + 3H 2 0 -> H 3 C 6 H 5 O 7 + 3 NH 4 OH, (3)
2CaHP0 4 + 2 H 3 C 6 H 5 O 7 —» Ca(H 2 P0 4 ) 2 + Ca(H 2 C 6 H 5 0 7 ) 2 . (4)

Hydrolysis of ammonium citrate is due to the fact that both
ammonium hydroxide and citric acid are weak electrolytes.
Because of this fact it is very difficult to prepare a solution in
which the two electrolytes are present in exactly equivalent
quantities (a “neutral” solution), using an indicator to determine
this condition. It is well to remember that the citrate is always
largely hydrolyzed and that it is, therefore, rather a solution of
(at best) equivalent quantities of the two constituents, acid and
base.

Ammonium Citrate Solution. —Two methods are approved
by "the A. 0. A. C. for preparing “neutral” ammonium citrate.
Iix one of them a stated amount of citric acid in solution is
neutralized by ammonium hydroxide, using corallin (rosolic

280

QUANTITATIVE AGRICULTURAL ANALYSIS

acid) as indicator. This method is unreliable because corallin is
not sufficiently sensitive to citric acid or ammonium hydroxide.

In the other method the solution is nearly neutralized and a
small excess of calcium chloride solution in water and alcohol is
added. Calcium citrate, a salt of small solubility, precipitates
as a result of such reactions as the following:

2 (NH 4 ) 3 C 6 H 6 07 + 3CaCl 2 Ca 3 (C«H 5 0 7 ) 2 + 6 NH 4 CI, ( 1 )
2(NH 4 ) 2 HC 6 H 5 0 7 + 3CaCl 2 -> Ca 3 (C 6 H 5 0 7 ) 2 + 4NH 4 C1

+ 2HC1, ( 2 )

2NH 4 H 2 C 6 H 5 0 7 + 3CaCl 2 -» Ca 3 (C 6 H 5 0 7 ) 2 + 2NH 4 C1

+ 4HC1, (3)

2H 3 C 6 H 5 0 7 + 3CaCl 2 -> Ca 3 (C 6 H 5 0 7 ) 2 + 6HC1. (4)

Equation (1) shows that if only triammonium (“neutral”)
citrate is present, no matter how highly this may be hydrolyzed,
the solution will be left neutral to all indicators by the removal
of calcium citrate. According to Eqs. ( 2 ), (3) and (4) any acid
citrate or free citric acid will produce free hydrochloric acid,
which may be made evident by the use of indicators. On the
other hand, if the citrate solution contained an excess of ammo¬
nium hydroxide this would remain after the precipitation of cal¬
cium citrate. According to the result obtained by testing the
filtrate with an indicator, either citric acid or ammonium hydrox¬
ide may be added, as necessary, to obtain the proper condition
of equivalent quantities of acid and base. That this solution
is not really neutral and that it does not really contain tri¬
ammonium citrate, has already been explained.

Preparation of Ammonium Citrate Solution: Calcium Chloride Method .—
To 370 gm of commercial citric acid, dissolved in 1500 cc of water, add
commercial ammonium hydroxide until nearly neutral, testing with recently
prepared corallin solution. Add water until the specific gravity is about
1.11 at 20°

Prepare a solution of fused calcium chloride, 20 gm to 100 cc, and add
400 cc of 95-per cent alcohol. Make this solution exactly neutral with
tenth-normal ammonium hydroxide or hydrochloric acid, as may be neces¬
sary, using freshly prepared corallin solution as a preliminary indicator;
test finally by diluting 2 cc with an equal volume of water and adding methyl
red (cochineal is the official indicator for this purpose). Approximately
50 cc of this solution will precipitate the citric acid from 10 cc of the citrate
solution.

t'Ki:n Litt

To 10 cc of the nearly neutral a- r • • a • ^ ^ r , { ae of

the alcoholic calcium chloride solution. ,?* web and ’ •: v\\r:u*fc a

folded filter. Dilute the filtrate w t ti- v ♦>.< { «- ■■»... ? lV ,*,=*■ } «• \ ♦»>-.* trie

reaction with a neutral solution .,f \tv >1 ',V7vhiv,--o ‘ "if or

acid, add citric acid or aiuinonuin hv4xe\id- a- :?,v \.o» ■ mav U\ to the
mam portion of the citrate solution. Mix ^ r « \ o >♦ -iri- e ; : .to. Repent
this process until a neutral reaction of the hlir.it, » A.Mu-d Aid tu&ient
water to make the specific gravity 1.09 at ivb

Determination. of Citrate-insoluble Phosphorus: l S —

Heat 100 cc of ammonium citrate sdut-n to 9V in a y*w • Erbumeyer
flask placed in a water bath at this ten ijx-rat' ur»n keeping t ";<■ fLi-k U unsttly
stoppered to prevent evaporation. l’#> a thermometer u: K.9; flask and
bath. The level of the water in the bath should he T n>ve r hat of t. he e it rate
solution in the flask. When the temperature nf the e.tran- elution has
reached 65°, drop into it the filter containing the cashed r>due obtained
in the determination of water-soluble phrwphoru* page 2T v , or a weighed
2-gm sample of the original fertilizer, if water-soluble phosphorus is not to
be determined. Close the flask tiddly with a Mm».>th rubber stnpprr and
shake violently until the filter paper is reduced X>- a pulp ,.t for “J or 3
minutes if no paper has been used a ocniji* »nally relievnijs the pressure* by
momentarily removing the stopper. Place the flask in the bath and main¬
tain its contents at exactly 65°. Shake the flask ewrv 5 minutes, At the
expiration of 30 minutes from the time trie filter and residue were introduced,
remove the flask from the bath and immediately filter the ointents as rapidly
as possible through quick-acting filter paper. Wash with recently boiled
water at 65° until the volume of the filtrate is about ;j5fl cc, allowing time
for thorough draining each time before adding new portions of water.
Either (1) transfer the filter and its contents to a crucible, ignite until t he
organic matter is destroyed, add 10 to 15 cc of concentrate! hydrochloric
acid and digest until all the phosphate is dissolved ; or 2 transfer the filiter
with contents to a digestion flask, add 35 ee of concentrated nitric acid and
10 cc of concentrated hydrochloric acid and warm until the phosphate is
dissolved. There may be an insoluble residue of silicates or silica in either
case. Ten minutes of digestion in the warm add should be sufficient to
dissolve all phosphates.

Dilute the solution as prepared in (1 or 2 to 200 cc. Mix well, filter
through a dry filter and determine the phosphorus as already directed for
total phosphorus, pages 270 to 27*. Calculate the per cent of e it rate-
insoluble phosphorus, as pentoxide, deduct from the per cent of total
phosphorus pentoxide and report the remainder as the percent of available
phosphorus pentoxide.

Nou-acululated Samples .—Treat 2 gm of the materia!, without previous
washing with water, as directed for acidulate samples, unless the substance
contains much animal matter (such materials as fish and bone in w hich ease
dissolve the residue insoluble in ammonium citrate hv one of the processes
(/>), (c) or (d) , page 270. Determine ns directed for total phosphorus.

282

QUANTITATIVE AGRICULTURAL ANALYSIS

Nitrogen.—Nitrogen is one of the most important of the
elements that are concerned in plant growth. Although abun¬
dant in the atmosphere in an uncombined form, it is an expensive
element when used in making up a fertilizer. This is because its
inert nature makes difficult the problem of forming nitrogen
compounds which may be used by plants. Nitrogen should
therefore be obtained, so far as possible, through growing inocu¬
lated legumes in rotation, rather than through purchase in the
form of fertilizers.

Nitrogen is usually present in a fertilizer in one or more of the
following forms: (1) Ammonium salts, such as ammonium sul¬
phate or nitrate; (2) animal or vegetable matter, such as dried
blood, cotton seed meal, stable manure and guano; (3) atmos¬
pheric nitrogen fixed by electrical energy, as various nitrates.
Sodium nitrate is found also as a natural product, chiefly in
South America.

Organic fertilizers have some advantages over the others in
that they promote bacterial action. Because of their limited
solubility they do not readily leach out of the soil, the result being
that they are used less rapidly and supply the plant with nitrogen
through a longer period of growing season. Calcium cyanamid
also acts like the organic forms as it slowly breaks down in the
soil, somewhat as follows:

CaNCN + C0 2 + 2H 2 0 CaC0 3 + CO(NH 2 ) 2 , (1)

Calcium cyanamid Urea

CO(NH 2 ) 2 + 2H 2 0 -> (NH 4 ) 2 CO,, (2)

ammonium carbonate being available to plants.

Nitrogen used in the form of ammonium sulphate has not the
most desirable action, as it finally leaves free acid in the soil,
due to hydrolysis and absorption of the resulting ammonia.
Chili saltpeter (sodium nitrate) has the opposite effect in the
soil as the nitric acid formed by hydrolysis is used, leaving
sodium hydroxide which lessens the acidity of the soil or even
causes a basic condition. This is sometimes desirable, although
excessive basicity may change the texture of the soil because of the
deflocculating effect upon the clay particles, thus resisting the
penetration of rain water and the normal movements of drainage
water. This was illustrated in the experiment on deflocculation,
page 268.

FERTILIZERS

283

Because of the differences in cost and availability of different
forms of nitrogen, it is often desirable to know the relative
amounts existing as nitrates, ammonia or organic forms in the
fertilizer. The following methods will give information of this
character.

Detection of Nitrates. —If sulphuric acid is added to a nitrate,
nitric acid will be set free. This will be reduced to nitric oxide
in the presence of ferrous sulphate, forming a brown ring
(FeS0 4 -N 2 0 2 or FeS0 4 -N0).

Treat 5 gm of fertilizer with 25 cc of hot water, then filter. Mix about
3 cc of this solution with an equal volume of concentrated sulphuric acid
(free from nitrates) in a test tube and cool, then pour 2 or 3 cc of concen¬
trated ferrous sulphate solution carefully down the side of the tube so that
the two liquids do not mix. In the presence of nitrates a brown or reddish
brown ring will form at the junction between the two solutions. If no color
forms immediately let stand 2 or 3 minutes.

Nitrogen of Ammonium Salts. —If a material containing
nitrogen in various forms is placed in water and heated with
magnesium oxide, ammonia is distilled and both nitrates and
protein nitrogen remain behind. Magnesium hydroxide is the
active agent:

MgO + H 2 0 —> Mg(OH) 2 , (1)

Mg(OH ) 2 + 2 NH 4 NO 3 -> Mg(N0 3 ) 2 + 2 NH 3 + H 2 0. (2)

The ammonia is absorbed in standard acid and the titration
finished as usual.

Determination of Ammonia Nitrogen: Magnesium Oxide Method .—Place
2 gm of sample in a Kjeldahl digestion flask with about 200 cc of water
and 5 gm or more of magnesium oxide which has been rendered free from
carbonates by a previous strong ignition. Connect the flask with a
condenser and distill 100 cc of the liquid into 50 cc of fifth-normal acid.
Titrate the excess with fifth-normal base solution, using methyl red. Calcu¬
late the per cent of ammonia nitrogen.

Determination of Organic and Ammonia Nitrogen: Kjeldahl Method .—
The method described for organic nitrogen in feeds, page 151, includes also
nitrogen of ammonium salts if present, as they may be in fertilizers. Deter¬
mine as there directed, tising accurately weighed samples of about 2 gm.

Determination of Organic and Ammonia Nitrogen: Gunning Method .—
Determine as for organic nitrogen in feeds, page 154.

Nitrate Nitrogen. —When nitrogen is determined by these
methods most of the nitrate nitrogen is volatilized and lost upon

284

QUANTITATIVE AGRICULTURAL ANALYSIS

digesting with sulphuric acid. In order to avoid this loss the
Kjeldahl method may be modified by adding benzoic acid, then
using permanganates to oxidize the nitrobenzoic acid to ammonia.
Phenolsulphonic acid may be substituted for benzoic acid, the
nitrophenolsulphonic acids formed being then reduced to amino-
phenolsulphonic acid by zinc dust. This compound is then
oxidized by heating with sulphuric acid.

Salicylic acid has now superseded both benzoic acid and
phenolsulphonic acid. The reducing agent is either sodium
thiosulphate or zinc dust:

2KN0 3 + H 0 SO 4 -> K 2 S0 4 + 2HN0 3 , (1)

.OH /OH

HN0 3 + C 6 H 4 <( -> C 6 H 3 /-COOH + 2H 2 0, (2)

X COOH ^N0 2

The nitro compound is then reduced by nascent hydrogen
from zinc and sulphuric acid:

/OH /OH

6H + C«Hj^-COOH -> C 6 H 3 ~COOH + 2H 2 0, (3)

\no 2 x nh 2

or by sodium thiosulphate:

Na 2 S 2 0 3 + H 2 S0 4 Na 2 S0 4 + H 2 S0 8 +S,

/OH /OH

3H 2 S0 3 + CeH^COOH + H 2 0—»3H 2 S0 4 + C 6 hAC00H.

Xn N0 2 ^nh 2

(4)

(5)

The amino acid is then oxidized by concentrated sulphuric acid,
ammonium sulphate resulting.

Determination of Total Nitrogen in Materials Containing Nitrates:

Modified Kjeldahl Method .—Weigh 2 gm of fertilizer and place in a Kjeldahl
flask. Add 30 cc of concentrated sulphuric acid containing 2 gm of sali¬
cylic acid (these must be added together) and mix by shaking vigorously.
After 30 minutes add 5 gm of sodium thiosulphate or 2 gm of zinc dust. If
zinc dust is used it must be added gradually, shaking the flask after each
addition. Heat gently until frothing ceases then boil for 10 minutes. Add
0.7 gm of mercury oxide or 0.3 gm of copper sulphate and continue the diges¬
tion, distillation and titration as in the Kjeldahl method. Make a blank
determination for nitrogen in the reagents, using sugar as already directed.
Calculate the per cent of total nitrogen in the fertilizer.

FERTILIZERS

285

Nitrate and Ammonia Nitrogen.—These two forms of nitrogen
may be determined together by first reducing the nitrate to
ammonia by nascent hydrogen, then distilling the solution made
basic by magnesium hydroxide.

