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ANALYSIS OF MILK 
 
 AND 
 
 MILK PRODUCTS 
 
 LEFFMANN 
 
SANITARY RELATIONS OF THE 
 COAL-TAR COLORS 
 
 BY 
 THEODORE WEYL 
 
 AUTHORIZED TRANSLATION BY 
 
 HENRY LEFFMANN 
 i2mo. 154 Pages. Cloth, net $1.25 
 
 EXAMINATION OF WATER 
 
 FOR SANITARY AND TECHNICAL PURPOSES 
 
 Seventh Edition, Revised 
 Illustrated. i2mo. Cloth, net $1.25 
 
 ORGANIC CHEMISTRY 
 
 A COLLEGE TEXT-BOOK 
 BY 
 
 Henry Leffmann and Charles H. LaWall 
 i2mo. Illustrated. Cloth, net $1.00 
 
 SELECT METHODS IN FOOD 
 ANALYSIS 
 
 BY 
 
 Henry Leffmann and William Beam 
 
 Second Edition, Revised 
 
 i2mo. Cloth, net $2.50 
 
 I Plate and 54 Illustrations 
 
 ALLEN'S COMMERCIAL ORGANIC 
 ANALYSIS 
 
 VOLUME 8 CONTAINS: 
 Methods of Analysis of Milk and Milk-Prod- 
 ucts, Meat and Meat- Products, Proteins, Pro- 
 teoids, Fibroids and Enzyms. 
 8vo. 696 Pages. $5.00 net 
 
ANALYSIS OF MILK 
 
 AND 
 
 MILK PRODUCTS 
 
 BY 
 
 HENRY LEFFMANN, M. D. 
 
 PROFESSOR OF CHEMISTRY IN THE WOMAN'S MEDICAL COLLEGE OF 
 
 PENNSYLVANIA AND IN THE WAGNER FREE INSTITUTE OF 
 
 SCIENCE OF PHILADELPHIA; PATHOLOGICAL CHEMIST 
 
 TO JEFFERSON MEDICAL COLLEGE HOSPITAL 
 
 FOURTH EDITION, REVISED AND ENLARGED 
 WITH ILLUSTRATIONS 
 
 THE FIRST TWO EDITIONS OF THIS WORK WERE 
 PREPARED AND ISSUED UNDER THE JOINT AUTHOR- 
 SHIP OF HENRY LEFFMANN AND WILLIAM BEAM 
 
 PHILADELPHIA 
 
 P. BLAKISTON'S SON & CO. 
 
 1012 WALNUT STREET 
 

 Copyright, 191 5, by Henry Leffmann 
 
 f z;?!' 
 
 THB MAFXiB FKISSB TORK PA 
 
 ©C!,A401417 
 
 K.-f^ 
 
PREFACE 
 
 This book is intended as a guide to the analysis 
 of milk and milk products in the routine of the 
 commercial and food-inspection laboratory. 
 Only processes of practical value have been given, 
 and nothing has been said as to the food value 
 of milk and its products, nor concerning the ef- 
 fects of the several adulterants that may be 
 detected. 
 
 A notable portion of the text has been taken 
 from Volume 8 of the Fourth Edition of Allen's 
 Commercial Organic Analysis, I am indebted to 
 the courtesy of Messrs. P. Blakiston's Son & Co. 
 for permission to use this matter. 
 
 An interesting point is to be noted in the com- 
 parison of this edition with the first, issued about 
 a score of years ago in association with Dr. 
 William Beam. In that, a considerable part of 
 the material was derived from the publications 
 of foreign workers; in the present, American in- 
 vestigations form the basis of many of the im- 
 portant processes. 
 
 " Westward the star 0} empire takes its way.^^ 
 
 H. L. 
 Philadelphia. 
 
CONTENTS 
 
 Milk. Page 
 
 Analytic Data and Processes 1-64 
 
 Milk Products. 
 
 Cream 65-68 
 
 Condensed Milk 69-8O 
 
 Butter 81-96 
 
 Cheese 97-109 
 
 Fermented Milk Products 110-113 
 
 Index 
 
 Vll 
 
MILK 
 
 ANALYTIC DATA 
 
 Milk, the nutritive secretion of nursing mam- 
 mals, contains water, fat, proteins, sugar, and 
 mineral matter. Cow's milk is meant in all 
 cases, unless otherwise stated. Milk as taken 
 from the animal is generally termed "whole 
 milk." 
 
 Fat. — This occurs in globules varying from 
 0.0015 mm. to 0.005 ^^- i^ diameter, in a 
 condition which prevents spontaneous coales- 
 cence. It is pecuHar among animal fats in 
 containing a notable proportion of acid radicles 
 with a small number of carbon atoms. 
 
 Proteins. — The nature of the proteins of 
 milk has been much discussed, but it is now 
 generally conceded that there are at least three 
 forms, casein, albumin, and globulin, the casein 
 being present in by far the greatest amount, 
 and the globulin as traces only. 
 
 Casein. — Casein is probably in part in 
 combination with phosphates. It is precipi- 
 
2 MILK 
 
 tated by many substances, among which are 
 acids, rennet, and magnesium sulfate, but not 
 by heat. Acids precipitate it by breaking up 
 the combination with phosphates. The action 
 of rennet is complex and probably partly hy- 
 hydrolytic, splitting the casein into several 
 proteins, some of which are precipitated in 
 the curd. Films of protein matter occur abun- 
 dantly in milk, for which reason it is distinctly 
 opaque, even when nearly all the fat has been 
 removed by contrifugal action. 
 
 The albumin of milk appears to be a distinct 
 form, and is called lactalbumin. It is not 
 precipitated by dilute acids, but is coagulated by 
 heating to 70° — 75°. The proportion in cow's 
 milk is usually from 0.35 to 0.50%, but col- 
 ostrum may contain much larger proportions. 
 
 Globulin is present only in minute amounts 
 in normal milk, but colostrum may contain as 
 much as 8%. It is coagulated on heating. 
 
 Lactose. — This is a sugar peculiar to milk. 
 
 Citric acid is a normal constituent of the milk 
 of various animals. In human milk, the quantity 
 is about 0.5 gram to 1000 c.c. ; in cow's milk, 
 from I to 1.5 grams. It is not dependent on 
 the citric acid present in the food. 
 
 Enzyms. — Several enzyms occur in milk but 
 they are chiefly known by effects and not as 
 isolated substances. Some are proteolytic, others 
 
ANALYTIC DATA 3 
 
 are oxydases, that is, decompose hydrogen per- 
 oxid and carry oxygen over to other substances. 
 
