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OJLa-w^ lO 0^ M.I
l^at&atti College 3.tbiars
GEORGE HAYWARD, M.D.
(CIiu of 1809}
SCIENCE CENTER LIBRARY
F. D. SNELL
D. VAN NOSTRAND COMPANY
Eight Wahreh Street
OCT I 1921* ) o
Copyright, 1 92 1
By D. Van Nostrand Company
Printed in thk United States of America
It has been the endeavor of the author so far as is
possible to avoid needless repetition of material in this
work. Therefore all the fine points as to theory, appa-
ratus and its use and the figuring of results which will
apply to practically every test given, have been gathered
together into three chapters at the beginning of the book.
From this it will be seen that a knowledge of these
chapters, particularly Chapters Two and Three, is neces-
sary to the success of anyone except an experienced oper-
ator, in the use of the methods of determination given on
the succeeding pages. It has been the endeavor of the
author to mention that a particular type of test was not
applicable to those cases where the choice of methods is
more limited than usual.
This book is, in essence, an attempt to combine in one
volume for ready reference, all the oolorimetric tests
which experience has shown to be at all practical. Much
material will be found here which has never been in print
outside of the scientific magazines as well as the stand-
ard tests which may be found by reference to any com-
plete work on chemical analysis. In going over the
material, it has been evident to the author that little has
been done with regard to the determination of the range
of greatest accuracy of many of the tests. Whenever
such information is available it has been incorporated,
so that the operator may know what degree of accuracy
he may expect from a sample after he knows the ap-
proximate amount of test substance contained in the
ly OOLOEIMETEia ANALTSIB.
It is hoped that this book will furnish a source to
which students may refer for a knowledge of the colori-
metric methods practical for use and a source to which
practical workers may refer for information as to the
methods of performing the particular tests with which
they are occupied. In all cases, weights of substances
to be dissolved as standard have been given to four
places, altho that by no means implies that absolute
accuracy is necessary in the last two places, since the
dilution will minimize any error made there. The giving
of these accurate weights will, however, show the operator
the direction in which the weight should tend in these
last two places and thus can assist to greater accuracy
without increasing the labor of weighing to any great
The author wishes to particularly acknowledge the
splendid assistance rendered him by the Library of the
Univei^ity of the State of New York in placing at his
disposal their files of magazines and reference works.
Acknowledgement is also made of the courtesy of Eimer
& Amend, C. J. Tagliabue Co. and Arthur H. Thomas
Co. in the furnishing of cuts. Acknowledgment is made
of the services of C. A. Tyler and W. H. Pearce in the
reading of proof.
All factors have been figured by the 1918 table of
F. D. S.
New York, N. Y.
CHAPTER SUBJECT PAGE
I. Conditions of Use of Colorimetric
II. Apparatus Used and Methods of Using It. 6
III. Figuring of Results 27
IV. Determination of Iron 31
A. By Potassium Sulfocyanate 31
B. As the Chloride in Concentrated
C. By Potassium Ferrocyanide 36
D. By Salicylic Acid 37
E. As the Sulfid 39
F. By Acetylacetone 41
G. By Dimethylglyoxime 42
V. Determination of Copper 44
A. By Ainmonia 44
B. As the Chloride in Concentrated
C. By Salicylic Acid 47
Z>. By Potassium Ferrocyanide 48
F. As the Sulfid 50
F. By Potassium Ethyl Xanthate 51
G, As the Bromide 53
VI. Carbon in Steel 55
VII. Lead, Bismuth and Arsenic 60
Lead as the Sulfid 60
Bismuth as the Iodide 62
A. Arsenic by the Stain Produced on
Mercuric Bromide Paper by Arsin. 64
B. Arsenic by Silver Nitrate 67
Vi COLOEIMETEia ANALYSIS.
CHAPTER SUBJEOT PAOS
VIIL Aluminum and Chromium 68
Aluminum by Alizarin-S 68
A. Chromium as the Chromate 70
B. Chromium by Disodium 1.8 dihydroxy-
naphthalene 3.6 disulfonate 71
IX. Nickel, Cobalt, Manganese and Zinc 73
A, Nickel by Potassium Thio-carbonate . . 73
B. Nickel as the Chloride in Concentrated
A, Cobalt as the Chloride in Concentrated
B. Cobalt by a-Nitroso-b-Naphthol 76
A. Manganese as Permanganate, Oxida-
tion by Persulf ate 78
B. Manganese as Permanganate, Oxida-
tion by Periodate 80
Zinc by Eesorcinol 81
X. Potassium and Magnesium 83
A. Potassium by Determination of the
Potassium Platino Chloride by Re-
duction with Stannous Chloride . . 83
B, Potassium as the Chlorplatinate by
Potassium Iodide 85
Magnesium by Determination of the
Phosphate as Phosphomolybdate . . 86
XI. Gold 89
A. Method of Dowsett 89
B. Method of Prister 90
C. Method of Doring 91
D. Method of Rose 92
E. Method of Cassal 93
F. By Decomposition of the Cyanide by
Potassium Bromide and Sodium
G. By Decomposition of the Cyanide by
H. By Metaphenylenediamine 94
CHAPTER SUBJECT PAGE
XII. Titanium, Vanadium and Tungsten 95
A. Titanium by Hydrogen Peroxide 95
B. Titanium by Thymol 97
A. Vanadium by Hydrogen Peroxide ... * 97
B. Vanadium by Strychnine 100
Tungsten as the Oxide in Colloidal
XIII. Fluorine, Chlorine and Perchlorates . . 102
Fluorine by Estimation of Its Bleach-
ing Action on an Oxidised Tita-
nium Solution 1 02
Chlorine by o-Tolidine 105
Perchlorates by Methylene Blue 106
XIV. Nitric and Nitrous Acids, and Ammonia . . 107
A. Nitric Acid by Brucine Eeaction 108
B. Nitric Acid by Diphenylbenzidene .. 110
C. Nitric Acid by Phenolsulfonic Acid . . Ill
/>. Nitric Acid by Pyrogallol 113
A, Nitrous Acid by Sulfanilic Acid and
B. Nitrous Acid by Metaphenylenedi-
amine Reaction 115
G. Nitrous Acid by Zinc Iodide Starch
D. Nitrous Acid by a-Naphthylamine Hy-
A. Ammonia by Nessler's Reagent 118
B, Ammonia by Phenol 119
XV. Phosphorus, Silica and Boron 121
A. Phosphorus as the Phosphomolybdate. 121
B. Phosphorus, Separated by Precipita-
tion as Magnesium Phosphate 122
Silica by Ammonium Molybdate in
the Presence of Phosphorus 124
A. Boric Acid by Curcumin 126
B. Boric Acid by Turmeric Paper 127
viii OOLOEIMETBIO ANALYSIS.
OHAPTBR SUBJECT PAGE
XVI. Oxygen and Hydrogen Peroxide 129
A. Oxygen by Cuprous Chloride 129
B. Oxygen by Adurol 132
Hydrogen Peroxide by Its Oxidising
Action on Ferrous Iron 133
XVII. Sulfur, Hydrogen Sulfid and Selenious
A. Sulfur by Paraphenylenedimethyldi-
B. Sulfur by the Action of Hydrogen
Sulfid on Arsenious Oxide Paper . . 136
Hydrogen Sulfid by Methylene Blue. . 137
Selenium as Selenious Acid by Potas-
sium Iodide 138
XVIII. Salicylic Acid and Cyanides 140
Salicylic Acid by Fehling's Solution. . 140
Cyanides by Changing to Sulfocya-
nates and Coloring with Iron 141
XIX. Color of Water, Oils and Dyes 144
Color of Water 144
Color of Oils 145
Color of Dyestuffs 145
XX. Nephelometry 147
CONDITIONS OF USE OF COLORIMETRIC METHODS.
CoLORiMETRic Hiethods of analysis consist of treating
a solution of the substance to be tested with a reagent, in
such a way as to produce a color which is proportional
in intensity to thelTmount of the substance being tested
for, present in the solution. The methods are not only ap-
plicable to the determination of many metals but also to
acid radicals and compound radicals to a limited extent.
The unlmown is therefore spoken of in this general dis-
cussion as the test substance. The color having been pro-
duced, the solution containing an unknown amount of
test substance is then estimated by comparison with a
standard solution by one of the following four methods:
1. The sample diluted to a definite volume may be
compared with a series of standards of the same volume,
previously prepared, the amount of test substance in
which is known and the value of the unknown then taken
to be that of the standard to which it conforms most
nearly. In this way the amount of test substance present
is obtained without figuring since, if the volume and color
of the unknown and the standard are the same, their
contents of test substance will also be identical.
2. The standard and sample may be placed in similar
graduated tubes and the darker diluted until its color
when observed horizontally thru the tube is the same as
that of the other. When this point is reached then each
2 OOLOBIMETBIC ANALYSIS.
C.C. of one solution must contain exactly the same amount
of test substance as each c.c. of the other and the amount
in the unknown is to the amount in the known directly
as their volumes. This is the method of dilution.
3. A definite sample of unknown may be placed in one
flat bottom graduated tube and amounts of the standard
poured into another similar tube until their colors, when
observed vertically thru the length of the columns of
liquid, are identical. The amount of test substance in
each tube will then be the same and since the amount per
c.c. in the standard is known the total amount in the
standard may be computed, which amount is identical
with the total amount in the sample. To state it more
briefly, their concentrations are inversely proportional to
their depths. This is the method of balancing.
4. The sample may be made up to a definite volume
and nearly that volume of water in a similar container
be treated with the same reagents for bringing out the
color of the solution as were used with the sample. A
concentrated solution of standard is then run into the
blank from a burette, adding it drop by drop when the
end point is near. The volume of the blank may be
brought up by the addition of more water until the two
colors and volumes are identical. The amount of stand-
ard used in the making of the duplicate is then a measure
of the amount of test substance in the sample. This is
the method of duplication.
In order for the colorimetric test to be accurate the
color produced by the action of the given reagent on the
test substance must be the only color present in the solu-
tion. Therefore a colorimetric test is not possible if the
original solution is colored before the test is begun, un-
less that color is produced by the test substance or will
be removed by the reagent used. In some particular in-
CONDITIONS OP USB. 3
stances a slight contamination of one color may be allowed
and equalized by contaminating the sample and standard
equally. Neither is a colorimetric test possible if the
solution to be tested contains anything other than the test
substance which will give a precipitate or color with the
given reagent. It is essential for the success of colori-
metric methods that the color produced be reasonably
permanent and that the conditions under which it was
produced be such that they can be duplicated without
great difficulty. Under certain conditions tests are made
with colors which fade after short exposure to the light.
Colorimetric tests may be classified into two classes
according to the reason for their use. Some find their
popularity because they are fast, and the accuracy of the
test is sacrificed for speed in obtaining the final result.
The second class find use because they furnish a method
of determination of small amounts of substances with
greater accuracy than is possible by gravimetric or volu-
metric methods. The first class may all be made in a
short time but it may often happen that the method of
preparation of the second class of tests may take hours
to insure the accuracy desired.
In spite of the limitations placed on its use by the
previous requirements the colorimeter is coming into use
more and more every day because of its answer to the
demand in nearly every laboratory for speed. Colori-
metric methods, used because of their speed, give results
in five minutes to one hour from the time the test is
begun which is in all cases less than half the time similar
tests could be made by other methods. A leading bra&s
manufactory of the country obtains an analysis of its
brass from the laboratory within forty-five minutes after
the delivery of the sample. Of the five constituents
determined, four are determined by colorimetric methods.
4 COIiOBIMBTBIC ANALYSIS.
Thus the main thing to be said for colorimetry is that
its methods are rapid and reasonably accurate.
A broad field of usefulness of colorimetry is the
analysis of salts or substances easily soluble in water
or acid for the amounts of various impurities present.
The methods are very delicate and accurate, some being
so delicate as to detect one part in one hundred million
parts of water, but they are seldom such as to permit
of the determination of quantities greater than one per
cent without resorting to aliquot parts and using a por-
tion of the solution of the sample instead of the whole.
The methods of accurate dilution are discussed in the
next chapter; the only drawback to their use is that the
use of a factor for determining the final result multiplies
the error made in the comparison, often as much as a
APPARATUS USED AND METHODS OF USING IT.
As previously outlined there are four types of deter-
minations made by colorimetric methods, each of which
uses a moi^ or less specialized form of apparatus.
In cases where a series of permanent standards are
made up these are usually placed in either round or
square glass bottles. Such a series of standards should
be placed in a row on a shelf, with sufficient space between
each two for setting in a similar bottle. The sample should
be treated in a similar bottle and, after making up to the
same volume as that of the standards, it may be set into
various of the gaps between the standards until the place
is found where one standard is higher than the sample
and the one on the other side lower, as estimated from
the intensities of their colors. The position of the
sample relative to these two known quantities can then
be estimated. In some cases when permanent standards
are used one bottle may be made to serve as two stand-
ards. This is accomplished by the use of a rectangular
bottle, twice as long as it is broad. The sample is then
compared in a similar bottle and results are as follows:
If the long way of the sample bottle compares with the
long way of the standard the amounts of test substance
in the two are the same. If the narrow way of the
sample compares with the long way of the standard the
sample contains twice as much test substance as the
standard. If the long way of the sample compares with
the narrow way of the standard the sample contains half
as much test substance as the standard. Altho no fur-
6 OOLOEIMETEIC ANALYSIS.
ther specific reference will be made to their use, this use
of these special bottles is applicable in all cases where
permanent standards are to be made up, except those
where the actual color rather than the depth of color
changes with the concentration. Care should be taken
to see that the bottles used in all cases are clear in color
and free from flaws.
In many cases the color produced by a reaction fades
in a short time in the light. In such a case either a
standard must be prepared at the same time as the
sample and test made by one of the other methods or
permanent artificial standards must be prepared. These
are conveniently prepared from solutions of inorganic
salts, combining the colors in such a way as to give the
desired color. The solutions which find the greatest
favor for this purpose are half normal solutions of the
nitrates or chlorides of cobalt, iron and copper.^ These
three solutions may be combined in such a way as to
form any color desired except the deep blues and reds.
To remedy this it has been found that some of the miss-
ing colors can be obtained by using a solution of potas-
sium dichromate instead of the iron solution and the
remaining colors are obtained by combinations of potas-
sium dichromate and potassium permanganate. As an
example it is found that a mixture of the first series
suggested, cobalt three parts, to iron nine parts, diluted
with water, corresponds to the color given by Nessler's
reagent in reaction with ammonia. Varied dilutions of
this may be used for a series of standards, making each
standard to correspond to the result obtained by the use
of that known amount of ammonia treated with the
reagents necessary to bring out the color. In a similar
manner permanent standards may be prepared for any
1 J. Franklin Institute, 180, 200.
APPABATtJS USED. 7
test, keeping in mind the fact that every standard must
be tested against a I^nown amount of the test substance
to make sure of its accuracy.
Pm. 1. Back of Straight Graduated Tubes.
For the production of nonpermanent standards plain
test tubes are ordinarily used. The solution may be
quickly and conveniently emptied from these and the
loss in case of breakage is not so great as from the use
of graduated tubes such as Nessler tubes or from the use
The apparatus for tests by the dilution method con-
sists essentially of a pair of graduated tubes. There is,
however, a very convenient device (Fig.l4) manufactured
for use with this method known as the colorimetric
camera. This is a light-proof box, painted black inside,
with holders for the two tubes near one end. The end
near the tubes is fitted with a ground glass screen; the
other end is fitted to the face of the observer so that no
side light may enter. By the use of this a more accurate
judgment as to the colors of the two tubes may be mad©
than if they are compared out in the open. One advan-
8 OOIiOBIMBTEIC ANALYSIS.
tage of this apparatus is that it does not tire the eyes
of the operator so quickly as do some of the types of
colorimeter used for the balancing method. In all cases
possible a colorimeter should allow the use of both eyes
for making the comparison so as to eliminate fatigue.
Sometimes the comparison of the two tubes is made by
holding them in the hand and looking at them against
a sheet of white paper.
Whether or not the camera is used for the comparison
the operation of the dilution method is always the same.
The standard and sample are in two graduated tubes or
in two Nessler tubes. The former are used when the
camera is used for the comparison, the latter are useful
when no further apparatus is used. The colors of the
two solutions should be nearly alike to begin with. The
experienced operator soon learns to choose his sample
so that the resultant color will be nearly the same as that
of the standard which he is using. Water is then added
to the solution of the darker, carefully mixing after each
addition, until the colors of the two solutions when ob-
served horizontally thru the tubes appear to be identical.
When this point is reached the concentration of the test
substance in each solution must be the same and their
contents are then to each other as the volumes. Since
the amount of test substance in the amount of standard
used is definitely known, it is easy to figure the test sub-
stance in the sample by a direct proportion. Care should
be taken that the tubes used are clear and free from flaws
and that their thickness of glass, internal diameter and
graduations are identical. A special type of tube (Fig.
13) manufactured for carbon determinations is applicable
to all dilution tests. This has a bend about two inches
from the top so that the tube may be lightly shaken to
mix the water added without danger of the contents being
APPARATUS USED. 9
spilled. Note that the standard may as well be diluted
to match the sample as the sample to match the standard,
provided only that the original volume of the standard is
recorded and that the final colors are not too deep or too
light to allow of accurate measurement.
Determinations by the method of duplication are
usually carried out in graduated Nessler tubes. The
sample is first diluted to some convenient, definite volume.
The same reagents as were added to the sample are then
added to a volume of water amounting to about half
the volume of the sample, this will usually be specified
for the particular experiment since the amount of water
used for the blank varies according to the concentration
of the standard to be used. To the blank containing the
same reagents as those used for the sample there is now
added a standard solution, carefully mixing after each
addition, until the color of the sample is duplicated by
that produced in the blank by the addition of the stand-
ard. The color of the blank having been made to bal-
ance that of the sample they will still differ in volume.
It is simple enuf to figure at this point by proportion the
amount of standard that would be necessary if the
volumes were equal but, to eliminate any chance of error
in that, it is best to duplicate the volume as well as the
color of the standard. This is accomplished by the addi-
tion of water and standard alternately until the two solu-
tions are identical in both color and volume. As said, a
little simple mathematics will tell an operator of compara-
tively little experience the exact amounts of standard
and water to be added after the colors have once been
duplicated. The same cautions apply to this test as to the
previous one insofar as apparatus is concerned ; the tubes
used must be of the same size, thickness of glass and
internal diameter and the graduations on the outside
10 COLORIMETRIG ANALYSIS
must correspond in height. That is, the ten c.c. mark on
each must be at the same distance from the bottom, other-
wise the contents are not the same or the tubes are not
The apparatus for the balancing method is the most
elaborate of all and the use of it, the simplest. The
various instruments used include
Hehner cylinders, Lovibond Tin-
tometer and various types of colori-
meters. The Campbell - Hurley,
Duboscq, Schreiner, Stammer, Say-
bolt, and White types are described.
Other specialized forms are used
in some special applications but
their use is mostly in physiological
Fia 2 Hehner ^^ ^^^^^^ ^^^^^^^ ^^^ ^^
Cylinders. . *^ ,
simplest of the instruments for
this use. They consist of two glass tubes with flat
bottoms and each has a side tube with stop-cock, about
three inches from the bottom. For the carrying out of
a determination the solution of the sample is placed in
one tube and the other tube is partially filled with the
standard so that the depth of color seen by looking verti-
cally downward thru the length of the column of liquid
is deeper than that seen by similarly looking down thru
the sample. An amount of standard is then drawn oflf,
such that the colors of the two tubes when observed in
this way are the same. The tubes are then said to be
balanced and the readings of the volumes taken. The
amount of standard used and its content of the test sub-
stance per c.c. is known. The test substance in the sam-
ple is then inversely proportional to the volume if the
content per c.c. is desired, or the total amount of test
PiQ. 3. Campbell-Hurley Colorimeter.
12 COLOEIMETRIO ANALYSIS.
substance in the two solutions is identical. For the con-
venient balancing of the two liquids several mechanical
appliances have been devised for the purpose of increas-
ing the speed of the determination or of increasing its
The Campbell-Hurley type of colorimeter illustrated
is the common form of such an instrument. This instru-
ment^ is a modification of the Kennicott- Sargent type of
apparatus and is sometimes known as the Kennicott
colorimeter. The following is the method of operation
as illustrated by the diagram. The unknown solution to
be tested is placed in the tube A and, since the volume
can be readily governed so as to come to some even
graduation, these are only placed at five c.c. intervals.
The standard solution is placed in the right-hand tube
B which, because of the fact that the accuracy of the test
depends upon the careful reading of the volume in this
tube, is graduated to single c.c. The readings of tubes
A and B have been given as in c.c. but, for such read-
ings to be accurate, tubes A and B must be of the
same identical bore. The same effect is obtained in less
accurately made instruments by having the graduations
to cm. rather than c.c. The proportion may then be
obtained between the heights of the two columns, the same
as tho the units used were c.c, since the columns will
have colors proportional to the depths regardless of
their amplitude. The method used for graduation must
be taken into account in figuring the results of the test
and will be discussed under that head. Tube B is per-
manently connected by a glass tube with the reservoir C
in which the glass plunger D works, so that the level of
the liquid in B may be readily controlled by raising or
lowering the plunger. As the tube B and the reservoir
I J. A. C. S., ss, 1112.
C are made in one piece the standard comes in contact
with glass only, thus preventing the possibility of chem-
1. ^ t ^ ' ^.n * ^ m.ti^^t.t.m.t.m* ^.ti.!.^^^ ^ ^r^
=— ": =A
Fig. 4. Campbell-Hurley Colorimeter.
ical change due to coming into contact with the container.
The plunger D is sometimes provided with a rubber
collar E to prevent it from coming into contact with the
14 COLORIMETEIO ANALYSIS.
bottom of the reservoir and the resultant breakage pos-
sible. The tubes A and B and reservoir C rest on wooden
supports with holes under A and B for the passage of
light. All glass parts are held in place by spring clips
which allow for the easy removal of the parts for cleaning.
For operation the colorimeter is turned with the back
toward a window, preferably a north one, and the mirror
G is so adjusted as to reflect skylight upward thru tubes
A and B. By this anangement the back of the colori-
meter serves as a screen to cut oflf all light except that
reflected upward from G. The light, passing upward
thru the tubes A and B, impinges on the two mirrors
H and / cemented to brass plates sliding in grooves cut
at an angle of 45° in the sides of the wooden box /.
This box has a loosely fitted cover so that it may be
removed for the cleaning of the mirrors. The mirror
// is cut vertically and cemented in such a position as to
reflect one half of the circular field of light coining thru
the tube A. The light, passing upward thru B^ is re-
flected horizontally by the mirror / thru a hole in the
brass plate supporting the mirror H. One half of the
circular field of light from the tube B is cut off by the
mirror ZT, the vertical edge of which acts as a dividing
line between the two halves of the circular field. The
image of one half of the tube B is then observed in juxta-
position to the opposite half of the image of the tube A.
The juxtaposed images are observed thru a tube K^
2.5 cm. in diameter and 16 cm. long, lined with black
felt and provided with an eyepiece having a hole 1.5 mm.
in diameter. At the point M in the tube K is placed
a diaphragm having an aperture 8 mm. in diameter. All
parts inside the box / except the mirrors are painted
black so that no light except that coming thru the tubes
A and B passes thru the tube K. By having the aper-
APPARATUS USED. 15
tures in the eyepiece and the diaphragm properly propor-
tioned only the images of the bottoms of tubes A and /?
can be seen, thus preventing the interference of side light
from the vertical sides of the tubes.
A person looking thru the eyepiece observes a single
circular field divided vertically by an almost imper-
ceptible line when the two solutions are of the same
intensity. By manipulating the plunger D the level of
the liquid in B can be easily raised or lowered, thus
causing the right half to assume a darker or lighter
shade at will. In matching colors with an ascending
column in iS, that is, gradually deepening the color of the'
right half of the field, the usual tendency is to stop a
little below the true reading, while in comparison with a
descending column the opposite is the case. At first the
operator should take a reading in each direction until
after a little practice this tendency to error has been
In tests on a large number of titanium solutions by
oxidation with hydrogen peroxide, using all concentra-
tions from a very dilute (light yellow) to a fairly con-
centrated (deep orange) solution, the average percent of
error was found to be less than one percent and the
median error less than one half percent.
In some cases the depth of the column of liquid ob-.
served cannot be used as a measure of the test substance
present as the concentration changes not only the depth
of the color but the color itself. In cases where that is
so, it will be mentioned in connection with the directions
for the particular test.
A modified form of balancing instrument has a mirror
directly over the tubes A and B reflecting forward the
two circles of light which come to it. The mirror is
encased in a lightproof box painted black on the inside
PiQ. 5. Lovibond Tintometer.
Fig. 6. Duboscq Colorimeter.
Ig COLORIMETRIC ANALYSIS.
and about eight inches long. This is fitted to the eyes of
the operator at the forward extremity so that side light
cannot enter. The arrangement of the tubes A^ B and O
and plunger D is the same as in the previous instrument.
By making the holes under the tubes A and B so small
that they do not extend to the side walls of the tubes
side light is largely eliminated and accurate results
secured. In this case the alteration is made in the color
of the right hand circle of light as compared with a
circle of similar size appearing beside it.
The Lovibond Tintometer is another type of instru-
ment, one which we shall not describe here at any length
on account of the limited use that it finds. The instru-
ment is expensive and so is comparatively rare. The
comparison is made by graduating a liquid to match a
glass of a certain color, thus doing away with the use
of a liquid standard. Since a permanent liquid standard
may be prepared for this use and so eliminate large
expense this is not recommended. Glasses may be ob-
tained for determining carbon in steel and color of water,
petroleum, etc., in addition to which by combinations of
glasses the color of any solution may be matched.