Determination of Nitrate and Ammonia Nitrogen: Iron Reduction
Method .—Place 1 gm of the sample in a 500-cc flask, add about 30 cc of
water and 3 gm of iron reduced by hydrogen. After standing long enough
to insure solution of nitrates and ammonium salts, add 10 cc of a mixture of
equal volumes of concentrated sulphuric acid and water; shake thoroughly,
place a funnel in the neck of the flask to prevent mechanical loss and allow to
stand until the reaction has moderated. Heat the solution slowly, then boil
for 5 minutes and cool. Add about 100 cc of water, a little paraffin to
prevent foaming and 10 gm of magnesium oxide, made free from carbonates
by previous strong ignition. Connect with the tin condenser and boil for
40 minutes, or nearly to dryness, collecting the distillate in 50 cc of fifth-
normal acid. Titrate the excess of acid with fifth-normal base, using methyl
red, and calculate nitrogen of nitrates and ammonia.

If the sample is known to consist of nitrates alone, proceed as above except
that 0.25 gm of the sample, is used, together with 5 gm of reduced iron.
After the boiling, add 75 cc of water and an excess of saturated sodium
hydroxide solution (instead of magnesium oxide), and distill as above
directed.

Availability of Nitrogen.—Mention has already been made of
the low fertilizing value of certain nitrogenous materials, due to
slowness of decomposition occurring when the fertilizer is added
to the soil. Nitrogen is probably directly assimilated by plants
only in the most highly oxidized form, i.e., that of nitrates.
Ammonium salts and certain organic materials, such as dried
blood, have almost as great value because they readily decompose
and oxidize in the soil, forming nitrates. Hoof, hair, leather
and hide are rich in nitrogen but they do not so decompose,
except very slowly, and a method for differentiating between
available and non-available forms of nitrogen is desirable. The
microscope will detect ground hair and other similar materials
but it can give only qualitative results. Fortunately qualita¬
tive results are all that are necessary where the addition of such
materials is contrary to law, but for scientific purposes a quantita¬
tive distinction between available and non-available nitrogen
may be of great practical use. An exact analytical method for
such a purpose seems to be impossible because there is no sharp
distinction to be made between the classes of fertilizer materials.

QUANT IT A VIVE AGRICULTURAL ANALYSIS

28 (>

Great reliance is placed upon culture experiments, comparing
the effect of using different fertilizers with plants under otherwise
identical conditions. However, such experiments are slow and
they have no value whatever for analytical purposes. An
approximate distinction can be made by the use of potassium
permanganate in either neutral or basic solution. Readily
decomposable materials are oxidized and the nitrogen is con¬
verted into ammonia. It is not yet entirely clear as to how much
reliance is to be placed upon these methods but they have been
adopted by the Association of Official Agricultural Chemists.

Determination of Total Water-insoluble Organic Nitrogen.—Place 1 gm
of the material upon an 11-cni filter paper and wash with recently boiled
water at room temperature until the filtrate measures 250 cc. Dry and
determine nitrogen in the residue by the Kjeldald method, making a blank
determination to correct for the nitrogen of the filter paper.

Determination of Water-insoluble Organic Nitrogen, Soluble in Potas¬
sium Permanganate.—Place a weighed quantity of the fertilizer, equivalent
to 50 mg of the water-insoluble organic nitrogen as determined above, on a
moistened 11-cm filter paper and wash with recently boiled water at room
temperature until the filtrate measures 250 cc. Transfer the insoluble
residue with 25 ce of water (at about 30°) to a 400-ee low-form beaker, add
1 gin of sodium carbonate, mix and add 100 cc of 2-pcr cent potassium
permanganate solution. Cover with a glass and immerse for .30 minutes
in a water or steam hath so that the; level of the liquid in the beaker is below
that of the heating medium. Keep at 100°, stirring twice at intervals of
10 minutes each. At the end of this time remove from the bath, add imme¬
diately 100 cc of cold water and filter through a heavy 15-cun folded filter.
Wash with Hmall quantities of cold water until the filtrate measures about
400 cc. Determine total nitrogen in the residue and filter by either of the
methods already described (not modified for nitrates) making a blank deter¬
mination to correct for the nitrogen contained in the filter. The nit rogen
thus obtained is th ('.inactive water-insoluble organic nitrogen. Subtract, this
per cent from the total water-insoluble organic nitrogen. The remainder is
the per cent of organic nitrogen soluble in neutral 'permanganate. As already
explained, this is an approximate measure of organic nitrogen easily avail¬
able for plant food.

Determination of Organic Nitrogen Soluble in Basic Permanganate.—

Prepare a solution of potassium permanganate by dissolving 25 gm in about
100 ce of water; dissolve 150 gm of sodium hydroxide in 500ccof water and,
after this lias cooled, mix with the potassium permanganate solution and
dilute the whole to 1000 cc.

(a) Mixed Fertilizers. —Place an amount of material equivalent to 50 mg
of total water-insoluble organic nitrogen, determined as above, on a filter
paper and wash with water at room temperature until the filtrate measures
about 250 cc.

FERTILIZERS

287

(b) Raw Materials. —Place an amount of material equivalent to 50 mg
of total water-insoluble organic nitrogen, determined as above, in a small
mortar. Add about 2 gm of powdered rock phosphate (to facilitate the
washing process) mix thoroughly by grinding, transfer to a filter paper and
wash with water at room temperature until the filtrate measures 250 cc.
When much oil or fat is present, it is well first to wash several times with
ether and to allow to stand until the odor of the latter has disappeared before
extracting with water.

Dry the residue from either class of materials at a temperature not exceed¬
ing 80° and transfer from the filter to a 500-cc Kjeldahl digestion flask.
Add 20 cc of water, about 1 gm of crushed porcelain to prevent bumping
and about 1 gm of paraffin to prevent frothing. Add 100 cc of the basic
permanganate solution and connect with the tin condenser, the lower end of
which dips into 50 cc of fifth-normal acid.

Digest slowly for at least 30 minutes, below the distillation point, with a
very low flame, using wire gauze and asbestos paper between the flask and
flame. Gradually raise the temperature and, after any danger of frothing has
passed, distill until 95 cc of the distillate (145 cc of distillate plus acid)
is obtained, then titrate as usual. If a tendency to froth is noticed lengthen
the digestion period. During the digestion gently rotate the flask occasion¬
ally, particularly if the material shows a tendency to adhere to the sides of
the flask.

The nitrogen thus obtained is the active water-insoluble orgariic nitrogen.

Potassium. —Most soils contain orthoclase (potassium alumin¬
ium silicate) but the potassium of this is unavailable or so slowly
available that the supply from this source is often not sufficient
to meet the needs of the rapidly growing plant. The need is
especially great in muck soils for plants such as potatoes or
sugar beets, which require a large amount of potassium.

Sodium compounds can take the place of potassium to only a
very slight extent, if at all. * It has been noted that in places
where sodium nitrate has been used for some time to supply
nitrogen, much less than the usual response could be obtained
from potassium fertilizers. It is assumed therfore, that the
sodium of the fertilizer tended partly to perform the function of
potassium. The effect of potassium starvation is more definite
than that resulting from phosphorus deficiency and it is indicated
by the color of the plant becoming abnormal and dull, the stem
weak and the ability to manufacture starch at the normal rate
lacking.

Preparation of Fertilizer Solution: (a) Mixed Fertilizers. —Place 25 gm of
the sample upon a 12.5-cm filter paper and wash with boiling witter until the

288 Q U A NT IT A TIVE AGRIC ULT URAL A NAL I 'S IS

filtrate measures about 200 cc. Add to the filtrate 2 cc of concentrated
hydrochloric acid, heat to boiling, transfer to a 250-cc volumetric flask and
add to the hot solution a slight excess of ammonium hydroxide and sufficient
ammonium oxalate to precipitate all of the calcium- Cool, dilute to 250 cc,
mix and pass through a dry filter. Reject the first 25 cc of the filtrate.

(b) Simple Potassium Salts, Potassium Magnesium Sulphate and Kainitc.-—
Dissolve 2.5 gm of sample in a 250-cc volumetric flask and dilute to the
mark without the addition of ammonium hydroxide or ammonium oxalate.

(c) Organic Compounds: Cotton Seed Meal, Tobacco Stems, Etc. Maturate
10 gm of sample with concentrated sulphuric acid, then evaporate and
ignite at a temperature not above that of dull redness to destroy organic
matter. A muffle furnace will be found to be convenient for this ration.
Add a little concentrated hydrochloric acid and warm slightly in order to
loosen the mass from the dish. Wash into a 500-cc volumetric flask, add
ammonium hydroxide and ammonium oxalate to precipitate calcium, dilute
to the mark and mix well. Filter through a dry paper and reject the first
25 cc of the filtrate.

(d) Ashes from Wood or Cotton Hulls. —Digest 10 gm with 500 cc of boiling
water for 30 minutes in a covered flask. Precipitate 1 , calcium with ammo¬
nium hydroxide and ammonium oxalate, as directed under (a), above, rinse
into a 500-cc flask, dilute to the mark and mix well. Filter through a dry
paper and reject the first 25 cc of the filtrate.

Determination of Potassium: (a) In Mixed Fertilizers and Ashes. —The
principles underlying the determination of potassium have been discussed
under the head of soil analysis, page 244. Directions for the preparation of
chlorplatinic acid solution and of 80-per cent alcohol also have been given.
Prepare, in addition, a 20-per cent ammonium chloride solution, saturated
with potassium chlorplatinate by agitating occasionally for several hours,
after having added about 10 gm of the salt for each 500 cc of solution.
Allow to settle and then filter.

Evaporate 50 cc of the prepared solution nearly to dryness in a dish, add
1 cc of sulphuric acid (1 to 1), evaporate to dryness and ignite at a dull red
heat until organic matter is removed and the residue is white. Dissolve the
residue in hot water, using at least 20 cc for each decigram of potassium
oxide present, add a few drops of concentrated hydrochloric acid and
enough chlorplatinic acid to precipitate all of the potassium and to leave
about 1 cc of platinum solution in excess. If the per cent of potassium is
approximately known the quantity of platinum solution that is necessary
should be calculated. Contamination with ammonia vapor must be avoided.

Evaporate the solution on a steam bath to a thick paste, cool and add to
the residue 25 cc of 80-per cent alcohol. Stir thoroughly and allow to stand
for 15 minutes. Filter through a weighed Gooch crucible. If the filtrate is
not colored, sufficient chlorplatinic acid solution is not present and the
analysis must be begun again with another portion of the solution, increasing
the amount of platinum solution.

Wash the precipitate with 80-per cent alcohol, continuing the washing
after the filtrate has become colorless. Remove the filtrate; and washings

FERTILIZERS

289

to the bottle which has been provided for waste platinum solutions and wash
the precipitate five times with 10-cc portions of the ammonium chloride
solution. Wash again thoroughly with SO-per cent alcohol, exercising par¬
ticular care to remove ammonium chloride from the upper part of the filter.
Dry the precipitate for 30 minutes at 100°, cool and weigh. The weight of
potassium chlorplatinate is given without further treatment. The precipi¬
tate should be completely soluble in warm water.

(b ) In Commercial Potassium Chloride { u Muriate of Potash”). —To 50 cc
of the solution already prepared add a few drops of hydrochloric acid and
10 cc of chiorplatinic acid solution. Evaporate over a steam bath to a thick
paste and treat the residue as in the case of mixed fertilizers.

(c) In Potassium Sulphate , Potassium Magnesium S'idphate and Kainite .—
Acidify 50 cc of the solution with a few drops of hydrochloric acid, add 15 cc
of chiorplatinic acid solution and evaporate on the steam bath to a thick
paste. From this point proceed as with mixed fertilizers, except that 25 cc
portions of the ammonium chloride solution should be used in the washing
process.

The potassium is reported as per cent of potassium oxide (often called
“potash”) instead of as the element.

Perchlorate Method. —In the discussion of methods for
the determination of potassium in soils, page 244, attention
was called to the fact that the increasing price of platinum has
greatly handicapped laboratory work of this character and that
methods not requiring the use of platinum solutions are rapidly
increasing in importance. The perchlorate method as described
for soil work is adapted also to fertilizer investigations. The
solutions of potassium, obtained by extraction of the fertilizer
for determinations by the chlorplatinate method, may be used for
this purpose, the determination of potassium in these being
performed exactly as directed for potassium in soils.

Centrifugal Method. —There is need for a short approximate
method for determining potassium which will fill somewhat the
same place as the Babcock method for determining fat in cream
and milk. A method has been devised by Sherrill 1 which is
based upon a comparison of the volumes of precipitates of potas¬
sium cobaltic nitrite formed from two solutions—the potassium
concentration of one being known. The precipitates are sep¬
arated into graduated tubes by centrifugal action and the
volumes noted. The method seems to be fairly accurate and it is
useful when a rapid determination for factory control is necessary.

1 J. Ind . Eng. Chem., 13, 227 (1921).

290

QUANTITATIVE AGRICULTURAL ANALYSIS

One of the writers has had some experience with this method
for determining potassium in fertilizers of various kinds, and it
has been found possible to check reasonably well with the results
obtained by the chlorplatinate method. Some results obtained
by the two methods are given in the following table:

Table XXV.— Comparison of the Per Cent of Potassium Oxide in
Fertilizers by Centrifugal and Chlorplatinate Methols

Sample No.

Chlorplatinate

method*

Centrifugal

methodf

1581

3.12

3.2

1604

1.74

1.8

1669

3.67

3.8

1823

8.04

8.2

1949

4.26

4.4

2176

. 9.38

9.1

2224

50.25

50.1

1979

4.83

4.9

* By the Indiana State Chemist,
f By one of the authors.

Special bottles have been described by Sherrill for this deter¬
mination. These are of the form shown in Fig. 60. Or the
older Goetz bulbs, as used for rapid determinations of phosphorus
in steel, will be found convenient. The precipitate is collected
and measured in the narrow, graduated portion of the tube.

If the potassium solution contains ammonia or ammonium
salts, these must be expelled by evaporating a measured portion
to a small volume with enough sodium hydroxide to render the
solution decidedly basic, or by evaporating to dryness and ignit¬
ing at dull redness. The solution is then acidified with acetic
acid and diluted to the original volume.

Determination of Potassium: Ceittrifugal Method. —Prepare solutions as
follows:

(а) Standard Potassium Chloride Solution. —Dissolve 15.83 gm of pure
potassium chloride in distilled water, add ten drops of glacial acetic acid and
dilute to 1000 cc. This makes a solution containing 1 per cent of potassium
oxide.

(б) Sodium Cobaltic Nitrite Solution. —Dissolve 225 gm of sodium nitrite in
400 cc of distilled water. Also dissolve 125 gm of cobalt acetate crystals

FERTILIZERS

291

in 400 cc of water. Mix the solutions, dilute to 1000 cc and mix. To 100 ce
of this solution add 65 cc of distilled water and 5 cc of glacial acetic acid,
mix and allow to stand over night. This diluted solution is unstable and it
should not be kept for use more than five days.