 Lecithin is also a usual ingredient of milk. 
 Nerking and Haensel found a range in cows' 
 milk from 0.03 to 0.11%. 
 
 Mineral Matter.— The ash of milk contains 
 calcium, magnesium, iron, potassium, and sodium 
 as chlorids, carbonates, sulfates, and phos- 
 phates. It does not exactly represent the salts 
 present in milk. 
 
 Richmond has determined the ratio of the 
 ash to the soHds not fat in 135 samples of milk. 
 This was found to range from 7.8 to 9.4%, 
 but more usually from 7.8 to 8.5 (average 8.2) %. 
 Many ashes were alkaline to turmeric, litmus, 
 and phenolphthalein, the maximum alkalinity 
 being 0.025% calculated as sodium carbonate. 
 
 Human milk is notable for a low protein 
 content hence the curd is less bulky and more 
 friable than that from cows' milk. The milk 
 of all animals is subject to modification by breed, 
 climate, season, feed, housing, exercise, time 
 of lactation, and in human beings (and possibly 
 in some other animals) by psychic influences. 
 
 As regards the proportion of proteins and 
 lactose, milks of the mare and ass agree closely 
 with human milk. 
 
 Normal milk is an opaque white or yellowish- 
 white fluid, with an odor recalling that of the 
 
4 MILK 
 
 animal, and a faint sweet taste. The opacity 
 is due largely but not entirely to the fat globules. 
 The reaction of freshly drawn milk to litmus is 
 usually alkaline, but is sometimes amphoteric; 
 that is, it turns the red paper blue and the blue 
 paper red. The sp. gr. varies between 1.027 
 and 1.035. It usually undergoes a gradual 
 augmentation (sometimes termed Recknagel's 
 phenomenon) for a considerable time after the 
 sample has been drawn. The increase may 
 amount to two units (water being 1000). The 
 sp. gr. becomes stationary in about five hours 
 if the milk is maintained at a temperature 
 below 15°, but at a higher temperature it may 
 require twenty-four hours to acquire constancy. 
 The change is not entirely dependent on the 
 escape of gases. 
 
 Unless collected with special care and under 
 conditions of extreme cleanliness, milk always 
 contains many bacteria, animal matter of an 
 offensive character, such as epithelium, blood 
 and pus cells, particles of feces, and soil. 
 
 At ordinary temperature milk soon undergoes 
 decomposition, by which the milk sugar is 
 converted principally into lactic acid, and the 
 proteins partly decomposed and partly coagu- 
 lated. The liquid becomes sour and the fat is 
 inclosed in the coagulated casein. In the initial 
 stages of decomposition the proteins frequently 
 
ANALYTIC DATA 5 
 
 undergo transformations into substances which 
 are the cause of the violent poisonous effects 
 occasionally produced by ice-cream and other' 
 articles of food into the preparation of which 
 milk enters. 
 
 Boiling produces coagulation of the albumin, 
 some caramelization of the sugar, and develops 
 a greater facility of coalescence on the part of 
 the fat globules. Enzyms are rendered inert 
 and most microbes are killed. 
 
 When milk is allowed to stand, some of the fat 
 rises gradually and forms a rich layer, constituting 
 cream. The proportion of cream depends on 
 several conditions. The amount formed in a 
 given time cannot be taken as a measure of the 
 richness of the milk. Water added to milk 
 causes a more rapid separation of the cream. 
 Centrifugal action separates nearly all of the fat. 
 The following figures, given by D'Hout as aver- 
 ages, show this effect : 
 
 Whole Separated i^„„.». 
 Milk Milk <-Rkam 
 
 Specific gravity 1032 1034 1015 
 
 Total solids 14.10 9.6 26.98 
 
 Sugar 4.70 5.05 3.32 
 
 Casein 3.50 3 . 62 2 . 02 
 
 Ash 0.79 0.78 0.58 
 
 Fat 5.05 0.20 21.95 
 
 Buttermilk is the residue after removal of the 
 butter by churning. Vieth gives the following 
 analyses : 
 
6 MILK 
 
 Total p._ Solids not a^„ 
 
 Solids ^^^ Fat ^^^ 
 
 9.03 0.63 8.40 0.70 
 
 8.02 0.65 7.37 1.29 
 
 10.70 0.54 10.16 0.82 
 
 Whey or Milk-serum is the liquid freed from 
 curd after precipitation by rennet or acids. In 
 most cases it contains a notable amount of 
 proteins, as shown in the following analyses by 
 Cochran : 
 
 Milk Whey 
 
 Total solids Solids not fat Total solids J^emoved 
 
 927 9-13 6.62 2.51 
 
 927 9.13 6.1 3.03 
 
 14-05 8.35 6.62 2.33 
 
 771 7-6i 5.98 1.63 
 
 8.91 8.71 6.50 2.21 
 
 The whey of any given milk has practically the 
 same composition, whether taken from the 
 original milk, skimmed milk, or cream. 
 
 Average Proportion of Solids in Milk. — The 
 most extensive data on this point are those 
 obtained by Vieth. The total number of samples 
 was 120,540. The averages of the entire series 
 are as follows : 
 
 Fat 4.1% 
 
 Non-fatty solids 8.8% 
 
 Total solids 12.9% 
 
 Lythgoe gives a table of averages of composi- 
 tion of 51 samples of genuine milk, each set of 
 
ANALYTIC DATA 
 
 averages being deduced by analysis of lo samples. 
 The following data are selected from this table. 
 For explanation of the figures in the last column 
 see page 42. 
 