In the Duboscq type of instrument the same result as
in the Campbell-Hurley type is obtained by a different
method. The two independent tubes, A and iS, are of the
same size and are for holding the solutions of the un-
known and the standard. Each is mounted in a wooden
holder, M^ N, which slides up and down in a slit cut in
the backboard of the instrument and which is fastened
at the chosen place by a thumbscrew. Light is reflected
upward thru the tubes by a mirror G. Directly over
tubes A and B which contain the solutions to be tested
are two glass plungers, (9, P, of a diameter equal to about
half that of A and B. The bottoms of these plungers
APPAEATUS USED, 19
are finely ground and in the best instruments are fused
on. In the cheaper instruments the bottoms are fastened
with some sort of adhesive.
The telescope, K^ for observation of the colors is per-
pendicular to the base so that the operator looks down-
ward into the instrument. The light reflected upward
thru the solutions in A and 5 is so reflected by the
prisms, /, /, in the box / that two fields appear side by
side, one from A and one from B, The arrangement of
the prisms is such that the images observed in the field
of the telescope are those of the bottoms of the plungers,
(9, P^ rather than of the entire depth of liquid in A and
B. By suitable cutting down of the aperture by screens
all reflection from the sides of the tubes is cut off.
For use, the instrument is set to face a source of light
and mirror G is set at the proper angle to reflect skylight
upward thru A and B, The cylinder having the lighter
color is then moved upward by sliding its holder in the
slit in the backboard until the plunger just touches the
surface of the liquid. The other container is then moved
upward observing its movement thru the telescope until
the image of the base of the plunger in that liquid ap-
pears to be of the same intensity as that observed from
the other field. The instrument is then said to be bal-
anced and the depths of liquid underneath the plungers
have the same relation to each other as the total depths
of liquid in A and B when the Campbell-Hurley instru-
ment is balanced. The slits cut in the backboard in
which the holders of A and B move are graduated so
that the depths of liquid may be read off directly from
these and possible errors in reading depths of liquid in
glass due to the meniscus are eliminated.
The laws relating to the depths of liquid when the
instrument is balanced are as follows. The concentration
20 COLORIMETRIC ANALYSIS.
per c.c. of the sample is to that of the standard inversely
as the depths of their liquids. Diameter of the contain-
ing vessels Iieing the same, the sample solution of the
Fio. 7. Large Duboaeq Colorimeter.
depth indicated by A contains identically the same
amount of test substance as a standard column of the
depth indicated by B. The figuring of results from this
data is taken up in the next chapter. The nephelo-
meter is a modification of this type of instrument. For
further information regarding that use see Chapter
APPABATirs USED. 21
The Schreiner colorimeter is a simple modification of
the Diiboscq instrument, eliminating many of the more
expensive features. The prisms are
omitted and two round fields near
each other are observed. The hold-
erg for A and B are two brass clips
and the reading is taken by gradua-
tions on the glass of these tubes.
The application of this instrument
is recommended by the manufacturers
for soil analysis.
The Stammer colorimeter is also
a modified form of the Duboscq, and
is particularly used for determination „ ^ ^ , ^ ,
. , , . , . , . Pig. 8. Small Duboscq
of the color of sugar solutions and of Colorimeter
oils. The colors of the fields are
transmitted to the telescope, K, by prisms, /, /, as in
the Duboscq type. The alteration is in the character of
the fields. Instead of two movable containers and two
fixed pistons as in the other instrument the containers are
fixed and one movable piston, /*, is provided for the
variation of the column in B. A false piston, (?, is pro-
vided so that the light thru A will have to pass thru a
similar thickness of glass. The column in A remains
absolutely permanent, no variation in that being jwssible.
Light is reflected upward by a mirror at G as in previous
Recently a new type of instrument has been evolved
from the combination of the Lovibond Tintometer and
the Stammer Colorimeter, known as the Saybolt Chromo-
meter. This instrument is intended solely for the evalu-
ation of the colors of lighting oils. This is similar to
the Stammer instrument in that two tubes are provided,
but the left-hand tube, 4, is modified to an empty tube
22 COLOEIMBTEIC ANALYSIS.
in which the color is obtained by the addition of one or
more carefully prepared glass disks. The sample in B
is drawn off until only
such an amount is left
as will duplicate the
color of the disk used,
From the graduations on
the glass of B and the di-
rections of the makers the
oil may then be graded as
so many degrees above or
fia. 10. StamineT Colorimetei.
APPAEATUS USED. 23
below the standard colors for lighting oils (see Chapter
Nineteen), depending on the disk used.
One other type, White's colorimeter,^ shows promise of
great importance because of its ease of operation. In
this the thickness of two glass prisms observed is the
variable. The apparatus consists essentially of two
wedge-shaped hollow glass prisms of exactly equal
dimensions, open at the large end for the introduction of
the solutions to be tested. The wedges are held in
vertical position side by side in a camera and may be
raised or lowered by rack and pinion actuated by thumb-
screws. The wedges are screened from view on the side
of the operator, except for a narrow horizontal slit across
the middle of the camera thru which the solutions are
observed when a test is being made. The carriers are
graduated to correspond to the length of the wedges, the
zero of the scale being opposite the indicator when the
sharp edge of the wedge is opposite the narrow opening
in the screen thru which the color is observed. The
screens are adjustable so that the opening may be altered
to suit the operator. The ground glass shutter at the
forward end of the camera, for diffusing the light, is
hinged in the manner of a door to facilitate the transfer
of the wedges to and from the camera. To carry out a
determination by this method equal quantities of the
standard and of the material to be tested are diluted to
equal volumes and convenient amounts of the solutions
transferred to the wedges. The wedge containing the
solution of unknown strength is set at the graduation
representing the percentage, or a multiple of it, of the
coloring matter in the standard. The wedge containing
the standard is then adjusted so that the two fields seen
thru the camera appear identical. The percentage of
1 J. A. C. S., S4, 659.
coloring matter in the unknown is then indicated by the
reading of the scale on the carrier containing the stand-
ard. If the depths of color compared at first are too
deep for accurate comparison the results may be checked
without changing the solutions by setting tlie wedge con-
taining the unknown at a new point on the scale and
Flo, 11. WliiM'8 Colorimeter.
again adjusting the other wedge until equality is reached.
The maximum error reported on a long series of experi-
ments with this instrument was .6 percent.
The figuring of results obtained by these balancing
methods is discussed in the next chapter.
In some cases it may be impossible to choose a sample
Al>PABATUa USED. 25
having as small a content of the test substance as speci-
fied in the method, particularly if the substance being
analysed is an ore or alloy containing a fairly large per-
centage of the test substance. In that case the sample
may be taken containing somewhat more of the test sub-
stance than specified for the test and dissolved as
directed. This solution may then be accurately diluted
and an aliquot part taken. If, for example, the method
specifies that a sample must be under .001 gram of the
test substance and the smallest sample of the substance
being analysed which can conveniently be weighed out
will contain nearly one tenth gram of the test substance,
this may be dissolved as specified and diluted to one liter
in a volumetric. Ten c.c. of this may then be analysed
as directed and the weight of test substance found in that
amount of solution multiplied by 100 will give the
amount in the original sample. In case it is necessary
to use such a method the final result cannot be expected
to be as accurate in regard to the amount of test sub-
stance by weight as shown in the result but the results
are identically as accurate so far as the percentage of error
is concerned. To illustrate, while accuracy to .6 percent
in the case of a w^eight of substance showing .001 gram
test substance would allow an error of only .000006 gram
test substance, if the sample showed .5 gram test sub-
stance (an amount greater than would ordinarily be
present in a weight of sample used), the maximum error
then possible would be .003 gram of the test substance.
The rapidity with which colorimetric tests may be
made often admits of the attainment of considerably
greater accuracy than the theoretical by rapidly doing
several tests and then averaging the results obtained.
The intensity of the color of the two solutions is an
important factor, so results may be expected to be more
26 COLORIMETRIG ANALYSIS.
accurate if the standard and sample have nearly the same
color before a test is carried out by dilution or balancing
methods than if the colors differ greatly. The intensity
should also not be too great or too dilute ; in either case
errors will be greater than if the color produced was
intermediate between the two extremes.
FIGURING OF RESULTS.
In case a series of standards is used the weight of test
substance in the unknown may be told at once by looking
at the amount in the standard to which it corresponds.
The percentage is then readily figured from this by
dividing by the weight of sample used, thus :
Weight of sample, 5 grams.
Weight of test substance present, .0004 gram.
Sample therefore contains .0004 -^ 5 = .00008 gram test
substance per gram sample = .008 percent.
The figuring of results when the dilution method is
used is somewhat more complex. In that case the darker
of the two solutions is diluted until the colors of the two
are identical when observed horizontally thru the tubes,
at which point the content of test substance per c.c, is
the same and the content of test substance of one is to
that of the other directly as their volumes. To illustrate :
Weight of standard used, .2 gram.
Weight of unknown used, .2 gram.
Standard contains .32 percent test substance.
Readings, standard 38 c.c, unknown 45 c.c.
The weights of the sample and standard being the
same in this problem we may eliminate the figuring of
the weight of test substance in the sample and proceed
directly to estimate by proportion the percentage. This
is estimated thus :
Percent in standard : Percent in unknown = Volume of
standard : Volume of unknown :
28 OOLOBIMBTEIG ANALYSIS.
Therefore we find that the sample being tested contains
.38 percent test substance.
The figuring of dilution method results does not always
resolve itself into a mere comparison of percents as
usually a definite volume of a standard solution whose
content of test substance per c.c. is known is used as the
standard. In that case the weight of test substance in
the standard must be figured and from that the similar
weight in the sample and then the percentage present in
the sample. The method follows:
Weight of sample used, 2 grams.
Standard used, 20 c.c. of a solution containing .00002
gram test substance per c.c.
Eeadings, standard 20 cc, unknown 48 c.c.
From the readings above it will be seen that in this case
the color of the sample was darker than that of the
standard and therefore the sample was diluted. There
would be no change in the method had the standard been
Weight of T. S. in standard : Weight of T. S. in
unknown = Volume of standard : Volume
Weight of test substance in standard is 20 X .00002 =
.0004:X = 20:48;
X = . 00096.
Therefore the two grams of sample used contained
.00096 gram of test substance and the percentage in the
sample was .048 percent.
Eesults by the method of duplication are easily ob-
tained. A standard solution is added to a blank con-
FTGUEING THE EESULTS. 29
taining the same reagents as the sample until the color
of the sample is matched. Water and standard are then
cautiously added, alternately, until the volume as well as
the color of the two solutions is identical. The result as to
how much test substance is present in the sample is given
by the amount necessary to form an identical standard.
The percentage in the sample is then figured, thus :
Weight of sample, 5 grams.
Standard used contains .0002 gram test substance
Standard used for duplication 2.3 c.c.
Then the total test substance used was 2.3 X .0002 =
Therefore the sample contained .00046-7-5 gram test
substance per gram of sample or .000092, which is .0092
Results obtained by the balancing method are some-
what more complicated to obtain, especially if the ap-
paratus used is graduated to cm. instead of cc.
To take, first, a case when the apparatus is graduated
to c.c. and tubes A and B are identical, whether they be
the Hehner cylinders or Campbell-Hurley apparatus or
some other type of instrument,
Standard used contains .00002 gram test substance
Volume of standard used to balance colors, 44 c.c.
Sample used, 4 grams.
The amounts of test substance in sample and standard
are the same when the colors are balanced, that is the
volumes differ but the total content is the same. There-
fore the amount of test substance in the sample being the
same as in the standard is
44 X .00002 = .00088 gram.
30 COLOBIMETEIG ANALYSIS.
Since the sample used was 4 grams it was therefore
.022 percent test substance.
To take the other case of cylinders graduated to centi-
meters, the results obtained with a cheaper instrument
are accurate but more calculation is involved, thus :
Weight of sample 2 grams.
Volume of sample after solution before addition to
tube A = 50 C.C.
Height of sample in tube A = 7.3 cm.
Height of standard in B to balance = 8.4 cm.
Content of standard per c.c. = . 00001 gram test sub-
When the colors of A and B are balanced the concen-
trations of the contained solutions are inversely propor-
tional to the volumes used, thus :
T. S. per c.c. in A: T. S. per c.c. in B = Depth
of liquid in B : Depth of liquid in A ;
X:. 00001 = 8.4: 7.3.
X = . 0000115 gram test substance per c.c. in sample
Then the total test substance in the sample is
50 X .0000115 = .000575 gram.
This is .0002875 gram per gram of sample and the
sample is therefore .02875 percent test substance.
DETERMINATION OF IRON.
The determination of iron is one of the important ap-
plications of colorimetry both because of the widespread
distribution of the metal and because of the inadequacy
of gravimetric or volumetric methods to measure small
amounts of the substance, especially in the presence of
the other third group metals. Lunge recommends that
some colorimetric method be used for the determination
of small amounts of iron in preference to other methods.
There are seven methods for the colorimetric determi-
nation of iron, details of which follow.
Method A — Iron by Potassium Sulfocyanate.
The sulfocyanate method for the determination of iron
depends upon the oxidation of all iron present to the
ferric condition after which the reaction between ferric
iron and potassium sulfocyanate is used to produce a
red color proportional to the amount of iron present.
It is a very rapid method and is delicate enuf for the
detection of one part of iron in fifty million parts of
water, especially in the presence of free mineral acid.^
Use is therefore made of the method for the determina-
tion of traces of iron in water supplies and of iron in
small content iron solutions such as solutions of salts and
minerals known or suspected to contain a small amount
of iron. It also furnishes a rough and ready method
for the approximation of the iron content of minerals
1 0. N., 51, 259.
which contain considerable amounts of the metal, even
up to 30 percent, when accuracy within one percent is
required rather than the greater accuracy
of the slow analyses. This latter determi-
nation of course calls for the methods of
accurate dilution given in Chapter Two.
Fluorides, phosphates, arsenates, oxal-
ates, citrates, tartrates and iodates inter-
fere, also acetates to a lesser degree.* It
is therefore necessary that these sub-
stances be albsent from the solution.
Since the presence of a small amount of
mineral acid has been found to make the
test more delicate the determination is
Fig. 12. Straight carried out in a solution slightly acidified
Graduated Tubes . ^ '^
with sulfuric acid. The amount of the
iron ionized is dependent upon the concentration of the
acid solution, so it is advisable to have the acid content
of sample and standard uniform for the attainment of
the correct results.
The amount of the sample must be so chosen that
the final solution contains between .000001 and .0002
gram iron per c.c, of which solution ten c.c. is taken for
the analysis. If the test is being made of a solid dis-
solved in water the sample may be so chosen as to con-
form to these limits, if the test is of a water for the iron
content the water may be concentrated. In some special
cases where great accuracy is not required it may be
found possible to use twenty or even forty c.c. of a solu-
tion somewhat more dilute than the limit as a sample.
To this solution add ten c.c. of concentrated sulfuric
2 J. A. C. S., iS9, 409.
DETEEMINATION OP IBON. 33
acid and oxidise with potassium permanganate until a
faint permanent blush appears. Then run in about five
c.c. of a solution of potassium sulfocyanate, 97 grams to
the liter, and dilute to fifty c.c. with pure water. The
color to be tested appears at once and ranges from a faint
pink to a deep red according to the amount of iron
present. The test may be made by duplication or by
balancing but the dilution and series of standards meth-
ods are not satisfactory in this test. The amount of
ionization changes with the acid concentration of the
solution and therefore the color would change with the
addition of water independent of the amount of iron in
the solution. A series of standards is not satisfactory
as they fade out in light so soon. The addition of a
small amount of potassium persulfate to a solution made
up will keep the iron oxidised for some time longer if it
is desired to preserve a sample or standard for several
The standards to be used in this test are made up as
follows, if the result is to be stated as Fe weigh out .1405
gram of ferrous ammonium sulfate [FeS04(NH4)2S04,
6H2O], if the result is to be stated as FcjOg the weight
of salt taken is .1473 gram. The weights given above
are dissolved in water with the addition of a little dilute
sulfuric acid. Ten c.c. of concentrated sulfuric acid are
then added to this and potassium permanaganate run
in until the iron has all been oxidised to the ferric state.
Twenty c.c. of the sulfocyanate solution are then added
and the beaker carefully washed out into a liter volu-
metric flask and the flask filled to the line. The addition
of the sulfocyanate to the iron solution before washing
it into the volumetric enables one to see that the beaker
in which the oxidation was carried on is thoroughly
washed out and all the iron transferred to the flask.
34 COLOBIMETRIG ANALYSIS.
This standard solution contains .00002 gram Fe or .00003
gram FegOg according to which weight was used. The
use of the appropriate weight thus allows for the figuring
of results more readily. It is well to add one tenth of
a gram of potassium persulfate to the standard before
dilution so that the color may remain clear for a longer
time. The standard should then be kept in the dark
and renewed at least once a week if used often.
This standard solution is to be added to thirty c.c. of
water, and ten c.c. of concentrated sulfuric acid, meas-
uring the amount of standard used accurately with a
burette. Not only the color but also the volume of the
standard must be identical with those of the sample
before the end point of this method has been reached.
The amount of iron in the sample is then measured by
that necessary to make up the duplicate. If the test is
to be made by the Campbell-Hurley apparatus or other
type of balancing apparatus the standard mentioned
above may be diluted to one tenth its present strength
(ten c.c. diluted to one hundred) unless the color of the
sample being tested is very deep.
It is often desirable to make a test of filter papers for
iron as impurity. Such tests may be made on the original
filter paper qualitatively by working the paper to a pulp
in concentrated hydrochloric or nitric acid but the quan-
titative determination is made by dissolving the ash in
acid, oxidation of the iron with permanganate, and test-
ing this sample as a whole by the method already given.
For the determination of iron in lead and similar sub-
stances^ soluble in acid a sample of ten to thirty grams,
dependent on the iron content, is dissolved in nitric acid,
thirty c.c. of sulfuric acid added, the precipitate allowed
to settle and filtered. The filter is well washed with warm
1 J. Ind. Eng. Chem., 7, 1035, 1915.
DETERMINATION OF IRON. 35
water, small amounts at a time, and the filtrate rendered
slightly alkaline by the addition of ammonia. This
solution is boiled for a minute and the precipitate filtered
out and well washed with warm water to remove traces of
lead. Eedissolve this precipitate which contains the iron
as the hydroxide in dilute hydrochloric acid and test by
the method given. If the amount of iron is too great
to test as a single sample dilute to 100 c.c. and use ten or
twenty c.c. of this solution for testing. For the oxida-
tion of the iron in this latter test it is possible to add a
slight excess of hydrogen peroxide to the iron solution
to be oxidised and thus save the trouble of assuring oxida-
tion with permanganate.
Method B. Iron as the CnLORroE in Concentrated
The yellow color of ferric chloride has been adapted to
the analysis of samples containing iron for their iron
content. The sample^ is dissolved in hydrochloric acid or,
if that is impossible, in aqua regia or nitric acid and the
nitric acid expelled by heating until all nitric fumes are
gone. The amount of iron present must be less than .0001
gram per c.c. and less than half this concentration is
better. The color concentration of ferric chloride reaches
its maximum when there is present 28 percent hydro-
chloric acid, so it is only necessary to make our solution
more concentrated than that to have the uniformity of
color desired. The presence of free chlorine will not
interefere but nitric acid or its oxides will and for that
reason it is necessary to remove every trace of nitrate if
nitric acid was used in the dissolving of the sample. If
copper is present it must be removed by hydrogen
1 Z. Anorg. Chem., 86, 341.
36 OOLOBIMETEIG ANALYSIS.
sulfid as its chloride, when water of crystallization is not
present, has the same color as iron. Manganese does not
interfere and the method is therefore applicable to the
analysis of iron in the presence of that substance and to
the testing of manganese precipitates for iron. In such
a dilute solution any small amount of cobalt or nickle
will not produce sufficient color to cover up the results.
If other substances with a red or yellow color are present
the metals which will precipitate with ammonia may be
separated by the addition of a slight excess of that re-
agent. The precipitate of hydroxides may then be dis-
solved in concentrated hydrochloric acid and tested as
The iron standard is best made up by dissolving one
gram pure iron wire or such a weight of an impure iron
that it is known to contain exactly one gram of pure
metal. This is dissolved in nitric acid, hydrochloric acid
added, and taken to dryness three times. In that way all
trace of nitrate will be removed. The residue after these
ignitions is made up to one hundred c.c. with concen-
trated hydrochloric acid. Ten c.c. of this solution is
made up to one liter with concentrated hydrochloric acid
and furnishes the standard for comparison. This stand-
ard contains .0001 gram Fe per c.c. The results may be
obtained either by the dilution method, using concen-
trated hydrochloric acid for the dilution, or by the bal-
ancing method. On account of the cost of hydrochloric
acid if a considerable number of tests are being, run it is
best to adopt the latter method.
Method C. Iron by Potassium Ferrocyanide.
Lunge^ recommends that for some cases the blue color
produced by the action on ferric iron of potassium ferro-
1 Technical Methods of Chemical Analysis, Lunge.
DETERMINATION OF IBON. 37
cyanide is the most convenient method of analysis for
iron. This method may be used to determine the ferric
iron in the presence of ferrous or it may be used to deter-
mine the entire iron content. In the latter case the
solution must first be oxidised with permanganate to
bring all iron present to the ferric condition. Owing to
the intensity of the color developed this method is only
applicable to the determination of traces of iron as, for
example, in water.
The solution to be tested should be suitably concen-
trated or diluted so that the iron content will approxi-
mate .000002 gram iron per c.c. The standards used are
the same as those for method A. Ferrous ammonium
sulfate [FeSO^CNHJ^SO^, GH^O], .1473 gram if the
result is to be determined as FcgOg or .1405 gram if the
result is to be determined as Fe. In either case the salt
is dissolved in water, five c.c. concentrated sulfuric acid
added, and the solution oxidised to the ferric condition by
permanganate. The solution is then diluted to one liter.
Ten c.c. of this are pipetted out, ten c.c. potassium ferro-
cyanide [K4Fe(CN)g] added and the whole diluted to
100 c.c. This standard now shows the characteristic color
reaction and contains .000002 gram Fe or .000003 gram
1^^^20s according to the weight taken.
For the test five c.c. of potassium ferrocyanide are
added to fifty c.c. of the solution to be tested and this
sample then compared with the standard mentioned above
by dilution or by balancing. These methods are more
applicable to the particular conditions of this experiment
than are the other two.
Method D. Iron by Salicyl.ic Acid.
Ferric iron in reaction with salicylic aoid produces an
amethyst coloration, but ferrous iron produces no color.
38 COLOBIMETEIG ANALYSIS.
This reaction^ is therefore applicable to the determination
of ferric iron in the presence of ferrous when the sample
can be so chosen as to come within the limits of test by
this method. The color will be too intense for satis-
factory work if the sample contains more than .0002 gram
of iron, the color may be detected if as little as .00001
gram of ferric iron is present. The method is applicable
to the analysis of salts for impurity except in the presence
of the following, which interfere with the test: phos-
phates, fluorides, thiosulphates, sulphites and bisulphites.
The presence of free mineral acid also interferes with the
test and it is therefore necessary that such be absent, pre-
ferably by the solution of the original sample in water,
if that is not possible then by the neutralization of the
acid by ammonium hydroxide after solution is complete.
The sample, if possible, is dissolved in twenty c.c. of
pure water and any turbidity, the cause of which is known
to contain no iron, is filtered out. If it is necessary to
dissolve the sample in acid as dilute hydrochloric acid as
possible is used, and the free acid after solution is com-
plete, is neutralized with ammonia, taking care that an
excess of the ammonia is not added as that would pre-
cipitate the iron. There should not be more than twenty
c.c. of the solution after neutralization. If the sample
to be tested contains organic matter it may be necessary
to heat to dryness with nitric acid and ignite to remove
such organic matter. If all the iron content is desired
the sample is next oxidised with permanganate so that all
iron is in the ferric condition. For this it may be nec-
essary to slightly acidify the solution with sulfuric acid
and later bring it back to neutrality after the oxidation.
If only the ferric iron is to be determined this step of
oxidation is omitted. Five c.c. of salicylic acid solution
1 Adapted from Method of W. S. Allen as given by W. W. Scott.
DETEEMINATION OF IRON. 39
ai'e now added and comparison made. Because of
the fading of the color by exposure to light^ it is not
advisable to make up a series of standards but rather the
test should be made by dilution or balancing. The use
of the duplication method is also inadvisable since for the
carrying out of it considerable time is required and
fading may occur during that time.
A convenient standard is made by dissolving in water
.0864 gram pure ferric ammonium alum [Fe2( 804)3
(NH4)2S04, 24H2O] with the addition of two c.c. of con-
centrated sulfuric acid and diluting accurately to one liter.
This solution contains .00001 gram F'e per c.c. or .000014
gram FegO,. For the use of this standard twenty c.c.
or other suitable quantity may be accurately measured
out from a burette and five c.c. salicylic acid added just
before it is used.
Method E. Iron as the Sulfid.