Measure 17 cc of solution ( b ) into each tube, the temperature being not
lower than 22°. Be sure that the graduated stems are filled, with entire
absence of air bubbles. To one of the tubes add 5 cc of
solution (a) and to each of the others 5 cc of the diluted
sample. Whirl immediately for one minute at the rated
speed for the centrifuge that is being used. Remove the
tubes and tap those in which the upper surface of the
column of precipitate is not practically plane. Whirl
again for 15 seconds. The reading of the precipitate in
the tubes containing the sample solutions should be
within 5 divisions (either way) of that of the standard.

If this is not the case, repeat the experiment, using more
concentrated or more dilute solutions, as indicated.

From the relative volumes of the precipitates and the
known potassium content of the standard solution, calcu¬
late the per cent of potassium (or of potassium oxide) in
the sample.

Methods of Pot and Field Culture. —From
analyses alone it is difficult to foretell just what
will be the response of a plant to any given ap¬
plication of fertilizer to a soil. The great variety
of soil components, including toxic substances
often contained in them, is responsible for this,
and it is very desirable that pot and field tests Graduated tube
be conducted for the purpose of gaining more tor determina-
information as to the needs of the soil for the ° k y po \ a k~
growth of any particular crop. This is analogous Sherrill centrif-
to conducting feeding experiments with animals ugal metho
for testing the degree of utilization and the physiological effects
of the feeds.

Much valuable information has been gained through sand and
water culture experiments, in which solutions of certain com¬
pounds are added. Reference may be made to the experiments
of Knop , 1 Shives 2 and Tottingham . 3

1 Landw. Vers. Sta., 7, 93 (1865).

2 N. J. Ex'p. Sta. Bull. , 319 (1917).

3 J. Am. Soc. Agron., 2, 1 (1919).

CHAPTER XIV

INSECTICIDES AND FUNGICIDES

The large number of insect and fungus pests with which the
economic entomologist and the horticulturist have had to
contend in recent years has caused a renewed search for methods
for more efficient control. The insecticides used for this purpose
belong to one of two classes, depending upon whether they are
for external or internal action. Paris green and London purple
are examples of those of internal application, while lime-sulphur
mixture and kerosene emulsion are examples of those designed
to kill by contact. Bordeaux mixture is a well known remedy
for fungus pests.

Character of Insecticide as Related to Insect Anatomy.—There
is a close relation between the general character of the insecticide
sprays to be applied and that of the mouth parts of insects.
Generally speaking, insects secure their food either by biting out
and swallowing plant particles or by sucking juices from interior
portions of the plant. Those of the biting kind have jaws and
also certain accessory parts which enable the insect to cut and
pass on the small parts of food to the digestive organs. Most
sucking insects have mouth parts of long bristle-like structure.
These are inclosed in a tube and the bristles and beak together
constitute a sucking apparatus for the extraction of the plant
juices. It is possible to kill both sucking and biting insects by
poisoning the air with hydrocyanic acid or other poisonous gases,
as well as by poisons that are to be eaten by the insect.

Action of Contact Insecticides.—Considerable attention has
been given to the method by which contact insecticides kill.
Shafer 1 found that in the case of certain volatile insecticides,
such as gasoline, carbon disulphide or chloroform, the fatty
membranes absorb some of the vapor, which renders them
less permeable to oxygen. The cells thus gradually cease to

1 Mich. Ex'p. Sta. Tech. Bull., 21 (1915).

INSECTICIDES AND FUNGICIDES

293

function in a normal way. Non-volatile insecticides in the
form of powdered solids may function by sticking to certain
body secretions, then being absorbed into the tissues. As
examples of this class, borax and sodium fluoride are frequently
used to exterminate cockroaches. The powder sticks to the body
of the insect and is partly absorbed but it also acts as a stomach
poison because some of it is usually licked off and swallowed
by the animal.

The vapor of white hellebore is insufficient to kill insects
but Shafer has noted that rose slugs which come into contact
with this insecticide gradually become numbed and fall from
the leaves. This occurred even in cases wdiere none of the
insecticide had been eaten. It is concluded that the numbing
effect is due to slight dissolving of the powder and surface
absorption by the excretions, little if any of the insecticide passing
through the cuticular covering, and that the cause of the final
death of the insect is due more to drying and starving than to
any other reason.

Finally, the natural cells of some insects contain enzymes,
the normal functioning of which is of the greatest importance to
the well-being of the insect. The interference of the various
insecticides with the activity of these enzymatic bodies is known
to be serious and this may be the cause of the death of the insect
in some cases.

Preparation of Insecticides. —The internal poisons are usually
prepared in considerable quantities and their preparation should
be under chemical control. The contact and fungicide poisons
are freshly prepared by the sprayer and their efficiency depends
upon the composition and proportions of the ingredients. Ar¬
senic has been so universally used as an active internal poison for
insects that the determination of this element is highly important.
Free arsenous acid in solution has a destructive action on foliage,
therefore it is necessary also to limit the per cent of arsenic in
this form. The maximum quantity which is safe for foliage
varies from 4 to 6 per cent.

Mixing of Sprays. —The question of combining insecticides
and fungicides for the control of orchard pests is important
from the standpoint of saving time and money as well as from
that of increasing the efficiency of the spray. Choosing the

294

Q VAN TIT A TIVE AGHICl ’LTV HAL A SAL YS1S

proper spray materials and mixing them so as to retain their
insecticidal or fungicidal value is often a difficult and complicated
problem. 1 Chemical or physical changes may take place on
mixing, resulting in compounds being formed which arc injurious
to foliage, or in some eases the spray may become worthless
because the active killing agent has heroine inert.

The various objectionable combinations arc* shown in Table
XXVI on page 295. It will be noted that Bordeaux mixture
(copper sulphate and calcium hydroxide) with arsenate of lead is
permissible. It has been shown by analysis that when these arc
mixed the amount of soluble arsenic is not much greater than
when lead arsenate is treated with pure watej. On the other
hand, lead arsenate and soap solution form an objectionable
combination because the haul arsenate reacts with the sodium
oieate of the soap, forming lead oleate (insoluble in water/ and
sodium arsenate. The latter is soluble in water and the foliage
is injured by the high concentration of soluble arsenic.

Lime-sulphur solution and lead arsenate may he safely mixed
because analysis shows that the soluble arsenic is not much
greater than when the arsenic compound is shaken with water.

The table shows also that Bordeaux mixture should not l*e
mixed with the group of “emulsified oils'* because the emulsion
of oils with water containing calcium hydroxide of Bordeaux
mixture is not very satisfactory, the result being that Home of
the unemulsified oil remaining will injure tin* plant. The reversi¬
ble nature of soap and oil emulsions in genera! is discussed by
Bancroft 2 as follows:

“Since sodium oleate emulsifies oil in wafer and calcium oleate emulsi¬
fies water in oil, a mixture of the two nieute* will behave differently,
depending on the relative amounts. There will also hi* ho me ratio of
calcium to sodium at which the two oleafes will practically balance each
other and the slightest relative change will change the type of the
emulsion.”

The reaction of calcium hydroxide of Bordeaux mixture with
sodium oleate of the soap will result in the formation of the
maximum quantity of calcium oleate and this will then reverse

1 Cal. Exp. Eta. Circ., 195 (191K).

2 “Applied Colloid Chemistry,” p. 207.

INSECTICIDES AND FUNGICIDES

295

Table XXVI. —Incompatibility of Insecticides and Fungicides

Spray compounds .

Objectionable combination
•with:

Questionable combination
with:

Stomach Poisons

Acid lead arsenate.

Alkali sulphide

Soaps

Soap-oil emulsion

| Lime-sulphur

Basic lead arsenate

Alkali sulphides

Paris green

Lime-sulphur

Alkali sulphides

Soaps

Soap-oil emulsion

Cyanide fumigation

Tobacco infusion

Zinc arsenite

Lime-sulphur

Alkali sulphides

Soaps

Soap-oil emulsion

Bordeaux mixture

Cyanide fumigation

Tobacco infusion

Tracheal Poisons

Tobacco infusion

Bordeaux mixture

Paris green

Zinc arsenite

Cyanide fumigation

Zinc arsenite

Paris green

Bordeaux mixture

Soap-oil emulsion

Zinc arsenite

Paris green

Acid lead arsenate
Lime-sulphur

Bordeaux mixture

Soaps

Zinc arsenite

Paris green

Acid lead arsenate

Lime-sulphur

Bordeaux mixture

Tracheal Poisons and Fungicides

Alkali sulphides

Zinc arsenite 1

Paris green

Acid lead arsenite

Bordeaux mixture

Basic lead arsenate

Sulphur

Lime-sulphur solution

Soap-oil emulsion

Bordeaux mixture

Zinc arsenate

Acid lead arsenate

Paris green

Soaps

Fungicides

Bordeaux mixture

Cyanide fumigation

Lime sulphur

Tobacco infusion

Alkali sulphides

Soaps

Soap-oil emulsion

Zinc arsenate

Other combinations of these sprays are thought to be safe.

296

QUANTITATIVE AGRICULTURAL ANALYSIS

the emulsion to the form of water in oil. The continuous film
of oil will then injure foliage with which it comes in contact.

Arsenic Sprays. —Since many insecticidal compounds rely
upon arsenic for their effective killing qualities it is important
that the student become familiar with a few of the large number
of available arsenic compounds. The more important ones are
as follows: Arsenic trioxide, As 2 0 3 (also called “arsenic” or
“white arsenic”); arsenic pentoxide, As 2 0 5 ; arsenic acid, H 3 As0 4 ;
metarsenic acid, HAs0 3 ; potassium arsenite, K 3 As0 3 ; potassium
arsenate, K 3 As0 4 ; Paris green, Cu(C 2 H 3 0 2 ) 2 -Cu 3 (As0 3 ) 2 ; lead
arsenate, Pb 3 (As0 4 ) 2 ; and calcium arsenate, Ca 3 (As0 4 ) 2 .

PARIS GREEK

This is seen from the formula given above to be an aceto-
arsenite of copper. Theoretically the compound contains 58.55
per .cent of As 2 0 3 , 31.39 per cent of CuO and 10.06 per cent of
(CH 3 C0) 2 0, the respective anhydrides. However, this does not
usually represent the actual composition, either of the solid Paris
green or of a solution in which it is suspended. Copper arsenate,
or even free arsenic or arsenous acids may be present.

Total Arsenic. —The determination of total arsenic in Paris
green is based upon the volatility of arsenic trichloride. Cuprous
chloride is added to the hydrochloric acid solution in which the
sample has been dissolved, and this reduces any pentavalent
arsenic to the more volatile, trivalent form. The distillate
containing arsenous chloride and hydrochloric acid is absorbed
in cold water. The acid is neutralized, sodium bicarbonate
is added in excess and the arsenic is titrated with standard
iodine solution. The arsenite is oxidized by free iodine as
follows:

Na 3 As0 3 + Io + H 2 0 -> Na 3 As0 4 + 2HI.

A neutral solution is maintained by the excess of sodium
bicarbonate, which neutralizes hydriodic acid as fast as the
latter is formed, thus preventing reversal of the reaction.

The apparatus for total arsenic determination is shown in
Fig. 61. A is a 250-cc distilling flask fitted with a 50-cc drop¬
ping funnel; B ) C, and D are flasks holding 500, 1000 and 100
cc respectively. B and C are surrounded by cracked ice and

INSECTICIDES AND FUNGICIDES

297

contain 40 and 100 cc of water respectively. The flask D
contains 50 cc of water, which serves as a trap to prevent
entrance of air.

Determination of Total Arsenic: Distillation Method— Prepare the following
reagents:

(a) Arsenous Acid .—Dissolve exactly 2 gm of arsenous oxide of known
purity (dried over calcium chloride for ten hours) by boiling with about
200 cc of water containing 10 cc of concentrated sulphuric acid. Cool and
transfer to a 500-cc volumetric flask, dilute to the mark and mix thoroughly.
Keep stoppered.

B C D

Fig. 61 .—Apparatus for the determination of total arsenic by distillation.

( b) Starch Indicator .—Mix about 0.5 gm of starch with cold water to form
a thin paste; add about 100 cc of boiling water and stir thoroughly.

(c) Iodine Solution .—Dissolve 6.35 gm of iodine and 12.5 gm of potassium
iodide in about 100 cc of water, decant from any sediment, dilute to 1000 cc
and mix well. Standardize against solution (a) as follows:

Using a pipette, measure 50 cc of the arsenous acid solution into an
Erlenmeyer flask, dilute to about 400 cc and neutralize with sodium bicarbon¬
ate, adding 4 to 5 gm in excess. Add the standard iodine solution from a
burette, rotating the flask continuously, until the yellow color disappears only
slowly, showing that the end point is near; then add 1 cc of the starch
solution and continue adding the iodine solution drop by drop until a per¬
manent blue color is obtained. Calculate the value of the standard iodine
solution in terms of arsenous oxide (As 2 Os). Keep the solution stoppered
and away from bright light. Even with this precaution the oxidizing value
changes and the solution should be standardized within a few hours of the
time when it is to be used.

298

QUANTITATIVE AGRICULTURAL ANALYSIS

Calculate the theoretical weight of Paris green that would be equivalent
to 250- cc of the standard iodine solution. Weigh out this amount and wash
it and about 5 gm of cuprous chloride into the 250 distilling flask with 100
cc of concentrated hydrochloric acid. Distill until the volume in the distill¬
ing flask is reduced to about 40 cc, then add 50 cc of concentrated hydro¬
chloric acid by means of the dropping funnel. Continue this process of
addition of acid and distillation until 200 cc of distillate has been obtained.
Wash down the condenser and all connecting tubes, allowing the rinsings to
run into the flasks. Transfer the contents of the receiving flasks to a 1000-
cc volumetric flask, rinsing the former well, dilute to the mark and mix
thoroughly. Measure 100 cc of this solution into a 1000-cc Erlenmeyer
flask, add phenolphthalein and nearly neutralize with a concentrated sodium
hydroxide solution. The solution should be kept cold. Add 10 gm of
sodium bicarbonate and titrate the arsenic with standard iodine solution,
using starch as indicator. Calculate the per cent of total arsenic, as both
element and arsenous oxide.

The official method for the determination of arsenic, which has
just been described, is in some respects less desirable than the
method which was formerly official. 1 One of the principal diffi¬
culties of the older method is the formation of a yellow colloidal
solution of arsenous iodide when potassium iodide and hydro¬
chloric acid are added to reduce the arsenic solution. This color
makes impossible the exact removal of iodine by sodium thio¬
sulphate but if the analysis is performed carefully as described
below, this difficulty will disappear.