 Total 
 Solids 
 
 15-70 
 15.00 
 14.50 
 14.00 
 13 50 
 13.00 
 12.50 
 12.00 
 
 11.50 
 11.00 
 
 10.70 
 
 Fat 
 
 6.01 
 5.62 
 530 
 4.78 
 4.61 
 4.24 
 3-99 
 3.45 
 3-33 
 3.02 
 2.90 
 
 Pro- 
 teins 
 
 4.13 
 3-75 
 3-6i 
 351 
 3-37 
 3.17 
 2.84 
 2.88 
 2.67 
 2.64 
 2.60 
 
 Lac- 
 tose 
 
 •79 
 
 .87 
 .82 
 
 •98 
 
 ■ n 
 
 .86 
 
 .94 
 .96 
 .80 
 .63 
 •49 
 
 Ash 
 
 0.77 
 0.76 
 
 0.77 
 0.73 
 0.75 
 0.73 
 0.73 
 0.74 
 0.70 
 0.71 
 0.71 
 
 Solids 
 
 NOT 
 
 Fat 
 9.69 
 938 
 9.20 
 9.22 
 8.89 
 8.76 
 8.51 
 8.55 
 8.17 
 7.98 
 7.80 
 
 Refraction 
 OF Copper 
 Serum 20° 
 
 38.1 
 38.3 
 38.3 
 38.5 
 38.1 
 
 37-9 
 38.0 
 
 37-7 
 37.3 
 37.0 
 
 36.4 
 
 From these figures Lythgoe derives the rule 
 that differences in proportion of solids not fat in 
 unadulterated milks are principally due to dif- 
 ferences in the amount of proteins. Lactose and 
 ash are fairly constant. On these facts depend 
 recently introduced methods of detecting water- 
 ing milk, as will be pointed out later. 
 
 Colostrum. — This is the secretion in the early 
 stages of lactation, and differs from ordinary 
 milk. It contains characteristic structures, 
 known as colostrum corpuscles, and usually 
 contains much less fat than fully developed 
 milk, but a larger proportion of proteins. Colo- 
 strum coagulates on boiling. Lactose is in small 
 amount. 
 
ANALYTIC PROCESSES 
 
 Specific Gravity. — The sp. gr. of milk rises 
 gradually for some time after it has been drawn, 
 and the determination is to be made only after 
 this action has ceased. This will require about 
 five hours after the milk is drawn, if it has been 
 kept 15°, but at a higher temperature it will be 
 necessary to allow at least twelve hours. For 
 all other determinations the milk must be ana- 
 lyzed as soon as possible. The following figures, 
 published by Bevan, show that a considerable 
 loss in total solids may occur in twenty-four 
 hours : 
 
 Total Solids Loss 
 Evaporated immediately ... 1 1 • 73 
 
 Evaporated after 24 hours, 10 -79 0-94 
 
 Evaporated after 48 hours, 10,38 1.35 
 
 Evaporated after 120 hours, 9.42 2,31 
 
 The decomposition is very irregular, and it is 
 not possible to determine, by estimation of the 
 lactic acid or other products, the original compo- 
 sition of the milk. 
 
 Air-bubbles are held rather tenaciously by milk, 
 and care must be taken in mixing, preparatory 
 to taking the sp. gr., to avoid as far as possible 
 
 8 
 
ANALYTIC PROCESSES 9 
 
 the inclosure of the air, and to allow sufficient 
 time for the escape of any bubbles that may be 
 present. Sp. gr. is understood to be taken at 1 5 . 5° ; 
 samples should be brought near to this. If at 
 a few degrees above or below, it will suffice to 
 make the determination at once and obtain the 
 correct figure by reference to the annexed table. 
 The sp. gr. of normal milk ranges between 
 1.027 and 1.035. The figure alone does not 
 indicate the character of the sample, but taken 
 in conjunction with the figure for fat or for 
 total solids, it is of value as a check on the 
 results furnished by other determinations. 
 
 The simplest method of determining sp. gr. is 
 by the lactometer, a delicate and accurately gradu- 
 ated hydrometer. The instrument must be im- 
 mersed carefully so as not to wet the stem above 
 the point at which it will rest. Its accuracy 
 should be verified by immersion in distilled 
 water at 15.5° and milks of known sp. gr. 
 
 More accurate determinations may be made 
 with a balance. A special form, the Westphal 
 balance, is adapted to the determination of 
 sp. gr. only, the weights being so arranged 
 that a simple enumeration of them gives the 
 gravity directly. The cheap forms of this in- 
 strument are not satisfactory, but some made 
 by German houses are excellent. The ordinary 
 
lO 
 
 MILK 
 
 Find the temperature of the milk in one of the horizontal lines 
 and the sp. gr. in the first vertical column. In the same line 
 with this and the temperature the correct figure is given. 
 
 °F. 
 
