QUANTITATIVE AGRICULTURAL ANALYSIS BY EDWARD G. MAHIN, Pn.D. PROFESSOR OF ANALYTICAL CHEMISTRY IN PURDUE UNIVERSITY AND RALPH H. CARE, PH.D. PROFESSOR OF AGRICULTURAL CHEMISTRY IN PURDUE UNIVERSITY FIRST EDITION McGRAW-HILL BOOK COMPANY, INC. NEW YORK: 370 SEVENTH AYENUE LONDON: 6 & 8 BOUVERIE ST., B, C. 4 192-3 COPYRIGHT, 1923, BY THE MCGRAW-HILL BOOK COMPANY, INC. PRINTED IN THE UNITED STATES OF AMERICA D THE MAPLE PRESS - YORK PA PREFACE The time is, happily, past when ''Chemistry for Medical Students," " Quantitative Analysis for Engineers" and similar titles, indicating treatises on the spoon-feeding of special dishes of easy chemical cookery to the classes of persons indicated, met any very general demand on the part of teachers. Even in our highly specialized chemical science of today and in its enormously diversified applications io industrial and economic problems, we recognize the futility of attempting to train students for technical or professional careers by teaching them only the mechanical notions and processes of chemistry without the scientific develop- ment of fundamentals. The authors have tried to keep this idea in view in the compila- tion of this book. The discussion of special methods (largely "official'/' wherever applicable) for the analysis of materials of prime importance to chemical students of agricultural mate- rials and of agricultural problems forms an important portion of the book; but we subscribe very heartily to the belief that one of the things most needed by scientific agriculture today is an increasing body of agricultural chemists who understand the importance of desiring to know why matters are thus and so. The introductory course in general quantitative analysis, in Part I, deals with a select list of such analytical processes as may be considered useful for impressing upon the mind of the student the principles of analytical work, as well as the importance of exercising intelligence and care in all work of the laboratory. Bearing in mincl the fact that in most college curricula this first course must necessarily be brief, the typical classes of methods for a given determination have been treated together. This, in turn, has involved a preliminary discussion of materials and methods of both gravimetric and volumetric analysis. Part II, dealing with certain special measurements, has been included in recognition of the fact that the highly important VI PREFACE instruments and methods there discussed are too seldom under- stood by the chemists who use them in industrial work. In our own classes we have found lectures upon the theoretical principles underlying the construction and use of these forms of apparatus to be of very great value. In Part III is included a treatment of the six classes of materials most often considered in courses in agricultural analysis, and probably of interest to the greatest number of agricultural chemists. The significance of the results of the analyses, in connection with agricultural problems, has been given as much attention as was thought possible, without going outside the proper scope of a book of this.character. This, it is believed, will add an interest to the laboratory work and supply a certain motivation, otherwise largely lacking. In certain parts of the book we have drawn rather freely upon portions of another text by one of us.1 This is particularly true in the discussion of materials and general operations, of the analysis of oils, fertilizers and dairy products and of the deter- mination of nitrogen. Certain cuts have been borrowed from the same source, while others are from original drawings, made by G. B. Wilson. Problems in analytical calculations have not been included. Several good problem texts are now available and the authors believe that a systematic course with one of these, as an accompaniment to the laboratory work and lectures, is the best method of impressing this phase of the subject upon the mincl of the student. E. G. MAHIN, R. H. CARR. PURDUE UNIVERSITY, September, 1922. IMAHIN, "Quantitative Analysis." CONTENTS PAGE PEEFACE............................ v INTRODUCTION.........................xiii PART I GENERAL ANALYSIS CHAPTER I THEORY AND GENERAL PRINCIPLES................ 1 Gravimetric analysis—Factors—Factor weights—Temperature systems. Volumetric analysis—Adjustment of sample weight—Normal system—Volumetric factor weights—Decimal system—Stand- ardization. Indicators—"Neutrality" indicators—Hydrogen ion concentra- tion—Phenolphthalein—Methyl orange—Methyl red. CHAPTER II GENERAL OPERATIONS...................... 17 Preparation of samples—Mixing and dividing—Quartering— Maximum size of particles—The riffle—Sampling liquids— Dissolving the sample—Fusion—Fluxes—Precipitation—Filtra- tion—Washing—Drying—Ignition—Crucibles—Care of plati- num—Platinum substitutes—Burners. Weighing—The balance—Weights—The rider—The chain rider— Differential weighing—Determination of zero point—Weighing by the single deflection method—Calibration of weights. Volumetric apparatus—Specifications—Calibration—C leaning solution—Calibration of flasks—Of burettes—Of pipettes. CHAPTER III QUANTITATIVE DETERMINATIONS.................48 Comparative usefulness of different methods—Scope of the . laboratory work. Chlorides—Gravimetric by weighing silver chloride—Volumetric by titration with silver nitrate—Use of a correction factor— Volumetric by titration with sodium carbonate—Volumetric by titration with potassium hydroxide. viii CONTENTS PAGE Sulphates—Solubility—Crystallization—Change of weight of barium sulphate—Gravimetric determination—Volumetric by titration with standard base or carbonate. Calcium—Gravimetric by weighing calcium oxide—Solubility— Purity of precipitate—Volumetric by titration with permanga- nate—Apparent valence. Iron—Volumetric by titration with permanganate—Volumetric by titration with dichromate. Aluminium—Solubility—Gravimetric determination. Carbonates—Gravimetric method—Volumetric by use of barium hydroxide—Alkalinity of carbonates—Alkalinity of limestone. Phosphates—Gravimetric by weighing magnesium pyrophosphate —Insoluble phosphates—Volumetric by titration of ammonium phosphomoly bdate. PART II SPECIAL MEASUREMENTS CHAPTER IV DENSITY AND SPECIFIC GRAVITY.................94 Density—Specific gravity—Baume* system—Methods for deter- mining specific gravity—The hydrometer—The lactometer— The Westphal balance—Use of the Westphal plummet on an analytical balance—Applications. CHAPTER V HEAT OP COMBUSTION (CALORIMETRY)...............103 Units of measurement—Apparatus—Emerson fuel calorimeter— Ignition wire—Formation of nitric acid—Radiation corrections —Time-temperature curves—Calculation—Determinations. CHAPTER VI INDEX OF REFRACTION......................113 Theory—Apparatus—Abb6 refractometer—Dispersion—Butyro- refractometer—Dipping refractometer—Pulfrich refractometer —Determinations. CHAPTER VII OPTICAL ROTATION (POLARIMETRY;................121 Theory—Specific rotation—The polarimeter—Making a reading—7 Polarizer and analyzer—The Nicol prism—Method of making observations—Light sourcfes—Quartz wedge compensation and CONTENTS ix PAGE the saccharimeter—Light filters—Sugar scale—The Ventzke scale and the normal weight—The International scale—The Laurent scale. The common sugars—Cane sugar—Commercial syrups—Correc- tion for volume of precipitate—Direct polarization—Invert polarization—Beet products—Commercial glucose—Detection of invert sugar—Determination of commercial glucose in syrups containing invert sugar. CHAPTER VIII HYDROGEN ION CONCENTRATION.................138 Methods—The potentiometer method—The indicator method— Table of indicators—Applications. PART III ANALYSIS OF AGRICULTURAL MATERIALS CHAPTER IX FEEDS..............................142 Composition of common feeds—Sampling—Moisture—Ash— Mineral analysis—Crude fat—Crude fiber—Crude protein— Nitrogen—Kjeldahl method—Gunning method—Kjeldahl-Gun- ning-Arnold method—Non-protein nitrogen. Carbohydrates—Reducing sugars—Determination of reduced cuprous oxide—Gravimetric method—Approximate volumetric method—Iodide method—Sucrose—Starch—Diastase method— Direct acid hydrolysis—Arabin, xylan and pentosans—Galactans. CHAPTER X SAPONIFIABLE OILS, FATS AND WAXES...............170 Composition—Separation and identification—Specific gravity— Index of refraction—Melting point of fats—Iodine absorption number—Acid value—Saponification number—Soluble and insoluble acids—Reichert-Meissl number—r-Butter and substi- tutes—Polenske value—Acetyl value—Maumene* number and specific temperature reaction. Qualitative reactions—Resin oil—Cotton-seed oil—Sesame oil— Arachis oil—Soybean oil—Marine animal oils—Color reactions. CHAPTER XI DAIRY PRODUCTS........................199 Milk—Sampling—Specific gravity—Added water—Use of dipping refractometer—Acidity—Total solids—Ash—Fat—P a p e r - c o i 1 X CONTENTS PAGE method—Rose-Gottlieb method—Babcock method—Protein and total nitrogen—Formal titration for proteins—Casein— Official method—Hart method—Albumin—Lactose—Reduction methods—Optical methods—Microscopic examination—Borates —Heated milk—Condensed milk—Sucrose—Powdered milk. Cream—Fat—Solids—Ash—Nitrogen—Lactose. Ice cream—Fat. Butter and substitutes—Adulteration—Sampling—Moisture—Fat —Casein—Salt—Oleomargarine—" Nut" butters. Cheese—Manufacture—Water—Ash and salt—Fat—Total nitro- gen—Acidity—Coloring matter. CHAPTER XII SOILS.............................230 Total and acid-soluble matter—Soil constituents—Classification of plant foods—Value of soil analyses—The report—Potential plant food—Available plant food—Sampling—Moisture—Opti- mum moisture—Total nitrogen—Nitrate nitrogen—Ammonia nitrogen—Nitrification—Denitrification—Phosphorus—Potas- sium—Chlorplatinate method—Perchlorate method—Recovery of platinum from waste—Organic matter—Carbonate carbon— Total carbon—Humus—Acid-soluble material. Other inorganic constituents—Silica—Aluminium—Iron—Calcium —Magnesium—Manganese—Sulphur—Lime re quire men ts— Veitch method—Truog method—Thiocyanate method—Hop- kins method—Flocculation and deflocculation of clay. CHAPTER XIII FERTILIZERS..........................270 Availability—Composition—Compatibility—Sampling—Mechan- ical analysis—Moisture—Phosphorus—Availability—Water-sol- uble phosphorus—Citrate-insoluble phosphorus—Nitrogen— Ammonia nitrogen—Nitrate nitrogen—Availability of nitrogen —Neutral and basic permanganate methods—Potassium— Chlorplatinate method—Perchlorate method—Centrifugal method—Pot and field cultures. CHAPTER XIV INSECTICIDES AND FUNGICIDES..................292 Character as related to insect anatomy—Contact insecticides— Preparation of insecticides—Compatibility. Paris green—Total arsenic—Water-soluble arsenous oxide. CONTENTS xi PAGE Lead arsenate—Moisture—Lead oxide—Total arsenic—Water- soluble arsenic oxide—Total arsenous oxide. Calcium arsenate—Total arsenic. Lime-sulphur solutions—Total sulphur—Sulphide sulphur—Total calcium. Nicotine insecticides—Determination of nicotine. Bordeaux mixture—Moisture—Carbon dioxide—Copper. Soap emulsions—Moisture in soap. Chlor picrin and the poison gases. TABLE OF LOGARITHMS AND ANTILOGAKITHMS............310 TABLE OF ATOMIC WEIGHTS.............Inside back cover. INDEX.............................317 INTRODUCTION For the most part the operations of analytical chemistry fall naturally into quantitative lines. This is particularly true of analysis as applied to agricultural problems because the qualitative composition of most agricultural materials is usually fairly accurately known from the nature and proposed use of the materials themselves. The qualitative method for the detection of a given element or compound frequently involves the use of the same reactions as those that are fundamental to the quantitative determina- tion of the same materials and in these cases, especially, it is most convenient to modify the details of the experiment so as to make a quantitative determination possible in the beginning, rather than to repeat the work in this manner after the com- pletion of a qualitative analysis. This is not universally true and there will be occasional instances in which the complete qualitative analysis will save the labor of quantitative deter- mination of elements n,ot present in any significant quantity. As the name implies, quantitative analysis has for its object the determination of the quantity (usually, though not always, expressed as per cent) of the various constituents of a material under investigation. The constituents determined may be elements or radicals of a compound, mixture or solution. The particular method to be used for a given material will be chosen according to circumstances and, to some extent, according to individual preference or available equipment. It will necessarily be modified if interfering substances are present. On this account it is desirable first to learn a few methods for the quan- titative determination of some common elements in pure com- pounds and later to apply these and other methods to a more extended analysis of more complicated materials. QUANTITATIVE AGRICULTURAL ANALYSIS PART I GENERAL ANALYSIS CHAPTER I THEORY AND GENERAL PRINCIPLES Gravimetric Analysis.—When the quantitative composition of a material is learned through the direct application of the analytical balance the method is known as a "gravimetric77 one. In principle the method is comparatively simple. A certain quantity of the well mixed sample is weighed accurately. It is then subjected to a series of operations, as a result of which a certain element or radical is finally separated from other con- stituents, either in its simple form or, as is more often the case, that of a pure compound of known formula. The latter is then weighed accurately. The two weights thus obtained and the known composition of the pure compound provide the necessary data for the calculations. The determination of phosphorus in a phosphate rock may be taken as an example. The rock may contain ordinary tricalcium phosphate, Ca3(P04)2, as its chief constituent but it will also contain varying quantities of other materials, such as clay, quartz sand, limestone and iron oxide, so that the formula as given above cannot be assumed to be a correct representation of the composition of the material. The latter is therefore care- fully sampled and a small portion is accurately weighed. It is then treated with an acid and the insoluble silica and silicates are removed by filtration. All of the phosphorus is then pre- cipitated as ammonium phosphomolybdate, a complex substance represented by the formula (NH4)3P04.12Mo03. This is filtered out, washed, redissolved and finally precipitated as magnesium 2 Q UANTITA TIVE AGRICULTURAL A NAL YfUfi ammonium phosphate, MgNH4P04, which is washed and then changed to magnesium pyrophosphate, Mg2P2O7, by heating strongly in a previously weighed crucible. From the weight of the crucible, with and without the pyrophosphate, the weight of the latter is found. Factors.— The formula for magnesium pyrophosphate shows (2P X 100 \ ____ = 27.87 j. Multiplying this figure by the weight of pyrophosphate found and dividing the product by the weight of sample gives the pot- cent of phosphorus in the phosphate rock. Stated a>s a formula : 2 X 3X° W where W = grams of magnesium pyrophosphate found and 8 = grams of sample taken. No matter how many different samples' of rock or other material might be subjected to this experimental process, the calculation would always follow the lines indicated in Eq. (1) and, since the only variables in this equation are the weights of sample and of pyrophosphate, the constants may be collected : 2 X 31.04 X 100 _ _ -, The quantity F is called a "gravimetric factor" and, since the procedure for phosphorus as already outlined is an illustration of the procedure for all gravimetric determinations, this factor may be calculated once for all for each type of determination arid recorded, together with its logarithm, in a convenient place*. Equation (1) is then a special application of the more general equation: F W ' /<>A -g~ = ^ Oi) -F always indicating the per cent of the determined element or combination of elements in the weighed precipitate, an calcu- lated from the chemical formula, and x representing the per cent of the same entity in the sample analyzed. As indicated in the preceding paragraph, a combination of elements (as an oxide or radical) may be calculated. For example the factor for phosphorus pentoxide would be 100 F205 _ 14208 _ Mg2P207 " 222.72 " W'7y' THEORY AND GENERAL PRINCIPLES 3 n Factor Weights.—In Eq. (3) F is a constant for all determina- g tions of the particular element or group of elements for which }f it has been calculated. It is possible to choose the weight of the }f sample taken so as to simplify the calculation of this equation. For instance, by taking a sample weight equal in grams to the F rs | value of the factor, « = 1 and Eq. (3) becomes: I- ' W=x. (4) d In such a case the weight of precipitate, expressed in grams or f rac- jr tions, becomes per cent, or fractions, of the constituent determined. i: A weight of sample equal in grams to the value of the factor is usually too large a quantity to be handled readily and a definite ' fraction of this weight (as 0.5, 0.2, 0.1, etc.) may be used instead. j Any such weight is called a "factor weight/7 which may be ^ defined as a quantity equal in weight units to the value of the s gravimetric factor, or to some simple fraction of this factor. e Continuing the illustration given above, the factor weight of g sample actually taken would be, for the sake of convenience, e 0.6379 gm, in which case the per cent of phosphorus in the sample would be one hundred times the weight, in grams, of magnesium pyrophosphate found. ) When a Factor Weight Should be Used.—In considering the actual practice of the operations with the balance it will be « $ found that the manipulation of the sample to obtain any pre- viously specified quantity requires considerable time, if the , weighing is to be done accurately. One cannot judge quantities [ accurately by means of the eye and it becomes necessary to 'j adjust the sample while it is on the balance pan, very carefully by removing or replacing very minute quantities. On the other \ hand, it is a comparatively simple matter to take approximately ) the required quantity and to weigh this accurately, using the figure thus found in later calculations. It may then easily be seen that all of the convenience and time-saving element , that is involved in the calculations where factor weights (or, in fact, any other definitely prescribed weights) have been used, may be more than lost in the time and trouble required for adjusting the sample weight to this exact value. For the reason just mentioned it is inadvisable to use factor weights except in cases where relatively large amounts of sample I 4 QUANTITATIVE AGRICULTURAL ANALYSIS I may be used or where no great accuracy is required. In such cases j the sample weight may be accurately and quickly adjusted to I the second or third decimal and the remaining uncertainty will | be relatively insignificant. For example, if a 10-gm sample of j soil is to be used for a nitrogen determination, an uncertainty i of 1 mg in weighing will involve only 0.01 per cent of the total nitrogen found. But if a 0.5-gm sample of limestone were to be used for a determination of calcium, this same uncertainty ] would amount tO o.2 per cent. ; Temperature Systems.—In nearly all scientific work the J Centigrade system is used exclusively for indicating tempera- . tures and in this book all temperatures mentioned are in Centi- grade unless otherwise designated. In some instances the special agricultural analyst will have to use the Fahrenheit system in | order to conform to established usage. When this is done in the following pages, the letter "F" will follow the figures indicating f, the temperature. ' Volumetric Analysis.—The final determination of per cent 1 by volumetric methods is not made by means of weighing a pre- \ cipitate. The balance is generally used, as in gravimetric I methods, for weighing the sample. The solution of the latter is then brought into definite reaction with another solution of an I appropriate reagent (a standard solution) until the reaction is * exactly completed. The concentration of the standard solution >' is accurately known as a result of a previous analysis (a stand- ardization) and the volume required is measured accurately by means of a graduated burette. The product of the required volume of the standard solution and its concentration, giving the weight of the dissolved reacting material, serves as a measure of the determined constituent of the sample, just as the weight of the precipitate does in gravimetric analysis, the only difference ; in principle being the use of the weight of a reacting body instead of that of a containing body as a measure of the thing to be ; determined. With this exception the calculations will be similar to those of gravimetric analysis, a titration serving instead of a weighing. ; As an illustration, the determination of sodium hydroxide in an impure sample may be cited. A weighed quantity of the material is dissolved and titrated by a standard solution of THEORY AND GENERAL PRINCIPLES 5 hydrochloric acid, a drop or two of an appropriate indicator, as methyl orange or methyl red, being added to show the end point of the reaction. If V = cubic centimeters of standard solution required, C = concentration of standard solution (gm of HC1 per cc), S — gm of sample used, Eq^cl — equivalent weight (see page 7) of hydro- chloric acid (36.468), and EqNaOU = equivalent weight of sodium hydroxide (40.008), then V C = gm HC1 used, (1) ^4r^^ = gm NaOH in sample used, (2) •&#HCI 100 V C EQNf.01g: . ,.,. X-XTT • T /ov - ^^ — ^£££E _ per cen£ NaOH m sample. (3) O -£#HCl Of course this derivation is based upon the assumption that sodium hydroxide is the only basic substance present in the sample. As in gravimetric analysis it is convenient to collect all of the constants of the final expression. For all determinations of sodium hydroxide that are made by means of this particular standard solution of hydrochloric acid, V and S are the only variables. The quantity: "Eqav 36.468 may be called the "base factor" of the acid. This can then be simplified and recorded upon the label of the bottle. Let this be designated by FB. Thereafter, so long as this solution is used for the determination of sodium hydroxide in other samples, the calculation of the results of titrations will be made by means of the equation: 100 V FB . TV T ^-o- ,.N - — £_ =per cent NaOH. (4) AJ If the same standard solution is to be used for the determination of any other base it will be necessary to recalculate the value for FB for this substance and to use the new value in an equation similar to Eq. (4). If a new standard solution of a different concentration is prepared, or if the concentration of the original standard has changed, a new value for FB is calculated. i'LTI'L\lL AXALYS1S of Weight— The volumetric itiidy * '\plahied liave been made upon the assumption th^"t trie ;ipV * *':nlt *»\a*» not adjusted to any particular value altti-O^g11 wit*-, < )+h uniiM\ accurately determined. In Eq. (4) F& 1S a -tunt t\»r this particular standard solution in this parti «3U»lar ut'tt nnniiitiuL. Thtrefore if some care is exercised in adj u^kmg; the MimpV weight, K so that it will bear some simple relation* tx> /"/. the emulations will be materially simplified. For if S is niadt to equal 100 F^ Eq. (4) will become: F = per cent XaOH. That is, each cubic centimeter of standard solution used iix lit uit ion represents a weight of sodium hydroxide which per cc*nt of the sample weight, so that the burette reading a percent :igo reading. From this the rule follows: To make tfa burette reading a dire-ct percentage reading, sa^iplc ic c:gM equal to 100 FB* In practice it often happens that such an adjustment calls for a too small weight of sample and it does not then provide for sufficient accuracy. Ten or one hundred times this weigh. -t is often taken, making 1 cc of standard solution indicate tent;lis or hundredths of 1 per cent. Use of Aliquot Parts. — -If the adjustment of sample we must be with a high degree of accuracy it may be that extra time involved in the adjustment will not be compensa/fced by time saved in calculations, in which case such adjustiraejat will not be desirable. But if relatively large samples may be used for the analysis an error in weighing becomes of proportion- ately less importance and adjustment may be made more rapidly less carefully. These considerations apply as in gravimetric analysis (page 4). The use of large samples is rendered practicable by the uso of the principle of aliquot parts. Some simple multiple of -fclxe required weight is taken and the solution is diluted to a definite volume in a volumetric flask and well mixed. A definite fraction of this solution is taken for the analysis and the proper factor ~fco correct for this is used in the calculation of results. For example, If a degree of accuracy carried to the fourth decimal place ' is required in weighing 0.3943 gin for a single analysis, ten tiin.es THEORY AND GENERAL PRINCIPLES 7 this weight, or 3.943 gm may be weighed to only the third deci- mal place, the same number of significant figures being determined in the two cases. This sample may be weighed much more rapidly than the first. One solution of sample thus serves for several different titrations. The principle of aliquot parts is of service also in the analysis of materials that are not homogeneous and that cannot be mixed readily, the larger quantity being more nearly representative than the smaller one and the mixing being accomplished after the weighed sample has been dissolved. Normal System.—In case it is possible to apply a given stand- ard solution to the titration of a number of different substances (as a standard acid for various bases or a standard base for various acids), there is a certain convenience to be derived from adjusting the concentration of the standard so as to make FB equal to one- thousandth of the equivalent weight of the substance determined, or to some other simple fraction of the equivalent weight, as 0.002, 0.0001, 0.0005, etc. The " equivalent weight77 of any element or group of elements is the number of weight units of this entity that is chemically equivalent to eight weight units of oxygen. In the case of elements this is the combining weight. In all cases the equivalent weights compose a series of relative weights of the various chemical entities, chemically equivalent to each other in reacting power. From this definition it is obvious that if FB is to be made equal in grams to one-thousandth of the equivalent weight of the substance determined (or 1 milligram-equivalent), 1 cc of the standard solution must contain 1 milligram-equivalent of the active constituent. A solution of this concentration is a normal solution and the following relations are consequences of the defini- tions discussed above: (a) One cubic centimeter of any normal solution is equivalent to 1 milligram-equivalent of any substance. (6) One cubic centimeter of any normal solution is equivalent to 1 cc of any other normal solution. Normal solutions are too concentrated to allow a very high degree of accuracy in analytical work and it is more often desir- able to use half-, fifth-, tenth- or even hundredth-normal solu- tions for accurate work. The relations existing between solutions I 01 a 1 * will be seen from relations (a) and (6) Weights.—If the rule given on page 6 f/»r M.akirii* rh- him tit reading a percentage reading is followed wb**!i IMIIC th' rormal system, the result is the volumetric factor of sample. This, of course, becomes one-tenth of the gram- oquivalont of the element or compound determined in the sample. System.—A further simplification may be made by adjusting the standard solution until each cubic centimeter is equivalent to a simple fraction of a gram of the substance to be titrated, instead' of to a simple fraction of a gram-equivalent as in the normal system. One cubic centimeter of a standard' iodine solution might then be equivalent to 0.005, 0,002, 0.001, etc., gm of sulphur. This results in a very much simplified cal- culation and a further saving of time is accomplished by using a sample weight which bears a simple relation to the equivalence of the standard. In the case just noted the sulphur sample might be used in portions of 0.5, 0.2 or 0.1 gm, or of ten times these weights. Then 1 cc of standard solution would indicate 1. per cent or 0.1 per cent of sulphur. Such solutions as these are frequently made for technical work in industrial laboratories, where large quantities of standard solutions are required for the titration of a single constituent of a large number of samples. Mention may be made of the use of potassium permanganate or potassium dichromate solutions for the titration of iron in ores, of sodium thiosulphate for the titra- tion of copper in ores or available chlorine in bleaching powder and of potassium ferrocyanide for the determination of zinc. In fact any standard solution may be made in this system and it be so made if its use is to be limited to the determination of one substance. Standardization.—Thus far we have dealt only with the calcu- lation of the results of volumetric analysis, assuming that the standard solution was ready for use in the experiment. The determination of the exact concentration of the standard solution is called "standardization." The details of the experimental work will be treated later and will be mentioned here only so far as they may serve to illustrate the methods used in the calculations. THEORY AND GENERAL PRINIPLES t Standardization may be accomplished Ibji pne ^ general methods: . ^ \ Direct Weighing. — The active substariib^/''of;Cthe accurately weighed and dissolved so as to of solution. The method is applicable to only as may be obtained in a pure state or in a state of uniform and accurately known composition. Most of such materials are crystallized salts or acids, or soluble gases. Weighing a Substance Produced by a Measured Volume of the Solution. — Sulphuric acid solution may be standardized by adding an excess of barium chloride to a measured volume of the solution. From the weight of barium sulphate found the weight of sulphuric acid may be calculated. Similarly hydro- chloric acid solution may be standardized by adding silver nitrate to a known volume of solution and weighing the silver chloride produced. Measuring the Volume of Solution Required to React with a Known Weight of a Substance of Known Purity. — An acid may be allowed to react with a pure carbonate and the required volume noted. Sodium thiosulphate may likewise be titrated against a weighed quantity of iodine or (indirectly) against a weighed quantity of arsenic trioxide. Titration against Another Solution Which Has Already Been Standardized. — This method is very much used in the laboratory. Primary Standards. — It will be noticed that in each of these cases there is some substance of known composition which is measured or weighed and the solution is somehow compared with this for standardization. This substance of known com- position is called the " primary standard/7 whether it be the substance dissolved in the solution, something produced by the solution or something reacting with the solution. The following examples will illustrate the methods of calcula- tion in each of the cases discussed. 1. The method of calculation for the first method of stand- ardization is self-evident. The normality is equal to the ratio of the number of grams dissolved in 1000 cc to the number of grams in 1000 cc of a normal solution. That is, ,.. imi per 1000 cc normality = -- .— ~r-«r- ------------ .---y-r - equivalent weight E AGRICULTURAL ANALYSIS 2. A solution of hydrochloric acid was standardl^0^ by precipitating the chlorine from 40 cc as silver chloride. weight of silver chloride found was 0.6327 gm. Required normality of the solution. • i i j- 0.6327 ., ul . , 1 cc acid solution =c= — TTT™ gm silver chloride* 1 cc normal acid solution =c= 0.1433 gm silver chloride- Therefore normality- ^fUo.I433 =40^^33 -O.HO7N. To make the solution decinormal 1000 cc would be diluted to 1107 ec. 3. A similar solution was standardized by titration of pure sodium carbonate in presence of methyl orange, the following reaction being completed: NajCOa + 2HC1 ->2NaCl + H2COS. It was found that 32.2 cc acid =c= 0.1638 gm of the primary standard, sodium carbonate. Required the normality. ., 0.1638 ,. , , , • 1 cc acid =£= -n-n' gm sodium carbonate and 1 cc normal acid =c= 0.053 gin sodium carbonate. Therefore normality = 32y^fo53= °-9598 N- 4. Another acid solution was standardized by titration against a measured volume of standard potassium hydroxide solution in presence of methyl orange according to the equation : One cubic centimeter of the primary standard contained O.OO468 gm of potassium hydroxide. It was found from the ti tra/tion that 50 cc of potassium hydroxide solution o: 43.5 cc of hydrochloric acid solution. The weight of potassium hydroxide in 50 cc of solution = 50 X 0.00468 gm. Since this weight was equivalent to -43.5 cc of acid, the potassium hydroxide equivalent to 1 cc sicici = 50 X 0.00468 -jg~ -------- gm. Ihe normality of the hydrochloric acid, solu- 50 X 0.00468 43.5 x THEORY AND GENERAL PRINCIPLES 11 In case the primary standard is a solution already standard- ized in the normal system the normalities of the solutions are inversely as the respective volumes that are equivalent to each other. 5. Thirty cubic centimeters of y~ sodium thiosulphate solu- tion is found by titration to be equivalent to 29.8 cc of iodine solution. The normality of the latter is required. 300 N = __ N 29.8* 10 This is If solutions are to be standardized in the decimal system the calculations involve nothing more than finding the weight of the substance in terms of which the standardization is to be ex- pressed, equivalent to 1 cc of the solution which is being stand- ardized, always using as the starting point the known weight of the primary standard. In many cases the standardization is to be expressed in terms of the primary standard itself. For example, iodine solu- tion is to he standardized against pure arsenic trioxide and expressed in terms of the same substance. Here we have the very simple method of weighing a- suitable amount of arsenic trioxide, then dissolving and titrating by the iodine solution. Then 1 cc iodine solution gm As203. cc I-solution Other familiar examples of this class of methods are the standardization of permanganate solutions against oxalates or against elementary iron or antimony for obtaining the weights of these elements equivalent to 1 cc of the solution. The following example will serve to illustrate the first case just discussed: 6. A solution of potassium permanganate was standardized against sodium oxalate as follows: 2.5340 gm of sodium, oxalate was dissolved and the solution was diluted to 1000 cc. Twenty- five-cubic centimeter portions were titrated and gave an average of 24.25 cc of potassium permanganate solution equivalent to the oxalate solution used. Required the weight of iron and of salcium equivalent to 1 cc of permanganate solution. 12 ^TAM/TATirE AGRICi'LTUKAL AXALYSIS Twenty-five cubic eeatimeters of the oxalate solution contained X gin and 1 cc of permanganate solution is equivalent to gin of sodium oxalate. This weight, multiplied by the ratio of the equivalent weight of iron or of calcium to that of sodium oxalate, will give the weights of these substances that are equivalent to 1 cc of the standard solution. Then ^ I.L025 X 2.5340 _XJ>o!8<8== Q 0021g m Fe IT solution =0= ....... 94.25'X.....67.005 or °-%X^ X 20ffl6 = Q 0(X)78 Ca. 24.2,3 X b/.OQo Indicators.—Any substance that is used to show the end point of a definite reaction is an "indicator/7 The indicator may do this by a change of color in solution or by the appearance of a precipitate. In some cases the standard solution itself or the substance titrated may act as indicator. A familiar example of this is the oxidation of iron by potassium permanganate. As long as any ferrous iron is present the intensely colored per- manganate is reduced to practically colorless manganese salts but the least drop of permanganate in excess colors the solution and indicates the complete oxidation of all iron present. In this case, as with other color changes and precipitations of in- organic compounds, the reaction at the end is definite and well understood. ^Neutrality1' Indicators.—The indicators that are used to show neutrality points in reactions of acids and bases with each other are usually organic and their color changes are reversible as the point of neutrality is passed in either direction. The color change is due to a change in molecular structure which, in turn, is in equilibrium with hydrogen or hydroxyl ions present in the solution. Hydrogen Ion Concentration.—The volumetric titration of acids with bases, or conversely, is a process of neutralization. This is the production of a condition where neither hydrogen nor hydroxyl ions are present in more than very slight and negligible excess. Neither of these ions can be absolutely eliminated from any aqueous solution. Both must be present and in such proper- THEORY AND GENERAL PRINCIPLES 13 tion that the product of their concentrations is a constant, 10~14 gram-ions per liter. This product is a very small quantity and it is obvious that an acid solution (essentially a hydrion solu- tion) must contain extremely minute quantities of hydroxylion, while basic solutions contain considerable concentrations of hydroxylion and correspondingly little of hydrion. At the "neutral point" the ion concentrations are equal, so that each of these two ions is present to the extent of 10~7 (=\/10-14) gram-ions per liter. This is the relation for pure water also and it is expressed as follows: [H+1 = [OE-]=10-7, (I) [H+] X [OH-] = Kw = 10-1*. (2) Since Eq. (2) expresses a condition existing in all aqueous solutions of electrolytes, it will be seen that the concentrations of the essential ions of acids and bases cannot be independent but that they must vary inversely, so that "both "acid" and "basic" conditions might be represented in terms of either one of these ions. Polio wing the suggestion of Sorensen the expression —log [H+] is used for this purpose and the symbol PH* is used to indicate this quantity. This symbol has been variously modified to pH or PH. So long as ion concentrations are ex- pressed as powers of 10, as a»bove, Ps will be the same as the negative exponents of 10. Eeference to Eq. (1) shows that the neutral condition will "be expressed by the statement PH = 7 (strictly, 7.03 at 20°). (3) For acid solutions P# is always less than 7 and for basic solutions it is always greater than, 7. Et has already been remarked that indicators are themselves acids or bases, as in solution they yield hydrion or hydroxylion, or both (amphoteric indicators) and the concentrations of these ions are definitely related to the equilibrium concentrations of the tautomeric forms of the indicator, finally responsible for the color changes. Therefore the color changes of the indicator will follow the change in the value of PH as neutralization of the solution is approached. The use of indicators for the determination of actual hydrogen ion concentration has been highly developed and this use finds a wide application in many fields of applied chemistry. This QrASTJTA 7717; AC,HH'rLTl'RAL 1 4 piuhsr of ! lir' Millet is tivatod on pages 13S to 140, Hpw- rvrr. nc should note here that in making titrations in analytical 4'hfmistry w aro usually not concerned with existing ion con- ct'utrati NaHC03 + H20. Any indicator whose color change covers only this portion of the curve will make a titration possible. Phenolphthalein, with a Pu range of 8.3 to 10, will serve for this purpose if the first appear- ance of pink (at the PH value of 8.3) is taken as the end point. This point is, of course, not as sharp as could be desired. No indicator can be found that will give a sharp change with equiva- lent quantities of carbonic acid and a base, because of the gradual slope of the neutralization curve at this point. Examination of the curves for boric and phosphoric (weakly ionized, polybasic) acids will show why these acids cannot be accurately titrated. The curve for boric acid shows a faint inflection at the point representing neutralization of the first of the three hydrogen atoms, but this would involve only a very gradual change in color of any indicator that would cover this range of PH values. The case is quite similar for phosphoric acid. Only a few of the common indicators are necessary for ordinary titrations in analytical work and three of these will be described briefly. PhenolphthaJein.— This compound is a white crystalline powder, almost insoluble in water but soluble in alcohol. For use in volumetric analysis a solution of 5 gm in 1000 cc of 50- per cent alcohol is suitable. One drop of this solution is sufficient for 100 cc of solution being titrated. The range of color change is PH = 8.3 to 10.0. Phenolphthalein is a derivative of phthalic anhydride and the solution contains two forms in equilibrium: CO COO <=» C6H/ +H \C6H4OH 16 QUANTITATIVE AGRICULTURAL ANALYSIS The second form predominates in basic solutions and the group [ = C6H4 =] is in some way responsible for the red color. The first form is colorless and predominates in acid solutions. Methyl Red. — This dye is p-dimethylaminoazobenzene-o carboxylic acid: The indicator solution is prepared by dissolving 1 gm of the solid in 100 cc of 95-per cent alcohol. The solution is pale yellow ii^ basic solutions and violet red with acids. It is especially good for the titration of ammonium hydroxide and the alkaloids, all being weak bases. It cannot be used if much carbonic acid is present, hence is useless for the titration of carbonates. The color range includes PH = 4.4 to 6.0. Methyl Orange. — The methyl orange of commerce is the sodium salt of a sulphonic acid: This is a yellow substance which forms a yellow solution in water. In presence of acids the salt is decomposed and a red form, previously existing in equilibrium, now predominates. The color range includes PH = 2.9 to 4.0. A water solution containing 0.5 gm in 1000 cc is used as indicator in volumetric analysis. A single drop is usually sufficient to give a perceptible color to 1000 cc of solution. The three indicators described above practically cover the range of hydrogen ion exponents from 2.9 to 10, with the excep- tion of a gap between 6.0 and 8.3. This fact makes unnecessary the employment of indicators other than these three for the great majority of volumetric analyses, even when quite weakly ionized acids or bases are being titrated. It is nearly always possible to choose a strong electrolyte for the standard solution and one of these indicators will then generally serve to cover the portion of the curve that represents equivalent neutrality. The number of indicators that have been proposed and used for analytical purposes is very large. Many of these are useful for the determination of existing hydrogen ion concentration and these will be mentioned in a later chapter (page 139). l * For an exhaustive discussion of the whole subject of indicators see PRIDEATDC : "The Theory and Use of Indicators." CHAPTER II GENERAL OPERATIONS Preparation of Samples.—The object of all preliminary work with samples is to make it possible to obtain, for the actual analy- sis, a portion that shall truly represent the average composition of the entire material at hand. This matter is likely to be treated lightly by the beginner, but proper sampling is often one of the most difficult problems of quantitative analysis. It is often necessary to use a quantity of 1 gm or less and if the substance is not homogeneous this small quantity may have an average com- position that is very different from the average composition of the entire material being investigated. No matter how carefully an analysis may be performed or how accurate the results ob- tained, if the substance used does not represent the average of the substance originally at hand the results become nearly or en- tirely valueless. If the substance is practically homogeneous the operation of sampling involves nothing more difficult than grind- ing down to a degree of fineness required for the work. This is the case when the substance is an approximately pure chemical compound, such as will be used for the earlier exercises. The gross sample, as the analyst receives it, may be in the form of lumps, as is frequently the case with minerals, or it may be in the form of small pieces, crystals, powder, or solution. In any case except that of liquid samples, the object is to reduce the size of pieces to that required for the analysis (usually a rather fine powder) and at the same time to select from the total mass such a quantity as is required for the experimental work. The original sample is often quite large. It is obviously unnecessary and practically impossible to grind the entire amount into a fine powder. The operation then resolves itself into a thorough mix- ing and progressive grinding and dividing. Many forms of both hand and power grinders are in common use. For the first exercises nothing more complicated than a porcelain mortar and pestle will be required. 18 QUANTITATIVE AGRICULTURAL ANALYSIS Mixing and Dividing.—The mixing and dividing is best carried out by using a sheet of oilcloth or paper and a spatula. In many laboratories it is customary to use oilcloth, particularly for mixing minerals. This is convenient but offers the possibility of con- tamination ("salting77) of one sample by the remnant of one that has preceded it. It is better to use a large sheet of tough, flexible paper, which can be discarded after using. The sample, after having been broken down to the proper maximum size of pieces, is placed on the paper and thoroughly mixed by rolling diagonally across the paper and alternating the direction of rolling as illus- trated in Fig. 2. The proper rapid manipulation of the paper is FIG. 2.—Manipulation of paper for mixing samples. attained only after considerable practice. One precaution is essential: the corner of the paper that is lifted must be drawn across, low down, in such a manner that the pile of material is not caused to slide along the paper but is turned over upon itself so that the bottom is brought entirely to the top. In this way only can a segregation of larger and smaller particles be prevented. Since the larger and smaller particles usually have different com- position it is essential that they should be thoroughly mixed. The number of times that the sample is rolled before dividing will depend upon the degree of homogeneity and the accuracy required in the analysis. In the assaying of gold and silver ores it is not unusual to require one hundred times. GENERAL OPERATIONS Quartering.—When the first mixing is finished the pile is made approximately circular and it is then divided, by means of a spatula, into quarters. Opposite quarters are carefully scraped to another sheet of paper, ground finer if necessary, remixed and quartered as before. This process of grinding, rolling, and quar- tering is continued until a sample is finally obtained, small enough in quantity and fine enough in texture to serve the pur- pose of the final weighing and analysis. Maximum Size of Particles.—The maximum size of particles to be allowed in any particular mixing and quartering will depend upon the total quantity of material being handled in this opera- tion. No particle should be so large that its inclusion in any quarter would cause the average composition of this quarter to be appreciably different from the average composition of the entire pile. This means that the ratio of the size of the largest particle to the size of the quarter should not be greater than a certain maximum value. What this maximum value shall be must be arbitrarily determined by the nature of the sample and the degree of accuracy required in the analysis. It is obvious that the part can perfectly represent, in composition, the whole only when the largest particle is infinitesimal. It is equally obvious that this limit is impossible and unnecessary in practice and we may say that, in general, the ratio of the largest particle to the portion that includes it should not be greater than 0.01 per cent. If this condition is met, then, after thorough mixing of the sample, the chance inclusion or exclusion of any given particle cannot modify the results of the analysis to any appreciable extent. Other Considerations.—The maximum size of the particles to be obtained in the final portion that is to be weighed and used in the analysis must be determined, not only from the above con- siderations, but also by the nature of the operation to follow the weighing. This is usually solution or fusion. If the substance is considered to be almost absolutely homogeneous and if it is easily soluble (as, for example, a crystal of cupric sulphate) then the grinding need be carried no farther than is necessary to per- mit the easy adjustment, between fairly narrow limits, of the weight taken for analysis. In such a case, if a sample of 0.3 to 0.5 gm is required, then no particle should weigh more than about 0.1 gm. If, however, the process of solution or fusion is a 20 QUANTITATIVE AGRICULTURAL ANALYSIS difficult one to accomplish or if the material is far from being homogeneous; the grinding is carried much farther, in order to provide a very large surface of contact between the particle and the solution or flux, or in order to conform to the rule of maxi- mum size of particles, stated above. In many cases, as with minerals, the maximum size of particles is fixed by causing the sample to pass through a sieve having meshes of stated dimen- sions. A gold ore may be ground to pass a sieve having 100 or FIG. 3.—Division by quartering. 200 meshes to the linear inch. In such a case one should not make the mistake of grinding and sifting a portion until a suffi- cient quantity is passed, discarding the remainder. This would cause an error because the particles that resist grinding longest are less brittle and have a composition different from that of the particles which pulverize easily. Ol'KltA Y • to nth the cm- » or ict ffi- ild sat he Effect of Quartering.—The reason for dividing into quartern after each mixing and for selecting opposite quarters will bo understood from the following: Close examination of the pilo of unmixed material will reveal the fact that, even after the* most thorough and careful mixing, it is not entirely homogeneous Around the circumference of the base the particles are coarser and they may be gathered toward one side. Around the apex of the conical pile there is a collection of coarser parti- cles. If we simply dig in at random for the portion to be removed the lack of homogeneity will alter the character of this portion. Figure 3 shows how the opposite quarters, no mat- ter in what direction the cuts be made, will obtain the average of a non- homogeneous pile, while a cut into halves will do so only in case* the out is made in the direction aft. In these diagrams the condi- tions are purposely exag- gerated. The Riffle.......-Various r . • i A- !''««*• '*' 'H"1 rifflr, forms of senn-automatic sampling devices arc4 in use, designed to carry out the mixing and dividing process without laborious hand work. Tho riflli* is one of these. AH shown in Fig. 4 this consists of a hopper, at the bottom of which are placed several narrow o.hutos, HO arranged as to transfer alternating adjacent portions of fh<» crushed material to opposite Hides and into separate* pans (not shown in the illustration). This will have approximately flu* same effect as would cutting the pile of material into vorfi<"»l, narrow .sections, alternate portions being united so that f ho pilo is finally halved. Tho riffle may bo made of any convenient si/o, to handle large* or small samples. 22 QUANTITATIVE AGRICULTURAL ,1 AM/,}'*/* Sampling of Liquids.—In case the substance to be* analyzed is a liquid the operation of sampling is usually a simple one, ,| consisting of thorough mixing before the removal of the proper quantity for analysis. Dissolving the Sample.—After the sample* of substance has been properly selected and weighed the next operation i.s usually one of solution. What the solvent shall be is determined by the nature of the sample and by the character of the oj>era- tions subsequently to be performed. Water may be used, or concentrated or dilute solutions of acids, base* or .salts, organic solvents or solid substances used as (luxes by heating to high temperatures. In case gravimetric methods an* to bet employed it is desirable to use a relatively small quantity of the solvent, not only because it must finally be entirely removed, but also because all precipitates dissolve to some extent and it is only by keeping the amount of solvent down to the least cjuant.it y that is workable that the loss of precipitate* is reduced to the minimum. Fusion.—For the purpose of quantitative analysis t he fusion of materials is almost always accomplished with the end in view of producing more soluble substances through the internet ion of an added agent, called a flux, and the refractory material. For instance, most of the natural silicates are practically insoluble in water and all ordinary reagents and therefore they cannot be analyzed by ordinary methods. By a preliminary heating to a high temperature in contact with a basic substance like sodium carbonate, a fusible mixture of new cxmipounds in formed and these will, for the most part, be soluble* in water and hydro- chloric acid so that the solution may be submitted to precipita- tion and filtration processes for the separation and dctterminuf ion of the elements. Similarly, refractory and insoluble metallic oxides may be heated with sodium pyroBulphate with the forma- tion of a fused mass consisting of soluble milphates of the inctjtR The necessary qualities of any useful flux arc (1) that it muni be of such a nature as to be capable of reacting with the refract ory body when heated with it and (2) that the refilling eotiipouitdH shall fuse at the prevailing temperature. To the.se. the* analyst [1 adds a th"*d requisite: (3) that the resulting compounds Khali [ \ be soluble in water or in the laboratory reagents. The* first OPERA T10NK 23 ton is met by choosing as the flux a substance of opposite U> that of the refractory sample. That is, if the latter is icld nature (as silica and polysilicates) the flux should be and conversely. Mlity.—No general statement can be made with regard relative fusibility of various compounds, as based upon emloal composition of these compounds. It may be noted refractory silicates are usually made more readily fusible ueitip; the ratio of silica to metal oxide through the introduc- f more metals, particularly of the alkali metals. Both of mints are made by using alkali metal carbonates as fluxes, the not. result of the reaction at high temperatures is to »arhon dioxide and to combine the alkali metal oxide with Fracitory silicate. This will explain why these carbonates noKt always chosen as fluxes for silicates. A reaction such following may occur when orthoclase is fused with sodium i ate: iSisO8+f)Na8CO8-*KaSiO8+5NaaSi08+2NaAlO2+6CO2, n or lean complicated mixture of aluminates and silicates alkali metals being formed. ic Fluxes."-—Sodium carbonate, potassium carbonate and u-potassium carbonate arc the most important of the basic that are used for analytical purposes. These are used ' for fusion with silica and the refractory silicates. Such as calcium oxide, used for fluxing silicates in the blast i€* for iron, are of little use for analytical purposes, partly *e the resulting compounds aro not soluble and partly ^o metals that arc to bo determined in the sample are need by the use of such materials. I Fluxes.- -Fluxes of an acid nature are valuable chiefly ming fusible, soluble compounds when heated with metallic or waits that are over-saturated with metallic oxides. The wsf ul of such fluxes are the pyrosulphates and the biborates him and potassium. 1 HulphatoH are often used instead of pyrosulphates. When rmer are heated they give off water arid they are completely rtcd into pyrosulphates by heating to higher temperatures: 2NaH804-* Na2Sa()7 + H«O. 24 QUANTITATIVE AGRICULTURAL ANALYMH Because of the excess of sulphur trioxide in the pyrosulphute, this readily reacts with metallic oxides when heated with the latter: Fe203 + 3Na2S207 -» 3Na2S04 + Fe,(S< )4)«. The biborates likewise combine with metallic oxides because of their excess of boric anhydride. FejOa + 3Na2B407"-»2Fe(BO,),'} + GNuRO,. Precipitation.—The process of precipitation is usually a chemical reaction between substances in solution, the result bring the production of another substance of relatively small solubility. The actual precipitation is always preceded by a condition of supersaturation (with respect to the precipitating substance) and this breaks down at different rates with different precipitates. In some cases equilibrium between the precipitate and the satu- rated solution of the same substance is attained only after Uw lapse of considerable time, while in other cases such equilibrium results very quickly. An example of the first- class of precipitates is found in magnesium ammonium phosphate. In order to obtain the greatest possible amount by precipitation the solution must be allowed to stand for some hours in contact with the crystals that have already been precipitated. Stirring usually serves to hasten the attainment of equilibrium by promoting contact of solid with the supersaturated solution. It is important to note that there is no definite relation between the degree of persistence of nuperxatumtion and the degree of solubility at final equilibrium. Solubility Product.—In order to diminish the solubility of the precipitate to the lowest possible figure, use in made* of the princi- ple that in any saturated solution the product of the concentra- tions of the constituent ions is a constant (the "solubility product") which cannot be exceeded without reproducing the abnormal condition of supcrsaturation. By adding an excrnn of the precipitating reagent (and therefore of one of the ioiw of the substance precipitating) the concentration of this ion in largely increased. There must then be a eorroKpoiidhig derreawt in the concentration of the ion that is being determined and thin results from increased precipitation. GENERAL OPERATIONS 25 Colloidal precipitates, such as aluminium hydroxide, manganese sulphide, etc., do not obey the law of solubilities referred to above. Size of Crystals of Precipitates.—Other conditions being unchanged, it may be said in general that slow precipitation results in the formation of relatively large crystals and conversely. The rule that the precipitating reagent should be added slowly and with continued stirring is a consequence of this fact. But if it has been found impossible to pro- duce a precipitate of sufficient coarse- ness to permit retention by the filter paper this fault may usually be reme- died by warming the solution and precipitate for some time. The actual result is the resolution of small crystals and the reprecipitation of their sub- stance upon the larger ones. This is due to the fact that very .small particles have a slightly greater solu- bility than larger ones. The process of heating a solution with its precipitate in this manner is called"digestion.77 Filtration.—After a precipitate has been separated by filtration and washed, it is either dried to constant weight or strongly heated ("ignited77) in a crucible, in order to bring about some definite change in its composi- tion before weighing. In the former case it is practically necessary to use a filter of inorganic material because FIG. 5.—Gooch or aiundum paper cannot be dried to any constant crucible with rubber filtering 1 T* , . ... ring in funnel. (In section.) degree of hydration. If strong ignition is to be employed, either paper or inorganic materials may be used unless burning organic matter exerts a reducing action upon the precipitate, in which case the use of paper filters is again excluded. Filter Paper.—For quantitative purposes a paper of very high grade is required. The texture must be close and uniform and the material as free as possible from inorganic matter 26 QUANTITATIVE AGRICULTURAL AXALYX/X which would be left as an ash on burning. To obtain the latter condition, paper is subjected to a preliminary extrac- tion with hydrochloric and hydrofluoric acids, thus dissolving all but a small trace of ordinary ash-forming matter, Such paper is usually called "ashless." Inorganic Filters.— To avoid the reducing action of the filter either an alundum crucible or a Caldwell crucible may be used. Alundum is a porous form of aluminium oxide, partly fused together with a hinder. A crucible of this material may be placed in a rubber holder placed in a funnel, as shown in Fig. 5, and the liquid drawn through by suction. The precipitate is then washed and ignited directly in the crucible* The Oaldwell crucible (usually known an a "(Joodh") is n tall crucible* of porcelain whose? bottom in perforated by small holes. This is used in a manner similar to that described for the alundum crucible, with the exception that ft pad of asbestos (see page 158) i& formed over the bottom *™I t/his provides the ttWK- sary filtering Hurfa,c<*. For high temperatures the platinum form m better. This in the* original Gooch crucible. Washing.— Wash bottles like Fig. 6 should be provided. A fine stream of water, hot or cold, may be blown on to the? filter, the precipitate and filter being thus washed free from Holuhkt impurities. To avoid unpleasant effects due to blowing bark of steam from the hot water bottle, or of volatile liquids when these are used for washing in special cases, a pressure bulb and vent may be provided. Great care must be used to avoid mechanical low of precipitate, It is well to remember also that the* most efficient wantiing in 6.— Common form of wiwh bottle, (SKXERAL Ul'KltA77O.V.S* accomplished by using several small portions of wanh water, rather than fewer and larger portions, Drying.............If a precipitate is to be subjected to strong ignition it is not usually necessary to carry out any preliminary drying, other than such as may be performed in tin* crucible over a low flame. But- some precipitates are to be weighed, after drying at a definite1 temperaf tire, in which eases u drying oven having a fairly close temperature regulation must be provided. For thin purpose the use of electrically heated ovens having automatic* temperature regulation is now almost universal. Any oven must have provision for con- tinuousdisplacemcnt of humidi- fied air by drier air. Passing t he entering air through a drying agent, such us calcium chloride or sulphuric acid, will facilitate the drying operaf ion but tltis is done only in special cases. In order to understand the principle of drying it is well to recall the law that any moist substance will continue to low moisture by evaporation until a certain definite* pressure of water vapor ("aqueous tension"; is established in ffje Minuititd ing space*, the value of this pressure depending upon «>ii lite nature of the moist substance and (ft) the temjHTHture. If I hi* pressure of the surrounding vapor in reduced bv moans, evaporation proceeds until equilibrium in linhed. Thiw by continuing to reduce the external vapor pri«H- sure, evaporation may be continued. However, it in important to note that the vapor pressure to be eoriHidfwd m not the lota) ptmsurc (Hitch im that of thfahnoMphcn*) but the partial |ir«'w«iir<< of the* vapor of water. AH lite latter priwtw i« directlv pt'iipnr* tiorial f.o the concentration of wafer vafnir in tin* Mirrotifjfijfi# •space, the name result will finally be produced (Vi) by rriiurtiitf the total presHure by means of a pump, f/>; by rf»fitjiiuf»u^lv ilr-.-,. placing the. nioiht air by itu'iins of some other dried w> nt vr-1 flV f 28 Q UA N TIT A TIVE A GHIC ULTI IRA L A A' .1L) ',S7N confining the moist substance in a space which contains some hygroscopic material. Certain types of ovens make use of methods (a) or (/>}, above. In such ovens an air-tight chamber is provided and a dried gas is passed through this or the chamber is exhausted by means of an air pump. Desiccators.—Method (c) is employed in the various types of desiccators, used at ordinary temperatures. Figure 7 illustrates a small desiccator suitable for carrying about flic* laboratory. In Fig. H in shown a desiccator in which are used the principles of methods (a) and (c). This is what is known as a "vacuum desiccator." In both illustrated forms of apparatus the dry ing agent, which may be calcium chlo- ride, sulphuric acid, or, in certain special cases, phos- phorus pentoxide, is placed in a layer on the bottom. Ignition of Precipitates. The term "ignition*1 in used in thin connection in a sense somewhat beyond its ordinarily accepted meaning, since it is applied to the heating to high temperatures of substances that are entirely incombustible. The* purjxwes of ignition are to destroy the filter, if paper has been used, to exjx'1 the last traces of moisture and volatile impurities flint have not been removed by washing and to cause the precipitate to change in a definite manner, if a change is to be made. If a pai>er filler has been used it is carefully removed from the funnel by slipping up the side. It is then folded as indicated in Fig. 9, the object, being so to enclose the precipitate that loss in impoHHible, If it is to be dried and removed it is then placed in the overt on n cover gla8s. . FIG. 8.—-" Vacuum " dcHimitor. A O/'A'AM V70AX Oxidation in the Crucible.......The crucible is ulnuwt invariably heated by means of a naked flame, being supported on a tri- angle l>y means of some* kind of .stand. When the obji*ri in fi* Mi'thmi of u fiii««r i»H|t«'r for iKuifi*«fi oxidize t.licv paper or precipitate ih«» erueibh1 is jilueele is liable to fall buck and It nmv times fall through and CAIIHI* a failure of the det« f 30 QUANTITATIVE jr,7 no redwing action upon the precipitate it in still desirable to complete the ruin- bustion of the paper at a comparatively low temperature, 77//.s- is a matter that is too often ignored //// flic ,v/////^///.^ <'rys- talline precipitates that are ordinarily regarded ji* infusible will often undergo softening at the sharp corners of I hi* crystals. This causes a certain sticking together which n*MiIts in flu* endo- sure of a small amount of carbon in such a. way as to make it* oxidation extremely difficult, If the paper containing flu* I1 FIG. 11. — Correct portion of crucible for oxidation. "f 6 InrMir*-«.» j« M.-l «f M,.,|4 precipitate is heated to a high temperature at tin* vn i it is often almost Impossible to make* if whit**. < IIP- »»f tin* IH^H! examples of this action is in the ignition of mague-Mum aiit!iir>» nium phosphate to convcsri it into inatfneMtim pyr«» Premature heating of thin HuhHtnnc^ f<» very high f^f will frequently result in a black or gray material that cannot. whitened by long ignition. Decomposition in the Crucible. ............ After oxidation nf tin* pnf is completed the temperature is raiml in order fi* completely any volatile impurities thai limy rciaaiti iirnl to fimw* whatever decomposition IK (Icvired. Hince ffxidaiifin in no l«*ngi*r an object the crucible in placed in an upright potion and tin* cover is placed over the* top. This given mi opportunity for the flame to bear directly on the boll-out of flu* eniriM** the precipitate lies. The CJOVPT ulno largely pri'vi-ntf* heat due to convection currents of air within tin* crueibli*, Crucibles.— Porcelain cruciblen of lii'irfi gradi iiuiv !»»• 11 most work, in cases where the precipitate i* nut to hi* Alundum already han been mentioned in connection with !i crucibles. When any compound or mixture i* I** l*e nf for f/A'A" KKA L OPERA Tin A*,S' porcelain is usually unsuitable because the funed material will combine with the glaze, or even with the porcelain itself. For such work platinum or OIK* of the newer Hubst.Itutes, palau or rhotanium, is (essential. Marking Crucibles. Metal crucibles should have permanent identification numbers stamped upon them by means of small dies. These numbers form a part of the analytieal record and they serve to prevent accidental transposition of weight records. Porcelain crucibles may best be marked by means of n pen and ink, the. marks being inconspicuous figure* or small dots, When the crucible is strongly heated the iron of the ink forms the red oxide, which burns into theglavse and forms a permanent identification mark. ((Vrtain common inks do not- contain iron, iso that they are unsuitable for this purpose.) Some manufacturers of chemical porcelain now furnish cruci- bles and dishes serially numbered with permanent marks. This is a great convenience to tint analyst.. Care of Platinum.- Platinum wan* will deteriorate rapidly unless the following precautions arc taken in its use and cure. 1. Handle* carefully to avoid bending, I'se clean crucible tongs and do not allow the tongs to come into contact, with fused materials within the crucibles or dishes. 2. For cleaning apply the appropriate1 solvent, according to the nature* of the material to be removed, C 'hromic ncid is suitable for removing organic nta.tt.cr, and hydrochloric or nitric acids for insoluble carbonates or metallic oxides; fusing with Bodiurn carbonate is suitable for removing silica or silicates, or with sodium pyroBiilphate for .such metals or metallic oxide?* »,M resist the* action of acids. 3. Do not heat platinum in contact, with the inner cone of the laboratory burner, an britiU*nc*HH results from mtch t*x(Mwun*. 4. Do not heat compounds of lead, tin, biwinuth, HrHrmc, antimony or mtc in run tart with platinum. Reduction may occur, the reduced metal alloying with the platinum, f>. Do not attempt to remove Fusions from platinum eruribli'M or dishes by means of files, glass rods or other bard too!*, l^r solvents or a rubber-tipped rod. 0. Dull surfaces should her polished tightly with wet emery slime or fine carborundum. fcl . 32 QUANTITATIVE AG'RK'WCIfAL J.V.i/.»'/.< Platinum Substitutes.—The increasing .scarcity of platinum has made the introduction of substitutes a practical necessity. While it is true that pure platinum ixxssesses certain prop- erties that cannot be duplicated by any other metal en- alloy, yet certain alloys have been found to he suitable for making into crucibles and dishes that will serve for many of the operations of the analytical laboratory, in place of the platinum that has been in use. Two of these will be mentioned. "Palau" is a trade name for an alloy containing about SO per cent gold and 20 per cent palladium. Its melting point IH about 1370°. "Rhotanium" is a name given to a series of gold-palladium alloys whose melting points range front 1150 to l-lalf. Hofh palau and rhotaniurn may be used in place of platinum exrept. where much oxidation is to be expected or where very high tem- peratures are employed. Unfortunately the manufacturer discourage the IIHI* of thene substitutes by maintaining the price of manufactured articles .so close to that of platinum ware that the* purchaser will usually pay the difference in order to obtain the more satisfactory platinum. Burners.—The burner that is to be used by flu* analyst may IN* anything from the cheapest and simplest burner of the Btmscn type to the most expensive and complicated burner obtainable. The purchaser has his choice* and probably certain advantages are possessed by each burner, The only feature that in really essential is independent regulation of air ami gas supply. The* requirements are quite different in different caws and I hi* mmlynt must have at his disposal all kinds of flume, from f hi* yellow illumi- nating flame to the most intensely hot and oxidizing flume, and he requires very small and very large fliiiwH nf iwh Hiuv. In order to obtain this variety of flame there must I** nome method of regulating the gas supply without changing the {irfwun* uf the* gas valve, since this also changes the amount of nir drawn in at the mixer. The simplest form of Hunwn burner dm** not, fx*rmit this gas regulation without unscrewing the upper itilw* itml ilmng- ing the gas jot by the um of pliera, Btieh regulation in w»t fu- sible in practice. GENERAL OPERATIONS 33 In the Teclu burner (Fig. 13) the gas is controlled by the screw on the side of the base while the disc at the bottom of the cone controls the air supply. In this burner the regulation of gas flow is not accomplished by altering the pressure under which it is delivered but by chang- ing the size of the orifice in the burner. The maximum pressure is thus used at all times and the result is a better mixture of gas with air than is obtainable by regulating the gas cock of the supply line. A very common error on the part of students lies in carelessness with regard to the regulation of flames. If a relatively cool flame is re- quired and if a deposit of carbon is not objectionable the air should be excluded from the mixer. If, on the other hand, the highest efficiency of the burner is desired, careful regulation of the air and gas is necessary. The inner blue cone should be well defined and it should not show a yellow tip. If more air is admitted than that required to burn the gas com- pletely with production of a "blue ^ flame, the result is a roaring and FIG. 13.—Section of Toolu burner, fluttering flame. This means that more air is being admitted than can be used and this air, in being heated by the flame, lowers the temperature of the latter. Meker Burner.