Determination of Total Arsenic and of Copper in Paris Green without
Distillation.—To 2 gm of Paris green in a 250-cc flask add about 100 cc
of a 2-per cent solution of sodium hydroxide. Boil until all the green
compound has been decomposed and only red cuprous oxide remains.
Cool, filter into a 250-cc volumetric flask, washing the paper well, dilute
to the mark and mix well. Reserve the cuprous oxide on the filter for the
copper determination.

Measure two or three portions of 50 cc each of the solution into 250-cc
flasks and concentrate by boiling to about half the original volume. Cool to
60°, add 10 cc of concentrated hydrochloric acid and 1 gm of potassium
iodide. Mix and allow to stand for 10 minutes. From a burette carefully
add sodium thiosulphate solution until the iodine is all reduced. Starch
should not be added but care should be exercised in reaching the end point.
If a persistent yellow color (see above) develops at this point, use starch
solution on a test plate as an outside indicator, touching drops of the titrated
solution to the starch. If the end point has been passed, add iodine solution
until the iodine-starch reaction is barely produced. Allow to stand for 5

1 U. S. Dept, of Agr., Chem. Bull , 107.

INSECTICIDES AM) Er.XtiJi IDEs

^tes longer and if iodine color reappears carefully add mare -sgirl*4*-

l °n. Immediately add, as rapidly as can he d«*ne w ;t ; ,vl -h by
-~vescence, 15 gm of sodium bicarbonate, free from ; n..rs. 'fhrato
) , nce w ^h standard iodine solution, deferring the addite oCjtar v.

near the end point. Calculate the per cent of total arsenic, f i \'prr-^e.i
-■rsenous oxide, in the Paris green. , J

e residue of cuprous oxide is treated on the filter with 5 ou* mtric
3 specific gravity 1.2, the solution being caught in a 250-ce
a,sh the paper well with hot water and proceed as direct v>\ kjs the
adardization ^of sodium thiosulphate against metallic copper,

.inning with “Boil until red fumes have been expelled . . " Caiei^te

per cent of copper in the Paris green. The result may also be expressed
cupric oxide, if desired.

distinction between Arsenates and Arsenites.—It is frequently

sirable to distinguish qualitatively between arsenates and
senites in spray mixtures. Probably the most accurate test
r an arsenate depends upon the formation of a precipitate of
agnesium ammonium arsenate when a magnesium salt is
d.ed to the basic solution:

H 3 As0 4 + 3NH 4 OH (XH 4 ) 3 As 0 4 4- 3H*O f 1)

(NH 4 ) 3 As 0 4 + MgCl 2 —* MgNH 4 As0 4 -f 2XH 4 CL 2}

Dissolve about 0.5 gm of sodium arsenite and sodium arsenate in separate
-cc portions of water. Add 3 cc of magnesia mixture to each tube and
ir. It will be noted that no precipitate will be produced in the former case
it a white crystalline one forms in the latter and adheres to the sides of the
;ssel. Repeat, using the filtered spray solution instead of known arsenic
Its.

Silver nitrate is a reagent which is useful for the detection of
rsenites. In a neutral solution of an arsenite this gives a yellow
recipitate of silver arsenite while with an arsenate, brown silver
rsenate is produced.

W'ater-soluble Arsenous Oxide. —It has already been stated
a at water-soluble arsenic (of free arsenous acid or sodium arsen-
;e) is very injurious to young foliage. The Federal insecticide
ct of 1910 specifies a maximum of 3.5 per cent of water-soluble
rsenous oxide in Paris green and not more than 0.75 per cent in
3 a,d arsenate paste.

It is very important that the directions as to temperature be
observed closely because the amount of soluble arsenic varies
onsiderably with small deviations in temperature.

300

QUANTITATIVE AGRICULTURAL ANALYSIS

Determination of Water-soluble Arsenic.—Weigh 2 gm (if a paste, use
4 gm) of the sample on a counterpoised glass or scoop, brush into a 1000-cc
volumetric flask, and add nearly 1000 cc of recently boiled distilled water
which has been cooled to exactly 32°. Stopper the flask and immerse in a
water bath which is kept at 32° (± 1°) by means of a thermostat. Digest
for 24 hours, shaking hourly for the first eight hours of this period. Dilute
to the mark, mix and filter through a dry filter, reject the first 25 cc and
collect exactly 250 cc in a volumetric flask. Rinse into a 1000-cc flask or
beaker and titrate with the standard iodine solution that was used for total
arsenic. Calculate the amount of water-soluble arsenic as arsenous oxide.

LEAD ARSENATE

Of the internal poisons for insects, lead arsenate is used most
extensively. Lead arsenate was recommended as an insecticide
in 1892 and it was first used against tent caterpillars. It is
made by treating disodium arsenate with either lead nitrate or
lead acetate. Lead arsenate made from lead nitrate contains
about 31.5 per cent of combined arsenic pentoxide while that
made from lead acetate contains about 25.5 per cent.

Lead arsenate (“neutral”) is gradually replacing Paris green
as a spray because of its low degree of solubility, it being a safer
spray on this account. The arsenic becomes more soluble if the
lead arsenate solution is prepared with water containing sodium
sulphate or sodium chloride. Solutions containing only 0.1 per
cent of the former or 0.05 per cent of the latter will dissolve an
appreciable amount of arsenic from lead arsenate. Spraying
tests have shown that 10 grains of sodium chloride per gallon,
when used with lead arsenate in the spray fluid, produced injury
and 40 grains per gallon injured about half of the foliage. It is
therefore important to avoid ordinary mineral water and salt
water in preparing the spray.

Lead arsenate has the advantage over Paris green in that it
sticks to the foliage well when applied as a spray.

Determination of Moisture: (a) In Powder .—Weigh a porcelain crucible
without cover, then add about 2 gm of sample and reweigh. Dry to con¬
stant weight at 105° to 110° and report the loss of weight as moisture.

(b) In Paste .—In a weighed dish dry 50 gm for one hour at 105° to 110°.
Cool and reweigh. Calculate the moisture thus obtained as p. Grind the
partly dried sample to a fine powder, mix well and transfer a small portion
to a sample bottle. Weigh 2 gm of this into a crucible and dry again for

301

IXsi-y TIC WES A XI) FVSUICIDES

two hours at 105 to 1IQ . C-delate the loss as per cent, on the basis of the

dried sample as 100 ami call this //. Total moisture = -V - /> +
/100 — p\ ,

\ lOO )P-

Use the anhydrous material for the determination of the total lead oxide
and total arsenic,

^©terrniiiatioii of Lead Oxide.—Heat on a hot plate about 0.5 gm of the
dry powdered sample with about 25 cc of dilute nitric acid (1 to 4) in a
500-co beaker. If neeessarv, remove any insoluble residue by filtration.
Dilute to about 400 ce and heat nearly to boiling. Add ammonium hydrox¬
ide to slight precipitation of basic lead salts, then add dilute nitric acid
(1 to 10) to redissolve the precipitate, adding about 2 cc in excess. Pipette
into thus solution, kept almost at boiling, 50 cc of a hot 10-per cent potassium
chromate solution, stirring constantly. Decant while hot through a weighed
Gooch. filter, previously dried at 150°. Wash several times by decantation
and tHen on the filter paper with boiling water until the washings are color¬
less. D rv the lead chromate at 140° to 150° to constant weight. Calculate
the per cent of lead monoxide in the dried sample. Multiply this per cent by

100 — p . _

fOO— (see determination of moisture) to obtain the per cent based upon
the original paste.

Determination of Total Arsenic-—Proceed as directed for the determina¬
tion of total arsenic in Paris green by the distillation method, page 297.
Use about 5 gm of the sample and after the distillate has been diluted to
1000 cc and mixed, measure 100-cc portions for titration. Calculate the
per cent of total arsenic, expressed as arsenic pentoxide.

Detenmination of Total Arsenic Oxide.—Prepare a standard iodine and
starch solution as directed in the determination of Paris green on page 297.
Prepare also:

Standard, Thiosulphate Solution. —An approximately twentieth-normal
solution of sodium thiosulphate is prepared by dissolving 13 gm of the
crystallized salt in recently boiled and cooled 'water. Filter and
make up to 1000 cc with water treated in the same way. Standardize
by the method given on page 162, or by that given on page 17S, in
either case modifying the treatment to take account of the fact that this
solution is only about half as concentrated as the ones described in these
references. Calculate the weight of arsenic pentoxide equivalent to 1 cc of
the solution.

Weigh accurately about 0.5 gm of the powdered sample, transfer to an
Erlenmeyer flask and add 25 cc of concentrated hydrochloric acid. If
necessary to effect solution heat on a steam bath, keeping the flask covered
in order to prevent evaporation of the acid. Cool to 20°, add 10 cc of 20-
per cent potassium iodide solution and 50 cc (more, if necessary to produce a
clear solution) of 25-per cent ammonium chloride solution. Immediately
titrate the liberated iodine with standard sodium thiosulphate. When the
color becomes a faint yellow, dilute with 150 cc of water and continue the

302

QUANTITATIVE AGRICULTURAL ANALYSIS

titration very slowly, using starch solution near the end point. Calculate
the per cent of total arsenic oxide, AS 2 O 5 .

Determination of Water-soluble Arsenic Oxide.—The agents needed are
starch indicator, standard arsenous oxide solution and a standard iodine
solution. These are prepared as directed on page 297.

To 2 gm of the original sample, if a powder, or 4 gm if a paste, in a 1000-
cc volumetric flask, add nearly 1000 cc of recently boiled water which has
been cooled to exactly 32°. Stopper the flask and place in a water bath
kept at 32° by means of a thermostat. Digest for 24 hours, shaking hourly
for eight hours during this period. Dilute to the mark, mix and filter
through a dry filter, rejecting the first 25 cc of filtrate. Transfer 250 or
500 cc of the clear filtrate to an Erlenmeyer flask, add 3 cc of concentrated
sulphuric acid and evaporate on a hot plate.. When the volume reaches
about 100 cc add 1 gm of potassium iodide and continue the boiling until
the volume is about 40 cc. Cool, dilute to about 200 cc, remove the excess
iodine with twentieth-normal sodium thiosulphate, avoiding the use of
starch solution, and proceed as directed on page 298 for the determination of
arsenic in Paris green, beginning with “nearly neutralize with sodium
hydroxide.”

Calculate and report as per cent of water-soluble arsenic oxide, AS 2 O 5 .

Determination of Total Arsenous Oxide.—Prepare the starch indicator,
standard arsenous oxide and standard iodine solution as directed in the
determination of Paris green on page 297. Prepare also:

(a) Dilute Sulphuric Acid Solution .—Dilute 15 cc of concentrated sul¬
phuric acid with 85 cc of water.

(b) Sodium Hydroxide Solution .—Dissolve 25 gm of sodium hydroxide
in 50 cc of water.

Weigh 0.25 gm of the powdered sample, transfer to a 200-cc Erlenmeyer
flask, add 100 cc of dilute sulphuric acid (a), and boil for 30 minutes. Cool,
transfer to a 200 -cc volumetric flask, dilute to the mark, shake thoroughly
and filter through a dry filter. Nearly neutralize 100 cc of the filtrate with
sodium hydroxide ( 6 ), using a few drops of phenolphthalein as indicator.
If the neutral point is passed, make acid again with dilute sulphuric acid.
Continue as directed in the determination of total arsenic in Paris green,
page 299, beginning with the neutralization by sodium bicarbonate.
Calculate the per cent of total arsenous oxide in the sample.

CALCIUM ARSENATE

This is one of the newer insecticides. It is somewhat similar
to arsenate of lead but, in its present form, it is not recommended
for use on the more sensitive foliage, such as that of the stone
fruits, because of the large amount of water-soluble arsenic it
often contains, this causing considerable damage to foliage.

INSECTICIDES AND FUNGICIDES

A 11 :->

Two of the arsenates of calcium are quite stable: tricaleium
arsenate, Ca 3 (As0 4 ) 2 and dicalcium arsenate, CaHAs0 4 . The
tricalcium arsenate may be made in. two ways, as follows:

3CaHAs0 4 *f 2NaOH — Ca 5 (As0 4 )2 + Na 2 HAs0 4 + 2H 2 G; j)
2H 3 As0 4 + 3C , a(OH)o —> Ca 3 (As0 4 ) 2 + 6H 2 0. 2 )

Dicalcium arsenate dissolves in water to the extent of 0.33 izm
in 100 cc at 25° while tricalcium arsenate is soluble to the
extent of only 0.014 gm at the same temperature. The solu¬
bility of the first salt is so large that there is danger of damage
when it is applied to tender foliage. Also, unless it has been
prepared with care, it may contain quantities of the easily
soluble disodium arsenate, as shown in Eq. (1). This has been
largely overcome by adding an excess of lime water, which
reacts with any dicalcium arsenate or disodium arsenate to form
the less soluble tricalcium salt. 1 The powdered calcium arsenates
on the market contain approximately 52 per cent of arsenic,
calculated as pent-oxide, while the paste contains less, according
to the proportion of water retained.

I>etermination of Total Arsenic.—Proceed by the distillation method as
with Paris green, using 2 to 2.5 gm of sample. Calculate as the pentoxicLe.

LIME-SULPHUR SOLUTION

This spray is important in the control of San Jose and other
scales. It is effective also in the extermination of numerous
insects. This is especially true when it is combined with lead
arsenate and nicotine and it is used then for the simultaneous
(destruction of many sucking and chewing insects and of fungus
diseases. The standard lime-sulphur solution consists of cal¬
cium tetrasulphide, pentasulphlde and thiosulphate in a water
solution. It is produced by boiling lime water containing
sulphur. The probable reactions are generally understood to be
ns follows:

3Ca(OH), + 10S -> 2CaS 4 + CaS 2 0 3 + 3H 2 0.

1 See also RKEDvand Haau, J . I nd. Eng. Chetn 13, 103S (1921).

( 1 )

304

QUANTITATIVE AGRICULTURAL ANALYSIS

The calcium thiosulphate thus formed is largely decomposed by
boiling, calcium sulphite and free sulphur being formed:

CaSo0 3 -> CaS0 3 + S. . (2)

The free sulphur formed in reaction (2) is dissolved by calcium
tetrasulphide to form pentasulphide.

CaS 4 + S -> CaS 5 . (3)

The insoluble sludge remaining consists of a mixture of calcium
sulphite and some calcium sulphate, the latter being formed by
oxidation of sulphite.