 50 
 
 51 
 
 52 
 
 53 
 
 54 
 
 55 
 
 56 
 
 57 
 
 58 
 
 59 
 
 60 
 
 61 
 
 62 
 
 Sp.Gr. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 21 
 
 20.2 
 
 20.3 
 
 20.3 
 
 20.4 
 
 20.5 
 
 20.6 
 
 20.7 
 
 20.8 
 
 20.9 
 
 20.9 
 
 21.0 
 
 21. 1 
 
 21.2 
 
 22 
 
 21.2 
 
 21.3 
 
 21.3 
 
 21.4 
 
 21.5 
 
 21.6 
 
 21.7 
 
 21.8 
 
 21.9 
 
 21.9 
 
 22.0 
 
 22.1 
 
 22.2 
 
 23 
 
 22.2 
 
 22.3 
 
 22.3 
 
 22.4 
 
 22.5 
 
 22.6 
 
 22.7 
 
 22.8 
 
 22.8 
 
 22.9 
 
 23.0 
 
 23.1 
 
 23.2 
 
 24 
 
 23.2 
 
 23-3 
 
 23-3 
 
 234 
 
 23-5 
 
 23.6 
 
 23.6 
 
 237 
 
 23-8 
 
 23-9 
 
 24.0 
 
 24.1 
 
 24.2 
 
 25 
 
 24.1 
 
 24,2 
 
 24.3 
 
 24.4 
 
 24-5 
 
 24.6 
 
 24.6 
 
 24.7 
 
 24.8 
 
 24.9 
 
 25.0 
 
 25.1 
 
 25.2 
 
 26 
 
 25-1 
 
 25.2 
 
 25.2 
 
 25-3 
 
 25.4 
 
 25.5 
 
 25.6 
 
 25.7 
 
 25.8 
 
 25-9 
 
 26.0 
 
 26.1 
 
 26.2 
 
 27 
 
 26.1 
 
 26.2 
 
 26.2 
 
 26.3 
 
 26.4 
 
 26.5 
 
 26.6 
 
 26.7 
 
 26.8 
 
 26,9 
 
 27.0 
 
 27.1 
 
 27.3 
 
 28 
 
 27.0 
 
 27.1 
 
 27.2 
 
 27.3 
 
 27.4 
 
 27.5 
 
 27.6 
 
 27.7 
 
 27.8 
 
 27.9 
 
 28.0 
 
 28.1 
 
 28.3 
 
 29 
 
 28.0 
 
 28.1 
 
 28.2 
 
 28.3 
 
 28.4 
 
 28.5 
 
 28.6 
 
 28.7 
 
 28.8 
 
 28.9 
 
 29.0 
 
 29.1 
 
 293 
 
 30 
 
 29.0 
 
 29.1 
 
 29.1 
 
 29.2 
 
 29-3 
 
 29.4 
 
 29.6 
 
 29.7 
 
 29.8 
 
 29.9 
 
 300 
 
 30.1 
 
 30.3 
 
 31 
 
 29.9 
 
 30.0 
 
 30.1 
 
 30.2 
 
 30.3 
 
 30.4 
 
 30.5 
 
 30.6 
 
 30.8 
 
 30.9 
 
 31.0 
 
 31.2 
 
 31.2 
 
 32 
 
 30.9 
 
 31.0 
 
 311 
 
 31.2 
 
 31.3 
 
 31.4 
 
 31-5 
 
 31.6 
 
 31.7 
 
 31-9 
 
 32.0 
 
 32.2 
 
 32.3 
 
 33 
 
 31.8 
 
 31-9 
 
 32.0 
 
 32.1 
 
 32.3 
 
 32.4 
 
 32.5 
 
 32,6 
 
 32.7 
 
 32.9 
 
 33-0 
 
 33.2 
 
 33.3 
 
 34 
 
 32.7 
 
 32.9 
 
 33.0 
 
 33.1 
 
 33-2 
 
 33.3 
 
 33-5 
 
 33.6 
 
 33-7 
 
 33-9 
 
 34-0 
 
 34-2 
 
 34-3 
 
 35 
 
 33.6 
 
 33.8 
 
 33-9 
 
 34-0 
 
 34-2 
 
 34.3 
 
 34-5 
 
 34-6 
 
 34-7 
 
 34-9 
 
 35.0 
 
 35-2 
 
 35-3 
 
 °C. 
 
 lO.O 
 
 10.5 
 
 II. I 
 
 11.6 
 
 12.2 
 
 12.7 
 
 13.3 
 
 13.8 
 
 14.4 
 
 15.0 
 
 15-5 
 
 16.1 
 
 16.6 
 
 analytic balance may also be used. A plummet 
 consisting of a thick glass rod (or short sealed 
 tube, weighted with mercury) of a bulk of about 
 10 c.c. is suspended from the hook of the balance 
 by means of fine platinum wire and the weight 
 ascertained. It is then submerged in distilled 
 water and the weight also noted. The water is 
 contained in a narrow upright cylinder resting 
 
ANALYTIC PROCESSES 
 
 II 
 
 Find the temperature of the milk in one of the horizontal lines 
 and the sp. gr. in the first vertical column. In the same 
 line with this and the temperature the correct figure is given. 
 
 63 
 
 64 65 
 
 66 
 
 67 
 
 68 
 
 69 
 
 70 
 
 71 
 
 72 
 
 73 
 
 74 
 
 75 
 
 21.3 
 
 21.4 
 
 21.5 
 
 21.6 
 
 21.7 
 
 21.8 
 
 22.0 
 
 22.1 
 
 22.2 
 
 22.3 
 
 22.4 
 
 22.5 
 
 22.6 
 
 22.3 
 
 22.4 
 
 22.5 
 
 22.6 
 
 22.7 
 
 22.8 
 
 23.0 
 
 23.1 
 
 23.2 
 
 233 
 
 23.4 
 
 23-5 
 
 23.7 
 
 233 
 
 23.4 
 
 23.5 
 
 23.6 
 
 23.7 
 
 23.8 
 
 24.0 
 
 24.1 
 
 24.2 
 
 243 
 
 24.4 
 
 24.6 
 
 24.7 
 
 24.3 
 
 24.4 
 
 24-5 
 
 24.6 
 
 24.7 
 
 24.9 
 
 25.0 
 
 25.1 
 
 25.2 
 
 25.3 
 
 25.5 
 
 25.6 
 
 25.7 
 
 25.3 
 
 25-4 
 
 25-5 
 
 25.6 
 
 25.7 
 
 259 
 
 26.0 
 
 26.1 
 
 26.2 
 
 26.4 
 
 26.5 
 
 26.6 
 
 26.8 
 
 26.3 
 
 26.5 
 
 26.6 
 
 26.7 
 
 26.8 
 
 27.0 
 
 27.1 
 
 27.2 
 
 27-3 
 
 27.4 
 
 27-5 
 
 27.7 
 
 27.8 
 
 27.4 
 
 27.5 
 
 27.6 
 
 27.727.8 
 
 28.0 
 
 28.1 
 
 28.2 
 
 28.3 
 
 28.4 
 
 28.6 
 
 28.7 
 
 28.9 
 
 28.4 
 
 28.5 
 
 28.6 
 
 28.728.8 
 
 29.0 
 
 29.1 
 
 29.2 
 
 29.4 
 
 29.5 
 
 29.7 
 
 29.8 
 
 29.9 
 
 29.4 
 
 295 
 
 29.6 
 
 29.829.9 
 
 30.1 
 
 30.2 
 
 303 
 
 30.4 
 
 30.5 
 
 30.7 
 
 30.9 
 
 310 
 
 30.4 
 
 30.5 
 
 30.7 
 
 30.8 
 
 30.9 
 
 311 
 
 31-2 
 
 313 
 
 31.5 
 
 31.6 
 
 31.8 
 
 319 
 
 32.1 
 
 314 
 
 31.5 
 
 31.7 
 
 31.8 
 
 32.0 
 
 32.2 
 
 32.2 
 
 32.4 
 
 32.5 
 
 32.6 
 
 32.8 
 
 32.0 
 
 33- 1 
 
 32.5 
 
 32.6 
 
 32.7 
 
 32.9 
 
 33.0 
 
 33-2 
 
 33-3 
 
 33-4 
 
 33.6 
 
 33-7 
 
 33-9 
 
 23.0 
 
 34.2 
 
 33-5 
 
 33-6 
 
 33-8 
 
 33-9 
 
 340 
 
 34-2 
 
 34-3 
 
 34-5 
 
 34.6 
 
 34-7 
 
 34-9 
 
 35.1 
 
 35.2 
 
 34-5 
 
 34.6 
 
 34-8 
 
 34-9 
 
 350 
 
 35-2 
 
 35-3 
 
 35-5 
 
 35.6 
 
 35-8 
 
 36.0 
 
 36.1 
 
 36.3 
 
 35-5 
 
 35-6 
 
 35.8 
 
 35-9 
 
 36.1 
 
 36.2 
 
 36.4 
 
 36.5 
 
 36.7 
 
 36.8 
 
 370 
 
 37.2 
 
 37-3 
 
 17.2 
 
 17.7 
 
 18.3 
 
 18. 819. 4 
 
 20.0 
 
 20.5 
 
 21. 1 
 
 21.6 
 
 22.2 
 
 22.7 
 
 233 
 
 23.8 
 
 on a bench or support above the scale pan. 
 The loss of weight of the plummet is, of course, 
 the weight of the bulk of water that it displaces. 
 The sp. gr. of any sample can be determined by- 
 weighing the plummet immersed in the sample 
 and dividing the loss in weight by the loss in 
 water. The quotient is the sp. gr. 
 