The determination of iron as the sulfid in alkaline solu-
tion is particularly applicable to the testing of drinking
water but may be adapted to any test for ferrous iron in
the presence of ferric, or to the analysis for the total iron
content of a solution by the reduction of the iron content
to the ferrous condition. If the test is to be made of
water it is best made immediately after taking the
sample. If the test^ is not to be made at once it is nec-
essary to add a few drops of hydrochloric acid and ten
c.c. hydrogen sulfid water to a sample of not over one
half liter and cork the bottle tightly at once. By the
use of these preservatives the oxidation of ferrous to
ferric iron may be prevented. The sample should have
an iron content betw^een .0015 and .0003 gram per liter.
1 Sclireiner and Ferris, J. A. C. S., 26 y 961.
2 Technical Methods of Chemical Analysis, Lunge.
40 COLOEIMETEIC ANALYSIS.
If the amount of ferrous iron exceeds this the solution
may be diluted, if the iron content is less than the pre-
scribed limits the results may be attained by the use of a
larger volume of solution than specified for the test.
For the determination of the entire iron content of a
sample of water or of some solid substance dissolved in
water or acid, the solution is evaporated to dryness with
a small amount of hydrochloric acid and potassium
chlorate. The residue is dissolved in warm water with
the addition of a few c.c. of hydrochloric acid and five
c.c. of hydrogen sulfide water. This solution is first fil-
tered to free from sulfur clots and then diluted to 100 cc.
This is then treated the same as the entire solution would
have been if analysis was being made for ferrous iron
A standard is made up by the solution in a liter of
water saturated with hydrogen sulfide of .7022 gram of
ferrous ammonium sulfate [FeS04(NH4)2S04, GH.O]
with the addition of one c.c. of sulfuric acid. This solu-
tion must be kept well corked and, if the gas gets free
to such an extent that the bottle no longer smells of it,
the liquid must be recharged. This standard contains
.0001 gram ferrous iron per c.c.
The comparisons are made in plain glass cylinders by
the method of duplication. The sample is 100 c.c. of the
solution to be tested, a blank is run of 95 cc. of distilled
water. To each, sample and blank, is added five c.c. of
an aqueous solution of hydrogen sulfid and two drops of
ammonia. The standard solution is then added to the
blank drop by drop until the colors of the two solutions
are approximately equal. The color of the standard will
show more of a brown hue than that shown by the sample
and it is therefore necessary to decolorize the standard
with a few drops of hydrochloric acid and then renew the
DETEBMINATION OP lEON. 41
color by the addition of a few drops of ammonia. The
color which comes back will be the same sort of a brown
as that shown by the sample. More standard can then be
added to the blank if necessary in order to bring it to the
point where the colors of the sample and standard are
If extreme accuracy is desired the standard may again
be decolorized and should come back by the addition of a
few drops of ammonia to identically the same color as
Method F. Iron by Acetylacetone.
The principal objection to the tests for ferric iron with
salicylic acid and potassium sulfocyanate already given
is that they fade in the bright light necessary for the com-
parison of colors. This test has as its merit the nonfad-
ing of the results. The color produced^ varies with the
amount of free acid present and therefore the solution
should not contain any appreciable amount of free acid.
The solution to be tested, whether a sample of water or
some substance in solution, is evaporated to dryness on
the water bath and a few drops of sulfuric and nitppc
acids added to the residue to remove any organic matter
present. If much iron is present the dilution will be
carried to a considerable degree and the amount of acid
used will not matter but if only a very slight amount of
iron is present it may be necessary to heat and drive off
most of the acid before adding water, in order that the
acid may not be too strong. The range of greatest accu-
racy is between .0006 gram and .00005 gram ; the sample
should therefore be so diluted that fifty c.c. will contain
an amount of iron somewhere between these limits. The
1 Pulsif er, J. A. C. S., fS8, 967.
42 COLORIMETRIC ANALYSIS
dilution should be to 100 c.c, 500 cc, or 1000 cc, in order
that the results may then be figured by aliquot parts.
The sample used is fifty c.c. of the solution above, to
which there are added two cc. of acetylacetone solution.
The best method of completing the analysis is by the
addition of a standard to a blank of 45 c.c. of distilled
water and two c.c. of acetylacetone solution. The stand-
ard should consist of .1405 gram ferrous ammonium
sulfate [FeSO^CNHJ^SO^, GH^O] dissolved in water,
oxidised with potassium permanganate to the ferric con-
dition and made up to one liter. This standard contains
.00002 gram of iron per c.c. The method of balancing
is not applicable to this test aS the color produced does
not conform to the necessary laws. If a considerable
number of tests are to be made it may be well to make up
a series of standards from the standard solution already
mentioned, using two to thirty cc. of the solution at two
c.c. intervals. For the determination of a few tests or
for experimentation as to its applicability to a given use
the method of dilution is easiest to arrange. The stand-
ard previously mentioned is further diluted by the dilu-
tion of ten c.c. to fifty with the addition of two c.c of
acetylacetone. This new standard for the dilution method
contains .000004 gram iron per c.c
Method G. Iron by Dimethylglyoxime.
The red coloration produced by this reaction is very
distinctive and permits of the estimation of the iron
within an accuracy of one half percent of the metal pres-
ent in the solution. The iron present^ in the solution for
this test should be between .00001 and .00006 gram per cc
The presence of large amounts of aluminum and zinc
must be avoided.
1 Z. Anorg. Chem., 89 ^ 401. --^ _- ,
DETERMINATION OF IBON. 43
To the sample of fifty c.c. of the solution to be
tested there is added one gram of hydrazine sulfate
fN2H4H2S04] and five c.c. of a saturated solution of
dimethylglyoxime in ethyl alcohol and the solution heated
to boiling. Add ten c.c. of a 25 percent ammonia solution
and continue the boiling for one half minute. Cool the
solution rapidly and dilute to 100 c.c. for comparison.
The comparison is carried out by any of the usual
As a standard the one prepared for methods A and C is
satisfactory. This consists of .1473 gram of ferrous am-
monium sulfate dissolved in water, five c.c. concentrated
sulfuric acid added, oxidised with permanganate and
made up to one liter. This solution contains .00003 grams
FCaOg per c.c. For the method of duplication this stand-
ard is added to seventy-five c.c. of pure water in a tube
similar to that containing the sample, after the dimethyl-
glyoxime has been added to the blank in the same propor-
tions as to the sample. The amount of standard neces-
sary to bring the blank to the same color as the sample
when it is of the same volume is the measure of the iron
present in the sample. For a series of standards varying
amounts of the standard are used and, after the addition
of the same reagents as to the sample, each is made up to
100 c.c. For the method of dilution ten c.c. of the above
standard are made up to 100 c.c. with the addition of the
above reagents and tested as usual. As a standard for
the balancing method it will be necessary to dilute a
greater quantity of the standard, 25 c.c. diluted to 250 c.c.
will be ample. The latter two standards after dilution
contain .000003 gram FcgOg per c.c.
DETERMINATION OF COPPER.
Altho not so widely distributed a metal as iron a greai:
deal of work has been done on the determination of
copper to afford methods both rapid and accurate taking
into account the many interferences apt to occur. The
seven methods now in use follow.
Method A. Copper by Ammonia.
The copper salt of nitric or sulfuric acid dissolves in
ammonia giving an intense blue color which is propor-
tional in intensity to the amount of copper present in the
solution.^ This method is particularly applicable to the
determination of traces of copper in ores and slags solu-
ble in nitric acid but is also useful in the analysis of
salts containing a trace of copper as impurity. Nickel,
cobalt, and manganese^ interfere with the test so that in
their presence the solution requires special treatment.
In the presence of this interference the metals of the
first two groups are precipitated by hydrogen sulfid in
acid solution and filtered out. This precipitate of sulfid?
is washed and redissolved in nitric acid and this solution
treated as tho it were the original. In the absence of
fourth group metals the precipitation mentioned above
The sample is chosen of from one tenth to ten grams
according to the approximate copper content, the sample
being so chosen as to include between .001 and .01 gram
1 Sutton, Volumetric Anal.
2 Lunge, Tech. Meth. of Chem. Anal.
DETERMINATION OP COPPER. 45
of copper. The sample is dissolved in nitric acid or, if
it dissolves readily in water, the solution is strongly
acidified with nitric acid, and placed in a bottle or com-
parison cylinder. Twenty c.c. of ammonia are then
added and the solution diluted to 100 c.c. If the solution
should be so strong that it was not neutralized by the
twenty c.c. of ammonia mentioned a greater amount
should be used until the ammonia has redissolved the
precipitate first formed on its addition. Comparison is
now made by one of the methods given in Chapter Two.
A standard solution is prepared by dissolving in nitric
acid, .5 gram pure copper and diluting the solution to
500 c.c. If it is desired to prepare a series of standards
these are made up by using from one to ten c.c. of this
solution. The standards should each have twenty c.c. of
ammonia added and be made up to 100 c.c. in bottles
similar to the one in which the comparison is made. For
the method of duplication seventy c.c. of water and
twenty c.c. of ammonia furnishes the blank to which is
added the standard specified above. This standard con-
tains .001 gram copper per c.c. If a series of standards
ai-e used it will be necessary to renew them onoe a month
as, altho they do not fade in the light, the ammonia pres-
ent forms a flocculent precipitate with the glass after a
time. A standard for the dilution or balancing methods
is made up by diluting ten c.c. of the solution above to
one liter with fiftv c.c. ammonia and 940 c.c. water. This
standard contains .00001 gram copper per c.c.
Experiment has shown that the greatest delicacy of
test is given when the solution contains .00001274 gram
copper per c.c. and that the addition of .000000016 gram
copper can be detected at that concentration. It is with
this experiment that the greatest amount of study as to
the delicacy of given reactions has been made.
46 OOLOBIMETRIC ANALYSIS.
In some cases it may be found desirable to use the sul-
fate rather than the nitrate for the foregoing procedure.
In case sulfuric acid is used for acidifying the sample
the standard solution used must also have been acidified
with sulfuric acid since, tho both the nitrate and sulfate
of copper dissolve in ammonia with a deep blue color, the
colors of the two for the same amount of copper are not
Method B. Copper as the Chloride in Concentrated
If no other metals whose chlorides are also deeply
colored are present the concentration of a copper solution
may be told, if over thirty percent hydrochloric acid, by
the intensity of the yellow color produced.^ The actual
intensity of the color reaches its maximum at an acid
concentration of 28 percent and after that remains con-
stant but in order to assure the full depth of color the
concentrated acid is used. Free chlorine does not inter-
fere but nitric acid or the presence of any of the nitrous
oxides does and these must therefore be removed. Cobalt
or nickel will have very little color in the concentrated
acid solution unless the amount of them is very great.
Manganese does not interfere. If nickel, cobalt or iron
are present in quantities great enuf to color the solution
the sulfid may be precipitated in acid solution and redis-
solved, thus getting rid of the disturbing factors quoted.
Second group sulfids have no effect except those of the
noble metals. Minute amounts of organic matter may
produce a yellow color and if present must be burned out
before dissolving in acid. Iron has a yellow coloration
which is to that of copper as nine to five.
1 Huttner, Z. Anorg. Ohem., 86^ 341.
DETEBMINATION OF COPPER. 47
For the test a sample is selected such that it contains
about .1 gram or .01 gram copper. This sample is dis-
solved in hydrochloric acid directly if possible but such
a solution is not usually possible. In case the sample
does not dissolve in hydrochloric acid readily it is dis-
solved in nitric acid or aqua regia and hydrochloric acid
added to the solution. This is evaporated to dryness,
more hydrochloric acid added and the process repeated.
After repeating the drying a third time the dilution is
made with concentrated hydrochloric acid. If the sample
was of one tenth gram of copper the sample is diluted to
one liter, if the sample was of .01 gram copper it is diluted
to 100 C.C. A standard is similarly prepared by the solu-
tion of .5 gram pure copper in nitric acid and subsequent
expulsion of the nitric acid by the use of hydrochloric
acid, as directed for the sample. This standard is finally
taken up with dilute hydrochloric acid and diluted to 500
c.c. with concentrated hydrochloric acid. This standard
contains .001 gram copper per c.c. Because of the con-
centrated acid used it is not advisable to try to keep per-
manent standards. The test may be made by dilution or
balancing, if by dilution concentrated hydrochloric acid
is used for the dilution.
This method is as accurate as the ammonia method and
is much easier to apply in some cases. Fifty c.c. of the
diluted sample is usually convenient for analysis by the
dilution or balancing methods.
Method C. Copper by Salicylic Acid.
The color produced by copper with salicylic acid may
be used for the quantitative determination of the copper
present altho the color produced is not permanent. The
presence^ of free mineral acids, citric and tartaric acids,
1 Zeitsch. Untersuch. Nahr. Genussm., S2y 727.
48 COLORIMETBIO ANALYSIS.
and more than a trace of iron, prevent the use of this
test. An amount as small as .00001 gram of copper may
be detected and estimated by this method.
The comparisons are always made against a series of
temporary standards made up at the time of the experi-
ment. A standard copper solution is made up by solu-
tion of .3928 gram of copper sulfate (CUSO4, SHgO) in
water and making up to one liter. Of this standard
amounts varying from one tenth to one c.c. are placed in
plain test tubes and the sample in solution in about ten
c.c. of water is placed in a similar plain test tube. The
standards are each diluted to the volume of the sample,
ten c.c, or if convenient a five c.c. sample may be used and
dilution made to five c.c. There is then added to each of
the tubes five drops of a two percent solution of potas-
sium nitrate and five drops of ten percent acetic acid,
then three c.c. of a one half percent solution of salicylic
acid in dilute alcohol. The tubes are next heated to boil-
ing in a water bath for three quarters of an hour. The
reading of the sample is taken to be that of the standard
to which it most nearly conforms. The standard solution
for making the series of standards contains .0001 gram
copper per c.c.
Method D. Copper by Potassium Ferrocyanide.
The amount of copper^ in dilute solutions may be deter-
mined by the intensity of the purple-brown color produced
in reaction with potassium ferrocyanide. The test is
rendered more delicate bv the addition of ammonium
nitrate, ammonium chloride or potassium nitrate to the
solution. In the presence of these salts the test will show
one part in 2,500,000. Lead forms a white precipitate
1 Sutton, Volumetric Analysis.
DETERMINATION OF COPPER. 49
with the ferrocyanide but unless the lead is in greater
excess than it might be expected to be in such a solution
the small amount of precipitate will be negligible. The
solution in which the test is to be made must be exactly
neutral; if it is acid the color produced will turn to an
earthy brown, if alkaline the color will be partly dis-
solved and removed by the alkali. In the presence of
large amounts of iron the solution may be rendered
alkaline with ammonia and the iron filtered out for use
in the determination of iron if one is to be made.^ If the
iron hydroxide is of large volume it may be well to dis-
solve in acid and reprecipitate to recover copper carried
down with the precipitate the first time.
The sample is so chosen as to contain between .005 and
.00005 gram copper.^ If the sample is a solid, difficulty
soluble, it is dissolved in nitric acid and the solution
boiled until the excess of acid has been expelled. P^ive c.c.
of sulfuric acid are then added and the solution boiled
again. Filter, wash the precipitate with warm water
and take the combined filtrate and wash water for the
test. The sample, if acid, is rendered slightly alkaline
with ammonia and the solution then boiled until the ex-
cess has been removed. Five drops of a 1 : 35 solution of
potassium ferrocyanide are then added to the sample and
the test made by duplication or dilution.
The standard is made up by the solution of .3928 gram
of pure copper sulfate (CUSO4, 5H2O) in water and
dilution to one liter. This standard contains .0001 gram
copper per c.c. For use with the method or duplication
the sample is diluted to 50 or 100 c.c. If the latter is
the case it may be advisable to divide the solution into
two parts and use one for testing. The blank is prepared
1 Jour. Ind. Eng. Chem., 7, 1035.
2 Mining Sci. Press, 114, 624.
50 COLORIMETRIO ANALYSIS.
by adding five drops of ferrocyanide solution to thirty-
five C.C. of pure water and five c.c. of ammonium chloride
solution in a tube similar to that containing the sample.
The standard mentioned above is then run in until the
color of the sample is duplicated and the volumes cau-
tiously equalized as described for this method of deter-
mination. The color produced is not satisfactory for the
balancing method and fades too soon to make the use of
a series of standards practicable. For the method of
dilution ten c.c. of the standard are diluted with twenty-
five C.C. of water, five c.c. of ammonium chloride and five
drops of ferrocyanide and made up to fifty c.c. The
standard if darker in color is now diluted until the colors
match, and the results figured.
In some cases for the purpose of concentrating the
solution the copper may be precipitated with aluminum
foil and the precipitate gathered and dissolved in nitric
acid after which the procedure is carried on as before.^
Method E. Copper as the Sulfid.
A trace of copper in solution may be determined by
the formation of the colloidal sulfid and the estimation
of the color of the resultant brown solution by the use of
a standard solution similarly prepared. The amount of
copper must not be more than .00025 gram and less than
half that amount is better.^ The method is not applicable
in the presence of lead but the ferrocyanide method can
be used in that case and the lead determined from the
same solution without separating the copper. The ad-
dition of ammonium chloride to the solution doubles the
To the sample in solution are added a few c.c. sodium
1 Jour. Ind. Eng. Chem., 7, 1035.
2 Sutton, Volumetric Analysis.
DETERMINATION OF COPPEB. 51
acetate, five c.c. saturated ammonium chloride solution
and three c.c. concentrated nitric acid. The addition of
two C.C. of hydrogen sulfid water will then produce the
brown coloration. If the precipitate shows a tendency to
gather in clots and settle another sample niust be pre-
pared and to this, in addition to the reagents mentioned,
add five c.c. of a clear syrup, half sugar and half water.
This will effectually prevent the settling of the precipitate.
The standard copper solution consists of .3928 gram
copper sulfate (CUSO4, SHgO) dissolved in a liter of
water. This contains .0001 gram copper per c.c. The
tests are made by any method except that of a series of
standards. The preparation of such a series even of the
artificial standards is not satisfactory. For duplication the
sample is diluted to fifty c.c, 25 c.c. of water are treated
with the reagents for the sample and the above standard
added a drop at a time. For dilution or balancing ten
c.c. of the standard above are treated with the reagents
specified for the sample with the exception that the
amount of hydrogen sulfid water is increased to six c.c.
This is then diluted to 100 c.c. and every c.c. contains
.00001 gram of copper.
Method F. Copper by Potassium Ethyl Xanthate.
Small amounts of copper in solution react with potas-
sium ethyl xanthate to produce a yellow color suitable for
colorimetric examination.^ If more than .001 gram cop-
per is present in the sample the solution will be too strong
and instead of the desired color there will be formed a
bright yellow precipitate of copper xanthate. In that
case the original sample chosen must be smaller and the
experiment repeated. The presence of small amounts of
1 Scott, Standard Methods of Chemical Analysis, p. 165.
52 COLORIMETBIO ANALYSIS.
iron, lead, nickel, cobalt, zinc or manganese does not
interfere. The test is one well adapted to the testing of
salts for copper present as impurity.
The sample graduated in size according to the copper
content is dissolved in water and diluted to 90 c.c. Ten
c.c. of a solution of potassium ethyl xanthate, one gram to
the liter, are then added. The yellow color appears at
once. It is not advisable to make up a series of standards
for the final test as after a time the copper shows a tend-
ency to precipitate out. A standard copper solution is
made up by dissolving .3928 gram of pure copper sulfate
(CUSO4, 5H2O) in water and diluting to one liter. Ten
c.c. of this solution are then diluted to 100 c.c. so that it
now contains .00001 gram copper per c.c. and serves for
the examination by duplication. The blank contains
sixty c.c. water and ten c.c. potassium ethyl xanthate
solution into which the above standard is run until the
colors match after which the colors and volumes are
cautiously balanced at the same time. For determining
the results by dilution or balancing another amount of
standard must be diluted. Ten c.c. of the standard are
diluted to five hundred c.c. with the addition of ten c.c.
of the reagent to produce the color. This solution then
contains .000002 gram copper per c.c. and is suitable for
the determinations by these other two methods mentioned.
This method is applicable to the testing of substances
insoluble in water by treating them with nitric acid to
render them soluble. If that method is used the nitric
acid must all be removed before completing the test.
This is accomplished by adding hydrochloric acid and
evaporating to dryness. The residue is then extracted
with water and the copper will be present in the solution.
If organic matter is to be removed by this ignition a few
c.c. of sodium hydroxide and a similar amount of sodium
DETEBMINATION OF COPPBB. 53
or potassium nitrate are added to the solution before
evaporation. The residue is then to be ignited until no
more fumes are given off. Water must now be added,
then hydrochloric acid and the residue again taken to dry-
ness to remove all trace of nitrate. Since the examina-
tion is to be made in neutral or slightly acid solution the
presence of any considerable amount of acid in the test
solution must be avoided.
Method G. Copper as the BROMroE.
This method^ is suitable for the determination of small
amounts of copper present as sulfates, nitrates or
chlorides. If the copper to be tested is present as some
complex compound it will first be necessary to treat with
concentrated acid to decompose the complex compound.
The solution for the test is treated with a reagent made
up as follows, 100 grams of potassium bromide are added
to 150 C.C. of boiled water and the solution well shaken.
This is then transferred to a 200 c.c. volumetric and
diluted to the line with warm water. After cooling again
bring up to the mark with cold water.
Five c.c. of the solution to be tested are used. If the
sample requires more than that amount of acid or water
to dissolve it, the above amount is taken from the total
and the result figured by aliquot parts. For use twenty
c.c. of the reagent above are precipitated by the careful
addition with cooling of ten c.c. of concentrated sulfuric
acid and the resultant potassium sulfate filtered off. Five
c.c. of this solution are then added to the sample with two
c.c. of concentrated sulfuric acid. For comparison sev-
eral standards are made up by the use of a solution of
.3928 gram of pure copper sulfate (CuSO^, SHgO) in a
liter of water. The standard contains .0001 gram copper
1 Bull. Soc. Phar. Bordeaux, Aug.-Dec, 1915.
54 OOLOEIMETBIC ANALYSIS.
per C.C. These standards are reasonably permanent and
so may be kept for some time. The ease with which the
production of new standards may be carried out renders
their use, after there is any doubt of their accuracy, un-
The reagent used is unstable and must be kept in
brown glass and in a dark place. Renewal not less than
twice a month is advisable, making up smaller amounts
at a time if desirable.
CARBON IN STEEL.
This is one of the best worked out and most used
methods of colorimetric analysis, finding use as ordinary
procedure for rapid determination of the carbon content
of steels in most works laboratories. The basic principle
assumed for the test is that a sample of steel when dis-
solved in nitric acid shows a brown color which is pro-
portional in intensity to the amount of carbon present
in the sample. The errors that enter into the determi-
nation of carbon by this method are these ; only the car-
bon present in the form of carbide is transformed to this
brown color, the composition of the brown coloration is
not constant, presence of many impurities will cause
colors which interfere. The carbon present in the steel as
graphite, as it is apt to occur in high carbon steels, is not
acted on by acids at all. In that case the flakes of carbon
will be visible in the solution so that one may know that
there is graphitic carbon present and therefore carry
out a determination by the combustion method. It is
sometimes assumed that in steels treated by the same
identical process the proportion of graphitic carbon to
carbide carbon will be the same and comparison therefore
made, even of steels which do contain graphitic carbon.
These results are not as accurate as those obtained by the
usual colorimetric tests on steel.
Manganese, if present, lowers the apparent carbon con-
tent but may be disregarded if the amount is less than
one percent. Nickel has a similar but much greater
eflfect. If much nickel is present a green color is pro-
56 OOLORIMETRIO ANALYSIS.
duced which is difficult of comparison. Over one percent
of silica also produces a green color which is difficult of
comparison. In cases where the presence of these sub-
stances is known, a standard should be taken which has
the same content of the interfering substance as that in
the sample. Comparison may then usually be made.
Copper, cobalt and chromium also interfere.
From the foregoing it follows that the standard used
should be as nearly as possible of the same composition as
the sample. The following conditions should be met,^
1. Sample and standard should be made by same
2. Sample and standard should have same physical
condition so far as this can be secured by mechanical
3. Sample and standard should not differ greatly in
percentage of carbon.
4. Solutions of standard and sample should be made
at the same time under the same identical conditions.
5. The standard used must be one whose composition
is accurately known.
The tints resulting from different forms of steel are
different, and cannot therefore be matched against each
other, so as specified above, Bessemer steel must be tested
against Bessemer steel and open hearth steel against open
hearth steel. The results obtained are more accurate for
mild steels than for hard steels.
Two methods are commonly used in steel works lab-
oratories, the dilution method and the method by a series
of standards. In the latter case the standards are arti-
ficially prepared from the cobalt, iron and copper solu-
tions described in Chapter Two. In the operation of the
dilution method the samples and standards are weighed
1 Steel Works Analysis, Arnold and Ibbotson, p. 50.
CARBON m STEEL.
out alternately into test tubes, using .2 gram of each. To
the tubes there is then added somewhat more than one
c.c. of nitric acid (1:1) for every tenth of a percent of
carbon supposed to be present in the steel. The color
produced will be darker than it should be if too little of
the reagent is used but an excess of acid may be added
without causing any considerable change in the color.
The test tubes are then placed in a special rack in the
water bath. If the carbon content of the sample is under
one percent it should go into solution in less than half
an hour. A paraffine bath at 120 to 150 degrees may be
used to hasten solution. Johnson^ sug-
gests a sand bath at 190 degrees and
recommends that the tubes be grouped in
bunches of six and each bunch covered
with a beaker to prevent too rapid evap-
oration of the acid. If a temperature
greater than 100 degrees is to be used
it is advisable to allow for it by the addi-
tion of excess acid. Tubes should never
be immersed in the heated medium below
the level of the top of the liquid as a
deposit of iron oxide will form. It is
always best to add a hollow glass bead to
each test tube after putting in the acid.