—A somewhat radical departure from the older types is found in the M£ker burner. This is shown in section in Fig. 14. The air is drawn in through several holes in the base of the tube. The delivery of the gas under pressure into the inverted cone which forms the burner tube causes a greater reduction of pressure within the tube than is the case with burners having cylindrical tubes. The result is a greater inflow of air, making possible the combustion of a greater amount of gas in a given space, and also more complete mixing of gas and air. fT M 34 QUANTITATIVE AGRICULTURAL ANALYSIS The nickel grid through which the mixture flows at the top of the burner causes the gas to burn exactly as though each mesh were a small individual burner. The tip of the inner reducing cone of each small flame is usually about one millimeter above the top of the burner and, as all of the small flames unite to form one large one, the result is a highly concentrated flame, every part of which is oxidiz- ing in character except a zone of about one millimeter in depth, immediately above the top of the burner. This is a distinct advantage, especially in heating platinum articles, since platinum is easily dam- aged by heating in a reduc- ing flame. A number of imitations and modifications of the M6ker burner are offered for use at this time. Most of these use the same combus- tion principle, the burners differing only in mechanical features. Blast Lamp.—In order to produce a higher temperature a burner may be constructed so as to consume a larger quantity of gas, depending for its complete combustion upon admission of air under pressure. A burner so con- structed is called a "blast lamp." Many forms of such burners are in use. The flame of the M£ker burner is nearly as hot as that of the ordinary blast lamp using the same gas and it may be substi- tuted for the blast lamp in many cases. There is also a M£ker blast lamp, similar in construction to the one already described but using air under pressure. FIG. 14.—Section of M£kcr burner. GENERAL OPERATIONS 35 Weighing.—From all of the foregoing discussion it will be seen that every analytical determination involves, at some point, obtaining an accurate estimation of weights. Even the volumet- ric process requires weighing the sample and a weight is usually involved, directly or indirectly,, in the standardization of the solutions used for the titrations. It is obvious from this that an accurately constructed weighing apparatus is a necessary part of the equipment of the analytical laboratory. Methods of Weighing.—Any method that depends upon the attainment of equilibrium between the force of gravity and the PIG. 15.—Essential parts of the balance. resistance to distortion of a spring is necessarily subject to considerable and variable errors. These are chiefly due to varia- tions in (a) elasticity of the spring and (5) the value of gravity for different altitudes. The only method that is free from these errors is weighing on a balance, a standard mass being compared with the object to be weighed and the former being varied until equilibrium is attained. The Balance.—The analytical balance should be so constructed as to provide means for accurate weighing to one ten-thousandth 36 QUANTITATIVE AGRICULTURAL ANALYSIS of a gram. In order that such weighing may be performed the balance must be constructed with mathematical accuracy. The three bearings are commonly of agate, ground to a very fine "knife" edge and each resting upon a smooth block of the same material. They must be so placed as to lie in the same plane while weighing (the central bearing is usually slightly below the plane of the end bearings, to allow for distortion of the beam when loaded) and absolutely parallel. The moving parts are as light as is consistent with the strength required to bear the rated load and they are provided with a mechanism for arresting their motion and for lifting the knife edges from their bearings. The entire balance is enclosed in a glass case, which is kept closed during the final adjustment of weights, so as to avoid inter- ference of air currents. These points will be made clearer by reference to Fig. 15, which shows only the skeleton of the balance. Weights.—Practically all weighing operations of analytical chemistry are carried out by means of metric weights. A balance is rated for a certain maximum load and the largest piece of the set of weights should not be heavier than half this rated load. A balance rated to carry 100 gm in each pan will thus require a set of weights having a 50-gm piece as the largest piece of the set. The smaller pieces will then be, in grams, as follows: one 20, two 10's, one 5, one 2 and three 1's. These will total 100 gm. The fractional pieces (milligram pieces) are then apportioned as follows: one 500, one 200, two 100's, one 50, one 20 and two 10's, with a movable " rider" on the right arm of the balance beam to make another 10 mg, the beam being graduated so that by shifting the rider, 0.1 mg fractions may be made. It will be seen that these milligram pieces total 1 gm. The Rider.—The reason for using a rider on the beam instead of the very small weight pieces on the pan is largely one of convenience. The rider may be adjusted with the balance case closed and this facilitates the final adjustment. This method also dispenses with the use of a large number of very small weights. The actual weight of a rider to be used on a given balance will depend upon the manner in which the beam is graduated. These graduations are to indicate a certain number of milM- I1 P GENERAL OPERA TIONS '*7 grams and fractions. The generally approved method is to have. the space between the central knife edge and the pan support marked in ten principal divisions, each with ten subdivisions. The number over the central pivot will then be 0 and that directly over the pan will be 10. If the rider is placed over the pan it will have the same value as if it were in the pan. Hence it should weigh, in milligrams, whatever is indicated by this number. Various balances have, instead of 10, the figures 5, 6 or 12 over the right pan. They will then require riders having these indicated values, in milligrams. The Chain Rider. — The " Chainomatic " balance entirely dispenses with a separate rider. One end of a small gold chain is permanently attached to the balance beam. The other end of this chain is fastened to a hook which may be moved up and down a scale (Fig. 16), this action being controlled by a knob outside the balance case. Movement of the hook on the scale varies in a definite manner the length of side of the loop which is supported by the beam and this may be adjusted while the beam is in motion. This is a distinct advance in balance design, although this improve- ment adds considerably to the cost of the balance. Use of the Balance.—It has already been stated thai/ the process of weighing involves the adjustment of weights upon one pan until they are in equilibrium with the material on the other pan. This is not done by noting when the? balance beam fails to swing but by the more accurate method of causing FIG. 10.—-"Chain ridor find part of scale as used on tho "ehumonm- tic" balance. F'l f. 38 QUANTITATIVE AGRICULTURAL AXALIMX it to swing several times in both directions, noting when a pointer attached to the beam swings equal distances on either side of a "zero point3' on a fixed scale. The balance should be adjusted so that without load it swings about the true zero of the scale but thermal changes, settling of buildings, etc., will cause this to change and the zero point must be determined occasionally and the adjustment changed, if found necessary. Differential Weighing. — Where the desired weights are found by a differential process it is not necessary that the adjustment of zero point should be made, or even that the zero point should be known. It is sufficient to assume the zero point- to be t he same as that of the scale. Although this may involve an error in weighing, this error will be the same for both weights obtained and the subtraction will eliminate it entirely. For example, a crucible is being weighed empty and again containing a pre- cipitate of barium sulphate, in order to find the actual weight of the latter. A plus or minus error may have been made in the recorded weight, due to an incorrect assumption of zero point, but this will be the same for both weighings and when I he* observed weight of the empty crucible is subtracted from the observed weight of the crucible and barium sulphate, this error disappears. To Determine the Zero Point.— (''lose the hfilnntw ciuw nnd lower the pan rests in such a manner a« to «top any hit oral winging f»f th« pans, then lower the beam ro«t8 and net the hr»am in motion In* allowing the rider to rest momentarily on the? beam, then mining it. Thin hhottid cause the pointer fco swing five* to ten divinionM on either wiclc* of the j?w> of the scale. Take at least throe roidingH on ono Hide and two OH the cither, Subtract the less average from the greater and divide the* remainder by two. This gives the zero point if the proper direction is noted. The zero point may be determined with ttufficient accuracy for mmt work by simple observations without compulation x, by noting that the amplitude of vibration of the pointer diminixhvx regular ly with each successive swing. Weighing by the Single Deflection Method.— This rapid method has been described by Brinton.1 The pan rests must first he adjusted HO that when rclfUHcd they shall give no swinging impulse to the system. That int if the 1 /. Am. (them. /for., 41, 1151 (1919), 7'i tul (iKXKKM, O/'A'AM'/VaVX •»•' loads are in equilibrium there, must be no swinging of the pointer at release of the pans, the* beam rests being clown. Kquilibrium is then destroyed by adjusting one of the screws on the bourn end, so that at release the pointer will swing X to 7 scale divisions in one direction. The point on the scale which tin* pointer reaches on its first excursion is taken as the "xoro point," f-ho pans having first boon steadied to stop lateral swinging. In weighing, the weights are adjusted as by arty other method, the rider finally being placed so that when, the pans are released the pointer will reach the same* " xero point," on its first, excursion, that was first determined. Although this method would seem, at, first, to be essentially incorrect in principle, it is capable of giving accurate results in the hands of a careful analyst,, with the following limitations: 1. It cannot be used with, balances having a single control, releasing beam, and pans at one* operation. 2. The pan rests are cleaned, if necessary, with alcohol to prevent sticking to the parts, an otherwi.se a swinging impulse would be given by release* of the hit tor. 3. Most balance's show a variation of sensibility with variation of load. The "xero point" must then be determined at the approximate load that is to ho weighed, if a single weighing is to be made, or at both loads in case* of differential weighing, unless the singlo load or the difference between the two loads is quite small. One of these two conditions is met in most unalytieul work, Sample weights or weights of precipitates are l«»ss than one gram, in the majority of canon. If a sample is to bo weighed on counterpoised glasses it in sufficient to determine the point reached on the first swing, with the empty glasses. If if, in to be weighed front a weighing bottle, or if the precipitate in to be weighed in a crucible, the point reached when the filled weighing bottle or the empty crucible, roHpoeftvoIy, in firing weighed, i« taken as the xero point for that particular pair of weighings. 4. It in obviouft that a single observation given no cheek upon chance causes of variation, sueh us vibration or air current* within the balance cane. The method is useful, especially for rapid work, if proj>or cure and consideration arc exercised, hi any evimt tht* hftiumw mnnt 40 QUANTITATIVE AaitfCCI/f'CliAL ,\\AlA'SfS bo carefully tested at the beginning, to give a^unmr can safely be used for this method of procedure. Calibration of Weights.— Mxponsive sets of weights are usually adjusted with sufficient accuracy for most analytical work, but with weights of the grade ordinarily available u calibration should be made. Weights that are found to be in error may then be either adjusted to accurate values or used with corrections. This is a matter that is given serious attention in Jar too feir laboratories, college or industrial. Conntwmal treujhh /m/w////// are in error to the extent of two or three per cent and mw Ittrtjer errors may be found, after the weights hare been in nwfur a year or more. To ignore such errors a,s- lh; not been rlmngcd by the substitution of weights, the standard piece and the experimental piece have the .same, value, irrespective of the value of the counterpoise-. If the xero point ha-H changed, shift, the rider to rcHtore equilibrium. The amount of shift given the numerical difference between the two piece;-,. If the shift of the rider is lo the, right the in pen- itiental piece is liyhtrr than the standard piece and if to the /*// it is htuntr. Apply the indicated / ^ correction. Repeal tin* process j»«t described, comparing each piece of the entire >>et with the correMponding piece of the standard set, finully tubulating the corrections. The*«* should l»e recorded on ?i card, which may be placed In the. balance cawe for future If ait iieeunitely ^liindjirdi/.ed complete xet. of weights in not uvuilablf*, th<* set may be calibrated to a Mingle stniitfanl piece, or simply relative vnlii4*H •!}|1||»r* .Ml of the* vnriouH pieces may b«* e«tahjh}n'*|, UHIIIK the i«,t t»»Iitu method of Kirhunb."' ife:rtlpft Volumetric Apparatus. It bus alrfwiy hr<*n .shown tlnit tlic baluiiec* in roiiwrnwi, *c»H. But tin* work in irefulially (IifTc»n*!it front gnivifiiHrte iiniily^is in fhiit in* final wHfiltiftu: of pn»<'ipitut«is is made, hint end fit' fluV a nH^u^tiri'tn^fif i^ inmli- of1 tin* volume of a stumiunl sohifitirt n*quir<* . c,, . t , (6) measuring -Bureau of Standards hat* under- pipettoa. taken a special study of thin .--.£ v IX. u t I'm, I!*,- -Showing tii.» am! gruel tuition* npprovwi for liiir«i!4*«* UKXKltA L 01 >KRA Y7OA',S' matter and has prescribed1 rules for the construction ami use of all volumetric apparatus. Home of the more important feat urns of these specifications are given below. Kvery good laboratory should prescribe* that apparatus shall conform to these specifi- cations wherever possible and upon receipt of tbe various pieces they should be calibrated, in order to establish any ni IIM**!, unle* •> the* use of an approximate weight iV sp* cifuvilly , if nm\ he M«en that the recoveu **?' chlorini or of «ilver may he regarded a«» prnctieidh eutupjHe, for all ordinary purpohe.v, However, if mu.vf he reinciiihered that silvei r'lilonde ili -jnUi*. (\*wily in ammonium hvrlroxide and to »in ;tf*pr«'cu»hle *nt»'iif in concentrated solutions of xoditun or polii -itiin chlori«Ii , ;»u*| «it hydrochloric* add. It in decompiled hy wanning mil it miitiiu ot jK>tUHsium hydroticie, silver otnle heirtg toimid, In the det«*rminafioit of chlorine in impure rhlnriiiiM if j n^ccvwiry to guard against the precipitation til nth««r -itvej saltH, Mich ah pho^pliiite or ntrbomtte, hy h;ivinjf a -tiuil! exce-, of add priHiif, Xifric acid j> M»tahl<* for ffii^ jwrpo-r »h*i 50 QUANTITATIVE AGRICULTURAL AXALYMX this serves also to insure against the objectionable action of bases, noted above. Silver nitrate being used EH reagent, the following reaction occurs: AgNO, + MCI -> AgOl + MNOs. The following experiments must be conducted in a room which is not brightly lighted and they should not be unduly prolonged. Gravimetric Determination.—Prepare two "Gooch" (Oaldwell) filters by the following procedure, first marking them I and II an directed on page 3!: Place the crucible in the holder as shown in Fig. 5, page 25. Apply the* suction and pour in prepared asbestos suspended in water until a felt of sufficient thickness is obtained on the perforated bottom. The* required thickness will vary according to the condition of the oslwstos, a compara- tively fine material making a compact pad which need not IKJ an thick an one of coarser material. These points must be determined by experiment, guided by the advice of the instructor. Place a small perforated porcelain plate on the pad, to prevent injury when solution is poured in. Finally give the crucible a single rinsing with redistilled alcohol to promote rapid drying, drawing out as much liquid as possible. Ho move the* cruci- ble, carefully wipe the outside and place in an oven which in maintained at a temperature between 105 and 110° and dry for at least 30 xninut.es. Place in the desiccator and weigh after 30 minutes cooling. If an alundum crucible is to be used instead of the Gooeh it is placed in the holder so that the top is even with the rubber. This in to provide for thorough washing of the entire body of the crucible, which is porous. No asbestos is used but a new crucible should be given a preliminary washing with hot water, followed by alcohol. It should then be dried at 105 to 110° before weighing. While the filters are drying proceed with the weighing arid precipitation processes. Fill a clean, dry weighing bottle with the powdered and well mixed chloride sample. Provide two clean, 250-cc beakers of Pyrex or other resistance glass and mark them I and II. If the substance is known to be unaffected by contact with air it may be poured directly into oni» of the counterpoised glasses on the balance, until about 0.2 gm is obtained, (The glasses should have been brought to balance by means of the rider.) This sample is then weighed accurately and brushed into one of the beakers by means of the small pencil brush of camel's hair. A second sample is weighed and brushed into the second beaker. The weights are recorded in tho proper places in the data book. If the nature of the sample is such that it should not be unnwwsarily exposed to air it must be weighed by difference. Place tho filled weighing bottle on the left pan of the balance, using for this purpose a pair of crucible* tongs having short pieces of clean tubing drawn over the tips, and carefully weigh. Record this weight in the data book at the top of the «pn«* marked Qt M.V777M 77 !7<; /;A7'A7i',U/,Y,t 77 for .sample I. Carefully remove the M«»pper, holding over beiiker I, and pour alnmt 0.2 to 0.5 grn info the beaker. Repine*' the .stopper, u*«ing great carol hut. no particles .shall fall outside the beaker and be lost, then re\\eigh tho bottle, and contents. For thc.se weighings flu* zero point of the balmier need not be. known, an explained on page ,'tH. Record the* last weight under the* first- and subtract to obtain tin* weight of wimple used, Heeord the laKt, weighing also at the top of \\\i\ space for sample II. Remove it. nrconti portion to iM'ukcr II and r*«wi%h tlu* hottlr, rwordiMg un«l<*r th^pn^MMlii^ weighing, Suhtnict again for th(* weight of sample II. Dissolve* <*:tfh wM'igtird .^ansph* in 75 re of disf ilh'd \vnt««r, inpn-«in'd with n fair dc'grrc of arfurary in a gnuhiati'd cylindrr, and add 1 <"'" of UO-prr rriit nitric acid. (\Vat«T an«l arid mu,Ht !»«• fn«J' from rhlorid«*:». T«'?*t. hy niuiiig the (juantiti^ inon!iom*d al»c»v<* and adding a f«*\v dr«tp^ of rli*jir Htlvrr nitrate .solution. ) Hi*at th«* chloride noliition nearly to boiling then pr«*ripi». tatc* with rl«*ar «Vper cent holulion of silver nitrate, adding drop l»y drop from a pipette and stirring continuously. Ten to 20 cc of Nolutiott may hi* rcMjuircd. acc«»r^ rod, If a f Sooeh eruciblc w uwd place* flit* rod ngain^t. flit* perforated plntr* c<»verinw; the n^tn^fim Rhine- nil IOOM* precipit itfi» into the filter, then clean the beaker by mean*) of thi* jMiliceiiiiiii 61 rublx*r-tipped rnd| ftinl wiwh hiitllf ami ftiifillv wash tin* entire precipitate and crticible. !»y pouring itt il--per cent, chloride- free nitric acid from u beaker until tfie witching** ?S!M»\V no eloudtnerc.t wiMi n drop or two of dilute hydrochloric acid, thwt »howin{( that nil ;ti!ver iMfrnfe ha« been removed. In making ^uch 11 t«**t ftrnt rin^e the ftntftnlr of Hi** |ow-ef Mid of the funitc! fJih*% then roller!, nlmtif. I ce of the wwihtntt** from flu- Kilvrr ehlorifie i« n cjeun ti^f. tu!i«* eontatrung is, drop of AgCl + MN03; (1) (2) This method may be employed to determine the chlorine of chloride solutions but the latter must be neutral before the titra- tion can be made. ' Equation (1), above, shows that the hydrogen equivalent of silver nitrate is 1 and its equivalent weight is therefore the same as its molecular weight. A tenth-normal solution (see page 7) ; will then contain 16.989 gm of the salt in each liter. Instead of this the solution may be made in the decimal system (page 8), 1 each cubic centimeter being equivalent to some simple weight of chlorine. If n is used to indicate this required weight of chlorine, > u r, * i *• , * • 1000 X 169.89 n * each liter 01 solution must contain - — -— - cm Of silver I 35.4o \ nitrate. \ ( * Volumetric Determination: Silver Nitrate Method. — Prepare the follow- I ' ing solutions: I (a) Silver Nitrate. — Calculate the weight of silver nitrate necessary to make 1200 cc of a solution, either tenth-normal or of such concentration that 1 cc is equivalent to 0.005 gm of chlorine, adding 1 per cent for possible impurities. Weigh to centigrams on counterpoised glasses and dis- solve in chloride-free distilled water. Dilute to 1200 cc, mixing the diluted solution very thoroughly. (6) Sodium Chloride. — Prepare 500 cc of a solution of pure sodium chloride which has been powdered and dried at 105°. The concentration should be equivalent to that desired for the silver nitrate solution. The equivalent weight of sodium chloride being its molecular weight (58.46), a tenth-normal solution must contain 5.846 gm of the salt in each liter. Ql 'AXTITA 77 VK DKTKKMIXA T *l'hiH At the ull*-'. *»f If, instead, 1 cc of the. .solution is to contain n rumple, definite, weight, n , IOOOX58.>If> /t , .. , . grn, of chlorine, each liter must contain ....... ,.r ,,, gm of Hodium chlo- ride. In this cane w may conveniently In* (UHI5 grn, Whatever its value, n Is the "chlorine factor", /'Vi (nee page* 5) of thw notation. Weigh thewilt carefully on counterpoised glasnen and diwnolve in chloride- free wafer in a calibrated flank, dilute to the tnark and mix thoroughly. (r) l*ulax*ium ('hromnte.- ..... -Prepare 50 cc of a 5-pcr rent notation of potm-*- Hium ciiroinate and llr mnlity f art or"), If the deeiniiil «yi'iti*in in to be twin! mid if tin* iKiditiiii chl*»ritle fioinUon hfw been miide HO »/* to coiit-nirt f)»i2*ri gin in 25 r*% iyi {ibfive ^itgge.fifivi, flu* dilution ntli'i for flu* «ih*er iijtriife wtlnlinn in iigiiiii flu* invrw nifift *if equiviileiit voluftien, exactly II.H illiwf rnti'd in tin* prreediftiC |}nrngrn|i!t. In thu ubovir #^niti|ile 1 <•) 35 i»c of wnter should lit! nddttd to <*n«fh liter of the utaitdurdtxitd witutioit of thi« example. -I.I 24,15 LCirifi fl)JCK!5 in iliii "tm 54 QUANTITATIVE AGRK.'UL'I'ritAL AXALYMX The dilution is carried out as follows: Fill a dry IMO-w volumetric flask exactly to the mark, add the necessary water from a burette and mix well. This requires a flask that will hold the required added water uhorc f.h<» mark. In case the dilution ratio has been found to be greater (ban about 1.010, as in this example, the dilution should be accomplished in two steps. Tim solution is first diluted, adding 3 or 4 ec of water lass than the calc-ulnfed amount. The solution is then mixed, ^standardized and the final adjust- ment is made with greater accuracy. Titration.—Weigh samples of about 0.2 to 0.5 gm of the chloride sample into 200-cc casseroles or beakers, liefer to the directions given on page 50 for weighing and recording weights. Dissolve the weighed samples in 50ccof chloride-free water, add 1 cc of potassium ehromute solution ami titrate as in the standardization of silver nitrate .solution. Multiply tin* number of cubic centimeters of standard solution required by its valw in terms of chlorine, divide by the sample weight and multiply by 100, to obtain the per cent of chlorine in the sample. Use of a Correction Factor.— There in a too common practice among chemists, and especially among industrial analysts, of using standardized solutions with a correction factor instead of diluting them to the desired concentration. In the example illustrated above the solution would be used an a tenth-normal solution, the factor 1.035 being used in the calculations of tit ra- tions to correct for the over-concentration. Or if a decimal solution were desired and if, for example, the first standardisation showed the chlorine factor to be 0.005012 gm, instead of 0,1)05 gm, the calculations corresponding to Eq. (4) of pages 5 would be 100 7 X 0.005 X 1.0024 - . - - __„,,_„ ..... __ ........ .5. » .,, 4 This common technical error is based upon fallacious reasoning. In actual practice the standard solution IB generally made in quantity for a considerable number of determinations, economy of time resulting from lining one standardisation for all. In such a case the solution should be diluted to the* denired con- centration, so that simplicity of calculations may result from the use of the milligram-equivalent (in the normal system) or of the simple factor of one significant figure, such as 0.005 an in the cane already considered, for the substance to be calculated. Even if the solution is to be used for only one or two determinations the (Jl .1.N TIT AT! \'K />ATA'AM//\ .177" NX use of the correction factor i> illogical. In I he equation above, ().()().") and 1.0024 are ronj-'fants and the\ should be 012 xtrrimj in tlnir jilnri' Thc> MI Hit1 n nxonhnj (ijt/tlit's to the normnl ,v//,\*/rw, The runt'lnno/i ?".v ///(// for n solution to or //.xrr/ /or <^//// o//r o/* tiro tlrti'i'wirut-* tionx, neither the thrhnnl nor the normal tuf^tcni xlnntltl In" tiflojtltd, 7////r.sx tin' ni'iwdrif tJurnltwl /.s ///r net ire nnttrn'ttl of Ihe dntnhirtl xolution, jo that il ftttii/ hr accurattli/ irritjhtd, o.; ix the cn:. chloridf. In &ueh a no atrwtiofi factor trill ht Volumetric, by Titration against Sodium Carbonate, 1 1 \ « 1 r< ipn» clil(>riroducrd: by ! For .Hodiiim hirurbonuiis pro • />3, while that of hydrochloric acid is 36.468, as usual. These points will be made clearer by reference to Pig. 1, page 14. The determination above discussed is introduced here as an example of a method for determining the concentration of any hydrochloric acid solution. The analysis of nuch a solution is expressed as grams per cubic centimeter or as per c-cni //// */v7f////. However, it should be remembered that the method will apply to similar determinations of concentration of other strong acids, such as sulphuric and nitric acids. Also it is a much uned method for standardizing volumetric acid .solutions, in which case the result of the experiment is expressed either in normality or in terms of the weight of some other element, or group of elements equivalent to 1 cc as explained on page H and an discussed in connection with standard silver nitrate* solution, above. This method for standardizing hydrochloric acid i» described on page 83, for the analysis of carbonate*. Volumetric Determination: Sodium Carbonate Method......-Thf laboratory stock of "dilute" acid in suitable for thi« ttx«rr«c», or a Hatupii* may h« furnished by the instructor. Calculates the dilution nwMwiry to iititki* tint solution approximately fifth-normal, If anything « known regarding th«* approximate concentration of the sample. If then* "w no avaiiuhlr infor- mation on this point determine the specific gravity with a floating hydrom- eter (see page 97) and calculate the approximate concent nit ion from thi? following table. QUANTITATIVE DETERMINATIONS TABLE III.—CONVERSION TABLE FOR SPECIFIC GRAVITIES 57 Specific gravity* Per cent, HC1 Specific gravity* Per cent, HCl 1.000 0.16 1.115 22.86 1.005 1.15 1.120 23.82 1.010 2.14 1.125 24.78 1.015 3.12 1.130 25.75 1.020 4.13 1.135 26.70 1.025 5.15 1.140 27.66 1.030 6.15 1.142 28.14 1.035 7.15 1.145 28.61 1.040 8.16 1.150 29.57 1.045 9.16 1.152 29.95 1.050 10.17 1.155 30.55 1.055 11.18 1.160 31.52 1.060 12.19 1.163 32.10 1.065 13.19 1.165 32.49 1.070 14.17 1.170 33.46 1.075 15.16 1.171 33.65 1.080 16.15 1.175 34.42 1.085 17.13 1.180 35.49 1.090 18.11 1.185 36.31 1.095 19.06 1.190 37.23 1.100 20.01 1.195 38.16 1.105 20.97 1.200 39.11 1.110 21.92 I ,: * At 15°. In carrying out the dilution the required amount of acid is measured in a dry volumetric flask. This is then poured into a 1000-cc volumetric flask, the smaller flask being rinsed several times with distilled water and the rinsings added to the solution in the larger flask. Dilute to the base of the neck of the 1000-cc flask and mix; finally dilute to the mark and mix thoroughly. Sodium Carbonate.—The sodium carbonate to be used as a standard is best made from sodium bicarbonate, as this salt can usually be obtained in a high state of purity, so far as other interfering solids are concerned, the only impurities being water and normal sodium carbonate. By heating to about 300° the following reaction is produced: 2NaHCO3 -> Na2CO8 + H20 + CO2. At the same time water of crystallization is expelled and pure dry sodium carbonate remains. I ' 58 QUANTITATIVE AGRICULTURAL AXALYMH I Heat about 25 gm of high-grade sodium bicarbonate in an elect ric oven j [ to 300° for three to five hours. A platinum dish is bc'.st for this purpoHf*. I < Cool the product in a desiccator and preserve in a tightly .stoppered hot lie. ! ], ' On a counterpoised glass weigh exactly 5.300 gm of the pure sodium car- ' ' bonate. Brush this into a dry funnel which rente in the nerk of a 5(X)-n; I \ volumetric flask. Jar most of the salt into the iia.sk and rin.se down the J | , remainder with distilled water. Remove the* funnel, gently agitate until ' the carbonate is dissolved, then dilute to the murk and rt.ix well. * Titration. — Fill two burettes with the respective solutions. Before ; \ • proceeding with the titrations, practice reading t he color changes a,s follows: 1 f , Place 100 cc of distilled water in a beaker and add a drop of methyl orange ! and 0.5 cc of carbonate solution. Drop in acid until'! he last drop changes ! ' the tint from yellow to pink. Now, drop in carbonate solution until tin? 'l yellow color reappears. Repeat the process until the color change can be 4 » observed when but one drop of cither solution is added. It will aid in thcs J next process if this solution is preserved and another prepared, the two I showing the two colors of methyl orange. These are set asid<* for comparison. "t Measure out exactly 25 cc of the sodium carbonate .solution into a ; beaker or Erlenmeyer flask, placed on a white, surface. Add a drop of I ' methyl orange and then carefully run in add solution from the other burette I f until one drop changes the color from yellow to pink. Record t he volume of ' I acid required to do this. In case the end point, has been overstepped, t I add 5 cc more of the carbonate solution to that already in the fla*k and [ I ; < continue the titration. Finally record the volumes of both carhoimte and I acid. I f I Since the carbonate solution was exactly fifth-normal, 1 «'<• is equivalent to ! < 0.007294 gm of hydrochloric acid. The concentration fin grains of H( 1 per cubic centimeter) of the titrated solution IK then " '"'' ••*» where \'f and Va are the volumes of carbonate and «cid, rcHpectively, t ,t ,., , .., . . . t . . * . to each other, and that of the original sample IH ' , r » where *S* * S \r a is the volume of sample used for the dilution. Gmwn />*r ruhir crnltmHcr may be converted into per cent by waif/hi by dividing by tin* specific gravity of the sample, measured at 20°. The nvnrutlUy of the* titrated ncid solu- tion is obtained, if desired, as in the case of «ilver nit rate Miiliif ion : ^ • 'r ...•< normality, Fa being the volume of acid equivalent to 25 re of t In- lift h-nor »i«I carbonate. For the original sample, normality - 1CX^ f^,2r>N . Volumetric, by Titration with Potassium Hydroxide. In the number of determmation.H of hydrochloric arid to !M* umd small, no advantage is gained by Urn UHCJ of standnnl | hydroxide. This m bccaunc th<» most sttfisfacfory nwtliod for Rtandardimtion of this nolution is by fitrafion apiinsf. an ari«I o n QT AST IT ATI YE DKTKltMlSATlOSX «>4«> solution which, In turn, is .standardized by the method usrd In the preceding exercise*. A.s tluit standardisation was, in rflVct, an analysis of the* acid solution no further experimental work should be necessary. But because of the fact that potassium hydroxide and sodium hydroxide solutions have* a wider applica- bility than do carbonate solutions, serving for the tit ration of a, great variety of strong and weak acids as well an of acid salts, the base solutions are more often kept as standards and, us such, may be conveniently used for the determination of hydrochloric acid in solutions. Volumetric Determination: I'otnxxiuin /Ij/fln^idc Mt'thml.- Calculate tin* weight <»f nolid potassium hydroxide necmsary for 1UIMJ er of fifth 'normal .solution. Acid I per rent fnr water and other implicit JCM arid di^olve fit** calculated quantity in recently boiled mid cooled diMtiHcd wafer. Th«* 'io|td bane need not be weighed on the nimlytical balance. Dilute the ;«»d if fhe base cotitaiiiHi nion* than very liiimll <|ttnntitit'M of pot/^Ntum c./irbouatc, | Thin IM nimply uri in» in «f mtd:»rd>/tn^ the lm««% i'Xccpi I hut fihettolphthjiiein IM iifii'd iw ifidfciifof for the wr?iti*"f acidn. In any **H,HI* th** uriwr inrli4'ttfar mu«t. he tw*«d when titmttfig fit*' hiisc ngiiirtMt flic iiifmiiciliiife »cid in i*tiiftdnriIi/Jii|i:, ^in*fe tip* j|i%-iiri»J#I*' presence of it HHiiiil aiiiiiiiiit of cnrhoitnh* in tin* biwicwiliitniti given a wfiglitlv ciiffcr<'nt noriiiiiiify, an niimliitcd from iilriitinfin in jirrj«»itc*« of diffwnf. Titi* tifnitioiiH miiy 1»<* carri«4cl cmt in either direction, l»{w bcinj? jyiil*-il f*» licidorai'id tolmn*, pn.tvi.«!f»d that thermite color tint t*tuk**fifuifh«*f«i!dpt»inf. indicntum in nil cit^fH with u icivi*tt ttt«licntor, II«»wi«v««r it m u^iiuHv ftu*« timf it iMt»HMJf*r to judgr' tli** firnt it|ijM«itrii!ir«' of fiiiik tliiin it-* liiinl i\iwn\*'-;.it* 60 QUANTITATIVE AGRICULTURAL ANALYM8 * i | ance. This means that it is usually better to add acid to haso in presence of I : methyl orange or methyl red, and base to acid in pmsnirc of phonolphf hnloin. < \ Methyl orange is the only indicator that can be used satisfactorily for c*ur- i \ bonate solutions. \ ! I : SULPHATES 5 Gravimetric, by Weighing Barium Sulphate. The basin for '. \ ' this method is the following reaction: | n : Bad.. + M2S()4 -> BaS04 + 2M( 51. \ Solubility.—The solubility of barium sulphate in water is ! quite low. At 20°, 1000 cc of water will dissolve* about 0.002B f , gm of the salt. This contains 0.00153 gm of barium and 0.00107 i gm of the sulphate radical. The precipitation of barium sulphate i is made the basis for the determination of either barium or * • sulphates. In either case it is necessary to maintain a slightly ,\ ' acid solution in order to avoid the possibility of precipitating < other barium salts, such as carbonate, oxulute or phosphate, in t case traces of these salts, or of their acids, an* present in the i sample or in the reagents. A slight excess of hydrochloric: acid ; f is used for this purposes. i \ Cry stallization.—Be cause of the ver> small solubility of barium Aj , sulphate it precipitates almost instantaneously as the n agent \\ 1 (a soluble sulphate or barium chloride) is added. On thin account it usually forms relatively small ciystals and these* may be so small as to pass through filters of ordinary density unless care is given to the precipitation process. The best conditions are provided by keeping the solution hot,, adding the reagent drop-wise and stirring continuously. This is followed by a process of digestion, which serves to enlarge the crystals already formed, as explained on page 25. Change of Weight of Barium Sulphate.—ronKicicrtihta care must be exercised in burning the paper upon which barium sulphate has been filtered and in subsequent ignition of the precipitate to expel traces of moisture. If the temperature in allowed to rise to too high a point barium sulphate* will gradually decompose, yielding sulphur trioxide and kming weight thereby: BaS04 -> BaO + 80». (1) 62 QUANTITATIVE AGRICULTURAL ANALYSIS I I by adding the reagent drop-wise and stirring vigorously. This method serves not only to minimize occlusion of the reagent but also to prevent the formation of a very finely divided precipitate. Determination of the Sulphate Radical.—Weigh duplicate samples of 0.25 gm of the sulphate into beakers and dissolve in 75 cc of distilled water. Add 1 cc of dilute hydrochloric acid, heat to boiling and add, drop-wise and with constant stirring, a clear 5-per cent solution of barium chloride until the sulphate is completely precipitated. Digest on the steam bath until the precipitate settles and the solution clears, then filter and wash with hot distilled water, testing the washings finally with dilute sulphuric acid to insure removal of barium chloride. While the digestion of the precipitate is proceeding the crucibles should be prepared. New crucibles generally lose weight slightly during the first heating. Clean two porcelain crucibles and mark them with small symbols, I and II (small dots are best), using an ordinary pen and ink. Allow the ink to dry, then place the covered crucibles over a blast lamp or a No. 4 Me"ker burner and heat with the full flame for 30 minutes. Remove the flames and allow the crucibles to cool to below redness, then place them in the desic- cators and, after 15 minutes standing, weigh accurately, handling only with the tongs. The rubber tipped tongs are conveniently used for the cold crucibles. After the paper and precipitate has been washed free from soluble salts, drain thoroughly and then slip the paper up the side of the funnel and fold as shown in Fig. 9. Place- the folded paper in the weighed crucible. The crucible is then inclined on the triangle, as indicated in Figs. 10 and 11, and the flame of the ordinary burner is applied, gently at first to avoid loss of precipitate by spattering. After the paper has become dry the temperature is raised, the burner being placed under the bottom of the crucible so that warm air, and not products of combustion, pass through the crucible. Proceed in this way until all carbon has been oxidized and the precipitate is white, but without allowing the crucible to become more than a dull red. When the precipitate is quite white the covered crucible is cooled in the desiccator for 15 minutes and weighed. The difference between this and the first weight represents barium sulphate, from which the per cent of the sulphate radical, of sulphur trioxide or of sulphur is calculated. In order to confirm, the accuracy of the work the covered crucible is heated for additional periods of 10 minutes and cooled and weighed after each heating. The weight should not change more than about 0.2 mg after such heating, unless the temperature has been carried too high. If any trouble has been experienced in obtaining constant weight it may be well to add a drop of dilute sulphuric acid to the cooled material, then to evaporate carefully over a flame, and finally to heat gently and reweigh. This will correct for the formation of barium sulphide or oxide, as already explained. Volumetric, by Titration with Standard Base or Carbonate.— Just as the chloride of hydrogen (hydrochloric acid) may be QUANTITATIVE DETERMINATIONS determined by titration with a standard solution of a base or carbonate, so may the sulphate of hydrogen (sulphuric acid) be determined. It is obvious that both determinations, as well as all other acidimetric determinations, are measurements of ionizable hydrogen alone, and that they can be calculated only to this hydrogen itself or, if other acids are known to be absent, to the acid present—in this case sulphuric acid. Such titrations could not properly be regarded as determinations of the acid radical, since salts of the essential acid are almost invariably pres- ent in small and variable quantities. Determination of Sulphuric Acid: Potassium Hydroxide Method.—Fifth- normal potassium hydroxide is prepared and standardized as in the deter- mination of hydrochloric acid, page 59. The sample of sulphuric acid, being non-volatile, may be weighed in a flask or beaker, if an accurate balance of sufficient capacity is at hand, or it may be measured and the specific gravity determined, the weight then being calculated. The dilution and titration are carried out exactly as directed on pages 57 and 59. The calculation of grams per cubic centimeter, per cent by weight and normality differ from that for hydrochloric acid only in the equivalent weights used. Sulphuric acid, being a dibasic acid, has a hydrogen equivalent of 2 and its equivalent weight is one-half of its molecular weight. CALCIUM Gravimetric, by Weighing Calcium Oxide.—If a neutral or basic solution of a calcium salt is treated with a soluble oxalate, as ammonium oxalate, a reaction like the following occurs: (NH4)2C204 -* CaC204 + 2NH4C1. (1) After filtering and washing the calcium oxalate this is ignited: CaC2O4 -> CaCOs + CO ; (2) » CaO + C02. (3) The calcium oxide is then weighed. The method is applicable only to soluble calcium salts and to calcium oxide, hydroxide or carbonate. The last three com- pounds dissolve in hydrochloric acid, with formation of water or carbonic acid as byproducts, and carbonic acid is expelled by heating. Calcium phosphate must be given a preliminary treatment to .separate phosphoric acid, as otherwise the phos- phate will reprecipitate as soon as the solution is made basic. i : 64 QUANTITATIVE AGRICULTURAL ANALYSIS 1 Solubility.—The solubility of calcium oxalate in water at I ordinary temperatures is about 0.0050 gm per liter, expressed 1 I , ' as the anhydrous salt, this containing 0.0016 gm of calcium. I j A slight excess of ammonium oxalate diminishes the solubility, as I explained on page 24, so that the recovery is very good. It ! , is necessary to precipitate from hot solutions in order to avoid the f ; , formation of very fine crystals. I j Purity of Precipitate.—Examination of physical data will ? ; show that oxalates of all of the alkaline earth metals and of the 1 * heavy metals have comparatively small solubilities in water. I If any of these metals are present it will therefore be necessary i to effect a preliminary separation before calcium can be pre- t ', < cipitated and recovered as pure oxalate. This will be given due 1 attention later in the work but in the following exercises calcium I is assumed to be the only metal present, with possible exceptions of the alkali metals. ! ! Determination of Calcium: Gravimetric Method.—From a closed weighing I { bottle or on counterpoised glasses (according to the nature of the sample) f weigh accurately two portions of about 0.2 to 0.4 gm of the prepared cal- | cium compound, placing in 200-cc Pyrex beakers. Add 75 cc of water and I 5 cc of a 10-per cent solution of ammonium chloride, the latter to prevent j the precipitation of possible traces of magnesium. I If the calcium salt contains carbonate it will not be completely dissolved | in water. In this case do not add ammonium chloride but provide cover f ' glasses for the beakers and add 10 cc of dilute hydrochloric acid. Calcium § carbonate will dissolve with effervescence. The covered solution is then | boiled for a few minutes to expel carbon dioxide. Now remove the covers | , and rinse them and the upper portions of the beakers with a jet of distilled water, allowing all of the rinsings to run back into the beakers. Dilute to about 75 cc. Having obtained a solution by either method add 15 cc of ammonium hydroxide (5-per cent ammonia). A distinct odor of ammonia should be perceptible after blowing away the vapors above the liquid. Heat nearly to boiling and add, from a pipette, a recently prepared saturated solution of ammonium oxalate, drop by drop and with constant stirring. Ten to 15 cc of solution may be required. Digest on the steam bath until the precipitate settles and test the solution above by adding another drop of oxalate solution. When precipitation has been completed, filter on a paper of medium density and wash precipitate and paper with hot water until the washings test free from chlorides, as determined by allowing the washings to fall into a test tube containing silver nitrate acidified with nitric acid. Finally drain as well as possible, remove the paper from the funnel and fold as shown in ,"> Fig. 0, page -0. Plan* in a porcelain or platinum crucible that, luu* been ignited to constant weight, incline the crucible and burn lit*' paper. When the precipitate is white plaee tin* crucible in an upright position, rover nnd heat with f IK* full flame of the Mast lamp or of the No. -t Meker burner until, after cooling for 15 minutes in the desiccator, the weight w eonstant. If the former burner w used tin* first weighing may be made after 15 minutes of heating. If the Me.kcr burner is used the precipitate .should lie heated for 30 minutes before the first weighing. From tin* weight of calcium oxide found e'alculiitc the per cent of cfdcium in the sample, Volumetric, by Titration with a Standard Solution of Potas- sium Permanganate.-- Instead of igniting calcium oxalate and weighing tin* oxide* t!u* purified oxalutr may 1«* n*(Iissolv<*(J in sulphuric arid and the* resultingoxalir acid t.iiratc»4 + 2KMn<>4 + :UI2S(>4.....^ K2S(>4 -f- 2MnS( )4 f XH2<) •( lOCOy. (2) Although this ronstitut.es a direct tit ration of oxalic arid it in indirect, so far as calcium is concerned, and the calculation of the latter curt be accurate only (1) if the precipitation has recovered all of the calcium, (2) if the calcium oxalafe has l«*en well purified and (Mj if the oxalic acid resulting front its deeom- position by sulpliuric acid has been recover***! ;« tem oflVi'H greater convenience, of course. If the M>lutiuu IM to IH« U8i»d also for the determination of iron and poHHibly of ot!n*r elementH, then the normal system offers udvantnges. In either cane it is necenHary to know the equivalent weights of ealrium and permanganate mid thene cunnot be cnlcniluted ILH simply HH in cases already coriHiderecL 66 QUANTITATIVE AMt/('l'//rr/{.\/, .l,Y.i/,)>7N Apparent Valence.—In ordinary reactions of double deeomposi- tion the valences of the dements and radicals which an* being transposed are measures of the respective ivacfiiiK powers of these entities. This is not true for reactions of oxidation and reduction. Here the reacting power of a compound is determined by the extent of change of valence. As an illustration may be taken the reversible oxidation of hydriodic acid by ferric chloride: 2FeCl8 + 2HI -»2I'V'I2 + 2IK'I f I,. The valence of iron in ferric chloride is % but this compound does not exchange three atoms of chlorine for an equivalent amount of another radical—it simply parts with one atom of chlorine which oxidizes hydriodic acid. The* hydrogen equivalent, of ferric chloride in this reaction is then equal to the chftHyc in valence of iron. This is 3 — 2 = L For the purpose of this inspection the actual valence of the elements undergoing the reaction need not be considered as this depends upon the structural composition of the compounds, which is not always known. The ay/wrcnf valence is that which is indicated by the simplest direct combination of positive and negative elements and it is therefore* a measure of combining power. In the above reaction iodine is tin* element that is oxidized and it is sufficient to regard its apparent valence in hydriodic acicl as 1 and in the form of the elemi'uf. H,H f). The hydrogen equivalent of hydriodic acid rn the difference between these two apparent valences, or 1. The reaction between potassium jwrmanganute ami oxalic acid may be inspected similarly. Omitting the roeiiirutntM given in Eq. (2), page 65, the empirical equation in H2C204 + KMn04 + H2S04~> K»SO4 -f M»SO4 ~|. Hso + CO,. Obviously, carbon is the element that in oxidiml mid mniigitiieHC! is reduced. The apparent valence of an flnnrnt whirh 5* in the negative radical of an oxyitdd or of itn salt is found by Mibf raeting the total valence of the positive rudira! from that of the other elements of the negative radical and dividing tin* twitlf, by the number of atoms of the element in question. In oxalic acid the apparent valence of carbon in f lieu ^ ""• • = 3, while in carbon dioxide it IK 4. The hyiirngi'ii ti io.i j ii|it?fuoj H'jj p?i« ?fm|,Ji?«u tujj fir H HI f| If) -irHH1 t- *<)Sf|M\T, 4, "os'M 4 'OH^'Xi; *-- N)SSHS 4 *O'*KMS 4 ;j*j|i| ij.)«.) ti; KI 1).}U|A\ JO [JIM JM .10 4ft 10 jii)fffJA\ .nn HI // j M * " oooi jo ^qlrfi^M n J t.)1M 111 jo tior JO tlOlS HI *r|inni)liiinifj,Kl *iq| ft; 'piosMjui !.|.>)1JA\ t).IIld A|]Utll,)!J|llK i>4)npt>4«l A[[11UKJ1 JJIAV HH.KKl.ld pooX y •^utKiii.i tjlrtnojotjj u A'q ]>«>A\o[[oj 'UOJJUJOK pint s'.J jpn|H nji pin? pin; (j U;H('| KI .rpnn^tiiHiuad inins'sirjod jo ^uopJ tMKL T» K! 1! ^'n^jdjnn ;)Ki)uirSuinn uj "£ :-.-- ] — (f, X f) K! ^ «ifMtnniu«xI imnsviqod tn iW^turSftnitu jo i.K>u^p?A '}u« mulch? oifX 7 * <> '^OA\ 'u;>?Anb«) .M-J «u si OK H! Z(O Ur j'i jo 'pioptAinba (i;>!rfo.ipA"T| oi{) (p;.ni ,>ipjxo jo iMio o) pioprAinbo si tUTUi>p?i) jo uioji: auo .)«>ujv^ '^ s; ful|| jit *JWIA\ III H1J *J»«.r|lIiU*| !J»!flfOtlIHI1! 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JO j.lj^'t«IA\ ; JJ JO A*llp!t pin: '. or|ii[OH «>f|j jo l («2HJi>llIi) JO I2OI 4oj A\O 70 QUANTITATIVE AdltH't'l.Tt'KM. .1 A AL 1 ,s7,S' IRON Iron is sometimes determined gruvimetrieally by precipitating ferric hydroxide by ammonium hydroxide, igniting aii<{ we;-1 * this aw ferric oxide: '; ft) 2Fe(OH)3 • > I«V2«>3 4- :t!U», (2) However ferric hydroxide is a colloidal Mib>tanei* whirl} adsorbs soluble Halts with great tenacity, so that it i> diffinilt ii> purify any but a small precipitate by washing. A!M» during ignition on paper, reduction of the oxide is liable tn o«vur. Fur these reasons volumetric methods are ustially prejrrabl**. Standard solutions of permanganates or of dirhromate* are .^uifable for this purpose. Volumetric, by Permanganate.- In acid Mention* potnssitiiu permanganate oxidizes ferrous salt** by the frtHmving reactions: KMn04 + 5F(K ?IS + HlfC 1 -- K( 1 -4 Mn< lv * :>rvri * in;,n: f|j 2KMn04+ 10FeS04 + 8H2S<>4 * K7SU4 f 2MnSo4 » SKivS* *i' ! SH (l '. S2) The equations show that the* added aciil j»Ia\> a fielinite part in the reactions and if an insufficient amount i* pre*i«nf tbe Hoiution will become basic and a precipitate will form, coiisi^ting of hydratcd manganeKe dioxide and ba-sir iron >*alf?*: 3Fe(Jl2 + KMn()4 + (// + 2)H3< * - * 3!"VI lr« HI -f- H7o -f- KoH. f;i Aside from the trouble* ex!*eri<»ncc«i in n*mling I fit* i-ni caused by the appearance of the precipitate, it in H*Hi from Kq. (3), above, that mungnnfw m reilureii In tbi* apparent valence of 4 instead of 2, HO thiit fhr» iron jn*r rent euitttot l«» calculated when bot.h reaclions faki* pliiri*. la presence of hydrochloric iirid won* (H*rtuaiiKaimt<* ttiurt the theoretical amount may be UH»df with lifierntion of HWW* free chlorine. Tim action may l«* itlnifmf ent iiely pre%*enti*«l by tnc addition of rna«Kun«HC! sulphate to fin* Miltitioii, < »i*!ii'rnl!y phosphoric acid also is added to prevrnl f h«- hy«IniI>>i.H t»f fi*rrir Qf'A.\T/TA 77 VK chloride*, thus avoiding the appearance of a red color which would mask the end point of tin* titrafion.1 Reduction of the Iron Solution.— Iron exists in tin* ferric con- dition iu most ores or other minerals. In order to reduce the solution of ferric, salt either stannous chloride, zinc, sulphurous acid or hydrogen sulphide may be employed. The first two are the only ones now commonly used. Stannous chloride, in solution, possesses the advantage of instantaneous action if added to the* hot solution of ferric chloride, If the* iron is to bo reduced by stannous chloride an addition of this salt to the ore during the. process of solution will materially hasten the action. For the* final reduction the stannous chloride solution may bo added from a pipette, the disappearance of the red color of basic ferric chloride providing an approximate indica- tion of the oiid-point. in the analysis of iron oros there is occasionally trouble at this point tmloss certain precautions have been taken. In the first places many iron oros contain appreciable quantities of organic, matter and this sorvos to produce a yellow color when the ore is dissolved. As color duo to this cause doe.s not, disappear when the iron has boon reduced it is not possible1 to determine when the correct amount: of sfannous chloride has boon added, This trouble may be avoided by igniting the weighed sample for a short time in a porcelain crucible, before* dissolving. The .second cause* of irremovable, color oome*s from fusion of insoluble renidueH in platinum crucibles. The* pyrosulphute* which in lined UK a fhix dissolves tntceH of platinum and thin, with starmouB chloride, forms a yellow solution containing a complex of tin and platinum. This interference is avoided by the sub- stitution of porcelain crucible's for t.hejse of platinum* After a slight e»xcons of Ktannotts chloride* has been added the* solution is cooled mid a considerable exce*ss of mercuric, chloride is added, the unused stannoUH chloride being thereby oxidised ; Mercuric chloride will not oxidize fermtiH rhloiitte and hence wav bo loft in the, solution. If an insufficient e*xe*e»ss of inere*uric 1 For the fxplftniition of thalt and dilute to the proper volume. In cane tit-ration for Htandardi/af ion in f n lie omit fed and direct weighing is to be made the ba«i.s for standardization, IfMiO en of the solution should be accurately made a ltd poured into a dry battle. {standardization, if this should be wfWHHtiry, in iieeomplinheil hy film- tion against ferrous ammonium sulphate. Write nnd }*iilniiei* flu* i'i|iia- tion for the oxidation of ferrous Kulplntte by potfi^sttm tiirhrtmtiifi* iii presence of sulphuric acid, referring, if nwwHnry, t«» tlie i*f|urutton for flie oxidation of the chloride, page 73. C'alriilnfe the weight of rn^fiilltxetl ferrous ammonium sulphate necesnary to rednee ,'ff* er nf the litehroitintit solution. Weigh four portions of exactly this weight i»t«i Hfiij-rr hrnkr*r* and dissolve each, jwt before titrating, in 50 cc of reeenl Iy b*»ileil nml e* rftnoving n drop by means of the stirring rod ami touching to n drop *»f |wifii^fiiii» fi*rri* cyanide solution on the spot platen llie end point PI r^nehi'tl whni a blue color is no longer produced on thfc plati*, after MnndntfC for J iitiiiiili*, (Dust or reducing gases will interfere by reducing trw«*« «*f ferrir ei«I*irid A1(OH)3 + 3NEUC1; (1) 2A1(OH)3 -» A1203 + 3H20. (2) If iron and aluminium occur together they are precipitated together and the product of ignition is a mixture of ferric oxide and aluminium oxide. In such a case the usual procedure is to weigh the oxide mixture, then dissolve and determine the iron volumetrically, calculating this to oxide and subtracting from the weight of mixed oxides to find the weight of aluminium oxide. Or the aluminium may be determined directly by precipitating as phosphate, first reducing the iron to the ferrous condition by sodium thiosulphate; ferrous phosphate is sufficiently soluble to make a separation possible. This method will be described later for the determination of aluminium in soils (page 258). Solubility.—The solubility of aluminium hydroxide in water is not definite as this substance belongs to the colloid class. The presence of various salts diminishes the solubility to a low 76 QUANTITATIVE AGMCrLTUKAL A\AL}'M8 figure, and especially so if the solution is boi>d to fame flocoula- tion of the colloid. Either acids or basos will dissolve* the pre- cipitate; acids form soluble aluminium salts and bases form soluble aluminates: Al(OH), + 3HOI-* AK'13 + »H«(>; (1) A1(OH)8 + NaOH -» XuAK), + 2H,O. (2) The possibility of the second reaction makes wroswiry the u«c of ammonium hydroxide, rather than sodium or potiiHHimn hydroxide, for the precipitation, as the excess of ammonia may be removed by boiling the solution. Determination of Aluminium.—Fill n weighing bottle with the powdered sample of an aluminium salt. ( HUM me the method tn he used in weighing according to the nature of the substance and weigh two wimples of about 1 grn each into Pyrcx beakcra. Dissolve in RH» ec of water ami add 'dilute, recently filtered ammonium hydroxide, stirring until the liquid is distinctly basic, as shown by a drop of methyl ml added to the solution. Boil until the precipitate is coagulated and until thi* iwlor of ammonia above the solution is faint. Boiling after the* odor has disappeared will fiiitst' «omc of the precipitate to return to the Molutiou: A1(OII)8 -f :JXH4C'1.......- AK'l, -i- :tNH3 -j- :Hii<). Allow the precipitate to Hc.t.tlo and thfn filter fhnnigh p»pcr, UMiiig a filter pump attached to a boll jar or filter ilmk mid plnnu^ u nupport-ing cone of hardened paper or platinum in thc» futtm*!. W»]t with hot d»tilk»d water containing 1 per ecmt of amtnontuin nitrate*, until tin* wanhingK arc free from chlorides, shown by adding a drop of nitric nri*I mid it f«*w drop of silver nitrate solution to a small amount of I In* wiwIiirigH naught in n tcwt tube; also from sulphates, as shown by adding a drop of dilute hydrochloric acid and a few drops of barium diloride, solution to (tnothi*r portion of the washings. Suck the precipitate HH Hourly dry n« poHMiliit* iiful tnstmfi*r the paper and precipitate to a porcelain or platinum rrurtble wliirli him been ignited and weighed, folding the paper in the manner already lenrned. Heat very gently in the covered erueihle until the ntomture i« vfilfttilixed, then raise the temperature and burn the paper, iiirlifiiiig the rrtiril»li« and placing the cover as in the case* of the ignition of the paper eontainmg cal- cium oxalate. Wlie.n all of the c-arbmi IIIIH be«*» tmnied, cover the crucible and heat over the blast lamp or the hirgi* Mclcer btinirr fc»r ao iiiiinito. Cool in the desiccator and weigh. Heat again for 10 tntnuteH, cool attci weigh. If necessary repeat this proeeHH until the weight i« constant. Calculate the per cent of aluminium in the nnU, Aluminium oxide absorbs watei fn»m the iiir, reforming the hydrcixidc with a corresponding gain in weight. On thin account the erueihle. m«l oxide should be weighed rapidly. QTAXTITA 77 I'A' IWI'Klt.}/1.\ .\TtO\X 77 CARBONATES The Carbonate Radical, The determination of the carbonate radical of solid carbonates can be made with accuracy only by decomposing the carbonate with a .stronger acid, then purifying the resulting carbon dioxide1 and absorbing it in Homo manner in another reagent. This is the basis for both gravimetric and volumetric methods. In the former class of methods (.he* earbon dioxide* is absorbed in a basic substance* (usually potassium hydroxide or soda lime) contained in a small apparatus that can he weighed, the gain in weight serving as a measure of the quantity of gas absorbed. Or it. is sometimes absorbed by a solution of barium hydroxide, I lie barium carbonate so formed being removed by filtration, dissolved in hydrochloric acid and the barium reprcci pi fated as sulphate. Front the weight, of barium sulphate the corresponding weight of carbon dioxide is calculated. In the volumetric modifications the absorbing reagent is a standard solution of a base, such as barium hydroxide*, u measured volume of this being titrated by a standard acid, solution after the absorption in finished. Hither method will give accurate results, if can* IK used. Gravimetric Method.............Tin* necessary parts of the apparatus are .shown in Fig. 20, In this figure, A represents a generating flask in which the weighed sample of carbonate is placed. It in a dropping funnel having a capacity of 50 ec and having the lower end drawn out to a point find turned upward. Thin part should extend to the* bottom of the flank. At the top of the dropping funnel a drying tube (' is connected by means of u rubber stopper and a bent- glass tube. The drying tube is filled with soda lime* for the absorption of carbon dioxide from the air that is later to be drawn through. Following the generating flask is a short-, condenser I) (the lower end of which should be beveled) and then I "-tubes #, /*' and (L The* first I'-fube is omitted if sulphuric acid is to lie used for decomposing the car- bonate or it is filled with nn absorbent for hydrochloric acid vapors if thin add in to be used. The l>tube« /'' mid N7'KltM/.\A 77O.V,Sr 71) calcium chloride. This prevents loss of moisture from the* weighed apparatus. Soda lime* is sometimes used for the* absorption of carbon dioxide*. This is made by fusing together sodium hydroxide and lime, the product being granulated during the cooling process, The chief objection to this use of soda lime is the, fact that it is HOinewhat uncertain in its act-ion and the absorption of gas in liable to be incomplete unless the moisture; content is kept within fairly narrow limits (about 15 per cent). Determination of the Carbonate JRadical: (frnvhm'trir Method. Procure. the following parts for jiHHrmblinp;; 1 dropping funnel, 50 ee, with one-hole rubber stopper, 1 short, wide iiask, 75r<% sueh an is used for fat. extractions, with two-hole rubber stopper, • 1 condenser with body nut more than (\ inches long, 3 I'-tubes with corks to fit, 1 I "-tube with ghiss stoppers, 1 Htraight drying tuh»* with one-hole nthber wtopper, 1 net (leiHsliT **p«»t!i>tli bulbn" or h«I!»« tif WHIK* other approved form, 1 aspirator bottle, tubulati'd near hottotn, with one-hole rubber stopper* to fit, 1 piece gliiHH tubing, about 2 fn»t l»y 12 inrh, for mtpporting iippamtim, 2 (•htitipK, 2 pinrli rocks, 1 wniill wrew ehimp rliofTuiait ,Mt?r<*wi, 2 n*torf stunds, * titan and rubber tubing fur cnimcrtionH, Fill and rtmnert the apparatus in tlie manner previously ir«* removed by remelting the xtirfare by a flame. When filling the absorption btilbii witlt potuHKiuiii hydroxid*! nohttioti thiif«.ide *»f the joint. I PW i 80 QUANTITATIVE AGRICULTURAL ANALYSIS I ! ; Place the bulbs in position, close the cock of the dropping fan**el an(* I " open the pinch cock at e to allow water to flow from the aspirator. J3u.bbles {' < of air will at first pass through the bulbs but this action will finally cease ; I ! unless there is a leak in the apparatus, in which case it must be found and | ' closed. It is important that all glass tubes be brought entirely together I e inside the rubber connections since rubber is slightly permeable to gases. > i After the apparatus has been shown to be free from leaks the pinch I ' cock at / is closed, the cock of the separatory funnel is slowly opened and, I r after equilibrium is established, the clamp k is so adjusted that when clamp [ \ /is opened air will pass through the bulbs at a rate not greater than three | 1 bubbles per second. Clamp k is not thereafter changed. This provides '< against too rapid flow of gas under any conditions. Clamp/is now closed, i , the bulbs are removed, the inlet and outlet tubes are closed by short rubber ; tubes containing glass plugs and the bulbs are Wiped clean and placed in the ; . balance case. A short glass tube is inserted to bridge the gap made by removing the bulbs. ; The bulbs should be allowed to stand for 15 minutes before weighing;. In the meantime about 1 gm of the carbonate is weighed and brushed into the generating flask and a small amount of water is added to moisten the sample. The stopcock of the funnel B and the clamp E are now opened „{ and 500 cc of air is drawn through the apparatus, measured by the out- flowing water from the aspirator. This frees the apparatus from eaxbon dioxide. After the absorption bulbs have stood for 15 minutes the tubes carrying the plugs are removed and the bulbs are weighed. The plxip;H llr<} > ' then replaced and left so until the bulbs can be connected in the ap pa, rut us. i , Fifty cubic centimeters of dilute sulphuric acid or hydrochloric acid is placed ' ' ' I m *ne dropping funnel, a test having previously been made to determine : | whether sulphuric acid will form a clear solution with the carbonate. If * such a solution is not produced, of course hydrochloric acid must be used and silver sulphate and pumice must be placed in tube E. Reconnect the apparatus and open all cocks except the stopcock in the dropping funnel, leaving the clamp k set for the proper rate of gas flow, as previously determined. Slowly open the cock of the dropping funnel, allowing acid to drop just fast enough to evolve carbon dioxide at the ! prescribed rate. The constant attention of the operator is necessary at this point, for by causing too rapid evolution of gas some moisture may escape absorption in the small tube of the absorption bulbs and the experiment 1 • . be rendered worthless. The acid should be allowed to run in until about 1 cc is left above the : stopcock, this acting as a seal during the subsequent boiling. After the decomposition of the carbonate is complete the solution in the flask is slowly heated until it boils, always with due regard to the rate at which the gas is made to flow through the absorption bulbs. The boiling is continued for one minute, when the flame is withdrawn, the cock of the dropping funnel being opened at the same time to allow air to enter BO that no back suction occurs, due to the cooling effect. Air is now drsawn. through the apparatus until 1000 cc of water has flowed from the suspira- si tor. Thin amount, of mr should be .sufficient to' sweep nil of the dioxide into the absorption bulbs. The clamp/is now closed, and the ab.sorplion bulb;; arc removed, and placed in the balance case. After 1T> minutes they are weighed without the rubber tubes and plu^s, the increase in weight being; the weight of carbon dioxide. From thin and the weight of Kample tbe per cent of carbonic anhydride (combined carbon dioxide; or of tin* carbonate radical in calculated. For the duplicate or any subsequent determination the generating flask and the dropping funnel ant washed absolutely Free from n.eid, so that no decomposition of the next carbonate sample may occur before the, bulbs are in place. If a large number of dftenninutions ure to be made wif h I he same appara- tus much time will be saved by providing two decomposition flasks and two absorption bulbs. While one determination in being made another sample. may be weighed into the duplicate flunk and the second absorption bulb may bo weighed. Tbe next determination may then be started while the first* bulb*? are .standing in the balance cane, preliminary to the final weighing, It is also nece.Hsary to determine when the various jibsorbeuts have become so sat united as to be inefficient for further work. Soda, lime in the tube (' In good until the lumps have begun to full info n powder. Silver sulphate in tin* pumice of tube* K may become inefficient through absorption of hydrochloric acid or through the accumulation of water in the tube, Tbe solubility of silver sulphate in water in much lesn than in concentrated sulphuric acid. If the acid solution lieeomen diluted the silver salt crystallises and will not thereafter reiidily alftorh hydrochloric acid, As theHilvernulpfmte becomes ftaturuted wit Is hydrochloric acii! it darkfiis, on account, of tbe action of light. When tin* darkening effect has proceeded as far im the middle of the tube the material xhotiifl be replaced. Oilritun chloride must be replaced when it becomes visibly moist/«r thr jimt third of any ubsorbing tube, Gravimetric by Absorption and Subsequent Precipitation*-............ Carbon dioxidr, <*volvrd by thr* inrthod just drseribfd, w timc*H absorbc**! In a hornrwhat cTonrf'ntritfod solution of b, hydroxide, UK.* bunion rurhonatf* thus fonwd biding then removed by filtration* washed, rrdissoivwl in hydrorhlorir wid and the* barium precipitated EH sulphate. The weight of this gives u mwiHiirc* of i*iirbon flioxiili* in the Hiiinjile, Mc»yron*dnri» nrc* offrri'd: f'l; The* KJIH IH >c*d in a ntaminni Hoiiilion <»f barium hydroxide*, t.ht* unused of the* latter lH*ing titrated by stjin«lard hydrcx*h!orir and without pr*»vioiiH filt.rufioij, (2) The* bariuni carboiutt** IH G < 82 QUANTITATIVE AGRICULTURAL ANALYSIS i ' ' removed by filtration "before titrating the unused base. (3) ' \ barium carbonate is filtered out, washed and dissolved In an I j excess of standard acid, the unused acid being then titrated by [ standard base. In method (3) a more concentrated solution, of 1 ' barium hydroxide may be used and it need not be standardised. j Phenolphthaleiri is used as indicator in all three methods. M^thod j (1) will be described. , < Apparatus.—Parts A, B, C, D and J (including clamps e, k and /) of the apparatus shown in Fig. 20 are used. If hyxlro- FIQ. 21.—The Meyer absorption tube. chloric acid is used for decomposing the carbonate, tube E, filled with pumice bearing silver sulphate in concentrated sulphuric acid, is required also. Drying tubes F and O are omitted. For the absorption the Meyer tube, shown in Fig;- 21, is suitable. Barium Hydroxide Solution.—A saturated solution of barium hydroxide is prepared by warming and stirring the solid base with recently foiled water, using a ratio of 70 to 100 gm of base to 1000 cc of water, accord- ing to the purity of the barium hydroxide. Cool to room tempera- ture and siphon into a bottle to be closed with a rubber stopper. Dilute 550 cc of this solution to 1000 cc with distilled water, mix and empty into a bottle which is provided with a siphon or similar outlet, from, which the solution may be drawn, and a guard tube of soda lime to remove c*xrr>on dioxide from the air which is drawn in. The last diluted solution should be about 0.25 normal. It is not adjusted to any exact normality because its concentration is subject to change with time. Instead, the standard acid to be prepared is taken as the primary standard and "blank" titrations are made frequently. Sodium Carbonate for Standardizing Acid.—Prepare as directed on pa/ge 57. Hydrochloric Acid.—From the known per cent of hydrochloric acid a,nd the specific gravity of the concentrated solution in the laboratory, calculate the volume of solution necessary to make a suitable quantity (12OO cc to 10 liters, according to whether this is to be an individual preparation, or Q UAN TIT A TIVE DETERMINA TIONS 83 laboratory stock) of'solution, either fourth-normal or of such strength that 1 cc shall be equivalent to 0.005 gm of carbon dioxide, calculating equiva- lent weights from the equations: CO2 + H2O Ba(OH)2-fH2CO3- Ba(OH)2 + 2HC1- + H2C03; > BaCO3 -f 2H20; > BaCl2 + 2H20. (1) (2) (3) Measure 2 per cent more than this amount, using a graduated cylinder. Empty into a bottle of suitable capacity and add the necessary quantity of water. Stopper and mix thoroughly. Since the solution has been warmed by the reaction between acid and water it should stand until the tempera- ture of the room is attained, before standardizing. Standardization.—Calculate the weight of sodium carbonate required for 250 cc of a solution of strength equivalent to that of the desired acid. Weigh this quantity of the prepared pure material on counterpoised glasses and brush into a funnel which is placed in the neck of a 250-cc volumetric flask. Rinse down with distilled water, remove the funnel and dilute to the mark on the flask. Mix thoroughly, best by pouring into a dry beaker or flask and back several times. Fill a burette with the solution and another with the acid solution already made and titrate as directed on page 58. Calculate the normality of the solution, also the volume of water to be added to each 1000 cc to make a solution of the exact concentration required. If water to be added is more than 10 cc add nearly the required amount to each liter of the acid, mix, and restandardize. If the quantity to be added is less than 10 cc the acid is diluted as follows: Fill a dry 10DO-cc graduated flask to the mark with the acid solution. This flask should be capable of holding the required amount of water above the mark. From a burette add the calculated quantity of water directly to the solution in the flask and mix thoroughly. Pour into a dry bottle and make more diluted solution in the same manner, having first rinsed and dried the graduated flask. Check the accuracy of the dilution by restandardization. A preliminary titration should be made to determine whether the barium hydroxide solution is approximately equivalent to the standard acid. Meas- ure 25 cc of the base into an Erlenmeyer flask, add a drop of phenolphthal- ein and titrate rapidly to the disappearance of the pink color. Twenty-two to 27 cc of acid should be required, although no special note is made of the exact quantity, the value of the basic solution being determined accurately by a blank titration, made at the time the carbonate analysis is carried out. Water, Free from Carbon Dioxide.