 The ordinary pyknometer is not convenient 
 
12 MILK 
 
 on account of the liability of the upper layer 
 of the liquid to be richer in fat than the lower ; 
 the overflow, therefore, does not represent the 
 mixture. 
 
 Total Solids. — This determination may often 
 be made with sufficient accuracy for practical 
 purposes by evaporating a measured volume 
 (^- g'j 3 or 5 c.c.) in a shallow nickel dish from 5 
 to 8 cm. in diameter. Nickel crucible-covers are 
 suitable. The thin glass (Petri) dishes used for 
 microbe culture are convenient. When greater 
 accuracy is required, and especially when the 
 ash is to be determined, platinum dishes are the 
 most satisfactory, but owing to the present price 
 of this metal, quartz dishes are now much used. 
 Either the translucent or transparent quartz is 
 suitable, the former being less expensive. 
 
 Good results may be secured as follows : A flat 
 dish, 3.5 cm. in diameter, with sides 0.5 cm. high, 
 is provided with a thin fiat watch-glass cover 
 that fits rather closely. The total weight of the 
 cover and dish is noted. 2 or 3 c.c. of the sample 
 are run into the dish from the pipet, the watch- 
 glass placed on, and the weight taken as rapidly 
 as possible. The glass prevents appreciable 
 loss from evaporation during an ordinary weigh- 
 ing. The cover is removed, the dish heated on 
 the water-bath or in the water-oven, and weighed 
 from time to time (with cover on it) until the 
 
ANALYTIC PROCESSES I3 
 
 weight is sensibly constant. The percentage 
 of residue can be easily calculated. About three 
 hours may be required to secure constant weight. 
 
 When high accuracy is not essential, it will 
 suffice to measure the milk. Vieth advised a 
 pipet graduated to deliver 5 grams, and found 
 that, working with whole and skimmed milk, 
 under the ordinary variations of temperature, 
 the error will not exceed o.i on the total solids 
 and less on the fat. The pipet should have a 
 rather wide opening so that no cream will be 
 retained. 
 
 The Massachusetts State Board of Health has 
 for many years used the routine method of 
 evaporating 5 grams for two hours in a flat plati- 
 num basin over boiling water. 
 
 The A. O. A. C. method is: Heat at 100° to 
 constant weight, about 3 grams in a tared plati- 
 num, aluminum or tin dish of 5 cm. diameter, 
 with or without the addition of 15 to 30 grams 
 of sand. Cool and weigh. 
 
 Ash. — The residue from the determination of 
 total solids is heated cautiously over the Bunsen 
 burner, until a white ash is left. The result 
 obtained in this manner is apt to be slightly low 
 from loss of sodium chlorid. This may be 
 avoided by heating the residue sufficiently to 
 char it, extracting the soluble matter with a few 
 CO. of water, and filtering (using paper extracted 
 
14 MILK 
 
 with hydrofluoric acid). The filter is added to 
 the residue, the whole ashed, the filtrate then 
 added, and the liquid evaporated carefully to 
 dryness. The ash of normal milk is about 0.7% 
 and faintly alkaline. A marked degree of alka- 
 linity and effervescence with hydrochloric acid 
 will suggest the addition of a carbonate. 
 
 The method of the A. O. A. C. is as follows : In 
 a weighed dish put 20 c.c. of milk from a weighing 
 bottle; add 6 c.c. of nitric acid, evaporate to 
 dryness, and burn at a low red heat till the ash 
 is free from carbon. 
 
 Fat. — Many methods for fat determination 
 have been devised. The following will suffice for 
 all practical work: 
 
 Adams' Method. — This consists essentially in 
 spreading the milk over absorbent paper, drying, 
 and extracting the fat in an extraction apparatus ; 
 the milk is distributed in an extremely thin layer, 
 and by a selective action of the paper the larger 
 portion of the fat is left on the surface. A 
 paper, manufactured especially for this purpose 
 by Schleicher & Schuell, is obtainable in strips 
 of suitable size. Each of these yields to ether 
 only from o.ooi to 0.002 gram of extract. 
 
 Coils made of thick filter-paper, cut into 
 strips 6 by 62 cm., are thoroughly extracted 
 with ether and alcohol, or the weight of the ex- 
 tract corrected by a constant obtained for the 
 
ANALYTIC PROCESSES 1 5 
 
 paper. From a weighing bottle about 5 grams 
 of the milk are transferred to the coil by means 
 of a pipet, care being taken to keep dry the end 
 of the coil held in the fingers. The coil is 
 placed, dry end down, on a piece of glass and dried 
 for one hour, preferably in an atmosphere of 
 hydrogen; it is then transferred to an extraction 
 apparatus and extracted with absolute ether, 
 petroleum spirit of boiling-point about 45° or, 
 better, carbon tetrachlorid. The extracted fat 
 is dried and weighed. 
 
 The above procedure is very satisfactory, but 
 the drying in hydrogen may usually be omitted. 
 After the coil has received at least twenty wash- 
 ings, the flask is detached, the ether removed by 
 distillation, and the fat dried by heating in an 
 air-oven at about 105°, and occasionally blowing 
 air through the flask. After cooling, the flask 
 is wiped with a piece of silk, allowed to stand 
 ten minutes, and weighed. 
 
 Richmond states that to perform a rigidly 
 accurate determination attention to the following 
 points is necessary : The ether must be anhydrous 
 (drying over calcium chlorid and distilling is 
 sufficient). Schleicher & Schuell's fat-free papers 
 should be used, and one should be extracted 
 without any milk on it, as a tare for the others. 
 Four or five hours' extraction is necessary, and 
 
l6 MILK 
 
 the coils should be well dried before extraction is 
 begun. 
 