This will float on the surface of the liquid and prevent the
formation of a film of iron oxide.
For convenience in keeping the samples separated it
is well to have a number scratched on the outside of each
test tube ordinarily used for this work. The number of
the test tube used for the sample may then be recorded
beside the weight when samples are weighed out. This
1 Chemical Analysis of Special Steels, Steel-making Alloys and
Fig. 13. Bent
is somewhat more satisfactory than gummed labels as
the later are apt to be steamed off. The samples are
removed from the heating medium as soon as it is seen
that everything has been dissolved, and cooled by plung-
ing in cold water. If solution is made by heating on a
water bath no harm is done by allow-
ing the sample to stay in the bath two
or three minutes after the solid matter
is all dissolved.
The solution now shows a brown
coloration w^hich is diluted by the
addition of two volumes of water to
the cooled solution. This coloration is
considered to be due to some variable
organic compound which at first is to
be seen as a precipitate in the solution
and is dissolved by heating.^ Another
experimenter finds that as much as
.03 percent of the carbon may be pres-
ent as CO and COg and therefore not
show in the results.
If the sample is to be tested by dilution this is usually
carried out by use of the camera described under appa-
ratus. Since the weights of sample and standard used
are identical the results are easily figured. The solu-
tions^ must be cooled below fifty degrees for this compari-
son, otherwise the iron will show color enuf to hide the
results. The use of ferric nitrate for dilution is some-
times advised since the solutions are of that salt. Scott
and Johnson recommend the use of tubes bent at the top,
for the comparison, so that the w^ater can be added to the
sample or standard to be diluted and mixed by a gentle
1 Levy, Analyst, 57, 392.
2 Ann. Chim. Anal., fS2y 193 and 225.
Fig. 14. Color
CAEBON IN STEEL. 59
rocking motion without danger of spilling. The manu-
facturers furnish both straight and bent graduated tubes
for this purpose. The sample is carefully washed from
the original test tube into one of these tubes and the
standard into another and comparison made.
Experiments with the balancing instruments seem to
show that because of the nonpermanenoe of the color ob-
tained by this method the use of that type of instrument
is not advisable. The duplication method is of course
impossible. Standards and samples should be protected
from light at all times as far as possible, as they fade with
exposure. Phosphoric acid is sometimes added to the
sample before dilution.
For convenience in dilution several little helps have
been worked out. The standard may be diluted to a
volume depending upon its carbon content, such as 6 c.c.
for .6 percent carbon and the sample when diluted to an
equal color will then give its carbon content by direct
reading from the scale. When this is not done it is
common to find an operator adding water, two tenths of
a c.c. at a time, until the solution being diluted either
equals the one which was lighter or has become lighter
than the other solution. If the two colors are identical
of course that reading is taken but if the solution has
now been diluted to less than the color of the other the
reading is taken as one tenth c.c. less than that shown by
the scale, or what would have been the reading if the last
addition had been of one tenth instead of two tenths c.c.
Samples for comparison with a series of standards are
similarly prepared and washed into containers the same
as those containing the standards,
LEAD, BISMUTH AND ARSENIC.
The presence of these substances is important partic-
ularly in food products because all are poisons. Lead is
apt to occur as an impurity in many places, notably in
water supplies not properly taken care of. Bismuth and
arsenic are not so apt to be found as natural contamina-
tions but the determination of small amounts of either
is a problem often apt to arise thru their use as drugs.
Lead as the Sulfid.
A small amount of lead in solution on the addition of
hydrogen sulfid will not precipitate but produces a brown
coloration due to the presence of the colloidal sulfid in
the solution.^ If nitric acid is present the color will not
appear unless sodium acetate is added to the solution. In
a solution containing hydrochloric acid, sodium acetate
must be added before the hydrogen sulfid or the solution
will become turbid on the addition of the latter. The
amount of lead in the sample must be between .00025
gram and .000005 gram. If the test is for a contamina-
tion in water the sample may be suitably concentrated or
diluted; if the test is of an ore or an alloy for the lead
content the operator may be governed in his choice of a
weight of sample by the above conditions.
The sample, if a solid, is dissolved in twenty c.c. of
nitric acid, the excess of acid boiled off and the solution
made up to fifty c.c. If the sample is of water fifty c.c.
1 J. Ghem. Soc, 97, 841.
LEAD, BISMUTH AND AESENIC. 61
are taken. Add a few drops of sodium acetate solution
and, if the solution is not already strongly acid, acidify
with two or three c.c. of nitric acid. The color will
appear upon the addition of two c.c. of a solution of hy-
drogen sulfid. Comparison is then made with a standard.
If the color produced shows a tendency to fade due to the
presence of particles of precipitate the operation must be
repeated on a new sample adding in addition to the above
reagents, ten c.c. of a strong sugar syrup, which must be
fresh and clear. This will prevent the formation and
deposition of the precipitate.
Since the color of the sufid fades in the light the use of
the natural series of standards is not satisfactory. The
directions already given for artificial standards admit of
the production of such standards where numerous tests
are to be made by this method. The dilution and bal-
ancing methods are also applicable. As a standard dis-
solve .1598 gram of pure lead nitrate [Pb(N03)2] in
water and dilute to one liter. This standard contains
.0001 gram lead per c.c. Amounts from one tenth to ten
c.c. of this may be used to make up permanent standards
by mixing the cobalt, iron and copper solutions specified
so as to duplicate the color produced. If it is desired to
use the duplication method this solution is run a drop at
a time into 45 c.c. of water containing the same reagents
as were specified for the sample. A standard for the dilu-
tion and balancing methods is made by adding to ten c.c.
of the above solution, 900 c.c. of water, five c.c. sodium
acetate solution, ten c.c. concentrated nitric acid and five
C.C. of hydrogen sulfid water. This is then made up to
one liter, so that the lead content will be exactly .000001
gram per c.c.
This test^ is hindered by the presence of any consider-
1 J. Soc. Chem. Ind., S8, 636.
62 OOLORIMETEIC ANALYSIS.
able amount of iron. This cannot be precipitated by
rendering the solution alkaline and filtering off the re-
sultant precipitate since the ferric hydroxide will carry
down with it the lead present in the solution. The ob-
struction caused by the iron may be overcome by adding
sodium thiosulphate to reduce the iron and then a few
c.c. of sodium or potassium cyanide. A colorless com-
pound of the ferrous iron with the cyanide is formed and
the lead may then be treated with sodium acetate and
ammonium or hydrogen sulfid without rendering the so-
It is often desirable to determine lead in the same
solution in which copper is determined. This is accom-
plished by determining the copper by the potassium
ferrocyanide method, then adding a few drops of potas-
sium cyanide, which will remove the red color leaving the
solution a light green, and determining the lead as the
sulfid in the alkaline solution by the method given above.
In case of the use of the latter procedure it is advisable
to use the dilution or balancing methods and to prepare
a special standard for the test, adding to it approximately
the same amount of copper per c.c. as is present in the
sample and treating it in the same way.
Bismuth as the Iodide.
A solution of bismuth in dilute nitric or sulfuric acid
when acted on by potassium iodide assumes a yellow color
due to the formation of bismuth iodide, which color is
proportional to the bismuth content and therefore suit-
able for colorimetric examination. The solution must be
free from large amounts of lead, copper, tin, antimony,
gold and silver.^ This is accomplished by precipitation.
1 J. Soc. Chem. Ind., IS7, 102.
LEAD, BISMUTH AND ARSENIC. 63
Arsenic, copper and iron cause the results to be too high
if they are present. The presence of hydrochloric acid
and ammonium chloride is also to be avoided for the
opposite reason. The weight of sample chosen must not
contain more than .00015 gram bismuth.^ This method is
suitable for the estimation of bismuth present anywhere
in small quantities as, for example, in impure copper.
The sample is dissolved in a small quantity of nitric
acid and the bismuth precipitated by the addition of an
excess of sodium carbonate. This will precipitate not
only the bismuth but also a considerable volume of pre-
cipitate of other metals. This precipitate is filtered oif
and a qualitative test made on the filtrate to find out if
the bismuth has all been removed. If not it must be
allowed further time to precipitate. In exceptional cases
it may take as long as five hours for this first precipita-
tion to be complete. This may be somewhat hastened by
stirring or shaking. The precipitate is well washed and
redissolved in nitric acid. Five c.c. of lead nitrate are
added, the solution nearly neutralized by the addition of
ammonia and ammonium carbonate added to slight ex-
cess. The subnitrate of bismuth will be precipitated rea-
sonably free from other metals. If this seems too impure
on first precipitation it may be redissolved in nitric acid
and reprecipitated. This purified precipitate is finally
carefully dissolved in nitric acid, washing all parts of the
paper with dilute acid. If the solution from which this
last precipitation was made shows a high color due to
copper a few c.c. of potassium cyanide are added before
precipitation, to decolorize the solution. If the volume
of the solution of the final precipitate in nitric acid is
greater than 25 c.c. it is concentrated to approximately
that volume. Ten drops of sulfurous acid are now added
1 Eng. Mining J., 104, 1091.
64 OOIiOEIMETEIC ANALYSIS.
and five c.c. of a solution of potassium iodide, 17 grams
to the liter. The color is then tested as desired.
The color produced is permanent and a series of stand-
ards may be produced. A standard may be made up by
dissolving .2327 gram bismuth nitrate, [Bi(N05)8, 5HjO],
in dilute nitric acid and making up to one liter. A simi-
lar standard may be made up by dissolving .1 gram of
pure bismuth in nitric acid and diluting to one liter.
Sufficient acid must be added to this solution in diluting
it so that the bismuth does not precipitate out as the sub-
nitrate. These standards will each contain .0001 gram
bismuth per c.c. This standard may be used for making
up the permanent standards or it may be added to 18 c.c.
water and five c.c. nitric acid, treated with sulfurous acid
and potassium iodide, and the result obtained by the du-
plication method. For dilution or balancing it is neces-
sary that the standard be further diluted. For this pur-
pose fifty c.c. of the standard are treated with ten c.c.
concentrated nitric acid, 800 c.c. water, 25 c.c. potassium
iodide solution and five c.c. sulfurous acid and diluted to
one liter. This standard then contains .000005 gram bis-
muth per C.C.
Method A. Arsenic by the Stain Produced on
Mercuric Bromide Paper by Arsin.
In the determination of arsenic by this method the
arsenic is reduced to arsenious acid and then, by treat-
ment in a hydrogen generator, to arsin. The arsin is led
over paper treated with mercuric chloride or better with
mercuric bromide^ and the stain produced compared with
stains produced by standard amounts of arsenic. Sulfid,
phosphoric acid and antimony compounds interfere. The
first two may be removed by oxidation with nitric
acid. When antimony is present the arsenic may be
1 U. S. Dept. of Agriculture, Bureau of Chem., Bull. No. 102.
LEAD, BISMUTH AND AESENIC. 65
removed from the solution by precipitation with mag-
nesium phosphate and filtration, but this method is not
to be recommended. If results show that antimony is
present it is advisable to concentrate a large amount of
substance and carry out the determination by gravimetric
Iron is necessary for the success of the experiment so if
the sample is iron-free this is added in the ferrous con-
dition before reduction of the arsenic.^ This reduction
is accomplished by heating near boiling in a 10 percent
hydrochloric acid solution with potassium iodide and a
few c.c. of stannous chloride. The stannous chloride is to
take up any iodine freed. It is possible to reduce arse-
nates to arsenious acid by the action of the nascent hydro-
gen in the hydrogen generator but this is very difficult
and the reduction previous to their introduction to the
generator is recommended.
The generator consists of a one or two ounce wide
mouthed bottle. An upright tube fifteen centimeters in
length is attached to this, which tube is divided into two
chambers. The upper chamber is filled with cotton
moistened with a five percent solution of lead acetate, the
lower chamber is filled with strips of lead acetate paper.
To the top of this tube is attached a capillary tube 3 mm.
in diameter and 12 cm. long. The lead acetate is for
removing hydrogen sulfid, which would also stain the
paper used. The sample chosen for analysis, which must
contain less than .00004 gram of arsenic is dissolved in
acid and reduced as previously mentioned. This is then
introduced into the generator after it has run blank for
one hour with 40 c.c. one : four sulfuric acid and four or
five drops of stannous chloride dissolved in hydrochloric
acid and approximately ten grams of arsenic-free zinc.
1 Orig*. Com. 8th Inter. Cong. App. ScL, 1, 9.
66 OOLORIMETRIC ANALYSIS.
The arsin evolved produces a characteristic stain on the
prepared paper suspended in the capillary tube, a deep
orange stain of varying length shading sharply to a light
yellow and then to the untouched paper.
For this paper the U. S. Dept. of Agriculture bulletin
previously quoted recommends that mercuric bromide be
used, since it does not require that it be developed if the
results are to be preserved. Other authorities recommend
the use of mercuric chloride. Strips of heavy drafting
paper, 2.5 mm. by 12 cm., are used. These are soaked in
a five percent solution of the salt for an hour, the excess
of solution squeezed out and then hung up to dry.
A standard is prepared by dissolving .1320 g. arsenious
oxide (AsgOg) in sodium hydroxide, partially diluting to
one liter, acidifying with hydrochloric acid, and com-
pleting the dilution to one liter. This is too strong and
ten c.c. of this solution are now to be diluted to 250 c.c.
This solution will then contain .000004 gram arsenic per
c.c. • Standards are to be prepared at intervals from
.000001 to .00005 gram arsenic. These are prepared in
identically the same manner as that specified for the
sample and are suitable for keeping for six months if
the bromide is used but will fade after a week or ten
days if the chloride is used. The different amounts of
arsenic present are shown by the differing lengths of the
orange stain. If the stain produced has been contami-
nated with antimony it will be longer and lighter in color
than the standard. This may be confirmed by exposing
the stain to the fumes of hydrochloric acid. A stain from
antimony will fade on exposure while an arsenic stain
will be intensified.^ It has been recommended that in-
stead of zinc in the generator, arsenic-free iron be used
for the production of hydrogen. This will produce^ the
1 Disc. 8th Inter. Con^. App. Sci., ;?7, 4.
2 Svensk, Farm, Tiskrift, 11, 468, 491.
LEAD, BISMUTH AND ARSENIC. 67
desired arsine (AsHg) but not the undesirable stibine
(SbHg) or phosphine (PH3). The use of a small amount
of stannous chloride in the generator serves to sensitize
the zinc. The generator must be so standardized that the
production of hydrogen is uniform, both while producing
the sample stain and the standard stains. If the sample
contains organic materials it must be so treated that these
will not interfere with the production of hydrogen at the
desired rate. More than a trace of fluorine must be
eliminated from the sample before testing.
Method B. Arsenic by Sil\^r Nitrate.
In this modification^ of the previous method the arsenic
is treated as before and passed thru the tubes with lead
acetate paper but instead of the use of mercuric bromide
paper the gas is then passed thru a tube containing a few
crystals of silver nitrate. The black stain produced by
the arsenic on these crystals is to be compared with stains
produced by known amounts of arsenic in a similar way.
The standards after production may be sealed in the
tubes in which they were produced and kept indefinitely.
1 Compt. Rend., 158, 869.
ALUMINUM AND CHROMIUM.
Of the members of the third group of metals, iron was
worthy of a chapter by itself, leaving us the remaining
two for discussion here. Aluminum, besides its occur-
rence in rocks and minerals, is determined in cements
and plasters. Chromium occurs in minerals to some ex-
tent but the big field of usefulness of this test for
chromium is the analysis of chromesteel for the chromium
Aluminum by Alizarin- S.
The sodium salt of alizarin monosulfonic acid is a com-
mercial indicator which shows purple with alkalies and
yellow with acids. The coloration produced in acid solu-
tion^ may be adapted to the determination of aluminum,
the test being delicate enough for the detection of one
part of aluminum in ten million parts of water. Small
amounts of chromium and iron do not interfere, in the
presence of large amounts of these metals it is necessary
to add citric acid or a citrate to prevent them from show-
ing. It is not advisable to render the solution alkaline
with ammonia for the precipitation of the hydroxides
from other substances present, as the reagents used are
almost certain to contain traces of aluminum. The
presence of phosphates or of moderate amounts of cal-
cium, magnesium or zinc salts has no effect on the results.
If cobalt is present the solution must never become alka-
line. The sample should be chosen to contain between
.00005 gram and .000005 gram of AI2O3.
1 J. Soc. Chem. Ind., 84, 936.
ALUMINUM AND CHROMIUM. 69
The sample taken is to be dissolved in ten to twenty
C.C. as dilute acid as possible or, if the sample taken ex-
ceeds the above limits, in a larger amount and an aliquot
part taken. If the acid is very concentrated it should be
partially neutralized so as to leave the final solution acid'
but not too strongly so. If the solution is made in water
it is acidified. The use of nitric acid is to be avoided as
far as possible since it tends to cause the color to fade
more than do the other acids, altho all cause a slow fading
of the color produced. Ten c.c. of glycerine are next
added to the solution to counteract the tendency of the
aluminum to precipitate and lastly five c.c. of a one per-
cent solution of the reagent. The solution must stand for
five minutes after which it is acidified with dilute acetic
acid until no further change in color occurs, diluted to
fifty C.C. and compared with a standard.
Because of the lack of permanency of the color a set of
natural standards is not satisfactory and, because the
solution is apt to fade more or less before the comparison
is made, the use of artificial standards is not advised.
The method of duplication is out of the question because
it takes some time for the color to be produced after the
standard comes into contact with the reagent. It is there-
fore better to use only the dilution method for this test,
since to place the standard in the balancing apparatus for
each determination would be a useless waste of time. A
standard is prepared at the same time as the sample and
subjected to the same conditions of temperature, etc.
Any fading will then be about the same in each. As a
solution for preparing the standard dissolve .9286 gram
common alum [K2SO4, Al2( 804)3, 24H2O] in water and
dilute to one liter. Ten c.c. of this solution are then to be
pipetted out and again diluted to one liter. The resultant
70 OOLORIMETRIG ANALYSIS.
solution contains .000001 gram AI2O3 per c.c. Five to
twenty-five c.c. of this may be taken as necessary for the
sample used and prepared as previously directed.
Method A. Chromium as the Chromate.
Small amounts of chromium may be determined by the
oxidation of the chromium to the form of a chromate.
This method is particularly designed for the analysis of
minerals but is also adaptable to steel analysis. The
sample chosen must contain not less than .002 gram
chromium as experiment shows that the error is too great
in the oxidation of a lesser amount. The color may later
be lessened by dilution and test of an aliquot part.
The sample is dissolved in as dilute sulfuric acid as
possible and if the acid is very strong it is nearly neutral-
ized by the addition of sodium carbonate. Concentrated
sodium thiosulfate is now added to the solution, which
precipitates chromium and manganese together with some
other metals which will not interfere with the test. This
precipitate is filtered off and dissolved in nitric acid.
A few c.c. of silver nitrate are added as a catlyzer
and then sodium persulfate which oxidises the chromium
present to the form of the chromate. If there was man-
ganese present in the original sample this will have been
carried thru and wuU now be present as the permanga-
nate. Since the color of the permanganate will cover up
the yellow of the chromate it is necessary to remove the
former, which is accomplished by adding ammonia and
heating the solution for a short time.^ The permanga-
nate will be precipitated as the hydroxide and the silver
as the oxide but the chromate will remain unchanged.
Hillebrand recommends the addition of methyl or ethyl
1 Z. Anorg. Chem., 80, 171.
ALUMINUM AND CHROMIUM. 71
alcohol to the solution to destroy the color of the per-
The precipitate is filtered off and if iron is present
sodium phosphate is added to prevent interference from
that source. The sample is then tested against a stand-
ard solution of potassium chromate (K2Cr04). This is
made up by dissolving .2555 gram of the pure salt in
water and diluting to one liter. The standard then con-
tains .0001 gram CraOg per c.c. The preparation of a
series of standards is possible as the standard is per-
manent, or the sample may be duplicated by running a
few C.C. of the above solution into a blank of water. The
use of the above solution for dilution and balancing
methods is possible or, if the sample is such that it seems
to require it, 50 c.c. may be diluted to 250 c.c. and will
then contain .00002 gram Cr^Og per c.c.
Method B. Chromium by Disodium 1.8 Dihydroxy-
naphthalene 3.6 dlsulfonate.
The analysis of steel for chromium has been simplified
by the adaption of the above i-eagent to the use. The
resultant color is pink and is so delicate that .0000008
gram of chromium can be detected. If a considerable
quantity of vanadium^ is present this produces a brown
color which is apt to obscure the results. If the vanadium
present is less than the chromium a correction may be
introduced. Subtract from the percentage of chromium
shown, one third of the percentage of vanadium as shown
by a separate analysis in order to obtain the true per-
centage of chromium present. If the ratio of chromium
to vanadium is high the error may be negligible and so
can be disregarded. A correction may be introduced by
using a similar amount of vanadium in the standard.
1 U. S. Geol. Surv., BuU. 176, p. 80.
2 J. Ind. Eng. Chem., 5, 298.
72 COLOEIMETEIC ANALYSIS.
The sample of .2 gram is dissolved in ten c.c. dilute
sulfuric acid, one half c.c. nitric acid added to oxidise the
iron and evaporated to fumes. This is then cooled,
slightly diluted with water, fifty c.c. of a ten percent
solution of sodium hydroxide and one gram sodium
peroxide added. After boiling for five minutes to de-
stroy the excess of hydrogen peroxide the solution is
cooled, diluted to 200 c.c, and filtered. Use as a sample
100 c.c. of this to which are added 2 c.c. of 85 percent
phosphoric acid and two c.c. of Konig's reagent. The
later is a one percent solution of the reagent for the test,
disodium 1.8 dihydroxynaphthalene 3.6 disulphonate.
The color will at once appear. For a steel low in
chromium (under .15 percent), so that the color does not
show up as very deep, it may be well to repeat the experi-
ment using a .4 gram sample.
The examination may be made by the dilution method
only, because of the peculiar character of the color devel-
oped and the danger of interference. The standard
selected is a steel of known chromium content. The
standard is treated by the same identical method as the
NICKEL, OOBAI/r, MANGANESE AND ZINC.
Or the members of this group, two are commonly used
in the form of alloys with steel and therefore their deter-
mination assumes vital importance in the steel industry.
The other two, zinc and cobalt, are of such frequent occur-
rence in inorganic salts that even the occasions of their
detection as impurity affords a considerable use of the
methods here given.
Method A. Nickel by Potassium Thio-carbonate.
When nickel in ammoniacal solution^ is acted on by
potassium thio-carbonate a rose red to brown red is pro-
duced, suitable for colorimetric examination. Metals of
the second group interfere but may be removed by pre-
cipitation with hydrogen sulfid. Manganese and iron are
precipitated from the solution free from hydrogen sulfid,
by bromine or hydrogen peroxide and ammonia. At the
same time any cobalt present as cobaltous compounds is
oxidised to the cobaltic state in which it does not inter-
fere. Zinc forms a white precipitate with the reagent
which is, however, so fine as not apt to obscure the test
unless a considerable amount is present. If there is any
doubt as to whether the zinc interferes a similar amount
may be added to the standard. The sample should be so
chosen as to contain between .0025 gram and .0004 gram
The sample is dissolved in nitric, hydrochloric or sul-
furic acid as is most convenient, altho nitric is recom-
1 Z. Anal. Chem., 5S, 165.
74 C50L0RIMETEIG ANALYSIS.
mended as ordinarily the quickest. If the sample is a
salt soluble in water the solution is slightly acidified.
The solution is then almost neutralized with ammonia
and a solution of potassium thio-carbonate added (five
c.c. is sufficient) and ammonia in excess. Comparison is
made by dilution as the color is not permanent.
The standard is made up by dissolving .6730 gram of
nickel ammonium sulfate [NiS04, (NH4)2S04, 6H2O] in
water and diluting to one liter. This solution contains
.0001 gram nickel per c.c. From one to twenty-five c.c.
of this solution are treated in the same way as the solution
of the sample and comparison then made by dilution. A
series of standards is not permanent enuf. The solution
may also be added to a blank containing the reagents,
for the making up of a duplicate.
Method B. Nickel as the Chloride in Concentrated
Comparatively large quantities of nickel may be esti-
mated by the intensity of the yellow color of the pure
chloride in concentrated hydrochloric acid solution. The
maximum color^ is reached with the solution about thirty
percent hydrochloric acid after which the color is con-
stant regardless of the concentration of the acid above
that point. The sample, if the ore or alloy to be ex-
amined contains from .1 percent to 10 percent nickel, is
.2 gram. If the nickel content is greater than that, .1
gram will do, if less, the sample may be increased. Iron
and copper must be removed. Copper is precipitated
with hydrogen sulfid after which iron is oxidised to the
ferric condition and precipitated as the basic acetate.
There must be no nitric acid or free chlorine present, the
presence of sodium chloride has no effect.
1 Z. Anorg. Chem., 86y 341.
NICKEL, COBALT, MANGANESE AND ZINC. 75
The sample of .2 gram or other weight as specified is
dissolved in concentrated hydrochloric acid if possible.
This will not usually be possible and the solution must
then be made iti nitric acid. In the latter case hydro-
chloric acid is added to the solution and it is taken to
dryness after which more hydrochloric acid is added and
the process repeated, likewise a third time. The residue
is taken up with concentrated hydrochloric acid, trans-
ferred to a colorimetric tube and diluted with concen-
trated hydrochloric acid to fifty or 100 c.c. as is most
convenient, taking into consideration the depth of color
Cobalt produces a color so that the correction for its
presence is introduced by the use of a standard solution.