Extensive investigations on the fungicidal value of sulphur
of polysulphides were carried on by Syre, Solmon and War-
mall, 1 using the hop-mildew at its most resistant stage as their
standard. They have expressed the opinion that the fungicidal
value depends upon the percentage of polysulphide sulphur in
solution, rather than the total sulphur content.

Lime-sulphur solutions, either upon standing exposed to air
or after being sprayed, slowly react with oxygen, forming calcium
thiosulphate and free sulphur:

2CaS 5 + 30 2 -> 2CaS 2 0 3 + 3S 2

Determination of Total Sulphur.—Weigh a closed weighing bottle then
add about 10 cc of the lime-sulphur solution, close and weigh again. Rinse
into a 250-cc volumetric flask and dilute to the mark with recently boiled
and cooled distilled water and mix thoroughly. Dissolve 2 to 3 gm of
sodium peroxide in 50 cc of cold distilled water in a 250-cc beaker. Pipette
10 cc of the prepared lime-sulphur solution to this solution, keeping the tip
of the pipette just under the surface of the solution until it is to be raised
for drainage at the end of the process. Cover immediately with a watch
glass and warm on a steam bath with frequent shakings until the sulphur is
oxidized to sulphate (the yellow color having disappeared), adding more
sodium peroxide if necessary. Dilute to 25 cc, acidify with hydrochloric
acid, evaporate to dryness, treat with 25 cc of water acidified with 5 cc of
hydrochloric acid, boil and filter to remove silica if present. Dilute the
filtrate to about 200 cc and heat to boiling. Add a drop of methyl red then
neutralize with sulphur-free ammonium hydroxide. Add 1 cc of approxi¬
mately normal (1 to 10) hydrochloric acid, then add 10 to 25 cc (as found
to be necessary) of 10-per cent barium chloride solution, slowly from a
pipette, stirring constantly. Digest on a steam bath until the precipitate

1 J. Agr. Set., 9, 283 (1919).

I.XSECT1<‘I1)E>< AXf> FVXGICIDEX

305

settles readily, then filter through quantitative filter paper. Wash until
free from chlorides ami burn the paper in an inclined weighed crucible at a !.
temperature (not above dull redness)- When the precipitate is white, ox.l
and. weigh. Calculate the sulphur from the weight of barium sulphate.
Corrections should he made for any sulphur present in the reagents, deter¬
mined by a blank experiment. Sodium peroxide, especially, is liable to
contain sulphates.

determination of Total Sulphide Sulphur.—Dissolve 50 gm of zinc chlo¬
ride in about 500 cc of water and add 125 cc of concentrated ammonium
hydroxide, which will redissolve the precipitate first formed. Add 50 gm
of ammonium chloride and dilute to about 1 liter.

IPipette 10 cc of the lime-sulphur solution (freshly made as for the
total sulphur determination) into a 250-cc beaker, dilute to 100 cc and add
ammoniacal zinc solution until the sulphide sulphur is all precipitated, as
indicated by the failure of a drop of the clear solution to darken a few drops
of dilute nickel sulphate solution. Filter immediately, wash the precipitate
thoroughly with cold water and return it and the filter to the beaker. Cover
with water, disintegrate with a glass rod and slowly add about 3 gm of
sodium peroxide, keeping the beaker well covered with the watch glass.
Warm on the steam bath, with frequent shaking, until all of the sulphur is
oxidized to sulphate and the precipitate is all dissolved, adding more sodium
peroxide if necessary. Make slightly acid with hydrochloric acid, filter to
remove shreds of filter paper, wash thoroughly with hot water, heat the
filtrate and washings to boiling and determine the sulphur as described for
total sulphur, neutralizing and acidifying in the same manner. Calculate
the per cent of sulphide sulphur in the sample.

Total Calcium. —The per cent of calcium in a lime-sulphur
solution will depend upon the character and purity of the lime
used in its preparation, as well as upon dilution and degree of
hydrolysis. It will vary over wide limits but as this element
is of relatively small importance in connection with insecticidal
properties, its determination is not often required. The fol¬
lowing method is official:

Determination of Total Calcium.—To 25 cc of the lime-sulphur solution,
prepared as for the preceding determination, add 10 cc of concentrated
hydrochloric acid and evaporate to dryness on the steam bath. Add 25 cc
of water and 5 cc of concentrated hydrochloric acid, warm until all of the
calcium chloride is dissolved and filter from sulphur and any silica that may
be present. Make slightly ammoniacal, boil and filter from iron and
aluminium hydroxides if these are produced. Heat to boiling and precipi¬
tate the calcium with am&ionium oxalate solution and finish the determina¬
tion as described on page 64 or 69, Part I. Calculate the per cent of calcium
oxide in the sample.

306

QUANTITATIVE AGRICULTURAL ANALYSIS

NICOTINE INSECTICIDES

Nicotine in solution is an effective agent for destroying many
soft bodied insects, as aphides and pear psyllse. Solutions of
nicotine are valuable as insecticides because of the intensely
poisonous character of nicotine, whether eaten by the insect
or absorbed through its exterior covering. They may be
applied in various dilutions and in combinations with other
sprays to treat, all at once, certain sucking and biting insects
and fungus parasites. Nicotine is not injurious to foliage, in any
concentration. As a vegetable alkaloid it is a weak base and this
makes it possible to determine the amount of nicotine present in
a solution by titrating with a standard acid.

Most dry tobacco waste contains from 2 to 3 per cent of
nicotine. An extract may be prepared for use as an insecticide
by stirring 25 to 30 lb. of the tobacco waste with 50 gal. of water.
This will make a solution averaging about 0.06 per cent of
nicotine. 1

The separation of nicotine from a solution is made by extract¬
ing with ether. The extracted residue is dissolved in a base

1 Va. Exp . Sta. Bull , 208 (1914).

INSECTICIDE# AXD FCXGICIDES

307

solution and the nicotine separated by steam distillation. The
nicotine in the distillate is titrated with a standard acid as follows:

determination of Nicotine.—Prepare the following solutions:

(a) Alcoholic Sodium Hydroxide Solution .—Dissolve 6 gm of sodium hydrox¬
ide in 40 cc of water and 60 ce of 90-per cent alcohol.

(b) Approximately tenth-normal sodium hydroxide solution , not standardized.

Weigh into a 50-cc beaker, 5 to 6 gin of tobacco extract or 20 gm of
finely powdered tobacco or tobacco waste which has been dried at 60°.
Add 10 cc of alcoholic sodium hydroxide and, in the case of tobacco extract,
follow with enough shredded filter paper to form a moist but not lumpy
mass. Mix thoroughly, transfer to a continuous extractor (page 146)
and extract for about five hours with ether. Evaporate the ether at a low
temperature and take up the residue with 50 cc of sodium hydroxide (5).
Transfer the residue by means of 200 cc of water to a 500-cc Kjeldahl flask,
add a piece of pumice or a small amount of crushed porcelain and a small
piece of paraffine, heat to boiling and distill by steam, passing the distillate
through a condenser cooled by a rapidly flowing current of water. Distill
from 400 to 500 cc, stopping the current of steam and using a flame under
the flask at a point such that only about 15 cc of the liquid finally remains
in the flask. Titrate the distillate with tenth-normal sulphuric acid, using
methyl red as an indicator. Calculate the per cent of nicotine in the
sample.

308

QUANTITATIVE AGRICULTURAL ANALYSIS

BORDEAUX MIXTURE

Bordeaux mixture consists of copper sulphate and calcium
hydroxide. It is one of the most reliable of the fungicides, its
poisonous properties being due to the copper and hydroxyl
ions. Chemical tests show that when Bordeaux mixture is
applied to the leaf, a small amount of copper enters and com¬
bines with chlorophyl of the cells. This seems to give the leaf
an increased resistance to insect injury. The spray spreads
rapidly over the leaf and forms a thin colloidal membrane
composed of basic copper and calcium salts. Both copper and
calcium hydroxide are fungicidal and when spores fall upon a
sprayed leaf, they are either killed or germinate very slowly.

Moisture. —The determination of moisture in Bordeaux
mixture powder is made by drying at 105° to 110° to constant
weight. The determination in the paste is complicated by the
fact that basic carbonates of copper (formed through interaction
of copper sulphate, calcium hydroxide and carbonic acid) lose
carbon dioxide during the first drying process:

(Cu0H) 2 C0 3 —>2CuO + C0 2 + H 2 0.

A determination of carbon dioxide must then be made and the
proper correction applied.

Determination of Moisture: (a) In Powder .—Dry 2 gm of sample as
directed for lead arsenate powder, page 300. Calculate the loss as moisture.

(b) In Paste .—Heat about 100 gm (weighed in a porcelain dish) at 90° to
100° until dry enough to powder readily. Weigh and calculate the per cent
loss. Denote this by a.

Powder the partly dried sample, mix and determine the per cent loss on
drying about 2 gm of this as directed above for powder. Call this b.
Determine carbon dioxide (see below) in both paste and partly dried powder.
Let c = per cent of carbon dioxide in the partly dried material and d the
total carbon dioxide in the paste. Since b and c are based upon a partly

dried sample the factor will correct these to a basis of the original

paste. Then total moisture

, / 100 -,

M - a + f - 100

<7> + c) - d.

(The .student should prove this formula. Note that the formula given in
the Official Methods, separate volume, first edition, is incorrect.)

Determination of Carbon Dioxide.—Weigh 2 gm of the powder or 10 gm
of the paste, place in the reaction flask together with 20 cc of water and

ArU .nine the carbon dioxide by one of the methods discussed on pages 77

Part I. Calculate the per cent of carbon dioxide in the sample as used.

INSECTICIDES AND FUNGICIDES

309

Determination of Copper.—Prepare solutions as directed for the determi¬
nation of copper in cuprous oxide, page 162 (feeds). Weigh about 2 gm of
the sample, dissolve in about 50 cc of 10-per cent nitric acid and add ammo¬
nium hydroxide solution in slight excess. Then without removing the
precipitate which has formed, add acetic acid to clear and 5 to 10 cc in
excess. Cool, add 10 cc of 30-per cent potassium iodide solution and titrate
with thiosulphate as directed on page 162. Calculate the per cent of
copper present in the sample (dried, partly dried or paste) and in the
sample as received.

SOAP SPRAYS AND EMULSIONS

Soaps are used to a considerable extent for making oil emul¬
sions and they are often added to other sprays to cause the latter
to spread uniformly and to adhere more closely to the foliage.
The soap-kerosene emulsions are used somewhat for the soft-
bodied sucking insects, such as aphides, but they are being
replaced, by solutions of nicotine sulphate. Soap-oil emulsions
are used for scale insects.

Determination of Moisture in Soap.—Weigh rapidly about 5 gm of the
carefully selected sample into a weighed 50-cc beaker in which has been
placed a one-half inch layer of recently ignited dry sand and a small glass
rod. If the soap is hard, cut it up into very thin strips. Add 25 cc of
alcohol (more if necessary) and dissolve the soap by warming on a steam
bath, stirring constantly. Evaporate the alcohol, heat in an oven at 110°,
stirring occasionally, until the soap is nearly dry, then weigh; dry again for
30 minutes and weigh. Continue this process until the weight changes only
a few milligrams during 30 minutes of drying.

CHLORPICRIN

Chlorpicrin is trichlornitromethane, CCI3NO2. It is rated
as 283 times as toxic as carbon disulphide, compared on a basis
of molecular weights. It is not as inflammable as is carbon
disulphide, and its vapor is about twice as heavy, which feature
makes it quite desirable for grain fumigation. Chlorpicrin
vapor is so very poisonous 1 and active that not more than one-
half pound is needed for the fumigation of 1000 cu. ft. of space.
Ten times this amount of carbon disulphide would be required.

Much work is being done upon the adaptation of other poison
gases to insecticidal and fungicidal uses. No doubt this field
will be developed very rapidly during the next few years and the
agricultural analyst will have many new problems presented
for his solution, as a result.

1 J. Econ. Ent. : 11, 4 (1918).

312

LOGARITHMS

Logarithms

Natural

Numbers

Proportional Parts

l»

0000

0043

0086

0128

0170

0212

0253

0294

0334

0374

0414

0453

0492

0531

0569

0607

0645

0682

0719

0755

0792

0828

0864

0899

0934

0969

1004

1038

1072

1106

1139

1173

1206

1239

1271

1303

1335

1367

1399

1430

1461

1492

1523

1553

1584

1614

1644

1673

1703

1732

1761

1790

1818

1847

1875

1903

1931

1959

1987

2014

2041

2068

2095

2122

2148

2175

2201

2227

2253

2279

2304

2330

2355

2380

2405

2430

2455

2480

2504

2529

2553

2577

2601

2625

2648

2672

2695

2718

2742

2765

2788

2810

2833

2856

2878

2900

2923

2945

2967

2989

3010

3032

3054

3075

3096

3118

3139

3160

3181

3201

3222

3243

3263

3284

3304

3324

3345

3365

3385

3404

3424

3444

3464

3483

3502

3522

3541

3560

3579

3598

3617

3636

3655

3674

3692

3711

3729

3747

3766

3784

3802

3820

3838

3856

3874

3892

3909

3927

3945

3962

3979

3997

4014

4031

4048

4065

4082

4099

4116

4133

4150

4166

4183

4200

4216

4232

4249

4265

4281

4298

4314

4330

4346

4362

4378

4393

4409

4425

4440

4456

4472

4487

4502

4518

4533

4548

4564

4579

4594

4609

4624

4639

4654

4669

4683

4698

4713

4728

4742

4757

4771

4786

4800

4814

4829

4843

4857

4871

4886

4900

4914

4928

4942

4955

4969

4983

4997

5011

5024

5038

5051

5065

5079

5092

5105

5119

5132

5145

5159

5172

5185

5198

5211

5224

5237

5250

5263

5276

5289

5302

5315

5328

5340

5353

5366

5378

5391

5403

5416

5428

6441

5453

5465

5478

5490

5502

5514

5527

5539

5551

5563

5575

5587

5599

5611

5623

5635

5647

5658;

5670

5682

5694

5705

5717

5729

5740

5752

5763

5775

5786

5798

5809

5821

5832

5843

5855

5866

5877

5888

5899

5911

5922

5933

5944

5955

5966

5977

5988

5999

6010

1 9

6021

6031

6042

6053

6064

6075

6085

6096

6107

6117

6128

6138

6149

6160

6170

6180

6191

6201

6212

6222

6232

6243

6253

6263

6274

6284

6294

6304

6314

6325

! 3

6335

6345

6355

6365

6375

6385

6395

6405

6415

6425

6435

6444

6454

6464

6474

6484

6493

6503

6513

6522

6532 i

6542

6551

6561

6571

6580

6590

6599

6609

6618

6628 i

6637

6646

6656

6665

0675

8684

6693

6702

6712

6721 i

6730

6739

6749

6758

6767

6776

6785

6794

6803

6812 1

6821

6830

6839

6848

6857

6866

6875

6884

6893

69021

3911

6920

6928

6937

6946

6955

6964

6972

6981

. 6

69901

3998

7007

7016

7024

7033

7042

7050

7059

7067

7076 '

r084

7093

7101

7110

7118

7126

7135

7143

7152

7160 :