—All water that is to be used for dilutions and for rinsing apparatus must be free from carbon dioxide and it must be neutral to phenolphthalein. Carbon dioxide is removed by boiling the water for 10 minutes, cooling and placing in a bottle provided with a guard tube filled with soda lime. Boiling large quantities of water is often not conveniently done in the laboratory. An equally satisfactory method is to provide the bottle with a two-hole stopper through which pass two glass 84 QUANTITATI VK ACRK',1 'l/l't:liAL .1 .V.I A r.s'AV tubes. One of these is for entering air. K. iHaUnrhed to ;i lube of .soda lin outside and it extends to the bottom of tin* bottle. (Tin- suda lime must b<> well confined by a filter of cotton.) The either tube is eonneetrd with an air pump. The purified air is then drawn through th«* w.'iter for an hour, after which the bottle is stoppered. The three reagents may be placed on n shelf «nd eonneeted us shown in Fig. 22, for convenient use. /" A Standard BafOHfe Standard HC1 0 Water/Oj-Frw /"„ < UN) < ;M " f PIG. 22.— Assembly of reason tn for flu* *lioxt«li» f)i*ti*rrninfitirm. Determination of the Carbonate Radical: VolurnHrir Mrtktxl. ..... - A«m?mble the apparatus discussed above, the Meyer absorption tut«* brniig half filled with distilled water. Close the cock of funwl /I find ti*«t fur li'iikn by opening cocks k, f and e. Water will flow from thi* nHpirntor until tho pressure within the apparatus IH reduced to equilibrium with the water column. If an air leak exists at any point between B am) the Meyer tubft air will bubble slowly through the tube. Any leak thus evidenced mu«t be located and stopped. The clamp at k is now closed and the. eock of the dropping funnel H in opened. With c and / left open k m no itdjusti'd IIH t itmy In* uned, if desired. This would be 0.2750 %m for a ftwrth-norniftl wilntioti, or 0.21500 gin for the solution of which 1 cc is equivalent to 0.005 grn of carbon dioxide. (The student should prove this statement,) Qt M.Y7'/7'.-t 77 VK 77CAVX 85 The flask is now replaced in the train and the dropping funnel and c.oc.kB e arid / an* opened. Two hundred cubic centimeter?-? of water in allowed to flow from tin* aspirator, to remove carbon dioxide from the apparatus The Meyer tube in now removed and emptied and 50 ec of barium hydroxide* Holution in weiistiretl into this tubtt from a burette* or an automatic pipette, first di.McardinK the few p.s that an* in the outlet of th<» mcuHuriuK in.Htru- rnent. Add t«» tin* tube, from a graduated cylinder, enough cold carbon dioxide-free water to taring the water to the lower edge of the upper bulb when gaH is flowing, The quantity of wat**r neeeKHary should he meanured, one*' for all, HO that it ear* be arlded without delay in nubsequent determinations. Replace f hi* Meyer tube in the train mid add 50 re, of dilute sulphuric or hydrochloric arid to flu* funnel /^, the stopcock hcirifi; closed. Now open raiu!/, then admit ii.fjd to the carbonate, at a moderate rate until the entire 50 ec has enh'ml. Finally close the stopcock and he/»t the aeid slf»wly to boiliiiK. Boil fur 1 mtttutf then remove* tin* flame anlor, Wlisle the fxjM'rimi'nt just dewribed m under way, inc*iiHun* *5C) cc of barium fiytlroMfii* into ant*t)it*r flank, add approximately UK* same ainfMtnt of carbon dio\in tin* [iKHititifftioii thai no oth<»r bawd Hulwlniici* JH pn'.Mi*nf. Thin aHHinnption is not always rom?<*t. For inHtunw, ncidii Iiini* fi!H«f»nfinlly a mixture of sodium hydroxide und cnleitnn oxiil«% but, always eoniaintn^ some carbonate) has n nitirb Kreat-er JKHVIT for ninifnili/Jitg a<(ie obtained more r|ui<*kly 86 QUANTITATIVE AGRICULTURAL ANALYSIS by a direct titration method. With carbonates that are soluble in water this is accomplished by dissolving a weighed sample, adding methyl orange and titrating with standard acid. If the carbonate is only slightly soluble in water an excess of standard acid is added. This dissolves the carbonate and the unused excess of standard acid is then titrated with a standard base. In this case, if the solution has been boiled to remove carbon dioxide, phenolphthalein or methyl red may be used as indicator but the same indicator must have been used when standardizing the base against the acid. Soda Ash.—The standard acid that was used in the preceding exercise is suitable for this determination. The soda ash may be weighed on a counterpoised glass, if this is done quickly. Determination of Alkalinity of Soda Ash.—Weigh about 2.5 gm of sample, dissolve in a small beaker and rinse the solution into a 500-cc volumetric flask. Dilute to the mark and mix well. By means of a pipette, measure 25 cc of the solution into a 250-cc Erlenmeyer flask or beaker, dilute with 50 cc of water, add a drop of methyl orange and titrate to the color change with standard acid. Calculate the per cent of sodium carbonate in the sample. This, of course, is upon the arbitrary assumption that no other carbonate or basic substance is present. Sometimes the alkalinity is expressed in terms of sodium oxide, Na20. Limestone.—Powdered limestone is used for neutralizing the acidity of soils. If the alkalinity is calculated in terms of calcium carbonate the result may be greater than 100 per cent in case of dolomitic limestones, on account of the presence of magnesium carbonate, a substance of lower equivalent weight than that of calcium carbonate. Although a figure so obtained would be fictitious, in one sense, it is after all a practical basis for calculat- ing the amount of stone required. If a determination of soil acidity should indicate n pounds of pure calcium carbonate required per acre, a sample showing by analysis a calculated per 71 cent of 105 would be used in the ratio of :™ pounds per acre, no matter what carbonates were actually present. Determination of Alkalinity of Limestone.—Prepare a solution of sodium hydroxide, equivalent to the standard acid already on hand, or use the basic solution prepared for acidimetry, page 59. This should be made from material as nearly as possible free from carbonates. Sodium hydroxide Ql "A .V 777'.! 77 VK 1 )/•!'/'N/fM/\'A 7 purified hy alcohol is bent and I he water should first be boiled, to expel carbon dioxide, then cooled. Standardize the solution by titniting n.gfi.inMt the standard aeid, using methyl re Mg(P03)2 4- 4NH3 + 2H2O. (5) Also, ^n'magnesium phosphate, Mg3(P04)2; may be precipitated if the solution contains too much ammonia and this will remain. unchanged by ignition. Insoluble Phosphates. — Phosphates of other than alkali metals are usually soluble in acids but a direct precipitation of magne- sium ammonium phosphate cannot be made because phosphates of the original metals reprecipitate as soon as ammonium hydrox- ide is added to neutralize the acid. For example, tricalcium phosphate, Ca3(P04)2, furnishes much of the phosphorus of fertilizers as the mineral apatite. This is soluble in acids but if" an attempt were made to determine the phosphorus by SL magnesium precipitation, the precipitate would be a mixture of phosphates of calcium and magnesium. In order to prepare such a phosphate for a determination of phosphorus a preliminary separation of the phosphate radical is made by the addition of ammonium molybdate to the solution in nitric acid. This results in the formation of a yellow pre- cipitate of ammonium phosphomolybdate : (NH4)3P04 + 12(NH4)2Mo04 + 24HN03 -> (NH4)3P04.12Mo03+24NH4N03 + 12H20. . (1) This is filtered out and washed free from the alkaline earth metals. The precipitate is then dissolved in ammonium hydrox- ide, reforming ammonium molybdate and ammonium phos- phate, both of which are soluble. This reaction is represented as follows : (NH4)3P04-12Mo03 + 24NH4OH -» (NH4)3P04 + . 12(NH4)2Mo04 + 24NH4N03 + 12H20. (2) The magnesium salt is now added and the precipitation and sub- sequent treatment are carried out as described for soluble phosphates. Determination of Phosphorus in Soluble Phosphates. — Prepare a solution of " magnesia mixture11 as follows: Dissolve 55 gm of crystallized magnesium •:bL QTA .V777M 77 VK DNTKHMIXA T1ONN chloride and 140 gm til" ammonium ehloridc in water, add l.'iOcc of ammo- nium hydroxide fnpccific gravity 0.1)0) and dilute to 1000 cc. If thin .solution Is kept in ntock for any considerable time it will acquire a floceulcnt precipi- tate* of hydrntcd nilica, derived from notation of the. glann by the bane. The Bolution must he clear whcm uned. Thin condition may bo innurcd by filtering the solution or by prepanng only enough of the reagent to hint a short time. Weigh duplicate samples of 0.2 to 0.4 gm of the plionphate into hcakcrn of re.nint.ance glzinn, diHsnlve and dilute* to 7/i cc. Add a. drop of methyl red and if a basic* reaction in not shown add dilute ammonium hydroxide until the notation beconicn yellow, avoiding an exccnn. Add 10 or. of a 10 per rent notation of amnionittm chloride, mix and then add, very slowly, "mag- nesia mixture" nuflicient in quantity to precipitate nil of tlu1 phonphatc. AH the precipitate doen not form rapidly in a barely banic notation it in not always easy to determine when enough of the wagont ban be.<»n addecl. It in then bost f o us*- \vliat in thought to be a good exwnn and to rely upon t«wting the fiitratf wbirh in obtained Inter. Allow to ntand for 1.5 minutfn until it roriHidernble part of the precipitate lion appeared, thi*n itdfl c-onrrntrated amntonimn hy« filtered out, Wfjwhet! ami *sid«li*cl to the main portiort. If iiCtiwirfi rnieibli* iiji-n bi*i*ii uni*«i for filtration, plan* the rap on the bottom and heat over tin? burwr tiist.il dr>% thini over the blant lump for 20 utimttcn. An ahindiiiit rrueiblc* in trt*nfi*d similitrly. If n puper filter wa« un«*il remove the paper from the fiifiiti*!, foltl and place in a weighed porrelain or platinum crucible*, liifliiii* tbe rrueible with th<* ifovi*r leaned ngainnt it find heat gently over fhi* burner until the paper in eonspletely burned mid. th<* pre- cipitate in iii*iirly whiti*. After tlte preripititti! is white or light gray the crucible in fi«*fit«*(NH4)3P04 + 12Na2Mo03 12H20. (1) Upon addition of acid any excess of base is neutralized and if the acid is added to a color change with phenolphthalein, tri- ammonium phosphate will have been changed to diammonium phosphate, since the normal salt is basic to this indicator. The net result is therefore to be expressed by the following equation: 2(NH4)3P04.12Mo03 + 46NaOH -* 2(NH4)2HPO4 + 23Na2Mo03 + (NH4)2Mo04 + 22H20. (2) It should be noted that it is necessary to have the solution cold when the excess of base is added and to have present suffi- cient water to prevent the escape of ammonia, which would be produced by reaction of ammonium phosphate with sodium hydroxide. Determination of Phosphorus in Rock Phosphate : Volumetric Method. — The molybdate solution that was used for the gravimetric determination may be used here also, first adding 5 cc of concentrated nitric acid to each 100 cc of solution. This additional acid serves to prevent the precipitation of molybdic acid. Prepare a half -normal solution of hydrochloric acid, standardizing against .sodium carbonate as directed on page 83, modifying the weights according to the different normality of this solution. Prepare a half- normal solution of sodium hydroxide in boiled and cooled water, standard- izing against the acid, using phenolphthalein. 92 QUANTITATIVE AGRICULTURAL ANALYSIS Use' 2.5 gm of sample, weighed accurately to milligrams. Dissolve as directed for the gravimetric determination of phosphorus in rock phos- phate, page 90, and dilute the solution to 500 cc in a volumetric flask. Mix well and pour into a dry filter. Reject the first 25 cc and collect the rest in a dry flask. Pipette 25-cc portions of this solution into 250-cc flasks. Add ammonium hydroxide until a slight precipitate persists and clear with a few drops of nitric acid. Place a thermometer in the flask, immerse in the water bath and heat to 65°, then add 35 cc of freshly filtered molybdate solution. Mix and leave the flask in the water bath for 15 minutes, then filter at once. Wash twice with water by decantation, using 25 cc each time, pouring the washings into the filter. Transfer the precipitate to the filter as thoroughly as can be done without the use of a policeman and wash the flask and filter with cold water until the filtrate from two fillings of the filter yields a pink color upon the addition of phenolphthalein and one drop of standard base. (Test the wash water in this manner before using.) Return the filter and precipitate to the flask in which precipitation was made and add 50 cc of cold water. Add half-normal base from a burette until all of the precipitate is dissolved, mixing by gentle rotation. Imme- diately add a drop of phenolphthalein and titrate with standard acid. From the total Volume of base used, deduct that equivalent to the acid required and from^e remainder-calculate -the per- cent of phosphorus and of phos- phorus pentoxide in the sample. irc?x *? S* y* - E i£ £• '£. y. J C* 2 H - — - -/> * •£ ^ * £ -*•* H. 5* n -^ 5 - ^* ^* ? x 2 ^. ^ ^ sr ^* _ -?r ^ >— 2, !£ *^ *~~" *"** *^ Z^* JH H~ nm>4 *^*" II — H 2. 5"?~£.~- > 2 -^P^X-^<":£ ^ c 5* 5 .=• 5 ~. ^ 2 -. ^ ^ * 3§ ^ 5 s- 5 = r- "H a ^ *^ ~L « x ^ **• ~ -^' »~ *— * _4 ^ E* "^ *^ V"*"J' * ~ ^ ^ - I I i CHAPTER IV DENSITY AND SPECIFIC GRAVITY Density.—The density of a given substance is the mass of unit volume. When the metric system of weights and measures is used, as is customary in most scientific work, the density equals the weight, in grams, of 1 cc of substance. Specific Gravity.—Specific gravity is the ratio of the density of a given substance to that of some other arbitrarily chosen substance. For liquids and solids the substance which is gen- erally chosen for reference is water. Since the weight of a milliliter (which, for all practical purposes, may be taken as a cubic centimeter) of water at 4° is, by definition, 1 gm, the density of any substance becomes its specific gravity if the latter is referred to watei^ at 4°. This is the preferred method for expressing specific gravity and the figure so determined is stated as t° specific gravity^0 for the specific gravity when the substance is at temperature f, Most of the laboratory methods for determining specific gravity involve measuring either (a) the buoyant effect of the (liquid) substance upon an immersed "float/' (6) the com- parative weights of equal, but unmeasured, volumes of the (liquid) substance and water, or (c) the weight of water displaced by a weighed, but not measured, quantity of the (solid) sub- stance. To carry out such experiments at 4° is a problem offering great experimental difficulties and the work is usually performed at some more convenient temperature, higher than 4°. On this account it is customary to express the results as f specific gravity*0 this quantity being the ratio of the density of the substance at t° to that of water at the same temperature. This quantity t° can be converted into the specific gravity at 75 by multiplying 94 //A'.Y.SV y r AM* WWIFIC (SUAVITY by the density of water at /°. Or it can be converted into specific, /° gravity at . 0 by multiplying by the ratio of the density of water at /° to that at t\\ the latter symbol representing any desired temperature. It cannot be too strongly emphasised that both temperatures represented in these symbols should always be expressed or understood. Because of failure to do thin there is much confusion in the records in scientific literature. Baume System. In this system two scales arc; used, one being for liquids lighter than wafer, the other for liquids heavier than water. The first is applicable, to petroleum products and to most other oils and fats. The; neeond Beale in used for most solutions iu wafer. In the original Baumc! scale, for liquids heavier than water the point to which it hydrometer float sinks in a solution of sodium chloride, 15 per cent by weight and at lf>**0'., wan taken as 1-5° Bituiiti' (abbreviated Be!.). The corresponding point for pun* water was taken as (f Be, and all other points were* located by thene two. For liquids lighter than water the- scale has the point 10n Be. for pure water and (f Be\ for a 10-per c«»nt, solution of Hodimii rhlf*rif!i», tlifscnh* fii'ing extended beyond 10° for lighter liquids. If will bt» 141*1*11 that this is u wholly arbitrary nywtcm itfid cfrnversion of degrees Baiim/* into HjH»rific gravity^ or vice versa, will involve ibi» u««* of s|M*ciul formuhin. Hevenil modifica- tions of the original Baunie* walon have c<»nu» into uwt and I lie (HfliciiltieH involved in interpmtHtion hav I and li 145 96 QUANTITATIVE AGRICULTURAL ANALYMti For liquids lighter than water: !*« h and 0 ~ 130 + B B = 1J° - 130, where B = degrees Baum6 and S = specific gravity at 15.5° C. Methods for Determining Specific Gravity. The Picnometer. The most accurate method for making this determination depends upon the use of a vessel known as a "piezometer." There are various forms of picnometers but the instrument is essentially a small flask which may be weighed, first filled with water and then with a liquid whose specific gravity is to be measured. Specific gravity at given by the ratio of the two weights, an ex- plained above. Two forms of picnometers are shown in Figs. 23 and 24. The picnorneter flask lias an accurately ground stopper which is borcnl longitudinally as a capillary tube. The dry flask in first weighed. Filled with distilled water, which has been boiled recently to expel dissolved air, it is then nearly immersed, in a constant temperature bath and when the water has been brought to the required temperature the surplus drop is removed from the top of the stopper. The flask in then removed from the bath, wiped dry and weighed. It is necessary that the room temperature shall be a few degrees lower than that of the bath, BO that the liquid may recede from the tip of the stopper after removing from the bath. After the weight of water contained at f has been determined the flank is emptied, rinsed with redistilled alcohol and dried. It is then filled with the liquid whose specific gravity in to be measured and this is treated in the same way as was the water. IG. 23.™—Picnometer bottle, with cap. ft ; ;. i i n - L .11 n;i|ii«>H -HIIOLHIA ui Mtiiptiai 'aicy|«iiiiojp^Ct{ fuwi p I m I 1 ipui A'tiui uurjH j^ouiojp^Cij «.»(•) uo Hiioi^trnptu}* Qqj, *iior)t?AJi«qi> tHj'j Huppnu joj KIIIMTII A*JI?KK«>O<)U •Mj'j HtipjAOjd «iw|H ijq'i iiodn ;)]T?i)H v *}i!nl);| *it{'| jo A'lumop i>i[;j iiodn u,iu| ir; HpUix!«>p ^iiiiiinn.riHiii II»IAJ^ 11 |H!if)JJ JO '}Ut)1U«M1{|(IU!p H')[ UOlIll HpUftJfH J[IA\ »i Mtii'|tio|| HI uq'l iii>ijA\ p.jHjtiiiii.in Ajp)jiid oq \ 11 HniAini puti mo|'|i{j *q7i«i Uq*| UIO.IJ p«)AOUl*)J UM\1 Ht HI pnibij «)ij;; pu«) .lixidn fiif) UIQJJ dI[!| KI .u))oiuoni)id tiiA%[ddir puu puibij t? (>')u; f} jo qi)uiu<[ ' *^ u i) 11 ui Sujiq uoq^ s; ^1 joqcjiu oq'j <>} uoipns ?A\ jo '|q^r*>A\ i>ij'} A'q • ° :pl AJJAIMlrf o' nil)t| sn|| jo • y S 01]') 98 QUANTITATIVE AGRICULTURAL which apply to special industrial uses. Two of these will be mentioned. Lactometer. — This is an instrument much used in dairy laboratories. Quovenne's lactometer is graduated in degrees from 15 to 4.0, corresponding to specific gravity 1.015 to 1.040. The New York Board of Health lactometer also is graduated in arbitrary degrees in such manner that 0° corresponds to specific gravity 1.000 and 100° to 1.029, the latter figure being con- sidered as the average specific, gravity of pure milk. Degrees on this lactometer would thus roughly indicate the per cent of whole milk in a milk and water mixture. Other special names, such as "saceharo- meter," "alcoholometer," etc., apply to hydrometers for sugar solutions, alcohol and other special uses. In using hydrometers the temperature at which the experiment is performed must be that for which the instrument is calibrated and care must be taken to remove* air bub- bles which might cling to the hydrometer and thus increase the effective displace- ment. The floating hydrometer in much used for measurements not requiring great, ac- curacy, as a reading is very quickly made. The scales found on the stems are fre- quently very inaccurate and any hydrom- eter should be calibrated by the use of liquids of known specific gravity. Westphal Balance.— In effect, this balance (Fig. 26) weighs the liquid which f^ _ >Sx^-> is displaced by an immersed plummet FIG. 25. — Pleating hy- whose displacement of water is known. drometer and cylinder, mi. t~ i /* i \ i ^ « ^ i • A I he balance is first brought into adjust- ment with the dry plummet hanging on the beam. A cylin- \l It DENSITY AND SPECIFIC GRAVITY 99 der containing the liquid is then brought under the beam in such a position as to allow the plummet to be totally immersed in the liquid. Weights are then placed on the beam to bring the balance again into adjustment. These weights are so related to the volume of the plummet and to the graduations on the beam v T "THTT"TT~TnrT-"3f A -— _ \^M IM| FIG. 26.—Westphal specific gravity balance. t° as to give directly the specific gravity at 75* Usually the dis- z> placement of the plummet in pure water at the rated temperature is 5 gm and the figure on the beam directly over the plummet is 10. Therefore the largest weight piece should weigh 5 gm. 100 QUA NT IT A TI \'K AGKK'VLTl 'H. \ 1. A .V .1 /, l',s7 ! n la pure water this would be placed at 10 to bring the balance into equilibrium. This would read 10 tenths, or 1. Three other denominations of weights are provided, reading to the second, third arid fourth decimal places, respectively. Calibration. — This instrument, like the floating hydrometer, must be used at the temperature for which its displacement of water is known. Any plummet may be calibrated for use at its rated temperature or at any other desired temperature by weighing it dry, and again suspended in distilled water which has been boiled to expel dissolved gases, then cooled to the desired temperature. The difference between these weights represents the weight of water displaced. If the displacement so found in not exactly 5 gm, all specific gravity determinations are corrected to take account of the deviation, thus: X e where Sto is the true specific gravity ,*SV" the figure found experi- mentally and d the water displacement at /°. The weights for the Westphal balance ant calibrated by the method described for analytical weights, page 41. Use of the Westphal Plummet on an Analytical Balance. The Westphal balance is a convenient and low priced piece of apparatus for making specific gravity determinations with a fair degree of accuracy. Determinations may be made* with a higher degree of refinement by using the Westphal plummet with a good analytical balance. The plummet in cleaned and dried, then suspended from a hook on the left arm of the balance. Weights are added to the right pan to counterpoise, then a cylinder of the liquid to be tested is placed on a bridge over the balance pan in such a way as to allow the balance to swing unimpeded, but supporting the cylinder HO that the plummet is entirely immersed in the liquid. A counterpoise in again effected by removing weights from the right pan. The* difference be- tween the two weights is the liquid displacement. Thin divided by the water displacement, found as already deHeribed, given t° the specific gravity at ,o" The mechanical arrangement is shown in Fig. 27. DENSITY AND SPECIFIC GRAVITY 101 Applications.—For the application of specific gravity deter- minations to the quantitative analysis of solutions, two condi- tions are necessary: The solution must be a binary one (having only two components, solvent and solute) and the variation of specific gravity with concentration must be great enough to make possible calculations of concentration to a reasonable degree of accuracy. Accurate tables have been worked out in a limited number of cases and for these the specific gravity deter- FIG. 27.—Westphal plummet as used with an analytical balance. mination frequently offers the most convenient method for the analysis. Examples of such cases are solutions of ethyl alcohol, methyl alcohol, various sugars and various acids in water. If it is known that only one of these compounds is present in a solu- tion, the concentration can readily be determined. Of course a good thermostat is necessary, in order to a void temperature errors. Such tables as those mentioned above are found in many of the standard handbooks. Quite elaborate tables are contained in "Methods of Analysis/7 published by the Association of Official Agricultural Chemists, and in U. S. Bureau of Standards Circular 19. The latter may be obtained from the Superintendent of Documents at small cost, 102 QUANTITATIVE AGRICULTURAL ANALYSIS Determination of Specific Gravity.—Make accurate determinations of specific gravity of solutions of methyl alcohol, ethyl alcohol, cane sugar, etc., as they may be furnished by the instructor, and using the methods described In the foregoing pages. Report the per cent concentration of the solutions, found by reference to tables such as those mentioned above. The tempera- ture used for the determination must correspond to that for which the table in question is constructed. In Chap. X this determination is applied to the identification of the various oils, fats and waxes and in Chap. XI, dealing with the analysis of dairy products, the application of specific gravity determinations to milk testing is discussed. CHAPTER V HEAT OF COMBUSTION (CALORIMETRY) All chemical reactions involve either evolution or absorption of heat energy. The measurement of the "heat of reaction" has proved to be a valuable method for investigation, in both pure and applied chemistry. We are here particularly concerned with the amount of heat evolved by the combustion of fuels and of foods. In the case of fuels this, of course, has a direct bearing upon the value of the fuel when it is burned for the production of useful heat, while the heat of combustion of foods and feeding stuffs is of interest in connection with their relative values as energy producers in the animal body. However, the student is cautioned against the fallacy that the "calorific value7' (heat of combustion) of a food is the only criterion as to its value. Even an elementary study of physiology should convince one that such matters as balancing of diet, proper proportioning of rougher and more refined foods, stimulation of appetite, per cent of contained nitrogen, etc., are of prime importance in this connection. Units of Measurement.—In scientific work the accepted unit of heat is the calorie. As ordinarily used this is the heat that is absorbed by 1 gm of pure water as its temperature rises 1° C. (strictly, from 15° to 16°). The specific heat of water is not the same for all temperatures but the variation is only 0.013 over a range of 0° to 100°. In engineering work, for expressing the value of fuels, the British thermal unit (B.t.u.) is more often used. This is the heat absorbed by 1 Ib of water as its temperature rises 1° F. The "calorific value," "fuel value" or "heat units," as it is variously expressed, is the number of calories per gram or of B.t.u. per pound, made available by burning the material. The following equations represent relative values: cal per gm X 1.8 = B.t.u. per Ib;1 (1) B.t.u. per Ib , /rtN --------f-------- = cal. per gm. (2) JL.o 1 For the derivation of these formulas see MAHIN, "Quantitative Analy- sis," 2nd ed., p. 314. 103 104 QUANTITATIVE AGRICULTURAL ANALYSIS Apparatus.—A great many forms of calorimeters have used for measuring heats of combustion but all of the successful of these are based upon a measurement of the FIG. 28.—Section of the Emerson calorimeter. in temperature produced by burning a weighed sample in oxygen. at high pressure, in such a way as to have the evolved hea/fc absorbed by a known quantity of water and by the material of HEAT OF COMBUSTION 105 calorimeter itself. The weights of these (and the known specific heat of the materials of the calorimeter), taken with the weight of the substance burned and the temperature rise, furnish the necessary data for the calculation. Emerson Fuel Calorimeter.—Following is a description of the Emerson calorimeter and also directions for making the deter- mination of fuel value. Bomb.—The bomb, made of steel, consists of two cups joined by means of a heavy steel nut. The two cups are machined at their contact faces with a tongue and groove, the joint being made tight by means of a lead gasket inserted in the groove. The lining is of sheet nickel, platinum or gold, spun in to fit. The bomb is closed by a milled wrench or spanner. The pan holding the combustible is of platinum or nickel, and the supporting wire of nickel. (See Fig. 28.) Calorimeter.—The jacket is a double walled copper tank, the space between the walls being filled with water. The calo- rimeter can is made as light as is possible, of sheet brass, nickel plated. Stirring Device.—The stirrer is directly connected to a small motor and it is enclosed in a tube to facilitate its action in circu- lating the water. The stirrer is mounted on a post on the calo- rimeter jacket as is also the thermometer holder. Ignition Wire.—Unless ignition of the fuel requires a very high temperature a platinum resistance wire is suitable. For ignition of such substances as are used in determining the water equivalent of the calorimeter (naphthalene or cane sugar) or of anthracite coal an iron wire is more certain in its action because it burns and produces a higher temperature. When iron wire is used a correction of 1600 calories per gram of wire is subtracted from the total calories obtained from the fuel combustion. This is the heat of oxidation of the iron. Formation of Nitric Acid.—When any nitrogenous organic matter is burned in air practically all of the nitrogen is liberated in the elementary form. On account of the high concentration of oxygen in the calorimeter bomb a considerable portion of the nitrogen is oxidized and the products dissolve in the water which is formed by the combustion of hydrogen. A dilute solution of nitric acid is thereby formed. This gives rise to a positive error 106 QUANTITATIVE AGRICULTURAL AXALYMH I i in the observation of fuel value, the magnitude of the error depending upon the extent to which nitric acid is formed. As a rule the error is small and it may be ignored for ordinary fuel test- ing but if a correction is to be made the nitric acid is titrated by standard base, at the end of the experiment. The heat of formation and solution of nitric acid from elemen- tary nitrogen is 230 calories per gram. It is convenient to use a standard solution of base, 1 cc of which is equivalent to 5 calories. The normality of such a solution is 230 X 0-06302 " ™*° N' The number of cubic centimeters of base required to titrate the nitric acid in the bomb after the combustion is multiplied by 5, the product being subtracted from the observed calories. Radiation.—Radiation or absorption of heat by the* calorim- eter may be avoided by making the calorimeter "aeliabatic." This may be done in a number of ways, three of which will be mentioned. 1. The water in the surrounding jacket may be heated by electrical means, so as to keep pace with the rise in temperature of the calorimeter water. This is the most satisfactory method, although somewhat complicated and expensive* apparatus in required. 2. The water in the jacket may be wanned by chemical action. By Richards' method a basic solution is used to fill the jacket and an acid is run in from a burette at a rale which depends upon the rate of change in temperatures of the* calorim- eter water and upon the concentration of the acid. The acid solution may be standardized in terms of the* number of calorics liberated by the action of each cubic centimeter upon the* bane, in which case the proper rate of addition is more easily determined. 3. The jacket of the calorimeter may be evacuated, on the principle of the Dcwar flask, the transfer of heat outwardly then being limited to that which occurs through conductivity of the glass of the jacket. This would appear to he* the leant trouble- some method but it has not worked well in practice. Radiation Corrections.—If adiabatie conelitionH cannot be maintained several methods for making radiation corrections are available. UKAT OF COMUl'XTION 107 1. The combustion may bo begun as far below atmospheric, temperature as it is to end above it. By this means absorption of heat in the first half of the experiment would appear to balance radiation during the last half. This is the roughest sort of approximation and it would not serve for ordinarily accurate work, 2. The rate of change of temperature may be observed for a certain period before firing and for another period after the calorimeter wafer has absorbed all of the beat from the bomb. The arcrayt- of these rates is then considered to be the? moan rate of absorption or radiation of heat for the entire experiment and if this is multiplied by the time elapsing between the firing and the maximum absorption the, net gain or loss during the? entire, observation period is given. This method is very commonly employed and it given a very close* approximation to the. true correction. 3. Observations are made in the, same* way as in method (2). In addition the time, n, required for six-tenths of the? total rise? in temperature* is observed, also the time, />, for the remaining rise. Instead of averaging the two radiation for absorption) rates the. preliminary rate, #,, is multiplied by a and the final rate!, /fo, by //. The corrected rise is then T + If in + Ay/, where* 7'-~ total rise, and I{\ and It* are regarded an positive for falling temperatures and negative for rising temperatures. Tin* observation of the* time, a, is subject to some uncertainty when the* temperature is rising rapidly ami on thin account the method is not HO easily applioel as is method (2). It will rarely be found that the difference between the oorroetionH calculated by the»«» two mothoels will differ by more than 0.2 per cent and as thin in well within the* permissible variation, mc*thod (2) is recommended for all but the mont rofinod work. 4. The llegniiult-Pfaumllor method approaches theoretical accuracy more nearly than any of the* methenln already doHcribed. For a eiisc.tiKsion of this method, HOO White., "(!as and Fuel Analy- sis" (International Chemical Morion) 2nd od., page* 20K. Time-temperature Curves......•.....-Thrcso typos of time-tempera- turo curve's are produeod, according to whefhor the experiment is 108 QUANTITATIVE AGIUCi'LTl-RAL ASALYMX (a) begun and finished below room temperature, (b) begun below and finished above or (c) begun and finished above. These types are illustrated in Fig. 29. The relative slopes of the ends of the curves represent R\ and R». It will be observed that these slopes are easily determined in curve (6) but that it is especially difficult to decide an to what temperature should be taken as the maximum produced by the fuel combustion, in the experiment represented by curve (a). Conditions represented by curve (6) are to be obtained when possible. TIME I<'HJ. 29.— Time-tarn jK'ruUm* cur VON. Determination of Heat of Combustion of Fuels, Foods or Feeds,*—Place the lower half of the bomb in the holder and the fuel pan in the, wire support, after having wired the fuse wire according to Fig, 2H. Extend the wire across the pan, allowing it to dip Mifltekmtiy to be in contact with the substance, which is later to he placed in the pan. The wire must in no ease touch the pan. The fune wire Hhould be phwcd in series with two 100-watt. lamps in parallel when the 110-volt power circuit w used for firing. The material whose calorific value in to be determined should be ground to pass a GO-mesh sieve and it should be dried at HX>" before, weighing the sample for combustion. If the material is a liquid, wich UK milk, or a sub- HEAT OF COMBUSTION 109 stance containing a large amount of water, 100 gm or more is first weighed (to centigrams only). It is then evaporated to dryncss over the steam bath and reweighed. The loss of water gives the necessary data for calcu- lating the fuel value of the dry material to a basis of the original sample. Thus, if M represents the per cent of water, c the calorific value of the dry residue and C that of the original sample, (100 - "loo" C As suitable materials for exercises in calorimetry of foods, such substances as dried egg albumen, starch, sugar and butter fat may be used. Coal, coke, crude oil, kerosene or gasoline are fuels whose calorific power may be determined. Volatile liquids, such as the last named two, can be weighed and burned in a gelatine capsule, such as are used for medical preparations. Blank determinations must then be run on other similar capsules, so that corrections may be subtracted. All of the capsules are weighed. Fill a weighing bottle with the prepared sample and weigh accurately to 0.1 mg. Pour from this into the pan in the bomb, until the pan is approxi- mately half full. Weigh the bottle again, the difference between the above weighings giving the weight of the fuel in the bomb. This weight should be greater than 0.5 gm and not more than 1.2 gm. For hard coal the charge should be not greater than 1 gm. Hard coal should not be as finely divided as soft coal or foods. The upper half of the bomb is now placed in position and the nut is screwed down as far as may be by hand, care being taken not to cross the threads. The shoulder on the upper half of the bomb, over which the nut makes bearing contact, should be lubricated with oil. Extreme care should be taken that no oil or grease is deposited on the lead gasket. The bomb is now ready to be filled with oxygen. The nipple is coupled to the oxygen piping by means of the attached hand union. In handling the bomb, care should be taken not to tip or jar it, as fuel may be thrown from the pan. The spindle valve on the bomb is opened one turn and then the valve on the oxygen supply tank is-very cautiously opened. The pressure gauge should be carefully watched and the tank valve so regulated that the pres- sure in the system shall rise very gradually. When the pressure reaches 300 Ib per square inch, the tank valve is closed and the spindle valve immediately afterward. The bomb should be immersed in water immediately to detect any possible leaks. The bomb is now ready for the calorimeter, which is prepared as follows: Nineteen hundred grams of distilled water, weighed or measured in a cali- brated flask, is placed in the calorimeter can at a temperature about 1.5° below the jacket temperature (which should be in the proximity of the room temperature). The bomb is then placed in the calorimeter and the stirrer and thermometer are lowered into position as indicated by Fig. 28. The thermometer is immersed about 3 inches in the water. The bulb of the ther- mometer should not touch the bomb. ! : ' i 110 QUANTITATIVE AGRTCn/rrRAL AXALYSIX The terminals of the electric, circuit used for tiring arc now attached, Care should be taken that neither the bomb nor tin* stirrcr in allowed to touch the sides of the can. Th(* Htirrcr is now si ailed and allowed to run 3 or 4 minutes to equalize the temperature throughout the calorimeter. Readings of the thermometer are. now taken for 5 minutes (muling to 0.001° or 0.002° every minute) at the end of which time fin* switch in turned on for an instant only, which will he found sufficient, to fire* the charge. In course of a few seconds the temperature begins to rise rapidly and approximate readings are takon every minute* until the rise become** slow, more accurate readings then being taken. After a maximum temper- ature is reached and the rate of change of temperature is evidently due only to radiation to or from the calorimeter, the readings arc continued for an additional 5 minutes, reading every minute. These readings, before the firings and after the maximum temperatures, are m*ci*ss»ry in the com- putation of the cooling correction. The time- elapsed from the time of firing to the maximum temperature .should be, in no case, more than 0 minutes. When through with the run, replace the bomb in the* holder ami allow the products of combustion to escape through the valve at the top of the bomb. Unscrew the large nut and clean the interior of the bomb. The inside of the nut should be kept greaned, also the* threaded part, at the top of the lower cup. Immediately after each run, the lining of the bomb should be washed out with a cloth moistened with a dilute solution of ammonium hydroxide and then with water. When the apparatus after using;, is to be left for several hours or more before making another test, the lining should be removed and the inner surface of the bomb slightly coated with oil. This oil under the linings should be removed when next preparing the bomb for use, as an excess of it may be ignited with a possible resulting injury to the* linings. Heavy Qih, Coke and Hard C'oal—The determination of the heat of combustion of heavy oils, such m crude petroleum, and ulno of eoke and extremely hard coals, is best made by mixing with u ready burning com- bustible, such as a high-grade bituminous coal or pure earbon. This auxiliary combustible facilitates the complete combustion of the whole mixture in the case of coke, and hard coal, and with the* heavy oil it acts its a holder and prevents rapid evaporation of the oil. The uuxiliary rornbuH- tihle should be placed at the bottom of the pan and the coke, roal or oil sprinkled over it. It should be dried with extreme cure mul carefully standardized as to the resulting rise in temperature, per gram in the calori- meter when completely burned. Calculation,—First plot a smooth curve, using temperatures as ordinates and time as abscissas, line only the* ntniight por- tions of the ends of the graph for calculating K\ and #2. ^ //AM 7' OF COMHUXTKW III The* difference between the to.mperature at maximum and the, tompenitiw at firing gives directly the total ruse in temperature in tin* ejilorimder. To this ri.se a cooling correction must he applied, which is computed as follown: The4 change in temperature (luring the* preliminary /> minutes of reading divided hy the time (5 minutes) gives the rate of change «*f temperature per minute, due to radiation to or from tin* calorimeter, and also any heating duo. to nl-irring. Thin factor is #j and in like manner the readings taken aft-or th(t tempor but it is better determined experimentally by burning a X>TLU*° substance of known heat of combustion, such as naphthaJone or cane sugar. jl '?! » r | •q i ' .' i i ; • It 'i'^i L ^ CHAPTER VI INDEX OF REFRACTION Theory.—When a ray of light passes from one transparent medium into another of different density, at the surface of nqMuni- tion the ray is always bent from its first course, unless it strikes this surface at an angle of 90°. This phenomenon in known as optical "refraction." The angle i, included between th<» incident ray and the normal to the separating surface (we Fig. 30) is the angle of incidence while the angle r, between the refracted ray and the normal, is the angle of refraction. The ratio n - is the index of refraction. If s and .5' represent, respectively, the speed of light in the* medium from -which the light emerges and in that into whirh it passes, then the Index of refraction of the latter medium with respect to the former IB greater than 1 if .v is greater than #', mid conversely. In a general way the* speed of light varies inversely with the* density of the medium, although this is not a strict mathematical relation. It will thus be neon that the* con- ception of index of refraction must involve two suhBtunww and that its value will depend upon the density of each. AH ordinarily used, it is undcrHtcxw! thitt the light emerges from ordinary air into the substances who«c index in being measured and the term "index of refraction'1 therefore signifies the ratio of the angle of incidence from air, to flic angle of refraction in the substance under cozu*itlc;rutum. 8 113 FIG. 30.—Illustrating refraction of light. il( fii'j 114 QUANTITATIVE AGRICULTURAL ANALYSIS Applications.—In a number of instances the measurement of index of refraction furnishes a means for identifying certain materials and in some cases a quantitative estimation is made possible, where the identity of all components in a given mixture is known. As an example of qualitative testing may be men- FIG. 81.—The Abb6 refractomotor. tioned the measurement of this property in oils and fats. This is discussed in Chap. X. The quantitative determination of alcohols and sugars in aqueous solutions and of milk fat in milk and the detection of added water in milk by the examination of milk serum are familiar examples of quantitative application of refractivity measurements. Some of these are given attention in Chap. XL INDEX OF REFRACTION 115 Light of short waves is refracted more than that of longer waves. Therefore in expressing the index of refraction the character of light must be indicated. Ordinarily the refraction for the DI sodium line of the spectrum is understood unless some other light is specified. Apparatus. — For the determination of refractivity an instrument must provide (a) a prism of known index of refraction, a plane surface of this lying against the liquid or solid under investigation and (6) an optical system of lenses for exam- ination of the effect of refraction. All other parts may be regarded as acces- sories, for adding convenience of manipu- lation or for increasing the accuracy of observations. Abbe Refractometer. — This instru- ment (Fig. 31) serves very well for measuring refractive indices of fairly viscous and non-volatile liquids. The optical system is represented in section in Fig. 32. The lower half of the prism (not shown in the figure) serves merely as a means for holding a layer of liquid in contact with the upper half. A mirror, below, reflects light into the system and this passes through the lower prism and the layer of liquid, emerging from the latter into the upper prism at all possible angles. The ray o, a' a", . ,, , „ » ,, grazing the lower surface of the upper prism, represents the limiting angle of incidence (90° to the normal) and the angle of refraction of this ray (or of one whose angle of incidence is infinitesimally less than 90°) forms the bounding line between a region of light and one of darkness. This will be seen as the line G in Fig. 32. If the liquid from which light emerges is exchanged for one of different index of refraction the angle of refraction of the grazing ray will be changed. In other words the boundary between . 32.— Path of rays in tho Abb6 refractometer. 116 QUANTITATIVE AGRICULTURAL AXALYXIS light and dark in the field of observation will be shifted. It is the observation of the position of this boundary that constitutes the determination of index of refraction by means of this instru- ment. The relative positions of telescope and prism system can be altered at will The prism system is tipped until the bounding line lies upon the cross hairs of the telescope. The index of refraction is then read on an outside scale. Dispersion.—The refractive effect at the surface separating transparent media varies according to the wave length of the light, shorter waves being most re- fracted. The result of using polychromatic light in a sys- tem like* that just discussed will therefore bo that the* light and dark fields will be sepa- rated by a colored zone of HJX ctral tints, instead of by a sharp, uncolored line. It then becomes necessary to use monochromatic light or else to introduce Home device for correcting the dispersion. In the Abb6 instrument a "com- pensator" provides this cor- rection, The Compensator.—T h e dispersive effect of different transparent media is not a definite function of the index of refraction for monochro- matic light. For example, two media might have* the same indices of refraction for yellow light but quite different indices for violet light. This principle is utilized in the construction of the Amici prism. In Fig. 33 the parts «, a' are prisms of crown glass and 6 is of flint glass. The angles and the dispersive powers of these prisms are so related that when they are cemented together the combined effect is to allow the. yellow (Di) ray of entering polychromatic light to pass through with its direction unchanged, while rays of all other wave lengths are refracted. FIG. 33.—-Single Amici prism, an used in dispersion compensators. INDEX OF REFRACTION 117 In other words, the part 6 has a refractive power which is greater for red, smaller for violet, and the same for yellow as the cor- responding powers of the combination of a and a'. If this Amici prism is placed in the path of light which has been refracted (and dispersed) by the prism-fluid system of the refractometer, it will either add its dispersive effect to that already produced or oppose the latter, according to the way in which it is turned about the axis of the instrument but, no matter what its position, the direction of the yellow ray is unchanged and the reading for index of refraction is not altered, since this value is usually stated in terms of yellow light. If the angle between the planes of dispersion of Amici and refractometer prisms is such that the dispersion of the latter is exactly neutralized, " compen- sation" is effected and the border line between light and dark fields becomes distinct and without color. 6-- D=-d D=-2cl FIG. 34.—Five typical positions of the units of a double compensator, showing net dispersive effect (JO) in the direction a&. If two Amici prisms are used, as is the case in the Abb6 refractometer, and if they are mounted in such a manner as to revolve in opposite directions, the dispersive effect of the com- bination may be varied between the limiting values of + 2 d and — 2 d, where d is the quantitative effect of one Amici. This widens the range of possible compensation. 118 QUANTITATIVE AGRICULTURAL ANALYMX The diagrams of Fig. 34 illustrate a few of the possible posi- tions of the two elements of a double compensator, with the, net effect of the altered system upon dispersion. In explanation of these diagrams the combined dispersive effect in the direction ab is represented by D and that of one unit in its own plane (repre- sented by the arrows) by d. It is evident that the component of dispersion in ab for any given position of a unit varies as the cosin of the angle, 6, between ab and the plane of dispersion for the unit. Any conceivable value between 2 d arid — 2 d may be obtained and compensation thus effected for any dispersion within this range. Butyro-refractometer.—The Zeiss butyro-refraetometor has an optical system similar to that of the Abl>6 instrument. The principal difference is in the fact that the telescope and prism system of the former instrument are rigidly con- nected so that the divided field cannot be shifted to bring the line of division upon the central crossing of cross hairs. Instead, a scale graduated in arbitrary degrees in fixed within the instrument and the position of the bounding line is read upon this. As its name indicates, the butyro-refraetometer in designed for use in dairy laboratories and its chief function is in the tenting of butter. Therefore, instead of being provided with a com- pensator the prisms of the instrument arc* "achromatized" for pure butter so that this fat gives no dispersion. This con- stitutes the basis for an additional qualitative test for butter, since other fats used as substitutes will have different dispersive power and the bounding zone in the field will therefore be spectrally tinted. Dipping Refractometer.—From an inspection of Fig. 32 it will be seen that the essential parts of the AbW refraetometer, from the optical standpoint, are the upper prism, the objective and an eyepiece for viewing the field. (The latter in not shown in the* figure.) The thickness of the liquid film is of no particular moment and the prism might as well be immersed in a quantify of the fluid. In the dipping refraetometer (Fig. 85) thin principle is utilized. The entire instrument is in one rigidly built piece, the prism being fixed at the lower end. The instrument it* hung 'INDEX OF R.KFRACTION KO that the prism is immersed in a bath of the liquid und< examination and the index is road on a scale within. The compensator for the dipping refraetometor / ^& consists of a single Amici prism (C of Fig. 35) rotated > Jp by the milled ring Y. The range of compensation is thus less than that of the double compensator but it is sufficient for this refraetometer, whose1 range for indices of refraction is comparatively narrow. In Fig. 35 two points are arbitrarily selected to represent the entire surface of the prism when* light enters. f/f/' is the ray of grazing incidence refracted and focused at (V, which boars the scale, a and a' represent rays onto ring at any other incident angle*, focused at A. Above is a projection of the field. At the right of (V the* field is (lark because the critical ray, refracted as it enters the prism, can make no greater angle of refraction for the given prism-fluid combina- tion. When the fluid is changed for another having a different index of refraction that angle of refrac- tion for the critical ray is changed and the border line within the field is shifted. Putfrich Refractometer.—Thin instrument is espe- cially adapted to use, with volatile liquids, although it is suitable also for exact determinations of index of refraction of any liquid whatever. The optical principle IB exactly the name an that of the Abbf. instrument, light entering the fluid-prism system *tt grazing incidence and the critical angle of total refl< c- tion being measured. The liquid in placed in a glass cup which is cemented to the top of the* refracting v/ / prism, and which may be covered to prevent evapo- /II ration of the liquid. Monochromatic light is used $^ and an observation telescope in swung upon an arm ^ :ifl ....„ in such a way as to bring the divinicm between light Dippin« r**- and dark fields upon ite crosn hairs. A circular nealc* J^7nTf Dextrose (grape sugar) ............................. 4-53. 1 Levulose . - 93 . 3 Sucrose (cane sugar) . ......... 4-66.5 Invert sugar ................................... -20.57 Lactose (milk sugar) -1-52.53 Maltose (malt sugar) . .... + 137.5 Starch ....................... .............. 4-190.0 Tartaric acid (ordinary) ............................ 4-12.0 Nicotine (in benzene) — 164 0 Cocaine (in chloroform) . ........ — 16 3 Quinine sulphate (in alcohol) ..................... —225.7 Camphor (in benzene) -1-41 4 Lemon oil (no solvent) . . 4-59 to 4-67 Orange oil (no solvent) . . ........ 496 to 4-98 * These figures represent mean values for ordinary concentrationn. There is nearly always a certain variation with concentration and when* this is large it must be taken into consideration. For example, the Hpc cific rotation of levulose is —88.13 — 0.2583 c, and of dextrose 4-52.50 4 0.0188 c 4- 0.000517 c2, c indicating grams of active material per 100 «LTl'RAL A A* A i f The Polarimeter.—Listed in what (perhaps somew] trarily) may be regarded as the order of relative import* not in the order in which they are fixed in the insl run essential parts of an instrument for measuring optical rot as follows: (a) An optical part, F, (Fig. 37) for polarizing monochromatic light in a definite plane. This is the " p< (6) A part, A, similar to the polarizer, which can I in the path of the light and rotated about the axis of pro of the beam. This is the "analyze*." With flic* fixed in position there will be a corresponding posit io 1 l\ ^zr-jr //vx^i f | i v "-*-1*-- " ——--•* \l IP S A PIG. 37.--- -DiaKrainmaUf! re pn '.Mentation of thr rflW-niinl part a nirn pic polariim't.4 •r. analyzer which will permit the maximum brightness c mittecl light and another which will cause total extinct first representing a coincidence of the planes of poll of polarizer and analyzer, the second an inclination of these planes. (c) A tube, S, to contain the solution under in vestigatk can 1)0 placed in the light path, between the analyser polarizer. This tube must bo of definite length and if nil plane, transparent ends, placed perpendicularly to the ii of light travel. (d) A lens, /, for directing parallel light into the* inst (e) A system of lenses, T, through which the operal observe the action of the first four parts, (/) A circular scale upon which is indicated tin:* angle i which the analyzer is rotated. The relative positions of these parts arc* shown in Kig. Making a Reading.—-Briefly .staled, the detennina rotatory power with the most simple instrument possible w made as follows: The analyzer is brought into a relation with the pr; such as to permit the maximum transmission or exfinc: light. This establishes the aero point of the instrument OPTICAL ROTATION 125 tube of solution is then placed in position and the analyzer is turned so that its plane of polarization lies in the new plane, which has been rotated by the solution from its original position. The magnitude and direction of the angle, a, through which the analyzer has been turned, is noted and from this and from the length of column and the known concentration of the solution the specific rotation is calculated. In the more common case the specific rotation of the substance is already known and the concentration of the active substance in the solution is the factor in question. For example, the per cent of cane sugar in a syrup is to be determined. A definite weight of the syrup is diluted to a definite volume and the angle of rotation produced by a column I dm in length is determined. The specific rotation of sucrose is given as +66.5. We have then the equation (from Eq. (1), page 123): 66.5 = 100 a, cl or c 66.5 r The length, Z, is known and the angle, a, is determined by observation. The concentration, c, of sugar in the solution, as well as the concentration of sugar in the original syrup, is then easily calculated. Construction of Polarizer and Analyzer.—In the most common form of this instrument the polarizer and analyzer are of identical construction. It is a well known fact that when a ray of light falls perpendicularly upon certain faces of a crystal of Iceland spar (natural, crystallized calcium carbonate) the light is broken into two rays which are unequally refracted, so that when any object is viewed through such a crystal two images are observed. What is equally important is that these two rays are polarized in planes perpendicular to each other. . The Nicol Prism.—This is made by cutting a crystal of Iceland spar into two wedge-shaped pieces and grinding the faces in such a manner that when these pieces are cemented together one of the plane-polarized rays may pass through while the other will be reflected to the side of the prism and there absorbed by a black- ened surface. In Fig. 38 the incident ray, W, is double-refracted and at the dividing surface between the two parts of the crystal, the "ordinary" ray, 0, is reflected to the side of the prism 126 Q UA NT IT A TIVE AflRlCriT 17M /, .-1 AM L )',S7X while the "extraordinary" ray, n, passes through. This ray Ls polarized in a plane which is perpendicular to the " optical principal plane77 of the prism, a term which need not be defined here. This Nicol prism, properly fixed in place in the end of the polarimeter nearest the light source, forms the polarizer. The analyzer is another Nicol of similar construction. When this is turned so that the optical principal plane is parallel to that of the polarizer, maximum brilliancy of transmitted light is ob- served. If these two planes are perpendicular to each other, Fro. 38.—Nicol pram. total extinction results because the extraordinary ray from the polarizer is now in the plane for the ordinary ray for the analyzer and it is therefore reflected to the side of the latter and there absorbed. Method of Making Observations.—In practice it in not easy to determine when either maximum brightnasB or maximum extinction of entering light occurs. Accordingly most polarim- eters are constructed with an additional device to aid in making the reading. In "half-shadow" instruments the field in divided into halves by interposition of a thin plate of quartz which covers half of the diaphragm of the polarizer. The thicknejw, method of grinding and position of this plate are such as to cause a small difference between the angles of maximum intensity or extinc- tion for the two halves. That w, an the analyzer is rotated, one half of the field gains in intensity while the other half diminishes. The zero of the instrument is the position of the analyzer which gives a uniformly lighted field. By use of a somewhat similar principle triple fields may be produced. The arrangement of the Nicol prisms is different in instruments using this principle but the effect IB «uch that the field is divided into three parts. The Hides have alwavs like OPTICAL ROTATION 127 intensities and these brighten as the middle section darkens. Here again, the field of uniform intensity is seen at the zero angle. Light Source. Many of the forms of polarization apparatus are constructed for monochromatic light of a specified wave length. White light cannot be used with such an instrument hecause its component rays suffer different rotation of their polarization planes, according to their wave lengths, the shorter waves being rotated to the greatest degree. Sodium light is most commonly used for this purpose as it contains rays from a very narrow band in the spectrum and it is therefore nearly homogeneous. A sodium light is easily produced by placing any suitable sodium compound in a non-luminous flame. So- dium carbonate or recently fused sodium chloride is writable for this purpose. The salt is placed in a platinum spoon or fused into a bead in a loop of platinum wire, or Home similar device may be employed. Quartz Wedge Compensation: The Saccharimeter.It has been stated in the preceding paragraph that the rotation of the planes of polarization varies for light of different wave lengths. If white light is used to illuminate the ordinary polarimeler the effect of interposing an active substance in the path of the rays is a dispersion of the various polarization planes. This in analogous, in a manner, to the dispersion of white light by refraction and it was noon in the discussion of the rofraetomctor (page 116) that this dispersion could be corrected by optical means without altering the refraction of a given ray, such as the yellow one, The quartz wedge compensator for the polarimetcr makes possible the two of white (polychromatic) light. Quartz in optic- ally actives and it occurs in both dextro- and lacvo-rotatory forum, the angle of rotation of sodium light at 20° for a plate .1 mm thick being ±21.72°. If absolutely similar platen of right and left rotating quartz should be placed between polarizer mid analyzer, the net effect would be zero rotation. If the thickness of either one of these could be varied at will the effect of the combination could be made either right or left rotating, within certain limits, and this effect might be made such as to com- pensate (neutralize) exactly the rotation of a solution which 128 QUANTITAT1VE AGRICULTURAL ANALYSIS , i is placed in the instrument and whose rotation is to be measured. In such a case both polarizer and analyzer might be made as rigid, stationary parts of the instrument, the only adjustable part being one of the quartz plates. This possibility of adjust- ment is accomplished by cutting one of the plates diagonally, making two wedge-shaped pieces which may be thrust past one another by means of an appropriate screw, the magnitude of the effect being noted upon a scale. Now it happens that the rotation dispersion of quartz for white, or other polychromatic, light is nearly identical with that of cane sugar in solution. Since, in using this instrument, the quartz wedge combination will always be adjusted to be equal in rotatory power to that of the solution being investigated, but in the opposite direction, it will also bo true that the dispersion of the sugar solution will be nearly compensated by the opposite, but otherwise nearly equal, dispersion of the quartz system. Because of these relations the instrument constructed in this FIG. 39.——Diagrammatic ropronontatioii of th<» oRs<»nf,ial purt.H of a quartz wedges mtcoharimotor, having double romponHating winifrcH. manner is known as a "saccharinieter." If used with other solu- tions than those of cane sugar the polarization dispersion could be compensated only approximately, at best, and readings of the angle of rotation could not be correct. In such a cane it would be necessary to use sodium light or a selective light filter. The relations of the optical parts of the quartz wedge saeehari- meter are shown diagrammatieally in Fig. 39. Light Filter for Use with the Saccharimeter.—The quartz wedge system fails to give exact compensation for the rotation dispersion of sugar solutions arid in order to avoid slightly high readings it is necessary to absorb a part of the blue and violet waves from white light, an those suffer the greatest dispersion. The International Commission for Unifying Methods of Sugar Analysis adopted the suggestion of Bryan1 that white light shall 1J. IntL Eng. Chwn., 6, 107 (19.13). OPTICAL ROTATION 129 be passed through a solution of potassium dichromate "of such concentration that the percentage content of the solution multiplied by the length of the column of solution in centimeters is equal to nine.77 The Sugar Scale.—The simplest and most generally useful scale for the polarimeter is the circular scale, divided into angular degrees, with a vernier for greater accuracy in reading. But in the practical use of the instrument for analytical purposes there arises (as is usually the case when scientific instruments are used for practical testing) a demand for a direct-reading scale that can be interpreted in terms of the per cent of active sub- stance, without calculations other than of the simplest sort. The largest commercial use of the polarimeter is for sugar testing and for this purpose there have come into general use three scale systems: the Ventzke (German), the Laurent (French) and the International, the latter being a development of the Ventzke scale. A scale of one of these types is usually placed upon the instrument, even when angular degrees also are indicated. The Ventzke Scale and the Normal Weight.—In this system a "normal77 solution of cane sugar was first defined as one having 17 5° a specific gravity of 1.100 at y^Vo- Of course this is an entirely arbitrary value but it served to fix the basis for the system. The scale values were fixed by polarizing a solution of this concen- tration in a 200-mm tube at 17.5°C., this defining the 100° point on the scale. Because of the difficulties involved in preparing solutions having this exact concentration by use of the hydrom- eter alone, it became customary to make the normal solution for fixing the scale points by weighing 26.048 gin of sucrose and making the solution to 100 cc at 17.5°. This is the same as Ventzke's solution. The "normal weight" was then 26.048 gm. The adoption of the Mohr unit of volume (1 cc "Mohr" = 1.00234 true cc) brought confusion into the scheme, as instru- ment builders for a time used the old normal weight with the new volume unit. The 100° point on the Ventzke scale was then fixed1 "by polarizing in a 200-mm tube a solution containing 26.048 gm of sucrose, weighed in air with brass weights, in 100 1U. S. Bureau of Standards, Circ. 44, 27, 2nd ed. (1918). 130 QUANTITA TIVK AGIUVVLTURAL AXALYH/ti 'H:i I* ••'•>< :f i ,-fffi f I 11 J$ Iff! 'J Mohr cc at 17.5°, the temperature of the quartz wedges, as well as the polarizing temperature, being 17.5°. This confusion has been still further increased by the more recent readoption of the true cubic centimeter as a unit for practically all scientific work (volumetric apparatus now being furnished by the manu- facturers, graduated upon this basis) and by the fact that there is frequently no indication upon the instrument as to what unit has been used in working out the scale. And it may be well to remark here that the all too general custom in industrial (and some college) laboratories of using all commercial volumetric and other apparatus, and even weights, without calibration leaves the accuracy of much analytical work in a very questionable light. The only way by which accuracy can be assured is by calibrating the flasks, burettes, pipettes arid weights to bo used in this work and by checking the saccharimeter scale against quartz plates that have been tested by the Bureau of Standards or by other competent standardizing bureaus. The International Scale.—In 1900 the International Sugar Commission recommended that the sugar scale be redefined, basing the 100° point upon the true cubic contimeter and a temperature of 20° 0. Introducing tho correction for the change of volume unit, and of the specific rotation of sucrose, tho expan- sion of the glass polarizing tube, quartz wedges and metal scale, between 17.5° and 20°, the normal weight of sucrose becomes 26.000 gm. The International sugar scale is then to bo defined as follows: "The graduation of the saccharimeter xhall he made at 20° C., 26 gm of sucrose dissolved in iDater and the volume made up to 100 metric cc. All weighings are to he made in air with brass weights, the completion of the volume and the polarization, are to be made at 20° C. This will determine the 100° point." In order to determine the per cent of sucrose in a material of unknown purity is only necessary to weigh 26.000 gin of tho sample, dissolve and dilute to 100 cc and then "polarissc*" in a 200-mm tube. If the material were pure cane nugar tho read- ing would be 100° International (100° I.). If it were 50 per cent pure the reading would be 50° I. In general, then, degrees on this scale indicate per cent of sucrose. Of course it is essential that no other active substance shall be present in the solution or that some method for accounting for these shall bo available. OPTICAL ROTATION 131 In order to make a simple reading possible it is not necessary to use the normal weight of sample or to polarize in a 200-mm tube. Any simple fraction or multiple of these numbers may be employed and due account taken in the calculation. Polariza- tion tubes are provided, varying by even stages from 100 to 400 mm in length. The sugar scale provides direct readings for other sugar's and for other optically active substances, not sugars, by use of a properly modified normal weight. Thus for laetoso (milk sugar) [a]" = 52.53, instead of (56.5 as for sucrose. Therefore it will require p0>-;j X 20 = 32.9 gin of lactose in each 100 ec to o^&. *)«> give a rotation of 100° on the sugar scale. 32.9 gm is then the normal weight for lactose and if, for example, 32.9 gm of milk were treated in sueh a manner as to obtain the clear serum and this diluted to 100 cc and then polarized in a 200-mm tube, degrees International would indicate directly the per cent of lactose in the milk. This determination in described in the section on Dairy Products, page 214, Part III. The Laurent Scale. -This in constructed so that a quartz plate 1 mm in thickness and cut so that its faces are perpendicu- lar to the optical axis will give a rotation of 100° L. The normal weight for this scale will then be such that when this quantity of substance is dissolved in 100 ee and the solution is polarized in a 200-mm tube it will give the name rotation as a quartz plate of the above description. Because of small differences in the specific rotation of quartz specimens there has been some uncer- tainty regarding the normal weight. The value now accepted for sucrose is 10.29 gm, dilution to 100 true ec being understood. Both Ventzke and Laurent scales are falling into disuse, being properly replaced by the more rational International scale. The Common Sugars.—Sucrose, or cane sugar, is the principal sugar of the juices of sugar cane, sorghum, beets and many fruits. It may be converted into a mixture of equal parts of dextrose and levulose by hydrolysis, induced by action of acids: The difference between the molecules of dextrose? and levulose in a structural one and this has a direct bearing upon the rotation 132 QUANTITATIVE AGRICULTURAL ANALYSIS ;i •M ' i ' ft4'! 1 * w« I1 } \#t *1 ..» of these sugars. The values for the specific rotation (for 20-per cent solutions) of sucrose, dextrose and levulose are +06.5, +53.1 and —93.3, respectively. The mixture of dextrose and levulose has a specific rotation, for these concentrations, of — 20.57, which is practically the mean of the separate values for the two sugars. Because of the change in the direction of rota- tion with this conversion of sucrose, the reaction is known as one of "inversion" and the resulting mixture of sugars is called "invert sugar." Cane Sugar.—Sucrose can be determined by a single polar- ization only in case no other active .substance is present in the solution. In case either dextrose or invert sugar is present a polarization before and after the inversion of cane sugar gives the necessary data for the calculation of sucrose by the modified Clerget formula. This formula is derived from the following considerations: From the values for [a]™*, given above: f* f* P\ _^. x 26 = 83.9. Therefore 83.9 gm is the normal weight (International) for invert sugar. Prom the equation for inversion: 26 gm of sucrose yields 27.37 27.37 gm of invert sugar and this is 00 n- = 0.3262 of the normal weight. (HerssfolcFs value, 0.3266 is now generally used.) If the normal weight of sample (based upon sucrose) has been used for making the solution for the direct polarisation (P), then each per cent of sucrose in the sample will give a rotation of + 1° (International scale) before the inversion awl —0.3266° after inversion. Therefore the change of rotation (P — I) would be 1.3266° for each per cent of sucrose. If # = per cent of sucrose, o P-I - m 1.3260" (l) This is for a temperature of 20° and it is found that between 0° and 20° the left rotation of invert sugar produced from the sucrose of a normal solution decreases 0.005° for each per cent, for 1° 0. rise in temperature. Thin is chiefly duo to a decrease in the rotatory power of levulose. At 0° C. the formula would then read: P- J 1.4266 * ' (2) OPTICAL ROTATION and, in general This is usually written: ,,_._ -__ 1.420(5 - 0.005 t tr ___ A — 100(7' - /) 142.00 - 0.5* 133 (3) (4) t indicating temperature in degrees Centigrade. Recent work1 at the Bureau of Standards has shown that the, (Uerget divisor should be, 143.25 instead of 142.00, in presence of the acid used to cause inversion. The method is applicable only to materials containing no other compounds whoso activity is changed by treatment with acids. Molasses from boots and, to somes extent, beet sugar contain certain quantities of ruffinoso (O^II.