The process also furnishes an estimate of the amount of
cobalt present. The standards made up are 4.9556 grams
of pure nickel nitrate [Ni(N03)2, 6H2O] and 4.9361
grams of pure cobalt nitrate [Co(N03)25 6H2O]. These
weights of the salts are dissolved in concentrated hydro-
chloric acid and each evaporated nearly to dryness.
More concentrated hydrochloric acid is now added to
each solution and the evaporation repeated, making sure
that all nitric acid is expelled. The residues are taken
up with hydrochloric acid and diluted to 500 c.c. each
with concentrated hydrochloric acid, content .002 gram
nickel or cobalt per c.c.
The determination of the nickel present in the sample,
if it contains no cobalt, may be carried out by the balanc-
ing method. The making up of a series of standards is
not advisable as this determination usually has two vari-
ables, the amount of cobalt solution added to the nickel
solution and the amount of nickel solution which is used
with pure acid. The dilution method is carried out by
diluting the nickel solution with concentrated hydro-
76 COLORIMETRIO ANALYSIS.
chloric acid. If the sample solution shows a more or
less green tinge the same tint is produced in the stand-
ard by the addition of the standard cobalt solution. The
amount of this used is then a measure of the cobalt pres-
ent in the sample. When the colors of the two solutions
are identical the results may then be figured and by the
usual proportions the weight and percentages in the
Caution, the nickel must always be in concentrated
acid or the yellow will turn to green and similarly the
cobalt must always be in concentrated acid or the blue
color will turn to pink.
Method A. Cobalt as the Chloride in Concentrated
This method for the determination of cobalt is iden-
tical with the determination of nickel^ which just pre-
cedes. The sample of .2 gram is dissolved in the same
way and in the absence of nickel, iron and copper having
been removed according to instructions given there, the
test is made by dilution, using the cobalt standard as
directed and diluting with concentrated acid. If nickel
is present sufficient is added of the standard solution to
duplicate the tint in the standard, after which dilution is
carried out as usual.
Method B. Cobalt by a-Nitroso-b-Naphthol.
The red color produced by cobalt in reaction with
a-nitroso-b-naphthol may be used for the quantitative
determination^ of small amounts of the metal. If more
than a trace of copper is present it must be removed by
precipitation with hydrogen sulfid in acid solution.
1 Z. Anorg. Chem., 86^ 341.
2 Analyst, 4S, 317.
NICKEL, COBALT, MANGANESE AND ZINC. 77
Nickel, if present, is removed by precipitation with
dimethylglyoxime, after which the excess of dimethyl-
glyoxime must be removed by evaporation to dryness and
treatment of the residue with aqua regia. The aqua regia
having been driven off by heating, the residue may be dis-
solved in hydrochloric acid and the process continued.
If the amount of manganese present is in excess it must
be removed by the addition, of an equal amount of nitric
acid to the solution and a small amount of sodium
bismuthate and boiling. If the manganese is not in ex-
cess of the cobalt it may be ignored. The manganese
will be precipitated by the sodium bismuthate and should
then be filtered off. Organic matter is removed by the
evaporation of the solution to dryness and taking up
with aqua regia, evaporating to dryness again and ignit-
ing, after which it is dissolved in concentrated hydro-
chloric acid and diluted for analysis. The addition of
ammonium citrate prevents the interference of metals
other than those mentioned above. The sample should
be so chosen as to contain .002 gram to .00005 gram cobalt.
The sample chosen according to the above limits is dis-
solved in concentrated hydrochloric acid, the total volume
of solution being about 25 c.c. Any of the interfering
metals whose removal is necessary are removed, and the
solution is then ready for treatment with the reagent.
The pure solution of the reagent does not keep satis-
factorily but by conversion to the sodium salt it becames
permanent. This is accomplished by boiling .1 gram
a-nitroso-b-naphthol with one c.c. caustic soda and dilut-
ing to 200 c.c. Before the addition of this to the sample
the solution is nearly neutralized with ammonia and five
c.c. of a solution of 500 grams citric acid in 250 c.c. of
water and 500 c.c. of ammonia, added. This should have
an excess of ammonia so that on addition of it the solu-
78 COLOEIMETRIO ANALYSIS.
tion will become alkaline. If the solution is not slightly
alkaline a small amount of ammonia is added to render
it so and then diluted to nearly 100 c.c. Five c.c. of the
reagent are then added and dilution to 100 c.c. completed.
A standard is prepared by dissolving .4936 gram of
cobalt nitrate [Co(N03)25 BHjO] in water and diluting
to one liter. This solution contains .0001 gram cobalt
per c.c. One to twenty c.c. according to the estimated
size of the cobalt content of the sample are taken as a
standard, treated with the reagents and comparison made
by the dilution method. A duplicate may be made up
by running this solution into a blank of 75 c.c. of water
with the same reagents added to it as to the sample. A
series of standards cannot well be made up as the cobalt
comes down after a short time as a red precipitate. For
the balancing method fifty c.c. of the standard solution
should be treated with double the quantities of reagents
specified for the sample and then diluted to 500 c.c. This
will then show the characteristic color and may be used
at once but after a time will precipitate out. The latter
solution contains .00001 gram cobalt per c.c.
Method A. Manganese as Permanganate OxroATiON
The red color of manganese after it has been oxidised
to the permanganate^ is used as a means of estimation
of the manganese content of an ore or an alloy. Prac-
tically no metal interferes except chromium and that not
unless it is in considerable excess of the amount of per-
manganate. If a large amount of iron is present as in the
analysis of a steel for the manganese content, phosphoric
acid is added to prevent the precipitation of the iron or
a yellow color from that source. The samples should be
1 Z. Anorg. Chem., 80, 171.
NICKEL, COBALT, MANGANESE AND ZINC. 79
chosen as follows, .02 percent to .25 percent manganese
take .5 gram, up to 4 percent use .25 gram. Above that
limit .1 gram is to be used or the sample diluted and an
aliquot part taken.
The sample is dissolved in dilute sulfuric or nitric acid
and any residue of silica filtered off. Ten c.c. of fifth
normal silver nitrate solution are then added as a catal-
yzer. If free chlorine or hydrochloric acid have entered
into the solution in any way it may be necessary to add a
considerable volume of silver nitrate to precipitate these
before the catalyzer can be added.^ Potassium persulf ate
is then added in sufficient quantity to oxidise all the man-
ganese present to the condition of permanganate. The
color will at once appear. If there is not too much chro-
mium present the solution is now ready for testing, other-
wise a further step must be gone thru.
In case too much chromium is present ammonia is now
added and the solution heated. The manganese will be
precipitated as manganese hydroxide and silver and a
few other metals present will come down also. The chro-
mium will, however, remain in the solution as the chro-
mate unchanged. This is the same method that is used
to purify the chromate solution for the obtaining of the
chromium content. The precipitate containing the man-
ganese is filtered off, dissolved in nitric acid and a further
quantity of potassium persulfate sufficient to again oxi-
dise the manganese is added. The permanganate color
will reappear and the solution is ready for testing.
An old standard permanganate solution which has been
used for iron analysis so that the iron factor is known,
is best used as the standard. In that case the changes
which occur in the solution when first made up are not
to be reckoned with. In such a case multiply the iron
1 C. N., 8S, 76.
80 COLORIMETRIO ANALYSIS.
factor of the solution by .2952 to get the manganese
factor. If a new standard must be made up .1439 gram
potassium permanganate is dissolved in 100 c.c. of water.
The water for this solution or for the dilution of the old
solution, if it is to be diluted, must be boiled and cooled
before it is ready for use. This 100 c.c. of solution is
then diluted to one liter with the addition of ten c.c. of
nitric acid. The latter standard contains .00005 gram
manganese per c.c.
The making up of a series of permanent standards is
not to be relied on. A blank may be prepared of twenty-
five c.c. of water and the sample diluted to fifty c.c. after
which the blank is made up as a duplicate by the addi-
tion of the above standard. The above standard may be
further diluted, 100 c.c. diluted to 500 c.c. if thought
desirable for the use of the dilution or balancing methods.
Water to be used in carrying out the dilution method
should have been boiled and cooled shortly before using.
Method B. Manganese as Permanganate, OxroATioN
Instead of the use of a persulfate which involves the
use of a catlyzer the oxidation may be carried out by
the addition of sodium periodate to the solution.^ It is
necessary that there be an excess of free mineral acid in
the solution, otherwise the manganese will precipitate out
as manganese periodate or some oxide of manganese.
The presence of much iron is taken care of by the ad-
dition of a few c.c. of strong phosphoric acid, which pre-
vents the yellow color due to the iron as well as a possible
precipitation. Other metals do not interfere unless they
produce a colored solution in which case they must be
1 J. A. 0. S., S9, 2366.
NICKEL, COBALT, MANGANESE AND ZINC. gl
The sample is chosen as in the preceding method and
dissolved in a mineral acid. The presence of hydrochloric
acid or free chlorine will not interfere with this method.
The concentration of the acid used is best, 15 c.c. concen-
trated sulfuric or 20 c.c. nitric acid or 10 c.c. strong phos-
phoric acid per 100 c.c. of solution. Any reducing sub-
stances may be removed by adding nitric acid and heating.
.4 gram sodium periodate is added to the sample and the
solution boiled for one minute, kept hot for ten minutes,
cooled and diluted. The comparison is made with stand-
ards as specified in the previous method.
Zinc by Resorcinol.
Zinc is acted on by resorcinol in alkaline solution to
produce a blue color.^ The character of this alters some-
what on exposure to the air. The addition of hydro-
chloric acid turns the solution red and this color is not
altered. Other metals do not interfere unless they have
a colored solution before the addition of the reagent. In
that case the metal causing the color must be removed.
A sample suitable for examination by this method must
contain between .003 and .000005 gram zinc.
The sample is dissolved in acid, diluted to 75 c.c. and
neutralized by the addition of ammonia. The solution
is diluted to 100 c.c. Two c.c. of ammonia are then
added and two c.c. of a five percent solution of resorcinol,
which will produce the characteristic color.
A standard is prepared by the solution of .1 gram of
pure zinc in nitric acid and dilution to one liter. A suit-
able amount of this is treated the same as the sample.
The standard so prepared must be very close to the color
of the sample as the dilution method does not hold thru
any considerable range in this case. The other methods
lAnales. Soc. Espan. Fis. Quim., 11, 98.
g2 COLORIMETRIO ANALYSIS.
are impracticable except the duplication method. For
that the blank should contain 70 c.c. of water. After
results have been obtained by the dilution method in
alkaline solution a slight excess of hydrochloric acid may
be added and the test checked by comparing the red color
produced in acid solution.
POTASSIUM AND MAGNESIUM.
The determination of potassium is of considerable im-
portance in the examination of soils and drainage waters
as well as the determination of traces of the metal in
analysis of minerals and substances of all sorts when an
accurate analysis is made. Magnesium occurs in minerals
and as one of the dissolved substances in natural waters.
Method A. Potassium by Determination of the
Potassium Platino Chloride by Reduction
WITH Stannous Chloride.
This method for the determination of potassium de-
pends on the precipitation and separation of potassium
as the platino chloride, the solution of this amount of
platinochloride and reduction with stannous chloride.
The color produced^ is a yellow proportional to the
amount of platinum present which is in turn proportional
to the amount of potassium present. Since the standard
is a similar salt the proportion may be taken as directly
resultant from the potassium without consideration of the
fact that the color is due to the platinum rather than to
the metal being tested for. This method admits of esti-
mation of amount so small that they could hardly be
detected by the usual gravimetric procedure. The amount
of sample should be so chosen that the potassium content
is between .00005 and .000005 gram per c.c. in a solution
of 25 c.c.
1 J. A. C. S., ^5, 991.
84 COLORIMETRIG ANALYSIS.
The sample, if a solid, is dissolved, in water if so solu-
ble, in hydrochloric or nitric acid if necessary. If the test
is being made on a solution it may be necessary to con-
centrate in order to come within the limits. The sample
solution is then evaporated to dryness with the addition
of one c.c. of concentrated sulfuric acid. The residue is
strongly ignited and dissolved in hot water, acidified
with hydrochloric acid and an excess of chlorplatinic
acid added. The solution is washed out of the dish onto
a filter with alcohol (80 percent concentration or more)
and washed with several successive small portions of
alcohol. The precipitate is now dissolved in boiling
water, cooled and made up to a definite volume. This
should be 50 c.c. if the potassium content is low or 100 c.c.
if the potassium content is high. In the latter case the
solution is divided into two parts and one half used for
the further procedure.
A stannous chloride solution is made up by boiling 75
grams of powdered or granulated tin in an erlenmeyer
flask with 400 c.c. of concentrated hydrochloric acid until
all the tin has dissolved. Three c.c. of this solution are
added to the solution of the sample and the yellow color
A standard is made up by dissolving .0516 gram of
potassium chlorplatinate (K2PtClo) in water and making
up to one liter. This solution will contain .00001 gram
K2O per c.c. If a series of standards is to be prepared
from one to twenty -five c.c. of this solution are used for
the original standards, treated with stannous chloride and
made up to 50 c.c. For the method of duplication the
above standard is run into a blank of 25 c.c. of water
treated with three c.c. of stannous chloride. A standard
solution showing the color so that it may be used for
comparison by the dilution or balancing methods is made
POTASSIUM AND MAGNESIUM. 85
by treatment of 200 c.c. of the solution with five c.c. of
hydrochloric acid and ten c.c. stannous chloride and mak-
ing up to 250 C.C. This solution will then contain .000008
gram potassium per c.c.
Method B. Potassium as the Chlorplatinate by
This method is for uses similar to those of the preced;
ing method but is more delicate. The sample should be
smaller than those recommended for the preceding method.
The sample is dissolved and treated similarly until the
solution of potassium chlorplatinate in water is obtained.
The washing^ of the precipitate should be with stronger
alcohol than in the preceding case and the last washing
must be with absolute alcohol. This must be allowed to
stand for a sufficient time for all of the alcohol to evapo-
rate before solution is made, otherwise the alcohol in the
final solution will cause an impediment to correct results.
The fifty c.c. of sample are then treated with five c.c. of
a solution of potassium iodide, 86 grams to the liter. A
red coloration is produced which is darker for the same
amount of potassium than that produced by reduction of
the chlorplatinate with stannous chloride. The standard
used is more dilute, .1032 gram of potassium platino
chloride (KoPtCle) is dissolved in one liter of water.
The standard for the series of standards or duplication
methods is made by dilution of ten c.c. of this solution to
100 c.c. so that it then contains .000002 gram KgO per c.c.
For the dilution or balancing methods five c.c. of the
standard solution are treated with five c.c. of potassium
iodide solution and made up to 100 c.c. The content per
c.c. of this is .000001 gram KgO per c.c.
1 J. A. C. S., fS5, 1063.
86 COLOBIMETRIO ANALYSIS.
Magnesium by Determination of the Phosphate
For the determination of magnesium the magnesium is
changed to the form of the ammonium phosphate.^ This
is then treated with a standard molybdate solution which
will give a yellow color proportional to the amount of
phosphate present, which is in turn proportional to the
amount of magnesium present. The standard is a phos-
phate solution and the amount of magnesium represented
by a gram of PjOg is known so that the percentage is
obtained by this factor. Calcium precipitates, if present,
but the addition of a few drops of ammonium oxalate
solution entirely prevents this interference. The sample
is so chosen as to contain between .0001 and .00003 gram
The sample, if a solid, is dissolved in as small an amount
of nitric or hydrochloric acid as possible, evaporated to
dryness to drive off the excess of acid and the residue dis-
solved in water. If some silica is present this may be
filtered off before evaporation to dryness. If the sample
is a liquid at the start such as, for example, a drinking
water it may be necessary to concentrate. The sample
should finally be concentrated to about five c.c. of solution
The phosphate reagent is made up by dissolving 17.4
grams potassium hydrogen phosphate (K2HPO4) and
100 grams ammonium chloride in 900 c.c. water, adding
fifty c.c. strong ammonia and diluting to one liter. The
cheaper sodium salt is not satisfactory as it is too diffi-
cult to wash because of its lesser solubility.^ To the
sample as specified above is added one drop of ammonia
and two or three drops of ammonium oxalate and the
1 J. A. C. S., S6f 961.
2 J. A. C. S., ^6, 1463.
POTASSIUM AND MAGNESIUM. 87
whole evaporated to dryness on the water bath* One c.c.
of the phosphate solution is added to this residue and the
whole thoroly stirred with a glass rod and allowed to
stand for two hours. The precipitate is washed out onto
a small filter with ammonium hydroxide and washed with
further quantities of ammonium hydroxide, five c.c. at
a time, until a total of fifty c.c. has been used. The
original dish is washed out with each addition before it
is added to the filter. The dish is washed out with five
c.c. of pure water and the filter also washed with this.
A clean beaker is placed under the filter and the dish
washed out with five c.c. of concentrated nitric acid.
This same acid is carefully poured over the filter so as
to dissolve all the precipitate present. The dish and
filter are washed with hot water, five c.c. at a time, until
nearly 45 c.c. have been used. The filtrate is cooled, four
c.c. of ammonium molybdate solution added and diluted
to fifty c.c. The yellow color now appears and is at its
greatest intensity after twenty minutes. The solution
must therefore be allowed to stand until that time before
A standard is made up by dissolving .5043 gram of
pure sodium acid phosphate (Na2HP04, I2H2O) in
water, adding 100 c.c. of nitric acid and making up to one
liter. This standard contains .0001 gram P2O5 per c.c.
The test cannot conveniently be made by the production
of a duplicate since an addition of the standard takes
twenty minutes to reach its full intensity. The standard
for use by the balancing or dilution methods is made up
by adding to ten c.c. of the above solution, 70 c.c. of
water, 9 c.c. nitric acid and 8 C.c. of ammonium molybdate
solution and making this up to 100 c.c. accurately. After
standing, this solution attains the color representing its
content of .00001 gram PgOg per c.c. or representing
88 CX)LORIMSTEIC ANALYSIS.
.00000342 gram magnesium. That is, the amount of
phosphorus present as PgOg is multiplied by the factor
.342 to give the amount of magnesium represented by this
result. The result is in terms of Mg. The factor to rep-
resent the result in terms of MgO is .568.
The quantitative estimation of gold in solution is one
field left almost exclusively to colorimetry. Tests may
be performed which are so delicate as to show the pres-
ence of one cent's worth of gold in a ton of water and by
concentration of the solution being tested even greater
delicacy may be secured. It is by these methods that the
well known fact that every ton of sea water contains a
few cents' worth of gold is proven.
Eight brief methods follow.
Method A. Gold by Method of Dowsett.
This method for the determination of dilute gold solu-
tions does not require the making up of a series of stand-
ards but requires that the worker have sufficient knowl-
edge of the colors after some use of the methods to be able
to estimate the gold content from the depth of color pro-
duced. A solution containing gold up to a value of 8
cents per ton may be used. If the test is to be made of
an ore this is dissolved in some manner. The most con-
venient method is usually by the extraction of the gold by
a dilute cyanide solution.
A sample^ of 500 c.c. of the solution to be tested is
poured into a bottle which has very little shoulder, such
as a large soft drink bottle, ten to fifteen c.c. of a satu-
rated solution of sodium cyanide added and two or three
drops of a saturated solution of lead nitrate. Two
grams of fine zinc dust are then added and the bottle
1 Met. and Chem. Eng., IB, 460.
90 COLORIMETRIO ANALYSIS.
corked and shaken until the precipitate formed settles
quickly, usually for about two minutes. The bottle is
then inverted into a casserole and the clear liquid decanted
off. Nitric acid is added to the precipitate until the
reaction ceases, a drop or two in excess added and the
solution evaporated to one or two c.c. This small volume
of solution is transferred to a small test tube and one c.c.
of stannous chloride solution added to bring out the
color. If the quantity of gold is small this may take two
or three minutes ; in case the color is faint it is more read-
ily detected by looking down the tube.
The colors produced are :
2 cents per ton — Very slight color.
3 cents per ton — Slight yellow color.
4 cents per ton — Slight pinkish yellow color.
6 cents per ton — Strong pink color.
8 cents per ton — Purple of Cassius.
For the experimenter to learn this method a few tests
on known solutions are advisable, to get the colors firmly
fixed in mind. The smallest amount of lead possible
should be used so that the precipitate to redissolve will
be small. Excess nitric acid will cause the colors to differ
from those specified, therefore the nitric acid should be
added cautiously. Mercury if present will cause a dark
color which will cover up the results of the test.
Method B. Gold by Method of Prister.
A copper solution^ for carrying out this test is made by
boiling a solution of two parts salt to one part copper
sulfate with ten parts water in the presence of scrap
copper for ten minutes and adding a few drops of acetic
acid to the solution on cooling.
A sample of 200 c.c. of solution is acidified with hydro-
1 Proc. Chem. Met. and Min. Soc. of So. Af ., IV, 235.
chloric acid and boiled several minutes to decompose
cyanide if present. A slight excess of the copper solu-
tion is then added and a few drops of sodium sulfid
solution. After boiling this solution for five minutes the
precipitate is allowed to settle and the liquid decanted
onto a filter. The precipitate in the beaker and on the
filter is dissolved in three c.c. of a five percent solution of
potassium cyanide to which has been added a few drops
of potassium hydroxide. Two grams of zinc dust are
added to this solution and the mixture then heated to 45
degrees for a half hour. The liquid is separated by
decanting thru a filter after which the excess of zinc is
removed by treatment with hydrochloric acid. The
residue is now treated several times with ten c.c. of aqua
regia passing it thru the filter and washing out the beaker
The color will be produced by diluting this solution to
twenty c.c. with stannous chloride. As in the preceding
case, tests must be made on solutions of known gold con-
tent to become familiar with the colors produced.
Method C. Gold by Method of Dorino.
This method is for the analysis of ores poor in gold.
One hundred grams of ore are slightly but evenly moist-
ened in a stoppered bottle with one or two c.c. of equal
parts of bromine and ether. This is to be shaken at
frequent intervals for two hours, during which time the
interior of the bottle must be filled with bromine vapor.
Fifty C.C. of water are added to the bottle and it is allowed
to stand for two hours shaking occasionally. The solu-
tion is then filtered, the filtrate evaporated to one fifth of
its former volume, a little bromine water added and the
solution treated with stannous chloride in a test tube.
Results are as follows:
92 COLOBIMBTBIO ANALYSIS.
.1 percent solution, deep brown color, opaque even in
.01 percent solution, brown violet immediately, 14 cm.
.001 percent solution, pale violet immediately, increases
after a time.
.0001 percent solution, evaporated to one fifth former
volume, and a drop of bromine water added
shows a distinct rose tint in a 14 cm. column.
.00005 percent solution shows faint but recognizable pink
in 14 cm. column, after undergoing the same
This method will show as little as one half gram per
ton of ore. From the percent of the solution the gold
content of the ore may be calculated.
Method D. Gold by Method of Rose.
This method is for detection of gold in substances
which can be dissolved in water, such as a trace of gold
in a salt, or similar tests. The sample^ is dissolved in
water, this solution heated to boiling and then poured
into a solution of stannous chloride. There is formed a
gelatinous precipitate which has the purple of Cassius if
considerable gold is present and shows a faint pink for
amounts as small as one part in one hundred millions.
The operator is expected to familiarize himself with the
colorations produced by known quantities of gold.
Rose suggests the making up of a standard by solution
of .00003 gram of gold in three liters of water. This
would be one part in one hundred millions and could be
concentrated to give a standard of the desired concen-
1 C. N., 66, 271.
This test used with sea water as a sample gives a very
Method E. Gold by Method of Cassal.
This method^ is for treatment of a cyanide solution for
determination of the gold content. To the sample of
50 c.c. of solution a small amount of potassium bromate
is added and then concentrated sulfuric acid until
effervescence starts. The action will continue without
further addition of acid until the cyanide is completely
decomposed. The bromine is then boiled off and stannous
chloride added in excess which will produce the color
desired. If the test is made quickly it is not necessary
to boil off the bromine before addition of the stannous
chloride but the color will not remain at its true intensity
for more than a minute unless the bromine is so removed.
The colors are determined from the memory of those
caused by standard amounts of gold. This test will show
a light color from the presence of as little as one cent a
ton. The purple of Cassius appears when only four dwt.
of gold per ton are present.
Method F. Gold by Decomposition of the Cyanide
BY Potassium Bromide and Sodium Peroxide.
This method^ is similar to method E except that potas-
sium bromide is added to the 50 c.c. of sample solution
and then sodium or potassium peroxide in excess.
Bromine will be freed and the cyanide will be decom-
posed. Sulfuric acid is then added to the solution until
neutrality is reached after which it is acidified with
hydrochloric acid, stannous chloride added and the deter-
mination made as in the previous method.
1 Eng. Min. Jour., 76, 661.
94 COLOBIMETRIO ANALYSIS.
Method G. Gold by Decomposition of the
Cyanide by Ammonia.
This method is similar to method E except in the
manner of reduction of the cyanide. To the solution^ to
be reduced is added one third its bulk of concentrated
ammonia. Concentrated sulfuric acid is then added until
neutrality is reached after which the solution is acidified
with hydrochloric acid and treated with stannous chloride
for the production of the color.
Method H. Gold by Metaphenylenediamine.
The solution of the gold as a cyanide is treated with
concentrated hydrochloric acid to decompose the cyanide
and change the gold to the form of the chloride.^ Five
c.c. of a solution of five grams metaphenylenediamine to
the liter are then added. Upon the addition of sulfuric
acid a yellow to dark brown color is formed, dependent
on the strength of the gold solution. The color shown is
due tx) the presence of colloidal metallic gold. A solution
as dilute as .005 percent will show a color by this method.