7168

7177’

*7185

7193

7202

7210

7218

7226

7235

, 7

7243 :

7251 '

7259

7267

7275

7284

7292

7300

7308

7316

7324 :

r332 ‘

7340

7348

7356

7364

7372

7380

7388

7396

1 3

LOGARITHMS

313

Natural

Numbers

7404

7412

7419

7427

7435

7443

7451

7459

7466

7474

7482

7490

7497

7505

7513

7520

7528

7536

7543

7551

7559

7566

7574

7582

7589

7597

7604

7612

7619

7627

7634

7642

7649

7657

7664

7672

7679

7686

7694

7701

7709

7716

7723

7731

7738

7745

7752

7760

7767

7774

7782

7789

7796

7803

7810

7818

7825

7832

7839

7846

7853

7860

7868

7875

7882

7889

7896

7903

7910

7917

7924

7931

7938

7945

7952

7959

7966

7973

7980

7987

7993

8000

8007

8014

8021

8028

8035

8041

8048

8055

8062

8069

8075

8082

8089

8096

8102

8109

8116

8122

8129

8136

8142

8149

8156

8162

8169

8176

8182

8189

8195

8202

8209

8215

8222

8228

8235

8241

8248

8254

8261

8267

8274

8280

8287

8293

8299

8306

8312

8319

8325

8331

8338

8344

8351

8357

8363

8370

8376

8382

8388

8395

8401

8407

8414

8420

8426

8432

8439

8445

8451

8457

8463

8470

8476

8482

8488

8494

8500

8506

8513

8519

8525

8531

8537

8543

8549

8555

8561

8567

8573

8579

8585

8591

8597

8603

8609

8615

8621

8627

8633

8639

8645

8651

8657

8663

8669

8675

8681

8686

8692

8698

8704

8710

8716

8722

8727

8733

8739

8745

8751

8756

8762

8768

8774

8779

8785

8791

8797

8802

8808

8814

8820

8825

8831

8837

8842

8848

8854

8859

8865

8871

8876

8882

8887

8893

$899

8904

8910

8915

8921

8927

8932

8938

8943

8949

8954

8960

8965

8971

8976

8982

8987

8993

8998

9004

9009

9015

9020

9025

0031

9036

9042

9047

9053

9058

9063

9069

9074

9079

9085

9090

9096

9101

9106

9112

9117

9122

9128

9133

9138

9143

9149

9154

9159

9165

9170

9175

9180

9186

9191

9196

9201

9206

9212

9217

9222

9227

9232

9238

9243

9248

9253

9258

,9263

9269

9274

9279

9284

9289

9294

9299

9304

9309

9315

9320

9325

9330

9335

9340

9345

9350

9355

9360

9365

9370

9375

9380

9385

9390

9395

9400

9405

9410

9415

9420

9425

9430

9435

9440

9445

9450

9455

9460

9465

9469

9474

9479

9484

9489

9494

9499

9504

9509

9513

9518

9523

9528

9533

9538

9542

9547

9552

9557

9562

9566

9571

9576

9581

9586

9590

9595

9600

9605

9609

9614

9619

9624

9628

9633

9638

9643

9647

9652

9657

9661

9666

9671

9675

9680

9685

9689

9694

9699

9703

9708

9713

9717

9722

9727

9731

9736

9741

9745

,9750

9754

9759

9763

9768

9773

9777

9782

9786

9791

9795

9800

9805

9809

9814

9818

9823

9827

9832

9836

9841

9845

9850

9854

9859

9863

9868

9872

9877

9881

9886

9890

9894

9899

9903

9908

9912

9917

9921

9926

9930

9934

9939

9943

9948

9952

9956

9961

9965

9969

9974

9978

9983

9987

9991

9996

Proportional Parts

12344566

12334566

12334556

12334556
12334556
1 2 3 3 4 5 5 6

12334456
12234456

12234456
12234455
1 2 2 3 4 4 5 5

1 2 2 3 4 4 5 5

12233455

12233445

12233445
12233445
12233445
1 2 2 3 3 4 4 5

1 2 2 3 3 4 4 5

12233445
1 2 2 3 3 4 4 5

11223344
1 1 2 2 3 3 4 4

1 1 2 2 3 3 4 4

11223344
11223344
11223344

1 1 22 3344
11223344
1 1 2 2 3 3 4 4

1 1 2 2 3 3 4 4

1 1 2 2 3 3 3 4

t \ ru.nt, 1 lil / // M:

A VMI.ru, MilTJIMS

Logarithm*

" i 1 i - ! •' i ‘

IV.J...,

1 ■• . t

0'*hnl J’mrtii

7 u

.00

1000 1CMI2 1004 IfM>7 1<M*»

.1012 OH4 1010 iMl't 0»2I

« * t j j i \ ** ,,

.01

1023 1020 102S 1030 1033! Jf»J.% JIMS lOJO 1012 Jhl5

*> t! i :: i 2 7

.02

1017 io:»o to:.:* io.m m.%7

•1050 On.7 OHH 0*07 1**00

on i a

* 12 2

.03

1072.1074 107n 1070 10HI

loxi ios»; joxo 1001 looi

0 h 2 2j l 2 2 2

.04

loin* niofi 1102 noi no7
III

1200 1122 UM 2 1 27 2 2 20
{ | I j

0 1 11,1 72 2

j • i

.or>

1222 1125 U27 1130 1132

‘II!

1135 Il.’IS HO* 1243 11 0.

! I '

«' J a 2. l 2 2 2

.00

ims mi ii /,3 ur,n n.v*

I 0*1 1104 1107 IVA 1177

o I 1 2 ' 2 2 2 :•

.07

117/* 117s i iso 11s;i Uhi,

nxo noi noi i o*7 w*'i

o, 2 2 J

i 2 2 2 2

.OH

1202 1205 120M 1211 1213

1210 120* 1227 1775 1277

* J l 1 2 2 2 2

.00

1230 123.3 12.30 1230 1242

I t

1245 1247 1250 2253 125*
l|,l

« 1 ! i 1 , , •

; . t . ,

.10

1 1 1 1

1250 1202 1205 120K 1271

1 1 1 I

1274 1270 1270 23X3 17X5

' : : j : 1 !

»• a J l! J 2 2 2

.11

12SS 1201 1204 1207 13**0

130,4 1,300 130*4 2317 2 325

0 2 2 3

M *. r* „

.12

131H 1321 1321 1.327 2330

1.334 1.337 23|o 2343 230

O l ] l' 7 2 2 2

. 23

1.340 1352 1355 1.35H 1,302

1.355 130S 2 57 J J074 2.377

0 2 12

n v

.14

1.3X1 i 13M! 1.3X7,1.300 2,303 ■
j

1.300 14*240.3 140*. 20^'

1 1 | j I

*222

7 7 2 ,3

.Xft *

till

Hi:?^ 115 1410 1122 1425

1 1 1 1 I

1420 H52 24.35 1430 |U2

0 1 2 J

.. ./ j J

.10

HI 5 1440 J I52 1455 1450;

1402 1400 I 400 2477 H7o|

o 2 J l

If 'i

.17

1470 HX.3 14Sf, I ISo tihii

1100 25?** 15**5 J 5**7 15jo|

o 2 2 1

2 2 2 ;r

1514 1517 1521 1524 I52sj

1531 1555 J53S 2547 1545,

0 2 2 J

,10

1540 1552 1335 1500 2303

lilt

15*0 I»*7 5 * 1574 15 ?x 25s*, * J 3 2

I j ,

*, ' 3 5

.20

till

15X5 15X0 1502 1505 1000

\ ! I 1 Mi*

2005 1007 mil 201 4 10 2 s! h \ \ t

; 1 j '

2 2 .3 .3

m.3.3 lfttfjiirii ion imx 1052 ion*.

iwk> ion;i i*i
iia*s i7ul* n
17.3X 17*2 17

I !

177S 17X2 17
1X20 1X21 \H

1W2 ixoo is

IHOft HUM JO
ItfftO H054 H*

1WWJ 2000 2004 2***0 2oj*'2nix 3034 20;
*2012 2o*r» •*»i51 2U4o 2***1*2005 2070 20?
*<wj» xm #mi 21m ;:}j^; ( j|:i am 21;

1700 1720 2714

j!7ix |777

1 77o

175 m

1734

, ** 3

1 2 7

1740,2750 1754
j j

175s 2707

1 i

27oo

f J

’ “7 •

,* ]

2774

r i ;

17X0 1701 1705

• l7oo jsrr;

! ;

1 sor

! *

ixu

1H In

] *5 3

I i

1, 2 7

IX2S 1S52 1H37

11X41 J X|.5

20 40

3 H54

JX5H

<0 3

; i: 2

1X71 1H75 1X701

2HX4 jsss

2307

l N07

1002

h 2

• i

10H jor*

202, J037

1030

2042

1045

u J

! 1,2

1050 1003 ions,
>

1077 3077

J0H7

20'Mi

2 oo |

‘ a

2 2

2' 3, 3- »
2. 3 »; 3 3
2 2 3 3 4

:: i i : i *

2. 2. ;i a* 4

2. :t : a; a| 4
2 ' a: a a; 4

2 ;i : 4 \ 4

2 3 3 4 4

*W,ri (iM.)*; , < » 4# >

2*>75 iuMi
212:1 212* ;?rn

3 a 4 4
3 3 4 4

213H

2 M3

224 x

2153

3155

2103

2lns

217

717-

21X3

- 1 1 3

'21XX

2I0X

230

270'.

2213

324 x

222:

222’.

7244

1 1 2 2

2230

2244

2240

2754

3250

2205

2270

227/

27X0

22X0

112 2

2201

2200

2.301

2;ih7

2312

2.317

232 3

237 S

2,333

2340

I 1 2. 2

; 2.3 41

235M

2.355

2.100

2300

2371

2-377

23X2

23 XX

2304

1 1, 2

12300

2404

2410

2415

2421

2427

2432

21 :r

2443

2**0

1 1 2, 2

'2455

2100

2400

2172

,•<77

24 S3

24X0

2405

2.V*i

:;m>

11 2, 2

2527

' . !

251X

2523

2520

2535

3541

2547

•If * M

f !

2**0

2504

1 1 1

I 1 2 f 2

,3'

< !

2570

75X2

25XX

2504

2000

20M,

2012

201X

2024

! l! 1. 2 2

! a

; *

’ll

•20.30

20.30

2042

2040

2055

20»il

2*;o7

2073

207^

20X5

I I 2 2

'2002

200X

2701

2710

2723

2*7 20

27.35

27*2

27* X

1! i 3; ;i

; *;

12754

2701

2707

2773

27X0.

27 m

t 4

27U3

2710*

2X0*..

2X12

1 1 ; a

! *

JSWIH

2X25

2X31

2X3 H

2X44

! *

2X51

2X5X

2X04

1 1

2H71

2x77

: i j

1 1 2 .3

*’

'2HX4

2X01

2X07

XHH

2017

y»24

;wi

2" »3X

2***4

1 1 2 a

ft,

20512U5X %w?t 2V72 2070 20x5 »arj ;vw .Or**. :*r»|:;j
j:toy< ;m7 ;to;j* ;m*i ;*04*jaws* awi;* :mu y*?n auxal
JW n :t ^7 :nofi 3112 anohign am am aHX’atfta!

3 3, 4 ft, ft, »
a 4 4, 5. o. e

ANTILOGARITHMS 315

Antilog ahithms

Logarithms

Proportional Parts

i\ 5| 6|

8| 9 |

.50

3162

3170

3177

3184

3192

3199

3206

3214

3221

3228

‘i

7 f ;

.51

3236

3243

3251

3258

3266

3273

3281

3289

3296

3304

7 jj

.52

3311

3319

3327

3334

3342

3350

3357

3365

3373

3381

7 ij

.53

3388

3396

3404

3412

3420

3428

3436

3443

3451

3459

.54

3467

3475

3483

3491

3499

3508

3516

3524

3532

3540

7 1

.55

3548

3556

3565

3573

3581

3589

3597

3606

3614

3622

7 i

.56

3631

3639

3648

3656

3664

3673

3681

3690

3698

3707

8 I

.57

3715

3724

3733

3741

3750

3758

3767

3776

3784

3793

8 1

.58

3802

3811

3819

3828

3837

3846

3855

3864

3873

3882

.59

3890

3899

3908

3917

3926

3936

3945

3954

3963

3972

8 1

.60

3981

3990

3999

4009

4018

4027

4036

4046

4055

4064

.61

4074

4083

4093

4102

4111

4121

4130

4140

4150

4159

9 a jl

.62

4169

4178

4188

4198

4207

4217

4227

4236

4246

4256

.63

4266

4276

4285

4295

4305

4315

4325

4335

4345

4355

9 :

.64

4365

4375

4385

4395

4406

4416

4426

4436

4446

4457

.65

4467

4477

4487

4498

4508

4519

4529

4539

4550

4560

.66

4571

4581

4592

4603

4613

4624

4634

4645

4656

4667

.67

4677

4688

4699

4710

4721

4732

4742

4753

4764

4775

.68

4786

4797

4808

4819

4831

4842

4853

4864

4875

4887

.69

4898

4909

4920

4932

4943

4955

4966

4977

4989

5000

.70

5012

5023

5035

5047

5058

5070

5082

5093

5105

5117

.71

5129

5140

5152

5164

5176

5188

5200

5212

5224

5236

.72

5248

5260

5272

5284

5297

5309

5321

5333

5346

5358

.73

5370

5383

5395

5408

5420

5433

5445

5458

5470

5483

ii :■

74 !