-^)^), a sugar whoso specific rotation is +104.5°. This rotation is diminished by one-half by warming with dilute acids. (See page 130.) Commercial syrups of various kinds usually possess a color which interferes with transmission of light and makes poluri- scopie readings difficult. This color is due to a variety of colored organic substances and to caramel formed during the heating processes. It can be removed in most cases by addition of a basic load salt, of which basic load acetate is most suitable, or of "alumina cream," a suspension of colloidal aluminium hydroxide in water, freshly prepared. In the case of load salts the action is partly chemical and partly physical. Complex lead salts of organic acids are formed and these, being colloidal in character, flocculate and carry with them other colloidal colored compounds. Neutral lead acetate is used in some* cases where a basic reaction is to be avoided. Correction for Volume of Precipitate.-—In the method an usually followed the clarified solution is diluted to 100 ee before filtration. This ignores the volume of the precipitate and an error is introduced from this source. However, the actual vol- ume occupied by this precipitate is much lens than the apparent volume, owing to its colloidal nature. If there is produced a larger quantity of precipitate than can safely bo ignored the double dilution method of correction is used. In this method one polarization is made on the clarified solution which has boon »U. S. Bur, Stand. Bd. Paper, 375 (1920). 134 QUANTITATIVE AGRICULTURAL diluted to 100 cc, as usual. Another sample of the normal weight is clarified and diluted to 200 cc and the filtrate is polarized. Let P = true polarization of a normal solution, Pi = polarization of the solution in the 100-cc flask, I , , ^ P<2 = that of the solution in the 200-cc flask and I * • \\ v = actual volume of solid precipitate. f ,, Then ; •>*! /> _ ipo p ( 100^ - v W IS 200 P \ 100 P ^ ( — v fpr 'ill I, . ...... 12 ~ (100 ~?;)(200 -v) _ P l 2~~ -0X200 - 0 "^ (1QO)«P From Eqs. 3 and 4, ._ _ (100 - ?;)(200 - 0) k ; Therefore the true rotation is the product of the two readings, divided by their difference. The Association of Official Agricultural ChemiHts ha« placed the arbitrary limit of 1 cc of precipitate from 2(J gm of sample, for the solution for which no correction need be made. Determination of Sucrose in a Commercial Syrup. Prepare a solution of basic lead axsctatc by one of the following methods: («) Add 215 gin of neutral lead acetate and 155 gut of litharge (PbO) to 500 cc of distilled water (or a smaller amount using the saniu proportions) and boil in a covered dish for 30 minutes. Cool, decant the dear nolution and determine the specific gravity by means of a hydrometer. Dilute until the specific gravity is 1.2.5, using recently boiled water. (k) Make the solution directly from dry basic lead acetate and dilute until the specific gravity is 1 .25. Direct Polarization.— Weigh a «mall dish, then drop in and weigh 26.000 grn of the commercial syrup or molasses. Rinse into a 100-cc volumetric flask with about 50 ec of water and then carefully add basic lead acetate solution until the sugar solution is decolorized as far as any effect can be noticed, avoiding an unnecessary excess of the clarifying agent. Dilute to the mark on the flask, mix thoroughly and filter through a dry filter, rejecting OPTICAL ROTATION 135 the first 15 cc. Polarize at a temperature of exactly 20°, using a 200-min tube unless the solution is still colored enough to make this difficult, other- wise use a 100-mm tube and double the reading. This is the quantity P in the Clerget formula (4) on page 133. Invert Polarization.—Precipitate the lead from the clarified sugar solution by adding either powdered anhydrous sodium carbonate or powdered anhydrous sodium oxalate, very carefully, until a very slight excess is indicated by failure to produce more precipitate. Filter on a dry filter to remove the lead salt. Reject the first 15 cc and save the remainder of the filtrate. Pipette 50 cc of the clear, lead-free filtrate into a 100-cc flask of ordinary form. If sodium carbonate has been used for precipitating lead, carefully neutralize the excess with hydrochloric acid. Invert the sucrose by one of the following methods: (a) Add 25 cc of water and then add from a pipette 5 cc of concentrated hydrochloric acid, dropping the acid slowly and mixing by rotating the flask. Place the flask in a water bath which is kept at 70°. The tempera- ture of the solution should reach 69° in about 3 minutes. After the flask has been in the bath for 10 minutes remove and cool to 20° in running water. Rinse into a 100-cc volumetric flask, dilute to the mark and mix. (6) Add 5 cc of concentrated hydrochloric acid, slowly and mixing well. Set the flask aside for 24 hours at a temperature of 20 to 25°, or for 10 hours at somewhat above 25°. Dilute to 100 cc and mix. On account of the considerable variation of the specific rotation of levti- lose with temperature it is necessary to polarize at a constant, definite temperature. For this purpose a water jacketed tube is used and water at 20° is circulated. Since the dilution of the solution was doubled after the direct polarization, the reading for the invert polarization is multiplied by 2 if a 200-mm tube is used, or by 4 for a 100-mm tube. Calculate the per cent of sucrose in the syrup. For low concentrations of invert sugar the variation of rotation with concentration is such .that formula (4) on page 133 will not apply. The official method specifies the following formula, where the concentration of sugar in the invert solution is less than 12 gm per 100 cc: S = 100(P - /) 142.66 - ~ - 0.0065[l42.66 - ^ - (P - /)] This might be further simplified to 100(P - I) S = 141.73 - 0.4967 t + 0.0065(P - I) (5) (6) 136 QUANTITATIVE AGRICULTURAL ANALYSIS & N •/ •' I •tl ,$ 1 Sii Iii these formulas the symbols have the significance expressed in the Clerget formula. Beet Products. — The interference of raffinose in the calcula- tion of sucrose from direct and invert polarizations has already been noted. If the direct polarization reads more than 1° I. higher than the sucrose calculated as already described, the presence of raffinose is indicated. In this case sucrose and raffinose are calculated by the formula of Herzfeld: S = R = 0.839 P -S 1.852' (7) (8) R indicating the per cent of raffinose and the other symbols having their former significance. Commercial Glucose.—This substance contains dextrin and maltose in variable quantities, in addition to the essential dextrose. The specific rotation of the various dextrines is usually about +193 and that of maltose is about +138, that of dextrose being only +53. On this account the specific rotation of commercial glucose is somewhat variable but it is always higher than that of dextrose. The investigations of Leach1 indicate that +175° I. is the average rotation for a solution con- taining 26 gm of commercial glucose in 100 cc polarized in a 200- mm tube. From this is deduced the formula: 100(a - S) Cf = 175 (9) a indicating the direct polarization in International degrees, S the per cent of sucrose, determined as already directed, and G the per cent of commercial glucose polarizing +175° I. If invert sugar is present the formula is inapplicable. In this case use is made of the fact that the left rotation of invert sugar decreases with rising temperature, becoming zero at 87° C. At this tempera- ture the mean rotation of commercial glucose has dropped to +163° L, so that the calculation is made by the formula: ao> where / is the corrected invert reading at 87° C. 1 U. S. Dept. of Agr. Chem. Bull 65, 48. L ^aiSilL^iSv- OPTICAL ROTATION 137 Detection of Invert Sugar.1—Dissolve about 20 gm of sample and dilute to 100 cc. Clarify, if necessary, before diluting. Filter and add a slight excess of sodium carbonate. Filter again if not clear. To 50 cc of the solution in a casserole add two drops of a 1-per cent solution of methyl blue and boil. If the color disappears after 1 minute, at least 0.01 per cent of invert sugar is present. If not completely decolorized after boiling for 3 minutes no invert s.ugar is present. Determination of Commercial Glucose in Syrups Containing Invert Sugar.—Prepare and clarify, if necessary, the solution of molasses or syrup, following the directions already given on page 134. Invert and obtain the invert reading at a temperature of 87°, using the water jacketed tube for this purpose. Calculate the per cent of commercial glucose by dividing the invert reading (corrected for dilutions) by 163 and multiplying by 100, as indicated in formula (10), page 136. LEACH, "Food Inspection and Analysis,'7 4th Ed., 613. CHAPTER VIII HYDROGEN ION CONCENTRATION In the chapter on indicators, in Part I, it was noted that the color change of the indicator bears a definite relation to the changing hydrogen ion concentration in the solution, and that upon this consideration rests the suitability of an indicator for a given titration. The investigation of hydrogen ion con- centration must necessarily precede this quantitative knowledge of color changes and such investigations may be made with a high degree of accuracy. Methods.—A number of methods have been used for the determination of hydrogen ion concentration. Of these, two will be mentioned. These are the potentiometer method and the indicator method. The manipulative details, necessary prc- cautions and the sources of error of these determinations lie outside the scope of this book. The brief discussion hero inter- posed is provided in order to give the, student an idea of the general principles involved in the laboratory methods and of the importance of such measurements to the problems of the agri- cultural chemist. For a full discussion and detailed directions for the determinations, refer to the numerous papers in the journals and to Clark's book, "The Determination of Hydrogen Ions." In this book is a tolerably complete bibliography of the various papers that have appeared on the subject. The Potentiometer Method.—In principle, this method depends upon measuring the electromotive force of a system in which are placed (a) a hydrogen electrode immersed in a solution of known hydrogen ion concentration, (/>) a hydrogen electrode surrounded by the solution whose Pu value in to be measured and (c) a potentiometer. From the measured o.m.f. of the system and the known hydrogen ion concentration around the standard electrode, the ion concentration in the unknown solution in calculated, usirg the equation: 4 c.m.f. ••- 0.059 log (,, '/I ' M where (' and (•' represent the hydrogen ion concent rations in the 111 two solutions. HYDROGEN ION CONCENTRATION .139 In practice, corrections must be applied to the above formula in order to account for certain effects not here discussed. It is possible also to substitute for the standard hydrogen electrode certain other well known forms of standard electrodes, such as the "calomel" electrode, in which case the measured e.rn.f. has to be corrected for the difference between the potentials of the calomel and the hydrogen electrodes. The Indicator Method.—This method may be used with greater convenience and at less expense for equipment than the potentiometer method, although it should be recognised that the latter is the fundamental method and that the indicators must themselves have been standardized, usually by the potentiometer method. For the test, there must be provided a series of indi- cators of which the color corresponding to a given hydrogen ion concentration is known, and extending over a wide range of PJI values. A set of "buffer" solutions is prepared, these being solutions of certain salts or acids whose hydrogen ion concentra- tion is definite and known and which are easily reproduced. By matching the color produced when definite quantities of suitable indicators are added to the solution under investigation, with those produced by the same indicators and the various buffer solutions, the P// value of the former is determined. The indicator** listed below are the selection of dark and Lubs and their preparation and use are described in detail by ('lark, in his work above cited. TAJBLK V.-—INDKJATOKH Color dmngc, j ne.id t Common name of indicator Thymol blue (acid range)............. .i Rod-yellow Brom phenol blue*..................... j Yellow-blue Methyl red........................... | Ked-yollow Brom eratol purple................,...! Yellow-purple Brom thymol blue. , . ,. ,.......!.,....! Yellow-blue, Phenol red......................... . . | Yellow-red Oresol red............................ Yellow-red Thymol blue (hanic range). . , , ,....... , . j Yellow-blue Cresol phthalein,.................... . | CoIorleHH-red rung*' K () S.2 2.8 4.0 0.0 o.x 7.0 X. -1 S.K «.) (\ If 0 140 QUANTITATIVE AGRICULTURAL ANALYX/ti The series of buffer solutions suggested by Clark and Lubs consists of mixtures of hydrochloric acid with potassium chloride and with potassium acid phthalate, and of sodium hydroxide with potassium acid phthalate, with moriopotassiurn orthophos- phate and with orthoboric acid. By mixing these in stated proportions and at stated dilutions the P// range is covered from values of 1.2 to 10.0, in steps of 0.2. Gillespie has described1 a method for dispensing with the use of buffer solutions. Applications.—A high degree of importance is attached to the application of P// values to problems of agricultural and biological chemistry. Mention may be made of the bearing of soil acidity upon productiveness and upon adaptation to different crops; of acidity of plant juices upon plant health and disease; and of acidity of milk upon butter and cheese production. Hydrogen ion concentration is of importance also in the culture and study of bacteria, yeasts and molds; in the study of physiological chemistry, particularly with relation to the digestive system and the blood. Many other applications might be noted, of not so direct interest to the agricultural or biological chemist and many interesting lines of research have been opened up by the high degree of development of this line of testing. i Soil Science, 9, 115 (1920); /. Am. Chem. AW., 42, 742 (1920). PART III ANALYSIS OF AGRICULTURAL MATERIALS The following chapters constitute an introduction to the appli- cation of quantitative analysis to the solution of agricultural problems. The subjects treated are typical phases of the broad field of agricultural analysis. The student is especially cau- tioned that if ho is to avoid the common danger of falling into ways of mere mechanical routine ho must, hero as elsewhere, cultivate the habit of looking for the scientific principles under- lying his work, as well as for the significance of its results in connection with scientific agriculture. 1 141 If' ^1 V,, CHAPTER IX '//!» J FEEDS I The raw materials of feeds vary greatly in their composition, j$j| their feeding and commercial values depending upon their con- .)' ;j tent of protein, fat, mineral matter, carbohydrates and vitamins and upon the ease with which food elements are digested and ;j'r assimilated. There is much difference in the feeding value ,f' of protein and fat, according to the sources from which they are f derived. The degree of utilization of these products can not !M' always be measured with exactness by chemical means but it *ft!j must be determined from feeding trials with animals. However, 4: chemical analysis furnishes the best available means for estimat- Jr! ing approximate feeding values from percentage composition. J This is especially true of commercial ready-mixed feeds, which [^ are often made up from many different plant and animal sources; ' 1 • chemical analysis furnishes the only quick method for determin- 4|1 ing their approximate commercial value. ; I ! Composition of Some Common Feeds.—If the feed is made (I j from the whole grain the composition of the groups will be about 'I j as represented in the table below and if made up of grain by- '4; | products, with the more valuable parts taken out and substituted j| j with cheaper materials, it is often possible to detect the deception •!$j j by analysis. The analysis of feeds commonly includes the determination of moisture, ash, crude fat, crude fiber, crude proteins, carbo- hydrates and pentosans. The entire carbohydrate group is often expressed as " nitrogen-free extract/' which is obtained by deducting the sum of all other groups from 100. Most states now have laws which control the manufacture and ;l'« ' sale of feeds. These laws usually require a guarantee of the J1 |}f j per cent of ether extract, crude protein, fiber and ash. The average •' 'iff ! composition of the principal cereal grains is tabulated as follows ' '# by Villier and Coffin. 142 l*i= bl (•I , M i |V|f)j| 11| ' FEMDti i43 TABLE VI.—-AVERAGE COMPOSITION OF PRINCIPAL CEHKALB Wheat Bur-ley Rye OatH Itiee ( Jorn Millet, Buckwheat Water ............. 13.05 13.77 15. 00 12 . 37 13. 11 13. 12 11.00 12.93 Crude protein (Nitro- gen CUB 8 U b- Htanren) ....... . 12.35 11. 14 1 1 . 52 10.41 7 . 85 9 . 85 9.25 10.30 ("rude fat ......... 1 , 75 2. 10 1 . 71) 5.32 O.H8 4 . 02 3 . 50 2. HI Sugar ...... . ...... I 45 1 50 0 95 1 91 2 40 Gum and dextrin. . . 2 . 38 1 . 70 4 . SO 1.79 16.52 3 . 3S 05.95 55. SI Starch .......... ... (54 . OS 01 (57 (32 00 54 OS 02 57 2 53 5 31 2 01 1 1 1 9 0 03 2 29 7 29 10 43 Ash 1 XI 2 09 1 SI 3 02 • >.u~ 1 01 1 5 1 2 3f> 2 72 Method of Sampling. -Commercial feeds are usually shipped to the consumer in sacks and it is important that the samples chosen from them shall be representative of the feed contained in all parts of the sack. A sample^*somewhat similar to that used for fertilizers (Fig. 59, page 273), but larger in diameter than this, may be forced to the bottom of the sack of feed, the slide covering the opening in the tube being moved to the* side and tapped so that the tube can fill with feed. The slide is again closed, the tube is withdrawn from the feed suck, and the con- tents of the sampler placed on a sheet of paper and thoroughly mixed. About a pint of this uniformly mixed feed is wived for analysis. Preparation of Sample.™The sample should be ground in a feed grinder (Fig. 40, suitable for grinding course feed materials) BO that it will pans a sieve having openings I mm in diameter (0.04 in). Sometimes it in quite difficult to reduce it to thin degree by grinding, in which case it should be, made an fine an possible by any other available means. A container which may be tightly stoppered should be provided to hold the sample. At the start, enough should be prepared and mixed to serve for the entire analysis. This will require about 200 gm. Moisture.—There are several minor factors which tend lo modify the results of moisture tleterrnmationH. One of UKJHO I 144 QUANTITATIVE AGRICULTURAL ANALYSIS is the loss of essential oils and other volatile bodies during the drying process. Partly compensating this is a possible gain in weight due to oxidation of fats and sugars, when drying takes place in the air. As these changes are variable the method of drying in air at elevated temperatures has been abandoned. If a temperature of 100° is to be used it is necessary to have avail- able an oven for drying at reduced pressure or in an atmosphere of an indifferent gas, such as hydrogen. FIG. 40.—One form of grinder for coarse feeds. (Shown disassembled*) Feeds dried at ordinary temperature under reduced pressure usually show about 1 per cent less moisture than is found by a direct heating method. About four to six days is usually required to obtain constant weight by the reduced pressure method, even if the sulphuric acid used in the desiccator is changed several times. The special advantage of the method lies in the thorough desiccation of the sample without the possibility of chemical changes brought about by heating and oxidation but the length of time required for the experiment makes the method imprac- ticable for all work except that requiring a high degree of refine- ment and accuracy. Determination of Moisture: At 100°.—Weigh about 2 gm of the feed in a weighed flat dish or, in case the fat is to be extracted, in a weighed alundum cup. Place in an oven which can be exhausted or through which dry hydrogen can be circulated and heat at 100° for at least five hours or FEEDS 145 until the weight is constant. After the sample has cooled in a desiccator ifc should be weighed as rapidly as possible in order to avoid undue exposure to moist air. Preserve the dried sample for the crude fat determination (page 147), or for the ash determination, described below. At Room Temperature.—Place 2-gm samples in separate 6-inch vacuum desiccators (see Fig. 8, page 28) containing 200 cc of fresh concentrated sulphuric acid and exhaust to a pressure of 1 mm by means of a pump. It will require about four to six days drying to secure constant weights. The desiccators should be rotated gently several times a day in order to mix the lower, more concentrated sulphuric acid and the upper layers that have become diluted by absorbed moisture. After 24 hours drying, carefully open the desiccator and weigh the sample. Place in a desiccator containing fresh sulphuric acid and repeat the process of drying and weighing until the weight becomes constant. Calculate the total loss as moisture. Preserve the dried sample for the crude fat determination (page 147), or for the ash determination, described below. Ash.—The ash determination requires much patience. The high carbon contained in oily seeds is very hard to oxidize so as to secure a white or gray ash but too high a temperature will cause volatilization of certain ash constituents, such as chlorides of the alkali metals. The ash should contain the mineral compounds (such as calcium phosphate, potassium or sodium chloride and some silicon compounds) of the plant tissues and sap. Some phosphorus and sulphur may be present as part of the protein molecule and these may be volatilized but they are not properly to be considered as part of the ash unless they are normally left upon burning (as phosphates or sulphates). This is usually the case in grasses and leaves but not in seeds. Determination of Ash.—Either the dried sample obtained in the moisture test or a new undried sample may be used for this determination. Ignite, cool and weigh a porcelain crucible, brush in the weighed sample and burn at a low temperature, using a burner, or place the uncovered crucible in a muffle furnace heated to about 700°. The crucible should be kept at dull redness until the carbon is all consumed and the ash becomes nearly white. A gray or black appearance of the residue indicates the presence of unburned carbon but a red tint may be given by iron oxide normally present. Cool in a desiccator, weigh and calculate the per cent of ash. Mineral Analysis.—The solution of the ash in hydrochloric acid is diluted to 250 cc and the mineral constituents determined as described under soil analysis, beginning on page 256. This analysis involves a considerable expenditure of time and it is rarely useful, except in the solution of certain research problems. I ] 146 QUANTITATIVE AGRICULTURAL ANALYSIS Crude Fat or Ether Extract.—The nature of the material obtained by extracting feeds with ether varies according to the nature of the feed. Grains and otheit seeds yield nearly pure fat, while in fibrous materials many compounds, such as waxes, resins and chlorophyl, also are extracted by the ether. FIG. 41.—Apparatus for extraction by volatile solvents. When there is present in the feed a considerable amount of soluble carbohydrates, such as starch or sugars, and a relatively small amount of fat, as in wheat and rye, it is best to dissolve out these substances with water before attempting to extract the fat. It is quite essential that samples to be extracted be thoroughly dried and that the ether be free from alcohol and FEEDS 147 water as otherwise various substances, soluble in water or alcohol (salts, sugars and amids) would be extracted. Certain other fat solvents have been used, such as benzol, gasoline and carbon tetrachloride, but none has been found to be quite as satisfactory as dry ether. One form of assembled extraction apparatus is shown in Fig. 41. Any number of separate pieces may be assembled upon one heater. In Fig. 41 the third extractor is shown in section. Ether (or other volatile solvent) is placed in the weighed cup a where it boils and the condensed vapor from, the condenser d falls to the sample in the porous cup 6. As the solvent fills the siphon cup c to the level of the siphon bend, the cup automatically empties into a, below. This process repeats itself indefinitely. Determination, of Crude Fat.—Wash commercial ether by shaking in a separatory funnel with two or three successive portions of water and drawing off and discarding the latter. Add solid sodium or potassium hydroxide and let stand until most of the water has been abstracted from the ether. Decant into a dry bottle, add small pieces of cleaned metallic sodium or sodium wire, freshly extruded from a sodium press, and let stand until there is no further evolution of hydrogen. Keep the ether, thus dehy- drated, over metallic sodium in lightly stoppered bottles. The sample is thoroughly dried at 100° in an alundurn cup or fat-free paper capsule (or the sample used for the moisture determination is taken), then placed in an extracting tube and sufficient ether, as above prepared, is added to the weighed cup a of Fig. 41 (previously cleaned, dried and weighed) to enable continuous extraction to proceed automatically. The alundum cup is a porous vessel, cylindrical in shape, and convenient to use because it is easily cleaned by burning, so that it may be used repeatedly. It is suitable to use also in fiber filtration, as it permits weighing and burning of the fiber without removal to another vessel The porous alundum cup, grade R. A. 98, permits rapid filtering and washing. Extract the sample for sixteen hours, saving the residue for the fiber determination (page 148), then remove the cup a and allow the ether to evaporate, or place the cup in a special apparatus for distilling and recovering the ether. Dry at 100° for 30 minutes, cool in a desiccator and weigh. Repeat the drying for 30-minute periods until the weight is constant. From the difference between the weights before and after extraction, calculate the per cent of crude fat. Crude Fiber.—The so-called "crude fiber" is a mixture of substances which make up the framework of a plant. It is composed of cellulose, part of the hemi cellulose and lignin of the 148 QUANTITAriYK AflHK'l'l/ri'ItA/, .1 .Y.IM'.S'/X cell walls. Lignin also is a collective name; applied to the ^in- crusting substances'7 formed with cellulose as the plant matures. Determination of Crude Fiber.-—Prepare the following .solutions: (a) Sulphuric Acid, 1.25 per cent (0.255 normal) as determined by titration against a fifth-normal base. (b) Sodium Hydroxide, 1.25 per cent (0.3125 normal). This solution should be practically free from sodium enr- onate. Use sodium hydroxide sticks that have been purified by alcohol. Titrate against a standard acid and adjust. Use the residue from the ether extrac- tion, page 147, or extract a fresit dry sample* (2 gin) with ether, using the apparatus already described. Rinse the residue into a 250-cc wide mouth flask connected with a return condenser (Kig. 42j, then add 200eeof sulphuric acid (a), previously heated to boiling. Boil gently for '10 minute**. After this time remove the residue from the* flask and filter the liquid through an alundunt cup, using suction. Wash the cup find contents until free from acid. Wash the residue from the cup buck into the flask with 200 cc of boiling sodium hydroxide (/;) and boil for 30 minutes. Filter through an alunclum cup us before and wash free from base. The cup is dried at 11(1' to constant* weight, then the residues IH burned and the per cent, of fiber calculated from the IOHH in weight. A linen filter may be used instead of an alundurn cup, in which case rinse the* washed fiber into a flat platinum dish by means of a stream of water; evaporate to dryncss on a steam bath, dry to constant weight at 110°, weigh, burn the organic matter and weigh again. The loss in weight is crude fiber. If a weighed paper in uned instead of alundum or linen, weigh in a weighing bottle. In any cane the* crude fiber after drying to constant weight at 110° must be burned and the loan of weight determined. Optional Method.1—Proceed as above until the acid extraction i» com- pleted. Neutralize the sulphuric acid without filtration, using 10-per cent sodium hydroxide and phenolphthalein. Add 200 cc of 2.6-per cent solution lOhioExp. *S7a. Bull, 256 (1913). FIG. 42.—-Apparatus for crude fiber determination. FEEDS 149 of boiling sodium hydroxide, make the volume up to 425 cc and boil for 30 minutes. Filter through an alundum cup and wash with hot water until neutral to phenolphthalein. Dry the residue in an oven for 3 hours at 110°, place in a desiccator, cool and weigh. Ignite as in the ash deter- mination, cool and weigh again. The loss in weight represents fiber. Cal- culate the per cent of crude fiber in the sample. Crude Protein.—"Crude protein/' is a conventional term, embracing all forms of plant nitrogenous bodies except nitrates. The latter are not usually found in feeding stuffs. There is no good direct method for determining protein and either pure or " crude" protein is calculated from the per cent of nitrogen. Since plant proteins contain about 16 per cent of nitrogen, the nitrogen per cent is multiplied by 6.25 (•= ~r^~) to convert it to the approximate corresponding per cent of protein. The nitrogen content varies for proteins of different classes. In the deter- mination of milk protein 6.38 is the factor used, but nitrogen found in grasses and fruits is partly in the form of amids and has a lower conversion factor because of somewhat higher per cent. Nitrogen.—From the above discussion it will be seen that the determination of protein rests upon the nitrogen determination. The Kjeldahl process for this determination consists in digesting the organic material with boiling concentrated sulphuric acid until complete decomposition has been effected. The exact course of the reactions cannot be traced but the carbon and hydrogen are completely oxidized and nitrogen is converted into ammonia, which immediately combines with sulphuric acid and remains as ammonium sulphate. The completion of decom- position is insured by the final addition of a small amount of potassium permanganate. The solution is then diluted with water, an excess of sodium hydroxide is added and the resultant" ammonia is distilled into a measured quantity of standard acid solution, the excess of which is then titrated by a standard base. Digestion.—The digestion with sulphuric acid is best accom- plished in a pear-shaped flask with a long neck, like that shown in Fig. 43. The concentrated sulphuric acid of commerce boils at temperatures ranging from 210° to 340°, according to the per- cent of water contained in it. Such a temperature is high enough above that of the surrounding air to permit condensation of 150 QUANTITATIVE AGRICULTURAL ANALYSIS nearly all of the vapor without the use of a water condenser, the long neck of the digestion flask serving for this purpose. It is convenient to distill from the flask in which digestion is accom- plished, in which case the capacity of the flask should be 500 cc. The digestion must be performed under a hood or some other provision must be made for carrying away the fumes. An excellent arrangement for this purpose is a lead pipe, 6 inches in diameter and with holes in the side so that the necks of a number PIG. 43.—Kjeldahl flask, stand and lead pipe ventilator. of digestion flasks may be inserted with the flask in an inclined position. The end of the lead pipe leads to a chimney. Catalytic Agents.—The addition of oxides or salts of mercury, copper or iron to the mixture of the organic material and sul- phuric acid considerably accelerates the reactions that occur during digestion. The action is of a catalytic nature and depends upon the capability of the metal of existing in more than one state of oxidation. The metal is thus alternately reduced by organic matter and oxidized by sulphuric acid, somewhat as follows: 2HgS04 -> Hg2S04 + S08 + 0. (1) The nascent oxygen thus formed attacks the organic matter and mercurous sulphate is immediately reoxidized: Hg2S04 + 2H2S04 -> 2HgS04 + 2H20 + S02. (2) FEEDS 151 Of the three metals named, mercury serves well because its salts are colorless and they do not obscure the end point of the oxidation. It is necessary in this case to precipitate the mercury by the addition of potassium sulphide, before distillation, in order to prevent the formation of mercurammonium com- pounds which later are not readily decomposed by sodium hydroxide. Copper sulphate as a catalyst is often preferred because it serves as an indicator when sodium hydroxide is added, a deep blue solution being formed when the solution becomes basic. Prevention of Bumping.—During the distillation of ammonia, after the addition of excess of sodium hydroxide, there is usually a tendency toward bumping. In order to prevent this, granular zinc or pumice stone may be used. An excellent substitute is a small amount (about 0.5 gm) of crushed porcelain from which the dust has been removed by sifting. Blank.—Sulphuric acid nearly always contains a small amount of ammonium sulphate. Distilled water which has been exposed to laboratory air also may contain a small quantity of ammonium hydroxide. In order to make the proper correction for the ammonia that will be derived from the reagents a "blank77 determination must be made, omitting the sample of feed but carrying out the operations exactly as in the real determination. In this case cane sugar is added to reduce possible traces of nitrates existing in the reagents, as they would be reduced by the organic matter of the feed. Determination of Organic Nitrogen (of Crude Protein): Kjeldahl Method.— Prepare the following reagents: (a) Hydrochloric or Sulphuric Acid Solution, Fifth-normal.—Standardize against pure sodium, carbonate as directed on page 58, making the necessary changes in weight of carbonate to account for the different normality of the acid here used. The standardization of these acids by weighing silver chloride or barium sulphate (the official methods) is not to be recommended because chlorides and sulphates, respectively, are nearly always to bo found in the acids. These would give high values for the acid content, so determined. (6) Sodium Hydroxide or Potassium Hydroxide Solution, Fifth^normal— Standardize by titration against the acid (a), using methyl red as indicator. (c) Sulphuric Acid.—The concentrated acid of the laboratory, specific gravity 1.84, as nearly as possible free from nitrates and ammonium salts. 152 QUANTITATIVE AGRH'ULTl'HAL AXALr,s*/,S' (d) Metallic Mvrcury, Mercuric Oj-.idc or (-n^n'r Xul.p/utic.-.....Mercuric oxide should be that prepared in the wet way but not from mercuric nitrate. («) Potassium Sulphide Solution.—Dissolve at the rate of 40 gm for each liter of solution. Commercial potassium sulphide is used. This solution is not required unless mercury or mercuric oxide is to be used as the catalyzer. (/) Sodium Hydroxide Solution.—A saturated solution (55 gm per 100 cc of water), free from nitrates and containing as little carbonate as possible. ((/) Methyl Red Solution.-— Dissolve 1 gm of methyl red in UK) cc of V/f 95-per cent alcohol. This is the solution ordinarily used in volumetric >' I! * i/ 'v I analysis. Add very dilute acid or base to make exactly neutral. »fjjjl If the approximate per cent of nitrogen in the sample is known, calcu- . *''^ late the weight that will yield ammonia equivalent to about 35 ec of the *', standard acid. If nothing is known of the nitrogen content use about ", 2 grn of sample. (For this method the sample must contain no nitrates, MJ nitrites, or nitro-compounds. This is ordinarily true with feeds.) Place •il two weighed samples in 500-cc Kjeldahl digestion flasks, holding the latter ;/ in a vertical position to prevent the sample from sticking to the sides of the '[t neck, which should be dry. Weigh 1 gm of sugar into each of two other '$, flasks and treat the same as the feed sample*. Add about 0.7 gin of /$' mercuric oxide or of mercury, or 0.3 gm of copper sulphate, also 25 cc of concentrated sulphuric acid. Incline the flask in a hood or with the neck inserted into a lead-pipe ventilator and heat gently until the violence of the reactions has moderated, then gradually raise the temperatures until the acid is boiling. The flask may be heated without protection by a gauze if it is of Pyrex or similar resistance glass and if if is placed over a hole in a stand of sheet iron in such a mariner that the flame*, cannot come into contact with the sides of the flask above the liquid. Digest by gently boiling until the solution is nearly colorless (blue if copper sulphate has been used). This may occur after a short time or the digestion may require several hours. Finally remove the? flame and at once drop into the flask small quantities of powdered potassium permanganate until the solution acquires a green or purple tint whicth persists after shaking. Allow the flask to stand until cool. (Do not and under a tap.) C itrefully add 200 cc of distilled water and mix by rotating the flank. Add about 0.5 gm of crushed porcelain and 25 cc of potai-wium sulphide solution (<"), shaking as the latter is added. (If cupric sulphate has been used OH a cataly- zer, omit the potassium sulphide solution.) Have the connections with a tin condenser ready and have 50 cc of stand- ard acid measured into a 250-cc flask into which the delivery tube (of glass) dips. Most laboratories in whicth much work of this kind is clone* will be equipped with a special form of apparatus for carrying on several distil- lations at once. Such an apparatus an is shown in Fig. 44 will be found convenient for individual work. The flask should bo in a vertical position and some kind of trap should be used to prevent spray from being curried over by the steam. The delivery tube should be capable of being detached from the condenser for the purpose of cleaning and mining it. The entire FEEDti 153 condenser must be thoroughly rinsed before each distillation, to insure freedom from basic solutions. Pour 50 cc of saturated sodium hydroxide solution (/) down the inclined flask in such a way that mixing does not occur. Immediately connect with the condenser, carefully mix the contents of the flask by shaking gently, then distill into the standard acid until about 150 ee of distillate has been collected. It sometimes happens that a considerable excess of sulphuric acid has been used in order to hasten a difficult digestion, or that the Bodium Fro. 44. ...... "Appuruturi for ammonia hydroxide solution is not saturated. The consequence ie that the solution still contains an cxc 1 I *• «»4 f '51 .1 digestible. Sugars and dextrins are the most important of these. Starch is next in importance as it is easily made soluble in digestive processes by hydrolytic action/ Other groups such as the hemicelluloses (examples of which are the pentosans, galac- tans and pectins) are made soluble with more difficulty and they are therefore less valuable as foods. That portion of the carbo- hydrates which does not yield soluble forms on hydrolysis is practically worthless for feeding purposes. It is chiefly cellulose and from the analysis it is reported as "crude fiber. " The pentosans are widely distributed in the vegetable kingdom, being present in the seeds, roots and leaves of all plants. One of the most common of the pentosans is gum Arabic, which occurs intimately associated with the other plant constituents. The galactans also are widely distributed in plants and they occur chemically combined with the pentosans in the plant. Agar-agar is one of the most common of the galactans. It yields galactose upon hydrolysis, while pentosans yield pentose sugars when similarly treated. Analytical Methods. — Carbohydrates in foods and feeds are determined (a) by direct acid hydrolysis and subsequent deter- mination of the reducing sugar thus formed, (fc) by hydrolysis of starch by diastase, thus forming dextrins, maltose and glucose, or (c) by difference, deducting from 100 the sum of the per cents of crude protein, crude fat, ash, crude fiber and moisture. This difference is reported as "nitrogen-free extract.77 True starch cannot be determined accurately by direct hydrolysis with acids because other polysaccharides, such as gums, pentosans and galactans, are hydrolyzed at the same time, yielding reducing sugars which are determined along with those that are derived from starch. The type reaction of hydrolysis is as represented in the equation : (C6H1005)n nC6H120(5. A separation from these hydrolyzable materials may be made by first digesting with the enzyme diastase, from malt extract, then washing out the soluble carbohydrates and hy drofyz- ing them to glucose by boiling with dilute acids. By this pro- cedure only the true starches are affected by the enzyme and a series of compounds of simpler structure are formed. A large FEEDS 157 number of dextrins are formed as intermediate products. Some of these (erythrodextrins) give a red color with iodine while others (acroodextrins) give no color. Under the influence of the acid these dextrins finally yield maltose, a sugar having the same molecular weight as sucrose. Polarimetric methods are not well suited to the determination of the carbohydrates in feeds, because of the relatively small amounts usually occurring in such materials. Greater reliance is placed upon chemical methods, such as those here to be described. Reducing Sugars.—"Reducing sugars'7 are those that have the power of reducing the copper from an alkaline solution of copper tartrate to cuprous oxide, Cu2O. Dextrose, levulose, maltose and invert sugar are examples of common reducing sugars while sucrose is a non-reducing sugar. It has already been stated that reducing sugars may either be present in the original material or they may be formed as a result of hydrolysis of other carbohydrates, such as starch or sucrose. Therefore the determination of original reducing sugars may conveniently be combined with that of sucrose. Calculation of Reducing Sugars from the Weight of Cuprous Oxide.—When the weight of cuprous oxide is used as a basis for calculating weights of sugars, the method of reducing and precipitating must be definitely standardized as the formation of cuprous oxide does not proceed according to an absolutely definite and constant reaction, depending not only upon the kinds and amounts of reducing sugars present but also upon the tem- perature and concentration of the solution and upon the length of time it is heated. Tables have been prepared for different sugars, giving the amount of cuprous oxide reduced by each under specified conditions. These are given in Table VII, pages 160 and 161. Methods for Determining the Reduced Cuprous Oxide.—A number of methods are in use for the determination of the cuprous oxide reduced by the sugars. Three of these will be described. In method (a) the solution is filtered through a Gooch crucible, the cuprous oxide then being dried and weighed as such or ignited and weighed as cupric oxide. Direct weighing is suitable 158 QUANTITATIVE AGRICULTURAL ANALYSIS only in the case of solutions of pure sugars. Molasses and syrups usually contain colloidal organic matter which cannot be washed out of the precipitate. It is then necessary to ignite in air, when cuprous oxide is oxidized to cupric oxide and organic matter is destroyed by oxidation. Method (6) is an approximate volumetric one, differing from method (a) in that a standard copper sulphate solution is used, whose sugar equivalent is known. In method (c) the cuprous oxide is removed and redissolved and the copper is determined volumetrically by the " iodide" method. Potassium iodide and acetic acid are added, cuprous oxide being precipitated and iodine liberated: 2Cu(C2H302)2 + 4KI -»2CuI + 4KC2H3O2 + I2. The free iodine is titrated with standard sodium thiosulphate and the copper equivalent to it calculated. It is also practicable to dissolve the cuprous oxide and to determine the copper by electrolysis or by any other standard gravimetric or volumetric method. Asbestos.—Since this is to be used as a filtering medium for strongly basic solutions it must be prepared with special reference to removing base-soluble materials. The amphibole variety is required, as serpentine asbestos is too easily soluble. Determination of Sucrose and Reducing Sugars.—Prepare the following materials: (a) Fehling's Solution (1).—Dissolve 34.639 gm of pure crystals of copper sulphate in distilled water and dilute to 500 cc. Filter, if not clear, through asbestos. (6) Fehling's Solution (2).—Dissolve 173 gm of sodium potassium tar- trate ("Rochelle salts7') and 50 gm of sodium hydroxide in water and dilute to 500 cc. Allow the solution to stand for two days and filter through asbestos, if not clear. (c) Neutral Lead Acetate.—Prepare a saturated solution of lead acetate (the normal salt). This is made by warming 50 gm of lead acetate with 100 cc of water until the salt is dissolved, then cooling to room temperature. (d) Asbestos.—Digest the fiber for three days with dilute hydrochloric acid. Wash free from acid in a large funnel fitted with a perforated porcelain plate, then digest for a similar period with 10-per cent sodium hydroxide solution. Drain away this solution and then treat for two or three hours with alkaline tartrate solution similar to solution (b), above described. Wash practically free from base and then digest for several hours with dilute nitric acid. Finally wash free from acid and shake the material to a pulp FEEDS 159 with distilled water. The prepared material is now to be used as any other asbestos for forming Gooch filters. Extraction of Sugars from the Feed.—Place 12 gm of the material in a 250-cc round flask and, if the substance has an acid reaction, add 2 gin of calcium carbonate. Add 150 cc of 50-pcr cent alcohol (volume) and boil on the steam bath for one hour, using a reflux condenser. Cool and allow the mixture to stand for several hours. Rinse into a 250-cc volumetric flask with 95-per cent alcohol which is not acid to phenolphthalein and dilute to the murk with this alcohol. Mix thoroughly, allow to settle, transfer 200 cc to a beaker with a pipette and evaporate on a steam bath to a volume of about 20 ee. (Do not evaporate to dryncss, a little alcohol in the residue doing no harm.) Clarijicatioji.-—Transfer to a 100-ec graduated flask and rinse the beaker thoroughly with water, adding the rinsings to the contents of the flask. Add enough Maturated neutral lead acetate solution (c) to produce* a flocculent precipitate, shake thoroughly and allow to stand for 15 minutes. Dilute to the mark on the flask, mix thoroughly and filter most of the solution through a dry paper, rejecting the first 5 ec of filtrate. Add sufficient anhydrous sodium carbonate to the filtrate to precipitate all of the lead, again filter through a dry paper and test the filtrate with a little more sodium carbonate, in order to be sure that all of the lead has been removed. This solution will serve for the determination of both sucrose and reducing sugars. Since the, insoluble material of grain or cattle food occupies some space in the flask as originally made* up, it is Decennary to correct for this volume*. Results of a large number of determinations on various materials have shown the average volume of 12 gm of material to be 9 ee, arid therefore to obtain the true amount of sugars present all results must be multiplied (250 — 9\ = "-"orQ""' I* ^ the sample weight wan not 12 gm (±0.5 gm) the factor should be modified accordingly. Reducing Sugars.—Measure 25 cc of the copper milphate solution (a) and 25 cc of the alkaline tartrate solution (6) into a 400-cc beaker. Add 25 cc of water and 20 cc; at the sugar solution already prepared. Cover the beakers with watch glasses and heat on an asbestos mat at such a rate that boiling begins in 4 minutes. Continue the boiling for exactly 2 min- utes. Filter through Gooch crucibles (weighed if method («), below, is to be followed) immediately after heating and wash thoroughly with hot water (about 60°.) Front this point proceed by one of the following methods: («) Gravimetric Method.—Th® Gooch filters must bo dried, ignited, cooled and weighed before filtration. After filtration dry the crucible and con- tents, then place in a muffle furnace which in heated to redness (about 700") and heat for 15 minutes. Cool and weigh and from the weight of cupric oxide find that of dextrose from Table VII. Multiply by 0.025(- ().9(H X 100 260N 20 X20()J and calculate the corresponding per cent of dextrose in the 12-gm feed sample, reporting as " reducing sugars/' 160 QUANTITATIVE AGRICULTURAL ANALYSIS TABLE VII.—MUNSON AND WALKER*s TABLE FOR CALCULATING DEXTROSE, INVERT SUGAR ALONE, INVERT SUGAR IN THE PRESENCE OF SUCROSE, LACTOSE, AND MALTOSE (All weights are given in milligrams) Invert sugar Lactose Maltose 0 and sucrose V *§ f-A cS "3 "ea *H o M "o O o to •3 1-1 OQ 01 +3 Qj 3 I a 2 •£ S £ sg, t CO AS >>•§ . ja o (rt p. . o «*< % M s *d ° &3 A O >*3 ft d O O Q t-H d w N m •< O^ -<^ o^ O 10 8.9 4.0 4.5 1.6 3.8 4.0 5.9 6.2 10 15 13.3 6.2 0.7 3.9 7. 1 7.5 9.9 10.4 15 20 17 8 8.3 8.9 6. 1 10.4 10 9 13.8 14 6 20 25 22 2 10 5 11*2 8*4 13.7 14.4 17 8 18'7 25 30 26.6 12.6 13.4 10.7 4.3 16.9 17.8 21.8 22.9 30 35 31.1 14.8 15.6 12.9 6.5 20.2 21.3 25.7 27.1 35 40 35.5 16.9 17.8 15.2 8.8 23.5 24.8 29.7 31.3 40 45 40.0 19.1 20.1 17.5 11.1 26.8 28.2 33.7 35.4 45 50 44.4 21.3 22.3 19.7 13.4 30.1 31.7 37.6 39.0 50 55 48.9 23.5 24.6 22.0 15.7 33.4 35.1 41.0 43.8 55 60 53.3 25.6 26.8 24.3 18.0 36.7 38.6 45.0 48.0 60 65 57.7 27.8 29.1 26.6 20.3 40.0 42.1 49.5 52.1 65 70 62.2 30.0 31.3 28.9 22.6 43.3 45.5 53.5 56.3 70 75 66.6 32.2 33.6 31.2 24.9 40.6 49.0 57.5 60.5 75 80 71.1 34.4 35.9 33.5 27.3 49.9 52.5 61.4 64.0 80 85 75.5 36.7 38.2 35.8 29.6 53.1 50.0 65.4 08.8 85 90 79.9 38.9 40.4 38.2 31.9 56.4 59 . 4 09.3 73.0 90 95 84.4 41.1 42.7 40.5 34 .-2 59.7 62.9 73.3 77.2 95 100 88.8 43.3 45.0 42.8 36.0 63.0 00.4 77.3 81.3 100 105 93.3 45.5 47.3 45.2 38.9 66.4 69.8 81.2 85.5 105 110 97.7 47.8 49.6 47.5 41.3 69.7 73.3 85.2 89.7 110 115 102.2 50.0 51.9 49.8 43.0 73.0 70.8 89.2 93.9 115 120 106.6 52.3 54.3 52.2 40.0 76.3 80.3 93.1 98.0 120 125 111.0 54.5 50.6 54 . 5 48.3 79.0 83.8 97.1 102.2 125 130 115.5 56.8 58.9 56.9 50.7 82.9 87 . 3 101.0 106.4 130 135 119.9 59.0 01.2 59.3 53.1 80.2 90.8 105.0 110.5 135 140 124.4 61.3 03.6 61.6 55 . 5 89 . 5 94.2 109.0 114.7 140 145 128.8 63.6 05.9 04.0 57.8 92.8 97.7 112.9 118.9 145 150 133.2 65.9 68.3 66.4 00.2 90.1 101.2 110.9 123.0 150 155 137.7 68.2 70.6 68.8 02.0 99.5 104.7 120.8 127.2 155 160 142.1 70.4 73.0 71.2 65.0 102.8 108.2 124.8 131.4 100 165 146.6 72.8 75.3 73.6 67.4 106.1 111.7 128.8 135.5 165 170 151.0 75.1 77.7 76.0 69.8 109.4 115.2 132.7 139.7 170 175 155.5 77.4 80.1 78.4 72.2 112.8 118.7 130.7 143.9 175 180 159.9 79.7 82.5 80.8 74.6 116.1 122.2 140.0 148.0 180 185 164.3 82.0 84.9 83.2 77.1 119.4 125.7 144.0 152.2 185 190 168.8 84.3 87.2 85.6 79.5 122.7 129.2 148.0 156.4 190 195 173.2 86.7 89.6 88.0 81.9 126.1 132.7 152.5 160.5 195 200 177.7 89.0 92.0 90.5 84.4 129.4 130.2 156 5 164.7 200 205 182.1 91.4 94.5 92.9 86.8 132.7 139.7 160.4 168.9 205 210 186.5 93.7 96.9 95.4 89.2 130.0 143.2 164.4 173.0 210 215 191.0 96.1 99.3 97.8 91.7 139.4 140.7 168.3 177.2 2 If> 220 195.4 98.4 101.7 100.3 94.2 142.7 150.2 , 172.3 181.4 220 225 199.9 100.8 104.2 102.7 96.6 146.0 153.7 176.2 185.5 22f> 230 204.3 103 . 2 106.6 105.2 99.1 149.4 157.2 180.2 189.7 230 235 208.7 105.0 109.1 107.7 101.6 152.7 160.7 184.2 193.8 23f> 240 213.2 108.0 111.5 110.1 104.0 156.1 164.3 188.1 198.0 240 245 217.0 110.4 114.0 112.6 106.5 159.4 167.8 192.1 202.2 245 250 222.1 112.8 110.4 115.1 109.0 162.7 171.3 196.0 200 . 3 250 255 220.5 115.2 118.9 117.6 111.5 166.1 174.8 200.0 210.5 255 i ow- ywfr OHt' yzt' ozt- 091- yyt- in* OH' 001' y<$8 008 t/Kf; OK8 yzt: OZ8 098 Oyfl im; 0*8 008 ' zw: O'OHfl Z' 9Z8 i'" 098 o' oyt: K • i w: Z'Zl'8 O'HIfi troit: I "908 o'sot: H • ZOS Z'80S (i" zzs Z' SOS 9' MJS V09S troys U'ZVS 8' 8*S 9 • «8S I ' LZZ o • css H'SIS Z'*IS y K i i; 9'908 z'sof: Z'80S H' *«S H'OOS °.i(!z2 1 nys 'yys ; (|t:s °!i££ Z'8SS L'(\\Z o'SH: I'" H88 H tut; 8 188 z" zsf; Z' 008 S " 908 0" I »S 8 " KHZ L " VHS I M«S O'ZZS 0 " \'LZ S ' ZIS Z'81S I 'OlS 9'90S ()'80S t-'SOI " KOI yozi I "9ZI 8 • SZ1 8' 08S 9' ZSS K' 1-SS O'SSS O'US Z' HOS y«os o •<)<)?; JS'OKl o'yzi S'8ZI O'OZl fryin Z'S9l I ' 091 yzyi 8 • vy i Z;OH fl'IVI 9 'OS I 9'IST O'OIl yon O'ni I' Z8S S" *8S !•' I8S 9' 8SS 0' 8SS s; oss Z'VIS S" (SOS y' WK, Z' 80S 0'IOS 8'80l yzwi (i * 891 O'lOl yyn VOH S'Z8l S'081 z;zsi rosi H'OVS — Ci2H220n. (Taka-diastase,1 if available, is more convenient to use, no blank determination being required with malt extract.) The enzymes thus introduced have no action on other carbohydrates present. Starches from the different grains are not acted upon with equal vigor by diastase so it is necessary to test with iodine solution to determine whether the conversion has been completed. iJ.Agr. Sci., 11, 9 (1921). I 164 QUANTITATIVE AGRICULTURAL ANALYSIS After hydrolysis of the starch by the enzyme, the resulting maltose and dextrin may be further hydrolyzed to dextrose under the influence of acid as follows : ''Hi '- f fil Cl2H220n + HoO Maltose Dextrose The dextrose so produced is then determined by methods already described for reducing sugars. The work should be so planned that the determination can be carried through without delay. If an interruption is necessary after the completion of the enzyme action, fermentation should be prevented by the addition of 0.2 gm of salicylic acid. Determination of Starch: Diastase Method. — Prepare malt extract as follows : Grind about 10 gm of malt and add to it 200 cc of water. Allow it to digest at the temperature of the room for about three hours, with occasional shaking. Filter. Determine the weight of reducing sugars in 40 cc of the extract, after treatment with hydrochloric acid as described below for the feed. Extract on a hardened filter 5 gm of the dry material, very finely ground, with five successive portions of 10 cc of ether. Wash with 150 cc of 10-per cent alcohol and then with a little 95-per cent alcohol. This removes all fatty material and sugars. Place the residue in a beaker with 50 cc of water, immerse the beaker in boiling water and stir constantly for 15 minutes or until all the starch is gelatinized. Cool to 55°, add 20 cc of malt extract and maintain at this temperature by placing in a water bath for an hour. Heat again to boiling for a few minutes, cool to 55°, add 20 cc of malt extract and maintain at this temperature for an hour or until particles of the residue treated with iodine show no blue color upon microscopic examination. Cool, make up directly to 250 cc and filter through a dry paper. Place 200 cc of the filtrate in a flask with 20 cc of 25 per cent hydrochloric acid (specific gravity 1.125). Connect with a reflux condenser and heat in a boil- ing water bath for 2.5 hours. Cool, nearly neutralize with sodium hydroxide solution, finish the neutralization with sodium carbonate solution (using methyl orange) and make up to 500 cc in a volumetric flask. Mix the solution well, pour through a dry filter and determine the dextrose in 50 cc as directed on page 159. Conduct a blank determination upon 40 cc of the malt extract by hydrolyzing with acid, with subsequent determination of copper reduced, and correct the weight of copper reduced by the feed solution accordingly. The weight of the dextrose obtained multiplied by 0.93 gives the weight of starch. Calculate the per cent. Direct Acid Hydrolysis, — Members of the starch group com- prised in the " nitrogen free extract" are often determined by direct acid hydrolysis. When the mixed feed is boiled with FEEDS 165 acid, after most of the fat has been removed, the starch and some of the pentosans are hydrolyzed to reducing sugars. It is due to the pentosans that these results, considered as starch, are too high when compared with the amount obtained by the diastase method just described. Determination of Starch: Direct Acid Hydrolysis.—Stir a quantity of the sample, representing 2.5 to 3 gm of the dry material, in a beaker with 50 cc of cold water for an hour. Transfer to a filter and wash with 250 cc of cold water. Heat the insoluble residue with 200 cc of water and 20 cc of 25-per cent hydrochloric acid (specific gravity 1.125) and boil for 2.5 hours, in a flask provided with a reflux condenser. Cool, rinse into a 250-cc volumet- ric flask and nearly neutralize with sodium hydroxide, using methyl-orange. Dilute to 250 cc mix and filter, and determine the dextrose in 50 cc of the filtrate as directed on page 159, omitting the addition of water just before mixing with Fehling's solution. The weight of the dextrose obtained multiplied by 0.93 gives the weight of starch. The factor 0.90 is the theoretical ratio between starch and glucose but, according to Noyes and other investigators,1 the factor 0.93 more nearly represents the analytical ratio. Arabin, Xylan and the Pentosans.—These are compounds of unknown constitution but they all yield pentoses (aldehyde sugars containing five carbon atoms) upon hydrolysis under the influence of hydrochloric acid. Arabin and xylan are constitu- ents of the plant gums. Arabin may be obtained from gum Arabic, while xylan is found in many woods, in straw and in corn cobs. Lignin is one of the most common of the pentosans. It occurs with cellulose in wood, straw, bran and similar materials. It will thus be seen that all of these substances will be probable constituents of the rougher materials of the sort to be found in animal feeds. The pentoses which are formed by hydrolysis of the com- pounds already mentioned are further converted into the alde- hyde furfural, upon distillation with hydrochloric acid. The type reaction is as follows: HO H OHH H H H—C H OHH OHH A pentose 1 /. Am. Chem. Soc., 26, 266 (1904). = C—C = 0 + 3H20. 0- H Furfural 166 QUANTITATIVE AGRICULTURAL AXALYMti In the analytical method, furfural is produced by hydrolysis and distillation with hydrochloric acid. Phloroglucin, an aro- matic alcohol, CoH3(OH)3, is added and this precipitates furfural phloroglucide: C5H402 + C6H8(OH)3 -> Ci,H»(>4 + H20 From the weight of furfural phlorogludde the corresponding weight of pentosans, may be found by referring to Krober's table, found on page 167. Determination of Pentosans and Allied Substances. —Prepare the follow- ing reagents: Phlorof/lutin.—Test the purity of the laboratory supply !>y dissolving a small amount in a few drops of acetic anhydrides healing almost, to boiling and adding a few drops of concentrated sulphuric acid. If more thiin a faint violet color appears the phlorogluein contains diresorcin and it muHt then be purified. 'For this purpose heat 11 gin of phlorogluein with .'I(K) cc of 12-per cent hydrochloric acid (specific gravity l.(MJ), adding the phloro- gluciri very gradually. Continue heating and stirring until solut ion in nearly complete. Pour the hot solution into 1200 cc of hydrochloric acid of the same concentration. Allow to stand for several days, to permit the dire- sorciri to crystallize. Filter just before using. Aniline Acetate Paper.—Th'w is prepared by mixing aniline* and water in equal volumes, then adding glacial acetic acid until the mixture is clear. Moisten filter paper with the solution. Place 2 to 5 #m of food in a 250-ce. distilling flunk which in fitted with a scparatory funnel and which in connected with a condenser. Add 100 cc of 12-per cent hydrochloric acid (1.06 specific gravity) and wvcral pieeenof pumice stone, dropped in while hot. Heat over a win* gaiix<* at such it rate that about 30 cc will distill over in 10 minutes, passing the. distillate through a Hinall filter paper into a 500»ee volumetric' flank. Add «'!0 cc of 12-per cent hydrochloric acid to the flank through t he separatory funnel. ('ontintie this process of distilling and replacing the distillate hy hydrochloric arid until the distillate amounts to about 300 cc and until a few drop« give no red or pink color to aniline acetate paper. Gradually add to the total distillate an amount of pure phUiroghtein about double the furfural estimated to 1m present. (Commit the instructor.) It will bo observed there an? several color changes taking place, the flotation becoming yellow, then green and finally an almost black precipitate uppeitw. The solution is diluted to 400 cc with 12-per cent hydrochloric acid and allowed to stand for 12 hours. Test, the solution with aniline acetate paper to see if precipitation of furfural has been complete, a red color developing if any furfural remains in solution. Kilter the precipitate through a dried and weighed Gooeh crucible. Wash with 150 cc of water (retaining «>me water in the Gooeh crucible until the last, during f lie wanhing) and dry lor 4 hours at 100°. Cover the crucible, cool and weigh rapidly. FEEDS 167 The weight of pentosans cannot be calculated accurately from that of phloroglucide by use of a constant factor which has been derived from the theoretical equation, because of variation in the composition of the furfural phloroglucide, according to the proportion of furfural present. TABLE VIII.—KROBER'S TABLE FOR DETERMINING PENTOSES, PENTOSANS AND RELATED SUBSTANCES Furfural-phloro-glucide Furfural Arabi-nose Arabin Xylose Xylan Pentosc Pentosan 0.030 0.0182 0.0391 0.0344 0.0324 0.0285 0.0358 0.0315 0.035 0.0209 0.0446 0.0393 0.0370 0.0326 0.0408 0.0359 0.040 0. 0235 0. 0501 0. 0441 0.0416 0. 0366 0. 0459 0. 0404 0.045 0.0260 0.0556 0.0490 0.0462 0.0406 0.0509 0.0448 0.050 0.0286 0.0611 0.0538 0.0507 0 . 0446 0.0559 0.0492 0.055 0.0312 0.0666 0.0586 0.0553 0.0486 0.0610 0.0537 0.060 0.0338 0.0721 0.0634 0 . 0598 0.0526 0.0660 0.0581 0.065 0.0364 0.0776 0.0683 0.0644 0.0567 0.0710 0.0625 0.070 0.0390 0.0831 0.0731 0.0690 0.0607 0.0761 0.0670 0.075 0.0416 0.0886 0.0780 0.0736 0.0647 0.0811 0.0714 0.080 0.0442 0.0941 0.0828 0.0781 0.0687 0.0861 0.0758 0.085 0.0468 0.0996 0.0877 0.0827 0.0727 0.0912 0.0803 0.090 0.0494 0.1051 0.0925 0.0872 0.0767 0.0962 0.0847 0.095 0.0520 0.1106 0.0974 0.0918 0.0808 0.1012 0.0891 0.100 0.0546 0.1161 0.1022 0.0964 0.0848 0.1063 0.0935 0.105 0.0572 0.1215 0.1070 0.1010 0.0888 0.1113 0.0979 0.110 0.0598 0.1270 0.1118 0.1055 0.0928 0.1163 0.1023 0.115 0.0624 0.1325 0.1166 0.1101 0.0968 0.1213 0.1067 0.120 0.0650 0.1380 ' 0.1214 0.1146 0.1008 0.1263 0.1111 0.125 0.0676 0.1435 0.1263 0.1192 0.1049 0.1314 0.1156 0.130 0.0702 0.1490 0.1311 0.1237 0.1089 0.1364 0.1201 0.135 0.0728 0.1545 0.1360 0.1283 0.1129 0.1414 0.1244 0.140 0.0754 0.1600 0.1408 0.1328 0.1169 0.1464 0.1288 0.145 0.0780 0.1655 0.1457 0.1374 0.1209 0.1515 0.1333 0.150 0.0805 0.1710 0.1505 0.1419 0.1249 0.1565 0.1377 0.155 0.0831 0.1765 0.1554 0.1465 0.1289 0.1615 0.1421 0.160 0.0857 0.1820 0.1602 0.1510 0.1329 0.1665 0.1465 0.165 0.0883 0.1875 0.1650 0.1556 0.1369 0.1716 0.1510 0.170 0.0909 0.1930 0.1698 0.1601 0.1409 0.1766 0.1554 0.175 0.0935 0.1985 0.1746 0.1647 0 . 1449 0.1816 0.1598 0.180 0.0961 0.2039 0.1794 0.1692 0.1489 0.1866 0.1642 0.185 0.0987 0.2093 0.1842 0.1734 0.1529 0.1916 0.1686 0.190 0.1013 0.2147 0.1889 0.1783 0.1569 0.1965 0.1729 0.195 0.1039 0.2201 0.1937 0.1829 0.1609 0.2015 0.1773 0.200 0.1065 0.2255 0.1984 0.1874 0.1649 0.2065 0.1817 0.205 0.1090 0.2309 0.2032 0.1920 0.1689 0.2115 0.1861 0.210 0.1116 0.2363 0.2079 0.1965 0.1729 0.2164 0.1904 0.215 0.1142 0.2417 0.2127 0.2011 0.1770 0.2214 0.1948 0.220 0.1168 0.2471 0.2174 0 . 2057 0.1810 0.2264 0.1992 0.225 0.1194 0.2525 0.2222 0.2102 0.1850 0.2314 0.2037 0.230 0.1220 0.2579 0.2270 0.2148 0.1890 0.2364 0.2081 0.235 0.1245 0.2633 0.2318 0.2193 0.1930 0.2413 0.2124 0.240 0.1271 0.2687 0.2365 0.2239 0.1970 0.2463 0.2168 0.245 0.1297 0.2741 0.2413 0.2284 0.2010 0.2513 0.2212 0.250 0.1323 0.2795 0.2460 0 . 2330 0 . 2050 0.2563 0.2256 0.255 0.1349 0.2849 0.2508 0.2375 0 . 2090 0.2612 0.2299 0.260 0.1374 0.2903 0.2555 0.2420 0.2130 0.2662 0.2342 0.265 0.1400 0.2957 0.2603 0.2465 0.2170 0.2711 0.2385 '0.270 0.1426 0.3011 0.2650 0.2511 0.2210 0.2761 0.2429 0.275 0.1452 0.3065 0.2698 0.2556 0 . 2250 0.2811 0.2473 0.280 0.1478 0.3199 0.2745 0.2602 0.2290 0.2681 0.2517 0.285 0.1504 0.3173 0.2793 0.2647 0 . 2330 0.2910 0.2561 0.290 0.1529 0.3227 0.2840 0.2693 0 . 2370 0.2960 0.2605 0.295 0.1555 0.3281 0.2887 0.2738 0.2410 0.3010 0.2649 0.300 0.1581 0.3335 0.2935 0.2784 0.2450 0.3060 0.2693 168 QUANTITATIVE AC.R.K'VLTUHAL ANALYHIH w ''1 i/S »n\i ( ' Krober's table, page 1G7, gives the weights of furfural, pentosea and pen to- sans for weights of phloroglucide between 0.03 and 0,30 gin. For weights less than 0.03 gm, use the following formulas: Furfural =0.5170 (a -f 0.0052), (1) Pentosos = 1.0170 (a + 0.0052), (2) Pentosans = 0.8940 (a -f 0.0052), (3) where a = weight of phloroglueide and 0.0052 represents weight of phloro- glucide soluble in the 400 cc of acid solution. Galactans.-—These are substances of unknown constitution which, like the pentosans, are widely distributed in the vegetable kingdom. Agar-agar is one of the important members of this group. Another is the principal carbohydrate of the soybean. When the galactans are hydrolyxed by adds they yield galaetose, a sugar having the same empirical formula as dextrose, and nitric acid further converts this into mucic a/M#0w.—Dissolve* 2 gin of ammonium carbonate in 38 cc of water and add 2 eo of concerntrated ammonium hydroxide. (b) Nitric AcwZ.—Prepare, 250 cc of nitric, acid, specific gravity 1.15. Extract an accurately weighed sample of about 2.5 gm on a hardened paper, with five successive portions of 10 cc each of ether, place the insoluble residue in a beaker, about .5.5 em in diameter and 7 cm deep, together with 00 cc of nitric acid (b) and evaporate the solution to exactly one-third of its initial volume in a water bath whose temperature in 94" to !H>". After Htanding for 24 hours add 10 cc of water and allow to stand another 24 hours. The mucic acid has, in the meantime, crystallized but. it is mixed with other material only partly oxidized by the nitric* acid. Filter, waifh with 30 cc of water to remove a« much of the nilru' acid aw poHHihlc* and replace the filter and contents in the beaker. Add 30 ce of ammonium carbonate solution (a) arid heat the mixture on a water bath at 80° for 15 minute**) with constant stirring. The ammonium carbonate reacts with the mucic acid, forming soluble ammonium rnueate. Wash the filter paper uwl contents Hcvc*nil timen with hot water by decantation, pausing tin* washings through the filter paper, to which finally transfer the material ami thoroughly wawh. Evaporate the filtrate to dry ness on a water bath, avoiding unnecessary heating (which causes decornposition), add 5 cc of nitric acid (fr)f stir the mixture thoroughly XSAIKI, /. Bid. Chem.., 2, 251 (1906). f iff I FEEDS 169 and allow to stand for 30 minutes. The nitric acid decomposes ammonium mucate, precipitating mucic acid; collect this on a weighed Gooch or alundum crucible, wash with 10 to 15 cc of water, then with 60 cc of alcohol, and finally several times with ether. Dry at 100° for 3 hours, cool and weigh. Multiply the weight of mucic acid by 1.33, which gives galactose, or by 1.197, which gives galactan. Calculate the per cent of galactan in the feed. f /J CHAPTER X SAPONIFIABLE OILS, FATS AND WAXES Composition. — The chief constituents of animal and vegetable oils are esters derived from fatty acids and glyccrol, a triatomic alcohol. Of the former the most important are palmitic, stcaric and oleic acids, the first two being saturated, the last an un- saturated acid. The glycerides of these acids are respectively known as palmitin, stearin and olein and they have the following composition: CaHB(Cl6H8i02)8, Palmitin Stearin In addition to these are esters of higher alcohols other than glycerine and of other saturated and unsatunited fatty acids, also in certain cases small amounts of free higher alcohols. The chief differences in properties of different oils arc* caused by varia- tions in the proportions of the constituent esters. Vegetable oils contain much palmitin while stearin predominates in animal oils. The more liquid oils contain more olein and eaters of acids having smaller molecular weights. The animal and vegetable oils and fats are thus in a class quite distinct from that of mineral oils, the latter being mixtures of various saturated and unsaturatocl hydrocarbons, not Hapomfi- able, as distinguished from the saponifiable esters of the former class. Waxes.— The true waxes differ chemically from the oils and fate in that they are not glycerides but arc* esters of mono- or diatomic, alcohols with the higher fatty acids. Those alcohols are either aliphatic; or aromatic. Following are some examples of such esters: Oetyl palmitate, derived from palmitic acid and cetyl alcohol, Oi«H3j»OH; thin is the chief constituent of sperma- ceti. Oeryl palmitate, the chief constituent of opium wax, IB derived from palmitic acid and eeryl alcohol, C«?HpOH. Myri- 170 * SAPONIFIABLE OILS, FATS AND WAXES 171 cyl palmitate occurs in beeswax. It is an ester of palmitic acid and myricyl alcohol, CsoHeiOH. Ceryl cerotate is the chief constituent of Chinese wax. It is an ester of cerotic acid, C25H5iCOOH, and ceryl alcohol. The most important aromatic alcohols occurring in waxes are the isomeric alcohols cholesterol and phytosterol, C26H43OH. These are found as esters of palmitic, stearic and oleic acids. Separation and Identification.—Notwithstanding the differ- ences in composition the task of separating and determining the per cent of different oils in a mixture is a difficult and sometimes impossible one, because of the fact that the same general com- pounds constitute the greater proportion of all fats and oils. The chemist must usually be satisfied if he can recognize single oils or, with the nature of a single oil known, determine the approximate extent and nature of adulteration. The differences in molecular weight and degree of saturation, the presence and per cent of free alcohols or acids and the occasional occurrence of traces of unusual substances, characteristic of certain oils, constitute the bases of the tests used in the effort to identify an oil. The examination becomes therefore not an analysis, in the usual sense, but a series of tests applied in order to gain informa- tion regarding the identity of a pure oil and, so far as is possible, the composition of a mixture. Certain physical and chemical "constants" are determined and compared with the constants obtained from examination of oils of known purity. The chief obstacle to the use of such figures lies in the fact that, for a given kind of oil they are actually variable within certain limits. These limits may be very narrow, but it sometimes happens that the ranges for two or more oils overlap. Thus olive oil from Italy is not chemically identical with olive oil from California. The soil, climate, variety of plant and method of expressing from the olive have their influence upon the properties of the various glycerides and other substances present in the oil. It is only when the ranges of variation for different oils do not overlap that it is easy to determine the identity of a single oil, although it usually happens that while overlapping occurs with a single con- stant it does not occur with others. The significance of the various constants and their methods of determination will be described. i 1 172 QUANTITATIVE AGRICULTURAL ANALYSIS Specific Gravity.—In a general way the specific gravity of oils increases with the per cent of (a) glycerides of unsaturated acids, (6) glycerides of soluble acids and (c) free fatty acids. Old oils also usually have higher specific gravities than the normal, on account of oxidation. The specific gravity of the waxes and of solid fats is usually higher than of liquid oils. These rules do not hold in all cases and the determination of specific gravity, like that of the other constants of oils, is made for com- paring with recorded data for the purpose of identification more often than for throwing light upon the chemical constitution of oils of known purity. The principles underlying the modes of expression and deter- mination of specific gravity have been discussed on pages 94 to 102, Part II. Unfortunately there has been a great lack of uniformity in selecting conditions and modes of expression for spe- cific gravities of oils as they are recorded in the literature. Tem- peratures of 15.5°, 17.5°, 20°, 25°, 40°, 60°, 100° and others are commonly used. In favor of the higher temperatures it may be said that the fats and waxes are all liquid at these temperatures so that determinations may readily be made. It has been found1 that a fair degree of approximation may be made in correcting the specific gravity to another temperature by using the coefficient 0.0007 as the change for each Centigrade degree. This is the average value for a considerable number of oils between tem- peratures of 15.5° and 98°. Of course this does not remedy the lack of uniformity of expression, noted above. For the determination use a picnometer, a Westphal balance or an accurately calibrated hydrometer. "If a Westphal balance is used the displacement of the plummet in pure boiled water should be accurately determined at the temperature at which the balance is to be used. The thermometer in the plummet should be compared with a standard ther- mometer. The picnometer method is recommended. 