The reagent may become pink on standing in the light
but may be decolorized by animal charcoal.
1 Eng. Min. Jour., 76, 661.
2 Chem. Ztg., S6, 934.
TITANIUM, VANADIUM AND TUNGSTEN.
These comparatively rare metals are not very widely
distributed but notwithstanding their scarcity are of
great importance. Their principal use is in alloys with
steel where the amount of the metal present would be
small and well adapted to this type of procedure.
Method A. Titanium by Hydrogen Peroxide.
This method of analysis for titanium is ordinarily
applied to the solution titrated for total iron, after the
titration has been completed. For use as standard the
titanium content of a standard ferrotitanium must be
known. The presence^ of less than half of one percent of
nickel or chromium may be equalized by the addition of
a similar amount to the standard, a greater amount than
this must be removed by methods to be given later.
The sample, if weighed out, is of .5 gram, the solution
titrated for iron is just as good and much more con-
venient. The standard is made up by weighing out an
amount of ferrotitanium such that its titanium content is
approximately that of the steel under examination and
adding to this enuf steel containing no titanium to bring
the weight up to .5 gram. This standard is then treated
as specified for the sample. If the sample contains more
than one half percent nickel or chromium they are re-
moved as follows : Fuse the .5 gram sample with 5 grams
sodium carbonate and one gram potassium nitrate. The
1 Chemical Analysis of Special Steels, Steel Making Alloys and
Graphites^ Johnson. ^
96 COIiOBIMETRIC ANALYSIS.
melt is heated with 30 c.c. of one-one hydrochloric acid
in a porcelain casserole for thirty minutes, filtered and
washed. Thirty c.c. of dilute sulfuric acid are then
added, the solution evaporated to fumes, transferred to a
test tube, five c.c. nitric acid added, the red fumes boiled
off and proceeded with as the solution of the sample.
The standard, and the sample if it does not have to
have nickel or chromium removed, is dissolved in ten c.c.
dilute sulfuric acid, five c.c. concentrated nitric acid
added and heated until red fumes cease to be given off.
The standard, and the sample obtained in one of the
ways mentioned, are then poured into Nessler tubes or
other tubes suitable for comparison by dilution. Hilde-
brand^ says that five percent of sulfuric acid is necessary
in this solution to make sure that any metatitanic acid
formed is reverted to the metal. If phosphoric acid is
present a similar amount must be added to the standard.*
Five C.C. of a solution of hydrogen peroxide are now
added to each of the tubes and the comparison made by
dilution. If hydrogen peroxide is not available it may
be supplied by dissolving 3.5 grams of sodium peroxide
in 125 C.C. of dilute sulfuric acid and diluting to 500 c.c.
Since the large amount of iron present is apt to cause
a yellow color, a correction is sometimes introduced for
this or the iron removed from the sample before addition
of the peroxide. The correction for iron present is as
follows, .1 gram Fe2O3 = .0002 gram TiOg or 10 grams
Fe2O8 = .02 gram TiOg.^ For the removal of the iron
the sample is fused with sodium peroxide.* This leaves
the iron as the insoluble oxide when the melt is extracted.
The solution is acidified with sulfuric acid, in which case
no hydrogen peroxide need be added as the excess of
1 XT. S. Geol. Surv. Bull,, No. 176, p. 80.
2 J. A. C. S., S9y 481.
TITANIUM, VANADIUM ANB TUNGSTEN. 97
sodium peroxide in solution will fonn a sufficient quan-
tity in reaction with the acid.
Method B. Titanium by Thymol.
This method admits of the determination of much
smaller amounts of titanium, as the color produced by
titanium in reaction with thymol is about twenty-five
times as intense as the yellow to orange produced by the
preceding method. This method produces a red colora-
tion. The only substance apt to be present which would
alter the color is tungstic acid.
The reagent^ is prepared by dissolving one gram thymol
in 5 c.c. dilute acetic acid and this is then added to 95 c.c.
of concentrated sulfuric acid. The thvmol if dissolved
directly in the sulfuric acid would give the solution a yel-
low color which is not present if solution is made first in
acetic acid as directed. The solution of the reagent must
be kept from bright sunlight or it will darken in a few
hours. The amount of thymol added should be such that
the ratio of thymol to titanium is less than 100 : 1.
The sample is placed in solution as in the preceding
method, using all the same precautions, and then poured
into Nessler tubes as in that case. Two c.c. of the above
thymol solution are then added to the sample and stand-
ard and dilution carried out.^ If desired a series of
standards may be prepared from a standard ferrotitan-
ium for this method. For convenience in dissolving the
original sample it may be desirable to fuse it with potas-
sium acid sulfate.
Method A. Vanadium by Hydrogen Peroxide.
This metal in alloys and ores is determined by solution
in acid and oxidation with hydrogen i)eroxide. The
1 J. A. C. S., S5, 138.
2 Orig. CJom. 8th Inter. Cong. App. Sci., 1, 285.
98 OOLOBIMETRIG ANALYSIS. "
resultant color is, in practice, always compared by dilution
or duplication. If chromium is present an equal amount
must be introduced into the standard under the same con-
ditions of temperature, acid concentration, etc. The
sample is two grams of a steel low in vanadium or one
gram of a steel with a high vanadium content. If of a
mineral the weight of sample may be judged by the prob-
able vanadium content.
The sample is dissolved in 40 c.c. of concentrated nitric
acid, one tenth gram permanganate added and the solu-
tion digested for two minutes. Ammonium bisulfite is
then added to clarify and the solution boiled to expel
sulfur dioxide. The solution is then cooled and made up
to 50C.C.1 (A).
As an alternate method of solution and treatment of
the sample it may be dissolved in ten c.c. of sulfuric acid
(1:3), two c.c. of concentrated nitric acid added, heated
until the solution clears and fumes disappear, cooled and
made up to definite volume of 50 c.c.^ (A).
If the original solution contained chromium the stand-
ard must also be made up to contain chromium. In that
case a standard vanadium steel is dissolved in 40 c.c. sul-
furic acid, an amount of chromium equal to the amount in
the sample added as potassium dichromate, ten c.c. of
nitric acid added and the solution heated for ten minutes
to complete solution and clarify. This standard so pre-
pared may then be made up to fifty c.c. and is ready for
comparison by dilution.
In case chromium is absent and the results are to
be obtained by dilution an amount of vanadium steel is
weighed out which contains approximately the same
weight of vanadium as the sample. This steel is treated
1 J. Ind. Eng. Chem., 5, 736.
2 Chem. World, ft, 341.
TITANIUM, VANADIUM AND TUNGSTEN. 99
identically the same as the sample and when it reaches
the point (A) in the process should be diluted to fifty
C.C. and have the same color as the sample. The color
present at this point, if any, will be entirely that of some
metal other than vanadium, if the color of the contami-
nation of sample and standard differs the determination
of results will be rendered incorrect. If the results are
to be obtained by duplication a blank of 45 c.c. of water
is prepared at this point in the process adding to it as part
of the total volume the same amount of the same kind of
acid as is supposed to be present in the sample. Note that
if nitric acid was used for oxidation the greater part of
it may have been boiled off as brown fumes before pro-
ceeding to the next process.
The solution for determination of the sample by dupli-
cation consists of .1784 gram of V2O5 dissolved in the
smallest possible amount of sulfuric acid and diluted to
one liter. Each c.c. of the solution will then contain
.0001 gram vanadium.
To the sample diluted to fifty c.c. and to the standard
diluted to equal volume or to the blank of 45 c.c. of water
and acid there is now added one c.c. of the commercial
3 percent hydrogen peroxide. The color resultant from
the vanadium present appears and the determination
is carried out by the method chosen. If commercial hy-
drogen peroxide is not available it may be made by ad-
ding two grams of sodium peroxide to 100 c.c. dilute
This method of determination of vanadium is accurate
to about .04 percent.^
1 Pickard, Chem. World, £, 341.
100 OOLOBIMETRIO ANALYSIS.
Method B. Vanadium by Strychnine.
By this method the vanadium is separated from the
solution containing the iron by precipitation with am-
monium molybdate/ oxidised with potassium chlorate
and sulfuric acid, treated with a solution of strychnine
in concentrated sulfuric acid and the results obtained by
dilution. Ten minutes is necessary for the full color to
appear after the addition of the last reagent so that deter-
mination by duplication is impracticable. The prepara-
tion of the large amount of standard necessary for the
method by balancing is not satisfactory and the color is
not permanent enough for the use of a series of standards.
The sample is chosen as one or two grams as in the pre-
The sample is dissolved in 45 c.c. nitric acid (1:2) and
one c.c. dilute sodium acid phosphate solution added.
The solution is then cooled and 14 c.c strong ammonia
added. Boil until all the ferric hydroxide has redis-
solved in the excess of the solution, remove from the
flame, add thirty c.c. of ammonium molybdate and shake
well. Filter and wash free of iron with two percent
nitric acid and then with water. The precipitate is then
washed into a large beaker, a small amount of potassium
chlorate and 20 c.c. sulfuric acid added and evaporated
until fumes of sulfuric acid begin to pass off. This is
then cooled and twenty c.c. of a solution of strychnine,
four grams to the liter, in concentrated sulfuric acid are
added. After standing for ten minutes the color will
appear in its full intensity.
The standard is made by solution of .1784 gram of VgOg
in as small an amount of sulfuric acid as possible and
diluted with concentrated sulfuric acid to 100 c.c. Each
C.C. contains .001 gram vanadium. An amount of this
1 Chem. World, fS, 341.
TITANIUM, VANADIUM AND TUNGSTEN. IQl
standard equal to the amount of vanadium estimated to
be present in the sample is treated with potassium chlorate
and sulfuric acid, carried on from that point, and used for
Tungsten as the Oxide in Colloidal Suspension.
The sample dissolved in acid is treated with titanium
trichloride. This frees the blue oxide of tungsten which
will remain in suspension about one half hour.^ More
than ten percent of hydrochloric acid in the solution
weakens the color. The method may not be applied in
the presence of vanadium, phosphorus and molybdenum
without first removing these factors. The amount of
tungsten in the sample must not be over .001 gram, other-
wise the oxide will precipitate.
Solution of the sample is made in five c.c. of hydro-
chloric acid, the solution boiled down to small volume,
two c.c. are practical, cooled and diluted to forty c.c.
Five C.C. of TiCla are then added to the solution and dilu-
tion to 50 c.c. carried out. This is compared with the
standard by dilution.
The standard for use by this method is prepared by
weighing out a standard tungsten steel, of which the
tungsten content is known, to an amount estimated to be
near the amount of tungsten contained in the sample and
adding nontungsten steel until the total weight is equal
to the weight of sample taken. In case the estimate is
being made of a mineral rather than of a steel it is
advisable to use a steel as high in tungsten as possible
and not to add the additional nontungsten steel as there
will be no iron in the mineral. This standard is dissolved
and treated by the same method as the sample.
1 Compt. Eend., 166, 416.
FLUORINE, CHLORINE AND PERCHLORATES.
Of the members of the halogens these two, fluorine and
chlorine, may be estimated by colorimetric methods and
also the compounds of one as perchlorates. The many
places in which traces of these occur need hardly be
mentioned, from drinking water to minerals they may be
found distributed thruout nature, and in synthetic prod-
ucts the occurrence of chlorine in particular is frequent.
Fluorine by Estimation of Its Bleaching Action
ON AN Oxidised Titanium Solution.
Small amounts of fluorine may be estimated by their
action on a titanium solution which has been oxidised by
the addition of hydrogen peroxide.^ The results are ob-
tained by one of two methods. There may be a similar
titanium solution containing a known amount of fluorine
prepared, such that its color is the same, or the bleached
solution may be examined for its apparent titanium con-
tent. By subtraction of the apparent content from the
real content and multiplication by a factor, the fluorine
which caused the bleaching may be estimated.
There are a large number of impediments to this
process. The presence of alkaline sulfates causes a bleach-
ing action similar to that of fluorine.^ Heating or the
presence of considerable free acid will serve to bring back
part of the color thus bleached. The color bleached
by fluorine as well as that by alkaline sulfates will be
1 Am. Jour. Sci. (4), S8, 119.
2 J. A. C. S., 30, 219.
FLUORINE, CHLORINE AND PERCHLORATES. 103
restored by a large amount of free acid. If a large
amount of silica is present, as usually is the case in
minerals containing fluorine, this must all be- removed
before the procedure is begun. The color is estimated to
be increased 5 to 15 percent by raising the temperature
30 degrees. Phosphoric acid also bleaches the titanium
solution and so must be absent. Aluminum also bleaches,
so if present it is removed by precipitation with ammo-
nium carbonate. Iron prevents the bleaching by fluorine
and by its color confuses the test, therefore it must be
removed. A suitable sample contains .01 to .00005 gram
fluorine. This method is more accurate than gravimetric
methods for amounts below two percent and will not only
detect but estimate amounts so small as not to be detected
by gravimetric methods.
The sample is fused with three to five grams sodium
potassium carbonate fusion mixture and the fusion dis-
solved in hot water as far as possible. Two grams of
ammonium carbonate are then added and the solution
evaporated on the water bath to small bulk, the ammo-
nium carbonate at the same time being decomposed.
Iron, aluminum and silica are precipitated and may now
be filtered out. A standard titanium solution is prepared
by the solution of one gram TiOg in concentrated sulfuric
acid and diluted to one liter.^ This solution contains
.001 gram titanium dioxide per c.c. Four c.c. of hy-
1 Scott gives a somewhat more elaborate method of solution. An
intimate mixture of one gram of TiOa and three grams of ammonium
persulfate is heated until the vigorous action has ceased and am-
monium sulfate is expelled. The residue is treated with twenty c.c.
strong sulfuric acid, heated to fuming and, when cold, poured into
about 800 c.c. of cold water. When the suspended salt has dissolved,
57.5 c.c. of strong sulfuric acid are added, and the solution made up
to 1000 c.c. Fifty c.c. or more of the solution should be analyzed
104 OOLOBIMETEIC ANALYSIS.
drogen peroxide are added to the solution to be tested,
followed by ten c.c. of the above titanium solution and
five C.C. of sulfuric acid. The addition of the acid should
render the solution slightly acid. If such is not the case
a further amount of acid is added until the solution is
very slightly acid. More acid is now added, dependent
upon the estimated fluorine content of the solution. For
the maximum sample, .01 gram, twelve c.c. of acid are
used, for the minimum sample, .00005 gram, one c.c. will
be sufficient. The amount used is graded according to the
amount present between these two extremes. The solu-
tion is then diluted to 50 to 100 c.c. according to the in-
tensity of color and the original amount of the solution
A standard fluorine solution must be made up if the
standard is also to be bleached. This consists of 1.2403
grams potassium zirconium fluoride (potassium fluozir-
conate, KgZrFe) dissolved in water and diluted to one
liter. This solution contains .0005 gram fluorine per c.c.
For determination by this method the fluorine in the
sample must be estimated, a similar amount added to
ten C.C. of titanium solution treated with hydrogen perox-
ide and the agreement with the sample noted. If this
does not agree it is only a matter of a short procedure to
make up another which will more nearly approximate the
The desired result may be obtained from the factor
figured by Steiger^ from a large number of experiments.
The solution bleached with fluorine may be estimated by
first determining the apparent titanium present and sub-
tracting this from the actual weight of titanium known
to be present. Results show that fluorine will bleach
slightly more than twice its own weight of titanium,
1 Steiger, J. A. C. S., SO, 219.
FLUORINE, CHLORINE AND PERCHLORATES. 105
accurately 35:75. For general estimation the difference
between the two titanium readings may therefore be di-
vided by two and this taken, for accurate work the differ-
ence between the titanium readings is multiplied by .4667.
Factors for allowing for the presence of acid and of alkali,
etc., have been figured but the tables are too long for
inclusion here. For those records reference should be
made to Steiger as indicated. The errors due to the
presence of alkaline sulfates and excess acid are so small
that they may well be neglected.
Chlorine by 0-Tolidine. ,
Free chlorine present may be estimated by the green
color produced by it in reaction with o-tolidine. The
method^ is especially designed for water analysis but may
be adapted to other determinations of free chlorine. The
reagent is so delicate that it will detect .00000005 gram
of chlorine per c.c. of water, or to phrase it in terms of
water analysis, .005 part per million. The sample should
be twenty-five c.c. of a water high in chlorine or fifty c.c.
of one low in that constituent.
Five C.C. of a solution of one gram of the reagent in a
liter of ten percent hydrochloric acid are added. The
color appears at once. The use of a natural series of
standards is not advisable as they will not keep from
day to day but the use of artifical standards made from
the copper-iron or copper-dichromate series is possible.
Because of the nature of the test substance the method
of duplication would be practically impossible to control.
Dilution or balancing methods may be used, the standard
should be another solution whose chlorine content has
been determined, treated with the same proportional
amount of the reagent as the sample.
1 J. Ind. Eng. Chem., 5, 915.
106 COLORIMETBIO ANALYSIS.
Perchlorates by Methylene Blue.
The reaction of perchlorates with methylene blue may
be used for the estimation of the amount of perchlorate
present.^ This method is used in the test of soluble sub-
stances such as salts for the presence of these compounds,
with particular reference to the analysis of Chili salt-
peter. The sample used is one gram except in rare cases.
The method has a considerable range.
The sample is dissolved in water and diluted to 25 c.c.
Two c.c. of a solution of one gram nitrosodimethylaniline
in alcohol diluted to one liter with water are then added.
The preparation of a series of standards for use with this
is advisable, not permanent standards but temporary
standards, easily replaced. A standard solution is made
up of potassium chlorate by the solution of .1468 gram
in water and dilution to one liter. For use ten c.c. of
this are diluted to 100 c.c. and will then contain .00001
gram ClOg per c.c. The non-permanent standards for
the test may be made up by use of one to ten c.c. of this
solution. If the tests are all being made on the same
basic substance as, for example, on Chili saltpeter it is
well to add that substance in large amount to the standard
solution before dilution to the line so that the standard
may contain approximately the same amount as the
sample solution. It is also possible to add the solution
of the salt upon which work is being done to the non-
permanent standards when diluting them to the same
volume as the sample, before treatment with the reagent.
It is necessary that the sample and standards be allowed
to stand for several hours to fully bring out the colors.
The sample is then compared with the series of standards
prepared at the same time and an estimation made of its
1 Arch. Sci. Phys. Nat., i^^ 210.
NITRIC AND NITROUS ACIDS, AND AMMONIA.
The occurrence of these nitrogen compounds is frequent
and the determinations made of them are many. The
test for ammonia with Nessler's reagent is one of the
oldest of methods for this sort of work. The above sub-
FlG. 15. Colorimeter with Lamp House Suitable for Night Work.
stances have to be frequently determined in water sup-
plies and sewage effluents. The presence of nitric acid
in sulfuric acid supposed to be chemically pure is also
often to be detected and estimated by these methods.
108 OOLOBIMBTEIG ANALYSIS.
Method A. Nitric Acid by Brucine Eeaction.
Nitric acid may be determined, colorimetrically, by its
reaction with brucine in the presence of sulfuric acid,
making the test by the sulfur yellow that follows the
initial red coloration rather than by the original colora-
tion which may not be relied on.^ If nitrous acid is not
to show in the final results there must be present two
parts of sulfuric acid for every part of water. This
method is given on the assumption that only nitric acid
is to be determined. In case it is desired to determine
nitrous acid as well as nitric acid, lessening the amount
of sulfuric acid used, so that there would be present two
parts of water to one of sulfuric acid, would have the
effect of causing both to show. In case the solution being
tested contains much organic matter or ferrous iron these
must be oxidised by the addition of permanganate until it
is in slight excess. If this oxidation is carried out it
must be taken into account that nitrous acid present will
be oxidised at the same time to nitric acid and that if the
nitric acid in the presence of nitrous acid is to be deter-
mined it will be necessary to separately determine the
nitrous acid, calculate it to the form of nitric acid and
subtract the result obtained from the total nitric acid
shown by the test.
This method is used for determinations on water,
sewage eflSuents, and sulfuric acid, also for the analysis
of salts for traces of nitric acid not removed in their
purification. The sample chosen for the test should con-
tain .00001 to .0002 gram nitric acid. If a liquid, a quan-
tity to fall within those limits may be chosen.
The sample, if a solid, is dissolved in water and diluted
to not over twenty c.c. The sample, if of a liquid, must
be under that volume and is diluted to approximately
1 Chem. Zeit, 23, 454; 25, 586.
NITEIC AND NITEOUS ACIDS, AMMONIA. 109
twenty c.c. The determinations are best made in Nessler
tubes or some type of graduated tubes. One c.c. of a con-
centrated solution of brucine is added to the sample and
then 30 c.c. of concentrated sulfuric acid. If the test is
being made on sulfuric acid for nitric acid as impurity,
ten C.C. of water and ten c.c. of acid are substituted for
this addition of acid, leaving the volume somewhat
smaller than in the other case. Care must be used in the
addition of this sulfuric acid as it must be carefully
poured down the side of the tube without causing the
water to boil. If care is not used the water will boil and
loss of nitric acid will result.
The most convenient method for making the test is
by duplication. The blank of fifteen c.c. of water and
five c.c. of sulfuric acid is treated as specified for the
sample. The blank should show no color at this point,
if it does the solution must be rejected unless it is known
that the sulfuric acid used contained a small amount of
impurity in the form of nitrate. In that case the con-
tamination of sample and blank may be assumed to be the
same and may be disregarded. The standard solution for
addition to the blank is made by dissolving .1872 gram
KNO3 in water and diluting to one liter. This standard
then contains .0001 gram N2O5 or .000115 gram NO3 or
.00002594 gram Ng per c.c. The standard is run in and
the sample duplicated in the usual manner.
The sample shows first an orange yellow changing to
light yellow, on the addition of the sulfuric acid. Simi-
larly the color of the blank will show first orange chang-
ing to yellow. If the carrying out of the test is delayed
the solutions may become cooled in which case the change
of color will be slowed down. In that case it is best to
heat the solutions over a flame, to have them at sufficient
heat to show proper color reactions.
110 COLOEIMETEIG ANALYSIS.
Method B. Nitric Acid by Diphenylbenzidinb.
The test for nitrates with diphenylamine is not abso-
lutely satisfactory as some elements of the test do not
seem possible to control.^ It has been found by experi-
ment that diphenylbenzidine is formed in the solution from
the diphenylamine and that the use of this as the original
substance gives more satisfactory results. In case di-
phenylbenzidine is not available diphenylamine may be
used as a substitute following the same directions as
those given for the former reagent. The sample chosen
is to be five c.c. of solution which should contain between
.000001 and .0000001 gram nitrogen per c.c. The best
way of handling the test is to make up simultaneously a
series of nonpermanent standards.^
A standard solution may be made up by dissolving
.3608 gram potassium nitrate in water and making up
to one liter. Ten c.c. of this solution made up to 100 c.c.
will then contain .000005 gram nitrogen per c.c. From
this solution standards are to be made up with .1, .2, .3,
c.c, etc., of the standard solution diluting each to five c.c,
similar to the volume of the sample.
To each of the standards and to the five cc sample
solution twelve cc of concentrated sulfuric acid are added
and the solutions set in water to cool. The reagent used
is .1 gram diphenylbenzidine in 100 cc concentrated sul-
furic acid. The tubes having been cooled, three c.c. of
this are added to each of the test tubes and the color of
the sample compared with that of the standards, after ten
minutes have been allowed for the color to show. If it is
desired to obtain the total nitrogen, nitrites may be oxi-
dised to nitrates by adding permanganate before proceed-
ing with the determination. For the determination of
1 Z. Anal. Chem., 56, 28.
2 Jour. Chem. Soc., 105, 1157.
NITRIC AND NITROUS ACIDS, AMMONIA. m
nitrites the total nitrogen and the nitrates may be deter-
mined and the nitrites present are then represented by the
difference in the two nitrogen determinations.
The mixing of the reagent with the solution is accom-
plished by lightly stirring. Shaking is to be avoided as
it lessens the color produced.
Method C. Nitric Acid by Phenolsulfonic Acid.
The yellow color produced by nitrates is reaction with
phenolsulfonic acid is found to be a satisfactory method
of determining the nitrates present in a solution such as,
for example, drinking water. The phenolsulfonic acid
for use is prepared^ by heating ten grams of phenol on
the water bath for two hours with 60 grams concentrated
sulfuric acid and 30 grams fuming sulfuric acid, or four
hours with 150 grams concentrated sulfuric acid. The
sample, if colored, must first be decolorized by the addi-
tion of aluminum hydroxide, as is usual in water purifica-
tion. The sample of water or solution selected should
contain less than .0001 gram nitrogen, preferably less than
half that amount.
The sample is evaporated nearly to dryness on the
water bath and the last few drops of solution then allowed
to evaporate at room temperature in a place sheltered
from dust. One c.c. of phenolsulfonic acid is then added
to the residue and thoroly rubbed over it with a glass rod.
Ten c.c. of distilled water are now added and stirred until
all is dissolved. Ammonium or potassium hydroxide is
then added until the solution is alkaline after which it is
poured into the tube or bottle in which comparison is
to be made.
The standard is made up by dissolving .7217 gram of
pure potassium nitrate in water and diluting to one liter.
1 American Committee on Standard Methods of Water Analysis.
112 COLORIMETEIC ANALYSIS.
Ten C.C. of this solution are then evaporated the same as
was specified for the sample, moistened with two e.c. of
phenolsulfonic acid and diluted to one liter for use as a
standard. Each c.c. contains .000001 gram nitrogen.