5495

5508

5521

5534

5546

5559

5572

5585

5598

5610

.75

5623

5636

5649

5662

5675

5689

5702

5715

5728

5741

.76

5754

5768

5781

5794

5808

5821

5834

5848

5861

5875

.77

5888

5902

5916

5929

5943

5957

5970

5984

5998

6012

.78

6026

6039

6053

6067

6081

6095

6109

6124

6138

6152

13 1

.79

6166

6180

6194

6209

6223

6237

6252

6266

6281

6295

13 I

.80

6310

6324

6339

6353

6368

6383

6397

6412

6427

6442

.81

6457,

6471

6486

6501

6516

6531

6546

6561

6577

6592

.82

6607

6622

6637

6653

6668

6683

6699

6714

6730

6745

.83

6761

6776

6792

6808

6823

6839

6855

6871

6887

6902

.84

6918

6934

6950

6966

6982

6998

7015

7031

7047

7063

15 ]

.85

7079

7096

7112

7129

7145

7161

7178

7194

7211

7228

13 S

.86

7244

7201

7278

7295

7311

7328

7345

7362

7379

7396

15 |

.87

7413

7430

7447

7464

7482

7499

7516

7534

7551

7568

10 j

.88

7586.

7603

7621

7638

7656

7674

7691

7709

7727

7745

.89

7762

7780

7798

7816

7834

7852

7870

7889

7907

7925

.90

7943

7962

7980

7998

8017

8035

8054

8072

8091

8110

17 ;

.91

8128

8147

8166

8185

8204

8222

8241

8260

8279

8299

17 j

.92

8318

8337

8356

8375

8395

8414

8433

8453

8472

8492

! 14

.93

8511

8531

8551

8570

8590

8610

8630

8650

8670

8690

! 14

18 *

.94

8710

8730

8750

8770

8790

8810

8831

8851

8872

8892

: 14

18 |

.95

8913

8933

8954

8974

8995

9016

9036

9057

9078

9099

! 15

19 |

.96

9120

9141

9162

9183

9204

9226

9247

9268

9290

9311

i 11

i 15

. 17

19 l

.97

9333

9354

9376

9397

9419

9441

9462

9484

9506

9528

' 11

t 15

i 17

20 l

.98

9550

9572

9594

9616

9638

19661

9683

9705

9727

9750

' 9

' 11

\ ie

i IS

20 P

.99

9772

9795

9817

9840

9863

19886

9908

9931

9954

9977

■ 7

' 9

i 11

l 1C

( IS

L22. 'r

33 33

INDEX

AlW>d ref racto meter, 114, 115, 174,

175

Acetyl value, 187, 190, 196, 197
AoicL, butyric, 181, 182, 186
eapric, 181, 182, 186, 225
ca/proic, 181, 182, 186, 225
cetprylic, 181, 182, 186, 225
Ghlorplatinic, 246
o retraction of soils, 252, 267
jHLuixes, 23

hydrochloric, standard, 250, 277
linolenic, 176
llnolic, 177
oleic, 176

p>lienoldisulphonic, 236
xdcinoleic, 177
value of oils, 180
Acidity of cheese, 228
of milk, 203
of soils, 86 , 263

Acids of arsenic, free, in insecticides,

293

fatty, in butter, 224, 226
insoluble, of oils, fats and waxes,
181, 225, 226

non-volatile, of oils, ^-, 183 > 226
soluble, of oils, etc., 181, 188, -25,

■unsaturated, of oils, etc 176, 195
volatile, of oils, etc., 183, il'o
Acroodextrins, 157
Adiabatic calorimeter, 10
A-cLjustment of sample weight,
jVcUilteration of butter, 221

Agricultural materials, analysis of,

141

Albumin in milk, 199, 21
Aliquot parts, 6

Alkalinity of carbonates, 85, 86
of limestone, 86
Aluminium, 75, 76 ^

Hydroxide, solubility of, /o
in soils, 254, 255, 257, 258
Amici prism, 116, H7
Amid nitrogen m feeds, loo
Ammonia distillation, apparatus,
153

in soils, 238

nitrogen in fertilizers, 283
Ammonium citrate, reagent, 279,

molybdate, reagent, 89, 276 277
phospho molybdate, 88 , 90,

salts in fertilizers, 283, 285

Analyzer in polarimetry, 124, 12o
Angle of incidence, 113

of refraction, 113

Aniline acetate test for fur ural 166
Antilogarithms, table of, 31-, <^
Apparatus, volumetric, calibration

of, 44

Apparent valence, 66
Arabin in feeds, 165, 166 1 '
Arachis oil, Benard test for, 193
Arnold .{See Kjeldahl).

Arsenates in insecticides, 299

j Arsenic acids, free, in insecticides,

293

’ Arsenic in calcium arsenate, 303

r in lead arsenate, 301

in Paris green, 296, 297, 298

Arsenical insecticides, 296
Arsenites in insecticides, 299
Asbestos for filtering, 15S
Ash in cheese, 227

f in cream, 220 , 221

in evaporated milk, 217, 218
in feeds, 142, 145
in milk, 199, 204

/ XDh'X

M2 0

(.-•urd in butter, 222
I)

Dairy produets, 109
Decimal system, S
Decomposition in the crucible, .‘JO
Defloocuhif ion of clay, 20S, 2S2
De Long on recovery of platinum,
2-1(5

Denitrification in soils, 240
Density, 04
Desiccators, 2S
Dewar flask, 10(5
Dextrins, 157
I )extro-rotation, 122
Dextrose, calculation from cuprous
oxide, 1(50

specific rotation of, 120
Diastase, 1(50

Diehromntes, standard solutions of,
70, 74

Differential weighing, OS
Digestion for nitrogen determina¬
tion, 140, 152, 154
I)ilution ratio for standard solution*,
50

Dipping refmctoineter, 1 IS, 110,
174 , 202

Direct, polarization, 104
Dispersion, chromatic, llfi, 175
compensator for, 11(5, 117, 175
rotational, 127, 12S
Displneement of specific gravity
plummet, 09
Dissolving of samples, 22
Distearin, acetyl value of, ISO
Distillation by steam, 000
Double dilution method, 104, 214
refraction of Iceland spar, 125
Drying of oils, 17(5
precipitates, 20
Dyer on root acidity, 200, 20K

KDdon on coconnut fat, 225
Finer* on calorimeter, 104, 105

Kmwlsions, soup-oil. 201, 205, 000
Kpple <S*r Spit zer .

Mquivalent Weight. 7
Krythro»le\f nu *. 157
I'ifher ex traet ns 0 * d . 1 52. 1 50
extraction of fat. 112. 150. 205,
21 s

Kvaporated null., 215*

Kxtraetion npparutii . 1 Pi
Kxfraordinarv ray nf double refrac¬
tion, 125

Factor, bn e, 5
gravimetric, 2
normn!it v, 50
weight . ... s

Fat, Habe.M-], met h mi 1 fur, 2! Hi, 20H
cocoatmt, ls«i, Is PO* 225. 225,
22 *»

ether extract am of, 2MI, 21s

globule* m milk. 215
in buffer, 222
in ch**r C 22#'
in cream, 220

in evaporated milk, 21 7 , 2 is
in milk, 190. 20-1. 205. 200, 20S

fe«t bottle , 2015, 220

Fatcomjeeufmii of, 17f*
mnsfjinfa, f able of, 107
halogen nbturpfiMjj of, 17*5, 197,
22*5

HeJilier value of, I Si
in oluble mud* of, lsj, 225. 22*5
fuelfiitg point of, 175
f’olen’ke value of , I Mi, JlSi. J07,
225. 22*5

Iteieher! \fi'i 1 number of FS.'h
IHK iso, 1 ss, 107, los, 225
saponification number of, inti,
lsj. 107. 22*5

soluble mud* of, JKJ, 225, 22*5
specific griivjtv of. 172, 107
I’VciIm, 1 J2

amid nitrogen m, 555
arirbin in, 105. IHf» ( 107
i»U in, 152, 115

INDEX

321

Feeds, carbohydrates in, 142, 155,
158, 163, 165, 167
composition of, 142, 143
crude fat in, 142, 146, 147
fiber in, 142, 147, 148, 156
protein in, 142, 149
ether extract of, 142, 146
galactans in, 168
grinder for, 144
heat of combustion of, 108
mineral analysis of, 145
moisture in, 142, 143, 144
nitrogen-free extract in, 142, 156,
164

non-protein nitrogen in, 155
pentosans in, 142, 165, 166, 167
pentoses in, 165, 167
protein nitrogen in, 155
reducing sugars in, 157, 158, 159
sampling of, 142
sucrose in, 158, 163
xylan in, 165, 166, 167
Fehling’s solution, 158, 159, 162,
165

Ferrous ammonium sulphate, pri¬
mary standard, 68, 74
Fertilizers, 270

availability of nitrogen in, 285,286
ammonia nitrogen in, 283, 285
citrate-insoluble phosphorus in,
279, 281

compatibility of, 271, 272
culture methods for availability,
291

mechanical analysis of, 273
moisture in, 274
nitrogen in, 271, 282, 283, 284
phosphorus in, 271, 274, 275, 276,
277

potassium in, 271, 287
sampling of, 273, 274
water-soluble phosphorus in, 278,
279

Filter paper, 25
Filters, inorganic, 26
light, 129
Filtration, 25
21

Fish oil, bromide test for, 194
Flocculation of clay, 268
Fluxes, 23, 253

Foods, heat of combustion of, 108

Formal titration of proteins, 209

Formaldehyde in milk, 215

French sugar scale, 131

Fryer and Weston on oils, etc., 196

Fuels, heat of combustion of, 108

Fungicides, 292

Funnel, hot water, 226

Furfural, 165

Fusibility, 23

Fusion, 22, 253

Galactans in feeds, 168
Gases, poison, 309
General operations, 17
German sugar scale, 129
Gillespie on Ph determination, 140
Glucose, commercial, 136, 137-
specific rotation of, 136
Glycine, 209
Glycylglycine, 209
Glymol in fat determinations, 220
Gooch crucibles, 26, 50
Gravimetric analysis, 1
factors, 2

Grazing incidence of light, 115
Grinder for feeds, *144
Guano, 272
Gum Arabic, 165

Gunning method for nitrogen, 154,
209, 210, 222, 283

Haag (See Reedy).

Half-shadow in polarimetry, 126
Halogen absorption of oils, etc., 176,
196, 197, 226

Halphen test for cotton seed oil, 192
Hardened oils, 194
Hart's method for casein, 210, 21 1
Heat of combustion, 103, 108
Heated milk, 216

322

INDEX

Hehner value of oils, etc., 181
Hellebore, 293

Henriques and Sorensen on protein,
210

Herzfeld formula for sucrose and
raffinose, 136

Hopkins method for lime require¬
ment, 267
on phosphates, 274
on soil analysis, 231
Hot water funnel, 226
Humus, 251, 252
Hunziker on cream testing, 220
Hydrochloric acid, specific gravity,
57

standard solution of, 82, 91, 250,
277

volumetric determination, 55, 5S,
59

Hydrofluoric acid, decomposition of
silicates, 253

Hydrogen ion concentration, 12, 138
Hydrogenation of oils, 194
Hydrolysis of carbohydrates, 156,
163, 164, 165

Hydrometers, floating, 97
I

Ice cream, 221

Iceland spar, double refraction of,
125

Identification of oils, etc., 171
Ignition of precipitates, 28
wire for calorimetry, 105
Immersion refractometer, 118, 119,
174

Incidence, angle of, 113
grazing, 115

Index of refraction, 113, 120, 174,
226

Indicator method for Pji, 139
Indicators, 12, 130
neutrality, 12
outside, 74
Ph values for, 139
potassium chromate, 223

Indicators, starch, 178, 297
Inorganic filters, 26
Inscriptions on volumetric appara¬
tus, 43

Insecticides and fungicides, 292
Insoluble acids of oils, etc., 181, 225,
226

International sugar scale, 130
Inversion of sucrose, 132, 135
Invert polarization, 135
sugar, calculation from cuprous
oxide, 160
detection of, 137
formation of, 132
specific rotation of, 123
standard solution of, 162
Iodide method for copper, 162
Iodine absorption number, 176, 179,
196, 197, 226

monobromide, standard solution
of, 178

standard solution of, 297
Iron ore, 72, 75
in soils, 254, 257

volumetric determination by per¬
manganate, 70, 72

Johnson on manganese in soils, 260
Jones and Bullis on manganese in
soils, 260

Kainit, 272

Kelley on manganese in soils, 260
Kjeldahl method for nitrogen, 149,
150, 209, 210, 222, 283
flask, 150

-Gunning-Arnold method for nitro¬
gen, 154

Knife edges of balance, 36
Knop on culture experiments, 291
Kottstorfer number of oils, etc., 180,
196, 197

Krober’s table, 167

I S'I) fi.X

Gtcvt^° ry WOrk ’ SCO i )( ‘ of * 4S

eto me ter , os

ctoso 3 calculation from eupr<u;>
. °^ido, 160
m Cl 'cani, 220,221

in. evaporated milk, 217. 219
lri ill ilk, 199, 212, 214
110 imal weight of, 213
^Pticof methods for, 218
specific rotation of, 123
aevo rotation, 122

' aurent sugar scale, 131
‘ eac la. on invert sugar, 137
jeadL acetate, reagent, 134, 15S
s^senate in insecticides, 294, 295,
300, 301

°^ide in lead arsenate, 301
-<emon oil, specific rotation of, 123
r'GV'U.lose, s P ecific rotation of, 123
Lewlcowitsch on oils, etc., 1S3. IDS
Ligla-b filter, 128, 129
^or polarimetrv, 127
for .xefractometrv, 115
Li goiri, 148
Lirtae, 272

requirements of soils, 263, 264.
265, 267

-snlphur solution, 294, 295, 303,
304, 305

Limes tone, alkalinity of, 86

Linolenie acid, 176

Lirxolic acid, 177

Lirxse^d oil, drying properties of, 177

Liquids, sampling of, 22

Logarithms, table of, 310, 311

Loss on ignition of soils, 247

3Vtagnesia mixture, reagent, 88
]VIagnesium ammonium phosphate,
ignition of, S7, S9, 90
in. soils, 256, 259
lVla.lt extract, 163, 164
IVLaltose, calculation from cuprous
oxide, 160

Mang j: ,v' 1

2**6 2* '» 3

Manures. 27*
Marita amm.

T':

Mark mg ennat »1» >

McHargu.M.nmaJ^
Mechanical .mah-

Mi »>;>>, 284
Meker burner. 85
Melting p**ii*r of fa*>, 17*
Mercuric i-i.kriik. rrug-35.. 7]
Mercury os a r.5.jh-:. 150. ]*;
Methods of \\ cighing.