20° Determination of Specific Gravity of Oils at r^p—Use a 25-cc specific gravity bottle (picnometer). Clean with chromic acid, followed by distilled water/then rinse with alcohol and dry in an oven at 100°. Cool in the bal- ance case (in which the air should be at a temperature not above 20°) and weigh. Fill with distilled water which has been recently boiled to expel dissolved gases and cooled to a few degrees below 20°. Insert the stopper and nearly immerse the stoppered bottle in a bath of distilled water which is 1 WRIGHT, J. 8nc. Chew. Intl., 26, 513 (1907). SAPONIFIABLE OILS, FATS AND WAXES 173 kept at exactly 20°. After 30 minutes take off the drop of water from the tip of the stopper, remove the bottle and wipe perfectly dry with a clean towel but without warming the bottle to above 20°. Place in the balance case and weigh after 15 minutes. Calculate the weight of con- tained water. Empty the bottle and dry inside and out, then fill with oil and ma- nipulate as before, calculating the weight of contained oil. This weight divided by the weight of contained water gives the specific gravity of the -1 4.2°° oil at 2Qo- If the specific gravity has been determined at any other temperature or if it is desired to calculate the specific gravity at any temperature from the determination at 20°, use the following formula: 0 = Gf 4- 0.0007 (*' - *), where G — specific gravity at temperature t, Gr = specific gravity at temperature t'. 20° Determination of Specific Gravity at -70--—Multiply the specific gravity 20° at SQO by 0.99897, which is the density of water at 20°. The product is the 20° specific gravity of the oil at-jr- (See page 94.) Determination at the Temperature of Boiling Water.—Fill a 25-cc picnometer, dried and weighed as above described, with freshly boiled hot water. Nearly immerse in a bath of briskly boiling water and leave for 30 minutes, replacing evaporated water with boiling distilled water. Insert the stopper, previously heated to 100°, remove the picnometer from the bath, wipe dry, cool to room temperature and weigh. Cal- culate the weight of contained water. Fill the flask, dried at 100°, with the dry, hot, freshly filtered fat or oil, which must be entirely free from air bubbles. Keep in the boiling water bath for 30 minutes then insert the stopper, which has been heated to 100°, wipe dry, cool to room temperature and weigh. Calculate the weight of contained oil and from this and the weight of water contained at boiling temperature calculate the specific gravity of the oil at the temper- ature of boiling water. This determination is necessarily less accurate than the one at 20°, on account of the difficulty involved in keeping the bath at any constant temperature. Superheating may easily occur with distilled water and less pure water may have a boiling point above 100°. Variation in barometric pressure will also change the temperature of the bath so that it becomes necessary to carry out both parts of the experiment at the same atmos- pheric pressure. However the determination is sanctioned and has been made official by the Association of Official Agricultural Chemists. •*! 174 QUANTITATIVE AGRICULTURAL ANALYSIS The specific gravity at any temperature other than 20 may be determined by the method outlined for this temperature or it may be calculated from the determination at this temperature, using the formula given above. It should be understood that the figure desired for purposes of identification is the specific gravity at the temperature for which data may be found in the literature. Index of Refraction.—A discussion of the underlying theory and of the determination of index of refraction is found on pages 113 to 120, Part II. The measurement of index of refraction is a valuable addition to the list of tests for oils. While not in all cases characteristic it will frequently serve to distinguish between certain possi- bilities when other tests, are not conclusive. The refractive index increases with (a) increasing molecular weight of the combined acids and (6) increasing unsaturation. If free fatty acids are present in an oil the refractive index will be lower than the normal value for the oil. In consequence of the latter fact one may expect to find abnormally low indices for old or rancid fats or oils. The selection of standard temperatures for the determination is highly desirable in order to make comparison data useful. Temperatures of 20° for oils and 40° or 60° for fats and waxes are suitable in most cases. For calculating the index of refrac- tion at any temperature from experimental results at another temperature the following formula may be used: R = R' + 0.000365 (f - f), where R and R' indicate indices of refraction at temperatures t and t', respectively. The coefficient 0.000365 is the average change of index for 1° for a large number of common oils. The index of refraction of oils is conveniently determined by use of any of the standard instruments, such as the Abb£, Pulfrich, Zeiss butyro-refractometer or the immersion refrac- tometer. Of those named the Abb6 instrument is probably the most generally useful because it may be used with liquids cover- ing a wide range of refractive indices and because it does not require the use of monochromatic light. The principles under- lying the use of this and other instruments are discussed on pages 115 to 120, Part II. jL SAPONIFIABLE OILS, FATS AND WAXES 175 Determination of Index of Refraction by Means of the Abbe Refrac- tometer.—Set up the instrument in front of a window or any artificial light •source, noting, that, monochromatic light is not essential. Connect a constant temperature apparatus furnished with the instrument and adjust the flow of water and the height of the flame until the desired temperature (20° for oils, 40° or higher for fats or waxes) is attained. Open the prism so that the lower half is in a horizontal position and place two or three drops of oil or melted fat or wax upon it; using a glass rod or pipette but avoiding scratching the prisms. Quickly close and lock the system, allow time for the temperature to become constant and then adjust the com- pensator and focus until the line of division of the field is sharply defined and bring this to the cross hairs. Read the index of refraction upon the scale. Clean the prisms by applying a mixture of equal volumes of alcohol and ether, using a tuft of absorbent cotton. Melting Point of Fats.—From the fact that fats are mixtures and not pure compounds, it will be seen that they cannot have definite and sharp melting points. The observation will there- fore be a somewhat arbitrary one. The following is Wiley's method. Determination.—Prepare discs of fat as follows: Allow the melted and filtered fat to fall a distance of about 20 cm, from, a dropping tube to a piece of ice or to the surface of cold mercury. The discs thus formed should be 1 to 1.5 cm in diameter and they should weigh about 200 mg. Since a recently melted and solidified fat does not have its normal melting point the discs should stand two to three hours before testing. Prepare an alcohol-water mixture of graduated density, as follows: Boil, separately, water and 95-per cent alcohol for ten minutes to remove dis- solved gases. While still hot pour the water into a 20 cm test tube until it is almost half full. Nearly fill the tube with the hot alcohol, pouring down the side of the inclined tube, to avoid too much mixing. Place the test tube containing the alcohol-water mixture in a tall beaker containing ice water, until cold. Drop the disc of fat into the tube and it will at once sink to a point where the density of the mixture is exactly equal to its own. Lower an accurate thermometer, graduated to tenths, into the test tube until the bulb is just above the disc, stirring very gently. Slowly heat the water in the beaker, stirring constantly with an air blast or mechanical stirrer. When the temperature of the alcohol-water mixture has risen to a point about 6° below the melting point of the fat the disc will begin to shrivel and roll into an irregular mass. Now lower the thermometer until the fat particle is even with the center of the bulb. Rotate the thermometer gently and regulate the temperature so that about 10 minutes is required for the last increment of 2°. As soon as the fat becomes a spherical globule read the thermometer. This serves as a preliminary determination of melting point. 170 QUANTITATIVE AGRICULTURAL ANALYSIS Remove the tube from the bath and place in the latter a second tube of alcohol and water. The latter, having been cooled in ice water, is sufficiently low m temperature to cool the bath to the desired point. Add another disc" of fat and regulate the temperature so as to reach a maximum of 1.5° above the melting point us already determined. Bun a third determination, which should agree closely with the second. The disc of fat should not be allowed to touch the side of the tube, in any determination. Iodine Absorption Number. — The iodine absorption number is the per cent of halogen, expressed as iodine, absorbed by the fat or oil when subjected to the action of a halogen solution under specified conditions. The absorption takes place because of the presence of glycerides of unsaturated acids, which contain double or triple bonded carbon atoms. This action is analogous to the absorption of oxygen. In the latter case saturated oxygen compounds are formed, often hard and resinous in nature. Absorption of oxygen from the air in this way is known as "drying," although the term is mis- applied, since no real drying occurs. The determination of halo- gen absorption number is, in a general way, a measure of drying proportion and it serves as a distinction between the somewhat arbitrary classes of drying, serai-drying and non-drying oils. Of the unsaturated acids whose glycerides commonly occur in fats or oils the following important members may be mentioned: Olcic Acid, OiKHruOjj.— The unsaturated character of this acid is indicated by the formula CH,(CH2)7CH « CH(CH2)7COOH. Olein, the triglyceridc of this acid, occurs to some extent in all oils and fats, but especially in the former. The empirical formula of the triglyceride is Olein is liquid at ordinary temperatures and its presence in oils in responsible, in a large number of cases, for their liquid character. Oleio. acid will absorb two atoms of bromine, iodine or chlorine, or one molecule of iodines monochloride ?'or monobromide, the double bonded carbon atoms thus becoming saturated. Simi- larly, cither oleic acid or olcin might be expected to absorb oxygen and to give drying properties to a fat or oil but this SAPONIFIABLE OILS, FATS AND WAXES 177 action does not take place readily and most of the oils of pro- nounced drying properties are found to contain considerable quantities of simple or mixed glycerides of linolic or linolenic acids, more highly unsaturated compounds than oleic acid. Linolic Acid, Ci8H3202, contains two pairs of doubly linked carbon atoms: This acid will absorb four atoms of halogen or two atoms of oxygen. It gives marked drying properties to oils, linolin being abundant in linseed, soybean and poppy seed oils. Linolenic Acid} dsHsoOs, probably to be represented as CH8-CH2-CH = CH-CH2-CH = CH-CH2-CH = CH- (CH2) 7COOH. This acid possesses three sets of double bonds and will absorb six halogen atoms or three oxygen atoms. It occurs as simple or mixed glycerides in linseed oil and, together with linolic acid, plays the most important part in the hardening or "drying" of this oil when it is exposed to the air. An isomer, isolinolenic acid, also occurs as a constituent of the glycerides of drying oils. Ricinoleic Acid, Ci8H3403, is hydroxyoleic acid and, like oleic acid itself, contains only one pair of doubly linked carbon atoms. It will not readily absorb oxygen from the air and it does not impart drying properties to an oil? It is, however, an important constituent of castor oil and will be mentioned later, in the discussion of acetyl value. The five acids named above serve to illustrate the principle that only those unsaturated acids which contain more than one pair of doubly bonded carbon atoms are important from the stand- point of drying. Also an interesting, although perhaps unex- pected fact is that trebly linked carbon atoms do not, under ordinary conditions, absorb halogens or oxygen to the point of complete saturation, only two atoms of halogen or one of oxygen adding to each such pair. Solvent. — Absorption of halogen by oil cannot readily take place unless there is present some solvent which can dissolve both oil and halogen. The halogen solution earliest used for this purpose was of iodine and mercuric chloride in alcohol. This has been almost entirely replaced by a solution of either 12 178 QUANTITATIVE AGRICULTURAL ANALYMfi iodine monobromide or iodine monochloridc in glacial acetic; acid. The monobromide solution was proposed by Hanus, that of monochloride by Wijs. As the former is somewhat more easily prepared its preparation and use will be described. The following solutions will be required for the determination of iodine number: (a) Potassium Bichromate.— -A tenth-normal solution, made by dissolving exactly the calculated weight of a salt of known purity, or standardize an directed on page 74. Five hundred cubic centimeters of this solution will be sufficient. (6) Potassium Iodide.—— Prepare 200 cc of a solution containing approxi- mately 25 gm of the solid. (c) Starch.— -Moisten 1 gm of potato starch with enough cold water to make a thick paste. Heat 100 cc of water to boiling and pour it into the starch paste. Boil gently, with constant stirring, for about a minute. The solution does not'keep well and it should be made each day, as required. The addition of preservatives, such as chloroform or zinc chloride, has been tried but the solution deteriorates, even with such additions. (d) tiodium 7Tto«wZ;p/i KBr + I2. (Of course the iodine is then present as Klj.) Determination of Iodine Number.—Half fill a 20-ce weighing bottle with oil, place in it a piece of glass rod and weigh without the stopper. Carefully pour about 0.25 gm of the oil into a 500-ec bottle or flask having a ground glass stopper, using the glass rod to assist in the transference. Reweigh and prepare another sample in the same manner. Dissolve the weighed sample of oil in 10 ce of chloroform then add 25 cc of iodine moriobromide solution, measuring from a pipette. Stop- per, mix and allow to stand for 30 minutes, shaking occasionally. The* bottle should riot be left in strong light. At the time that the iodine rnonobromide solution is measured into the oil solution, measure the same amount of solution into two bottles, containing the chloroform but no oil. Treat those in exactly tho sumo manner as the solution containing oil. Thin in for the, "blank "determination. At the end of the absorption period add 15 cc of potassium iodide solution (b). Add 100 cc of water, washing down any iodine that may be on the stopper. Titrate the unabsorbod iodine; with standard sodium thioHulphuto, shaking constantly. When only a faint yellow remains add 1 ec, of Htiiroh solution and finish the titration. At the la«t the bottle* should be cloned and shaken until all iodine remaining in the chloroform has boon extracted by the potassium iodide. The temperature should be kept as nearly con- stant as possible throughout the experiment. From the volume of sodium thiosulphate required for the iodine solu- tion alone subtract that required for the oil and iodine solutions. Tho remainder is the volume corresponding to the absorbed iodine. Calcu- late the por cent of iodine absorbed. 180 QUANTITATIVE AGRICULTURAL ANALYSIS f, '11 I Iodine monobromide is absorbed at a double bond thus: —C = C 4- IBr -»—C—C— I 1 I Br Acid Value.—Fresh oils sometimes contain small amounts of free fatty acids produced during the process of extraction. Rancid fats and oils, contain free acids as products of hydroly- sis of the glycerides composing them. The acid value is defined as the number of milligrams of potassium hydroxide required to neutralize the free fatty acids in 1 gm of oil or fat. Acidity is also sometimes expressed in terms of oleic acid as per cent, or as "acid degree," which is cubic centimeters of normal base equivalent to the free acids in 100 gm of oil or fat. The determination of acid value is made for the purpose of determining the condition of the oil and its fitness for a given use, rather than for the purpose of identifying it, since the acid value is a variable within rather wide limits for any oil. Determination of Acid Value.—Weigh 20 gm of oil or fat into a 200-cc flask and add 50 cc of 95-per cent alcohol which has been made neutral to phenolphthalein by a dilute solution of sodium hydroxide. Heat to the boiling-point in a steam bath and agitate thoroughly. Titrate with a tenth- normal solution of sodium or potassium hydroxide, using phenolphthalein. Shake vigorously during the titration and add the standard solution until the pink color persists for a short time. An absolutely permanent color cannot be obtained because any excess of base will finally saponify the oil and thereby become neutralized. Saponification (Kottstorfer) Number.—The saponification number is the number of milligrams of potassium hydroxide required to saponify 1 gm of oil or fat. Different oils show differ- ent saponification numbers because of variation in the molecular weight of the esters contained in them, those of relatively low average molecular weights requiring more base for the saponifica- tion of a given weight of oil than those of higher molecular weights. The variation is, however, not as great as is the case with iodine absorption numbers and the saponification number is consequently not as valuable for use in identifying oils as is the iodine number. Notable exceptions to this rule are butter and cocoanut fat, on the one hand, and the true waxes on the other. Of these the SAPONIFIABLE OILS, FATS AND WAXES 181 first group contains appreciable quantities of the glycerides of butyric, caproic and caprylic acids, in addition to those of oleic, palmitic and stearic acids, which make up the bulk of most other oils and fats. The lower molecular weights of these acids raises the saponification number of butter to about 227 and that of cocoanut fat to 255. The .true waxes are not glycerides but esters of mono- and di-hydric alcohols, usually of higher molecular weights than that of glycerol and always of higher equivalent weights. Most waxes contain also acids of higher molecular weight than that of stearic acid, as constituents of the essential esters. This gives lower saponification numbers to waxes, as will be noted from an inspection of Table XII on page 198. It will thus be seen that the determination of saponification number will be useful chiefly in identifying materials of the classes just named. In most other cases this constant will fall between the approximate limits of 190 and 210. Insoluble Acids (Hehner Value) and Soluble Acids.—The determination of the saponification number may be conveniently combined with the determination of soluble acids and insoluble acids. Among the most important of the acids of smaller molecular weight than oleic acid, combined as glycerides, are butyric, caproic, caprylic and capric acids, discussed above. These acids are soluble in water, the solubility decreasing as the molecular weight increases, so that, while butyric acid is infi- nitely soluble, capric acid dissolves only to the extent of 1 part in 1000 parts of boiling water. The next acid in the series, lauric acid, is almost insoluble while the still higher acids are prac- tically insoluble. An approximate separation of the lower acids from the higher ones may be accomplished by saponifying the oil, decomposing the resulting soap with sulphuric acid and washing the fatty acids with water. The per cent of insoluble acids is called the Hehner value. An inspection of the formula for a typical triglyceride, as that of palmitin, CsH^CieHgiC^s, shows that the acid residue comprises the greater part of the compound. Also since the variation in the molecular weights of the three acids, palmitic, stearic and oleic, which make the greater part of the acids of most oils and fats, is small as compared with the molecular 182 QUANTITATIVE AGRICULTURAL ANALYSIS weights themselves, it is not to be expected that there would be a large variation in either the Hehner value or the per cent of soluble acids. The former has an average value of about 95 and the latter of considerably less than 1. Therefore these numbers are without any great significance in most cases and their determina- tion will give little assistance in the task of identifying most oils. A few exceptions to this statement should be noticed. Butter has already been mentioned as containing unusually large quantities of butyric, caproic, caprylic and capric acids. Consequently its Hehner value falls to 88-90 and its per cent of soluble acids rises to about 5. Other notable exceptions are cocoanut, palm nut and croton oils. Practically, it is in these cases only that the determination of soluble and insoluble acids will be of any great use. Determination of Saponification Number.—Prepare the following solutions: (a) Alcoholic Base.—Purify 2 liters of alcohol by heating on a steam bath for 3 hours with about 10 gm of sodium hydroxide, using a reflux condenser. Distill and make 1000 cc of a solution of 40 gm of potassium hydroxide in the alcohol. The potassium hydroxide should be as nearly free from carbonate as is possible. Allow the solution to stand until the small amount of potassium carbonate that is always present has settled out, then decant into another bottle. The concentration does not remain constant for long and the solution should not be standardized, except by a blank determination, made at the time saponification number is determined. (6) Prepare also a half-normal solution of hydrochloric acid in water. Select two ordinary flasks of 250-cc capacity having, if possible, necks of slightly larger diameter at the top than at the bottom, though this feature is not essential. Clean with alcohol. Weigh into each flask about 5 gm of oil or fat, using a small bottle and glass rod as in the determination of iodine number. Add to each flask 50 cc of the alcoholic solution of potas- sium hydroxide'from a calibrated pipette or burette, place in the neck of the flask a funnel having a short stem and warm on the water bath until the alcohol boils, though it should not be evaporated more than is necessary. The oil is usually saponified in about 30 minutes. A homogeneous solution must be produced, so that no separation will occur when boiling is inter- rupted. Measure 50 cc of the alcohol solution of potassium hydroxide into each of two other flasks, for standardization. While saponification of the oil is proceeding titrate these solutions with the half-normal acid, using phenol- phthalein. Cool the flasks in which the oil was saponified, add a drop of phenolphthalein and titrate the excess of base with half-normal acid, deduct from the volume used for 50 cc of the base in the standardization and calcu- late the saponification number. SAPONIFIABLE OILS, FATS AND WAXES 183 If ifc is desired to determine insoluble and soluble acids the solution which has just been used for the determination of saponification number may be used for this purpose. For detailed directions refer to other works on this subject.1 Reichert Number and Reichert-Meissl Number.—There is no sharp line of division between the fatty acids volatile with steam and those not volatile and it is not possible to effect more than a very approximate separation by a method of distillation unless this is continued for a very long time. On the other hand fairly constant proportions of acids may be distilled if the method is rigidly standardized. In this way figures may be obtained that have a value in identifying certain oils and fats. The determination is made chiefly in the examination of butter and its substitutes. Pure butter contains volatile acids to the extent of nearly 10 per cent of the total fatty acids. The saturated acids to and including capric acid are the only ones of the series that may be distilled without decomposition. They are therefore known as "volatile" acids while the higher acids (above lauric) decompose when distilled and are therefore called '"non-volatile." Lauric acid distills with steam but is slightly decomposed. Although the volatile acids boil at tem- peratures higher than 100° they can be distilled with steam. The method proposed by Reichert and modified by Meissl has been extensively adopted. It should be understood that neither method gives the correct per cent of volatile acids but simply the proportion that will be distilled under certain stated conditions. The Reichert Number is the number of cubic centimeters of tenth- normal base required to titrate the adds obtained from 2.5 gm of oil or fat by Reichert's distillation process. The Reichert-Meinsl number is the same as the Reichert number except that 5 gm of oil or fat is used. The Reichert-Meissl number is not exactly double the Reichert number. The Reichert-Meissl number of most oils, fats and waxee in less than 1 and the determination will be of little service in identifying these oils. The following oils are exceptional in this respect. i LEWKOWITSCH, "Chemical Technology and Analysis of Oils, Fats and Waxes;" Assoc. Off. Agri. Chemists, "Methods of Analysis;" MAHIN, '' Quantitative Analysis.'' tfi; w .1S-1 QUANTITATf FABLE AGRICULTURAL ANALYSIS -HEICHERT-MEISSL NTJMBEKS Oil or fat Xteichert- Mcissl number Oil or fat Reichert-Meissl number Butter fat .......... 2S.5 7 13 7 5 47 Cocoanut ....... .... Oroton ....... Palmnut ........ Porpoise .......... Butter and Substitutes. — Practically speaking, the deter- mination of Reichcrt-MCelssl number is a test chiefly of value in the dairy laboratory. Butter substitutes are of two general classes: (a) Oleomargerlrxes, made chiefly from refined lard and "olco oil" (the olcin of beef tallow) and (6) preparations in which cocoanut fat is one of the essential constituents. For members of the first class the Reichert-Meissl number will be less than 1, while mixtures of the second class will show numbers ranging up to 7, according to the per cent of cocoanut fat in the preparation. The riuml>er for pure butter is about 28.5, as noted in the table above. Applications to butter testing are noted in the chapter on Dairy Products, page 223. Spitzcr and Kpple1 have constructed the chart shown in Fig. 45 for the application of Iteichert-Meissl and saponifi cation num- bers to the approximate calculations of the proportion of oleo oils, cocoanut fat and butter fat in adulterated butters and butter substitutes. While no great accuracy is claimed for this pro- cedure, it will undoubtedly give useful information in the inter- pretation of analytical results. Determination of Reich ert:—3MCeissl Number. — Prepare the following (a) tiodium hydroxide notation in water, 50 per cent by weight. (b) Alcohol, 95 per ccrtl, redistilled from sodium or potassium hydroxide. (r) Sulphuric «aW, 1 part concentrated acid in 5 parts water. (d) PotanHium hydroxitle, approximately tenth-normal; standardized afcainHt Htamia.nl acid, uning phexiolphthalein as indicator. If the Hampki is either real or imitation butter it will contain water and curd. Mdt and keep at 60° until the fat has separated and, if necessary, filter the fat through a dry p^per placed in a hot-water funnel (Fig. 60, page 226). lhuL Kjcp. £to. Bull, 284 SAPONIFIABLE OILS, FATS AND WAXES 185 Ordinary flasks of 200-cc capacity, are cleaned and dried. The oil or melted fat is dropped in from a weighed bottle until 5 gm, measured to within one drop, is obtained. The oil must not be left on the neck of the flask. Record the exact weight. Add 10 cc of alcohol and 2 cc of 50- per cent sodium hydroxide solution, connect with a reflux condenser and heat upon the steam bath until the oil is saponified. Remove the con- denser and evaporate the alcohol on the steam bath. Add 135 cc 95 UJ^^s^mwWw^ ^^S^^^^^S^^ *• TA „• J. A. rAi ' -f^r ^^rrraApr - v iu y* TI Aicrifx1 AU ^-AI A! •*• fn fi A ,70 aiROI^w^jg^mtVi ' j£-" TJt LJr- K X'-"Lft1 I J(l-'I^-V j-/ r T ¥• aJ -Y ~1 bLL»"*"^T- T-'tY"^! ••' V . I I -i ^ ¥T i\ «\i> Xn ^MtfiW^^j^W WPg^^j^Pg^^^wP8^ •/I—1-1 7\ I i-A-'T Wl LJOrfT''A -J>J-f^'Ti J J-/T*! r7.'---^r i Al J. 4^0 ' la ^ "A ' *A t^. -Jri 1 AJ- j"l\ n. ^»a4tfs^ffi?R«ft f „ 259 267265253 2512492472*5243 24l;289 237235233281229 227226 223221219217'215 213211209207205203201199197 ap.No. 268258 254 252.250 248.246244 242 240238236234 232.23022822b 224 222220.218210214. 212210206200204202200198196 a % 100 95 90 85 80 75 70 65 60 55 60 45 40 35 30 25 20 15 10 50 "—" Saponifrcation Numbers Lower — Percent Cocoaimt Fat FIG. 45.—Spitzer and Epple's chart for composition of butter substitutes. of recently boiled water and warm on the water bath until solution is complete, then cool. Add two or three pieces of pumice stone or about 1 gm of crushed porcelain to prevent bumping, then add 10 cc of the diluted sulphuric acid. Again attach the reflux condenser and heat on the steam bath until the acids form a clear layer. Connect the flask with a distilling tube (Fig. 46) and a condenser and distill over a flame at such a rate that 110 cc shall be obtained in approximately 30 minutes. The distillate is received in a flask which is graduated to contain 110 cc. Mix the distillate, and filter through a dry filter to remove traces of insoluble H 186 QUANTITAT1 VK AGltK'ULTl'RAL AXA/A'MH acids carried over by the steam, receiving the filtrate in a flask graduated to contain 100 cc. Titrate 100 cc of the filtrate with standard potassium hydroxide. Make the proper correction for the fact that only 100 cc of the distillate was used, also correct the number of cubic; centimeters of standard potassium hydroxide used, in case this solution was not exactly tenth-normal or in case the sample weight was not exactly 5 gm. The* result IB the Jleichert-Meissl number. Polenske Value.—-One of the very important constituents of some butter substitutes is cocoanut oil, a pure white vegetable fat having a pleasant taste* and a con- sistemjy which is about the same as that of butter. Its Iteieheirt-MeiHsl number is lower than that of butter, as is shown in Table IX, pages 184. The ve>latile acids obtained from cocoanut oil in the Reiehertr-Meissl distillation contain much larger quantities of adds insoluble at 15° than do the volatile* adds from butter. Butyric aciel comprises from 00 te> 70 per cent of the* volatile acids fmm butter and this aciel in soluble in water in all proportions. The volatile^ acids from cocoanut oil contain larger quantities of e*aproic, cuprylie, capric anel lauric acids, these* being almost insoluble at 15°. The Polenske value (called by its author the "new butter value1') is the number of culric centimeters of tenth-normal bane required to titrate Ike insoluble acids obtained in the Reichert-Meixxl distillation. The Polenske value for pure butler varicw from 1.5 to 3.0, while that for cocoanut oil varies from IB to 18. It is necessary to avoid the use of alcohol in the Haponification of the fat and therefore the determination of Keiehert-Meissl number must be modified if the two determinations are.to be combined Polenske's modification IB essentially an follows: Betennination.—Saponify 5 grn of the fat by healing in n 250-fc* round flask, using a reflux condenser. For the* HapomhVation use 20 #m of glycs erol arid 2 cc of a /K)-per cent solution of sodium hydroxide in water. When «ape>nifie.ation in complete dissolve the soap in 135 ee of recently i)oile CH3COOH + K2SO4. (4) 188 QUANTITATIVE AGRICULTURAL ANALYSIS Effects of Soluble or Volatile Acids.—It should be noticed that whether the distillation or the filtration process is employed, the standard base required finally to titrate the acid will include that equivalent to acids other than acetic. That is, the distilla- tion process will yield a distillate of acetic acid and volatile organic acids while the filtration process will yield a filtrate con- taining acetic acid and soluble organic acids. The close relation between soluble acids and volatile acids has already been dis- cussed (page 183). To correct for the presence of these acids in the solution containing the acetic acid one may either subtract the volume of base used in the determination of soluble (or vola- tile) acids, or a different method may be used. As a rule this correction will be small except with oils showing a high soluble- acid number or Reichert-Meissl number and in these cases the acetyl value is nearly zero, so that it is of little use as a means for identifying the oils. The "acetyl value7' is defined to be the number of milligrams of I potassium hydroxide required to combine with the acetic acid lib- I erated from 1 gm of acetylated fat or oil. Certain oils are charac- | terized by unusually high acetyl values and it is only in these cases that the determination will be of value for oil testing. \ Castor oil is the most noteworthy of these, having a value of about 150. Another class of oils having high acetyl values is composed of "blown" or "oxidized" oils. By blowing air through oils at somewhat elevated temperatures (70° to 115°) the \ viscosity and specific gravity are considerably increased and they • become suitable for use as lubricating oils. The chemical changes that take place are not thoroughly understood but j oxidation is known to occur. This is partly due to combination with unsaturated acids (evidenced by a diminished iodine absorp- \ tion number) and partly to the formation of hydroxyl radicals 1 from hydrogen. The latter change results in an increased j acetyl value and this may even reach a number as great as that j for castor oil. \ The large variation in acetyl values recorded in Table X will I indicate the value of this determination for the identification of f certain oils and fats. In other cases the determination will have '' little value. XAPOXW1AULK AV17W AND WAX EX I 81) TABLE X.-—ACETYL VALUES OF OILS Oil or fat Acetyl value (average) Oil or fat Aeetyl value (average) Castor ............. 150 Fish .......... 41 Colza .............. 17 Olive ....... 13 Cotton seed ......... 13 Shark liver ..... IS Croton ............. 20 Abnormal Variation in Acetyl Values.—Certain abnormalities in acetyl values should be noticed and due allowance made in specific cases. Since acetic anhydride is absorbed by the hydroxyl radical it might be expected that free acids, free alcohols or partly hydrolyzecl glycerides or other esters would show such absorption and that their occurrence in oils or fats would cause these to exhibit unusually high acetyl values. This is found to bo the ease and, since the three classes of substances named above are the direct products of hydrolysis, it follows that rancid oils or fats will not give normal acetyl values. For example, hydrolysis of stearin will yield free stearic acid, together with distoarin, monostearin or glycerol, according to the degree of hydrolysis: Stwrin HaO-»C,H.OH(OC!18H«0), C,H8OH(OC,8H,60), MonoHtoariu C,»H,B0,, Stoane uoi C3JI6(()H), + Olyc«rol Compound Distearin. . , . Monostearin. Glycerol..... Aeetyl vu H4.2 25IJ. 9 772.0 100 QUANTITATIVE AGRICULTURAL ANALYSIS Glycerol and acetoglycerol are easily soluble in water and they would therefore be removed in the process of washing the acetylated oil, so that no error would result from this source. On the other hand both distearin and monostearin, as well as their acetylated products, are insoluble in water. On this account the acetyl value of the partly hydrolyzed oil would be materially increased. The free acids produced by hydrolysis, themselves containing a hydroxyl group, will combine with acetic anhydride to a varying degree and this will still further increase the acetyl value of such rancid materials. It is to be noted also that many of the waxes contain certain quantities of free higher alcohols and free acids. In consequence, these waxes will show moderately high acetyl values, as will be noted in table XII, page 198. It will be obvious from these considerations that acetyl values cannot be used with safety for identifying oils unless these are reasonably fresh. This will be indicated by the acid value, which should be low. The most important application of this determination is in the identification of castor oil. This oil is nearly pure ricinolein, a glyceride of ricinoleic acid. The latter is hydroxylated oleic acid, CHa(CHa) 8CH-OH-CHa-CH = CH(CH2) 7COOH, and the glyceride, ricinolein, has a theoretical acetyl value of 159.1. Its abundance in castor oil gives the latter an actual acetyl value of about 150, a value which is far above that of any other natural oil, only blown oils approaching it in this respect. Lastly may be mentioned the occurrence of certain quantities of free alcohols, especially in the waxes which have, on this account, appreciable acetyl values. Cholesterol, C27H46OH, in fats, oils and waxes of animal origin, and its isomers, the phytos- tcrols, in vegetable oils, are the most important of such alcohols. Determination of Acetyl Value.—Place about 20 gin, approximately weighed, of oil or fat in a 100-cc flask, add an equal volume of acetic anhy- dride, insert a short-stemmed funnel and boil gently for two hours. Cool and pour into 500 cc of water contained in a beaker. Pass a current of car- SAPONIFIABLE OILS, FATS AND 191 bon dioxide into the beaker through a fine orifice of a glass tube to agitato the liquid and hasten the washing. Boil for 30 minutes. At the end of thifl time siphon out the water layer and repeat the treatment with water and boiling until the water is no longer acid, as sr^own by a litmus test, Separate the acetylated oil in a separatory funnel, filter in a drying oven or hot-water funnel (Fig. 50, page 226) and dry. Weigh accurately 2 to 4 gm of the acetylated oil into a flask and saponify according to the method used in determining the saponification number, measuring the alcohol solution of potassium hydroxide accurately and running blank determinations for standardization. Evaporate thcMitoohol and dissolve the soap in water. Add standard hydrochloric acid in H quantity exactly equivalent to the potassium hydroxide added, warm ^ to melt the fatty acids and filter through a wet paper. Wash with boiling waiter until the washings are no longer acid, testing with. litmus paper by barely touching a corner to the bottom of the funnel. The combined filtrate and washings are titrated with tenth-normal base. Calculate the acetyl value according to the definition of this number. Maumene Number and Specific Temperature Reaction,—All oils and fats react with concentrated sulphuric acid, heat being evolved. The reactions are complex and cannot be exprcHHed by a simple equation but oxidation occurs to a considerable degree. The heat evolution varies with different oils arid it in, to some extent, characteristic. The Maumen6 number in the number of Centigrade degrees rise in temperature caused b'}/ mixing 10 cc of concentrated sulphuric acid with 50 gm of oil. A small variation in the proportion of water in the acid cannon a considerable variation in the heat evolved and to this extent the figures recorded by different investigators are not comparable because "concentrated sulphuric acid/' as obtained commer- cially, is not a substance with any definite per cent of water. In order partly to eliminate the errors due to variation in water another determination may be made, using the same amount of acid but substituting 50 gm of water for the oil. The ratio Rise in temperature with oil Rise in temperature with water is known as the "specific temperature reaction." Thin number is not subject to as great variation as is the Maumon6 number. These determinations are necessarily very crude* and a con- siderable variation may be expected, even under the, bent of conditions. Variable radiation is one of the important Hources 192 QUANTITATIVE AGRICULTURAL ANALYSIS of error. These " constants" will be of use chiefly in the detec- tion of drying oils, all of which show high values. Determination of Matimene Number.—Place a beaker, about 5 by 1.5 inches, inside a somewhat larger one and pack the open space between with wool, asbestos or cotton. Cover the beakers with a piece of cardboard through which passes a thermometer. Weigh into the inner beaker 50 gm of oil. Bring concentrated sulphuric acid to the same temperature as that of the oil, and then add, under a hood, 10 cc of this acid, stirring thoroughly with the thermometer. When the acid is all in, place the thermometer in the center of the oil-acid mixture and note the highest point attained by the mercury. The total rise in temperature is the Maumene* number. Determine also the specific temperature reaction as follows: Clean the inner beaker and introduce 50 cc of water. Add 10 cc of acid as before and note the rise in temperature. The Maumene* number divided by this rise is the specific temperature reaction. The drying oils often develop so much heat that active foaming results. Such oils should be first diluted with petroleum oils or olive oil and the proper correction made in the temperature rise. Qualitative Reactions.—If simple and reliable qualitative tests were known for all of the oils, it is not likely that the work outlined in the preceding pages would often be carried out. It has already been explained that comparatively few such tests are known because of the similarity in the composition of the various animal and vegetable oils. Aside from the mere varia- tion in the proportion of the various glycerides, free alcohols and free acids, there are certain constituents of certain oils that will give color reactions which are characteristic. A few of those that are reliable will be described. In most cases these tests should accompany the determination of the analytical constants, rather than be substituted for them. Resin Oil.—Polarize the oil in a 200-mm tube. If the oil is too dark in color for this purpose it may be diluted with petroleum ether and the proper correction made in the reading. Resin oil has a polarization in a 200-mm tube of from +30° to 40° on the International sugar scale (see page 130) while other oils read between +1° and —1° Cotton Seed Oil: ffalphen Test.—Mix carbon disulphide containing about 1 per cent of sulphur in solution, with an equal volume of amyl alcohol. Mix equal volumes of this reagent and the oil in a test tube and heat in a bath of boiling, saturated solution of sodium chloride for about an hour. In the presence of as little as 1 per cent of cotton seed oil a characteristic red color is produced. Lard and lard oil from animals fed on cotton seed meal will give a faint reaction for cotton seed oil. The unknown con- SAPONIFIABLE OILS, FATS AND WAXES 193 stituent which gives the color apparently is assimilated by the animal without change. A negative result does not prove the absence of cotton seed oil because heating the oil for 10 minutes at 250° renders it incapable of giving the color. Sesame Oil: Baudouin Test.—Dissolve 0.1 gm of finely powdered sugar in 10 cc of hydrochloric acid (specific gravity 1.20), add 20 cc of the oil to be tested, shake thoroughly for a minute, and allow to stand. The aqueous solution separates almost at once. In the presence of even a very small admixture of sesame oil this is colored crimson. Some olive oils give a slight pink coloration with this reagent, but they are not hard to distinguish if comparative tests with sesame oil are made. Arachis (Peanut) Oil.—The constants of arachis oil are almost identical with those of olive oil and the difficulties involved in detecting admixtures of the two are correspondingly great. The Renard test for arachis oil is based upon the isolation and weigh- ing of the small amount (about 5 per cent) of arachidic acid (C2oH4oOs) that occurs as its glyceride in arachis oil. The method must be carried out with great care or stearic acid (CigHseOs), whose solubility is not far from that of arachidic acid, will be obtained and mistaken for the latter. The Renard method is fully described elsewhere.1 Soybean Oil.—This oil is increasing very much in importance as a commercial product, on account of the large increase in production of soybeans for food products and for feeding to farm animals. The oil possesses drying properties, having an iodine absorption number of about 136, which is not far from that of linseed oil. For this reason soybean oil is used to some extent as an adulterant of linseed and china-wood oils. It is used also very largely in the manufacture of butter substitutes and of high-grade soaps. A modification of Settings test2 has been given by Newhall.3 This is performed as follows: Add 5 cc of chloroform to 5 cc of the oil in a test-tube, then add a few drops of a solution of gum Arabic and 5 cc of a 2-per cent solution of uranium nitrate or acetate. Shake vigorously to form an emulsion. Soybean oil will give a characteristic lemon-yellow emulsion, while other oils will give only faint yellow or brown. 1 Assoc. Off. Agr. Chemists, ''Methods of Analysis," 253; MAHIN, "Quan- titative Analysis," 2nd Ed., 383. 2 Chem. Abstr., 7, 908 (1913). ' 3 J. Ind. Eng. Chem., 12, 1174 (1920). 13 194 QUANTITATIVE \ \ MM'.s'/.S Newhall states that as little as 5 per rent, of soyboan oil may be detected in a mixture, by this test. To the limited extent to which this teat has boon used by the, mil liors if has \m-n found to be reliable but see also a criticism by Honiuy and Whitescarver.1 Fish and Marine Animal Oils in Mixtures with Vegetable Oils.— Practically all of these oils have very c'onsito "drying" properties, as shown by their iodine absorption numbers. They are chameforixod by the prewwe of glyreriden containing highly unsatuntted acids. The* peculiar "'fishy1'' odor of these oils is probably due to the presence of the glymides of such acids. Absorption of bromine by unsatuntted acid* or their Klycc»ridon produces bromides of limited solubility and high melting point, Octobromstoarin, obtained! from .such acids, melts at a higher temperature (above 200°) and has a lower solubility f him liexu- bromstearin, obtained by bromlnntiug linoleum, and fbis alno differs in a similar manner from tef.rabrorn?ttearinf obtained from linolin. Therefore the* separation of oefobrowHtwirm from brominatcd fish and blubber oils provides a means for detecting marine animal oils in the. presence of vegetable oil*. The* test in performed as follows ; in a tout-tube about 0 gm of the* oil its I'J «•<• f»f u mi^titr** of equal ]>nrtH of chloroform ami glnc'ial itfrlir add, Add hrninitt*1, drop by drop, until a Blight, oxccss w imiimtff! by tin* rolor, kf*(*pinfc thf maiutiott at about 20°. Allow to Htund for 15 minutcM or inc»n* nwl fhou jiliwr flir* tcHt-tuhd in boiling watr T. If only vIc <>»!« »ri* pnvMfnf ili»» Noltifion will hecome porfectly diwr, while fwli uiJn will rmuim rhnirly or «»nf.«Iri a precipitate of insoluble h Color Reactions.— A large* ntimlH*r of r|ualitaiivo twin, l>ow»d upon certain color roactioriH, have* bi«c»n prof)cjHi*il uncl ron»ifif»ral>iy usod in the pant for thu d<»t(*«tiV)ii of varioii« oil*. ( j»br r«*act,ic «w produced by adding • O O • (M >O oo • oo o i 0 | iH r-( 1 S § CQ ... . . o co »o . O CO . g •« -§ > o s § . . . . 03 ^ * K3 O > 1 - .... z , Q"S "33 o K» » « -Q 5 »| a . 1-1 . . 1 3 ^ g u =0" S G ^ d g .2 a CO (N N *& O3 CO «3 -# « N CN OS *^ O O5 (N CO •* O 10 « M N O ^ !"§ 25 «J 'UK V^UMMVJ Iodine number <* 00 10 tO tO 10 1C tO -^ 00 W W «0 if! *•< »•< »H *•< iH U9 »H O T-l O o to co oo o « oo oo en oo o to to tO 10 ^ N rH T-< vH v-l 5 » I :§o0 « ^ i s l> l> cq «3 t>- • **• 00 **- -^ ** ^ *«K rf if -^ (M 00 «tf -f b- b- i> i^ rf TH -^ ^ O O C» O CQ If- f t>. C- t^. «tfl <« ^ ^ ^ O O 10 O 00 00 IN. l*- '*"*'«*•* 7 fl W § w ^ 3 s H 0 5 «1 . S >> W ^ QJ W N- 00 d O t- iM O CO ^ (M (M 0» 0> O5 <3> 1C «3 »HI -^ Cfl O5 Ol O Oi O> W 1> >O W 1 -5 r2 3 d 1 . . • o ; ; i {£ • •' : ca -w -rj "CJ c ' S co « 2 •' rt S - « d 0 ^ ^i^lfel^g Ifiall^l Vegetable semi-dry Cotton seed ..... Croton .......... Maize .......... Sesame ......... Vegetable non-dryi Almond ......... Arachis (peanut) Castor .......... Olive ........... Rape ........... ^ 03 a "5 • oJ 0) a 'E 03 Codliver ........ Menhaden ...... Seal ............ Whale .......... TABLE XII—(Continue Land animal oils: Specific gravity at 20° Index of refraction at 20° Iodine number Saponifica-tion number Reichert-Meissl number Polenske value Acetyl value Maumen6 number Neatsfoot 1 Sheep's foot / ............... 0.912 1.467 70 195 22 50 Vegetable fats: at 60° at 60° Melting point, °C. Cacao butter 0 929 1 450 36 194 33 Cocoanut oil* 0 897 1 441 9 255 7 17 25 Japan wax* 0. 744 1.450 10 225 28 52 Myrtle wax* ................ 0.964 1.444 3 209 40 Palm oil * ............... 0. 890 1.450 54 200 18 40 Animal fats: Butter .................. 0.902 1.448 35 227 28.5 2.3 31 Lard 0.905 1.454 60 196 42 Lard oil Tallow (beef and mutton). . . 0.915 1.451 42 195 48 Waxes: Beeswax Carnaubi Spermaceti Sperm oil Wool wax 0.938 1.450 9 94 15 63 a wax. 0 964 1 463 13 85 55 84 eti . . ................ 0.901 1.440 4 127 50 il* ... (at 20°) 0. 851 (at 20°) 1. 468 86 130 :::: tx ... ... 0.913 1.473 23 100 23 35 . I ^ 2! H *Xote: Terms noted are misnomers. Cocoanut "oil," Japan "wax," myrtle "was" and palm "oil" are vegetable fats, not oils or waxes. ^ Sperm "oil" is a liquid wax, S 14 1: •:l 198 QUANTITATIVE AGRICULTURAL ANALYSIS Analytical chemistry has made little progress in this direction. The application of delicate tests for metals (nickel, palladium, etc.) that are used as catalyzers in the hardening process, may sometimes serve to prove that the material is a hardened oil, rather than a natural fat. Other than this one can say very little. But the knowledge of the nature of the changes caused by hydro- genation should serve to make the analyst more cautious than he might otherwise be when interpreting the results of his analytical data on oils or fats of unknown origin. Interpretation of Analytical Data.—In the discussion of each so-called "constant," in the foregoing pages it has been shown that each determination will be of importance in the identifica- tion of a certain limited number of oils, fats or waxes and that f | in cases other than these the figures will give only negative 4 j! results. The materials for which such figures have proved to be * ;'^ of significance were given in most of the discussions of these ^ /Ij/j \ determinations. '''?] | In Table XII the various "constants" for a number of the more 1 "^ 'I common oils, fats and waxes are collated and the ones that are of particular value in each case are printed in bold face type. The iodine number will be of value in practically all cases, since it is characteristic of classes, even when not of the individuals of a given class. Although only one value is given in each case, it should be remem- bered that these are merely approximate averages and exact agree- ment with experimental results should not be expected. Where i || ; blanks occur in the table this is either because no value is on record or because the figure is so low as to be practically negligible. For additional special tests and for a complete description of the individual oils, consult special treatises on the subject, such as Lewkowitsch, "Chemical Technology and Analysis of {If Oils, Fats and Waxes," and Fryer and Weston, "Oils, Fats and * , Waxes." CHAPTER »XI DAIRY PRODUCTS The rapid development of the dairy industries in recent years has made it imperative that dairy products be standardized to a . greater degree than ever before. In most of the states legal standards have been established for dairy products so that it is unlawful to offer such food materials for sale unless they conform to certain rigid requirements as to composition and cleanliness. The standardizing of dairy products has thus made necessary the services of many technically trained men, not formerly required. MILK The milk of different mammals varies greatly in composition, depending to a great extent upon the time required for their young to reach maturity. This is shown in the following table: TABLE XIII.—AVERAGE PERCENTAGE COMPOSITION OF MILK OF VARIOUS KINDS Kind of milk Water Total solids Protein Fat Lactose Ash Casein Albumin Human 87.6 87.3 86.9 83.6 82.2 87.1 12 12 13 16 0.8 2.9 2.9 4.2 4.3 3.5 8.4 1.3 1.2 0.5 0.9 1.0 0.4 0.4 1.5 0.7 3.7 3.7 4.0 6.2 7.5 2.9 17.0 1.1 4.5 43.6 6.4 4.9 4.6 4.7 4.7 5.4 2.8 5.8 3.1 0.3 0.7 0.8 0.9 0.8 0.7 1.4 0.3 1.0 0.4 Cow .............. Goat ................ Sheep ............... Buffalo (Indian) ...... Camel ........ Reindeer ............ Horse ............... 67.2 90.6 84.0 9 * Swine . . 7.23 7.11 Whale ........ 48.6 i 199 200 QUANTITATIVE AGRICULTURAL ANALYSIS It is thus seen that the milk of most mammals has been analyzed and its composition determined but, for practical purposes, the analyst rarely has to do with any other than cow's milk and human milk. The analysis of cow's milk may be made for purely scientific purposes as, for instance, the determination of the relation between the composition of milk and the breed of animal, the season of the year or the rations upon which the animal is fed, or the determination of the changes that occur in composition during the period of storage, and other similar questions. The analysis may also be made for purposes of legal control to detect sophistication. The analysis of woman's milk is usually made for hygienic purposes, in order to provide a basis for modification of the mother's diet, in cases where the infant is not thriving. The percentage composition of milk varies rather widely although the same substances are found in practically all milk from a given species of animal. It is therefore not possible to fix, by legal enactment, the exact composition of milk that is to become an article of commerce, but certain minimum figures are usually established by law and any milk containing a con- stituent in quantity below the legal minimum is considered to be adulterated. Milk is a very complex fluid, secreted through the alveoli cells of the udder. The fat is present as a suspension (emulsion) of very small globules. The milk sugar and inorganic salts are present in true solution while the proteins, casein, albumin, globulin and fibrin, are in colloidal solution. According to Bab- cock, the composition of cow's milk is as follows: DAIRY PRODUCTS 201 Milk 100.0 Fat.....3.6 Milk serum. .96.4 Glyceridee of insoluble and non-volatile acids Glycerides of soluble and volatile acids Containing nitrogen pro- teids Olein Palmitin Stearin Myristin Butin (trace) J aumB Fat....... 3.6 Butyrin Caproin Caprylin (trace) Caprin (trace) Casein......... 3.0 Albumin....... 0.6 Lactoglobulin Galactin Fibrin (trace) Lactose....... Citric acid.......................... 0.1 Solids not Potassium oxide....... 0.175 f fat....... 9.1 Sodium oxide........... 0.070 Calcium oxide......... 0.140 Magnesium oxide...... 0.017 Ferric oxide........... 0.001 Sulphur trioxide....... 0.027 Phosphorus pentoxide.. 0.170 Chlorine.............. 0.100 . Water.............................................. 87.3 3.3 0.3 3.8 4.5 Ash... 0.7 100.0 Preparation of Sample.—When milk is allowed to stand the fat rises slowly to the top. Before the analysis is started it is therefore necessary to mix the rnilk thoroughly by pouring from one vessel to another several times, but without shaking vigor- ously as air would thus be incorporated with the liquid anid there would be also a coalescence of fat globules. The following table will serve to indicate how far each deter- mination must be carried before it can be stopped with safety: TABLE XIV.—PROGRESS OF DETERMINATIONS Determination Stage after which work may be interrupted Specific gravity...... Acidity............. Total solids.......... Ash................. Total nitrogen....... Casein and albumin.. Lactose............. Fat, paper coil....... Rose-Gottlieb___ Babcock........ Cannot be delayed Cannot be delayed Evaporation of sample Weighing sample Addition of sulphuric acid Filtration of proteins and addition of sulphuric acid Addition of mercuric iodide or nitrate solution Drying milk on paper coil Extraction of the fat Addition of sulphuric acid ilji 202 QUANTITATIVE AGRICULTURAL ANALYSIS i.'^sl ::?.ii It may sometimes be impossible to begin the analysis before bacterial action begins. In such a case add formaldehyde at the rate of 1 cc of the 40-per cent solution to 2 liters of milk. Specific Gravity.—This determination is usually made with a lactometer, which is a hydrometer of a special form. However, it can be determined also by a Westphal balance or a picnom- eter. For a discussion of the use of these instruments, see pages 96 to 100, Part II. Added Water.—As a means for detecting adulteration the specific gravity determination alone is of little value. The spe- cific gravity of butter fat is about 0.93 and of milk solids other than fat is 1.5, while that of whole milk is 1.030 to 1.034. If water is added the specific gravity is lowered but if milk is skimmed the specific gravity is raised because the lighter portion has been removed. Therefore fat could be removed and water added in such a way as to keep the specific gravity unchanged. A more certain method for the detection of added water is in the examination of milk serum, from which all of the fat and proteins have been removed. Determination of Specific Gravity.—A sample of fresh milk is thoroughly mixed by pouring from one vessel to another several times, avoiding violent agitation. Determine the specific gravity at 20° within 2 minutes after mixing. Detection of Added Water.—The ash and milk sugar are the least variable constituents of milk and they afford a suitable basis for the detection of adulteration. A clear serum may be obtained by precipitating the proteins with acetic acid or copper sulphate or by spontaneous souring, and filtering. Examine the filtrate for ash, also for other dissolved solids by means of a dipping refractometer. This instrument is described on page 118, Part II. Examination of Acetic Serum: (a) Zeiss Dipping (Immersion) Refractom- eter Reading.—To 100 cc of milk at a temperature of 20° add 2 cc of 25-per cent acetic acid (specific gravity 1.035) in a beaker and heat the mixture, covered by a watch glass, by immersing in a water bath at 70° for 20 minutes. Place the beaker in ice water for 10 minutes and separate the curd by filtering through a 12.5-cm folded filter. Transfer about 35 cc of the serum to one of the beakers that accompanies the temperature control bath used in connection with the Zeiss dipping refractometer or fill the metal cup that is attachable to the instrument; take the refractometer reading at 20°, using a thermometer graduated to tenths of degrees. A reading below 39 indi- cates added water. If the reading is between 39 and 40 the addition of water is not certain but is to be suspected. DAIRY PRODUCTS 203 (6) Ash.—-Transfer 25 cc of the serum to a fiat bottomed platinum dish and evaporate to dryness on a steam bath, then heat over a low flame until the solids are thoroughly charred. Place the dish in a muffle furnace and ignite to a white ash at a temperature not higher than 500°, cool and weigh. Express the results as grams per 100 .cc. Multiply by the factor 1.02 to correct for the dilution by addition of acetic acid. The result is the ash on the undiluted sour serum. An ash content below 0.715 gm per 100 cc indicates added water. Examination of Sour Serum: (a) Zeiss Dipping Refractometer Reading.— Allow the milk to sour spontaneously, filter and determine the dipping refractometer reading of the clear serum at 20°. A reading below 38.3 indicates added water. (6) Ash.—Determine the ash in 25 cc of the sour serum, using the method as directed for ash of acetic serum. Ash lower than 0.730 gm per 100 cc indicates added water. Examination of Copper Serum: Zeiss Dipping Refractometer Reading.— Use a solution of copper sulphate containing 72.5 gm per liter, adjusted if necessary to read 36 at 20° on the scale of the dipping refractometer. To one volume of this solution add four volumes of milk. Shake well and filter. ^Determine the refractometer reading of the clear serum at 20°. A reading below 36 indicates added water. P H & \ m Acidity of Milk. — Acidity of milk is due to acid phosphates and lactic acid, the latter being produced by bacterial action upon milk sugar. Tfcds is the "souring" of milk. Determination of Acidity. — Place 20 cc of milk of known specific gravity in a 100-cc porcelain casserole and add tenth-normal (to phenolphthalein) sodium hydroxide from a burette, using phenolphthalein as an indicator, until a pink color appears and remains for 1 minute. Calculate the per cent of lactic acid, HCaHaOa, in the milk. Total Solids. — In order to dry the solids rapidly without decomposing them it is desirable to use a weighed flat porcelain or aluminium dish in which has been placed enough sand or asbestos fiber to cover the bottom. The sand or asbestos increases the drying surface and hinders the formation of a scum, which would interfere with the evaporation of the liquid beneath. The solid thus formed should be nearly white except as it may be colored by sand. If there is any considerable browning or blackening it is probable that the milk sugar has been partly caramelized and the resulting loss would therefore not indicate correctly the evaporated water. of Iota! Solids.—Use a flat porcelain or aluminium dish, ,-, «., 10 ,-i ii; .iuiM-t'T. ami add 10 to 15 gin of white sand. Heat the dish ,,vl /.^j »i( ^...,,.,T.i;,! vu'iiiht at KM.')3, then add about 5 gin of milk, cover and r,'rtV^h * (',r , j i ;, v.< if milk to the weighed ''•;' t}..' nu.'4-ifn- privity. Dry at 100° until the weight is constant. O^nl'm *» d*>if-.u!or :irid \vt.-jgh'rapidly. Calculate the per cent of solids. Ash.-—Tho ii>h doos not represent all of the inorganic constitu- ent,* of in ilk in their original combinations because certain fhrniir- tak> place during the burning of the organic matter. HM- :i»ii ^huuld m>t l>e heated to a temperature higher than wji? :t> tlif dilorides of sodium and potassium might be vola- tilized at a liiglter temperature. Nitric acid may be added to aid in oxidizing the organic matter. of Ash.—Weigh accurately a flat platinum or porcelain di>h h'liiir.a: J5 to 30 ec\ Add 20 ec of milk of known specific gravity or obtain riif ui-igli! l»y direct weigliing. In the latter case the dish must be fi»Ye'fvd U'tV>?v aiul ufkT adding the milk. Add five drops of concentrated fistrh' -ii-id ,i!«-d t'vapnrate to tlryness on the steam bath, then ignite at a tte3ow redness until white. Cool in a desiccator and \vrigh. i'aifulate the pc^r cent of ash. Fat.—-Tho fat contained in milk is usually given, more con- jsidmttion than any other constituent, since milk is bought and jsokl largely tin the basis of its fat content. To some extent this is uufurtunato as it has tended to underrate the other constitu- ents, which may be of equal or greater value as food. "Paper Coif1 Method.—In this method the milk is absorbed on porous fat-free paper and dried. In this condition the fat I< easily and quickly extracted as most of it is on the surface of the paper and it is thus somewhat separated from the proteins present. Ether is generally used to extract the fat. This must be anhydrous in order to avoid dissolving some of the milk sugar present. Petroleum ether is sometimes used but it lias the disadvantage of dissolving fats more slowly than ordinary ether. Tho fat extractor, shown in Fig. 41, page 146, is used for the deU'rinination. if other forms of extractors employing cork stoppers are used the corks must be made free from ether-soluble waxes and resins by previous extraction with ether and they must fit tightly enough to prevent the escape of any considerable amount of ether. Fat. paper as * ? * . "(Vmtiinu th«* 2 hours. Finely d^ uiht* before -ttao t ths i ih n ndy f> remove tlit* t'xtnic ti< n tul« ru*ir.iin Evaporate tLe tthiT r< mtdirnR in • (a) on tlic* stttini hath, tinidlnoinpl ing In tKe? ovon at 101)3. Wd that is xmeehanicaly enclc^ed in the dried casein. DeteraxaJnation of Fat: Method.— Place 10 cc of In. a Rolirig "fci^fee (Fig, 47) or other similar tube and add 2 cc (2.5 ee if milk: is sour) of c-oncentrated ammonium, hydroxide. Mix thoroughly by inversion. tit 47-~Rsferis QrA\T/TA T1VE AGRICULTURAL ANALYSIS of the stoppered tube. Add 10 cc of 95-per cent alcohol and ink again. Add 25 CT of dlivl t'ther, stopper the tube and shake vigorously for 30 M'ronds, tlien add 25 cr of petroleum ether (distilled below 60°) and stopper siml shake again for 30 seconds. Let stand until the bubbles of air have disappeared from die lower layer. Both layers should be clear and free from suspended particles. Draw off most of the upper layer of ether-fat solution by opening the stop cock and tipping slightly to make the separation more complete, but without removing any of the lower layer. The fat solution is run through a small (about 5 cm), dry filter, into a dried and weighed fat flask. Repeat the extraction, using 15 cc of each ether as before. Wash the tip of the outlet tube, the funnel and the filter with a small amount of the ether mixture, then evaporate the ether from the fat and ether mixture. Dry the flask at 100°, coo! and weigh. Calculate the per cent of fat in the sample. Babcock Method.—This method is rapid and convenient for genera! dairy control testing. The test is based upon the fact that concentrated sulphuric acid will dissolve all proteins in milt or cream and thus enable the fat to separate when whirled rapidly in a centrifuge. When the acid is added to the milk, the casein, is first precipitated and then dissolved in the excess of acid. The solution darkens because of the charring of the milk sugar, due to the heat of reaction. It is important that the acid should have a specific gravity of 1,82 to 1.83. If the acid is too dilute the fat will have a white appearance with gray particles beneath it, while if too concen- trated the fat Trill be dark colored with black charred particles beneath. The temperature of the fat should be about 60° (140° F.) when the fat reading is made. Appreciable errors will result from volume changes if the temperature of reading is allowed to vary more than 10° (18° F.) either way. The fat should have a clear, golden 3rellow color and it should be separated clearly from the chocolate-colored acid solution beneath. Standard Babcock Test Bottles.1—The standard Babcock test bottles for milk and cream are as follows: 1. Eigkt-per cent, 18-gram, 6-ni. Milk Test Bottle.—The total per cent graduation is 8. The total height of the bottle is 150 to 165 mm. The capacity of the bulb up to the junction with the neck is not less than 45 cc. The graduated portion of the neck has a length of not less than 63.5 mm, and the neck 19 1 Assoc. Off. Agr. Chemists, "Methods of Analysis/' 227 (191S). DAIRY PKUUL'CT* 2()7 cylindrical for at 9 mm below the lowest and above the highest graduation marks. The graduations represent per cents, halves and tenths of a per cent. 2. Fifty-per centt 9-gram, 6-/w. Crcattt TV.y/ Bottlt.—The total per cent graduation is 50. The total height of the bottle is loO TT 30 r FIG. 48.—Test bottles for fat in (a) cream, (6t milk and (c) skim-milk. to 165 mm. The capacity of the bulb up to the junction with the neck is not less than 45 cc. The graduated portion of the neck has a length of not less than 63.5 mm and the neck Is cylindrical for at least 9 mm below the lowest and above the highest gradua- tion marks. The graduations represent five per cents, whole per cents and halves of a per cent. 3. Fifty-per cent, 9-gram, 9~z'w. Cream Test Bottle.—Same as (2) except that the total height of the bottle Is 210 to 225 mm. Certain forms of test bottles are illustrated in Fig. 48. Ql'AXTITATirE AGRICULTURAL ANALYSIS Standard Babcock Milk Pipette.—This pipette is graduated to deliver 17.6 cc of water at 20° in 5 to 8 seconds. CaHbration.—The official method for calibrating Babcock test bottles is to fill the dry bottle to the zero mark with pure mercury at 20°, weigh, fill to the highest mark and reweigh, cal- culating the bulb and stem capacities on the basis of 13.5471 gin of dry mercury for eaAh cubic centimeter at 20°. It is difficult to see what advantage this possesses over the method of calibrating by weighing water at 20° especially since the Babcock bottle filled with mercury must weigh more than 600 gin. Accurate weighing of such a quantity would require a special balance, as sensitive as the analytical balance and having large capacity. Milk pipettes and graduates are calibrated according to the official method by measuring in a burette the quantity of water delivered by the instrument at 20°. Unless care has been exer- cised in wetting the inner surface of the burette, using the standard method by which the burette was calibrated, this method will be subject to considerable error since all burettes are graduated for delivery and not for capacity. A better method for calibrating pipettes is described on page 46. Determination of Fat: Babcock Method.—Fill a 17.6-cc pipette to the mark with mixed milk sample and deliver to the graduated test bottle. Add to this 17.5 cc of sulphuric acid (specific gravity 1.82 to 1.83), pouring it in slowly so as to form a layer beneath the milk. Prepare an even number of bottles, up to the capacity of the centrifuge. After the acid has been added to all the bottles, mix the acid and milk by giving it a gentle rotary motion, being careful to keep the liquid from collecting on the neck of the bottle. Place the bottles in the centrifuge in such a way that they will be counter- balanced and rotate for 4 minutes at the required speed for the machine used. This is about 1,000 revolutions per minute for a wheel 10 inches in diameter or 700 for a 24-inch wheel. Add hot water to each bottle until it is filled to the neck and whirl 1 minute longer. Again add enough boiling water to bring the fat column into the graduated portion of the neck and whirl for another minute. Place the bottles in a glass vessel which is filled with water at a temperature of 57° to 60°. The water should surround the neck of the bottle to a point above the fat layer. After 1 minute measure the fat column from the top of the upper meniscus to the plane of separation between fat and aqueous solution, using a pair of dividers if considered desirable. DAIRY PRODUCTS 209 Proteins and Total Nitrogen.—Of the nitrogenous materials in milk, the principal protein, casein, makes up about 3 per cent of the total 3.8 per cent usually present. Globulin, albumin and fibrin comprise the other 0.8 per cent. Casein and albumin together are at least 95 per cent of the total protein content and analysis shows these two proteins to contain slightly less than 15.7 per cent nitrogen. The factor to convert the per cent of total nitrogen to protein is thus 6.38. m Either the Kjeldahl or the Gunning method may be used for * •;! the nitrogen determination. These are discussed in connection || with the analysis of feeds, page 149. Determination of Total Nitrogen.—Measure out 5 cc of well mixed milk of which the specific gravity has been determined, using a pipette and delivering into a 500-cc Kjeldahl digestion flask. Determine the per cent of nitrogen by the Kjeldahl or Gunning method, described on pages 151 and 154. Multiply the nitrogen per cent by 6.38 and report as total nitrogenous material. Formal Titration for Total Proteins.—Proteins and their derivatives are related to certain amino acids. This is illus- trated by the simple dipeptide, glycylglycine, which is derived from two molecules of the amino acid glycine, as follows: 2NH2-CH2-COOH -> NH2-CH2-CO-NH-CHaCOOH + H20. Glycine Glycylglycine These substances are amphoteric, possessing basic properties on account of the amino group (NH2) and acid properties through the carboxyl. Proteins, as well as their decomposition products, will react with formaldehyde, forming derivatives of the amino acids which have lost their basic character through substitution in the amino group: NHrCHj-CO-NH-CHj-COOH + 2HCHO^2CH2N-CH2-COOH Glycylglycine Formaldehyde + H20. Thus the proteins of milk are neutral to phenolphthalein but upon addition of formaldehyde they become decidedly acid. The equations given above are presented merely to show the supposed general nature of certain changes. Calculations of the results of titrations cannot be based upon these equations because the true formulas of the proteins are not known. 14 210 QUANTITATIVE AGRICULTURAL ANALYSIS Determination of Total Protein: Formaldehyde Method.