This standard is suitable for making up a series of stand-
ards or for the method of duplication.
For duplication the sample mentioned above is poured
into a Nessler tube and diluted to 50 c.c. The standard
is then run into a blank of 25 c.c. and colors and volumes
equalized. For the preparation of a series of standards
the following volumes of the dilute standard solution are
used. The amount of nitrogen represented by each is
shown opposite. The sample should be diluted to 100 c.c.
for this method, as should also each of the standards.
Five c.c. of concentrated ammonia are to be added to the
solution of standard before it is made up to the final
Vol. of Dil. Stan. Sol. Usecl. Nitrogen Represented in Grama.
In case chlorides are present add two c.c. of the reagent
to the solution and 1.5 c.c. concentrated sulfuric acid be-
fore evaporation to small volume.^ The evaporation to
small volume may then be carried out on the steam bath,
1 J. Ind. Eng. Chem., 9, 585.
NITRIC AND NITROUS ACIDS, AMMONIA. 113
completing evaporation to the final small volume on a
water bath at not over 70 degrees, after which the method
is followed out. Chlorides are thus removed without
serious loss of nitrates.
Method D. Nitric Acid by Pyrogallol.
This method is more suited to confirmation of another
estimate or to quick guesses at the approximate nitrogen
contents of a sewage effluent or of water than to other use.
Ten c.c. of the sample are placed in a test tube and ap-
proximately .2 gram pyrogallol added and thoroly mixed
with the sample.^ A pipette partially filled with sulfuric
acid is then inserted, the acid being held in the pipette by
keeping the finger over the upper end until inserted, and
two c.c. of sulfuric acid allowed to flow out as a seperate
layer at the bottom of the tube, the pipette being again
removed with the finger over the aperture. Upon the
addition of .1 gram of dry powdered sodium chloride an
effervescence is set up at the point where the two layers
join and a purple ring proportional in size and intensity
to the amount of nitrate present, is formed.
A standard solution is made up by dissolving .1872
gram potassium nitrate in water and diluting to one liter.
This solution contains .0001 gram NgOg per c.c. or .000115
gram NO3. The eye of the operator using this test soon
becomes so used to the estimation that he can tell pretty
accurately from the first glance the amount of nitrate
present. For confirmation of this he may take that
amount of standard and another sample and, by carry-
ing the two tests thru at once, see if they appear to be
1 Report of the Royal Commission on Sewage Disposal, Vol. IV,
Part V, p. 23.
114 COLORIMETRIC ANALYSIS.
Method A. Nitrous acid by Sulfanilic Acid and
The red coloration which appears after a time when
acetic acid solutions of sulfanilic acid and a-naphthyla-
mine are acted on by nitrous acid may be used for the
determination of the amount of nitrous acid present. In
the process^ the sulfanilic acid is converted by the nitrous
acid into the corresponding diazo compound and the
latter reacts with the a-naphthylamine to form a red azo
dye. The full color which will result does not appear
for several hours, often not for days, but if the tempera-
ture and other conditions of the standard and sample are
identical the color will appear at the same rate and after
only a very short time the estimation may be made.
The standard solution of nitrite is made by preparing
nitrosyl sulfuric acid. .0493 gram pure sodium nitrite is
dissolved in 100 c.c. water, and ten c.c. of this solution
added to 90 c.c. concentrated sulfuric acid. This solution
contains .00001 gram nitrogen per c.c. in the form of
nitrite. The solution of sulfanilic acid is prepared by
warming one gram with 14.7 grams glacial acetic acid
and 15 c.c. water. A further 270 c.c. of water are then
added, the solution being kept stirred. Similarly the
a-naphthylamine is prepared by dissolving .2 gram in
14.7 grams glacial acetic acid and 25 c.c.^ water, after
which 300 c.c. of water are added. The solutions are
mixed for use but only small quantities should be so pre-
pared at a time.
For the analysis twenty c.c. of the sample are placed in
one color comparison tube and eighteen c.c. of pure water
in the other. Two or three c.c. of a mixture of the above
reagents are added to each and an amount of the standard
1 Fowler, Sewage Works Analyses, p. 64.
NITRIC AND NITROUS AClBS, AMMONIA. US
added tx) the blank equal to the amount of nitrite esti-
mated to be present. The colors will be dark enuf after
five minutes for the operator to see how well they com-
pare. If they are not identical an experienced operator
can tell the variation in the amount of nitrous acid be-
tween the two solutions and may confirm his view by
adding that amount of standard to a blank and running
that with a new amount of sample, comparing these after
Method B. Nitrous acid by Metaphenylenediamine
Metaphenylenediamine reacts with nitrous acid in solu-
tion to produce triaminoazobenzene (bismark brown), a
substance of pronounced color.^ Ferric compounds are
apt to cause trouble but will interfere less if a consider-
able excess of sulfuric acid is present. The presence of
organic matter has no effect. The color produced ranges
from yellow to a yellowish brown.
The reagent is prepared by dissolving 5 grams of
metaphenylenediamine in water, adding sulfuric acid at
once until the liquid is distinctly acid and diluting to one
liter. If the solution so made up shows color it may be
decolorized with animal charcoal. The standard solution
is the same as in the preceding test, .0493 gram pure
sodium nitrite dissolved in 100 c.c. water and ten c.c. of
this solution diluted to 100 c.c. with concentrated sul-
furic acid. The standard contains .00001 gram nitrogen
The comparison is made on 100 c.c. of the solution to be
tested, acidified with two c.c. dilute sulfuric acid, to which
is added one c.c. of the reagent. A series of standards
may be prepared, using the nitrosyl sulfuric acid pre-
1 Ber., 11, 624.
116 COLORIMETRTG ANALYSIS.
pared above and diluting the amount used to 100 c.c.
before the addition of the reagent. The color appears
quickly so that a duplicate may conveniently be prepared
from 75 c.c. of water. A standard for dilution and bal-
ancing methods is prepared by treating ten c.c. of the
nitrosyl sulfuric acid with two c.c. of the reagent and
diluting to 100 c.c. The resultant standard contains
.000001 gram nitrogen per c.c.
Method C. Nitrous Acid by Zinc Iodide Starch
The blue color produced by nitrous acid in reaction
with zinc iodide starch solution is the basis for this
determination. The test has been estimated to be twenty
times as delicate^ as the metaphenylenediamine reaction
(method B). A color will show in seven minutes if
.00000025 gram nitrous acid is present.
The starch solution is prepared by boiling five grams
of starch and 20 grams stannous chloride in 100 c.c. dis-
tilled water for some hours until the starch has almost
entirely disappeared. The water is replaced as it evapo-
rates. To this solution add two grams zinc iodide (Znl2)
and dilute to one liter. This solution should 'be allowed
to settle for several weeks, decanting the clear solution as
needed. For the determination add four c.c. of this solu-
tion to fifty c.c. of the sample acidified with two c.c. sul-
furic acid. The blue color develops most rapidly in the
light. A standard solution of sodium nitrite is made up
by dissolving .4925 gram pure sodium nitrite in water
and making it up to one liter. Ten c.c. of this solution
are then accurately pipetted out and made up to one liter
giving a standard solution containing .000001 gram nitro-
1 Analyst, S9, 350.
NITRIC AND NITROUS ACIDS, AMMONIA. ny
gen or .000003285 gram NOg or .000004426 gram NO3 per
c.c. For making up a series of standards this standard
is used in varying amounts. Because of the fact that the
color takes some time to appear the use of the duplication
method is not advisable. The balancing method and di-
lution method are carried out by using the same standard
but before the last dilution to one liter fifteen c.c. of the
reagent are added. This will then show the characteristic
color and have the same value as the standard above.
Method D. Nitrous Acid by a-Naphthylamine
A very delicate nitrous acid test is obtained by use of
a-naphthylamine hydrochloride with tartaric acid. The
reagent may be made up in such a form that it will keep
indefinitely. The content of nitrous acid of the water
must be very small, not over .00015 gram per liter or the
addition of the reagent will cause a precipitate.^ The
sample may be diluted if the content is too high.
The reagent for the test consists of one part a-naph-
thalamine hydrochloride to ten parts sulfuric acid and
89 parts tartaric acid. A fifty c.c. sample is treated with
one c.c. of this reagent and the results will show at once.
If the sample is very dilute it may be well to use 100 c.c.
A standard nitrite solution is made up by dissolving .4925
gram pure sodium nitrite in a liter of water. A series
of standards is not to 'be recommended for as delicate
a test as this. For duplication the above standard is
diluted, ten c.c. to 100, and will then contain .00001 gram
nitrogen per c.c, as nitrite. For factor as nitrate see pre-
ceding test. As blank for the duplication method use
48 c.c. water and one c.c. of the reagent. A standard for
1 Chem. Weekblad, ii, 1115.
118 COLORIMBTRIO ANALYSIS.
the use of dilution or balancing methods is made by ad-
dition of one c.c. of the above standard to 800 c.c. of
water, adding one c.c. of the reagent and making up to
one liter. This solution will show the color representing
.0000001 gram nitrogen as nitrite per c.c. Dihite as this
is, it is nearly to the upper limit that may be tested by
this method so from this some idea of the delicacy of the
test may be gained.
Method A. Ammonia by Nessler's Beagent.
In reaction with ammonia Nessler's reagent produces a
yellow to brown color which is a very accurate indicator
of the amount of ammonia present in the solution. The
presence of calcium or magnesium is undesirable as those
are precipitated with the reagent and the presence of the
precipitate obscures the results. Rather than precipitate
and filter it is usual to hold them in solution by adding a
few c.c. of a solution of 50 grams Rochelle salt in 100 c.c.
of water. For the preservation of this solution five c.c.
of Nessler's reagent should be added to it at the time of
Nessler's reagent, by a recent and highly approved
formula is prepared as follows,^ dissolve 2.5 grams KI in
three grams water, add 3.5 grams Hgig and, when this is
all dissolved, add 100 grams of a 15 percent solution of
KOH. Allow this to stand and settle and decant. If
it is necessary to use the reagent at once it should he
mixed with a little talc, and filtered thru sand if possible.
The sample used may be of drinking water or sewage
effluent, or a solution of some substance containing am-
monia as impurity.
To 100 c.c. of the sample solution add two or three
C.C. of the Rochelle salt solution followed by the same
X Apoth. Ztg., S9, 972.
NITRIC AND NITROUS ACIDS, AMMONIA. HQ
quantity of Nessler's reagent. The color appears at once.
The color is fairly permanent and a series of standards
may satisfactorily be produced. For this a standard
solution is prepared by dissolving .3140 gram ammonium
chloride in water and diluting to one liter. The stand-
ard then contains .0001 gram ammonia per c.c. For the
duplication method the blank should be 95 c.c. of water.
A standard for the dilution or balancing methods is made
up by adding to 100 c.c. of the above standard, twenty
c.c. of the Rochelle salt solution and twenty c.c. of Ness-
ler's reagent and diluting to one liter. This latter stand-
ard then contains .00001 gram ammonia per c.c. For
some uses it may be necessary to again dilute this latter
standard to one tenth of its strength.
Method B. Ammonia by Phenol.
The reaction of ammonia with phenol^ gives a method
of estimation of ammonia more rapid than the test with
Nessler's reagent and just as delicate but not one admit-
ting of as grea4; accuracy. For careful work its accu-
racy is not to be depended on. The time for a complete
determination should not exceed four minutes. The
method is applicable to all cases where ammonia is to
be determined. Calcium is not affected by the test but
the presence of a considerable amount of free acid spoils
To five c.c. of the solution to be tested add one c.c. of a
dilute solution of sodium hypochlorite (NaOCl) and one
c.c. of a 4 percent solution of phenol. This is then
diluted to ten c.c. The full intensity of the color shows
on heating in boiling water for two minutes.
Comparison may be made with a series of standards.
For their preparation an ammonium chloride solution
iGaa World (Coking Section), 64, No. 1654, 10.
120 (X)LORIMBTBia ANALYSIS.
containing .3140 gram to the liter is prepared. Ten c.c.
of this solution are diluted to 100 c.c. thus containing
.00001 gram ammonia per c.c. This standard is also
suitable for determination of results by the duplication
method, using a blank of five c.c. of water but diluting to
only nine c.c. instead of ten before the addition of the
standard. The application of the duplication method is
not very satisfactory. Ten c.c. of the original am-
monium chloride solution treated with five c.c. hypo-
chlorite solution and five c.c. 4 percent phenol solution are
diluted to one liter and will then on heating show the
color. The content of this standard is .000001 gram am-
monia per c.c, an amount suitable for dilution or balanc-
ing methods. The method is delicate enuf to detect
.0000001 gram ammonia in the five c.c. sample.
PHOSPHORUS, SILICA AND BORON.
These three substances, found occurring naturally in
the earth, are conveniently determined by colorimetric
methods in small amounts, somewhat more accurately
than by gravimetric methods. The first two conflict
when determined in the same solution so that it has been
found advisable to work out a new method whereby, by
introduction of the proper corrections, both may be deter-
mined in the same solution, each in the presence of the
other. Boron is to be determined in the form of boric
acid in which form it occurs to some extent as a preserva-
tive in food.
Method A. Phosphorus as the Phosphomolybdate.
Since the gravimetric method of analysis for phos-
phorus by precipitation of the phosphomolybdate is very
inaccurate for small amounts of phosphorus, the solution
of these small amounts of phosphomolybdate may be
tested colorimetrically.^ Silica must be removed or the
results will be too high, for which removal a method is
given here. The silica forms a silioomolybdate which
has a color similar to that of the phosphomolybdate. A
method has also been worked out for the determination
of the two in the presence of each other. For further
details of that method see Silica, this same chapter.
Ten to 100 c.c. of solution which must contain less than
.0005 gram phosphorus are evaporated to dryness. When
the solution is partially dry add three c.c. nitric acid.
1 J. A. C. S., 26, 975.
122 COIiOBIMETBlO ANALYSIS.
The residue is then heated at 100 degrees for two hours.
If the substance being tested is such that it contains no
silica this dehydration may be omitted. The residue
after dehydration is dissolved in water. It will not be
necessary to filter as the loss due to filtration would be
greater than that possible due to the presence of a small
amount of precipitate of silica in the solution. Two
c.c. of nitric acid are added and four c.c. of a solution of
50 grams of ammonium molybdate in a liter of water.
After three minutes the color is suitable for comparison.
As a standard dissolve .5043 gram of pure crystallized
sodium acid phosphate (NajHPO^, I2H2O) in water,
add 100 C.C. nitric acid and dilute to one liter. This
solution contains .0001 gram P2O5 per c.c. A series of
standards prepared from this must be replaced daily as
the darker solutions precipitate out after a time and the
lighter solutions fade. The fact that the color is not
complete for some minutes renders duplication incon-
venient. For use with the dilution or balancing methods
ten c.c. of the standard are diluted with 75 c.c. of water,
five c.c. of the molybdate solution added and the solution
made up to 100 c.c. This standard will contain .00001
gram PgOg per c.c.
Method B. Phosphorus, Separated by Precipitation
AS Magnesium Phosphate.
This method is similar to that given for magnesium.
The phosphate^ is precipitated as magnesium phosphate
by the addition of an excess of magnesium chloride, the
precipitate is filtered off, dissolved in nitric acid and
tested colorimetrically by the addition of a solution of
ammonium molybdate. The advantages of this method
are that all silica is removed from the solution being
1 J. A. C. S., fS6, 1463,
PHOSPHORUS, SILICA AND BOBON. 123
tested, thus preventing errors due to the silicomolybdate,
and that the organic matter is removed from the final
solution. The interference of calcium is prevented as in
the magnesium test by the addition of ammonium
oxalate. Experiments have shown that satisfactory
samples should range between .004 and .0005 gram phos-
phorus. Results obtained in the presence of various dis-
turbing factors were uniformly satisfactory.
One drop of ammonia and two or three drops of am-
monium oxalate are added to the sample solution after
which it is evaporated to dryness on the water bath. A
solution is made up of 13 grams magnesium chloride and
twenty grams ammonium chloride in a liter of water
which includes fifty c.c. strong ammonia. One c.c. of
this solution is added to the dried precipitate and the
two well mixed with a glass rod. The precipitate is then
washed out onto the filter with five c.c. dilute ammonia
and the dish and filter washed with further successive
portions until the volume of the filtrate reaches 50 c.c.
The dish and filter are next washed with five c.c. pure
water and a new beaker substituted to catch further
washings. Five c.c. of concentrated nitric acid are used
to dissolve any precipitate remaining on the dish and the
precipitate on the filter carefully dissolved with this same
acid. Dish and filter are washed with successive five c.c.
portions of hot water until the filtrate amounts to 45 c.c.
Four c.c. of a solution of 50 grams ammonium molybdate
in a liter of water are then added and the comparison
made after twenty minutes.
The standard is made up by solution of .5043 grams
sodium acid phosphate (Na2HP045 I2H2O) in water
with the addition of 100 c.c. nitric acid, and dilution to
one liter. A series of standards may be prepared from
this solution, which contains .0001 gram P2O5 per cc.c. A
124 OOLOBIMBTRIO ANALYSIS.
duplicate cannot well be made up since the color is so
long in coming. A standard for dilution or balancing
methods is made up by adding to ten c.c. of the above
standard, 70 c.c. water, 9 c.c. nitric acid and 8 c.c. am-
monium molybdate solution and making up to 100 c.c.
This standard which contains .00001 gram PgOg (per c.c.)
must stand for twenty minutes before use in order to bring
out the color.
Silica by Ammonium Molybdate in the Presence of
In reaction with ammonium molybdate silica produces
a compound, ammonium silicomolybdate, which has a
color similar to that of ammonium phosphomolybdate,
a greenish yellow. When silica is to be tested for in the
solution and it is known that no phosphorus is present
the test is carried out identically the same as in the test
for phosphorus. Method A. The color caused by the
silica diflPers from that caused by the phosphorus in that
it reaches its full intensity only after some hours, whereas
phosphorus shows its full color after twenty minutes.
Another property of the silica coloration, upon which this
test is based is that its intensity at the end of an hour
and twenty minutes is twice that at the end of twenty
The samples are treated as in the preceding Method A
up to the addition of the ammonium molybdate. Two
samples of the same substance or solution to be tested
must be so prepared at the same time. Also a standard
must be available which contains only phosphorus. One
sample and the standard are acidified and allowed to
stand for twenty minutes and tested against each other.
At the time these are acidified and the ammonium molyb-
date added a similar amount of ammonium molybdate is
1 J. A. C. S., S6, 975.
PHOSPHORUS, SILICA AND BORON. 125
added to the other sample but no nitric acid. After one
hour has elapsed this second sample is acidified with nitric
acid and allowed to stand for twenty minutes. It is then
tested against the same standard as the other sample.
The reading of the first sample is called the A reading
and the reading of the second sample the B reading.
From the law given above the phosphorus can then be
If B reading is twice A reading there is no phosphorus
present but only silica. If B reading is not twice A
reading the difference between them is subtracted from A
reading and the remainder is phosphorus. To repeat,
the silica reading at the end of one hour and twenty
minutes from the time the ammonium molybdate as
added and the end of twenty minutes from the time the
nitric acid was added to it represents the same amount
of phosphorus as the reading at the end of twenty
minutes by the first sample and in addition a reading for
silica twice that given at the end of twenty minutes by
the first sample.
The phosphorus having been determined by this method
the silica may be determined by the same method taking
no account of the phosphorus and making the test
against a standard containing only silica. This silica
determination may then be corrected by allowing for the
phosphorus previously determined. This silica standard
may be prepared at the same time as the original samples
and the same solution used, as the first sample may be
kept for four to five hours and tested against a standard
prepared a similar time before. The test is by dilution
If a solution of known silica content is available it is
best to use that. If such is not available .3657 gram
potassium silioo fluoride (potassium fluosilicate KaSiFg)
126 (X)IX>BIMBTRia ANALYSIS.
is dissolved in hydrochloric acid using as little acid as
posible, and diluted to one liter. This standard contains
.0001 gram SiOg per c.c. Such quantities of it may be
used as are estimated to be necessary to counterbalance
the contents of the solution being tested.
Method A. Boric Acid by Curcumin.
The red coloration produced by boric acid when treated
with oxalic acid and curcumin is especially adapted to
the estimation of the quantity of boric acid present in food
as in adulterant. The advantage is not in the speed but
in the greater accuracy of the method over the gravimetric
method. The weight of B2O3 present may be as much as
The sample^ placed in a platinum or porcelain casserol
is made strongly alkaline and evaporated to dryness.
The residue is acidified with hydrochloric acid and ex-
tracted with several successive portions of hot water.
The extracts are filtered and the filter transferred to a
dish, made alkaline with barium hydroxide and burned
to ash. This ash is dissolved in hydrochloric acid and
added to the original filtrate, and the volume of the filtrate
made up to 100 c.c. Ten c.c. of this solution are then
mixed with ten to fifteen grams purified sand in a porce-
lain dish and made alkaline with barium hydroxide.
Evaporate to dryness on a paraffine bath, add enough
dilute hydrochloric acid to make the contents of the dish
acid, two c.c. saturated solution of oxalic acid and two c.c.
of an alcoholic solution of curcumin, one gram to the liter.
Mix the contents of the dish well and cover with a glass
funnel whose stem is connected to a set of potash bulbs
containing barium hydroxide. The other end of the set
of potash bulbs is connected to an aspirator, the dish
placed on a paraffine bath, the potash bulbs set in water
1 C. N., 87, 27.
PHOSPHORUS, SILICA AND BORON. 127
and air passed thru by suction until the mass is dry. One
c.c. of the curcumin solution is added to the dish and it is
Extract the contents of the dish with several portions
of alcohol and add the contents of the bulbs to the residue
in the dish. This is dried, made acid with hydrochloric
acid, treated further with reagents as was the original
substance, and dried. The alcoholic extract from this is
added to the previous extract and the color is thus
A standard solution of boric acid is made up by solu-
tion of .2886 gram sodium tetraborate (borax NagB^O^,
lOHgO) and contains .0001 gram BgOg per c.c. Ten c.c.
of this solution are treated in the same manner as the
sample and analysis made by dilution with alcohol. It is
obvious that the series of standards or duplication methods
would be out of the question. If one tube apparently has
more of an orange tint than the other that is due to the
presence of an excess of curcumin and a drop or two
should be added to the other tube until the colorations are
similar, after which dilution may be more accurately car-
Method B. Boric Aero by Turmeric Paper.
The amount of boric acid in a sample may be esti-
mated by treatment with methyl alcohol, distillation of
the resultant methyl borate into alkali and, after further
treatment, comparing the stain made on a standard tur-
meric paper with those made by known quantities of
boric acid. The sample is chosen according to the
amount of boric acid suspected. If the matter is of
animal origin ten grams are ordinarily used, if of vege-
table origin one gram is usually suflScient.
The sample^ is heated in platinum until the organic
1 Oompt. Rend., 157^ 1433.
128 COLOBIMETBia ANALYSIS.
matter is all removed. Then treat the ash with five to
ten c.c. of phosphoric acid and rinse into a flask. Wash
out the dish with twenty c.c. methyl alcohol and add to
the solution in the flask. Distill on the steam bath re-
ceiving the distillate in a platinum crucible containing a
few drops of normal sodium carbonate solution. Add
ten c.c. more of methyl alcohol to the flask and distill
this over into the original distillate. This should carry
over with it the last traces of methyl borate. Evaporate
the distillate to dryness, cool and add four drops hydro-
chloric acid and one half c.c. of water. Wash this into a
small vial and dilute to one and a half c.c.
A turmeric paper is made by soaking in a solution of
turmeric and drying, after squeezing out the excess of
the solution. It is essential that the papers be of uni-
form thickness, width and saturation with the reagent. A
good grade of drafting paper is very satisfactory. The
width may be made such that it readily admits of their
introduction into the vial used for the determination. A
strip of this paper is immersed in the vial to a depth of
15 mm. and the vial exposed to a heat of 35 degrees for
three hours. If time is not a consideration the vials may
be allowed to stand at room temperature for 24 hours
after which the results will be the same as by heating.
The intensity of the red coloration produced on the
paper is a measure of the amount of boric acid present in
The same standard as in the previous test, .2886 gram
sodium tetraborate (borax, NagB^Oy, lOHgO) to a liter
of water, is used for the preparation of the standards.
This standard contains .0001 gram BgOg per c.c. The
color of the standard papers so prepared is permanent
and by protecting them from dust they may be kept
OXYGEN AND HYDEOGEN PEROXIDE.
The determination of the dissolved oxygen in drink-
ing water and in sewage effluents is of vital importance
as it is also in the preliminary examination of streams
proposed as sources of sewage disposal. The use of hy-
drogen peroxide as an antiseptic and as a reagent requires
that its strength be known.
Method A. Oxygen by Cuprous Chloride.
The properties of the copper chlorides in ammoniacal
solution, cuprous chloride being colorless and cupric chlo-
ride a deep blue, may be made use of for the determination
of oxygen in a solution.^ The addition of cuprous chlo-
ride to the water will result in a blue color due to its
oxidation to cupric chloride which color will be propor-
tional to the amount of available oxygen in the solution
tested. If the sample contained much calcium this would
become turbid on the addition of the ammonia to make
the solution alkaline, therefore two or three c.c. of hot
saturated solution of ammonium chloride are added to
the sample before the addition of the other reagents. If
the test is being made on a sewage effluent or other solu-
tion which is slightly colored, a similar yellow may be
added to the standard in the form of some yellow dye
such as paranitrophenol. The error which will be intro-
duced by the original solution being slightly yellow is not
1 J. Soc. Chem. Ind., SO, 1071.
130 COLORIMETRIO ANALYSIS.
The . sample is gathered in a bottle and the bottle
tightly corked, taking care that there is not an air bubble
left below the cork. A special apparatus is used to
transfer this to the tube in which the test is to be made.