 Thimble-shaped cases made of fat-free paper 
 are now obtainable and are convenient for holding 
 the absorbent material on which the milk is 
 spread. The fine texture prevents undissolved 
 matter escaping. A case may be used repeatedly. 
 Sour milk may be thinned with ammonium hy- 
 droxid before taking the portion for analysis. 
 
 Babcock Asbestos Method. — This is recom- 
 mended by the A. 0. A. C. : Provide a hollow 
 cylinder of perforated sheet metal 60 mm. long 
 and 20 mm. in diameter, closed 5 mm. from one 
 end by a disk of the same material. The per- 
 forations should be about 0.7 mm. in diameter 
 and 0.7 mm. apart. Fill the cylinder loosely with 
 from 1.5 to 2.5 grams of freshly ignited woolly 
 asbestos free from fine or brittle material. 
 Cool in a desiccator and weigh. Introduce a 
 weighed quantity of milk (about 4 grams) and 
 dry at 100°. The cylinder is placed in the ex- 
 traction tube and extracted with ether in the 
 usual way. The ether is evaporated and the fat 
 weighed. The extracted cylinder may be dried 
 at 100° and the fat checked by the loss in weight. 
 A higher degree of accuracy is secured by per- 
 forming the drying operation in hydrogen. 
 
 For thorough extraction, especially with diffi- 
 culty soluble materials and volatile solvents, the 
 
ANALYTIC PROCESSES 1 7 
 
 continuous extraction apparatus devised by 
 Szombathy, but commonly called the Soxhlet 
 tube, is most suitable. 
 
 The material may be placed in a fat-free paper 
 thimble and covered with a plug of cotton to 
 prevent loss of fine particles. In place of the 
 cotton plug, a porcelain or platinum Gooch 
 crucible may be used, as shown in the cut. 
 The top of the thimble should be a short dis- 
 tance below, and the top of the crucible a short 
 distance above, the bend of the siphon. The 
 thimble should be supported by a section of 
 glass tubing, i to 2 cm. long, with rounded 
 edges; the edge on which the thimble rests should 
 be a little uneven to prevent a close joint, which 
 would hinder the siphoning of some of the 
 liquid. 
 
 Alundum cylinders will probably be useful. 
 
 Loss of solvent by leakage often occurs. It 
 may be diminished somewhat by soaking the 
 corks in rather strong hot gelatin solution, 
 draining them quickly and then exposing them 
 for some hours to formaldehyde vapor. 
 
 The solvents most generally employed are 
 ether and petroleum spirit, but carbon tetra- 
 chlorid is well adapted for extraction purposes 
 as it has high solvent power for fats and is not 
 easily inflammable. 
 
 When extraction is completed, the carton and 
 
1 8 MILK 
 
 materials may be removed from the tube, and, 
 replacing the parts of the apparatus, much of 
 the solvent may be redistilled into the extractor, 
 thus recovering the liquid. Care must be taken 
 not to distil the contents of the flask closely or 
 heat strongly, lest some of the more volatile of 
 the dissolved matters pass into the distillate. 
 
 Roese-GoUlieh Method. — This is now being used 
 for milk-products as well as for milk. For de- 
 tailed description, see page 72. 
 
 Centrifugal Methods. — Although almost all the 
 fat of milk may be separated by the centrifuge, 
 the emulsion is not destroyed and the volume of 
 cream is merely suggestive as to the fat-content 
 of the milk. To obtain a clear fatty layer in 
 condition for close measurement it is necessary 
 to use chemicals. The methods at present most 
 employed depend essentially on one devised by 
 Gustaf DeLaval, who took out a patent in Sweden 
 for the use of a mixture of twenty volumes of 
 strong acetic acid and one volume of strong 
 sulfuric acid. This mixture coagulates and then 
 dissolves the proteins, destroys the emulsion, but 
 does not otherwise affect the fat and does not 
 act on the lactose. By brief whirling in a cen- 
 trifuge the fat collects in a clear sharply defined 
 layer. DeLaval took out patents in several 
 countries subsequent to the above date. 
 
 Leffmann and Beam devised a method in which 
 
ANALYTIC PROCESSES 1 9 
 
 a small amount of amyl alcohol with an equal 
 volume of hydrochloric acid was added to the 
 milk, and the proteins thus coagulated dissolved 
 by strong sulfuric acid. About the same time 
 Babcock devised a process in which sulfuric acid 
 was used alone. Subsequently Gerber published 
 a process in which the essential feature of the 
 Leffmann-Beam method, namely, the use of amyl 
 alcohol, was advised. 
 
 The test-bottles have a capacity of about 30 c.c. 
 and are provided with a graduated neck, each 
 division of which represents 0.1% by weight 
 of butter fat. 
 
 15 c.c. of the milk are measured into the 
 bottle, 3 c.c. of a mixture of equal parts of amyl 
 alcohol and strong hydrochloric acid added, 
 mixed, the bottle filled nearly to the neck with 
 concentrated sulfuric acid, and the liquids mixed 
 by holding the bottle by the neck and giving it a 
 gyratory motion. The neck is now filled to 
 about the zero point with a mixture of sulfuric 
 acid and water prepared at the time. It is then 
 placed in the centrifugal machine, which is so 
 arranged that when at rest the bottles are in a 
 vertical position. If only one test is to be made, 
 the equilibrium of the machine is maintained by 
 means of a test-bottle, or bottles, filled with a 
 mixture of equal parts of sulfuric acid and water. 
 After rotation for from one to two minutes, the 
 
20 MILK 
 
 fat will collect in the neck of the bottle and the 
 percentage may be read off. It is convenient to 
 use a pair of dividers in making the reading. 
 The legs of these are placed at the upper and lower 
 limits respectively of the fat, allowance being made 
 for the meniscus; one leg is then placed at the 
 zero point and the reading made with the other. 
 Experience by analysts in various parts of the 
 world has shown that with properly graduated 
 bottles the results are reliable. As a rule, they 
 do not differ more than o.i % from those obtained 
 by the Adams process, and are generally even 
 closer. 
 
 For great accuracy, the factor for correcting 
 the reading on each of the bottles should be de- 
 termined by comparison with the figures obtained 
 by the Adams or other standard process. 
 
 Cream is to be diluted to exactly ten times its 
 volume, the sp. gr. taken, and the liquid treated 
 as a milk. Since in the graduation of the test- 
 bottles a sp. gr. of 1.030 is assumed, the reading 
 must be increased in proportion. 
 