Methyl orange. 16. ],3
red. 16. 189

Meyer absorption tube. *2
MicruMVpic examination

215

Milk, 199

acidity of, 208
albumin in. 199. 211
a>h in, 204-
casein in, 199, 210
composition of, 19\», 201
condensed. 217
evaporated, 217
fat in, 205, 206. 208
globules in, 215
heated, 216

lactose in, 199, 212. 214
microscopic examination of. 2
nitrogen in, 209
pipette, 208, 218
powdered, 219
preservatives in. 215
proteins in, 199. 209, 210. 215
refractmneier reading of 202
sampling of, 20!
specific gravity of, 20
total solids in. 199. 298. 204
water in. 199. 202

IN DICK

Mineral analysis of f***•<is, I 1.1
Mixing ami dividing, IS
Moeaya oil, Heiehcrf-Meissl number
or, IK l

Mohr unit of volume, 120
Moisture in Bordeaux mixture, 2US
in hut ter. 222
in cheese, 227
in feeds, 1 12, I 12, 1 f t
in fertilizer^, 271

in lend arsenate, 250
in soap, 200
in noil s 224, 225

Molybdate, ammonium, reagent,
271 h 277

Monostearin, acetyl value of, ISO
Muiei'ii i»n<l \\ alker . tulde, 150
Mut arnt at ion, 122
Myricyl palm Hate, t 75

Neutrality indicator , 12
New hull on soybean oil, 102
Nieol pri* ut , 12.1

Nicotine m imreti* r i«Ir* , 2Mb, 21)7
j perific rot at inti of, 12*1
Nitratee in fertilizer , 2K2. 2s J
in mmIs, 225

Nitric neid, fnj notion in calon
metry, !t)5

Nitrification m oil . 222
Nitrogen, availability in fertilizer:',
2*5

enluSv-it- for du?« tion of, 150 152
digestion for, 1 |2, 152. 151
dlMM xfrurt in feed , 112, 155, 151
* »>mumg ue fhod for, 151, 200,
212 , 222
in ejire e. 22 *

III feed . 1 |*l, 151, 151
in fertilizer*!, 271. 2*2
in milk 200
in ; oil-. f 225

Kj«ddah! ( dinning \ruold method
hu 151

Kj*“Mahl method for, 1 10, 1511,
20*t. 2 h*. 222

Non-protein nitrogen in feeds, 155
Xon-volatile acids of nils, etc.. 1S2,
225

Normality factor, 52
Normal system, 7

weight for lactose, 212
in sacehariinetrv, 12*.I
Noyes on starch and glucose, 155
Nut murgerine, IX*I, 221. 225

()

Oil, nraeltis, Kenard’s tc*st for, 102
castor, acetyl value of, ISO, 100,
ion

rot toil seed, Halplien t <*st for, 102
croton, Ueichert-Mei.ssl number
of, ISt, ion

tidi. bromide test for, 101
linseed, unsut united character of,

177

peanut, Kenard test for, 102
resin, optical rotation of, 102
sesame, Knudouin test for, 102
.sovhenn v qualitative teat for, 102
nil-, acetyl value of. 1H7, 100, 105,
107

acid value of, ISO
blown, IKS
composition of, 17t)
const ant.'i of, 105, 157
drying <»f, 175

fata and waxes, saponifiable, 170
halogen absorption of, 17(1, 170,
I! Mi, 107
hardened, 151
l Miner value of, lS1

hydrogenated, 104
identification of, 171

insoluble acids in, IH1

iodine manlier of, 175, 17*0, MM4,
157

hot5 forfer number of, 1*0, IXI,
1K2, 105, 157

marine animal, bromide test for,
154

Mauiiienc numher of, 151, 152,
55, 107

7XDF.X

Oils, Polenske value of, 1 st;, 196, PC
Heichert-Meissl imiuhf-r of. is:;.

1S4, ISO, 1SS, 196, PC, 22"*
saponification number of. lsU. 1M,
182, 1%, 197
soluble acids of, 181, 1SS
solvents for, 177
specific, gravity of, 172. 190, 197
Oleic acid, 176
Olein, 170, 176, 195
Oleo oil, 184

Oleomargerine, 1S4, 224, 220
Opium wax, esters in, 170
Optical methods for lactose, 213
rotation, 121

Optimum moisture in soils, 234, 235
Orange oil, specific rotation, 123
Ordinary ray of double refraction,
125

Organic matter in soils, 24S
Outflow time for volumetric appara¬
tus, 43

Outside indicators, 74
Oxidation in the crucible, 28

Palau, 32

Palm nut oil, Hehner value of, 1S2
Palmitin, 170, 181
Paper, filter, 25
Paris green, 295, 296, 297, 29S
Peak (See Warrington).

Pentosans in feeds, 142,165, 166, 1th
Pentoses, 165, 167
Perchlorate method for potassium,
247, 289

Permanganate method for calcium,
65, 68, 69
for iron, 70, 72

Permanganates, standard solutions
of, 65, 67, 6S, 72

Persulphate method for manganese,
260, 262

Ph, definition of, 13

values for indicators, 139
Phenol red, 139
Phenoldisulpbonic acid, 236

Phenolput h.tlvm, 17

p}i!»>r*>iiI! j. r* * 1 •*-.

r ■

tiTum../ .• • ;

Pho.'.phan -. >7
insoluble, phr .* .vs
n-vrM^n of. 27."

St*lub]e. pl:.->pii-oni'

Pho>ph<*ru-. av.oLr;L’J
in fertilizer'. 271 27 1. 27

in insoluble ph^p:
in rock pliospiut*«• • '-t. -p

in soils. 240,. 242
in so]uhi** phosphate*. vs
Picnometer, 1*6, 97. 172
Pipette. milk. 20*. 217
Pipettes. 42
calibration of, 46. 20*
Plane polarization. 121
Platinum, care of, 31
enicibles, 31
substitutes, 32
Plummet, specific grav/y
br.ttion of. 100
displacement of. on
use on an analytical hunr
Poison gases, 309
Polarimeter, 124
Polarimetry, 121
light source for, 127
Polarization, invert. 135
Polarized light. 121
Polarizer. 124. 125
Polenske value for butter
225. 226

for cocoa nut fat. l v * :
for oils, etc.. 1*6. Ph*.
226

Policeman, 51
Porcelain crucibles. 30
Porpoise oil. Reichert-M'
l>er of. 1S4

Potassium, centniu^a: tic

IS9. 290

326

INDEX

Potassium, chlorplatinate method
for, 244, 245, 288
chromate, indicator, 223
dichromatc, light filter, 129
standard solution of, 178
hydroxide, standard solution of,
277

in fertilizers, 271, 287
in insoluble minerals, 243
in soils, 243
iodide, reagent, 178
perchlorate method for, 247, 289
permanganate for nitrogen availa¬
bility, 286

standard solution of, 65, 67, 68,
72

sulphate in nitrogen determi¬
nation, 154

thiocyanate for soil acidity, 265
Potential plant food in soils, 233
Potentiometer method for Ph, 138
Powdered milk, 219
Precipitate, correction for volume of,
133

Precipitates, drying of, 26
ignition of, 28
size of crystals, 25
Precipitation, 24
Preparation of samples, 17
of insecticides, 293
Preservatives in milk, 215
Prideaux on indicators, 16
Primary standards, 9
Prism, Amici, 116, 117
Nicol, 125

Protein nitrogen in feeds, 155
Proteins, formal titration of, 209
in cheese, 227

in evaporated milk, 217, 218
in milk, 199, 209, 210, 213
Ptyalin, 163

Pulfrich refractomcter, 119, 174

Quantitative determinations, 48
Quartering samples, 19, 20, 21

Quartz, optical activity of, 127
wedge compensation in polari-
metry, 127

Quinine sulphate, specific rotation
of, 123

Radiation corrections in calorimetry,
106,111

Raffinose, 133, 136
Reducing sugars in feeds, 157, 158,
159

Reduction of iron, 71, 74
Reedy and Haag on soluble arsenic,
303

Refraction, angle of, 113
index of, 113, 120, 174, 226
Refractometer, Abb6, 114, 115, 174,
175

butyro-, 118, 174
dipping, 118, 119, 174
Pulfrich, 119, 174
Refractometry, 113
light for, 115

Regnault-Pfaundler radiation cor¬
rection, 107

Reichert-Meissl number for butter,
197, 225, 226

for oils, etc., 183, 186, 188, 196,
197, 225, 226

Resin oil, optical activity of, 192
Reversion of phosphates, 275
Rhead and Ridgell on organic matter
in soil, 248
Rhotanium, 32
Richards on calorimetry, 41
Ricinoleic acid, 177
Ricinolein, 190
Rider, chain, 37
weight, 36
Ridgell iSee Rhead).

Riffle, 21

Ripening products of cheese, 227
Rock phosphate, phosphorus in, 89,
91, 279

Rohrig tube, 205, 218, 221

IXDEX

Hose-Got tlich method for fat, 205,

2 IS, 221

Hotation, doxtro, 122

dispersion of polarized light. 127,
128

laevo, 122
optical, 121
specific, 122, 123

Saccharimeter, 127
Saccharometer, 98
Saiki on galactans, 168
Salt in butter, 223
in cheese, 227

Sample weight, adjustment of, 6
Samples, preparation of, 17
Sampling of butter, 221, 226
of condensed milk, 217
of feeds, 142
of fertilizers, 273, 274
of liquids, 22
of milk, 201
of soils, 234

Saponifiable oils, fats and waxes, 170
Saponification number of oils, etc.,
ISO, 1S2, 106, 197

Scholl on determination of potas¬
sium, 247

Schreiner color comparator, 237
Scope of laboratory work, 48
Sensibility of balance, 39
Sesame oil, Baudouin test for, 193
Settinion soybean oil, 193
Shafer on insecticides, 292
Sherrill on potassium determi¬
nations, 289

Shives on culture experiments, 291
Silica in soils, 254, 256
Silver chloride method for chlorides,
49, 50

solubility, 49

Silver chromate, indicator, 52
Single deflection method for weigh¬
ing, 3S

Slag, Thomas, 272

Size of crystals 1 n p Tr .
Smith method for p>,*\ 1.
Soap-oil emulsions,

Soap, moisture in. 360
Soda ash, alkalinity *
Sodium carbonate, rrn
ard, 57, S2

chloride, standard ] r
cobaltinitrite. reagen-*
in soils, 243

light in polariinet ry. 12
in refractometry, \) '

oxalate, primary
thiosulphate, standar i
17S

Soils, 230

acid extraction of. 252
acidity of, S6, 2tv>
aluminium in. 254. 255
ammonia in, 23S
available plant food it:
267

calcium in, 255, 25>
carbon in, 249
classification of, 232
decomposition by fas:

by hydrofluoric acid
denitrification of,
humus in, 251, 2.5
iron in, 254, 257

lime requirements of,
loss on ignition of, 245
magnesium in. 256. 25
manganese in. 259. 26
moisture in, 234, 235
nitrification of, 239

nitrogen in, 235
organic matter in. 24S
phosphorus in. 240, 2-4
potassium in. 243
potential plant food :■
sampling of, 234
silica in, 254, 256
sodium in, 243

sulphur in, 262
Solmon (See Syre
Solubility product. 24

ci n

328

INDEX

Soluble acids of oils, etc., 181, 18S,
225, 226

Solvents for oils, 177
Sorensen (See Henrique).

Soybean oil, Sett-ini-Newhall test
for, 193

Special measurements, 93
Specifications for volumetric appara¬
tus, 43

Specific gravity, 57, 94, 102, 172,
173, 196, 197, 202, 220
Baumc, 95

methods for determination of, 96
of cream, 220
of hydrochloric acid, 57
of milk, 202

of oils, etc., 172, 196, 197
Specific rotation, 122, 123
temperature reaction, 191, 192
Spermaceti, esters in, 170
Spindle, specific gravity, 97
Spitzer on milk proteins, 211

and Epple on butter substitutes,
184

Spot plate, 74
Sprays, mixing of, 293
Standard solutions, 4
correction factor for, 54
dilution ratio for, 53
Standardization of solutions, 8
Standards for calorimetry, 105
primary, 9

Stannous chloride, reagent, 71
Starch, diastase method for, 163,164
hydrolysis of, 163, 164
indicator, 178, 297
specific rotation of, 123
Steam distillation, 306
funnel, 226
vStearin, 170, 189, 195
Stewart on availability of phos¬
phates, 274

Substitution method for weighing,
40

Sucrose, Clerget formula for, 132,
135

in condensed milk, 218

Sucrose, in feeds, 158, 163
inversion of, 132, 135
specific rotation of, 123
Sugar, invert, standard solution of,
162

scale, French (Laurent), 131
German (Ventzke), 129
International, 130
Sugars, common, 131
in beet products, 136
Sulphates, gravimetric determi¬
nation of, 60, 62
Sulphur in insecticides, 295
in lime-sulphur solutions, 304, 305
in soils, 262

Sulphuric acid, volumetric deter¬
mination of, 62, 63
Superphosphate, 272
Syre, Solmon and Warmall on
insecticides, 304
Syrups, commercial, 133, 134

Taka-diastase, 163
Tartaric acid, specific rotation of,
123

Teclu burner, 33

Temperature corrections in cali¬
brating, 44
systems, 4, 49

Test bottles for fat, 206, 220
Theory and general principles, 1
Thomas slag, 272
Thymol blue, 139

Time of outflow for volumetric
apparatus, 43

Time-temperature curves, 107, 108,
110

Titration, 4
curves, 14

Tobacco insecticides, 295, 306
Total solids in cream, 220, 221
in milk, 199, 203, 204
Tottingham on culture experiments,
291

Transfer pipettes, calibration of, 46

/A />/ A

Tnpio-diaduvv in pf-Lrau- ’ n . ]j»,
iVn\4>ndgeo m >oi! e u^-Uieaton, J..-2 ; ,

men:, 2»*4

I"nit>, tir.it. in.;

Client 11 rated acid- ;-
1 Oft

1 se of I nor, 37

Vacuum desiccator'-. jv
Valence. apparent. *»ti
A’i*i toll method for km* n ip; sn--
merit, 2t>4

Ventilator for nstr; a

1 AO

Ventzke sugar scab . I2 ; . 1
Villier anti Colli 21 nr, .•<-.! e-j •. =f
cereals, 142

Volatile acids in mi-. « a* . Ni. J‘J“>
Volumetric analyse. 1
apparatus. 41
factor weights, s

AValker on tU^nipo-urior. of min¬
erals, 243
(See Munson).

Warm all [See Sy re
Warrington and Peak m; organic
matter in soil*. *24s
AVash bit ties, 2(4
Washing precipitates, 20
Water, carbon dioxide-fret*. s;»
equivalent of calorimeters. 10A

Avian m fee

Zei>.- bury r«
Z»T< ■ }>« 5 i at o
Zinc arson it

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