A double-hole stopper is prepared to fit the sample
bottle, with two tubes, one of which runs to the bottom
of the bottle and one of which only enters the cork. A
rubber tube is attached to the shorter tube. For the trans-
fer of a sample from the bottle to the tube in which it
is to be tested the rubber tube, which should be about a
foot long, is filled half full with kerosene oil. The size
of tubing used should not be over five to eight mm.
internal diameter. The double hole stopper is then care-
fully fitted to the bottle of sample without introducing
air. The liquids are next allowed to flow out the rubber
tube. The oil will flow ahead if the tube is carefully
managed and thus sweep out all air and prevent contact
of the sample with the air. In the tube in which com-
parison is to be made the oil will rise to the surface and
the sample then be run in under the layer of oil. The
long tube added to the bottle serves as an air inlet, that
the contents may run out. A small amount of the oil
will always be introduced into the bottle in the process
of fitting the stopper, which will rise to the upper sur-
face of the liquid. The bottle is to be inverted as soon as
satisfactory connections have been made and the oil will
then form a layer at the upper, formerly the bottom,
part of the bottle. The long tube used will let in air
above this layer so that the sample has no chance to ab-
sorb oxygen from it.
The reagent for the test is prepared by warming a
solution of cupric chloride with some scrap copper and
pouring into water. The white precipitate which forms
is filtered and washed, first with hot water, then with
OXYGEN AND HYDROGEN PEROXIDE. 131
alcohol and then with ether. The powder is then dried
and must be pure white. For use a small amount of the
powder is dissolved in concentrated hydrochloric acid.
This is added to the sample by placing the solution of
the reagent in a tap funnel and inserting the tip of the
tap funnel in the oil layer before the reagent is allowed
to run into the solution. In that way the introduction
of air is prevented.
The test is performed by dilution. A standard water
for use is made by shaking pure water in a bottle until
the air bubbles remain in the liquid and then allowing
this to stand until the air bubbles vanish. A table may
then be consulted to find the amount of oxygen necessary
for saturation of a water solution at the given tempera-
Temp. Soluble in One Liter.
5.2*» 8.&56 C.C.
5.65** 8.744 cc.
14.78« 7.080 cc.
24.80'^ 5.762 cc.
30.00** 2.610 cc
As a standard one part of this is to be used to three
parts of boiled water which has shown no oxygen under
test. The mixing is to be done in the colorimetric tube
in which the test is to be made and under oil. To each,
sample and standard, there are added a few cc. of the
solution of cuprous chloride dissolved in hydrochloric acid
and immediately after that a few cc. of ammonia. The
white precipitate which appeared on the addition of the
cuprous chloride must entirely disappear, otherwise too
much of the copper solution has been added and a yellow
interference will result. The anmionia brings out the
blue colors of the solutions. The boiled water contain-
iPor further solubilities see Seidell, Solubilities of Organic and
132 COLOBIMETBIO ANALYSIS.
ing no oxygen is then used for dilution of the darker
until results are identical. The readings taken are those
at the top of the aqueous solution, below the level of the
oil. Since oil will transmit oxygen after a few hours
it is necessary that this test be carried along to com-
pletion in a reasonable length of time.
If it is desired to make up permanent standards this
is accomplished by dissolving three grams of copper wire
in hydrochloric acid and evaporating to dryness. More
acid is added and this repeated several times. The white
residue is now dissolved in water, ammonia and hydro-
chloric acid added until the solution shows a deep blue
color and the solution smells strongly of ammonia, and
dilution to one liter carried out. Permanent standards
-may be made by addition to 100 c.c. of water of the
following amounts of the standard made up.
Represents in c.c.
Standard per 100 c.c. Oxygen per Liter.
Method B. Oxygen by Adurol.
The reagent for this test is adurol with ammonium
chloride or a mixture of dry powdered borax and adurol.
The method is not so accurate as the preceding because,
from the conditions of the method, as great care as to
accuracy cannot be used.
The sample of 50 or 100 c.c. water and the standard,
prepared by saturation of a volume of water, are placed
in bottles.^ A pinch of adurol is added to each and .5
1 Z. Angew. Chem., fS4, 341.
OXYGEN AND HYDROGEN PEROXIDE. 133
C.C. ammonia containing about 20 percent ammonium
chloride in solution. This solution sinks to the bottom.
The standard may be varied by the use of varying
amounts of boiled water with the saturated aqueous solu-
tion. To prevent the absorption of oxygen from the air
in the bottle, before shaking at this point, it is well to
allow carbon dioxide to flow into the bottles and thus
displace the air which is present over the liquids. The
bottles are then corked and shaken. The standard must
be very nearly the same in color as the sample so that a
guess may be made as to the content from the experience
of the operator. Dilution is not satisfactory.
Borax heated for some hours at 50 degrees and mixed
six parts of borax, one part adurol and three parts
Eochelle salt furnishes a convenient reagent.^ This is
added instead of the adurol at the point in the test. The
function of the Eochelle salt is to prevent the precipita-
tion of calcium.
Hydrogen Peroxide by Its Oxidising Action on
For the analysis of a solution of hydrogen peroxide the
sample solution is allowed to act on a solution of ferrous
iron and the amount of the iron oxidised is tested by the
addition of potassium sulfocyanate as in the iron test.
The comparison may be made by any method.
Ten grams of ferrous ammonium sulfate [FeSO^
(NH4)2S04, 6H2O] are dissolved in 100 c.c. of water. A
test should be made on this with potassium sulfocyanate
to make sure that all iron is in the ferrous condition. If
not it must be reduced with hydrogen sulfid or by acidi-
fying with sulfuric acid and adding zinc. This reagent
must finally be available in a freshly reduced condition
1 Ihid,, 26y 134.
134 COLOBIMBTRIG ANALYSIS.
free from reducing agents. If not already acidified it
must be made acid for use. The test is made by the addi-
tion of one c.c. of this solution to a sample of ten c.c. of
the solution to be tested and then the addition of one c.c.
of a dilute solution of potassium sulfocyanate. The color
produced may be compared with a series of standards.
For these a solution of ferric iron and potassium sulfo-
cyanate is made up and diluted with water until it is of
the desired concentration for the varying standards.
These fade after a time and must be renewed. A blank
of nine c.c. of water may be used and hydrogen peroxide
from a known solution added to it. The difficulty with
that method is the obtaining of a definitely known solu-
tion. The commercial solution is approximately 3 per-
cent when fresh. Similarly a standard for the dilution
or balancing methods is made up by the addition of fer-
rous iron and potassium sulfocyanate to 25 c.c. of a solu-
tion of known peroxide content and suitable dilution.
SULFUR, HYDROGEN SULFID AND SELENIOUS ACID.
The methods for the determination of sulfur given here
are those for the determination of sulfur in iron and steel
and in similar substances from which it is possible to
release it as hydrogen sulfid by the action of an acid.
The method for hydrogen sulfid is for the analysis of a
liquid containing dissolved hydrogen sulfid, as for ex-
ample natural waters in some localities. A method is
also given for the analysis for selenious acid, an acid of
the rare element selenium which occurs in the presence
of sulfur and has properties similar to those of sulfur.
Method A. Sulfur by Paraphenylenedimethyl-
The sulfur in iron may be determined by the intense
blue color produced by its reaction with paraphenylene-
dimethyldiamine^ (unsymmetrical). The color is so in-
tense that it is necessary to dilute the sample to a con-
siderable extent or to use a very small sample. The
former method is more satisfactory.
A convenient sample is two grams. This is treated
with hydrochloric acid and the i-esultant hydrogen sulfid
absorbed in caustic soda, drawing the air from the flask
where decomposition is carried on thru a potash bulb,
by suction. This caustic soda solution is then diluted to
100 c.c. and ten c.c. pipetted out as a sample. To the
sample add 1.5 c.c. dilute sulfuric acid and dilute to 50 c.c.
1 Columbia University, School of Mines Quarterly, fSS, 24.
136 COLORIMBTRIG ANALYSIS.
To this 50 c.c. of solution add .1 c.c. of a two percent
solution of the reagent above and finally a drop of a five
percent solution of ferric chloride. The color results im-
mediately on the mixing of these reagents and compari-
son of the color may then be made by any of the standard
As a standard dissolve .2435 gram sodium sulfid (NagS)
in a liter of water. For making up a series of standards
five c.c. of this solution are to be diluted to 100 c.c, at
which concentration the sulfur content will be .000005
gram per c.c. A series of standards from a solution of
this concentration would use one to 25 c.c. for the vary-
ing concentrations. As a basis for duplication use the
same standard and a blank of twenty-five c.c. of water
to which have been added the same reagents as to the
sample. Standards do not keep very well. For dilution
or balancing treat five c.c. of the standard sohition first
proposed with double the quantities of reagents specified
for the sample and dilute to 500 c.c. The standard will
then contain .000001 gram sulfur per c.c.
The dilution and aliquot parts of the sample specified
allow for the testing of one tenth of the sample chosen.
Simple multiplication of the result obtained, by ten, will
then give the weight of sulfur in the sample and division
of the weight of sulfur by the weight of sample will give
the percent of sulfur. Others of the diamines may be
used for this reaction as for example p-phenylene-
Method B. Sltlfur by the Action of Hydrogen SuLrro
ON Arsenious Oxide Paper.
The comparison of stains made by known amounts of
sulfur on arsenious oxide paper with those made by a
sample of steel or similar substance furnishes a method
SULFUR, HYDROGEN SUMTD, SELENIOUS ACID. 137
for the rapid estimation of the sulfur content of a
sample.^ The standards do not keep well and it is there-
fore necessary to prepare temporary standards at the
time the test is made.
The prepared paper is made up by soaking a good
grade of drafting paper in a solution of 10 grams AsgOg
in 30 C.C. hydrochloric acid and 970 c.c. water. The
paper is soaked, the excess of the reagent removed and
the paper carefully dried. It is then to be cut into
squares ten cm. on a side. The sample is placed in a
glass tumbler and the varying standard amounts of a
steel of known sulfur content are placed in other tum-
blers of the same size. Each tumbler is covered with a
piece of the prepared paper, a piece of felt and a weight
to hold the paper tightly to the top of the tumbler. To
each tumbler there are then added, 10 c.c. benzine, sp. gr.
.710, and 50 c.c. hydrochloric acid sp. gr. 1.1. The stain
on the prepared paper produced by the sample may then
be compared with that produced by the standard amounts
and from that, estim^^tion made. For the analysis of
several samples at one time it is possible to run them
simultaneously and compare with the same standards.
Hydrogen Sulth) by Methyi^ene Blue.
This method is an adaptation of Method A for sulfur
in iron and steel to the analysis of natural waters and
other solutions containing a trace of hydrogen sulfid.* As
the color produced is very permanent, standards may be
prepared and kept several weeks before renewal. The ad-
dition of the reagents in the order specified is imperative
as the order in which they are added will make a diflfer-
ence in the tint of the solution produced. Satisfactory
1 Iron Age, 9S, 1253.
2 Z. Anorg. Chem., 86, 143.
138 COLOBIMETRIO ANALYSIS.
results may be obtained from solutions containing as
little as .00001 gram hydrogen sulfid per liter.
The sample is five hundred c.c. of the solution. For
contents of more than .001 gram hydrogen sulfid per liter
add ten c.c. concentrated hydrochloric acid, .025 gram
p-phenylenedimethyldiaminesulfate and 2.5 c.c. tenth
normal ferric chloride in hydrochloric acid solution. If
the content of the sample is less than .001 gram per liter
add ten c.c. hydrochloric acid, .01 gram of the diamine-
sulfate and one c.c. tenth normal ferric chloride. The
solutions must stand several hours before comparison is
For the preparation of the standard a solution of hy-
drogen sulfid in water must be determined by the usual
iodometric method or some other similar way. Known
quantities of this may then be treated as the samples
were for their production of color.
Selenium as Selenious Acid by Potassium Iodide.
The amount of selenious acid present in a solution may
be estimated from the intensity of the coloration pro-
duced in reaction with potassium iodide. The method is
delicate enuf to show .000001 gram per c.c.^
The sample, if fairly concentrated, is five c.c. If the
sample is very dilute, more may be used. The sample is
diluted to 70 c.c, one drop gum arabic solution and five
drops 5 percent hydrochloric acid added, the whole mixed
and diluted to 99 c.c. Add one c.c. potassium iodide solu-
tion, allow to stand for five minutes and compare with a
standard by dilution. The potassium iodide solution
must be colorless.
A standard is prepared by the solution of .1632 gram
crystalline selenious acid (HgSeOg) in water and dilution
1 Z. Anal. Chem., 55, 29.
SULFUR, HYDROGEN SULFID, SELENIOUS ACID. 139
to one liter. This standard contains .0001 gram selenium
per c.c. as selenious acid.. If it is desired to obtain the
results in terms of selenious acid the standard should be
made by solution of .1 gram selenious acid when the same
weight per c.c. would be present of selenious acid instead
of selenium. One c.c. of this standard is diluted, treated
with the same reagents as the sample and results obtained
SALICYLIC ACID AND CYANIDES.
These two substances are of very infrequent occur-
rence. The first, salicylic acid, finds a limited use as an
antiseptic and is used as a cheap wintergreen flavor. The
method given for cyanides was developed for the deter-
mination of the cyanides present in poisonous plants sus-
pected to derive their poisonous nature from that source
but is applicable to all determinations of small amounts
of the simple cyanides.
Salicylic Acid by Fehling's Solution.
This method is the opposite application of Method C
for copper.^ In this method the salicylic acid solution
is treated with Fehling's solution and compared with a
series of standards prepared at the same time. The
determination is prevented by the presence of free min-
eral acid, citric and tartaric acids and any considerable
amount of iron. The presence of .000001 gram per c.c.
may be detected in a ten c.c. sample and correspondingly
smaller amounts by suitable concentration. The sample
may contain up to .0001 gram in a ten c.c. sample but if
its content is over .00001 gram per c.c. the sample solu-
tion of ten c.c. should be diluted to 100 c.c. and ten c.c.
taken for analysis.
A standard salicylic acid solution is made up by solu-
tion of .1 gram of the substance in water and made up
to one liter. By the solution of .1160 gram sodium sali-
1 Zeit. Untersuch Nahr. Gfenussm., 22, 727.
SALICYLIC ACID AND CYANIDES. 141
cylate the same strength solution as above may be ob-
tained. Each contains .0001 gram salicylic acid per
c.c. Temporary standards are prepared by the use of
0, .2, .4, .6, .8, and 1.0 c.c. of this solution in plain test
tubes. The use of graduated tubes for the sample and
standards is not necessary in this case. The sample is
concentrated to two or three c.c. and placed in a similar
tube. To each tube of standard and to the sample there
are now added two c.c. of a solution of one part Fehling's
solution to ten parts water, five drops of two percent
potassium nitrate solution, five drops ten percent acetic
acid and enough water to bring the volume of each up to
about five c.c. The volumes must be the same of each.
The tubes are then heated in boiling water for 45 minutes
and are ready for comparison. The results must be ob-
tained by inspection of the temporary standards only, as
dilution of the samples does not prove satisfactory.
Fehling's solution is made by mixture of equal volumes
of the following two reagents just before using, 34.64
grams pure copper sulfate in 500 c.c. of water, and 60
grams caustic soda and 173 grams Kochelle salt (sodium
potassium tartrate, NaKC4H40e, 4H2O) in 500 c.c.
water. The reagents keep perfectly unmixed but the
solution must be used immediately after mixing.
Cyanides by Changing to Sulfocyanates and Coloring
If the solution is an inorganic one it is only neces-
sary to render the solution slightly alkaline with caustic
soda. In the solution of a salt or solid substance to be
analysed for cyanides the solution should be kept alka-
line to prevent loss. The preparation of a solution of
an organic nature is somewhat more complicated.^ The
1 J. A. C. S., 55, 1624.
142 coLOHnfETRia analysis.
substance to be tested is macerated and digested with 100
C.C. of wat^r for some time. The extract is then filtered
off and the solid residue washed with another 100 c.c. of
water. This solution is to be placed in a flask, acidified
with hydrochloric acid and three fourths of the volume
distilled over into fifty c.c. of potassium hydroxide. This
solution is then diluted to a convenient volume and fifty
c.c. taken for the test.
To the sample of 50 c.c. of solution is added one c.c. of
ammonium sulfid and the whole evaporated to dryness on
the water bath. The residue is taken up with ten to fif-
teen c.c. hot water and slightly acidified with hydrochloric
acid. Filter off the sulfur, add one half c.c. hydro-
chloric acid and boil for five minutes. The sulfur is now
filtered off and the operation repeated, until the final
solution comes clear. An alternate method is to use five
c.c. of a solution of 40 grams potassium sulfid in one liter
of water, instead of the one c.c. of ammonium sulfid.
Less trouble will be experienced with sulfur if this is
used. The clear solution from the previous operation is
diluted to fifty c.c. and fifteen drops of a five percent
ferric chloride solution added.
If the iron is precipitated on addition of this ferric
solution it indicates that the solution was alkaline and
must be acidified more. A lemon yellow rather than a
red color indicates that the solution is too strongly acid.
The red color produced is a result of the cyanide which
has been changed to the form of the sulfocyanate. The
standard is prepared directly from the sulfocyanate since
the relation between the two compounds is known. A
standard solution is made up by solution of 1.4923 grams
potassium sulfocyanate in water and dilution to one liter.
Each C.C. of this solution contains .001 gram KCN in
which terms the results of this test will be stated. Per-
SAXIGYLIC ACID AND CYANIDES. 143
manent standards may be made up but possess the same
properties as the results of the iron-sulfocyanate reaction
always do, that they fade in the light after a time. Du-
plication is possible by the addition of this standard to a
blank of 40 c.c. of water containing the ferric solution.
For dilution ten c.c. of this solution may be diluted to
fifty c.c, treated with fifteen drops of ferric chloride and
the sample or standard diluted for obtaining the result.
The amount used here may be suitably varied from ten
c.c. if the solution so made is too strong or too weak. As
a standard for balancing add two c.c. of ferric chloride
to twenty-five c.c. of the standard and dilute to 250 c.c.
This latter standard for balancing will then contain .0001
gram KCN per c.c.
COLOR OF WATER, OILS AND DYES.
The color of water is one of the things determined in
water analysis in comparison with a standard solution
officially specified. Oil is graded according to its color.
The preliminary examination of dyes by colorimetric
methods is possible in some cases.
Color of Water.
The color of water is graded by comparison with a
standard platinum and cobalt solution made up as fol-
lows, dissolve .1426 gram platinic chloride and .1 gram
cobaltous chloride in water, add ten c.c. concentrated
hydrochloric acid and make up to 500 c.c.^ The usual
method is to make up a series of standards of 100 c.c. vol-
ume. These should be at five point intervals up to 40 c.c.
and at ten point intervals from that point to 70 c.c.
Grading is never made higher than 70. The number of
c.c. used, of the solution above specified, is the measure of
the number of the grade indicated by that standard.
For the preparation of a standard to be used by the
balancing method the above 500 c.c. of standard may be
diluted to one liter. The color value of this solution will
then be 50 and, after balancing the instrument, the color
value of the sample will be to that of the standard in-
versely as the volume of the two used. For rapid work
in the field permanent glasses are made having the va-
rious standard colors as given by the official solution
1 Olsen, Quan. Oliem. Anal.
COLOB OP WATEB, OILS AND DYES. 145
Color or Oil8.
All oil is graded by color, both the refined grades and
the lubricants and crude oils. The instrument in ordi-
nary use for this purpose is the Stam-
mer form of colorimeter. Lovibond's
Tintometer is also used with a special
series of glasses for oils. The grad-
ing of kerosene is into four classes,
water white, superfine white, prime
white and standard white. These
grades all turn yellow on exposure to
light but that has no effect on their
burning qualities. The grading of
oils other than lighting oil is too
lengthy a subject for discussion here.
Recently there has appeared on the
market a new instrument, the Say-
bolt Chromometer which combines the
Lovibond Tintometer and the Stam-
mer Colorimeter. This is treated at
greater length under Apparatus,
Color of Dtestutfs.
The use of the colorimeter for de-
termination of the strength of solu-
tions of dyestuffs is very limited in ex- ^^^ ^g^ B^jhoU
tent, inasmuch as it is not reasonably Chromometer,
accurate in practice in a majority of cases. It is however
useful as a method of preliminary classification and may
then be followed by the longer and more accurate test
necessary after this preliminary has given a clue to the
concentration to be expected.
146 COLOBIMETBIO ANALYSIS.
Any of the four methods of colorimetric analysis are
applicable to this use under the proper conditions. Lovi-
bond's Tintometer finds some use in this field. It is of
course necessary to dilute the sample to be used as com-
mercial solutions of dyes are ordinarily so concentrated
that the eye cannot penetrate the solution.
In closing a word about the methods of nephelometric
measurement may not be amiss. The tests given are
entirely those depending upon colorimetry, the measure-
ment of the intensity of light of a given color trans-
mitted thru a solution. The methods of nephelometry
measure the amount of a finely divided precipitate sus-
pended in a solution. This was first tried by a method
similar to that of colorimetric determination, passing a
ray of light thru the solution and estimating the amount
of precipitate present from the interference with light
caused by its presence. Experiment has shown that the
measurement of such a precipitate is made many times
more delicate by measuring the amount of light reflected
from it rather than the interference of the precipitate
The instrument used for such determinations is a
modified form of the Duboscq colorimeter with an opaque
bottom to the cup. Precipitates suitable for such ex-
amination are those of silver chloride and barium sulfate
in dilute solutions where the precipitate is described as
an opalescence. Many applications to bacteriological and
physiological work have been found. For more complete
information on this subject see Journal Industrial and
Engineering Chemistry, Vol. 10, No. 7, P. A. Kober.
Acetyl acetone, 41
Ammonia, 44, 94, 107, 118, 119
Ammonium molybdate, 124
Arsenic, 60, 64, 67
Arsenious oxide, 136
Balancing method, 2, 10
Benzidene, diphenyl, 110
Bismuth, 62, 66
Bleaching of Titanium solution,
Boron, 121, 126, 127
Bromide, mercuric, 64
Calculation of results, 27
Campbell-Hurley Colorimeter, 12
Cassal method for gold, 93
Chlorides, 35, 46, 74, 76
Chlorine, 102, 105
Chlorplatinate of potassium, 83,
Chromium, 68, 70, 71
Ghromometer, Saybolt, 21
Cobalt, 73, 76
Colloidal suspension, 161
Color camera, 8
Colorimetric apparatus, 5
Colorimetrie methods, 1
Colorimetric results, 27
Cuprous chloride, 129
Cyanides, 93, 94, 140, 141
Diamine, m phenylene, 94, 115
Dilution method, 1, 7
Disodium 1.8 dihydroxynaphtha-
lene 3.6 disulfonate, 71
Doring, method for gold, 91
Dowsett, method for gold, 89
Duboscq colorimeter, 18
Duplication method, 2, 9
Ethyl potassium xanthatc, 51
Ferrie iron, 31
Ferrous iron, 31, 133
Hehner cylinders, 10
Hydrogen peroxide, 95
Iodide of Zinc, 116
Lovibond tintometer, 18
Magnesium phosphate, 122
Manganese, 73, 78, 80
Metaphenylene diamine, 94, 115
Balancing, 2, 10
Dilution, 1, 7
Duplication, 2, 9
Series of standards, 1, 5
Methylene blue, 106, 137
Naphthalene derivative, 71
a Naphthylamine, 114
a Naphthylamine hydrochloride,
Nessler's reagent, 118
Nessder tubes, 8
Nickel, 73, 74
Nitrate, silver, 67
Nitric acid, 107
a Nitroso b naphthol, 76
Nitrous acid, 107, 114
Oils, 144, 145
Oxide of tungsten, 101
Oxygen, 129, 132
Perchlorates, 102, 106
Permanganate, 78, 80
Peroxide of hydrogen, 95, 97,
Phenol sulfonic acid, 111
m Phenylene diamine, 94, 115
p Phenylene dimethyldiamine,
Phosphomolybdate, 8-6, 121
Phosphorus, 121, 122
Potassium, 83, 85
Potassium bromide, 93
Potassium ethyl xanthate, 51
Potassium ferrocyanide, 36, 48
Potassium iodide, 138
Potassium platino chloride, 88,
Potassium sulfocyanate, 31
Potassium thiocarbonate, 73
Prister, method for gold, 90
Rose, method for gold, 92
Salicylic acid, 37, 47, 140
Saylbolt ohromometer, 21
Schreiner colorimeter, 21
Selenious acid, 135, 138
Series of standards method, 1, 5
Silica, 121, 124
Silver nitrate, 67
Sodium peroxide, 93
Sodium salt of alizarin, 68
Stammer colorimeter, 21
Stannous chloride, 83
Sulfanilic acid, 114
Sulfides, 39, 60, 135, 136
Sulfur, 135, 136
Titanium, 95, 97, 102
Tungsten, 95, 101 White's colorimeter, 23
Xanthate, potassium ethyl, 51
Vanadium, 95, 97, lOQ
Zino, 73, 81
Water, color of, 144 Zinc iodide, 116
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