*—Weigh out, 20 gm of milk and place in a 200-cc beaker. Add 1 cc of phenolphthalein, then add from a burette twentieth-normal sodium hydroxide (standardized using phenolphthalein) until a distinct pink color appears. This neutralizes any lactic acid present in the milk. Next add 10 cc of formaldehyde which is neutral (a single drop of twentieth-normal base should produce a distinct pink color in 10 ec) to phenolphthalein. Stir thoroughly and add twentieth- normal sodium hydroxide until a faint pink color remains after mixing. Note the total volume of basic solution added after introducing the formaldehyde and from this calculate the per cent of total protein present. One cubic centimeter of twentieth-normal base has been found by experiment to be equivalent to 0.0864 gm of milk proteins. Casein.—Casein exists in milk in a colloidal condition. When a dilute acid or an alum solution is added casein is flocculated. To effect complete separation the acid must be very dilute because casein and other proteins are somewhat soluble in a small excess. The separation is most nearly complete at a temperature of 40°. Determination of Casein: Acetic Acid Method.—To 10 cc of milk of known specific gravity, add 90 cc of water at a temperature of 40° to 42°, stir well, add 1.5 cc of 10-per cent acetic acid and allow to stand until a flocculent precipitate settles out and a clear liquid is obtained. This should not take more than 5 minutes. Filter, wash three times with cold water and add the washings to the clear filtrate. Save the filtrate and washings for the albumin determination. Place the paper and precipitate in a Kjeldahl flask and determine nitrogen by the Kjeldahl or Gunning method as described for total nitrogen. Use the factor 6.38 to convert the per cent of nitrogen to that of casein. Determination of Casein: Alum Method.—To 10 cc of milk add 50 cc of water at a temperature of 40°. Then add 2 cc of a solution of potassium alum (saturated by heating 25 grn of crystals with 100 cc of water, until dissolved, then cooling to 40°) and stir. A flocculent precipitate forms and it should settle rapidly. Let the precipitate settle for 5 minutes or more and then filter and wash with cold water. Save the nitrate and washings for the albumin determination. The nitrogen is determined in the residue by the Kjeldahl or the Gunning method and multiplied by 6,38 to obtain the equivalent of casein. Casein by Hart's Method.2—The methods described above are rather long and tedious. The Hart volumetric method is based upon the fact that the amphoteric casein has properties of IHENRIQUES and SOKENSEN, Z. physioL Chem., 64, 120 (1909). a Wis. Exp. Sta. Res. Bull, 10 (1910). m an acicl^ as explained on page 2lK), ai.*t i»t luHnr- T«\; lairiy constant proportion*.. If ai4 tx*v-x » f Iu^ dissolve the casein, the unet mhinod Ht>r tL. The average milk being 1.032, 10.5 cc may be .iieaM accuracy for most work. * n train I \vlll ife gravity 'vit> -n^i of Casein: Hart's Method.—Place 10.3 f 200-cc Erlenmeyer fl.ask containing 75 cc of distilled water freed from carbon dioxide by boiling, then cooled to 20". 10-per cent acetic acid, warm to about 40° and filter off the e. 10-cra filter. Wash the paper and precipitate thorough! 250 cc of cold water. Return the paper and contents to f flask, add. 75 cc of carbon dioxide-free water and a drop of p] To this add 10 cc of tenth-normal potassium hydroxide. St and sbiaJke vigorously. When solution of the protein is com; the disappearance of the red color, using tenth-normal acid, to run a blank as this will usually require 0.2 cc or more of tf: potassium hydroxide. The number of cubic centimeters of I titratloxij thus corrected, will express the per cent of .—Albumin Is soluble In the milk serum and Is lable by heating to 100°. It Is necessary, however, first "to neutralize part of the acetic acid. If this was to precipitate casein. D etemainatioii of Albumin.—Xeutralize the filtrate from the casein deter- mination (acetic acid method) with tenth-normal sodium hydroxido or potaussium hydroxide, using phenolphthalein, or use the filtrate from the alum precipitation of casein without neutralization. Add 0.3 cc of 1O—pier cent acetic acid and heat in a boiling-water bath until the5 precipit.*xf:-e becomes settled. Filter, wash with cold water and determine the nitrogen and albumin as in the casein determination, using the same factor. A comparison of the results obtained by various methods for determining milk proteins has been made by Spitzer,1 \vlio concluided that where speed and convenience are important tfa.e forra.a.1 titration is to be preferred. Ind. Acad. Sri., p. 173 (1915). 212 QUANTITATIVE AGRICULTURAL AXALrSIS Lactose.—This sugar is the only carbohydrate occurring in appreciable quantity in milk. It is not as sweet as cane sugar and it is not fermentable by yeast. It readily reduces Fehling's solution (a basic solution of copper sulphate and a tartrate), forming cuprous oxide (Cu20) and use is made of this fact in its quantitative determination. It is optically active and this affords another method for its quantitative determination. It is necessary to remove the proteins and fat from milk before the lactose can be determined by Fehling's solution. This is one of the objections to this method but if the milk can thus be made reasonably free from other reducing agents the method is capable of yielding fairly accurate results. If the cuprous oxide formed were to be weighed directly there would be an error due to inclusion of organic impurities in the precipitate. This error can be lessened by heating the cuprous oxide in a muffle furnace for 20 minutes to a dull redness. This converts the cuprous oxide to cupric oxide (CuO), which can. be weighed free from organic impurities, the per cent of sugar being then calculated. A better way, however, is to dissolve the' cuprous oxide from the filter with dilute nitric acid and to determine the copper electrolytically or volumetrically. All of these methods are discussed in connection with feed analysis, pages 157 and 158. Determination of Lactose: Reduction Method.—Pipette 25 cc of well mked milk into a 500-cc volumetric flask. Add 350 cc of water, 10 cc of Fehling's copper sulphate solution (page 158) and 44 cc of tenth-normal sodium hydroxide or an equivalent volume of a solution of any other nor- mality. Colloidal cupric hydroxide flocculates, carrying down fat and pro- teins. Copper will be present in very slight excess. Make the volume up to 500 cc and mix thoroughly. Although the apparent volume occupied by the precipitate is considerable, its actual volume is relatively small and an approximate correction is made as noted below. Filter through a dry filter and use 50-cc portions in making the lactose determination. It is necessary to follow directions carefully as the reactions taking place are modified by variation in time of heating or in the concentrations of the solutions. Into a 400-cc Pyrex beaker, pipette 50 cc of the clarified milk serum and 25 cc each of the two Fehling's solutions prepared as described on page 158. Heat at such a rate that the boiling begins in about 4 minutes and continues for exactly 2 minutes. Keep the beaker covered, while heating. Filter off the cuprous oxide through a Gooch crucible. Wash five or six times with hot water. Dissolve in a warm mixture of 2 cc of concentrated nitric acid DAIRY and 2 cc of water, wash the solution through with hot water and determine copper by any of the methods In £et\i analysis? described on pages 159 to 16:1 Optical Methods.—The ability of carbohydrates containing one or more asymmetric atoms to rotate the plane of polarization of polarized affords the basis for an Important method for determination. The proteins of milk are slightly optically active, hence they must be removed before ^se can be determined. subject of polarimetry Is discussed on 121 to 137, Part II. This should be reread before starting the determination of lactose. The instrument de- signed especially for sugar determinations is called a saccharimeter. Its graduations read directly in per cent of sugar when a definite specified weight ft he "normal weight)" Is contained In 100 cc when the polarization Is made in a 200-min tube. The following determination is based upon the use of an instrument bearing the International scale. (See page 130, et seq.) ^Protein Precipitation.—By treatment of milk with a^n acid solution of mercuric Iodide the proteins are combined with the mercury and flocculation results. If the solution is then diluted to a definite volume without previous filtration the solids present cause a volume error unless a correction is applied. It has boon, found that a close approximation may be made "by deducting 2.6 cc for the volume of precipitate obtained from, the sample as specified below, the dilution being accomplished in a flask graduated to contain 102.6 cc. If a flask graduated in this manner Is not at hand, prepare one as follows: Fill a 100-cc volumetric flask exactly to the mark with distilled water. From a burette add 2.6 cc more and mark the position of the bottom of the meniscus with a strip of label. Mark permanently, if desired, by the method described on 45, Part I. SSStt y m. 49.- determina- tion. 214 QUANTITATIVE AGRICULTURAL ANALYSIS A still more accurate method involves the double dilution, discussed on page 133. The normal weight for lactose, 32.90 gm (see page 131), is^too small a quantity of milk for convenient accurate determinations and it is customary to use twice this amount or 65.80 gm. In order that the sample of milk may be measured instead of weighed the following table may be used and a special pipette like Fig- 49 will be found convenient. TABLE XV.—VOLUME OF MILK FOR LACTOSE DETERMINATION_____ Volume of milk (cc) for a lactose Specific gravity of milk double normal weight (International scale) 1.024 64.26 1.025 64.20 1.026 64.13 1.027 64.07 1.028 64.01 1.029 63.94 1 . 030 63.88 1.031 63.82 1.032 63.76 1.033 63.70 1.034 63.64 1.035 63.58 1 . 036 63.51 Determination of Lactose.—Prepare acid mercuric iodide solution as follows: Dissolve 33.2 gm of potassium iodide, 13.5 gm of mercuric chloride and 20 cc of glacial acetic acid in 640 cc of water. Determine the specific gravity of milk by means of a sensitive hydrometer or a picnometer. Refer to the table and measure, at the temperature at which the specific gravity was taken, the quantity of milk indicated in the table above, the sample having been mixed thoroughly immediately before making both measurements. The milk is run into a volumetric flask, graduated at 102.6 cc. Add 30 cc of acid mercuric iodide solution, dilute to the mark on the flask, mix well and allow the precipitate to settle. Filter through a dry filter, rejecting the first 25 cc of the filtrate and receiving the remainder in a dry flask. Polarize in a 200-mm tube, having the solution at a temperature of 20°. The reading on the sugar scale is to be divided by two lM-,.,t.lM ,rtlll Mi, ;.,„ ' it^- * . the t>0r ,M,Jit v f ja, )4§M, i!fc t; „ Ir| ^ Examination of - 1 in the >izt4 *>*' fat uloj'il*- .1. * Of the same hivpti or • f htf^.i * • betweon Jersey and Hollar ai.Lna,-. VN»' Hkoelifl^ the size and grouping of fa J/ »**;'* - F were made by Woll' cu the 21:^1! er UL 1 M " ...* modified by the period of !aota*5o!i. un Is 1HS, at !*• » ^* P.;T;II » j period, and at its end b67. Tin u\ trace "r. !i (per c*ent of fat divided by the rumUr ^ f ^1 cmrn.) of fat globules was found to Iv 290, 217 Jersey, Guernsey and Shorthorn, respectively. 17" of Number of Fat Globules ™D" f 1 of froslh. milk to 500 cc and mix well. Prepare M\ tip ' i ' 0.1-m.ncx inside diameter by heating 5-mm t iMriK ^ i ^ 4 ..' Cut Irrfco pieces about 3 cm long. Dip tht t1 d >*' »M i a the diluLted milk (recently mixed) and wfae i fJ id- i ' tubes t»y dipping them into vaseline. Place 01r f *!" • upon -w filch lias been placed a drop of glycurir** aic< d'tt^ inside diameter by placing it in the field of a Ji^n^enr micro xxx eter eye piece having 0.01-rnm divlsini^. Afff « makio a, count of the number of fat globules contained i»,1 -r equivalent to 20 or 30 divisions of the so *!«•. Repe it t n and coxint, using another capillary tube. Fr< ni th*» d^ 21 and *klio length of the section in which tht count \\a-s r\ nunalxer of fat globules in 1 cubic millimettr of urtHatu1 forna of the fat globules in this and in a port'oi, i f t^t ~w'i «» xt ^T i .• ized a-t 140° F. In. -the experiment just described, the function ot the civ,; is to eover the capillary tube with a fluid medium haviiu i^ the sa,me index of refraction as that of the gla#^, thu^ av ^* I the m.agn.ifying effect of the curvature of the tulu, a- wtL prevonting the apparent distortion of form of fat glo»n.li. Foxnoaaidehyde Is very efficient as a preservative a*vl \v] presort in so small an amount as 1 part in it will extend the t>irne of milk preservation at least 24 hours at 15° '•£». Exp. Std. Ann. Rep. II (1894). N *:IA L»rlv 216 QUANTITATIVE AGRICULTURAL ANALYSIS in commercial milk is usually forbidden, as is that of most other preservatives. Test for Formaldehyde.—In a porcelain dish mix 5 cc of milk with 10 cc of concentrated hydrochloric acid, containing 0.2 gm of ferric chloride per liter. Heat cautiously nearly to boiling and keep near the boiling point for 1 minute. A violet color indicates the presence of formaldehyde. Test for Berates.—Make 25 cc of milk slightly basic with lime water and evaporate to dryness in a porcelain dish over the steam bath. Char the residue in the dish and when cool add 15 cc of hot water, then boil. Add hydrochloric acid drop by drop until neutral to litmus, then add an excess of about ten drops. Filter and evaporate to dryness on a steam bath. Immerse turmeric paper in the solution while the evaporation is taking place. If borax or boric acid is present, the turmeric paper will turn cherry red when dry and it will change to a bluish green when moistened with ammonium hydroxide. Cane Sugar.—Cane sugar is occasionally present in milk which has been thickened with calcium saccharate or which has been mixed with sweetened condensed milk. Test for Cane Sugar.—Mix 10 cc of milk in a test-tube with 0.5 gm of ammonium molybdate and 10 cc of 3-per cent hydrochloric acid. Make a blank test using milk of known purity. Place the tubes in a water bath and gradually raise the temperature to 80°. A blue color will develop in normal milk but if sucrose is present the milk remains unchanged in color. The test is quite delicate as even 1 gm in a liter may be detected by the reaction. Heated Milk.—One method for the detection of heated milk is based upon the presence in raw milk of an enzyme which, in the presence of hydrogen peroxide, is capable of producing color changes with certain organic substances, the enzyme probably acting as a catalyzer. Bacteria in normal fresh milk will change methylene blue to a colorless compound in about 20 minutes. But when milk has been heated these bacteria are present in greatly diminished numbers and are no longer capable of decolorizing the solution. This furnishes another test for heated milk, since by this reaction one may detect milk which has been pasteurized at 65° and held at that temperature for 30 minutes, or at 70° for 10 minutes. Test for Heated Milk.—(a) To 10 cc of milk add about three drops of a freshly prepared 2-per cent solution of £>-phenylenediamine hydrochloride and a few drops of hydrogen peroxide. Shake well. Milk which has not been heated will give a blue color. DAIRY PRODUCTS 217 (6) Prepare a test solution of methylene blue by mixing 5 cc of saturated alcoholic solution with 5 cc of 40-per cent formaldehyde and 190 cc of water. Add 1 cc of this solution to 20 cc of milk in a test-tube, and place the tube in a water bath at 45°. Cover the liquid with a layer of paraffine oil to exclude the air. Repeat the test on a heated sample of milk. It will take about 20 minutes for the unheated milk to decolorize while the heated sample will require considerably more time. Condensed Milk.—" Condensed " milk is made by evaporating either whole or skimmed milk under reduced pressure and adding cane sugar. " Evaporated" milk does not contain cane sugar. The Federal standard provides that in evaporated milk there shall be not less than 34.3 per cent solids, including fat, that the fat content must be at least 7.8 per cent and that it must not be made up to this minimum by adding butter oil.1 The composi- tion of three commercial brands of evaporated milk is given in the following table:2 TABLE XVI.—COMPOSITION OF EVAPORATED MILK 1 Sample Water Fat Lactose Protein Ash 1 70.75 9.42 9.75 8.44 1.54 2 70.90 8.35 10.37 7.86 1.62 3 72.11 8.69 9.66 7.52 1.54 1 The methods of analysis of condensed and evaporated milk are similar to those described for raw milk, except in the determination of cane sugar and of lactose. Preparation of Sample: (a) Unsweetened.—Dilute 40 gm of the homo- geneous sample with 60 gm of water and make the mixture uniform by pouring from one beaker to another. (6) Sweetened.—If the can is cold, place it in water at about 35° until the temperature of the contents becomes uniform. Open, scrape out all the milk adhering to the interior of the can and mix by transferring the contents to a dish sufficiently large to permit stirring thoroughly to make the whole mass homogeneous. Weigh 100 gm into a 500-cc volumetric flask and, make up to the mark with water. If the milk will not dissolve completely, weigh out each portion for analysis separately. lFood Insp. Decision, 131 (1911). *Ind. Exp. Sta. Bull, 134 (1909). I I ii 218 QUANTITATIVE AGRICULTURAL ANALYSIS Determination of Total Solids.—Use 10 cc of the solution just prepared and dry as directed on page 204, drying on either sand or asbestos fiber. Determination of Ash.—Evaporate 10 cc of the solution to dryness in a platinum or porcelain dish on the water bath and ignite the residue as directed on page 204. Determination of Protein.—Determine the nitrogen in 10 cc of the solution using the Kjeldahl method as described on page 151 and multiply by 6.38 to obtain the equivalent of protein. Determination of Fat.—Weigh 4 to 5 gm of the homogeneous sample into a Eohrig tube or similar apparatus, dilute with water to about 10.5 cc and proceed as directed on page 205. Determination of Sucrose in Sweetened Condensed Milk.—Prepare a reagent for clarification as follows: To 220 gm of yellow mercuric oxide add 400 cc of water and sufficient concentrated nitric acid to form a clear solution, being careful to avoid an excess. Dilute to about 900 cc and add sodium hydroxide solution, slowly and with constant shaking, until a slight permanent precipitate is obtained. Dilute to 1000 cc and filter. The solution will become acid in time, due to hydrolysis and precipitation of basic mercuric nitrate. Dilute base solution may be added to correct this. Introduce 50 cc of the milk solution already prepared into a 100-cc volumetric flask, add 25 cc of water, mix, add 5 cc of mercuric nitrate solu- tion arid shake. Without delay, and while stirring constantly, add enough of a 2-per cent sodium hydroxide solution to render the solution neutral to litmus paper, being careful to avoid a basic reaction. Dilute to the mark on the flask, mix thoroughly and filter through a dry paper, discarding the first 10 cc of filtrate. Polarize the filtrate in a 200-mm tube at 20°, then invert as follows: Pipette 50 cc of the filtrate into a 100-cc volumetric flask and add 5 cc of concentrated hydrochloric acid, slowly and mixing well. Set the flask aside for 24 hours at a temperature of 20° to 25°. Polarize the solution of invert sugar in a 200-mm tube at 20° and multiply the reading by two, to correct for the dilution. Correct both direct and invert readings for the volumes occupied by the precipitated protein and fat at the time dilution was made, using the per cents of these substances as already determined and assuming a volume of 0.8 cc and 1.075 cc, for 1 gm of protein and fat, respectively. The volumes of these substances will be: „ _10(0.8P + 1.075F) 3^1^12 = o.08 P + 0.1075F, 100 and the corrected readings on the saccharimeter: /100 - V \ 100 where V = volume, of protein and fat precipitate, P = per cent of protein, R /100-0.08P-0.1075F\ I __ _____________I rp \ 100 r (2) it Ml DAIRY PRODUCTS 219 F * per cent of fat, R = corrected reading and r = observed reading. Ten grams is the weight of the original undiluted sample in the solution as finally used for polarization. Calculate the per cent of sucrose by Clerget's formula, developed on page 132, Part II. Taking account of the fact that less than the normal weight of milk sample was used this formula becomes: 27600(a-16) ~ S = per cent of sucrose in the sample, a = corrected direct polarization, " b = corrected invert polarization, t — temperature of solution polarized (20°), w = weight of sample taken (in this case 10 gm). Determination of Lactose. — On account of the presence of sucrose in condensed milk, the lactose cannot be determined directly by polarization. The copper reduction method is suitable for this purpose, as sucrose does not reduce Fehling's solution. Measure 100 cc of the milk solution already prepared into a 250-cc volu- metric flask and dilute to about 200 cc. Add 6 cc of Fehling's copper sul- phate solution (see page 158) and make up to the mark. Mix well, filter through a dry filter and determine lactose as directed on page 212. Powdered Milk. — The rapid progress made in recent years in producing a high grade of powdered milk has greatly stimulated its use by bakers and confectioners. It also is used in ice cream to give body and smoothness to the product. The spray process now used in its manufacture probably owes its success to the comparatively low temperature at which evaporation and con- densation take place. Milk or evaporated milk is dried by forcing a fine spray into a current of warm air, thus causing the milk particles to remain in suspension long enough to lose most of their water before depositing on the sides of the container. For the analysis, dissolve 10 gm in water, dilute to 100 cc, mix well and proceed as outlined for condensed milk. To determine moisture, dry about 2 gm to constant weight at 100° and calculate the per cent loss. CREAM Commercial cream must contain not less than 18 per cent of fat according to the Federal standard. The following table gives some figures on the composition of a typical milk, cream and 220 QUANTITATIVE AGRICULTURAL ANALYSIS skim milk, the latter obtained by separating the cream with a centrifugal separator. TABLE XVII.—COMPARATIVE COMPOSITIONS OF MILK, CREAM AND SKIM MILK Fat Ash Casein Lactose Total solids Specific gravity Milk ...... 5.0 0.79 3.50 4.70 14.0 1.032 Cream ....... 21.9 0.58 2.02 3.32 27.0 1,015 Skim milk 0 2 0 78 3.62 5.05 9 6 1 034 Fat.—The Babcock bottle used for testing milk is not suitable for cream on account of the higher proportion of fat. If the cream were 25 per cent fat, 18 gm would contain 4.5 gm of pure fat. Assuming 0.9 as the average specific gravity of butter fat, it will be seen that 5 cc of space would be required for the fat. Various forms of bottles are used for this purpose, one of which is shown in Fig. 48. Either 9 or 18 gm of cream is weighed into the counterpoised test bottles. Fat is determined by the Babeock" method as used for rnilk, described on page 208; with the exception of the method for reading the position of the upper end of the fat column. First determine the value of the upper meniscus (in per cent) between the extreme upper and lower points of the curve. Add one-third of this value to the reading of the lowest part of the curve and consider this the final reading.1 The fat column may be read more easily by adding a light mineral oil which has been colored red with a vegetable pigment. There are several such preparations on the market under trade names such as "glymol," "alboline77 and "red top/7 The use of a colored mineral oil was suggested after extensive investigation of various compounds.2 If such an oil has practically the same surface tension as that of melted butterfat the surface divid- ing the two liquids is approximately plane. While the use of such a device for making easier readings has become quite 1 HUNZIKER, Ind. Exp. Sta. Bull, 146 (1910). . *Ibid. DAIRY PRODUCTS 221 extensive there seems to be some evidence to the effect that lower readings are obtained in this way. Total solids, ash, total nitrogen and lactose are determined as with whole milk. A somewhat smaller sample (2 to 3 gm) is used for the total solids determination. The gravimetric method for lactose is preferred. ICE CREAM ;jpl 3H.61 — . St(^ari(*, ( ' 1 7 II ,-uX '( X ) II 1 ill 1 . H3 Ohtic, CnlWOOH....,, 3395 32 . 50 «. DihydroxyHtoaric, Ci7HM(blI)2(!OOH.... 1,04 UK) — Total . . ..... , . ..... 100 00 94 75 * Solubility is at 15", KI von in approxiru ate* ti'rrns. Butter Substitutes. •/I'lhc oleoniargariiic^ of c.onnucrcc is usually coia|>os(kcl of rdined oloin of h<*//«......- Prepare an alcoholic solution of the oil-aoluhle dye by one of the following methods, which is to be applied to the oil or fat obtained by extraction with ether or gasoline. (a) Shake the oil or melted fat with an equal volume* of !M)-per cent alcohol. The alcohol after separation will contain aniline yellow, "butter yellow," arninoaxotoluem; and aurainim*, or such of thiw us may be* present. (/;) Dilute 20 to 200 grn (according to the in tensity of color I of the* oil or melted fat with two volumes of gasoline and shake out suwHsively with 4-percent potassium or .sodium hydroxide solution „ I5-|«»r cimt hydrochlork acid, and phosphoric-sulphuric acid mixture, prepared by mixing Hf*-per cent phosphoric acid with about 20 jwr cent by vcihuuu of concentrated sul- phuric acid. The dilute bases extracts Sudan 0 End nnnatto. The* dilute hydrochloric acid extracts aniline yellow, ainimttuotolumw finrl *'btitt«*r yellow/* the first two forming orange-red, tht latter cherry-red solutions in thin HO!vent. The phosphoric acid mixture w necwwary for th«» extraction of Hudan I, Sudan II, Sudan III and Sudan IV. Brnrnwuxo-ii-rmphthylafttin and hornologues also come in thin group, though they readily undergo chemical changes in the strongly acrid mixtures. The* procedure is not very suitable in the presence of aurarnine but this dyi* in si'ldoiti found in oils. Neutralixcj the alkaline and dilute* hydrochloric acid «»Iiitioii«, Dilute the phosphoric acid mixture and partially mmtniiizt*, cooling thi* liquid during the operation. Extract the dyes from the neutral solution** by shaking with ether or ganoline. For the direct dyeing tent tuK* thi! alcoholic* ftolution obtainrtd in (a). Evaporate to dryncaw the* ether or grutoltni) noiutionff, obtained an directed in (M, and dissolve the residue in 10 to 20 cc of 9«Vprr ccmt alcohoL To the alcoholic solution add some strandn of white Milk and n little water and DAIRY PRODUCTS 229 evaporate on the steam bath until the alcohol has been removed or until the dye is taken up by the silk. The dyeing test is sometimes unsatisfactory, and in all cases a small portion of the alcoholic solution should be tested by treating with an equal volume of hydrochloric acid or stannous chloride solution. The common oil-soluble coal-tar dyes are rendered more red or blue by the acid and are decolorized by the reducing agent. Most of the natural coloring matters become slightly paler with the acid and are little changed by the stannous chloride solution. (2) Annatto Coloring Matter.—Pour on a moistened filter a basic solution of the color obtained by shaking out the oil or melted and filtered fat with warm, dilute sodium hydroxide solution. If annatto is present the filter paper will absorb the color so that when washed with a gentle stream of water it will remain dyed a straw color. Dry the filter and add a drop of stannous chloride solution. If the color changes to pink the presence of annatto is confirmed. CHAPTER XII SOUS A soil analysis is made to find out the extent and distribution of plant food elements aad thus to determine which elements are the limiting factors in crop production. The term " soil fertility " is often used to express this relation and this is understood to mean the crop producing power of any soil under specified climatic conditions. "Fertility'7 is really an Indefinite term as the property indicated is the resultant of many forces which are frequently opposed to each other in their action. Total and Acid-soluble Material.—The analysis of soils with a view to measuring their fertility and studying their geological origin has received much attention in recent years. It -was formerly thought, and it is still held to some extent, that the fertility can best be measured by extracting the soils with strong acids, thus obtaining an invoice of the total plant food con- tained. But by this method there is left some available potas- sium and a mass of substances of unknown composition, which yet need to be determined in order to have complete information concerning the geological origin of the soil. On this account the value of many early analyses is being called into question and at present it is regarded as desirable that the total constitu- ents of the soil should be determined. The complete examina- tion of a soil involves its study, from chemical, physical and biological points of view. The chemical phases of this subject will be given most attention here. Soil Constituents.—Soil has been defined as that portion of the earth's surface, climatic conditions being favorable, which makes possible complete growth and development of plants. Ordinarily soils are made up of mixtures of organic matter, rock at various stages of disintegration, water, gases and bacteria. The great mass of this material is not directly essential to the growth of plants but aids in holding moisture and making a medium in which the roots may anchor themselves. 230 2:u Classification of Pfant Food Elements in the Soil.—Thr plant- food elements of the soil occur principally as follows: 1. Nitrogen is found in soils as a constituent of organic matter, nitrates, a*xxruouium salts and aniino acids. 2. Phosphorus js present jn organic forms or combined with calcium, iron or aluminium as phosphate. 3. Potassium js widely distributed in all soils of granitic origin. It is combined with silica as silicates in granite, ortho- clase and trxica. 4. Calciuxn is found as carbonate and silicate, as sulphate In gypsum, as a constituent of rock phosphate and in organic forms. 5. Sulphur occurs combined with calcium as gypsum. It Is quite deficient in some soils. 6. Iron and manganese are found as oxides and silicates. 7. Magnesium is associated with calcium as dolomitic stone, also as silicates. Aluminiuioti, sodium and silicon are probably non-essential to plant growtli. Value of Soil Analysis.-—There has been much concerning -fclie adequacy of soil analysis as a means of soil fertility. Many writers confuse the narrow purpose of simply deterj^mining the plant food immediately available with the broader one of obtaining an extensive knowledge of the plant food supply and a determination of the possible origin of the soil in order to plan better for permanent improve- ment. The "value of the analysis is expressed by Hopkins1 as follows: "The chief "value of a chemical analysis is to serve as an absolute foundation upon which methods of soil treatment can safely be for the adoption of a system of permanent soil enrichment, not for crop or for one year only but for progressive improvement/" . The Ohio Station has shown2 how accurately the excesses : ftp] deficiencies may be measured by analysis when good and poor : ||| methods of sericulture have been practiced for a period of fifteen ||] years. Thore is no other tool which compares with it for |. ] purpose and as an aid in unlocking soil secrets. The value of I ! 1 "Soil Fertility and Permanent Agriculture," p. 568. ml \ 2 Ohio Exp~ are at band to aid in such an interpretation. Soil Classification Based upon Mode of Formation.—For con- venience in the study of soils they may be divided according to manner of formation into eight groups1 as follows: Cumulose soils are chiefly deposits of vegetation in various stages of decay. Residual soils—unmoved from the rocks from, which they were formed. Lo^ss—residue deposited as dust carried by wind. Glacial soils are deposits which have developed from glacial action. Cdluvial soils are deposits which ha~ve been moved down hill by gravity. Alluvial soils consist of residues deposited from flowing water. Marine soils are formed by deposits carried Into seas. Lacustrine soils are formed by deposits carried into lakes. Classification Based upon Composition.—It is to be expected that soils whose origin is so different as is noted above would vary greatly in chemical analysis. Ames has made a study (unpublished work) of the relation between soil "type and compo- sition, considering at the same time the geological formation. The chief differences observed were with respect to the calcium carbonate, total organic matter and nitrogen content. For example the soils of limestone origin, as compared with, those from sandstone and shales, contained larger amounts of calcium, and magnesium. In many cases these larger amounts of calcium and magnesium are accompanied by larger amounts of phos- phorus, organic matter and nitrogen. It is evident that if only disintegrating forces had been active the soil pairticles would be of the same general composition as the original rock. However, many agencies tend to change this original material until only the most resistant minerals remain.2 The Report.—Determinations of the inorganic constituents of soil are usually reported in terms of their most stable compounds or of their oxides although nitrogen is reported astho element. The determination is usually made on an air-dried sample. Besides reporting results as per cents on this basis it is sometimes desir- able to report the amount per acre (2,000,000 Ib. is considered as ITROWBRIDGE, /. GeoL, 22, 420 (1911). 2 See also A7. C. Exp. Sta. Tech. Bull., 9 (1914). the approximate weight of a soil 6^i In, over an aere | of land, while 1,000,000 Ib. is as the of a | muck soil over the same area). * Analytical Methods.—The methods for studying th*.1 $^ soil may be considered under the : |,' (a) Complete analysis. | , (6) Potential plant | (c) Available food. ^ Complete Analysis.—The inorganic is ^ by fusing the soil with alkali carbonates, the ||; forming alkali silicates which can be in fe' acid. From this solution the total constituents, i the exception of carbon dioxide, sulphur, \ may be determined. The latter group, as well as | nitrogen, phosphorus, and organic matter, are In / separate samples. ! Potential Plant Food.—This is by the ,/ soil in hydrochloric acid of constant (specific gravity 1.115, containing about 23 per of HC1), the ratio of 1 part of soil to 10 of acid, thus the or partial decomposition of soil minerals. This formerly the official method. Available Plant Food.—This is the part of the supply which is immediately available to plants. There are many ' f natural agencies tending to make plant food as > bacterial action, plant decay and root acidity, it is /' to determine the part played by any one, especially by I » acids. After making an extensive study of the acidity of £f \ plant roots it was suggested by Dyer in 1894 solubility in a J , 1-per cent solution of citric acid most nearly measured the t * availability, as indicated by the ability of to |;// absorb material from the soil. Various other solvents have £, [ tried, such as distilled water, carbonated distilled K' acid, aspartic acid and fifth-normal hydrochloric nitric acids. ^ The latter seems to give more consistent results on many soils fj than does citric acid. However, all lalx>ratory results obtained |'^! by the use of weak solvents are only approximations to the action |j i. of natural solvents in the soil 1 234 QUANTITATIVE AGE/CULTURAL Choosing Samples.—In choosing soil samples it is very important to secure representative ones. The sampling should be done when th.e ground. is dry enough to plow. An area should be selected such that the soil is typical with respect to texture and color. Note should be made of any available information concerning the geology of the area, original timber of the land, the present productivity, or any peculiarities in location which may aid in interpreting its analysis. The surface accumulations of such. materials as decaying grass should be removed and the borings for samples then made with a soil auger or other soil tube. Composite samples are taken from different depths as follows: (a) surface to 6 in., (&) 6 to 2O in., (c) 20 to 40 in. For each depth ten to fifteen borings are taken and well mixed. About a pint of soil from each depth should finally be preserved. Sample (c) need not be mixed with as great care as are samples (a) and (b) since it is not usually taken for analytical purposes but for obtaining some insight into the physical nature of the subsoil, drought resistance and drainage depending to some extent upon the nature of substrata. The borings are placed in. clean cloth sacks in the field and immediately sent to the laboratory. Here they are dried and later ground for analysis. Preparation of Samples.—Spread the samples on paper or in shallow pans in a dry place, in clean air, and allow to remain until apparently dry. Pul- verize lumps and divide each sample into two fractions by use of a 4-mesh sieve. The stone remaining in the sieve is weighed and its per cent of the total is calculated. Grind the finer soil portion in a porcelain pebble mill or other pulverizer until it will pass a 40-mesh sieve. Mix fhoroughly and then grind about 100 gm of this sample until it will pass a 100-mesh sieve. Riffles of different sizes may be used for .sampling, or rolling on paper or oilcloth may be employed. (See the discussion of sampling, Part I, pages 17 to 22.) The samples should be placed in stoppered bottles and carefully labeled. Moisture.—The proportion of moisture in air-dried soil depends largely upon the proportion of organic matter. The water-holding power of soil is of great significance from a, prac- tical standpoint. Determination of Moisture.—Weigh accurately 5 gm of finely pulverized 100-mesh soil into a flat porcelain crucible about 4 cm in diaraeter and pro- Tided witli a glass cover. Remove the cover and dry the sample at 110° for five hours. Cover and cool the crucible in a desiccator and then ^weigh. Preserve the dried sample for the determination of volatile matter. Calcu- late the per cent of moisture in the prepared soil. Optimum Moisture of Soils.—The water-holding capacity of a soil depends upon its content of organic matter and its structure. The amount of water which just permits a soil to crumble is considered the optimum. This is about one-third of its total water-holding capacity. If SOILS 235 1f Approximate Determination of Optimum Moisture Content of Soils.— Weigh three 25-gm portions of the 40-mesh air-dried soil and place them in 200-cc beakers or wide-mouth bottles. Add to the three portions, 5, 6 and 7 cc of water, respectively. Cover the bottles with watch glasses and allow to stand for two days. Remove the soil and see if any sample is wet {;» t M enough to form balls. If not, repeat the experiment with modified quantities 11 j of water. The optimum moisture should be just a little less than this j j! j' amount. jl^jlfi 4 l!i*; Total Nitrogen.—The relative amount of nitrogen in soils ;ij«j varies greatly, although it is usually approximately in proportion bj * j to the organic matter. A soil in Manitoba is reported to contain fl,) as high as 20,100 Ib. per acre (1.005 per cent) while a sample jljij from the " Jack Pine" plains of Michigan is said to contain only }jj \ I jjjl 740 Ib. per acre of 2,000,000 Ib. (0.0037 per cent) of soil (4| jf j | Nitrogen is one of the most important of all elements in the soil. It is absolutely essential to plant existence and it cannot be taken from the abundant supply of the air by the plant itself. Certain forms of soil bacteria cause the fixation of this elementary nitrogen in the form of nitrates, which can then be utilized by the plant. The chief purpose of nitrogen in plant t^\ j economy is to provide for the construction of protein by the ,*j' plant. The deep green color of plant leaves is often an indica- ;'j tion of an abundance of available nitrogen. ,jn ill Determination of Total Nitrogen.—Place 10 gm (5 gm if a muck soil) f ] of 40-mesh soil and 30 cc of concentrated sulphuric acid in a 500-cc Kjeldahl jf flask. Proceed as described on page 151, and following. Calculate the «Jj s per cent of nitrogen. 1 f*» 1 J,| (> Nitrate Nitrogen.—The amount of nitrate nitrogen present in jjjj a soil depends mainly upon the amount and kind of vegetation, ||| and upon the degree of compactness, the temperature and the f J water content of the soil. The most favorable temperature seems to be about 35° and the most favorable water content is one-third of its saturation. These factors largely determine whether or not a soil is suitable for bacterial development. gH| The amount of nitrate present in a soil at any one time is &** seldom very large, ranging from zero to 1000 Ib. per acre (0.05 per cent). It is difficult to find more than a trace of nitrate sij nitrogen in soil just under an old sod whereas in some western *' ! i If 236 QL'A\TITAT1\'E AGRICULTURAL soils nitrates have accumulated in such, amounts as to interfere with plant growth.1 The plienoldisulphoiiic acid method is used for the deter- mination of nitrates, the following equations representing the reactions : 2KNOS -» 2HNOa + K2SO4; (1) ; (2) C6H3OH(S03H)2 + HNOs-> kQH2OH-N02(SO3H)2 -h Pbcnoldisulphonic acid A * Nitrophenoldisulplionic acid C6H2OH-N02(S03H)2 4- 3NH4OH->C6HsONH4(S + 3H20. (3) The ammonium salt of nitrophenoldisulphonic acid, thus formed, is intensely yellow and the color so produced is compared with that formed from a standard nitrate solution. FIG. 51.—Mixing machine. Determination of ITitrate Nitrogen.—Prepare the following reagents: (a) Phenoldisulphonic Add.—Mix 30 gm of pure crystallized phenol with 370 gm of concentrated sulphuric acid. Immerse the flask in boiling water for six hours. When cool store in an amber colored battle. A smaller quantity of the solution may be made, if desired. (b) Standard Color Solution,.—Prepare a standard solution .of potassium nitrate by dissolving 0.7215 gm of dried pure potassium nitrate in distilled water and diluting to 1 liter. Each cubic centimeter of this solution will contain 0.1 mg of nitrogen. Pipette 10 cc of this solution, into a dish and evaporate to dryness over a steam bath. Cool and moisten the dry nitrate with 2 cc of phenoldisulphonic acid, rubbing together with a glass rod, 1 Colo. Exp. Star. BitlL, 178 SOILS mrtri » -i a df| , },'M|?; • !| il !(l :ii ff! Ms 8! fl f FIG. 52.—Schreiner color comparator. 238 QUANTITATIVE AGRICULTURAL ANALYSIS After 5 minutes dissolve and dilute to 1000 cc in a volumetric flask. This makes a permanent color standard, 1 cc of which will contain 0.001 ing of nitrate nitrogen. Place two 100-gm samples of 40-mesh soil and 5 grn of calcium hydroxide (to aid in securing a clear solution) in salt mouth or shaker bottles and add 400 cc of nitrate-free distilled water (tested as below) to each bottle. Mix in a machine for 30 minutes and then remove the bottles and let stand over night. Pipette 10 cc or more of the clear, supernatant solution into a 8-cm porcelain evaporating dish and evaporate to dryness on a steam bath. Remove from the steam bath as soon as dry, cool, add 2 cc of phenoldi- sulphonic acid and mix well with the aid of a glass rod. After the acid has stood in contact with the residue for 15 minutes add 5 cc of cold dis- tilled water, stir and add enough ammonium, hydroxide (1 to 1) to produce a permanent yellow color. The standard (a suitable measured quantity of which has been made basic with ammonium hydroxide in the same mariner as the unknown) is rinsed into a cylinder for a colorimeter, such as that illus- trated in Fig. 52, and diluted to the 100-mm mark. Rinse the unknown into another tube and dilute to the 100-mm line, provided that the color of this solution is not over two-thirds as intense as that of the standard. Place both tubes in the colorimeter and move the tube containing the more intense color up or down until the intensities of color in the two are equal. The nitrogen concentrations are inversely as the lengths of column equiva- lent in intensity of color. Take three readings on each sample and from these calculate the per cent of nitrate nitrogen in the sample. Ammonia.—The amount of ammonia nitrogen in soils is usually very small, although in certain, swamps it is present in considerable quantities as ammonium, salts. Such plants as rice, which grow in water, secure considerable nitrogen in the form of ammonia or of nitrogenous organic decomposition products- Among these compounds are amino acids, e.g., arginine and glycocoll. The chemistry of a possible mode of ammonia production from amino acids may be represented by the following equations: RCHNH2COOH + O2-» RCOOH -f CO2 + NH3; (1) • Amino acid Patty acid RCHNHsCOOH + H2O -» RCHOHCOOH + NH3. (2) Thus an arnino acid when oxidized or hydroli^ed produces ammonia as an end product. Determination of Ammonia.—Place 25-gm samples of soil, together with 5 gm of sodium carbonate, in aeration flasks (Fig. 53), add three drops of light hydrocarbon oil (to prevent frothing) and 1OO ec of boiled distilled water to each flask. Connect the flask with a wash bottle containing 25 cc of wuuja-jQjornial F iM '.T; < -i, i lO-percent sulphur/- if * \*> -*« gas, as slicMui. AI"-M*» M from the utration f! i-v • */ - end of methyl the* soil : j A I S / FI . : i -\> i. ,. lM , NitribBLcataan.—A prottuetivt H*H I-T t -it1 in whicfc the plant can fix ;^l! a-i«.I *:o:i ^ "by processes of solution ami diiLixvir i\ teeraio.g with living 01 gani*-!!^ whvb 5 ' diffiexilti to duplicate In the laboratory. B> food which otherwise might not l>c n-c %i •* i» plairfc. Two important organism* have ' called **nitrosococcus/* caiin^ cnldati^n o: and "tlic? other, **nitrohaet«r/* eaiiM*-*»jM nitrates, according to the following riatt.^i ^ 3C\ — ; i :a V *^ t T • I i »\i * »• ' "' i * ^ t* tl -H Mestsmiremeat of Jlitrificttioa —I rrparc 4^^ 4f if UP arpr-x.** fifth-noirmal solution of ammonium «alhhat* r. n &\)-r vi « . *t^ and adc3 0.3 gin of dipoto& nitrites and nitrates to the form of elementary nitrogen. This is usually brought about in a water-logged soil or in the presence of an excess of nitrogenous organic matter. The amount of released element- ary nitrogen may be measured and the bacterial activity noted. FIG. 54. Percolator. Demonstration of Denitrification.—In a 250-cc wide mouth flask or bottle place 20 gm of horse manure and add 100 cc of water containing 1 gm of potassium nitrate. Fill the bottle with water and close the mouth with a rubber stopper connected with a delivery tube. The tube is inserted into a 500-cc graduated cylinder wHich has been previously filled with a 5-per cent sodium hydroxide solution and inverted into a 1000-cc beaker containing about 300 cc of water. The method of assembling the apparatus is shown in Fig. 55. After standing 24 hours at about 35° a mixture of carbon dioxide and nitrogen will begin to be produced. The former will be absorbed by the sodium hydroxide while the latter will be caught in the cylinder and can be measured. Calculate the per cent of denitrification of the nitrate addecL Phosphorus.—Phosphorus is present in all soils, usually in small amounts, varying from 300 to 5000 Ib. per acre of 2,000,000 Ib. of soil (0.015 to 0.25 per cent). The plant demand for phosphorus is large, as crops remove from 5 to 30 .Ib. per acre ft H01LS 241 annually. It occurs in the soil chiefly as apatite (calcium fluoro- phosphate) and, to some extent, in organic forms. The most pronounced effect of phosphorus upon the plant is noted in the greatly increased development of lateral and fibrous roots. This feature is of much importance in clay soils, especially as it induces the formation of an extensive system of roots, thus enabling the plant more successfully to withstand drouth. A FIG. 55.—Denitrification apparatus. deficiency of phosphorus is often shown by late maturity of crops and, in the case of cereals, in the lack of good grain development. Before phosphorus in soil can be determined it is necessary to remove organic matter, oxidizing phosphorus so held to phos- phoric acid, and to bring the phosphorus of both organic and inorganic matter into solution. The methods now in use for this purpose are (a) oxidation of organic matter by heating with sodium peroxide, with subsequent solution of phosphates by hydrochloric acid, (6) a procedure similar to (a) but substituting magnesium nitrate for sodium peroxide, and (c) oxidation of organic matter and solution of phosphates by heating with 16 I 242 [• w h.'S> QUANTITATIVE AGRICULTURAL ANALYSIS concentrated sulphuric acid, with or without the addition of a catalyzer. From the solution produced by any of these methods phosphorus is precipitated with a molybdate solution as am- monium phosphomolybdate. The precipitate is either dissolved in standard base and the excess of the latter titrated, or it is dissolved in ammonium hydroxide and the phosphorus precipi- tated as magnesium ammonium phosphate, ignited to magnesium pyrophosphate and this weighed. The principles of these meth- ods are discussed in Part I, pages 88 and 91. Determination of Phosphorus.—Use one of the following methods for obtaining the phosphate solution: (a) Place 10 gm of sodium peroxide in an iron crucible, add 5 gm of the soil and mix thoroughly by means of a glass rod. If the soil contains only a small proportion of organic matter add 0.5 gm of starch and mix as before. The starch will hasten the action. Heat the mixture by applying the flame of a burner directly upon the surface of the charge and the sides of the crucible until the action starts. Cover the crucible until the action is over and continue heating at a temperature of dull redness for 15 minutes. The residue in the crucible should not be fused. Transfer the charge to a 250-ce beaker with about 150 cc of water; add hydrochloric acid until acid to methyl red and boil. Cool, rinse into a 250-cc volumetric flask, dilute to the mark and mix. If the action has taken place properly there should be no particles of undecomposed soil in the bottom of the flask, although the solution will usually be turbid from silicic acid. (6) Place 5 gm of soil in a 50-cc porcelain crucible and moisten with 5 cc of 50-per cent magnesium nitrate solution. • Evaporate to dryness on the steam bath and ignite at dull redness. Let the crucible cool and add 5 cc of water and 10 cc of concentrated hydrochloric acid, then cover and heat on the steam bath for two hours. Stir several times while digesting. Transfer the contents of the crucible to a 250-cc volumetric flask, cool to room temperature, dilute to the mark and mix well. (c) Place 5 gm of soil in a 500-cc Kjeldahl flask and digest with 30 cc of concentrated sulphuric acid and 0.5 gm of mercuric oxide until the carbona- ceous matter has been oxidized. Cool to room temperature (do not place the flask in cold water until it has cooled somewhat in air), then add 100 cc of water, 5 cc of concentrated hydrochloric acid and 2 cc of concentrated nitric acid. Boil for 5 minutes, cool, dilute to 250 cc in a volumetric flask and mix well. Filter the phosphate solution through a dry folded filter until the filtrate is no longer turbid. By means of a pipette or volumetric flask measure 100 cc of the clear solution and deliver into a 10-cm porcelain dish. Evapo- rate on the steam bath to dryness, take up with 5 cc of hydrochloric acid and an equal amount of water, filter to remove silica and wash. From this point proceed as directed in Part I, page 90, beginning with "Add ammonium SOILS 243 or its until a slight precipitate of hydroxides..........- - • ' . 02, beginning with "Add ammonium hydroxide uu^11 a sll«ht persists............." aJid Sodium.—Potassium is essential to plant |, a,nd it is present in most soils in sufficient ^mounts to |i plant needs, but only partly in an available form, it j j very gradually changed to soluble potassium carbonate by Ij of carbonic acid upon orthoclase, which is nearly insoluble g\ xxs not readily available to plants. Sandy soil often con- »| -Oiss than 0.1 per cent of acid-soluble potass!"U^*1* sandy j|J f rom O.I to 0.3 per cent, loams from 0.3 to 0.45 per cent jj clays 0.45 to 0.8 per cent. | functions notably in the photosynthesis and I of starch within the plant. Lack of starch- formation I ovement is one cause of shriveled and sterile grain. An- | effect of a lack of potassium is to make the plan-t less resis- I > disease. This may be said of a plant suffering from any jj ^ood deficiency but it seems to be especially ~fcrxie in the |l potassium. urn. is not of great importance in plant nutrition. It is d with delaying potassium starvation but i"fc will not y [prevent this condition. rrtethod generally used for decomposition of insoluble Is, preliminary to the determination of potassium and L, is the J. Lawrence Smith method. It is based upon sion. of calcium chloride (formed from calcium, carbonate xmonium chloride) upon complex silicates at temperatures n 800° and 900°. Sodium and potassium chlorides, . a,s silicate of calcium, are formed. The reaction taking 1 b>ei>ween orthoclase, calcium carbonate and ammonium e maay be represented as follows: l*O8 + 6CaCO3 + 2NH4C1->2KC1 + Al2O3-h 6CaSi03 + H20 + 2N"HC3 -f 6CO2. platinum crucible (Fig. 56) is preferable for -fche decom- f! \ • OL but an iron or nickel1 crucible of 50-cc capacity may be 11 ( S\zch base metal crucibles deteriorate rapidly when used nil . , J. Ind. Eng. Chem., 11, 1139 (1919).. 244 QUANTITATIVE AGRICULTURAL ANALYSIS In the solution of salts finally obtained potassium may be separated from sodium by the chlorplatinate or the perchlorate method or it may be precipitated as potassium sodium cobalti- nitrite and a volumetric method used for its determination. The accuracy of the various methods is in the order named, although the high cost of platinum is a great obstacle to the continued use of the chlorplatinate method and its re- covery from residues involves con- siderable expense and loss of metal in each operation. Chlorplatinate Method.—This con- sists in the precipitation of potassium chlorplatinate from an alcoholic solu- tion by chlorplatinic acid: 2KC1 + H2PtCl6 -> K2PtCl6 + 2HCL Sodium chlorplatinate is soluble in alcohol and this fact is used in its separation from potassium. Ammo- nium chlorplatinate, also, is only slightly soluble in alcohol. It is therefore necessary that ammonium salts be expelled by heating, before the „„ T _ „ . . ... reagent is added, and that the work be FIG. 56.—,T. L. Smith crucible. , . . . done in a room tree from ammonia. Decomposition of Soil Sample.—Grind in an agate mortar 0.5 gm of soil, accurately weighed, with 0.5 gm of ammonium chloride. When thoroughly mixed, add 4 gm of precipitated calcium carbonate and mix well by grinding. Place about 2 gm of calcium carbonate in the bottom of the crucible then add the ground mixture from the mortar and rinse the latter with about 0.5 gm of calcium carbonate. Brush the mortar well and add any traces of material to the charge in the crucible. Settle the mixture well by tapping gently, place the crucible in a hole in an asbestos board and heat in such a way that only the lower portion is reddened. After ammonia ceases to escape, turn on the full heat of the burner to all but the upper portion of the crucible and continue the heating for 45 minutes. The crucible should be red hot. The entire heating may be done more conveniently by placing the asbestos carrying the crucible over the top of a small electric furnace of crucible type, the lower portion of the crucible being in the furnace. The XOILti 245 temperature of the latter is gradually raised to 800-900°, as shown bv a pyrometer. After the crucible has been cooled transfer the contents to a 300-oc porcelain dish, add sufficient hot water to cover the semi-fused mass, heat to boiling and let stand until the whole mass is completely slaked. Some samples are difficult to slake, due usually to heating to too high a temperature or to the presence of too little calcium carbonate in the mixture. These require digesting for some time on a steam bath; or the solution and residue rnay be placed in a porcelain dish and ground gently with an agate pestle. Filter the solution containing the disintegrated mass, collecting the filtrate in a 400-cc Pyrex beaker. Macerate the residue in a mortar, rinse several times with boiling water and finally filter and wash with boiling water until about 350 cc of filtrate has been collected. To the filtrate add enough ammonium hydroxide to make basic, then ammonium carbonate to precipitate calcium. Heat to boiling then filter into a platinum dish, evaporate to dryness on the steam bath and heat to dull redness to expel most of the ammonium salts. Dissolve the residue in 5 cc of hot water. If any insoluble residue remains, repeat the addition of ammonium hydroxide and carbonate, filter through a small paper, wash the paper with hot water, add 1 cc of dilute hydrochloric acid to the filtrate and evaporate filtrate and washings in a platinum dish. Heat to dull redness for a short time to expel ammonium salts. This residue of potassium and sodium chlorides is ready for the determination of potassium. Determination of Potassium: CUorplatinate Method.—(To be performed in an atmosphere which is free from ammonia.) Dissolve the residue of potassium and sodium chlorides, obtained as above directed, in 50 ec of hot water and then add chlorplatinic acid (containing 10 per cent of platinum or 26.5 per cent of chlorplatinic acid crystals), using about 1 cc more than the theoretical amount, calculated upon the assumption that the chloride residue was all potassium chloride. Evaporate on the steam bath to a thick paste but not to dryness, cool and add 50 cc of 80-per cent alcohol, stir up the solid matter and allow to stand, covered, for 30 minutes. If the liquid is not visibly colored too little reagent has been used. In this case new samples should be taken and the quantity of chlorplatinic acid increased. Filter and wash the precipitate thoroughly with 80-per cent alcohol, washing several times after the washings pass through colorless. The wash bottle should be provided with ground-glass joints so that no rub- ber will come into contact with the alcohol. Remove the filtrate and washings, pouring these into the bottle provided for platinum waste residues^ and wash the precipitate again, thoroughly, with 80-per cent alcohol, using particular care in washing the upper part of the paper. Wash until only a faint turbidity is produced by the addition of a drop of silver nitrate solution to the last washings. Drain most of the alcohol from the paper (or see next paragraph), slip the latter out of the funnel and dry in the oven at 100°. Place a weighed porcelain crucible upon a piece of glazed paper, remove most of the precipi- tate to the crucible, brushing up any particles that may have fallen upon the ||| 246 QUANTITATIVE AGRICULTURAL ANALYSIS glazed paper, and then replace the paper in the funnel. Place the crucible under the funnel and dissolve the remainder of the precipitate in the smallest amount of nearly boiling water, allowing the solution to run into the crucible. Evaporate to dryness on the steam bath, carefully wipe the outside of the crucible with a clean towel and dry for 30 minutes at 105°. Weigh and calculate the per cent of potassium in the soil. Use of a Gooch or Alundum Crucible.—Proceed as above until ready to filter out the potassium chlorplatinate. Prepare two Gooch niters as directed on page 50, paying attention to the precautions suggested, and using strong suction in forming the asbestos felt; or wash alundum crucibles with hot water, using suction. Finally rinse the crucibles with alcohol, remove, wipe the outside and dry at 100° to 105° for 30 minutes or until the weight is constant. Weigh and replace in the holder. If Gooch crucibles were used, moisten the asbestos with one or two drops of alcohol before the suction pump is again turned on. Start the pump, then filter and wash the precipi- tate exactly as above directed. Remove the crucible, dry in the oven and weigh. Calculate potassium as before. Recovery of Platinum from Waste and Preparation of Chlorplatinic Acid.1—Place the waste solutions in an evaporating dish having a capacity of 2 liters for each 100 gm of platinum and evaporate until most of the water has been expelled. Make basic with sodium hydroxide and add, stirring, sodium formate, either solid or in concentrated solution. A quantity of sodium formate equal to about half the weight of platinum to be reduced will be required. If foaming occurs, add more sodium hydroxide. Heat on the steam bath for one hour, stirring occasionally, then acidify with hydrochloric acid (25-per cent solution) stirring during the addition of acid. Filter off the precipitated platinum on a soft paper, using suction. Wash twice with hot 2-per cent hydrochloric acid, then with hot water until free from acid. Separate the platinum from the paper, dry, ignite and weigh. Pour over the plabinum in a porcelain dish five times its weight of 25-per cent hydrochloric acid, heat on the steam bath and add slowly 50-per cent nitric acid until no more gas is evolved. About 1 cc of nitric acid will be required for each gram of platinum. After the platinum is in solution, add 10 cc of 25-per cent hydrochloric acid, evaporate to small volume and repeat this process twice. This reduces and eliminates nitric acid. Dilute with water and evaporate, two or three times, to expel hydrochloric acid. Finally dilute, cool and filter on a soft paper whose approximate weight is known. If the filtrate is not per- fectly clear, refilter. Wash the paper free from any platinum stain and if any appreciable residue remains on the paper, dry and weigh it on the filter. Correct the weight of platinum for this weight of carbon, or other residue, then make the solution to the desired concentration. For potassium determinations the solution should contain 10 per cent of the element platinum. 1 BELONG, Chem. Weekblad, 10, 833 (1914). *'» ,it r SO/LS .247 Perchlorate Method.--Potassium perchlorate is nearly insolu- Jj J ble in 97-per cent alcohol while sodium perchlorate is quite fj! 1 1 soluble. Potassium may be precipitated and separated from jj f * sodium by making use of this difference in solubility. A 60- (ft per cent solution of perchloric acid is generally used. This ' j/f solution does not deteriorate on standing and it is not dangerous 1f to handle, as is the pure acid. It is necessary to have the solu- I tion free from ammonium salts since ammonium perchlorate is » ^ . only slightly soluble in alcohol. i*1; Determination of Potassium: Perchlorate Method.1—The solution of jj ' j potassium and sodium salts, obtained by the Smith method (page 244) is ||^ ^ used for this determination. Evaporate to about 25 cc and add 1 to 2 cc ;| '\ ' of 60-per cent perchloric acid solution. Evaporate in a hood until white M fumes of perchloric acid appear, cool and dissolve the residue in a small |J I amount of hot water. Again add 1 cc of perchloric acid solution and evaporate until the solution evolves dense white fumes of'perchloric acid. Cool to room temperature and add 25 cc of a solution made by mixing 1 cc of 60- per cent perchloric acid with 300 cc of 97 to 98-per cent alcohol. If the jj insoluble potassium perchlorate is caked it should be broken with a stirring \t f rod so that no soluble salts will escape the action of the alcohol. j<| During the process of evaporation of the various solutions a Gooch filter [i '• should be prepared, the asbestos felt being washed with the perchloric acid- |M ; alcohol mixture. The filter is dried for one hour at 120° to 130°, cooled and if t f weighed. Filter the solution on this prepared filter, removing every trace }{ ^ i of the precipitate from the beaker by means of a policeman and the prepared |11 washing solution, and wash four or five times with this solution. Dry for *j j' one hour at 120° to 130°, cool and weigh. I \ \ From the weight of potassium perchlorate thus obtained calculate the I \ J per cent of potassium in the sample. | | Loss on Ignition.—Loss due to igniting the soil in contact with air includes that due to the volatilization of ammonium salts and water of hydration, to combustion of organic matter, and to decomposition of carbonates and sulphides. This loss may be if 4^ reduced, in some instances, by the oxidation of ferrous iron. « ^ '< Determination of Loss on Ignition.—The samples of dry soil obtained in the moisture determination are heated slowly to redness in a muffle furnace, using the same crucibles, until the organic matter is destroyed. The crucibles are then cooled in a desiccator and weighed and the per cent of loss is calculated. 1ScHOLL, /. Am. Chem. Soc., 36, 2085 (1914). Bit 111 :1 f/f j I1 IN 248 QUANTITATIVE AGRICULTURAL ANALYSIS l-'-l 1 Organic Matter.—In a natural soil there is a close relationship between the proportion of organic matter and the fertility. The cause of this is partly physical (improving the texture of a soil increases its absorbing capacity) and partly biological in that promoting the growth of bacteria, molds and protozoa helps to release essential elements to further availability. Organic matter also furnishes plant food directly. Many definite chemical compounds have been isolated1 from the complex soil organic materials. Methods for Determining Total Organic Matter.—An ap- proximate calculation of organic matter may be made from the per cent of carbon, the average carbon of soil organic matter being taken as 58 per cent.2 Loss on ignition, as already determined, is sometimes taken as an approximate measure of organic matter. The results obtained by this method usually differ considerably from those obtained by calculating the organic matter from carbon, for reasons already explained. Of the various methods that have been used for the determina- tion of carbon, direct combustion and oxidation by a mixture of chromic and sulphuric acids have been most widely adopted. At present, due chiefly to the efficiency of the modern electric furnace and to failure to obtain complete oxidation by other methods, the direct combustion method has found greatest favor. By any of these methods, carbon dioxide of carbonates is measured along with that produced by the oxidation of organic carbon and this occasions an error in organic matter calculations, unless carbonate carbon is determined and a correction applied. The combustion method is similar to that used for the deter- mination of carbon in iron and steel. It depends upon the direct combustion of the soil in a current of oxygen, the carbon dioxide produced being absorbed in standard barium hydroxide and the excess of base titrated. Warrington and Peak illustrate the discrepancies between the results obtained by calculating organic matter from loss on ignition and from carbon determinations by the following table: 1 U. S. Dept. ofAgr., Soils, Bull. 74 (1910). 2 See also READ AND RIDDGELL, Soil Sci., 13, 1 (1922). til -. SOILS 249 TABLE XXII.—ORGANIC MATTER BY Two METHODS Kind of soil Per cent loss on Ignition after drying at Organic matter calculated from carbon 100° 120° ; 150° ^"fcxire 9.27 7.07 5.95 9.06 6.88 5.70 5.39 ! 8.50 ! 6.55 1 5.61 4.76 6.12 4.16 2.44 0.65 pas-fcure . £ soil subsoil ...... •T Donate Carbon. — Carbon dioxide of carbonates varies from to 0.25 per cent in all but limestone soils. It is necessary aow the amount of carbonate carbon in a soil before that *rfc in organic form can be calculated. ie method for the determination of carbonate carbon depends i "the decomposition of the carbonate with dilute hydrochloric £tn.d the passing of the gas into standard barium hydroxide, excess of base being titrated with standard acid. See page I, for details of the method. 'termination of Total Carbon. — The apparatus (Fig. 57) consists of the ving parts: A steel cylinder, A, containing oxygen under pressure; a e, J3, containing 30-per cent potassium hydroxide solution followed by B B C D F G 57.—Apparatus for the determination of carbon by combustioa. H Dirkaining soda lime to remove possible traces of carbon dioxide from the 5en. D, an electric tube furnace 30 cm long fitted with a combustion j, J57, of fused quartz, vitreous silica or porcelain, 60 cm long and with an le.cliameter of 2.5 cm, to serve for the combustion. To insure complete .a-fcion of carbon monoxide, the last half of the portion of the combustion 3 "which is inside the furnace is filled loosely with platinized asbestos, 3hi a,cts as a catalyzer. ortn-ection with the combustion tube is made by means of one-hole rubber >pers and short glass tubes. The ends of the combustion tube, contain- tlio rubber stoppers, are cooled by means of cotton wicks which dip into *••'. / il 1* £ \ \! \ if I I it < » J f I ' ' r i> 250 QUANTITATIVE AGRICULTURAL A bottles containing distilled water. (Ordinary ground \v&>*>er will deposit a crust of salts in the wick, this finally stopping capillary a^'fcic-n.) A small bottle, 'F, containing granulated zinc, is attached *o the combustion tube. This absorbs chlorine and oxides of sulphur from the products of combustion. Connected with this bottle is the set of 3Vteyer absorption bulbs, Q, containing standard barium hydroxide. The tu*>e H contains soda lime and this protects the barium hydroxide from the carbon dioxide of the air. The furnace should be heated to about 950° (bright red) «-nd the stopcock opened so as to permit oxygen to pass through at the rate of about 1000 cc in 20 minutes. Prepare solutions as follows: (a) Barium Hydroxide—A. saturated solution of the ba.se is first made by warming and stirring the solid with recently boiled watei", using a ratio of 70 to 100 gm of the base to 1000 cc of water, according "to the purity of the barium hydroxide obtainable. Cool to room tempera/fcwe and siphon into a bottle, which is then closed with a rubber stopper. Dilute 550 cc of this solution to 1000 cc with recently boiled and cooled d-istilled water, .mix and place in a bottle which is provided with a guard tube of soda lime and a siphon or similar outlet. (For a method for protecting -fcfris and the other solutions, see Fig. 22, page 84.) (6) Hydrochloric Add.—Calculate the dilution such -bliat 1 cc shall be equivalent to 0.002 gm of carbon and make the solution from recently boiled and cooled distilled water. Standardize against sodium carbonate, using methyl orange. Refer to page 82, Part I. • (c) Water, Free from Carbon Dioxide.—Boil distilled wa/fcer for 5 minutes and then cool rapidly and preserve in bottles provided wi"fcH siphon outlets and soda lime guard tubes. Instead of boiling, a currerrfc of air may be drawn through the water (best slightly warmed) for one Jtxour, the air first passing through soda lime. This water is not to be used in, am ordinary wash bottle, from which water is expelled by blowing. Blanks.—Rinse the Meyer bulbs with water (c), then irtoasure into them from a burette or an automatic pipette attached to the bottle, 50 cc of the dilute barium hydroxide solution, first discarding the few drops that are in the outlet of the measuring instrument. Add to the bulbs from a graduated cylinder enough water (c) to bring the liquid to the lower edge of the upper bulb when the gas is flowing. The quantity necessary shouild be determined, once for all, so that it may be added without delay in subsequent determina- tions. With the furnace already heated, connect the bult>s in place while the oxygen is flowing at the rate of about three bubbles per second. At the end of 15 minutes, disconnect the bulbs without stopping ttto flow of gas and replace with a second set of bulbs, similarly charged. Rinse the barium hydroxide solution from the first sot into a 500-cc Erlenmeyer flask, using water (c). Pay no attention to any precipitate that may remain in the bulbs. Add a drop of phenolplvfcli«,lein and titrate* at once with the standard hydrochloric acid. The acid rri utnt not be added too rapidly and the solution must be stirred continuously, HO that no local SOILS 251 excess of acid may be attained. Note the volume of acid required to dis- charge the color. The pink color may return as the solution is allowed to stand but this is not considered in the reading. . At the end of 15 minutes from the time the second set of bulbs was inserted, replace the first bulbs, recharged with barium hydroxide. The titration of the second solution constitutes the second "blank" and the average of this and the first is to be taken as the acid equivalent of the barium hydroxide ', I solution. i * While one or more blank determinations are running weigh 2 gm of 100- I \ mesh soil and transfer it to an alundum boat (about 10 cm long and as wide ' f , as the tube will allow) and mix the soil with aa equal weight of 20-mesh / TI J alundum. Replace the Meyer absorption tube by another, containing , ,, r exactly 50 cc of fifth-normal barium hydroxide solution. Place the boat in ^ ; the combustion tube, connect and continue to pass oxygen for 20 minutes. ^ \ \ At the end of this period, disconnect the absorption tube and replace by a ' j second, containing barium hydroxide as before. Without interfering with „ ^ the flow of oxygen, immediately withdraw the boat from the tube and insert { * ,' another, containing a sample weight as before. Insert the stopper carrying \ , the oxygen tube and while combustion is proceeding with the second sample, ' / * rinse the barium hydroxide from the first Meyer tube into a 500-cc Erlen- ' meyer flask, using 50 cc of carbon dioxide-free water, and titrate the unused i J 'f excess with standard acid, using phenolphthalein as indicator. Calculate } 111 the per cent of total carbon and from this the per cent of organic carbon, ', \ * deducting that present in the carbonate form. ' \ \ I \ , * f * Soil Humus.