 A more accurate result may be obtained by 
 weighing in the test-bottle about 2 c.c. of the 
 cream and diluting to about 15 c.c. The read- 
 ing obtained is to be multiplied by 15.45 and 
 divided by the weight in grams of cream taken. 
 
 The mixture of fusel oil and hydrochloric acid 
 seems to become less satisfactory when long 
 
ANALYTIC PROCESSES 21 
 
 kept. It should be clear and not very dark in 
 color. It is best kept in a bottle provided with a 
 pipet which can be filled to the mark by dipping. 
 Rigid accuracy in the measurement is not needed. 
 
 [The Leffmann-Beam method is often erro- 
 neously called the *'Beimling" method, but 
 Beimling was merely the deviser of a cheap 
 centrifuge. To protect the interest of a manu- 
 facturer who had invested in the Beimling 
 machine under the impression that it was a 
 practicable method for fat estimation, it became 
 necessary for Leffmann and Beam to take out a 
 patent (now expired) and assign the same to this 
 investor.] 
 
 Calculation Methods. — Several investigators 
 have proposed formulae by which when any two 
 of the data, sp. gr., fat, and total solids, are 
 known, the third can be calculated. These differ 
 according to the method of analysis employed. 
 That of Hehner and Richmond, as corrected 
 by Richmond, was deduced from results by the 
 Adams method of fat extraction. It is : 
 
 T — 0.25 G + 1.2F + 0.14; 
 
 in which T is the total solids, G the last two figures 
 of the sp. gr. (water being looo), and F the fat. 
 Patrick has proved that with American milks the 
 constant should be dropped, the formula reading : 
 
 T = 0.25 G + 1.2 F 
 
22 MILK 
 
 Babcock's formula has been much used in the 
 United States. It is adapted to calculating the 
 solids not fat. In this formula g is the entire 
 figure for sp. gr. referred to water as i. 
 
 Snf^i ^""g-/V -x)x2.5 (100^/) 
 \ioo- 1.0753 /g / ^ ' ■" 
 
 Babcock has also given a much simpler form 
 adapted for total solids. This differs but slightly 
 from Richmond's. 
 
 Total Proteins. — 3 types of processes are 
 employed for this estimation: Calculation from 
 the total nitrogen; precipitation and direct 
 weighing ; calculation from the * ' aldehyde-figure. " 
 Milk contains appreciable amounts of non- 
 protein nitrogen, but the fact is usually disre- 
 garded. According to Munk, this may range, in 
 cow's milk, from 0.022 to 0.034%, and from 
 0.014 to 0.026% in human milk. By these 
 figures, the average protein nitrogen in cow's milk 
 would be 94%, and in human milk 91%, of the 
 total nitrogen. 
 
 Kjeldakl-Gunning Method. — (Calculation from 
 total nitrogen). 
 Reagents : 
 
 Potassium sulfate. — A coarsely powdered form 
 free from nitrates and chlorids should be selected. 
 
 Sulfuric acid. — This should have a sp. gr. 
 1.84 and be free from nitrates and ammonium. 
 
ANALYTIC PROCESSES 23 
 
 Standard acid. — ^/a Sulfuric or hydrochloric 
 acid, the strength of which has been accurately 
 determined. 
 
 Standard alkali. — ^/lo Ammonium hydroxid, so- 
 dium hydroxid, or barium hydroxid, the strength 
 of which in relation to the standard acid must 
 be accurately determined. 
 
 Sodium hydroxid solution. — 500 grams should 
 be added to 500 c.c. of water, the mixture al- 
 lowed to stand until the undissolved matter 
 settles, the clear liquor decanted and kept in a 
 stoppered bottle. It will be an advantage to 
 determine approximately the quantity of this 
 solution required to neutralize 20 c.c. of the 
 strong sulfuric acid. 
 
 Indicator. — Cochineal solution is recommended 
 by the A. O. A. C, but methyl-orange and sodium 
 alizarin-monosulfonate are satisfactory. Methyl- 
 orange solution should be very dilute; i part in 
 1000. A drop is sufficient for 100 c.c. of liquid. 
 Phenolphthalein is not well adapted to tritation 
 of ammonium compounds. 
 
 Digestion and distillation flasks. — Jena-glass 
 round-bottomed flasks with a bulb 12.5 cm. 
 long and 9 cm. in diameter, the neck cylindrical, 
 15 cm. long and 3 cm. in diameter, flared slightly 
 at the mouth. 
 Process 
 
 5 c.c. of the sample are placed in a digestion 
 3 
 
24 MILK 
 
 flask, lo grams of powdered potassium sulfate* 
 and 15 to 25 c.c. (ordinarily about 20 c.c.) of the 
 strong sulfuric acid are added and the diges- 
 tion conducted as follows: The flask is placed 
 in an inclined position and heated below the 
 boiling-point of the acid for from five to fifteen 
 minutes, or until frothing has ceased. Excessive 
 frothing may be prevented by the addition of 
 a small piece of paraffin. The heat is raised 
 until the acid boils briskly. A small, short- 
 stemmed funnel may be placed in the mouth 
 of the flask to restrict the circulation of air. 
 No further attention is required until the liquid 
 has become clear and colorless, or not deeper 
 than a pale straw. 
 
 When Kjeldahl operations are carried out in 
 limited number, the arrangement used in my 
 laboratory has been found very satisfactory. A 
 double- Y, terra cotta drain-pipe, about 20 cm. 
 internal diameter, is connected by an elbow 
 directly with the chimney-stack. The digestion 
 flasks are supported as shown in the rough 
 sketch, figure i (not drawn exactly to scale). 
 Two flasks can be operated at once. The 
 central opening is convenient for other opera- 
 tions producing fumes. Openings not in use 
 are closed by circles of heavy asbestos. 
 
 Apparatus for use when many determinations 
 are made are figured in the catalogs of supply- 
 
ANALYTIC PROCESSES 
 
 25 
 
 houses. As corrosive vapors are given off, it 
 must be placed under a hood; but a special 
 form of apparatus is now made which does not 
 require an escape-pipe. 
 