—This is a somewhat indefinite term, used to f fi designate an intermediate stage of decomposition of the complex ': 11 organic residues usually found in the soil. The term " humus" is '3/1f arbitrarily used to include that part of the soil organic matter ;, J ? which has reached a stage of decomposition in which it is soluble ? < in 4-per cent ammonium hydroxide. Part of this decomposed ; ^ / organic matter contains certain substances having acid prop- ,' 11 erties, which combine with basic materials to form organic ' I ' r f salts called humates. Total humus material is the active avail- - '/ T | able organic plant food, while the residual organic matter is V, useful in improving the soil texture. j \ There has been considerable discussion concerning tbe real 4* value of the humus determination. While it must be admitted I that the term " humus " does not cover a sharply defined class of \;. compounds and that the result of the determination is subject || to considerable variation unless the method is rigidly standard- |* ized, it yet appears that some useful information is obtained, {i in at least approximately classifying organic matter into easily || li ' FP 252 QUANTITATIVE AGRICULTURAL ANALYSIS and immediately available forms and those not so available.1 The determination is no longer official. Determination of Humus.—Five-gram samples of air-dried soil, ground to pass a 60-mesh sieve, are placed in 500-cc wide-mouthed bottles and washed repeatedly by shaking with a 1-per cent solution of hydrochloric acid until calcium and magnesium are no longer extracted, as shown by testing a small quantity of filtered solution with ammonium hydroxide and ammo- nium oxalate. The first washings need not be tested. The wash- ing can be hurried by manipulating the bottle in a shaking machine for 15 minutes (Fig. 51). After calcium and magnesium have been removed, filter the solution and wash the soil free from acid by decantation. Return the filter and its contents to the bottle and add 250 cc of 4-per cent ammo- nium hydroxide. Shake in the machine for three hours, or every 30 minutes by hand for six hours, then place the bottle in a horizontal position for twelve hours. Again shake the bottle well and pour the contents upon a 24-cm filter paper in a funnel. Cover the funnel with a watch glass. The filtrate may be very turbid for an hour or more. In this case, refilter. When the filtrate comes through clear, save 100 cc or more of it in a clean flask. Pipette 50 cc of the clear filtrate into an 8-cm evaporating dish. Evaporate to dry- ness on a steam bath, dry in the oven for an hour at 100°, cool in a desiccator and weigh. Burn the carbonaceous matter to an ash in the muffle furnace, cool, weigh and calculate the difference between the two weights as per cent of humus. Extraction of Material Soluble in Strong Acid.—As in the case of organic matter, the inorganic constituents of the soil are combined in forms which differ widely in degree of availability. Calcium may be present either as limestone (calcium carbonate) which is easily soluble in acids, or as one or more of a variety of silicates, such as anorthite (calcium aluminium silicate) which is nearly insoluble. A similar variation exists with potassium, which may be present as a soluble carbonate or as orthoclase, a silicate of potassium and aluminium which is highly insoluble. Extraction of the soil with hydrochloric acid provides an approxi- mate distinction between materials of small availability and the more available ones. The acid extract may be evaporated to dryness and the extract simply weighed, or the residue may be subjected to a partial or complete analysis as outlined for the original soil. The amount of material dissolved by the acid varies with the concentration of the latter, the fineness of division of the soil 1 Soil Science, 3, 515 (1917). SOILS 253 |!H particles and the length of heating. It is therefore obvious that tj H such an extraction constitutes only a conventional division into j ] | somewhat arbitrary classes of materials. "^ Other Inorganic Constituents.—The methods outlined in the jj^ following pages may be applied to the analysis of the original ||| I i soil or of an acid extract, as explained above. As the soil always -j| j j contains a large proportion of materials insoluble in acids the jj H2Si03 + 2NaCL (2) 254 QUANTITATIVE AGRICULTURAL ANALYSIS There are also formed soluble chlorides of iron, aluminium, calcium and such other metals as were present in the soil. The silica is separated almost completely from the other compounds by evaporation to dryness and heating to about 120° to decompose the silicic acid: H2SiO3 -» H20 + SiO2. (3) The residue is taken up with water and hydrochloric acid and the insoluble silica is separated by filtration. However, this separation is incomplete as there is a tendency to form a hydrosol of silicic acid. The error thus produced may be avoided by filtering off the silica formed on first evaporation and repeating the dehydration of soluble silica by a second evaporation. The silica finally obtained is not pure but the amount of impurities may be determined by treating the ignited and weighed pre- cipitate with hydrofluoric acid, thus converting the silica into silicon tetrafluoride. The latter is volatilized by heating, leaving oxides of iron and aluminium as a residue. Silica.—The function of silicon in plant growth is not well understood. There is a considerable amount of this element in some plants (notably oat and rye straw) and it may serve some useful purpose, not yet understood. Aluminium.—Compounds of aluminium are present in normal soils in rather large quantities.. The per cent of aluminium in sandy loam is about 1.5, in clay loam, 4.5, and in residual soils formed from gneiss or limestone about 13. Residual soils usually contain much more aluminium and iron than do glacial soils. Salts containing aluminium are present in some acid soils in sufficient amount to exert a toxic influence on certain plants; barley and corn are particularly sensitive t'o it. This effect is probably due to the existence of colloidal basic aluminium salts which are capable of being absorbed by the plant. The toxicity may be corrected to a considerable extent by an applica- tion of calcium silicate, acid phosphate, or limestone to the soil, thus causing the aluminium to form a less soluble compound. Iron.—The iron content of soils is quite variable. In soils only slightly tinted, from 1.5 to 4 per cent of iron, calculated as ferric oxide, is found. Ferruginous loams contain from 3.5 to 7 per cent and the red lands from 7 to 14 per cent. SOILS f 255 1 ' | / Iron and aluminium are precipitated together as hydroxides. *) \ If titanium is present In the soil the precipitate will contain also / | titanium hydroxide. Phosphorus will be precipitated here as I \ basic ferric phosphate. The combined precipitate is ignited and ] * the oxides and phosphate weighed together. Iron is then ' * / 1 determined by dissolving and titrating with a standard per- ' * •' < manganate or dichromate solution. Phosphorus is determined , ; ] in a separate sample and calculated to . the pentoxide, while \ I titanium is usually ignored unless it is known to be present in ; s !*| appreciable quantities, as it has no known biological signifi- / f | cance. The sum of the per cents of oxides of iron and phos- phorus, subtracted from the per cent of total residue, gives the per cent of impure aluminium oxide. Direct Method for Determining Aluminium. — The above | procedure necessarily throws the combined errors of all of these , J determinations upon aluminium. If an accurate determination i of the latter is required, a direct determination may be made. i In this case the precipitate of hydroxides is redissolved without « ' J previous ignition and the iron is reduced to the ferrous condition by sodium thiosulphate : { 2Na2S203 + 2FeCl3 -^ Na2S4O6 + 2FeCl2 + 2NaCl. The aluminium is then precipitated as phosphate, ferrous phos- phate remaining in solution. \ Purification by Double Precipitation.—The precipitates of f iron and aluminium hydroxides, of calcium oxalate and of mag- nesium ammonium phosphate are difficult to purify by simple washing. If accuracy is important, purification is usually accomplished by dissolving the partly washed precipitate, redissolving and reprecipitating. In the solution from which the second precipitation is made the concentration of soluble salts is only a small fraction of that in the original solution and the amount now carried down by the precipitate and not removed ! by washing is extremely small. ! I Calcium.—Many soils that are noted for their fertility have a high calcium carbonate content. Examples of such are the blue grass soils of Kentucky, the calcareous prairie soils of * fc Illinois and Indiana and the black prairie soils of Texas and Mississippi. 256 QUANTITATIVE AGRICULTURAL ANALYSIS Calcium functions particularly in stimulating root develop-" ment and it is thought to be connected in some way with the development of cell wall material. Some crops, such as alfalfa, clover, and tobacco, require large amounts of calcium for good growth and development. For the determination, calcium is precipitated from, the filtrate from iron and aluminium as calcium oxalate. The calcium may then be determined gravimetrically, as oxide, or volumetrically by titration with standard potassium, perman- ganate. These determinations are discussed on pages 63 to 69, Part I. Magnesium.—This is a plant food element which plays an important part in seed production as magnesium, like phosphorus, moves to the seed to a great extent. In this respect it is unlike potassium and calcium, which remain largely in the stem and leaf. Magnesium appears also to function in oil and chlorophyll production. Magnesium is determined in the filtrate from calcium oxalate by precipitating as magnesium ammonium phosphate in a solu- tion previously made basic with ammonium hydroxide. The precipitate is ignited and weighed as magnesium pyrophosphate. The principles underlying this determination have been discussed in connection with the analysis of phosphate, page 87, Part I. When magnesium is being determined, a soluble phosphate is used as the reagent. Determination of Total Silica.—Weigh accurately about 1 gm of soil into a platinum crucible, burn off the organic matter and when cool mix with approximately 10 gm of sodium carbonate. Place the cover on the crucible slightly to one side so that the contents may be observed. Heat gently at first, using a small burner. Gradually raise the temperature to that of the full flame and heat until gas evolution is only slight. Place the crucible over a blast lamp and heat for at least 15 minutes after the evolution of carbon dioxide has ceased. While it is still hot, rotate the crucible by manipulating the triangle, so that the fused mass will spread over the sides as it solidifies. When it has cooled, place the crucible on its side in a casserole and cover with hot distilled water. Heat until the fused mass has disintegrated, cover and gradually add 15 ec of concentrated hydrochloric acid from a pipette through the lip of the cas- serole. Place on a steam bath and, after all effervescence has ceased, remove the crucible and cover, rinsing well. Use a stirring rod for this purpose. By inserting this in the mouth of the crucible the latter can be raised out of SOILS 257 the solution and the outside thoroughly rinsed. It can then be taken in the hand and the interior rinsed. A policeman may have to be used if silicic acid adheres to the crucible. Do not use metal crucible tongs for removing crucibles from solutions, especially if the latter are acid, as in this case. Evaporate the liquid to dryness over a steam bath, or keep the casserole in. constant motion over a low flame. Heat for 15 minutes at 120° in an oven constructed of material that will not be damaged by acid vapors, or to just below redness over a flame. When cool, add 5 cc of concentrated hydrochloric acid and 75 cc of water, heat until soluble salts are dissolved, filter off the silica and wash the paper and silica with hot water until free from acid. Repeat the evaporation of the filtrate and washings and treat as before, using a different filter paper. Save the filtrates and washings for the determination of other inorganic constituents. Rurn both filter papers in one platinum crucible (which need not be weighed previously) then ignite over a blast lamp, cool and weigh. Add a few drops of sulphuric acid and about 5 cc of hydrofluoric acid (pouring the latter directly from the bottle) to the material in the platinum crucible and volatilize the silicon tetrafluoride and acids by evaporation to dryness under a hood. Ignite the residue and weigh. The loss in weight represents silica. Calculate the per cent. The residue in the crucible consists of oxides of iron and aluminium. Add about 1 gm of potassium pyrosulphate and heat, gradually raising the tem- perature to redness, until solution of the oxides is complete. Cool and dissolve the fusion in hot water. Precipitate the metals as hydroxides, as directed below, wash and discard the filtrate and washings. Preserve the precipitate on the paper, so that it may be burned in the same crucible as the main precipitate of iron and aluminium hydroxides, the total oxides being weighed together. X>etermination of Iron and Aluminium: Direct Method for Iron, Indirect Method for Aluminium.—Dilute the filtrate from the determination of silica to about 75 cc. Add a drop of methyl red and then add dilute ammo- nium hydroxide until the solution is distinctly basic, avoiding an undue excess. Boil for 5 minutes or until the odor of ammonia is faint, but without prolonging the boiling until the solution becomes acid in reaction. Filter the precipitate through an extracted paper and wash with hot water two or three times. Return the precipitate to the first beaker and dissolve in warm water containing a small amount of hydrochloric acid. Reprecipitate, filter and wash the precipitate free from chlorides. Save the filtrate and washings from both precipitations for the determination of calcium and magnesium. Burn the paper at a low temperature in a weighed platinum crucible, inclining the crucible to facilitate oxidation. When most of the carbon has been removed, add the paper containing the iron and aluminium hydroxides from the silica determination (see above) and burn this in the same manner. Finally heat to bright redness, cool in a desiccator and weigh as oxides of iron (ferric), aluminium, titanium and phosphorus. Unless the residue of oxides is white, add about 2 gm of potassium pyrosulphate and heat* gradually raising the temperature to bright redness. 17 258 QUANTITATIVE AGRICULTURAL ANALYSIS Afl,<>,r solution appears to be complete, cool and place the crucible on its side in 50 cc of hot water in a beaker or casserole. Warm to hasten solution of the mass of sulphates. Remove and rinse the crucible, heat to boiling and add 1 cc of 5-per cent stannous chloride solution to reduce the iron. Cool rapidly in running water and add, all at once, 50 cc of 5-per cent mercuric chloride solution. This must produce a precipitate of pure white mercurous chloride. If no precipitate is produced, not enough stannous chloride was added. If the precipitate is gray, instead of white, too much stannous chloride was used. Titrate at once with standard potassium dichromate, following the details of the method described on page 74, Part I. Or the determination may be made with standard potassium permanganate as directed on page 72, Part I. Calculate the per cent of the total oxide and phosphate residue and of ferric oxide in the soil sample. The latter, together with the per cent of phosphorus pentoxide (as determined in a separate sample), subtracted from the per cent of total residue, gives the per cent of aluminium oxide and titanium oxide. The titanium is usually ignored, as already stated. Determination of Aluminium: Direct Method.—Make the double pre- cipitation of hydroxides and wash free from chlorides, as directed above, saving the filtrates and washings for the determination of calcium and magnesium. Place a 500-cc beaker under the filter and redissolve the precipitate with warm dilute hydrochloric acid. Pierce the filter and wash the paper well with hot water. Dilute the solution to about 400 cc. Add 30 cc of a 10-per cent solution of ammonium phosphate and then stir and add dilute ammo- nium hydroxide until a precipitate appears. Add 1.5 cc of concentrated hydrochloric acid and 50 cc of a 20-per cent solution of sodium thiosul- phate and boil for a few minutes. Now add 15 cc of a 20-per cent solution of ammonium acetate and 8 cc of 30-per cent acetic acid and boil for 15 minutes. The colloidal aluminium phosphate becomes granular and it is then easily filtered and washed. Save the filtrate and washings for the iron determination unless the original precipitate of hydroxides was per- fectly white, indicating the presence of no more than a trace of iron. Redissolve the phosphate on the filter with concentrated hydrochloric acid, wash through with hot water and reprecipitate aluminium phosphate exactly as before. Wash with hot water, ignite and weigh as aluminium phosphate, A1PO4. Calculate the per cent of aluminium oxide in the sample. Determination of Calcium.—Evaporate the combined filtrates from. aluminium and iron hydroxides to about 50 cc, cool, add ammonium sul- phide to precipitate the manganese, filter and wash with hot water. Discard the precipitate. Again evaporate the solution to about 50 cc, make slightly basic with ammonium hydroxide and add, while still hot, 4-per cent ammo- nium oxalate solution, dropwise and with stirring, so long as any precipitate is produced. Heat to boiling, allow to stand one hour or longer, decant the clear solution on a filter, pour about 20 cc of hot water on the precipitate SOILS 259 and again decant the clear solution on the filter. Dissolve the precipitate in the beaker with a few drops of hydrochloric acid, add 15 cc of water and reprecipitate by adding ammonium hydroxide and ammonium oxalate solution as before. Allow to stand for an hour and filter through the same paper. Wash the beaker and precipitate with hot water until free from chlorides. Save the filtrate and washings from both precipitations for the detsrmination of magnesium. Determine the calcium either gravimetrically or volumetrically. 111 I (a) Gravimetric Method.—Place the paper and calcium oxalate in a weighed I! i I crucible, heat carefully until dry and then ignite in the covered crucible for ' j »-' 30 minutes over a blast lamp or a M6ker burner. Weigh as calcium oxide j'j and calculate the per cent of this in the sample. I (b) Volumetric Method.—Dissolve the calcium oxalate and titrate with j' : potassium permanganate, following the details outlined on page 69, Part I. j Calculate the per cent of calcium oxide in the soil sample. . j' Determination of Magnesium.—Acidify the filtrate from calcium with |4 hydrochloric acid and evaporate until ammonium chloride or oxalate begins j * to crystallize. Add 10 cc of water and stir until the salts are in solution. |'] To the filtrate add a drop of methyl red and sufficient ammonium hydroxide j / to make the solution barely basic. Now add from a pipette, slowly and with stirring, 20 cc of a 10-per cent solution of disodium orthophosphate. Let stand for 20 minutes or until crystallization begins, then stir and add a quantity of concentrated ammonium hydroxide about equal in volume to one-ninth of the total. Cover the beaker and let stand for three hours or over night. Filter on paper, making no effort to remove adhering precipitate from the beaker. Wash two or three times with dilute ammonium hydroxide and discard the filtrate and washings. Dissolve the precipitate on the filter j J with hydrochloric acid and allow the solution to run into the beaker contain- ing some of the precipitate. Wash down the paper thoroughly with hot water, dilute to about 75 cc and precipitate the magnesium as before. Filter the precipitate in an ignited and weighed alundum crucible and wash until free from chlorides with a 2-per cent solution of ammonium hydroxide, test- ing the washings finally with silver nitrate solution made acid with nitric acid. Cover the crucible and heat gently over a burner until dry and finally | ', heat for 20 minutes, using a blast lamp. Cool in the desiccator and weigh. | * * From the weight of magnesium pyrophosphate calculate the per cent of I magnesium in the sample. Manganese.—Manganese is present to some extent in alluvial clay soils but it is more abundant in volcanic clays. In small amounts, approximating not more than abou.t 50 Ib. of manganese per acre of soil, 6% in. deep (0.0025 per cent), it seems to have \i4 a stimulating effect on plant growth. Many plant compounds \ j contain manganese but its biological function is not well !# understood. 260 QUANTITATIVE AGRICULTURAL ANAL The manganese content of a large number of different legumes (aerial portion) vas determined by Jones and Bullis,1 who found alsike clover to have the greatest amount, averaging 0.068 per cent, while alfalfa had the least, with 0.023 per cent. Work on the effect of manganese has been done also by Kelley,2 who concluded that manganese is a plant food, when present in small amounts, but that in larger quantities it becomes toxic. In some Hawaiian soils the per cent of manganese is so high as to interfere with the growth of the pineapple, causing a depres- sion in iron assimilation.3 The bismuthate method for the determination of manganese is one of the best. It is based upon the use of sodium bisrnuthate to oxidize bivalent manganese to heptavalent manganese in the form of permanganic acid. When a solution of manganous nitrate is treated with sodium bisrnuthate the reaction proceeds thus: 2Mn(N03)2 + 5NaBi03 + 14HN03 -* 2NaMn04 + 3NaN03 + 5Bi(NO3)3 + 7H20. Sodium permanganate so produced is reduced by means of a standard reducing agent, the excess of which is then titrated with standard permanganate solution. Persulphate Method for Manganese. — Manganese may be oxidized by ammonium persulphate, in the presence of silver nitrate, from a bivalent to a heptavalent condition, producing permanganic acid: > Ag2S2Os + 2NH4N03, (1) Ag2S208 + 2H2O -> 2H2SO4 H- Ag2O2, (2) 5Ag202 4- 2Mn(NOs)2 + 6HNO3 -+2HMn04 + lOAgN03 + 2H2O. (3) The manganese is determined in an extract from the soil fusion by comparing the intensity of color produced in this manner with that of a manganese solution of known concentration, similarly 1 J. Ind. Eng. Chem., 13, 6 (1921). See also McHABGUB, J. Am. Chem. Soc.t 44, 1592 (1922). 2 Hawaii Exp. Sta. Bull 26 (1912). 3 JOHNSON, Ibid., 9, 1 (1917). -treated, or by tit rat ion with a ferrous ammonium sulphate* or ^Ki^ 44r^>u 2HMn04 -f e ape-it Mich :iri u Dete ing solution (a} Potassium pertnatt-gan 4u* > j \o ^*i, centrated acid with three volumes o* uuUr. (d) Nitric Add, Specific Gra^ly I Olo.~I)J jtt *1 -t*- v * ^ ceatrated acid with 100 volumes of \\attr. Ignite 1 gin of soil gently in air until al or« >r*<* n.itttr i- i the ignited soil as directed for the aiileon dtttnmiuit, i, j - the fusion is perfectly fluid plain the cooled rrae>It on ;t& - casserole and add nitric acid c until t lie »di 1,1. jurh Rinse and remove.tlie crucible and tvaporatt4 tit MI atiun tc. dni t^x c^ +| steam bath. Finally take up \\ith 5(1 ei of i.itnc avid ( . Ht\*t to a i ^i solution but do not evaporate much of tht ae'd O>i>l, add about iU" #*i of sodium bisrauthate and stir. A^ttr It) inlr-jtos acid ,V) cc of nlt-Ii at* d (d) and filter the whole through a GotH'h Mlttr, usrirg&uttion. .\fttrftir- ing? wash the beaker and crucible with 5(1 cc of the sane Ritr.e iu . From a burette add to the filtered solutior 45 ce 'mort if netts-a.ry to reduce all permanganate) of ferrous ammornini j^u'p^iatt. fc-olufor. ^ T* i permanganate is reduced and t.lit re is an t.\ct.ss of ferrous salt prti*,&t. Titrate this excess to a faint pink color with standard potassium perman- ganate solution (G). A blank determination Is made, using 50 cc of dilute nitric acid, 50 ce of nitric acid (d) and 0.25 gm of sodium bisniuthate. Filter through a^best*** and wash with 50 cc of nitric* acid as in the previous determination. From a burette add 35 ec of ferrous ammonium sulphate solution arid immediately titrate with the standard potassium permaiifciiuite. The difference between the volumes of permanganate- required for the blank and • the manganese determination, respectively, is that equivalent to manganese in the sample of soil. Calculate the per cent of manganese. If:) n/ r it; f* fi M 262 QUANTITATIVE AGRICULTURAL ANALYSIS Determination of Manganese: Persulphate Method.—The standard per- manganate solution prepared as for the bismuthate method is used in this case. One gram of soil is fused and treated as directed above for the bismuthate method. Do not add sodium bismuthate but after the residue from, evapora- tion has been dissolved in nitric acid, add 15 cc of a 0.2-per cent silver nitrate solution, following immediately by 1 gm of ammonium persulphate. Heat by placing the beaker or casserole in hot water until the pink color is fully developed. Cool and rinse into a tube of a color comparator. Place in another tube enough of the standard permanganate solution (measured accurately) to make a somewhat greater intensity of color, when viewed from above, dilute to the mark and mix. Place both tubes in the comparator (Fig. 52, page 237) and adjust to equality of color. Calculate the per cent of manganese in the sample. Sulphur.—The sulphur content of most soils is usually less than that of phosphorus, while considerable sulphur is needed by certain plants to produce proteins and flavoring oils. It has been shown that onions, mustard, and cabbage usually respond favorably to the addition of either elementary sulphur or sul- phates to the soil. The function of sulphur in the plant metab- olism is not well understood. The determination of sulphur in soil is preceded by fusion with sodium carbonate in the presence of a small amount of an oxidiz- ing agent, the latter in order to convert protein sulphur to the form of sulphates. The sulphate thus formed, together with sulphates originally present as such, is later precipitated and weighed as barium sulphate. The heating should be done with an alcohol burner or in an electrically heated muffle furnace instead of with a gas flame because of danger of absorption of sulphur dioxide from the burning gas (which always contains hydrogen sulphide) by the sodium carbonate. Determination of Sulphur.—Mix 2 gm of 100-mesh soil with 7 gm of anhydrous sodium carbonate (free from sulphates) and 0.5 gm of potassium nitrate in a platinum crucible. Place the covered crucible in an electrically heated muffle and heat to dull redness until well fused, after which remove the crucible and tip it in such a manner as to cause the contents to solidify on the sides. While it is still hot place the crucible in 75 cc of cold water in a 200-cc beaker (use care). Cover and heat the beaker and contents to boiling. Stir until all lumps of the fused mass have been disintegrated, then filter into a 400-cc beaker and wash the residue until the volume is about 200 cc. Reduce any sodium manganate present by boiling with a few drops alcohol, add :i drop ,,f n HHI lt,; iT, \ tU* until neutral \m\ i |tl i u .. (or an cquivMfei f v< }Uiii» t • „,. i ,, and add, dropwise arid with « ,M • -4 • .* solution of barium chloral* t,, pro pit i boiling until the prwipituto *» ttl* - n barium sulphate and \\ath \\nli i,.»t \u>tt fully burn the paper in an indmtd ITU' white but do not allow the indhlt t > >< longer than is necessary to burn a'a ^ sulphur in the soil, expressing as the element Lime Requirements of Soils.—Lime ^ ad(k\I n a<-«I ^"*:^ A^ the purpose of neutralizing their exeex- of a<';«i i -r J J!M» :- i *zi - the physical texture of the soil. la atMiti* ?i ti th* ^ t£r t-, there is a precipitation of iron ami aluiiiini^>^ as hydroxides, in this way lessening their toxicity. Calcium itself is regarded as one of the necessary elements in the plant economy. There is considerable difference with regard to the need of different plants for calcium and also with respect to their ability to draw this element from the less available sources. Alfalfa Is an example of a that needs inndi cal- cium in its metabolic processes but having a rather limited feed- ing power while, on the other hand, the rye plant much ^ less calcium but possesses ample feeding capacity to secure the t'f{i little it requires. , '] « It is generally considered that many soils possess acidity through the presence of insoluble acid salts of organic ami I>! inorganic acids and a number of methods in use for the deter- I * inlnation of soil acidity are based upon this assumption. Certain 'f ^ fertilizers have a tendency to cause a soil to become acid. This \, f» is especially true of ammonium sulphate. As nitrogen Is taken >,( \ from this salt by the plant, sulphuric acid remains as a \^\ residue in the soil. Green manures have been credited also with £J \ producing acid soils, acid being formed during fermentation. I| | However, much confusion still exists concerning the true nature //j | of soil acidity and consequently there is no generally accepted ^ f method for its determination. The lime calculated to be { ^ required to neutralize acidity varies, therefore, according to the method employed for the determination of acidity. 204 QUANTITATIVE AGRICULTURAL ANALYSIS Veitch Method.1—In the Veitch method for the determination of soil acidity a measured quantity of lime water solution of known concentration is evaporated to dryness with a definite amount of soil. The mass is then extracted with distilled water, phenolphthalein is added and the solution is concentrated by boiling. If the quantity of calcium hydroxide added was more than sufficient to neutralize soil acids, an indication of this will be given by a pink color from the phenolphthalein. By this method there is probably some error due to a combination of calcium hydroxide with organic matter and possibly with carbon dioxide from the air. Determination of Lime Requirement of Soil: Veitch Method.—Weigh five portions of 10 gm each of the soil into 8-cm porcelain evaporating dishes. Add fiftieth-normal calcium hydroxide solution in such amounts that it will range from 2 cc below to 2 cc above the probable amount of calcium hydroxide needed, making a difference of 1 cc in the volume of calcium hydroxide for each pair of consecutive members of the series. A series extending over 5 to 10 cc of solution may be used as a beginning. Evapo- rate all to dryness over the steam bath and immediately take up the residues with distilled water and transfer to 300-cc flasks, using 150 cc of water, previously freed from carbon dioxide by boiling for several minutes in an open beaker or dish. Shake well, stopper and let stand over night, then pipette 50 cc of the clear liquid from each flask into Pyrex beakers. Add a drop of phenolphthalein and heat to boiling, continuing the boiling until two-thirds of the liquid has been boiled away. Note in what beakers, if any, the liquid has turned pink. Repeat, using a narrower series whose limits are indicated by the results on the first series. The least volume of calcium hydroxide solution required to cause a pink tint is equivalent to the lime requirement of 10 gm of soil. Calculate the pounds of calcium carbon- ate needed on the basis of 2,000,000 Ib. of soil per acre. The Tniog Method.2—If barium chloride and zinc sulphide are added to an acid soil, evolution of hydrogen sulphide takes place: 2RCOOH + BaCl2 -» (RCOO)2Ba + 2HC1, (1) ZnS + 2HC1 -» H2S + £nC!2. (2) This gas coming in contact with lead acetate paper produces a degree of blackening somewhat in proportion to the amount of acid present. H2S + Pb(C2H302)2 -> PbS + 2HC2H302. (3) 1 J. Am. Chem. Soc., 26, 261 (1904). 2 Wis. Exp. Sta. Bull, 249 (1915). •so/ix Potassium Thiocyanate Method.—\Vi * - * of calcium or magnesium carbo^i' ^ J ^ } iron present combine with any fiv«. ftl < 1 i i i t these metals. If an alcohol Voiat'\»" «,' is added to such a soil the solution n; intensity of which has been shown to tional to the acidity of the soil Al^ alcoholic solution of logwood he :uM* <] the intensity of which is again propt it of both aluminium and acidity in tia M >•' As an explanation of this color format:, that, in an acid soil, iron and aluiiiir^ti: partly hj^drolyzed, largely colloidal MI^^ 1 weakly ionised soil acid. These sa!t> an* i such salts as potassium thiocyanaU, wrj,* insoluble oxides or silicates, such :i*» would or basic soil. This might be expressed thus: 0\ M\» V "1» < < V x prt ^on1" in a neutral + H2O <=± FeOH-.4, + HI, FeOH.A2 + 3KCNS + H.4. *=* FeiCXS.h + 3K.4 ~t- i I -2 where A represents any acid radical The ferric t thus produced colors the solution somewhat in pioportluii to the amount of acid which made iron available for this reaction. The addition of a standard solution of a ferric thiocyanate and destroys the color. It has been noted in making soil acidity by method that certain soils cause the supernatant to assume a green color, as the red color of the ferric thiocyanate Analysis has shown that this color is doe to the formation of a manganese compound, which is produced after the solution been made basic. This green color develops if the contains as little as 0.008 per cent of soluble manganese. In cases it has been found that it starts to develop as as the red color entirely disappears, but its intensity is increased if o ce more of base be added than that required to titrate to the disappear- ance of red. This red color disappears when Pa equals 5.5 while manganese does not start to precipitate as hydroxide until J. Ayr. AV/., 10,420 (1920:'. 266 QUANTITATIVE AGRICULTURAL ANALYSIS PH equals about 7.2, this being completed at about 7.9. It is evident that with such a soil a large amount of limestone would have to be applied to precipitate all of the manganese, and in some instances this cost would be prohibitive. Determination of Soil Acidity: Potassium Thiocyanate Method.1—Prepare the following reagents: (a) Potassium Thiocyanate Solution.—Prepare a 5-per cent solution in 95-per cent ethyl or methyl alcohol. This solution should become slightly pink (Pn = 5.4) upon the addition of methyl red. If neces- sary, add very dilute potassium hydroxide or hydrochloric acid, drop by drop, until this color is obtained with a few drops added to methyl red on a test plate. (b) Alcoholic Solution of Potassium Hydroxide.—Prepare a tenth-normal alcoholic solution of potassium hydroxide by dissolving the base in 95-per cent ethyl or methyl alcohol. Titrate against (c), using methyl red. (c) Alcoholic Solution of Hydrochloric Acid.—Prepare a tenth-normal alcoholic solution of hydrochloric acid by diluting concentrated acid with 100 volumes of 95-per cent ethyl or methyl alcohol. Standardize against sodium car- bonate, first dissolving the weighed salt in a small amount of water. See page 83. Place 50 gm (25 gm of muck) of 10-mesh air-dried soil in a 100-cc glass-stoppered cylinder or in the lower chamber of the specially designed glass tube shown in Fig. 58. Add 30 cc (50 cc for muck) of potassium thiocyanate solution. Stopper the cylinder and agitate for two minutes. Place in an upright position, allow to settle for several minutes and note the color of the supernatant liquid. If the solution is pink or red, add from the upper burette a few tenths of a cubic centimeter at a time (depending upon the color) of tenth-normal alcoholic solution of potassium hydroxide. Shake well after each addition and allow several minutes to settle. Continue the addition until the red or pink color has just disappeared. Let stand fifteen hours and add more base, if necessary, to remove any pink which may have developed. If too much base has been added titrate back to a faint pink color using tenth-normal alco- holic acid. Note the volume of tenth-normal base required and calculate the pounds of calcium carbonate required to correct the acidity of the soil, on a basis of 2,000,000 Ib. of ordinary soil or 1,000,000 Ib. of muck soil per acre. The time required for complete development of color in the thiocyanate solution may be shortened by use of the mixing machine. 1CARB, J. Ind Eng. Chetn., 13, 931 (1921). ISOcc FIG. 58.—Soil acidity burette. SOILS 267 If no red color has developed in the extract, the soil is already basic. +.< In this case, add from a burette tenth-normal alcoholic solution of hydro- { chloric acid until a pink color develops after standing several minutes, agitat- »I* ing after each addition and then allowing the soil to settle. From the ! | volume of acid used calculate the calcium carbonate equivalent of the soil. If there is any indication of a green color developing after the disappearance of red and after standing over night, add 5 cc more of base. If a green color j.j j should develop, it would require from 40 to 50 cc (corresponding to 4 to 5 tons of limestone) of base, in addition to that added to remove the red color. Hopkins Method.—The acids of the soil (existing in equilib- rium with partly hydrolyzed salts, as shown in equation (1), page 265) are not easily extracted with water. If a solution of potassium nitrate is added, such a reaction as the following |fl may occur: H.A + KN03 *=» KA + HN03 Equilibrium is established with the weakly ionized acid pre- * dominating but if the solution is removed and replaced by more potassium nitrate solution, the reaction will proceed still farther. By repeating this process several times, a result is finally obtained, approximating complete extraction of the acid. It has been found by working with a number of different soils that the sum of the acid of such a series of extracts is about two and one-half times that of the first extract. In the Hopkins method the assumption is made that the value of the first titra- tion may be multiplied by 2.5 to give total acidity. The method seems to be more reliable with clay and loam than with muck j j soils. i!||| Determination of Acidity of Soil: Hopkins Method.—Place 100 gm of soil j and 250 cc of normal potassium nitrate solution in a 400-cc wide mouthed j bottle, stopper and shake continuously in a machine (Fig. 51) for three hours, 1 or every half hour for three hours by hand. Allow to stand for fifteen hours. j Draw off 125 cc of the clear solution, using a pipette, boil for 10 minutes to j expel carbon dioxide, cool and titrate with tenth-normal sodium or potassium I hydroxide, using phenolphthalein as indicator. Multiply the figure so j obtained by 2.5 and calculate the number of pounds of calcium carbonate « required per acre of 2,000,000 Ib. of soil. i The titrations of duplicate samples should not differ by more than 0.8 cc »] *! for soil samples requiring less than 100 cc of sodium hydroxide. " I Active Plant Food.—The amount of nitrogen, phosphorus and potassium that may be made available in a soil during a given I 1 268 QUANTITATIVE AGRICULTURAL ANALYSIS year is of interest and importance. Various weak acids, which imitate the action of the plant roots, have been used for extract- ing available plant food. Dyer1 has shown that root acidity (expressed as citric acid) varies from 0.34 to 3.4 per cent of the weight of the plant. He found the average acidity of one hundred plants (root and top) to be about equal to that of 1- per cent citric acid and so used this acid for soil extraction. Fifth-normal nitric and oxalic acids are other solutions that have been used for this purpose. Fifth-normal nitric acid has given best results2 in field tests and this has been quite widely adopted. The amount of acid capable of being neutralized by materials already present in the soil also is a factor of importance in fertility work. This is estimated by titrating the solution after the extraction has been completed. The amount of acid con- sumed depends considerably upon whether the soil is calcareous, it being much greater in this case. Flocculation and Deflocculation of Clay.—When "silt" soil is suspended in water it may be easily flocculated by a calcium salt, such as calcium nitrate. However, if calcium hydroxide is added so that the solution becomes basic, flocculation is more difficult. A clay responds in just the opposite manner, being easily precipitated from suspension by a basic solution. Determination of Comparative Degree of Flocculation and Defloccula- tion.—Place about 3 gm (not accurately weighed) of a clay soil in a mortar and add sufficient water to make a thin paste when rubbed, then dilute to one liter and mix. Repeat this process, using a "silt" soil. Pipette 25 cc of each turbid liquid into each of nine test tubes and add each of the following solutions in order to test its power to flocculate or deflocculate clay and silt soils. The solutions should have approximately the concentrations indi- cated but they need not be accurately standardized. (1) Use as a control—water and soil suspension only. (2) 5 cc of tenth-normal sodium chloride. (3) 5 cc of tenth-normal monosodium phosphate. (4) 5 cc of tenth-normal sodium hydroxide. (5) 5 cc of tenth-normal hydrochloric acid. (6) 5 cc of tenth-normal ammonium sulphate. (7) 5 cc of tenth-normal monocalcium phosphate. (8) 10 cc of twentieth-normal calcium hydroxide. (9) 5 cc of tenth-normal calcium nitrate. 1 J. Chem. Soc., 65, J15 (1894). 2 Ohio Exp. Sta. Bull, 261 (1913). 200 the reagents have all been added, shake each Lube Urn times and f* fiiw :uid flu* order in which the turbidity of the liquid disappears. the ,sh:ikiriK until Lite time of clearing is (established for eae.h oom- n«!«led. Xot.(» what ion or iotm appear to be the most effective in fioi'ruhition of the .soil parti(dc;s in l)oth types of soils. CHAPTER XIII FERTILIZERS Fertilizers, or manures, are those materials which either increase the supply of elements in the soil, needed for the growth of plants, or exert a corrective action in making conditions more favorable for the plant's best development. Farm manures are usually mixtures of the excrement and urine of farm animals with stable litter. A distinction is sometimes made between materials which furnish plant food directly, such as nitrates, phosphates and potassium and ammonium salts, and indirect fertilisers like calcium carbonate, which neutralize soil acid as well as serve as plant foods. There are also those which furnish plant food and aid in loosening hard clay, as is *the case with manures. The direct fertilizers containing nitrogen, phosphorus and potassium furnish the elements that are most frequently lacking in soils. Availability.—The value of a fertilizer is usually determined by the per cents of the fertilizing elements and by the solubility of the compounds containing these elements in water or soil acids, also by absence of injurious salts, such as those containing boron or aluminium. Solubility is an obvious measure of avail- ability to plants. The most commonly used, easily available water-soluble salts containing nitrogen are sodium nitrate, ammonium sulphate and calcium cyanamid. Materials in which the nitrogen is available more slowly are manures, legumes ia green manuring, stubble and dead roots of plants. In these, nitrogenous organic matter is gradually broken down into simpler, soluble compounds, by bacterial action. Examples of nitrogenous materials in which the nitrogen is practically unavailable are hair, hoof, horn and leather. These are rich in nitrogen but they are insoluble and decompose very slowly in the soil. The phosphate fertilizers also present considerable variation in solubility. This subject is discussed more fully on page 275. 270 FERTILIZERS 271 It is therefore a matter of great importance to the analyst that he should know the origin of the constituents of a fertilizer because the methods of analysis and the interpretation of results differ according to the nature of the material present. The composition of some of the more common fertilizers is indicated in the following table: TABLE XXIII.—APPROXIMATE COMPOSITION OF CERTAIN COMMERCIAL SAMPLES OF FERTILIZERS WITH RESPECT TO THREE ESSENTIAL ELEMENTS Name of material Fresh farm manure............. Dried blood.................... Sodium nitrate (com.)........... Ammonium nitrate (com.)....... Acid phosphate (com.).......... Acidulated bone meal........... Steamed bone meal............ Raw bone meal................ Raw rock phosphate........... Basic slag..................... Potassium sulphate (com.)....... Potassium chloride (com.)...... Wood ashes................... Pounds of element per ton of fertilizer Nitrogen | Phosphorus I Potassium 10 280 310 400 40 20 80 125 140 250 180 250 160 10 850 850 100 Ill Compatibility.—When artificial manures are to be mixed it is important to know what ones can be combined without loss of fertilizing value. Losses may be caused by reactions that release combined nitrogen, usually in the form of ammonia, or that make a phosphate less available to the plant by producing less soluble compounds. When an acid phosphate, for example, is mixed with sodium nitrate or calcium nitrate free nitric acid is produced and this may be partly lost: Ca(H2P04)2 + 4NaN03 -» CaNaP04 + Na8PO4 + 4HNO3. 272 QUANTITATIVE AGRICULTURAL ANALYSIS TABLE XXIV.—FERTILIZER COMPATIBILITY ________ I Should not be mixed ' Mixed just before using with I Fertilizer ''Superphosphate,1 Ca(H2PO4)2 Lime Ammonium sulphate lime Thomas slag calcium cyanamid sodium nitrate basic calcium nitrate superphosphate ammonium sulphate bone meal barnyard manure guano kainit potassium salts i Calcium cyanamid CaNCN Potassium salts Sodium nitrate Bone meal Kainit, MgSO4-KCl-3H20. Basic calcium nitrate Barnyard manure and j guano Basic slag ("Thomas slag") ! lime calcium cyanamid basic calcium nitrate Thomas slag ammonium sulphate superphosphate barnyard manure guano Thomas slag calcium superphosphate lime Thomas slag ammonium sulphate superphosphate barnyard manure guano_______ lime calcium cyanamid basic calcium nitrate potassium salts sodium nitrate kainit basic calcium nitrate calcium cyanamid lime basic calcium nitrate calcium cyanamid basic calcium nitrate calcium C3ranamid lirne ! basic calcium nitrate calcium cyanamid potassium salts sodium nitrate kainit kainit potassium, salts ammonium sulphate superphosphate Any of the above fertilizers may be mixed, at any time, except as noted otherwise. /'A'/// ,7. ///7,'. A similar resutjin, ix I •, j.^ ., >. mixed with kav.'t n ^ i >> s 1 ... • case hydrochhhi** fcr «1 > t ., ; j detected with U n ]•*;, f> |(|h( , \ be mixed with Mich ! a-i * on«^ 'i , i- slag slnee a losh d* iAi*ro^< r in t- * f -h (1a nil fc-*f.i XH ^-Ml , I These basic eonipoiiiij> ^h/nl I n »f «> : A^ > *! '. • for the same ro:iM)n. If hydrated liino, or any «»T;, f< "u,-\* ^*.*; f* r 4 with calcium add plio>pkitt, ;!^ s.wy\ r* -I*^ 4' phate would be proilimd: Ca(H2PO4). + 2C "a I III : — (\\ F* >, . -*• 4H la some case<; it Is no: donabJo i^v +»> , Jx *f r do not react witheaeii ollur « ^. ^hl' iri ii f \*.*« .it because the large tiifft*iviu'o in th«» .3« L- f /-« ft:it*.k or bin by means of a sampler, one form of which is shown in Pig. 59, This should ^eenre a the whole mass. MechJuaica! Analysis.—-Mix the well and 100 p^ of It to a sieve circular 0.5 min in diameter. up the soft lumps with a then sift. the portitm 274 QrA\TITATIVE AffRICl'LTUEAL ANALYSIS Ing ou tin* sieve. The percentage of the. tine portion is determined by difference. Preparation of Sample.—Refer to the discussion of sampling, pages 17 to 21. Reduce the remainder of the gross sample, by quartering or by use of a riffle, to an amount sufficient for analytical purposes (25 to 50 gm), transfer this to a sieve with 1-mni openings and sift, breaking the lumps with a, pestle. Grind the part remaining on the sieve in a mortar until the particles will pass through, mix thoroughly and preserve in tightly stoppered bottles. Carry out these operations as rapidly as possible to avoid loss or gain of moisture during the operation. Moisture.—Loss of weight on drying may be.due to escaped hygroscopic water, chemically combined water or ammonia or, to some extent In certain cases, to oxidation of organic matter. For this reason "moisture7' as usually reported, is not a strictly accurate term. Determination of Moisture.—Weigh 2 gm of the sample into wide crucibles or small dishes and heat for five hours at 100°. In the case of potassium salts, sodium nitrate aad ammonium sulphate, heat at about 130° to constant weight. Calculate the loss as percent of moisture. Phosphorus.—Phosphorus is deficient in soils more often than are the other necessary elements. The mineral phosphates form the chief commercial source of phosphorus, although a considerable amount is obtained from bone, Thomas slag (from the basic Bessemer steel furnace), tankage and fish scrap. Calcium orthophosphate, Ca3(P04)23 is the chief constituent of "raw" rock phosphate. Its solubility in water is very small, in absence of acids, and therefore it is advisable to use it only in a soil where there is considerable decaying organic matter to furnish carbonic acid, as otherwise its availability is small.1 Large amounts of rock phosphate are now commercially made into acid phosphates by treating the finely ground stone with sulphuric acid, thus converting the normal phosphate to a soluble form, suitable for use as a fertilizer. The character of the result of this treatment depends upon the concentration of acid and upon the relative amounts of rock phosphate and acid employed in the treatment. Dicalcium or monocalciuni phosphate, or even phosphoric acid itself, may be formed, accord- 1 See also HOPKINS, III Exp. Sia. Circ., 167 (1913) and STEWABT, Ibid., 246 (1920). r Kuril. i z EH* 27.5 ing to whether one, twn or three atoms of hydrogen are 2sul>- stitiitecl for ruldmtL The Lust t w named phosphates are easily soluble in water. \vhereus liicaldum phosphate is nearly insoluble (0.136 gin in gm Of water at 20°) but soluble in soil acids. In practice the reaction is never allowed to proceed as far as the formation of phosphoric acid. The possible reactions involved in the commercial process are indicated as follows : Can(Pl)4i, 4- H2SO4 — CaSO4 + 2CaHPO4, (1) Diealeium phosphate Cas(P04) 2 + 2H2SO4 — 2CaS04 + Ca(H2P04)2, (2) » Monocaicium phosphate ("Superphosphate'*) Ca3(P04)2 + 3H2SO4 — 3CaSO4 + 2H3PO4. (3) Phosphoric acid Sulphuric acid of 60-per cent concentration is most suitable for making acid phosphates because this produces the maximum quantity of monocaleium phosphate, the "water-soluble form. "Reversion" may occur during storage if unchanged tricalcium phosphate remains in the mixture. This is due to the inter- action of rxionocalciuni phosphate with tricalcium phosphate, the dicalcium salt being produced : Ca.i(;P(>4>2 + Ca(H2P04)2 -^ 4CaHPO4. Measure of Availability. — -Dicalcium phosphate Is soluble in salt solutions, such as ammonium citrate, as well as In salt or acid soil solutions. Hence both citrate-soluble and water-soluble phosphorus are rated as available to plants. The phosphate found in bone is in the form of the tricalcium phosphate but in this case it is in a more porous condition and it is also inter- mingled with organic matter. It is soluble to the extent of SO to 40 per cent in ammonium citrate solution and it is somewhat soluble in soil acids and salts. The principles Involved in the determination of phosphorus in phosphates are discussed on pages 87 to 92, Part I. This should be reread before beginning the following determinations. Determittttioa of Total' Phosphorus. — The choice of method for dissolving the sample will depend upon the nature of the latter. 276 QUANTITATIVE AGRICULTURAL ANALYSIS Preparation of Solution.—Treat 2.5 gin of the sample by one of the following methods: (a) Ignite in a crucible until organic matter is removed (the residue will not necessarily be white), then dissolve in hydrochloric acid. (6) Evaporate with 5 cc of magnesium nitrate solution, made as follows: Dissolve 320 gni of calcined magnesium oxide in nitric acid, avoiding an excess of the latter; add a little calcined magnesium oxide in excess, boil, filter from the residue and dilute to 2000 cc. After evaporating the fertilizer and magnesium nitrate solution, ignite until organic matter is removed and dissolve in hydrochloric acid. (c) Boil with 20 or 30 cc of concentrated sulphuric acid in a Kjeldahl flask, adding 2 to 4 gm of sodium nitrate at the beginning of the digestion and a small quantity after the solution has become nearly colorless, or adding the nitrate in small portions from time to time during the digestion. After the solution is colorless add 150 cc of water and boil for a few minutes. (d) Digest in a Kjeidahl flask with concentrated sulphuric acid and such other reagents as are used in either the plain or modified Kjeldahl or Gunning method for the determination of nitrogen (page 152). Do not add any potassium permanganate but, after the solution has become colorless, add about 100 cc of water and boil for a few minutes. (e) Dissolve in 30 cc of concentrated nitric acid and 5 cc of concentrated hydrochloric acid and boil until organic matter is destroyed. (/) Add 30 cc of concentrated hydrochloric acid, heat and add cautiously, in small quantities at a time, about 0.5 gm of finely pulverized potassium or sodium chlorate to destroy organic matter. (g) Dissolve in 15 to 30 cc of concentrated hydrochloric acid and 3 to 10 ce of concentrated nitric acid. This method is recommended for fertil- izers containing much ferric or aluminium phosphate. After the sample of fertilizer has been brought into solution by any of the methods described above, cool, dilute to 250 cc, mix and pour into a dry filter, discarding the first 10 cc of the filtrate and allowing the remainder to run into a dry flask which can be stoppered. Gravimetric Determination.—Prepare solutions of ''magnesia mixture" and ammonium niolybdate as directed on pages 88 and 89, Part I. Prepare also: "(a) Ammonium Hydroxide.—Dilute the concentrated solution ten times. (5) A nmonium Nitrate.—A 10-per cent solution. Measure 25, 50 or 100 cc of the fertilizer solution, according to the probable per cent of phosphorus, using a pipette or volumetric flask. Trans- fer to a 250-cc flask of resistance glass, neutralize with ammonium hydroxide and clear with a few drops of nitric acid, thus dissolving the small amount of precipitated hydroxides of iron and aluminium. In case hydrochloric or sulphuric acid has been used as a solvent for the fertilizer material add also 15 gm of dry ammonium nitrate. To the hot solution add ammonium molybdate solution, about 70 cc for each decigram of phosphorus pentoxide thought to be present. Immerse in water and digest at 65° for an hour and determine whether the phosphorus FERTILIZER* 277 . completely precipitated, by addirjcr em xnr ybditt bclu.*?^ t * tit supernatant liquid. L mon preup.utt f» ~* * \:r -i« t*- d #** ,^t 'ed by testing as before. Filtt r on paj t • a: J T\ ar , s *ir 4« It: r /t , . r *xrnonmm nitrate sc/ation , * . Durmjrt' > ^i^ti IT T +.+» *c i* ®ss to the flask need m 11 e touplt ti !v n»' , »s ," i' + »^ >* *^ - 4-l' *i. c^ the flask in whid- prenpitaa* n na,- \idi \\.it I i> ^%« ,i ti ^v n< -ur ' ,e ^ *j /.>ilr *- -C5 acid, the reformation of tht yellow pret*jita » ^ n nu i* i Ji*^* r, isolve the precipitate that finallj ft mis i v tht ,4dd,t *- ^ a Trm d^»p« f ' u.*fce ammonium hydroxide. Co<>t and add, TTV >' »i v j,r:J mifh \ "K* I stirring, 25 cc of magnesia mixtim . Artcr 15 ^\ n ^< - a Is! ^1^:1 > <"MI 9 I : ^cicie (specific gravity 0.00- upial ,« oiJMkiit. «f t"1«» . ^t t, T~^ia \c * T J ! oluition, stirring as this is added. Oner ar ! :^\ \\ t> ** u d fi« F+T** I ' 5- Filter and wash with dilute amn*( nil ir ! \drov»i* i TS* 1 L". t- I y ^"ree from chlorides, as shown by auditing tf f va> i.r,o< \\'tTi '< *»• » j adding silver nitrate solution. Dry tht Hilt:, j,nd pn*'I| ita**1 a,i 1 | the latter to a porcelain eraubie, prev'oiir.y isnitid ar.d \irI0 nl I • e -fc°he filter separately and transfer it.« ash, when write, to the rrur*b e \ lining the main precipitate. Ignite to w! ittne&i o* gravish vhiU ovo* I »la,st lamp or Meker bumtr, weigh and calculate the per cent of \ us pentoxide. j Itxxnetric Determination.'—Have the following ready: I MohjMMte.—To each 100 cc of the molybdate prepared for the gravimetric determination of 5 cc I >n.oentrated nitric acid. The solution should be immediately re rising. ) Standard potassium hydroxide I cc of which Is to ; of phosphorus. (Refer to equation (2} on . Part I.) This » n.oarly free from carbonates as possible and is made as follows: Dissolve r cent more than the calculated quantity for 1000 ce, dilute to 100 cc add 1 cc of a saturated solution of barium hydroxide. Stopper the . and allow to stand until the precipitate of barium carbonate has settled. &n-fc and dilute to 1000 cc. Standardize by titration using phenolphthalein. Adjust so that 1 cc is equivalent to 0.1 mg of sjpttoras. ) Standard Hydrochloric or Nitric Add—This solution should be vaJent in strength to the standard base. It should be from ioxisly boiled and cooled water and it should be standardizes! by titration ELS* the basic solution, using phenolphthalein as indicator. h.o fertiliser is dissolved by either of methods {&), f», (/) or (g}, 276. -h-od (e) is to be preferred if the material will yield to this treatment. solution is to be diluted and filtered as already directed. 278 QUANTITATIVE AGRICULTURAL ANALYSIS In the case of fertilizers containing less than 5 per cent of phosphorus pentoxide, use an aliquot corresponding to 0.4 grn of substance. If the percentage is between 5 and 20 use an aliquot corresponding to 0.1 gin of substance. Add 5 to 10 cc of concentrated nitric acid, the amount depending upon whether this acid has been used in making the solution; or add ammonium nitrate equivalent to this amount of nitric acid. Nearly neutralize with ammonium hydroxide, precipitation of hydroxide of iron or aluminum serving as indicator. Clear with a drop of nitric acid, dilute to about 100 cc and heat by immersing in water at 60° to 65°. For phosphorus pentoxide per cents below 5 add 25 cc of freshly filtered molybdate solution; for percentages between 5 and 20 add 35 cc of molybdate solution. For percentages greater than 20 add sufficient molybdate solution to insure complete precipitation of the phosphorus. Stir, allow to stand in the bath for 15 minutes and filter at once. Wash twice with water by deeantation, using 25 to 30 cc each time and agitating and settling each time before decanting. Transfer the precipitate to the filter as thoroughly as can' be done without the use of a policeman and wash the flask, paper and precipi- tate with cold, recently boiled water until the nitrate from two fillings of the filter yields a pink color upon the addition of phenolphthalein and one drop of the standard base. Remember that a trace of acid left in any of these materials will vitiate the results of the titration. Return the filter paper and precipitate to the flask in which precipitation was made. Add a measured, small excess of the standard base to dissolve the yellow precipitate, then add a few drops of phenolphthalein and titrate the unused excess of base with standard acid. Calculate the per cent of phosphorus pentoxide in the sample. The following changes in the method just described are made optional: (a) Heat the solution to only 45° to 50° and allow to stand in the bath, after the addition of the molybdate solution, for 30 minutes. (6) Cool to room temperature before adding the molybdate solution. Add the latter at the rate of 75 cc for each decigram of phosphorus pentoxide present, place the stoppered flask containing the solution in a mixing appa- ratus (Fig. 51) and mix for 30 minutes at room temperature. Filter at once and proceed as already directed. Determination of Water-soluble Phosphorus: Gravimetric Method.— Place an accurately weighed 2-gm sample on a filter and wash with small portions of cold water until about 250 cc of washings has been obtained. Allow each portion of water to run through before adding another. Keep the residue for the determination of citrate-insoluble phosphorus. Dilute the filtrate to exactly 500 cc and mix. Place 50-cc aliquots in flasks, add 10 cc of concentrated nitric acid and then ammonium hydroxide until a slight permanent precipitate is formed. Clear with a few drops of nitric acid, dilute to about 100 cc and determine the water-soluble phosphorus gravimetrically as in the case of total phosphorus. Report as phosphorus pentoxide of water- soluble compounds. Hydrolysis of ammonium citrate is due to the fact that both ammonium hydroxide and citric acid are weak electrolytes. Because of this fact it is very difficult to prepare a solution in which the two electrolytes are present in exactly equivalent quantities (a "neutral" solution), using an Indicator to determine this condition. It is well to remember that the citrate Is always largely hydrolyzed and that it is, therefore, rather a solution of (at best) equivalent quantities of the two constituents, acid and base, Ammonium Citrate Solution.. — Two methods are approved by the A. 0. A. C. for preparing Ci neutral " ammonium citrate. In one of them a stated amount of citric acid in solution is neutralized by ammonium hydroxide, using corallin (rosolic i" 279 Volumetric Determination.— Wash - gin of the sample as clim-h-d :i!w»\v r the gravimetric method. Measure the aliquot of the filtrate, and neutralize as there directed. Dilute to C>0 cc and precipitate the phosphorus as directed for the volumetric determination of total phosphorus. Calculate the per cent of phosphorus pent-oxide of water-soluble compounds. Citrate-insoluble Phosphorus. — The value of a fertilizer Is frequently rated upon the degree of solubility or the availability of its constituents to plants, as already explained. For this puxpose it is desirable to imitate the solvent action of solutions found In soils. The use of ammonium citrate solution provides an approximate distinction between available and non-available phosphates, although it should be noted that there is still con- siderable disagreement among agricultural chemis s as to the true availability of the different compounds of phosphorus. The solvent action of this solution upon calcium phosphate is largely due to the presence of free citric acid or of acid citrates, caused by the hydrolysis of the ammonium citrate (i.e., to the ; I fact that chemically equivalent quantities of ammonium hydrox- ide and citric acid in solution yield an acid condition, P% being less than 7). (NH4)3C6H507 + H20 -» (]SrH4)2HC6H507 + NH4OH (1) (NH4)3C6H507 + 2HS0 -> NH4H2C6H507 + 2NH4OH, (2) (NH4)3C6H507 + 3H20 -> H8C6H507 + 3NH4OH, (3) 2CaHP04 •+ 2H3C6H507->Ca(H2P04)2 + Ca(H2C6H5C>7)2. (4) \ < it a3(C6H507)2 + 6NH4C1, (1) Ca3(C6H507)2 -i h 4NH4C1 + 2HC1, (2) Ca3(C6H507)2 - \- 2NH4C1 + 4HC1, (3) Ca3(C6H507)2 H '- 6HC1. (4) 280 QUANTITATIVE AGRICULTURAL ANALYSIS acid) as indicator. This method is unreliable because corallin is not sufficiently sensitive to citric acid or ammonium hydroxide. In the other method the solution is nearly neutralized and a small excess of calcium chloride solution in water and alcohol is added. Calcium citrate, a salt of small solubility, precipitates as a result of such reactions as the following: 7 + 3CaCl2 -> 5O7 + 3CaCl2 507 + 3CaCl2 2H3C6H507 + 3CaCl2 Equation (1) shows that if only triammonium ("neutral") citrate is present, no matter how highly this may be hydrolyzed, the solution will be left neutral to all indicators by the removal of calcium citrate. According to Eqs. (2), (3) and (4) any acid citrate or free citric acid will produce free hydrochloric acid, which may be made evident by the use of indicators. On the other hand, if the citrate solution contained an excess of ammo- nium hydroxide this would remain after the precipitation of cal- cium citrate. According to the result obtained by testing the filtrate with an indicator, either citric acid or ammonium hydrox- ide may be added, as necessary, to obtain the proper condition of equivalent quantities of acid and base. That this solution is not really neutral and that it does not really contain tri- ammonium citrate, has already been explained. Preparation of Ammonium Citrate Solution: Calcium Chloride Method.— To 370 grn of commercial citric acid, dissolved in 1500 cc of water, add commercial ammonium hydroxide until nearly neutral, testing with recently prepared corallin solution. Add water until the specific gravity is about 1.11 at 20° Prepare a solution of fused calcium chloride, 20 gm to 100 cc, and add 400 cc of 95-per cent alcohol. Make this solution exactly neutral with tenth-normal ammonium hydroxide or hydrochloric acid, as may be neces- sary, using freshly prepared corallin solution as a preliminary indicator; test finally by diluting 2 cc with an equal volume of water and adding methyl red (cochineal is the official indicator for this purpose). Approximately 50 cc of this solution will precipitate the citric acid from 10 cc of the citrate solution. r I L*^ 1 t., ri'1 To 10 ce of the nearly iu*u*r.L the alcoholic calcium dilon ?e % , folded filter. Dilute tin «itr.*** * *• ' . reaction with a neutral « Lit? - »' * , 1 acid, add citric acid or u:u m i ** j > main portion of theeitrut«»s%ol it, *i». NJ this process until a ntutrairtu 41-) »/,* t' ' water to make the specific xr u it v I I,M Determination of Citrate-iaxsolutte Heat 100 cc of ainnuniir > t t fcv •*, flask placed in a water bat 'i a* t!. > t stoppered to prevent ovaporutii \. I bath. The level of the \vatt?r ri k! i solution in the flask. \VLer thv ft ? reached 65°, drop into it t?it f lt i> 2-gm sample of the oriidnal ,\ *t*'i7i r 'f *v ,., ,.*, » be determined. Close the fkuA t ^ t,\ u,* , i , shake -violently until tht tilto- p.ptr . n :,-••,* t minutes if no paper tuib 'H^II n-i I , « r L. i 4 - - , momentarily removing the stoppt r. 111,« +' « i*. .- tain its contents at exactly 55°. >i in t . *'i^ «\» r expiration of SOmmutesfrom thot nn t .r * t, T ^ i r ^ remove the flask from the hath aiu' in i r ,s »*, "v i, ti r * as possible through quick-*ictin«, ffitt^ |up«r \\ i^*1 water at 55° until the volume tit th+> ^xtra^o ^ i >* ** for thorough draining each tinu vf»»rt idairA r * Either (1) transfer the filter and *th u^ati^fv to A <-'i organic matter is destroyed, add into 1.5 v of ..^ >t acid and digest until all the phtnphutt +*> «LSM 'v* 4 k r with contents to a digestion fljihl, t *id «i>»*• if 1*02^ivn* VUl »^aflis LI * .^ ^- t to ' r J . r ;$ n^h iTc* l>y . At t at- ^rap.cily v ,i*r time til the 10 cc of concentrated hydrtvhlom icul dissolved. There may be an insoluble rmiiiaM i v4 \\i case. Ten minutes of digestion in tl»e vam» a* i J sL dissolve all phosphates. Dilute the solution as prepared in vi «>r - to 2n (/>), (c) or (d)t page 27(5. Determine !*a direetttl for tot;il jtL«»p}'r.ru-*. » gr-V un - t a*i*% r th . ititi iufi* J.eiii and * t t'ie pb gphiite is tei* "**^a *K eitHer /"alJ b^ ftuffeient to »*t Mix AC'!, filter already d nct^i. ^or ^w^ »^nt *f citrate- r D» r n^t «>f total t of available il \uthout previous mikss tl-t- s jhstance I ^orie m \v huh ease f I; 282 QUANTITATIVE AGRICULTURAL ANALYSIS Nitrogen. — Nitrogen is one of the most important of the elements that are concerned in plant growth. Although abun- dant in the atmosphere in an uncombined form, it is an expensive element when used in making up a fertilizer. This is because its inert nature makes difficult the problem of forming nitrogen compounds which may be used by plants. Nitrogen should therefore be obtained, so far as possible, through growing inocu- lated legumes in rotation, rather than through purchase in the form of fertilizers. Nitrogen is usually present in a fertilizer in one or more of the following forms: (1) Ammonium salts, such as ammonium sul- phate or nitrate; (2) animal or vegetable matter, such as dried blood, cotton seed meal, stable manure and guano; (3) atmos- pheric nitrogen fixed by electrical energy, as various nitrates. Sodium nitrate is found also as a natural product, chiefly in South America. Organic fertilizers have some advantages over the others in that they promote bacterial action. Because of their limited solubility they do not readily leach out of the soil, the result being that they are used less rapidly and supply the plant with nitrogen through a longer period of growing season. Calcium cyanamid also acts like the organic forms as it slowly breaks down in the soil, somewhat as follows : CaNCN + C0a + 2H20 -» CaC08 + CO(NH2)2, (1) Calcium cyanamid Urea CO(NH2)2 + 2H20 -> (NH4)aC03 , (2) ammonium carbonate being available to plants. Nitrogen used in the form of ammonium sulphate has not the most desirable action, as it finally leaves free acid in the soil, due to hydrolysis and absorption of the resulting ammonia. Chili saltpeter (sodium nitrate) has the opposite effect in the soil as the nitric acid formed by hydrolysis is used, leaving sodium hydroxide which lessens the acidity of the soil or even causes a basic condition. This is sometimes desirable, although excessive basicity may change the texture of the soil because of the deflocculating effect upon the clay particles, thus resisting the penetration of rain water and the normal movements of drainage water. This was illustrated in the experiment on deflocculation, page 268. FERTILIZERS 283 Because of the differences in cost and availability of different forms of nitrogen, it is often desirable to know the relative amounts existing as nitrates, ammonia or organic forms in the fertilizer. The following methods will give information of this character. Detection of Nitrates.—If sulphuric acid is added to a nitrate, nitric acid will be set free. This will be reduced to nitric oxide in the presence of ferrous sulphate, forming a brown ring ( | (FeSOrN202 or FeS04-NO). jjf ! i' Treat 5 gm of fertilizer with 25 cc of hot water, then filter. Mix about 3 cc of this solution with an equal volume of concentrated sulphuric acid (free from nitrates) in a test tube and cool, then pour 2 or 3 cc of concen- trated ferrous sulphate solution carefully down the side of the tube so that the two liquids do not mix. In the presence of nitrates a brown or reddish brown ring will form at the junction between the two solutions. If no color forms immediately let stand 2 or 3 minutes. Nitrogen of Ammonium Salts.—If a material containing nitrogen in various forms is placed in water and heated with magnesium oxide, ammonia is distilled and both nitrates and protein nitrogen remain behind. Magnesium hydroxide is the active agent: MgO + H20 -> Mg(OH)2, (1) Mg(OH)2 + 2NH4N03 -* Mg(N08)s + 2NH3 + H2O. (2) The ammonia is absorbed in standard acid and the titration finished as usual. Determination of Ammonia Nitrogen: Magnesium Oxide Method.—Place 2 gm of sample in a Kjeldahl digestion flask with about 200 cc of water and 5 gm or more of magnesium oxide which has been rendered free from carbonates by a previous strong ignition. Connect the flask with a condenser and distill 100 cc of the liquid into 50 cc of fifth-normal acid. Titrate the excess with fifth-normal base solution, using methyl red. Calcu- late the per cent of ammonia nitrogen. Determination of Organic and Ammonia Nitrogen: Kjeldahl Method.— The method described for organic nitrogen in feeds, page 151, includes also nitrogen of ammonium salts if present, as they may be in fertilizers. Deter- mine as there directed, using accurately weighed samples of about 2 gm. Determination of Organic and Ammonia Nitrogen: Gunning Method.— Determine as for organic nitrogen in feeds, page 154. Nitrate Nitrogen.—When nitrogen is determined by these methods most of the nitrate nitrogen is volatilized and lost upon ,*' •IK (i •j hi f f 11 284 QUANTITATIVE AGRICULTURAL ANALYSIS digesting with sulphuric acid. In order to avoid this loss the Kjeldahl method may be modified by adding benzoic acid, then using permanganates to oxidize the nitrobenzoic acid to ammonia. Phenolsulphonic acid may be substituted for benzoic acid, the nitrophenolsulphonic acids formed being then reduced to amino- phenolsulphonic acid by zinc dust. This compound is then oxidized by heating with sulphuric acid. Salicylic acid has now superseded both benzoic acid and phenolsulphonic acid. The reducing agent is either sodium thiosulphate or zinc dust: 2KN03 HN03 + C6H4 / / H2S04 OH K2S04 + 2HN03, OH 2H20, (i) (2) The nitro compound is then reduced by nascent hydrogen from zinc and sulphuric acid: xOH -COOH • OH 6H + C6H3~COOH -» CeHsf-COOH + 2H20, (3) or by sodium thiosulphate: Na2S203 + H2S04 -» Na2SO4 + H2S03+S, (4) /OH /OH 3H2S03 + CeHs^COOH + H2O-H>3H2S04 + C8H3^-COOH. (5) \NH2 The amino acid is then oxidized by concentrated sulphuric acid, ammonium sulphate resulting. Determination of Total Nitrogen in Materials Containing Nitrates: Modified Kjeldahl Method.—Weigh 2 gm of fertilizer and place in a Kjeldahl flask. Add 30 cc of concentrated sulphuric acid containing 2 gm of sali- cylic acid (these must be added together) and mix by shaking vigorously. After 30 minutes add 5 gm of sodium thiosulphate or 2 gm of zinc dust. If zinc dust is used it must be added gradually, shaking the flask after each addition. Heat gently until frothing ceases then boil for 10 minutes. Add 0.7 gm of mercury oxide or 0.3 gm of copper sulphate and continue the diges- tion, distillation and titration as in the Kjeldahl method. Make a blank determination for nitrogen in the reagents, using sugar as already directed. Calculate the per cent of total nitrogen in the fertilizer. FERTILIZERS 285 Nitrate and Ammonia Nitrogen.—These two forms of nitrogen may be determined together by first reducing the nitrate to ammonia by nascent hydrogen, then distilling the solution made basic by magnesium hydroxide. Determination of Nitrate and Ammonia Nitrogen: Iron Reduction Method.—Place 1 gm of the sample in a 500-cc flask, add about 30 cc of water and 3 gm of iron reduced by hydrogen. After standing long enough to insure solution of nitrates and ammonium salts, add 10 cc of a mixture of equal volumes of concentrated sulphuric acid and water; shake thoroughly, place a funnel in the neck of the flask to prevent mechanical loss and allow to stand until the reaction has moderated. Heat the solution slowly, then boil for 5 minutes and cool. Add about 100 cc of water, a little paraffin to prevent foaming and 10 gm of magnesium oxide, made free from carbonates by previous strong ignition. Connect with the tin condenser and boil for 40 minutes, or nearly to dryness, collecting the distillate in 50 cc of fifth- normal acid. Titrate the excess of acid with fifth-normal base, using methyl red, and calculate nitrogen of nitrates and ammonia. If the sample is known to consist of nitrates alone, proceed as above except that 0.25 gm of the sample, is used, together with 5 gm of reduced iron. After the boiling, add 75 cc of water and an excess of saturated sodium hydroxide solution (instead of magnesium oxide), and distill as above directed. Availability of Nitrogen.—Mention has already been made of the low fertilizing value of certain nitrogenous materials, due to slowness of decomposition occurring when the fertilizer is added to the soil. Nitrogen is probably directly assimilated by plants only in the most highly oxidized form, i.e., that of nitrates. Ammonium salts and certain organic materials, such as dried blood, have almost as great value because they readily decompose and oxidize in the soil, forming nitrates. Hoof, hair, leather and hide are rich in nitrogen but they do not so decompose, except very slowly, and a method for differentiating between available and non-available forms of nitrogen is desirable. The microscope will detect ground hair and other similar materials but it can give only qualitative results. Fortunately qualita- tive results are all that are necessary where the addition of such materials is contrary to law, but for scientific purposes a quantita- tive distinction between available and non-available nitrogen may be of great practical use. An exact analytical method for such a purpose seems to be impossible because there is no sharp distinction to be made between the classes of fertilizer materials. 28(> QVANTITA TIVK AGRICULTURAL A Great reliance is placed upon culture experiments, comparing the effect of using different fertilizers with plants under otherwise*, identical conditions. However, such experiments are slow and they have no value whatever for analytical purposes. An approximate distinction can be made by the use of potassium permanganate in either neutral or basic solution. Readily decomposable materials are oxidized and the nitrogen is con- verted into ammonia. It is not yet entirely clear as to how much reliance is to be placed upon these methods but they have been adopted by the Association of Official Agricultural Chemists. Determination of Total Water-insoluble Organic Nitrogen.—Place 1 gm of the material upon an 11-cm filter paper and wash with recently boiled water at room temperature until the filtrate measures 250 cc. Dry and determine nitrogen in the residue by the Kjeldahl method, making a blank determination to correct for the nitrogen of the filter paper. Determination of Water-insoluble Organic Nitrogen, Soluble in Potas- sium Permanganate.—-Place a weighed quantity of the fertilizer, equivalent to 50 ing of the water-insoluble organic nitrogen as determined above, on a moistened 11-crn filter paper and wash with recently boiled water at room temperature until the filtrate measures 250 cc. Transfer the insoluble residue with 25 cc of water (at about 30°) to a 400-ce low-form heakcr, add 1 gm of sodium carbonate, mix arid add 100 cc of 2-per cent potoHStum permanganate solution. Cover with a glass and immerse for .'$0 minutes in a water or steam bath so that the level of the liquid in the }maker is below that of the heating medium. Keep at 100°, stirring twice at intervals of 10 minutes each. At the end of this time remove from the bath, acid imme- diately 100 cc of cold water and filter through a heavy 15-crn folded filter. Wash with small quantities of cold water until the filtrate nieamireH about 400 cc. Determine total nitrogen, in the residue and filter by either of the methods already described (not modified for nitrates) making a blank deter- mination to correct for the nitrogen contained in the filter. The nitrogen thus obtained is the inactive watcr^inxoluhle organic nitrogen. Subtract this per cent from the total water-insoluble organic nitrogen. The remainder is the per cent of organic, nitrogen soluble in neutral permanganate. AH already explained, this is an approximate measure of organic nitrogen easily avail- able for plant food. Determination of Organic Nitrogen Soluble in Basic Permanganate.— Prepare a solution of potassium permanganate by dissolving 25 gm in about 100 cc of water; dissolve 150 gm of sodium hydroxide in 500 cc of water and, after thin has cooled, mix with the potassium permanganate solution and dilute the whole to 1000 cc. (a) Mixed Fertilizers.—Place an amount of material equivalent to 50 ing of total water-insoluble organic nitrogen, determined as above, on a filter paper and wash with water at room temperature until the filtrate measures about 250 cc. FERTILIZERS 287 (6) Raw Materials.—Place an amount of material equivalent to 50 mg of total water-insoluble organic nitrogen, determined as above, in a small mortar. Add about 2 gm of powdered rock phosphate (to facilitate the washing process) mix thoroughly by grinding, transfer to a filter paper and i l\ When much oil or fat is present, it is well first to wash several times with ether and to allow to stand until the odor of the latter has disappeared before extracting with water. Dry the residue from either class of materials at a temperature not exceed- ing 80°- and transfer from the filter to a 500-cc Kjeldahl digestion flask. Add 20 cc of water, about 1 gm of crushed porcelain to prevent bumping and about 1 gm of paraffin to prevent frothing. Add 100 cc of the basic permanganate solution and connect with the tin condenser, the lower end of which dips into 50 cc of fifth-normal acid. Digest slowly for at least 30 minutes, below the distillation point, with a very low flame, using wire gauze and asbestos paper between the flask and flame. Gradually raise the temperature and, after any danger of frothing has passed, distill until 95 cc of the distillate (145 cc of distillate plus acid) is obtained, then titrate as usual. If a tendency to froth is noticed lengthen the digestion period. During the digestion gently rotate the flask occasion- 11 ally, particularly if the material shows a tendency to adhere to the sides of j.| the flask. The nitrogen thus obtained is the active water-insoluble organic nitrogen. Potassium.—Most soils contain orthoclase (potassium alumin- ium silicate) but the potassium of this is unavailable or so slowly available that the supply from, this source is often not sufficient to meet the needs of the rapidly growing plant. The need is especially great in muck soils for plants such as potatoes or sugar beets, which require a large amount of potassium. Sodium compounds can take the place of potassium to only a very slight extent, if at all." It has been noted that in places where sodium nitrate has been used for some time to supply nitrogen, much less than the usual response could be obtained from potassium fertilizers. It is assumed therfore, that the sodium of the fertilizer tended partly to perform the function of potassium. The effect of potassium starvation is more definite I! than that resulting from phosphorus deficiency and it is indicated by the color of the plant becoming abnormal and dull, the ntcrn weak and the ability to manufacture starch at the normal rate lacking. Preparation of Fertilizer Solution: (a) Mixed Fertilizers.—-Place 25 ^m of the sample upon a 12.5-cm filter paper and wash with boiling wiitor unl.il the 288 QUANTITATIVE AGRICULTURAL ANALYMlti filtrate measures about 200 cc. Add to the filtrate 2 cc of concentrated hydrochloric acid, heat to boiling, transfer to a 250-cc volumetric flask and add to the hot solution a slight excess of ammonium hydroxide and sufficient ammonium oxalate to precipitate all of the calcium. Cool, dilute to 250 cc, mix and pass through a dry filter. Reject the first 25 cc of the filtrate. (6) Simple Potassium Salts, Potassium Magnesium Sulphate and Kainite.— Dissolve 2.5 gm of sample in a 250-cc volumetric flask and dilute to the mark without the addition of ammonium hydroxide or ammonium oxalate. (c) Organic Compounds: Cotton Seed Meal, Tobacco tite.mx, /<^c.—Saturate 10 gm of sample with concentrated sulphuric acid, them evaporate and ignite at a temperature not above that of dull redness to destroy organic matter. A muffle furnace will be found to be convenient for thih ration. Add a little concentrated hydrochloric acid and warm slightly in order to loosen the mass from the dish. Wash into a 500-cc volumetric flask, add ammonium hydroxide and ammonium oxalate to precipitate calcium, dilute to the mark and mix well. Filter through a dry paper and reject the first 25 cc of the filtrate. (d) Ashes from Wood or Cotton Hulls.—Digest 10 gm with 300 cc, of boiling water for 30 minutes in a covered flask. Precipitate calcium with ammo- nium hydroxide and ammonium oxalate, as directed under (a), above, rinse into a 500-cc flask, dilute to the mark and mix well. Filter through a dry paper and reject the first 25 cc of the filtrate. Determination of Potassium: (a) In Mixed Fertilizers and A«fos.—The principles underlying the determination of potassium have been diHCusncd under the head of soil analysis, page 244. Directions for the preparation of chlorplatinic acid solution and of 80-per cent alcohol also have been given. Prepare, in addition, a 20-per cent ammonium chloride solution, saturated with potassium chlorplatinate by agitating occasionally for several hours, after having added about 10 gm of the salt for each 500 cc of solution. Allow to settle and then filter. Evaporate 50 cc of the prepared solution nearly to dry ness in a dish, add 1 cc of sulphuric acid (1 to 1), evaporate to dryncss and ignite at a dull red heat until organic matter is removed and the residue is white. Dissolve the residue in hot water, using at least 20 ec for each decigram of potassium oxide present, add a few drops of concentrated hydrochloric acid and enough chlorplatinic acid to precipitate all of the potassium and to leave about 1 cc of platinum solution in excess. If the per cent of potassium is approximately known the quantity of platinum solution that is necessary should be calculated. Contamination with ammonia vapor must be avoided. Evaporate the solution on a steam bath to a thick paste, cool and add to the residue 25 cc of 80-per cent alcohol. Stir thoroughly and allow to stand for 15 minutes. Filter through a weighed Gooeh crucible. If the nitrate is not colored, sufficient chlorplatinic acid solution is not present and the analysis must be begun again with another portion of the; solution, increasing the amount of platinum solution. Wash the precipitate with 80-per cent alcohol, continuing the washing after the filtrate has become colorless. Remove the filtrate and washings FERTILIZERS 289 to the bottle which has been provided for waste platinum solutions and wash the precipitate five times with 10-cc portions of the ammonium chloride solution. Wash again thoroughly with SO-per cent alcohol, exercising par- ticular care to remove ammonium chloride from the upper part of the filter. Dry the precipitate for 30 minutes at 100°, cool and weigh. The weight of potassium chlorplatinate is given without further treatment. The precipi- tate should be completely soluble in warm water. (6) In Commercial Potassium Chloride ("Muriate of Potash").—To 50 cc of the solution already prepared add a few drops of hydrochloric acid and 10 cc of chlorplatinic acid solution, Evaporate over a steam bath to a thick paste and .treat the residue as in the case of mixed fertilizers. (c) In Potassium Sulphate, Potassium Magnesium Sulphate and Kainite.— Acidify 50 cc of the solution with a few drops of hydrochloric acid, add 15 cc of chlorplatinic acid solution and evaporate on the steam bath to a thick paste. From this point proceed as with mixed fertilizers, except that 25 cc portions of the ammonium chloride solution should be used in the washing process. The potassium is reported as per cent of potassium oxide (often called "potash") instead of as the element. Perchlorate Method.—In the discussion of methods for the determination of potassium in soils, page 244, attention was called to the fact that the increasing price of platinum has greatly handicapped laboratory work of this character and that methods not requiring the use of platinum solutions are rapidly increasing in importance. The perchlorate method as described for soil work is adapted also to fertilizer investigations. The solutions of potassium, obtained by extraction of the fertilizer for determinations by the chlorplatinate method, may be used for this purpose, the determination of potassium in these being performed exactly as directed for potassium in soils. Centrifugal Method.—There is need for a short approximate method for determining potassium which will fill somewhat the same place as the Babcock method for determining fat in cream and milk. A method has been devised by Sherrill1 which is based upon a comparison of the volumes of precipitates of potas- sium cobaltic nitrite formed from two solutions—the potassium concentration of one being known. The precipitates are sep- arated into graduated tubes by centrifugal action and the volumes noted. The method seems to be fairly accurate and it is useful when a rapid determination for factory control is necessary. 1 J. IncL Eng. Chem.} 13, 227 (1921). 19 290 QUANTITATIVE AGRICULTURAL ANALYSIS One of the writers has had some experience with this method for determining potassium in fertilizers of various kinds, and it has been found possible to check reasonably well with the results obtained by the chlorplatinate method. Some results obtained by the two methods are given in the following table: TABLE XXV.—COMPARISON OP THE PER CENT OF POTASSIUM OXIDE IN FERTILIZERS BY CENTEIFUGAL AND CHLORPLATINATE METHOLS Sample No. Chlorplatinate method* Centrifugal method t 1581 3.12 3.2 1604 1.74 1.8 1669 3.67 3.8 1823 8.04 8.2 1949 4.26 4.4 2176 . 9.38 9.1 2224 50.25 50.1 1979 4.83 4.9 * By the Indiana State Chemist, f By one of the authors. Special bottles have been described by Sherrill for this deter- mination. These are of the form shown in Fig. 60. Or the older Goetz bulbs, as used for rapid determinations of phosphorus in steel, will be found convenient. The precipitate is collected and measured in the narrow, graduated portion of the tube. If the potassium solution contains ammonia or ammonium salts, these must be expelled by evaporating a measured portion to a small volume with enough sodium hydroxide to render the solution decidedly basic, or by evaporating to dryness and ignit- ing at dull redness. The solution is then acidified with acetic acid and diluted to the original volume. Determination of Potassium: Centrifugal Method.—Prepare solutions as follows: (a) Standard Potassium Chloride Solution.—Dissolve 15.83 gm of pure potassium chloride in distilled water, add ten drops of glacial acetic acid and dilute to 1000 cc. This makes a solution containing 1 per cent of potassium oxide. (6) Sodium Cdbaltic Nitrite Solution.—Dissolve 225 gm of sodium nitrite in 400 cc of clistilled water. Also dissolve 125 gm of cobalt acetate crystals FERTILIZERS 291 in 400 cc of water. Mix the solutions, dilute to 1000 cc and mix. To 100 cc of this solution add 65 cc of distilled water and 5 cc of glacial acetic acid, mix and allow to stand over night. This diluted solution is unstable and it should not be kept for use more than five days. Measure 17 cc of solution (6) into each tube, the temperature being not lower than 22°. Be sure that the graduated stems are filled, with entire absence of air bubbles. To one of the tubes add 5 cc of .___________, solution (a) and to each of the others 5 cc of the diluted sample. Whirl immediately for one minute at the rated speed for the centrifuge that is being used. Remove the tubes and tap those in which the upper surface of the column of precipitate is not practically plane. Whirl again for 15 seconds. The reading of the precipitate in the tubes containing the sample solutions should be within 5 divisions (either way) of that of the standard. If this is not the case, repeat the experiment, using more concentrated or more dilute solutions, as indicated. From the relative volumes of the precipitates and the known potassium content of the standard solution, calcu- late the per cent of potassium (or of potassium oxide) in the sample. Methods of Pot and Field Culture.—From analyses alone it is difficult to foretell just what will be the response of a plant to any given ap- plication of fertilizer to a soil. The great variety of soil components, including toxic substances often contained in them, is responsible for this, and it is very desirable that pot and field tests be conducted for the purpose of gaining more information as to the needs of the soil for the growth of any particular crop. This is analogous to conducting feeding experiments with animals for testing the degree of utilization and the physiological effects of the feeds. Much valuable information has been gained through sand and water culture experiments, in which solutions of certain com- pounds are added. Reference may be made to the experiments of Knop,1 Shives2 and Tottingham.3 lLandw. Vers. Sta., 7, 93 (1865). 2 N. J. Exp. Sta. Bull, 319 (1917). 3 J. Am. Soc. Agron., 2, 1 (1919). FIG. 60.— Graduated tube for determina- tion of potas- sium by the Sherrill centrif- ugal method. CHAPTER XIV INSECTICIDES AND FUNGICIDES The large number of insect and fungus pests with which the economic entomologist and the horticulturist have had to contend in recent years has caused a renewed search for methods for more efficient control. The insecticides used for this purpose belong to one of two classes, depending upon whether they are for external or internal action. Paris green and London purple are examples of those of internal application, while lime-sulphur mixture and kerosene emulsion are examples of those designed to kill by contact. Bordeaux mixture is a well known remedy for fungus pests. Character of Insecticide as Related to Insect Anatomy.—There is a close relation between the general character of the insecticide sprays to be applied and that of the mouth parts of insects. Generally speaking, insects secure their food either by biting out and swallowing plant particles or by sucking juices from interior portions of the plant. Those of the biting kind have jaws and also certain accessory parts which enable the insect to cut and pass on the small parts of food to the digestive organs. Most sucking insects have mouth parts of long bristle-like structure. These are inclosed in a tube and the bristles and beak together constitute a sucking apparatus for the extraction of the plant juices. It is possible to kill both sucking and biting insects by poisoning the air with hydrocyanic acid or other poisonous gases, as well as by poisons that are to be eaten by the insect. Action of Contact Insecticides.—Considerable attention has been given to the method by which contact insecticides kill. Shafer1 found that in the case of certain volatile insecticides, such as gasoline, carbon disulphide or chloroform, the fatty membranes absorb some of the vapor, which renders them less permeable to oxygen. The cells thus gradually cease to 1 Mich. Exp. Sta. Tech. Bull, 21 (1915). INSECTICIDES AXD FUNGICIDES 293 function in a normal way. Non-volatile insecticides in the form of powdered solids may function by sticking to certain body secretions, then being absorbed into the tissues. As examples of this class, borax and sodium fluoride are frequently used to exterminate cockroaches. The powder sticks to the body of the insect and is partly absorbed but it also acts as a stomach poison because some of it is usually licked off and swallowed by the animal. The vapor of white hellebore is insufficient to kill insects but Shafer has noted that rose slugs which come into contact with this insecticide gradually become numbed and fall from the leaves. This occurred even in cases where none of the insecticide had been eaten. It is concluded that the numbing effect is due to slight dissolving of the powder and surface absorption by the excretions, little if any of the insecticide passing through the cuticular covering, and that the cause of the final death of the insect is due more to drying and starving than to any other reason. Finally, the natural cells of some insects contain enzymes, the normal functioning of which is of the greatest importance to the well-being of the insect. The interference of the various insecticides with the activity of these enzymatic bodies is known to be serious and this may be the cause of the death of the insect in some cases. Preparation of Insecticides.—The internal poisons are usually prepared in considerable quantities and their preparation should be under chemical control. The contact and fungicide poisons are freshly prepared by the sprayer and their efficiency depends upon the composition and proportions of the ingredients. Ar- senic has been so universally used as an active internal poison for insects that the determination of this element is highly important. Free arsenous acid in solution has a destructive action on foliage, therefore it is necessary also to limit the per cent of arsenic in this form. The maximum quantity which is safe for foliage varies from 4 to 6 per cent. Mixing of Sprays.—The question of combining insecticides and fungicides for the control of orchard pests is important from the standpoint of saving time and money as well as from that of increasing the efficiency of the spray. Choosing the 294 QUANTITATIVE AUHWt'LTUKAL ANALYSIS proper spray materials and mixing them so an to retain their insccticidal or fungicidal value is often a difficult and complicated problem.1 Chemical or physical changes may take place on mixing, resulting in compounds being formed which are injurioun to foliage, or in some eases the upray may become worthlw-w because the active killing agent has heroine inert. The various objectionable combinations are shown in Table XXVI on page 295. It will Ixs noted that Bordeaux mixture (copper sulphate and calcium hydroxide) with arsenal e of lead in permissible. It has been shown by analysis that when these arc* mixed the amount of soluble* arsenic is not mueh greater than when lead arson ate is treated with pure watei. On the other hand, lead arsenate and soap solution form an objectionable* combination because the load arsenale reacts with the sodium oleate of the soap, forming lead oleate (insoluble in water) nnd sodium arscnatc. The latter in soluble in water and the foliagf* in injured by the high concentration of soluble ar^enie. Lime-sulphur solution and lead arsenalc may !•«* safely mixed because analysis shows that the soluble arsenic is not tiitidt greater than when the arsenic compound in shaken with witter, The table shows tilao that Bordeaux mixture should not. In* mixed with the group of "emulsified oils" beeauw the emulsion of oils with water containing calcium hydroxide of Bordeaux mixture in not very satisfactory, the* result beinfc fhnf Mime cif the unemuisified oil remaining will injure the plant. The reverw- ble nature of soap and oil exnulKionn in general is diwunml by Bancroft2 as follows: "Since sodium oleate emulHificn nil in water nnd ealrium ulejite <«niul*i- fics water in oil, a mixture of the* two ^leufe* will Iwhiive differently, depending on the relative amounts. There will aln* he w?w* ratio of calcium to sodium at which the two oleates will praHindly !»iilnnci» other and the nlightest relative change will chungc flu* type of I lie emulsion." The reaction of calcium hydroxide of Bordeaux mixture with Bodium oleate of the soap will result in flu* formation of the? maximum quantity of calcium oleate* and thw will then 1 CM. Kxp. Kta. Circ., 195 (19IK), 2"Appli(i) Starch Indicator.—Mix about 0.5 gm of starch with cold water to form a thin paste; add about 100 cc of boiling water and stir thoroughly. (c) Iodine Solution.—Dissolve 6.35 gm of iodine and 12.5 gm of potassium iodide in about 100 cc of water, decant from any sediment, dilute to 1000 cc and mix well. Standardize against solution (a) as follows: Using a pipette, measure 50 cc of the arsenous acid solution into an Erlenmeyer flask, dilute to about 400 cc and neutralize with sodium bicarbon- ate, adding 4 to 5 gm in excess. Add the standard iodine solution from a burette, rotating the flask continuously, until the yellow color disappears only slowly, showing that the end point is near; then add 1 cc of the starch solution and continue adding the iodine solution drop by drop until a per- manent blue color is obtained. Calculate the value of the standard iodine solution in terms of arsenous oxide (AsaOa). Keep the solution stoppered and away from bright light. Even with this precaution the oxidizing value changes and the solution should be standardized within a few hours of the time when it is to be used. 298 QUANTITATIVE AGRICULTURAL ANALYSIS Calculate the theoretical weight of Paris green that would be equivalent to 250- cc of the standard iodine solution. Weigh out this amount and wash it and about 5 gm of cuprous chloride into the 250 distilling flask with 100 cc of concentrated hydrochloric acid. Distill until the volume in the distill- ing flask is reduced to about 40 cc, then add 50 cc of concentrated hydro- chloric acid by means of the dropping funnel. Continue this process of addition of acid and distillation until 200 cc of distillate has been obtained. Wash down the condenser and all connecting tubes, allowing the rinsings to run into the flasks. Transfer the contents of the receiving flasks to a 1000- cc volumetric flask, rinsing the former well, dilute to the mark and mix thoroughly. Measure 100 cc of this solution into a 1000-cc Erlenmeyer flask, add phenolphthalein and nearly neutralize with a concentrated sodium hydroxide solution. The solution should be kept cold. Add 10 gm of sodium bicarbonate and titrate the arsenic with standard iodine solution, using starch as indicator. Calculate the per cent of total arsenic, as both element and arsenous oxide. The official method for the determination of arsenic, which has just been described, is in some respects less desirable than the method which was formerly official.1 One of the principal diffi- culties of the older method is the formation of a yellow colloidal solution of arsenous iodide when potassium iodide and hydro- chloric acid are added to reduce the arsenic solution. This color makes impossible the exact removal of iodine by sodium thio- sulphate but if the analysis is performed carefully as described below, this difficulty will disappear. Determination of Total Arsenic and of Copper in Paris Green without Distillation.—To 2 gm of Paris green in a 250-cc flask add about 100 cc of a 2-per cent solution of sodium hydroxide. Boil until all the green compound has been decomposed and only red cuprous oxide remains. Cool, filter into a 250-cc volumetric flask, washing the paper well, dilute to the mark and mix well. Reserve the cuprous oxide on the filter for the copper determination. Measure two or three portions of 50 cc each of the solution into 250-cc flasks and concentrate by boiling to about half the original volume. Cool to 60°, add 10 cc of concentrated hydrochloric acid and 1 gm of potassium iodide. Mix and allow to stand for 10 minutes. From a burette carefully add sodium thiosulphate solution until the iodine is all reduced. Starch should not be added but care should be exercised in reaching the end point. If a persistent yellow color (see above) develops at this point, use starch solution on a test plate as an outside indicator, touching drops of the titrated solution to the starch. If the end point has been passed, add iodine solution until the iodine-starch reaction is barely produced. Allow to stand for 5 1 U. S. Dept. ofAgr., Chem. Bull, 107. INSECTICIDES AXD Fr.WIClDES ? longer and if iodine color carefully mid more tion. Immediately add, as rapidly as can f* done wit I. -~vescence? 15 gm of sodium bicarbonate, free from luia 3nce with standard Iodine solution, deferring the additu il near the end point. Calculate the per cent of arsen -rsenous oxide, In the Paris green. he residue of cuprous oxide is treated on the with 5 1, specific gravity 1.2, the solution in it 250-i.- ^a-sh. the paper well with hot water and as direct«ni Sx the adardization of sodium thiosulphate copper. ;inning with i4Boi! until red fumes have . . .'* per cent of copper in the Paris green. The also be .. cupric oxide? if desired. distinction between Arsenates and Arsenites.-—it is frequently sirable to distinguish qualitatively senites in spray mixtures. Probably the : an arsenate depends upon the of a of ignesium ammonium arsenate a salt is . to the basic solution: 2XH4CL uU* ar J i r % asi» a , f the arsen;? 3NH4OH -+ (NH4)3AsO4 - 3As04 + MgCla -» MgNHiAsO i -Dissolve about 0.5 gm of sodium arseniteandsod'un >-cc portions of water. Add 3 cc of nnxturt t*/ eot'ls t ir. It will be noted that no precipitate will be pro«iui*od ir th« f rr it a white crystalline one forms in the ad! to the Kdt :ssel. Repeat, using the filtered spray solution instead of known Its. Silver nitrate is a reagent which is useful for the of rsenites. In a neutral solution of an this a reclpitate of silver arsenite while with an rsenate is produced. Water-soluble Arsenous Oxide. — It has aat water-soluble arsenic (of free arsenous or ie) is very injurious to young foliage. The Federal insecticide ct of 1910 specifies a maximum of 3.5 per cent of rsenous oxide in Paris green and not more 0.75 per in 3ad arsenate paste. It is very important that the directions as to be observed closely because the amount of soluble varies .onsiderably with small deviations in temperature. 300 QUANTITATIVE AGRICULTURAL ANALYSIS Determination of Water-soluble Arsenic.—Weigh 2 gm (if a paste, use 4 gm) of the sample on a counterpoised glass or scoop, brush into a 1000-cc volumetric flask, and add nearly 1000 cc of recently boiled distilled water which has been cooled to exactly 32°. Stopper the flask and immerse in a water bath which is kept at 32° (± 1°) by means of a thermostat. Digest for 24 hours, shaking hourly for the first eight hours of this period. Dilute to the mark, mix and filter through a dry filter, reject, the first 25 cc and collect exactly 250 cc in a volumetric flask. Rinse into a 1000-cc flask or beaker and titrate with the standard iodine solution that was used for total arsenic. Calculate the amount of water-soluble arsenic as arsenous oxide. LEAD ARSENATE Of the internal poisons for insects, lead arsenate is used most extensively. Lead arsenate was recommended as an insecticide in 1892 and it was first used against tent caterpillars. It is made by treating disodium arsenate with either lead nitrate or lead acetate. Lead arsenate made from lead nitrate contains about 31.5 per cent of combined arsenic pentoxide while that made from lead acetate contains about 25.5 per cent. Lead arsenate (" neutral") is gradually replacing Paris green as a spray because of its low degree of solubility, it being a safer spray on this account. The arsenic becomes more soluble if the lead arsenate solution is prepared with water containing sodium sulphate or sodium chloride. Solutions containing only 0.1 per cent of the former or 0.05 per cent of the latter will dissolve an appreciable amount of arsenic from lead arsenate. Spraying tests have shown that 10 grains of sodium chloride per gallon, when used with lead arsenate in the spray fluid, produced injury and 40 grains per gallon injured about half of the foliage. It is therefore important to avoid ordinary mineral water and salt water in preparing the spray. Lead arsenate has the advantage over Paris green in that it sticks to the foliage well when applied as a spray. Determination of Moisture: (a) In Powder.—Weigh a porcelain crucible without cover, then add about 2 gm of sample and reweigh. Dry to con- stant weight at 105° to 110° and report the loss of weight as moisture. (6) In Paste.—In a weighed dish dry 50 gm for one hour at 105° to 110°. Cool and reweigh. Calculate the moisture thus obtained as p. Grind the partly dried sample to a fine powder, mix well and transfer a small portion to a sample bottle. Weigh 2 gm of this into a crucible and dry again for >* AM) 301 two hours at 105 ' to 1 W\ Calculate thfc loss as per cent, on the basis of the «lried sample as 100 and «\ili this //. Total moisture = AT = p + / l V ^ iob" the anhydrous material for the determination of the total lead oxide and total arsenic. etenninatiom of Lead Oxide. — Heat on a hot plate about 0.5 gin of the po\vdered sample with about 23 cc of dilute nitric acid (1 to 4) in a 500-cc beaker. If necessary, remove any insoluble residue by filtration. Dilute to about 400 cc and heat nearly to boiling. Add ammonium hydrox- ide to slight precipitation of basic lead salts, then add dilute nitric acid (1 to 10) to redissoive the precipitate, adding about 2 cc In excess. Pipette into this solution, kept almost at boiling, 50 cc of a hot 10-per cent potassium chrom a,te solution, stirring constantly. Decant while hot through a weighed Goocli filter, previously dried at 150°. Wash several times by decantation and thten on the filter paper with boiling water until the washings are color- less. Dry the lead chromate at 140° to 150° to constant weight. Calculate the per cent of lead monoxide in the dried sample. Multiply this per cent by 100 - 7) — (see determination of moisture) to obtain the per cent based upon the original paste. Determination of Total Arsenic. — Proceed as directed for the determina- tion of total arsenic in Paris green by the distillation method, page 297. Use about 5 gm of the sample and after the distillate has been diluted to 100O cc and mixed, measure 100-cc portions for titration. Calculate the per cent of total arsenic, expressed as arsenic pentoxide. Determination of Total Arsenic Oxide. — Prepare a standard iodine and starch, solution as directed in the determination of Paris green on page 297. Prepare also: Standard Thiosulphate Solution. — An approximately twentieth-normal solution of sodium thiosulphate is prepared by dissolving 13 gni of the crystallized salt in recently boiled and cooled water. Filter and make up to 1000 cc with water treated in the same way. Standardize by t>He method given on page 162, or by that given on page 178, in either case modifying the treatment to take account of the fact that this solution is only about half as concentrated as the ones described in these references. Calculate the weight of arsenic pentoxide equivalent to 1 cc of the solution. \\relgh accurately about 0.5 gm. of the powdered sample, transfer to an Erlenrneyer flask and add 25 cc of concentrated hydrochloric acid. If necessary to effect solution heat on a steam bath, keeping the flask covered in order to prevent evaporation of the acid. Cool to 20°, add 10 cc of 20- per cent potassium iodide solution and 50 cc (more, if necessary to produce a clea,r solution) of 25-per cent ammonium chloride solution. Immediately titrate the liberated iodine with standard sodium thiosulphate. When the color becomes a faint yellow, dilute with 150 cc of water and continue the 302 QUANTITATIVE AGRICULTURAL ANALYSIS titration very slowly, using starch solution near the end point. Calculate the per cent of total arsenic oxide, AsaOs. Determination of Water-soluble Arsenic Oxide.—The agents needed are starch indicator, standard arsenous oxide solution and a standard iodine solution. These are prepared as directed on page 297. To 2 gm of the original sample, if a powder, or 4 gm if a paste, in a 1000- cc volumetric flask, add nearly 1000 cc of recently boiled water which has been cooled to exactly 32°. Stopper the flask and place in a water bath kept at 32° by means of a thermostat. Digest for 24 hours, shaking hourly for eight hours during this period. Dilute to the mark, mix and filter through a dry filter, rejecting the first 25 cc of nitrate. Transfer 250 or 500 cc of the clear filtrate to an Erlenmeyer flask, add 3 cc of concentrated sulphuric acid and evaporate on a hot plate.. When the volume reaches about 100 cc add 1 gm of potassium iodide and continue the boiling until the volume is about 40 cc. Cool, dilute to about 200 cc, remove the excess iodine with twentieth-normal sodium thiosulphate, avoiding the use of starch solution, and proceed as directed on page 298 for the determination of arsenic in Paris green, beginning with "nearly neutralize with sodium hydroxide............." Calculate and report as per cent of water-soluble arsenic oxide, As206. Determination of Total Arsenous Oxide.—Prepare the starch indicator, standard arsenous oxide and standard iodine solution as directed in the determination of Paris green on page 297. Prepare also: (a) Dilute Sulphuric Acid Solution.—Dilute 15 cc of concentrated sul- phuric acid with 85 cc of water. (6) Sodium Hydroxide Solution.—Dissolve 25 gm of sodium hydroxide in 50 cc of water. Weigh 0.25 gm of the powdered sample, transfer to a 200-cc Erlenmeyer flask, add 100 ce of dilute sulphuric acid (a), and boil for 30 minutes. Cool, transfer to a 200-cc volumetric flask, dilute to the mark, shake thoroughly and filter through a dry filter. Nearly neutralize 100 cc of the filtrate with sodium hydroxide (6), using a few drops of phenolphthalein as indicator. If the neutral point is passed, make acid again with dilute sulphuric acid. Continue as directed in the determination of total arsenic in Paris green, page 299, beginning with the neutralization by sodium bicarbonate. Calculate the per cent of total arsenous oxide in the sample. CALCIUM ARSENATE This is one of the newer insecticides. It is somewhat similar to arsenate of lead but, in its present form, it is not recommended for use on the more sensitive foliage, such as that of the stone fruits, because of the large amount of water-soluble arsenic it often contains, this causing considerable damage to foliage. INSECTICIDES AXD FUNGICIDES of the arsenates of calcixun are quite stable: arsenate, Ca3(As04)2 and dicalcium arsenate, CaHAsO4. tri calcium arsenate may be made in two ways, as follows: 7* e 3CaHAs04 + 2NaOH-» Ca3(AsO4)a + Na*HAsO4 +2HaO; 2H3As04 4- 3Ca(OH)a — » Cas(As04)2 + 6H2O. arsenate dissolves in water to the extent of 0.33 In 100 cc at 25° while tricalcium arsenate is soluble to the extent of only 0.014 gni at the same temperature. The sola- bility of the first salt Is so large that there Is danger of damage when it is applied to tender foliage. Also, unless it has prepared with c4arCj it may contain quantities of the easily soluble disodium arsenate, as shown in Eq. (1). This has been largely overcome by adding an excess of lime water, whirh reacts with any dicalcium arsenate or disodium arsenate to form the less soluble tricalcium salt. 1 The powdered calcium arsenates on the market contain approximately 52 per cent of arsenic, calculated as pentoxide, while the paste contains less^ according to the proportion of water retained. IDetermination of Total Arsenic. — Proceed by the distillation method as with Paris green, using 2 to 2.5 gm of sample. Calculate as the pentoxide. LIME-SULPHUR SOLUTION This spray is important in the control of San Jose and scales. It is effective also In the extermination of numerous insects. This is especially true when it is combined with arsenate and nicotine and it Is used then for the simultaneous destruction of many sucking and chewing insects and of fungus diseases. The standard lime-sulphur solution consists of cal- cium tetrasulphide, pentasulphide and thiosulphate in a water solution. It is produced by boiling lime water containing sulphur. The probable reactions are generally understood to be iFts follows: 3Ca(OH)2 + 10S -» 2CaS4 + CaS203 + 3H2O. (1) i See also RKEDV and HAA«, J. I nd. Eng. Chem., 13, 1038 (1921). 304 QUANTITATIVE AGRICULTURAL ANALYSIS The calcium thiosulphate thus formed is largely decomposed by boiling, calcium sulphite and free sulphur being formed: CaS203 -» CaS03 + S. . (2) The free sulphur formed in reaction (2) is dissolved by calcium tetrasulphide to form pentasulphide. CaS4 + S -» CaS5. (3) The insoluble sludge remaining consists of a mixture of calcium sulphite and some calcium sulphate, the latter being formed by oxidation of sulphite. Extensive investigations on the fungicidal value of sulphur of polysulphides were carried on by Syre, Solmon and War- mall, 1 using the hop-mildew at its most resistant stage as their standard. They have expressed the opinion that the fungicidal value depends upon the percentage of polysulphide sulphur in solution, rather than the total sulphur content. Lime-sulphur solutions, either upon standing exposed to air or after being sprayed, slowly react with oxygen, forming calcium thiosulphate and free sulphur: 2CaS5 + 302 -> 2CaS203 + 3S2 Determination of Total Sulphur.—Weigh a closed weighing bottle then add about 10 cc of the lime-sulphur solution, close and weigh again. Rinse into a 250-cc volumetric flask and dilute to the mark with recently boiled and cooled distilled water and mix thoroughly. Dissolve 2 to 3 gm of sodium peroxide in 50 cc of cold distilled water in a 250-cc beaker. Pipette 10 cc of the prepared lime-sulphur solution to this solution, keeping the tip of the pipette just under the surface of the solution until it is to be raised for drainage at the end of the process. Cover immediately with a watch glass and warm on a steam bath with frequent shakings until the sulphur is oxidized to sulphate (the yellow color having disappeared), adding more sodium peroxide if necessary. Dilute to 25 cc, acidify with hydrochloric acid, evaporate to dryness, treat with 25 cc of water acidified with 5 cc of hydrochloric acid, boil and filter to remove silica if present. Dilute the filtrate to about 200 cc and heat to boiling. Add a drop of methyl red then neutralize with sulphur-free ammonium hydroxide. Add 1 cc of approxi- mately normal (1 to 10) hydrochloric acid, then add 10 to 25 cc (as found to be necessary) of 10-per cent barium chloride solution, slowly from a pipette, stirring constantly. Digest on a steam bath until the precipitate 1 /. Agr. Sci., 9, 283 (1919). X Axr> FTXGICIDES settles readily, then filter through quantitative filter paper. Wash until free from chlorides and burn tht* paper in an inclined weighed crucible at a W temperature (not above dull redness). When the precipitate is white, cool and. \veigh. Calculate the sulphur from the weight of barium sulphate. Corrections should lie made for any sulphur present in the reagents, deter- mined by a blank experiment. Sodium peroxide, especially, is liable to contain sulphates. Determination of Total Sulphide Sulphur. — Dissolve 50 gm of zinc chlo- ride in about 500 cc of water and add 125 cc of concentrated ammonium hydroxide, which will redissolve the precipitate first formed. Add 50 gm of ammonium chloride and dilute to about 1 liter. Pipette 10 cc of the lime-sulphur solution (freshly made as for the total sulphur determination) Into a 250-cc beaker, dilute to 100 cc and add ammoniacai zinc solution until the sulphide sulphur is all precipitated, as indicated by the failure of a drop of the clear solution to darken a few drops of dilute nickel sulphate solution. Filter immediately, wash the precipitate thoroughly with cold water and return it and the filter to the beaker. Cover with water, disintegrate with a glass rod and slowly add about 3 gin of sodium peroxide, keeping the beaker well covered with the watch glass. Warm on the steam bath, with frequent shaking, until all of the sulphur is oxidized to sulphate and the precipitate is all dissolved, adding more sodium peroxide if necessary. Make slightly acid with hydrochloric acid, filter to remove shreds of filter paper, wash thoroughly with hot water, heat the filtrate and washings to boiling and determine the sulphur as described for total sulphur, neutralizing and acidifying in the same manner. Calculate the per cent of sulphide sulphur in the sample. Total Calcium. — The per cent of calcium in a lime-sulphur solution will depend upon the character and purity of the lime used in its preparation, as well as upon dilution and degree of hydrolysis. It will vary over wide limits but as this element is of relatively small importance in connection with insecticidai properties, its determination is not often required. The fol- lowing method is official: Determination of Total Calcium. — To 25 cc of the lime-sulphur solution, prepared as for the preceding determination, add 10 ce of concentrated hydrochloric acid and evaporate to dryness on the steam bath. Add 25 cc of water and. 5 cc of concentrated hydrochloric acid, warm until all of the calcium chloride is dissolved and filter from sulphur and any silica that may be present. Make slightly ammoniacai, boil and filter from iron and aluminium hydroxides if these are produced. Heat to boiling and precipi- tate the calcium with am&ionium oxalate solution and finish the determina- tion as described on page 64 or 69, Part I. Calculate the per cent of calcium oxide in the sample. 20 306 QUANTITATIVE AGRICULTURAL ANALYSIS NICOTINE INSECTICIDES Nicotine in solution is an effective agent for destroying many soft bodied insects, as aphides and pear psyllse. Solutions of nicotine are valuable as insecticides because of the intensely poisonous character of nicotine, whether eaten by the insect or absorbed through its exterior covering. They may be applied in various dilutions and in combinations with other sprays to treat, all at once, certain sucking and biting insects and fungus parasites. Nicotine is not injurious to foliage, in any concentration. As a vegetable alkaloid it is a weak base and this makes it possible to determine the amount of nicotine present in a solution by titrating with a standard acid. Y) A B D FIG. 62.—Apparatus for distillation with steam. Most dry tobacco waste contains from 2 to 3 per cent of nicotine. An extract may be prepared for use as an insecticide by stirring 25 to 30 Ib. of the tobacco waste with 50 gal. of water. This will make a solution averaging about 0.06 per cent -of nicotine.1 The separation of nicotine from a solution is made by extract- ing with ether. The extracted residue is dissolved in a base 1 Va. Exp. Sta. Bull, 208 (1914). INSECTICIDES AXD FL'XtUCIDES 307 solution and the nicotine separated by steam distillation. The nicotine in the distillate is titrated with a standard acid as follows : CH -CH9 HCji HC* C HCi + HC1- CH N CH8 CH2 HC Determination of Kicotfne.—Prepare the following solutions: (a) Alcoholic Sodium Hydroxide Solution.—Dissolve 6 gm of sodium hydrox- ide in 40 cc of water and 60 cc of 90-per cent alcohol. (b) A pproximaiely tenth-normal sodium hydroxide solution, not standardized. (c) Tenth-normal sulphuric add, accurately standardized against pure sodium carbonate (see pages 5S et seq, Part I). Weigh into a 50-ec beaker, 5 to 6 gm of tobacco extract or 20 gm of finely powdered tobacco or tobacco waste which has been dried at 60°. Add 10 cc of alcoholic sodium hydroxide and, in the case of tobacco extract, follow with enough shredded filter paper to form a moist but not lumpy mass. Mix thoroughly, transfer to a continuous extractor (page 146) and extract for about five hours with ether. Evaporate the ether at a low temperature and take up the residue with 50 cc of sodium hydroxide (b}. Transfer the residue by means of 200 cc of water to a 500-cc Kjeldahl flasks add a piece of pumice or a small amount of crushed porcelain and a small piece of paraffine, heat to boiling and distill by steam, passing the distillate through a condenser cooled by a rapidly flowing current of water. Distill from 400 to 500 cc, stopping the current of steam and using a flame under the flask at a point such that only about 15 cc of the liquid finally remains in the flask. Titrate the distillate with tenth-normal sulphuric acid, using methyl red as an indicator. Calculate the per cent of nicotine in the sample. 308 QUANTITATIVE AGRICULTURAL ANALYSIS BORDEAUX MIXTURE Bordeaux mixture consists of copper sulphate and calcium hydroxide. It is one of the most reliable of the fungicides, its poisonous properties being due to the copper and hydroxyl ions. Chemical tests show that when Bordeaux mixture is applied to the leaf, a small amount of copper enters and com- bines with chlorophyl of the cells. This seems to give the leaf an increased resistance to insect injury. The spray spreads rapidly over the leaf and forms a thin colloidal membrane composed of basic copper and calcium salts. Both copper and calcium hydroxide are fungicidal and when spores fall upon a sprayed leaf, they are either killed or germinate very slowly. Moisture. — The determination of moisture in Bordeaux mixture powder is made by drying at 105° to 110° to constant weight. The determination in the paste is complicated by the fact that basic carbonates of copper (formed through interaction of copper sulphate, calcium hydroxide and carbonic acid) lose carbon dioxide during the first drying process : (CuOH)2C03->2CuO + C02 + H20. A determination of carbon dioxide must then be made and the proper correction applied. Determination of Moisture: (a) In Powder. — Dry 2 gm of sample as directed for lead arsenate powder, page 300. Calculate the loss as moisture. (b) In Paste. — Heat about 100 gm (weighed in a porcelain dish) at 90° to 100° until dry enough to powder readily. Weigh and calculate the per cent loss. Denote this by a. Powder the partly dried sample, mix and determine the per cent loss on drying about 2 gm of this as directed above for powder. Call this 6. Determine carbon dioxide (see below) in both paste and partly dried powder. Let c — per cent of carbon dioxide in the partly dried material and d the total carbon dioxide in the paste. Since b and c are based upon a partly dried sample the factor — r^r — will correct these to a basis of the original paste. Then total moisture - d. (The student should prove this formula. Note that the formula given in the Official Methods, separate volume, first edition, is incorrect.) Determination of Carbon Dioxide. — Weigh 2 gm of the powder or 10 gm of the paste, place in the reaction flask together with 20 cc of water and ,1^4 — njn(J £}ie carfoon dioxide by one of the methods discussed on pages 77 Part I. Calculate the per cent of carbon dioxide in the sample as used. INSECTICIDES AND FUNGICIDES 309 Determination of Copper.—Prepare solutions as directed for the determi- nation of copper in cuprous oxide, page 162 (feeds). Weigh about 2 gm of the sample, dissolve in about 50 cc of 10-per cent nitric acid and add ammo- nium hydroxide solution in slight excess. Then without removing the precipitate which has formed, add acetic acid to clear and 5 to 10 cc in excess. Cool, add 10 cc of 30-per cent potassium iodide solution and titrate with thiosulphate as directed on page 162. Calculate the per cent of copper present in the sample (dried, partly dried or paste) and in the sample as received. SOAP SPRAYS AND EMULSIONS Soaps are used to a considerable extent for making oil emul- sions and they are often added to other sprays to cause the latter to spread uniformly and to adhere more closely to the foliage. The soap-kerosene emulsions are used somewhat for the soft- bodied sucking insects, such as aphides, but they are being replaced, by solutions of nicotine sulphate. Soap-oil emulsions are used for scale insects. Determination of Moisture in Soap.—Weigh rapidly about 5 gm of the carefully selected sample into a weighed 50-cc beaker in which has been placed a one-half inch layer of recently ignited dry sand and a small glass rod. If the soap is hard, cut it up into very thin strips. Add 25 cc of alcohol (more if necessary) and dissolve the soap by warming on a steam bath, stirring constantly. Evaporate the alcohol, heat in an oven at 110°, stirring occasionally, until the soap is nearly dry, then weigh; dry again for 30 minutes and weigh. Continue this process until the weight changes only a few milligrams during 30 minutes of drying. CHLORPICRIN Chlorpicrin is trichlornitromethane, CC13N02. It is rated as 283 times as toxic as carbon disulphide, compared on a basis of molecular weights. It is not as inflammable as is carbon disulphide, and its vapor is about twice as heavy, which feature makes it quite desirable for grain fumigation. Chlorpicrin vapor is so very poisonous1 and active that not more than one- half pound is needed for the fumigation of 1000 cu. ft. of space. Ten times this amount of carbon disulphide would be required. Much work is being done upon the adaptation of other poison gases to insecticidal and fungicidal uses. No doubt this field will be developed very rapidly during the next few years and the agricultural analyst will have many new problems presented for his solution, as a result. iJ.Econ. Ent., 11,4 (1918). 312 LOGARITHMS LOGAEITHMS Natural Numbers 0 1 2 3 4 5 6 7 8 9 Proportional Parts 1 2|3|4|5|6|7[8|9 10 0000 0043 0086 0128 0170 0212 0253 0294 0334 0374 4 8 12 17 21 25 29 33 37 11 0414 0453 0492 0531 0569 0607 0645 0682 0719 0755 4 8 11 15 19 23 26 30 34 12 0792 0828 0864 0899 0934 0969 1004 1038 1072 1106 3 7 10 14 17 21 24 28 31 13 1139 1173 1206 1239 1271 1303 1335 1367 1399 1430 3 6 10 13 16 19 23 26 29 14 1461 1492 1523 1553 1584 1614 1644 1673 1703 1732 3 6 9 12 15 18 21 24 27 15 1761 1790 1818 1847 1875 1903 1931 1959 1987 2014 3 6 8 11 14 17 20 22 25 16 2041 2068 2095 ,2122 2148 2175 2201 2227 2253 2279 3 5 8 11 13 16 18 21 24 17 2304 2330 2355 2380 2405 2430 2455 2480 2504 2529 2 5 7 10 12 15 17 20 22 18 2553 2577 2601 2625 2648 2672 2695 2718 2742 2765 2 5 7 9 12 14 16 19 21 19 2788 2810 2833 2856 2878 2900 2923 2945 2967 2989 2 4 7 9 11 13 16 18 20 20 3010 3032 3054 3075 3096 3118 3139 3160 3181 3201 2 4 6 8 11 13 15 17 19 21 3222 3243 3263 3284 3304 3324 3345 3365 3385 3404 2 4 6 8 10 12 14 16 18 22 3424 3444 3464 3483 3502 3522 3541 3560 3579 3598 2 4 6 8 10 12 14 15 17 23 3617 3636 3655 3674 3692 3711 3729 3747 3766 3784 2 4 6 7 9 11 13 15 17 24 3802 3820 3838 3856 3874 3892 3909 3927 3945 3962 2 4 5 7 9 11 12 14 16 25 3979 3997 4014 4031 4048 4065 4082 4099 4116 4133 2 3 5 7 9 10 12 14 15 26 4150 4166 4183 4200 4216 4232 4249 4265 4281 4298 2 3 5 7 8 10 11 13 15 27 4314 4330 4346 4362 4378 4393 4409 4425 4440 4456 2 3 5 6 8 9 11 13 14 28 4472 4487 4502 4518 4533 4548 4564 4579 4594 4609 2 3 5 6 8 9 11 12 14 29 4624 4639 4654 4669 4683 4698 4713 4728 4742 4757 1 3 4 6 7 9 10 12 13 30 4771 4786 4800 4814 4829 4843 4857 4871 4886 4900 1 3 4 6 7 9 10 11 13 31 4914 4928 4942 4955 4969 4983 4997 5011 5024 5038 1 3 4 6 7 8 10 11 12 32 5051 5065 5079 5092 5105 5119 5132 5145 5159 5172 1 3 4 5 7 8 9 11 12 33 5185 5198 5211 5224 5237 5250 5263 5276 5289 5302 1 3 4 5 6 8 9 10 12 34 5315 5328 5340 5353 5366 5378 5391 5403 5416 5428 1 3 4 5 6 S 9 10 11 35 6441 5453 5465 5478 5490 5502 5514 5527 5539 5551 1 2 4 5 6 7 9 10 11 36 5563 5575 5587 5599 5611 5623 5635 5647 5658 5670 1 2 4 5 6 7 8 10 11 37 5682 5694 5705 5717 5729 5740 5752 5763 5775 5786 1 2 3 5 6 7 8 9 10 38 5798 5809 5821 5832 5843 5855 5866 5877 5888 5899 1 2 3 5 6 7 8 9 10 39 5911 5922 5933 5944 5955 5966 5977 5988 5999 6010 1 2 3 4 5 7 8 9 10 40 6021 6031 6042 6053 6064 6075 6085 6096 6107 6117 1 2 3 4 5 6 8 9 10 41 6128 6138 6149 6160 6170 6180 6191 6201 6212 6222 1 2 3 4 5 6 7 8 9 42 6232 6243 6253 6263 6274 6284 6294 6304 6314 6325 1 2 3 4 5 6 7 8 9 43 6335 6345 6355 6365 6375 6385 6395 6405 6415 6425 1 2 3 4 5 6 7 8 9 44 6435 6444 6454 6464 6474 6484 6493 6503 6513 6522 1 2 3 4 5 6 7 8 9 45 6532 6542 6551 6561 6571 6580 6590 6599 6609 6618 1 2 3 4 5 6 7 8 9 46 6628 6637 6646 6656 6665 6675 6684 6693 6702 6712 1 2 3 4 5 6 7 7 8 47 6721 6730 6739 6749 6758 6767 6776 6785 6794 6803 1 2 3 4 5 5 6 7 3 48 6812 6821 6830 6839 6848 6857 6866 6875 6884 6893 1 2 3 4 4 5 6 7 8 49 6902 6911 6920 6928 6937 6946 6955 6964 6972 6981 1 2 3 4 4 5 6 7 8 50 6990 6998 7007 7016 7024 7033 7042 7050 7059 7067 1 2 3 3 4 5 6 7 8 61 7076 7084 7093 7101 7110 7118 7126 7135 7143 7152 1 2 3 3 4 5 6 7 8 52 7160 7168 7177 Vl85 7193 7202 7210 7218 7226 7235 1 2 2 3 4 5 6 7 7 £3 7243 7251 7259 7267 7275 7284 7292 7300 7308 7316 1 2 2 3 4 5 6 6 7 54 7324 7332 7340 7348 7356 7364 7372 7380 7388 7396 1 2 2 3 4 5 6 6 7 LOGARITHMS 313 LOGARITHMS Natural Numbers 0 1 2 3 4 5 6 7 8 9 Proportional Parts 1 2 | 3| 4 |5 1 6 j 7| 8 9 55 7404 7412 7419 7427 7435 7443 7451 7459 7466 7474 1 2 2 3 4 5 5 6 7 56 7482 7490 7497 7505 7513 7520 7528 7536 7543 7551 1 2 2 3 4 5 5 6 7 57 7559 7566 7574 7582 7589 7597 7604 7612 7619 7627 1 2 2 3 4 5 5 6 7 58 7634 7642 7649 7657 7664 7672 7679 7686 7694 7701 1 1 2 3 4 4 5 6 7 59 7709 7716 7723 7731 7738 7745 7752 7760 7767 7774 1 1 2 3 4 4 5 6 7 60 7782 7789 7796 7803 7810 7818 7825 7832 7839 7846 1 1 2 3 4 4 5 6 6 61 7853 7860 7868 7875 7882 7889 7896 7903 7910 7917 1 1 2 3 4 4 5 6 6 62 7924 7931 7938 7945 7952 7959 7966 7973 7980 7987 1 1 2 3 3 4 5 6 6 63 7993 8000 8007 8014 8021 8028 8035 8041 8048 8055 1 1 2 3 3 4 5 5 6 64 8062 8069 8075 8082 8089 8096 8102 8109 8116 8122 1 1 2 3 3 4 5 5 6 65 8129 8136 8142 8149 8156 8162 8169 8176 8182 8189 1 1 2 3 3 4 5 5 6 66 8195 8202 8209 8215 8222 8228 8235 8241 8248 8254 1 1 2 3 3 4 5 5 6 67 8261 8267 8274 8280 8287 8293 8299 8306 8312 8319 1 1 2 3 3 4 5 5 6 68 8325 8331 8338 8344 8351 8357 8363 8370 8376 8382 1 1 2 3 3 4 4 5 6 69 8388 8395 8401 8407 8414 8420 8426 8432 8439 8445 1 1 2 2 3 4 4 5 6 70 8451 8457 8463 8470 8476 8482 8488 8494 8500 8506 1 1 2 2 3 4 4 5 6 71 8513 8519 8525 8531 8537 8543 8549 8555 8561 8567 1 1 2 2 3 4 4 5 5 72 8573 8579 8585 8591 8597 8603 8609 8615 8621 8627 1 1 2 2 3 4 4 5 5 73 8633 8639 8645 8651 8657 8663 8669 8675 8681 8686 1 1 2 2 3 4 4 5 5 74 8602 8698 8704 8710 8716 8722 8727 8733 8739 8745 1 1 2 2 3 4 4 5 5 75 8751 8756 8762 8768 8774 8779 8785 8791 8797 8802 1 1 2 2 3 3 4 5 5 76 8808 8814 8820 8825 8831 8837 8842 8848 8854 8859 1 1 2 2 3 3 4 5 5 77 8865 8871 8876 8882 8887 8893 $899 8904 8910 8915 1 1 2 2 3 3 4 4 5 78 8921 8927 8932 8938 8943 8949 8954 8960 8965 8971 1 1 2 2 3 3 4 4 5 79 8976 8982 8987 S993 8998 9004 9009 9015 9020 9025 1 1 2 2 3 3 4 4 5 80 0031 9036 9042 9047 9053 9058 9063 9069 9074 9079 1 1 2 2 3 3 4 4 5 81 9085 9090 9096 9101 9106 9112 9117 9122 9128 9133 1 1 2 2 3 3 4 4 5 82 9138 9143 9149 9154 9159 9165 9170 9175 9180 9186 1 1 2 2 3 3 4 4 5 83 9191 9196 9201 9206 9212 9217 9222 9227 9232 9238 1 1 2 2 3 3 4 4 5 84 9243 9248 9253 9258 9263 9269 9274 9279 9284 9289 1 1 2 2 3 3 4 4 5 85 9294 9299 9304 9300 9315 9320 9325 9330 9335 9340 1 1 2 2 3 3 4 4 5 86 9345 9350 9355 9360 9365 9370 9375 9380 9385 9390 1 1 2 2 3 3 4 4 5 87 9395 9400 9405 9410 9415 9420 9425 9430 9435 9440 0 1 1 2 2 3 3 4 4 88 9445 9450 9455 9460 9465 9469 9474 9479 9484 9489 0 1 1 2 2 3 3 4 4 89 9494 9499 9504 9509 9513 9518 9523 9528 9533 9538 0 1 1 2 2 3 3 4 4 00 9542 9547 9552 9557 9562 9566 9571 9576 9581 9586 0 1 1 2 2 3 3 4 4 01 9590 9595 9600 9605 9609 9614 9619 9624 9628 9633 0 1 1 2 2 3 3 4 4 02 9638 9643 9647 9652 9657 9661 9666 9671 9675 9680 0 1 1 2 2 3 3 4 4 03 9685 9689 9694 9699 9703 9708 9713 9717 9722 9727 0 1 1 2 2 3 3 4 4 04 9731 9736 9741 9745 9750 9754 9759 9763 9768 9773 0 1 1 2 2 3 3 4 4 05 9777 9782 9786 9791 9795 9800 9805 9809 9814 9818 0 1 1 2 2 3 3 4 4 06 0823 9827 9832 9836 9841 9845 9850 9854 9859 9863 0 1 1 2 2 3 3 4 4 07 0868 9872 9877 9881 9886 9890 9894 9899 9903 9908 0 1 1 2 2 3 3 4 4 08 0012 9917 9921 9926 9930 9934 9939 9943 9948 9952 0 1 1 2 2 3 3 4 4 09 0956 9961 9965 99B9 9074 9978 9983 9987 9991 9996 0 1 1 2 2 3 3 3 4 I if t> V» t f i v t f; f f « '; * fr II V I 'f ft i * > i « i i • « ,* f « *? i i f t f i: i i i r i' I l i: tf l l i4 §lfi t f f; f* f l t. f t i r i' t * i: L< r f pit! l p »>i, «»/*!.• f> *f; j: **,• V'rfftfciHtw: l ,;*, .£t»,: M*** l i •WH^HA*: U* ««/«* MitiS £« ¥«>*,. ,*•!'»,» f*i*f»:'v/t»«'* »iiit»* «*(M»! *M «*; «r'j«*f /',* *nf/*ff »*!,!,! *Hl," 'MI i (*»i»::'»./.'»/'.! oiv ;»»&**»'*&. tt*/,?; ^ws t*»tr *A*?; » h tt* ii.t ,*t/ «• i* "»»iA*t.' !*,'!*: HIii! rji**m:t?\ i I U. r^!^ i,,*t: 11K f.l f»t M»J«: t itn <.«rfi«: f iKi»:l«%iK:| l f ! t ,« 'i' t 'c t; i: t a- ji * t c K r. f 1: r »: « « i4 ^ fi f t; •: i: c »: r i, / i: t f t: i* i: t* r f i: f i ::SI : f c *, c r, T. ?« I f f . i;! i }\ : i r".:<'V''.....)t':i"')si"'H ' i FIM: ,uf M, t "^i • ^ 'i 't?«i • lit «,v.i , /j «tu ftui< »l *\tit ,!','t It4*! ft ^ , f»t ii^i tf t :***i ui i ;,! i ,.** t • ,"t M' t tir I ^»' i !».t' I ,v> t *«,« i M»VI ,M U ;» p«t.n yi;i I .:*;u *," Mlfll oiHJl : t,.vi /j*4 ! *M I i'Vt 1 tj/M : f'*'f l ni 11 *•! i-1 ! fill I HI! V;tt! *i * iirt • IM ott I /i f; » 'vfl.I .!tt,l t^ifJ **lff,4 'ifif:iii*nf (Hit.*i IM:I tst.*i »*ill *.» II IMI !» U »MI v II *:sll HSU till «mt M ljt/!i »,* 11 //in nai !'»n'f.';u 'i*;n in* P'U sm » ill i,'f li Mill u*n n:ijL*rit oi'ii IITII wu zr.n 1 in zii! nn rni *yiri^nii ton sou rw>i('io f'^tl tt^Jl fmfl! 'Mil I^OlUhOf tiiO! '»/.<»! titll ol *»'«il /.'ml tf*ot «*'««! »»M»f J/*;ni tviil .:voi o«-oi il- 1,'uF l.tltl 'ItU! IKlI .":H»rMH»I ,'(H)I "lienoldisulphonic, 236 ic-Icinoleic, 177 value of oils, 180 A.cIu< , 160 ? 220,221 evaporated milk, 217 'M.!t *^Ilk, 199, 212, 214 rraal weight, of, 213 °P"tica,l methods for, 213 rotation of 123 rotation, 122 sugar scale, 131 on invert sugar, 137 jeadL acetate, reagent, 134, 15S in insecticides, 294, 2f°C», 300, 301 in lead arscnato, 301 oil, specific rotation of, !2:> , specific rotation of, 12M on oils, etc., 1S3, 198 fflter, 128, 129 polarimetry, 127 ^refractonietn-, 115 14S 272 of soils, 2t53, 264, 265, 267 -sulphur solution, 294, 295, 303, 304, 305 e, alkalinity of, 86 acid, 176 acid, 177 il, drying properties of, 177 Llq^uids, sampling of, 22 Logarithms, table of, 310, 311 Loss on ignition of soils, 247 M IS^Ca^gnesia mixture, reagent, 88 ]Vt agnesium amnioniuiu phosphate, ignition of, 87, 89, DO . in soils, 256, 259 3VTa.lt extract, 163, 164 3?v{Ea,ltose, calculation from cuprous oxide, 160 .XL;- .. M .i A.: M ' . ^ • M:J / • XMi.t^. M .Lai. 215 Milk, IW9 acidity of, 203 albumin in, 19»>. 211 :i>h in, 204 casein in, lift), 210 composition of. l*»v*, 201 eonden^t'd. 217 evaporated, 217 Cut in, 205, 2«X», 2l)S globules in, 215 heated, 216 Lieto,se in, 199, 2i'J. 214 iniowseupic examinatum of. 215 mtivigeii in, 20!> pipette, 208, 213 powdered, 21P preser\*utives in, 21."> proteins in, 199, 2I.W, 210, 2U rofractomoier reading of, 2^2 sampling of, 201 tfptvifie gravity of, 20 total solids in. 1 *.*»*. 2iXl 2i>l water in, 191K 202 INDKX ill Mineral analysis of feeds, M.I Mixing ami dividing, IS Moenya oil, HeH'h«Tf~MU'is>l number of, ix-i Mohr unit of volume, 12!) Moisture in Bordeaux mixture, I JOS in tmtter, 222 in rlieese, 227 in fwls, 112, I 111, Ml in fertilisers, 271 in lead ar.seiuife, oOO in Houp, HOU in noils, 2:-M, *j:ir> Molybdate, ammonium, reagent, 27fK 277 .\loriOHlenrif J4 JH'Hyi value of, 1S!» Mun^en am! \\':ilki-r"i:' tul,li., HiO Mil! arnlntiuji, I2«"i Myriryl iKihnit-'itf, I 7U \ NVufntiily iu«lir{i('»rf-', 12 Nt'wlml! (*n ?4uyhf»nii oil, I *.!.'*» ific' r«»t?if ioit i*f, 12."» nN'H in frrdli/rr-, "-Jslt. 'js-1 in ?*<»il'4( 2.15 Nit rir ju'icl. fununfiitit in rulftri nil-fry, HKr> Nitrttinitt«)fi in M»»i1--. «.TJ Nilrnuji'ti, iiv;iiiu)tittfy in frrtilix«'r>. , 142, , I.VJ . H»» 2 If i, 221! lii r In ••".-.*•. 22S ill ffi'fli... I -W, i;,J, l.r>4 in f«*rtih/ir»!, 271, 2H2 tii in ••^ K ji' f».r, I.*V1 Kjrl.liih! fim-lli...! («,r. Ill*, ISO, 'JHi 2 If*, 222 Non-protein nitrogen in feeds, lf>5 Xon-volatile aeids of oils, etc'., ISii, Nonnalily factor, ">!) Normal system, 7 weight for lactose, 21.1 in .siicrharimetry, 12!) Noyes on starch and glueose, 105 Nut mar^erine, 1H4, 221. 220 Oil, ,'trarhis, Kenanl's t(»st for, 1!)!^ pastor, iHM'tyl value of, 1S',», 1!N), I'.m cotton s«M»d, Iliilphcn tost for, M>2 proton, U^ichcrt-MrissI nutuln'r of, 18-1, I*H» iiNh, l)n»ini(l<- test for, 1!M Iins««i»(i, unMjttitrntfd rha ructiT oft 177 peanut, Hi'ttnrd tt-st f«>r, 1 '.».'» ri'.Hin, ciptiral relation of, l'J2 Ki'sariii*, Handouin ti*>t. for, HKt w»yl»<'nnt qiiiilifntivc li'.nt for, 1*JM Oils' ucTtyl vnhip of, 187, UK), 1«W, l'.*7 jtcid vahu* of, ISO blown, 1HH cc)iii|H»Hif ioit of, 170 of, I7t> ami waxen, Niponif table, 170 gi'it ab?4or|>tioii of, 170, 17(1, HMi, 1117 H«'liiw*r value of, IS1 i«lrntifiruti(in of, 17! tfiHoIttl»I<' uricln in, IHi ii»«iiiH« number of, 1711, 171), HM'it M»7 KottNlorfer tuunlwT of, ISO, 1KI, 1H2, HMi, 197 martite animal, hroini. I'Mom^Im- 184, 186, iSS, 1W», H*7, ±2."» Pirn-phut*- saponification number of. I Si), isl, tt-m 182, 196, 197 soluble acids of, 181, 188 solvents for, 177 specific gravity of, 172, 196, 197 Oleic acid, 176 Olein, 170, 176, 195 Oleo oil, 184 Oleomargarine, 184, 224, 22t> Opium wax, esters in, 170 Optical methods for lactose, 213 in rock i rotation, 121 in soils. ; Optimum moisture in soils, 234, 235 in soluhl Orange oil, specific rotation, 123 Picnonietei Ordinary ray of double refraction, Pip* 125 Organic matter in soils, 248 Outflow time for volumetric appara- tus, 43 Outside indicators, 74 Oxidation in the crucible, 28 Platinun 4 .in PI .mum* S Palau, 32 Palm nut oil, Hehner value of, 1S2 Palmitin, 170, 181 Paper, filter, 25 Paris green, 295, 296, 297, 298 Peak (See Wanington). Pentosans in feeds, 142,165, 166,167 Polarization, invert. 13, Pentoses, 165, 167 Polarized lipi'ht, 121 Perchlorate method for potassium. Polarizer. 124, 125 247, 289 Permanganate method for calcium, 65, 68, 69 for iron, 70, 72 Permanganates, standard solutions of, 65, 67, 68, 72 Persulphate method for manganese, Porcelain crucible*. ;>o 260, 262 Porpoise oil. Reieht:T:-Mo> PH, definition of, 13 t»er of, 1S4 values for indicators, 139 Potassium, eentrifii^ii ir.f! Phenol red, 139 18i>. 2*.H"> Phenoldisulphonic acid, 236 chloride-, standar;! -*.!nt;«-: I oliinmett ,121 Polurirnetry, 121 light source for, !27 Polenske value for burtor, 225, 226 for ciM-iniiii.it fat, ist^, for oils, ete., 1M». IVMi. 226 Policeman, 51 326 INDEX Ma } ,'Jh!'! *V! i Potassium, chlorplatinatc method for, 244, 245, 288 chromato, indicator, 223 dichromate, light filter, 129 standard solution of, 178 hydroxide, standard solution of, 277 in fertilizers, 271, 287 in insoluble minerals, 243 in soils, 243 iodide, reagent, 178 perchlorate method for, 247, 289 permanganate for nitrogen availa- bility, 286 standard solution of, 65, 67, 68, 72 sulphate in nitrogen determi- nation, 154 thiocyanate for soil acidity, 265 Potential plant food in soils, 233 Potentiometer method for Pjy, 138 Powdered milk, 219 Precipitate, correction for volume of, 133 Precipitates, drying of, 26 ignition of, 28 Hisso. of crystals, 25 Freeip itatio n, 24 Preparation of samples, 17 of insecticides, 293 Preservatives in milk, 215 Prideaux on indicators, 16 Primary standards, 9 Prism, Amici, 116, 117 Nicol, 125 Protein nitrogen in feeds, 155 Proteins, formal titration of, 209 in cheese, 227 in evaporated milk, 217, 218 in milk, 199, 209, 210, 213 Ptyalin, 163 Pulfrich refractometer, 119, 174 Q Quantitative determinations, 48 Quartering samples, 19, 20, 21 Quartz, optical activity of, 127 wedge compensation in polari- metry, 127 Quinine sulphate, specific rotation of, 123 R Radiation corrections in calorimctry, 106, 111 Raffinose, 133, 136 Reducing sugars in feeds, 157, 158, 159 Reduction of iron, 71, 74 Reedy and Haag on soluble arsenic, 303 Refraction, angle of, 113 index of, 113, 120, 174, 226 Refractometer, Abbe", 114, 115, 174, 175 butyro-, 118, 174 dipping, 118, 119, 174 Pulfrich, 119, 174 Refractometry, 113 light for, 115 Regnault-Pfaundler radiation cor- rection, 107 Reichert-Meissl number for butter, 197, 225, 226 for oils, etc., 183, 186, 188, 196, 197, 225, 226 Resin oil, optical activity of, 192 Reversion of phosphates, 275 Rhead and Ridgell on organic matter in soil, 248 Rhotaniuni, 32 Richards on calorimetry, 41 Ricinoleic acid, 177 Ricinolein, 190 Rider, chain, 37 weight, 36 Ridgell iSee Rhead). Riffle, 21 Ripening products of cheese, 227 Rock phosphate, phosphorus in, 89, 91, 279 Rohrig tube, 205, 218, 221 INDEX Hose-Gottlieb method for fat, 205, 218, 221 Isolation, dextro, 122 dispersion of polarized lip;ht, 127, 128 lacvo, 122 optical, 121 specific, 122, 123 Saccharimeter, 127 Saccharometer, 98 Saiki on galactans, 168 Salt in butter, 223 in cheese, 227 Sample weight, adjustment of, 6 Samples, preparation of, 17 Sampling of butter, 221, 226 of condensed milk, 217 of feeds, 142 of fertilizers, 273, 274 of liquids, 22 of milk, 201 of soils, 234 Saponifiable oils, fats and waxes, 170 Saponmciition number of oils, etc., 180, 182, 196, 197 Scholl on determination of potas- sium, 247 Schreiner color comparator, 237 Scope of laboratory work, 48 Sensibility of balance, 39 Sesame oil, Baudouin test for, 103 Settinion soybean oil, 193 Shafer on insecticides, 292 Sherrill on potassium determi- nations, 289 Shives on culture experiments, 291 Silica in soils, 254, 256 Silver chloride method for chlorides, 49, 50 solubility, 49 Silver chromate, indicator, 52 Single deflection method for weigh- ing, 38 Slag, Thomas, 272 Size of crystals in pivnpn . -. , Smith met hod f o r j >. ^••l'^: .. Soaj>-oil emulsions. 2VM ^>"' Soap, moisture in, ;^^i Soda ash, alkalinity <»f. .%»-> Sodium carbouatv. prir;j ••.*-• .« ard, 57, S2 chloride, standard .*uhr :< • - * cobaltinit ri te, re-na > r, t • * * :, in soils, 243 light in polariiaerrv. 127 in ref ractomet ry, 1 ]." oxalate, priniary $t:tiuLiT.i. ^ thiosulphate, st andar^ ^ -<>'< 178 Soils, 230 acid extraction of, 2,52.. 2-» " acidity of, 86, 2tvi aluminium in. 254, 25.". -J:«T ammonia in, 23S available plant food in,, 2.^; 267 calcium in, 255, 2">8 carbon in, 249 classification of, 252 decomposition by fusion.. j.Vi by hydrofluoric ant I,, ^,.J denitrification of, 24(> humus in, 251, 252 iroa in, 254, 257 lime requirements of, 2t» loss on ignition of, 247 . magnesium in, 256, 2,59 manganese in, 259. 2t>l moisture in, 234, 2:>5 nitrification of, 2I5V* nitrogen in, 235 organic matter in, 24S phosphorus in, 240. 242 potassium in, 243 potential plant loot.I ir,,. 2;>5 sampling of, 234 silica in, 254, 256 sodium in, 243 sulphur in, 262 Solinon (See Syre'.;. Solubility product, 24 328 INDEX l« |);d I '<•$ :?!^ | I 4 »t 'I rj.?,' f >, V I ft1' >' •<• ; 4t , 5 « i * tfpjf i fb, , ! Soluble acids of oils, etc., 181, 188, 225, 226 Solvents for oils, 177 Sorensen (See Henrique). Soybean oil, Settini-Newhall test for, 193 Special measurements, 93 Specifications for volumetric appara- tus, 43 Specific gravity, 57, 94, 102, 172, 173, 196, 197, 202, 220 Baumc, 95 methods for determination of, 96 of cream, 220 of hydrochloric acid, 57 of milk, 202 of oils, etc., 172, 196, 197 Specific rotation, 122, 123 temperature reaction, 191, 192 Spermaceti, esters in, 170 Spindle, specific gravity, 97 Spitzer on milk proteins, 211 and Epple 011 butter substitutes, 184 Spot plate, 74 Sprays, mixing of, 293 Standard solutions, 4 correction factor for, 54 dilution ratio for, 53 Standardization of solutions, 8 Standards for calorimetry, 105 primary, 9 Stannous chloride, reagent, 71 Starch, diastase method for, 163,164 hydrolysis of, 163, 164 indicator, 178, 297 specific rotation of, 123 Steam distillation, 306 funnel, 226 Stearin, 170, 189, 195 Stewart on availability of phos- phates, 274 Substitution method for weighing, 40 Sucrose, Clerget formula for, 132, 135 in condensed milk, 218 Sucrose, in feeds, 158, 163 inversion of, 132, 135 specific rotation of, 123 Sugar, invert, standard solution of, 162 scale, French (Laurent), 131 German (Ventzke), 129 International, 130 Sugars, common, 131 in beet products, 136 Sulphates, gravimetric determi- nation of, 60, 62 Sulphur in insecticides, 295 in lime-sulphur solutions, 304, 305 in soils, 262 Sulphuric acid, volumetric deter- mination of, 62, 63 Superphosphate, 272 Syre, Solmon and Warmall on insecticides, 304 Syrups, commercial, 133, 134 Taka-diastase, 163 Tartaric acid, specific rotation of, 123 Teelu burner, 33 Temperature corrections in cali- brating, 44 systems, 4, 49 Test bottles for fat, 206, 220 Theory and general principles, 1 Thomas slag, 272 Thymol blue, 139 Time of outflow for volumetric apparatus, 43 Time-temperature curves, 107, 108, 110 Titration, 4 curves, 14 Tobacco insecticides, 295, 306 Total solids in cream, 220, 221 in milk, 199, 203, 204 Tottingham on culture experiments, 291 Transfer pipettes, calibration of, 46 K1' i " ^ ' I. H L.^'m /.VM'.Y l"mt>, fit-at, it'U \ it u nil "k >A« < a? ir*- j-v V:dtT»'t , app.irt'ii! « t Vt'iteli nit fi « o>i!:i!.ni i»f m oreds, 243 f^N'ec Munsen). Warmall (Set' Syre1. Warrlngton uiui IVuk nn «»nju matter in soil^, 24b Washing precipit;ttt>, 2i» \\"atrr, carlxm dio.\ide-iVi>. s;> equivalent of crduriuit'tfrs, ll)«j Wright on -pt-exti^ gravity . 1 X Xylan in iml^ H>o. RV». 167 Z Zi'i;» biity rn-ivi'r.u'^iiivTsT . 1 ZlTO p«»il!t of inil:i!h.'f;, 3^, ;>!*