 When the liquid has become colorless or very- 
 light straw yellow, it is allowed to cool, diluted 
 with 100 c.c. of water if the smaller form of 
 
 Fig. I. 
 
 flask has been used, the liquid transferred to 
 the distilling flask, and the digestion flask rinsed 
 with two portions of water, 50 c.c. each, which 
 are also transferred to the distilling flask. With 
 the larger form of flask the dilution is made at 
 once by the cautious addition of 200 c.c. of 
 water. Granulated zinc, pumice stone, or 0.5 
 
26 MILK 
 
 gram of zinc dust is added. 50 c.c. of the strong 
 sodium hydroxid solution, or sufficient to make 
 the reaction strongly alkaline, should be slowly 
 poured down the side of the flask so as not to mix 
 at once with the acid solution. It is convenient 
 to add to the acid liquid a few drops of phenol- 
 phthalein or azolitmin solution, to indicate when 
 the liquid is alkaline, but it must be noted that 
 strong alkaline solutions destroy the former 
 indicator. The flask is shaken so as to mix the 
 alkaline and acid liquids and at once attached to 
 the condensing apparatus. The receiving flask 
 should have been previously charged with a 
 carefully measured volume of the ^/a acid (10 c.c. 
 diluted with distilled water to 100 c.c. is a 
 convenient amount). The distillation is con- 
 ducted until about 150 c.c. have passed over. 
 A small amount of indicator is added, the liquid, 
 titrated with standard alkali, and the amount 
 neutralized by the distilled ammonium hydroxid 
 determined by subtraction. Each c.c. of ^/a 
 acid neutralized is equivalent to 0.007 nitrogen. 
 The nitrogen multiplied by 6.38 gives the 
 total proteins. 
 
 The distillation in this operation requires 
 care, as the amount of ammonium hydroxid is 
 determined by its neutralizing power, hence 
 solution of the alkali of the glass will introduce 
 error. Common glass is not satisfactory. Block 
 
ANALYTIC PROCESSES 27 
 
 tin is a good juaterial. Moerrs found that Jena- 
 glass tubes resist the action of the ammonium 
 hydroxid. Distillates should be titrated promptly 
 as alkali may be dissolved from the glass. 
 
 A satisfactory condensing arrangement for 
 general laboratory use is a copper tank of good 
 size, through which several condensing tubes pass. 
 
 Aldehyde Number. — The addition of formalde- 
 hyde to milk increases the acidity by an action on 
 the proteins. As commercial formaldehyde is 
 always acid, the acidity must be either determined 
 or neutralized in applying the following method. 
 The application of the reaction to determination 
 of proteins in milk is due to Steinegger. Rich- 
 mond and Miller investigated the method and 
 suggested the use of strontium hydroxid instead 
 of sodium hydroxid. Richmond gives the 
 following details : 
 
 To 10 c.c. of milk at least i c.c. of a 0.5% 
 solution of phenolphthalein is added and the 
 liquid neutralized with standard strontium hy- 
 droxid solution. To the faintly pink liquid, 2 
 c.c. or more of 40% formaldehyde solution are 
 added and the titration made to the same tint 
 as the former. The strontium hydroxid required 
 by the formaldehyde solution must be known, 
 and this being deducted from that which was 
 used in the titration and the remainder calculated 
 
28 MILK 
 
 to c.c. ^/i acid per looo c.c. of milk will give 
 the "aldehyd number." Richmond finds that 
 this multiplied by 0.17 gives in most cases a close 
 approximation to the total proteins obtained by 
 the Kjeldahl method. 
 
 Calculation Method. — Olson has shown that in 
 normal milks the proteins may be calculated with 
 close approximation by the formula 
 
 t 
 p = t- 
 
 1-34 
 
 in which p is protein and / total solids. 
 
 Determination of special proteins. — 
 Casein and albumin may be determined by Sebe- 
 lein's method: 20 c.c. of the sample are mixed 
 with 40 c.c. of a saturated solution of magnesium 
 sulfate and powdered magnesium sulfate stirred 
 in until no more will dissolve. The precipitate 
 of casein and fat, including the trace of globulin, 
 is allowed to settle, filtered, and washed several 
 times with a saturated solution of magnesium 
 sulfate. The filtrate and washings are saved for 
 the determination of albumin. The filter and 
 contents are transferred to a flask and the 
 nitrogen determined by the method described 
 above. The nitrogen so found, multiplied by 
 6.38, gives the casein. 
 
 The filtrate and washings from the determina- 
 
ANALYTIC PROCESSES 29 
 
 tion of casein are mixed, the albumin precipitated 
 by Almen's tannin reagent, filtered, and the 
 nitrogen in the precipitate determined as above. 
 The same factor is used. 
 
 Almin's reagent is prepared by dissolving 4 
 grams of tannin in 190 c.c. of 50% alcohol and 
 adding 8 c.c. of acetic acid of 25%. 
 
 In a mixture of milk and whey (prepared with 
 rennet) in about equal parts, Richmond and 
 Boseley found about 0.3% of albumoses not pre- 
 cipitated by the copper sulfate nor by magnesium 
 sulfate, but precipitable, along with the albumin, 
 by a solution of tannin. The separation may be 
 effected by diluting the filtrate from the magne- 
 sium sulfate precipitation, acidifying slightly with 
 acetic acid, and boiling, when the albumin will be 
 coagulated and precipitated. The albumoses 
 may be separated by filtering the solution and 
 precipitating with tannin solution. The pre- 
 cipitated proteins are best estimated by de- 
 termining the nitrogen in the moist precipitate. 
 The separation of the proteins may be effected, 
 though less accurately, but the use of acetic acid, 
 as recommended by Hoppe-Seyler and Ritt- 
 hausen. 
 
 Leffmann and Beam have modified the process 
 to avoid the delay and trouble of washing the 
 precipitate, as follows: 10 c.c. of the milk are 
 mixed with saturated magnesium sulfate solu- 
 
30 MILK 
 
 tion and the powdered salt added to saturation. 
 The mixture is washed into a graduated measure 
 with a small amount of the saturated solution, 
 made up to loo c.c. with the same solution, 
 mixed, and allowed to stand until the separation 
 takes place. As much as possible of the clear 
 portion is drawn off with a pipet and passed 
 through a dry filter. An aliquot portion of the 
 filtrate is taken, the albumin precipitated by a 
 solution of tannin, and the nitrogen in the 
 precipitate ascertained as above. 
 
 The following are A. O. A. C methods: 
 I. Provisional Method for the Determination of 
 Casein in Cows' Milk. — The determination should 
 be made when the milk is fresh. When it is not 
 practicable to make the determination within 
 twenty-four hours, add one part of formaldehyd 
 to 2500 parts of milk and keep in a cool place. 10 
 grams of the sample are diluted with about 90 c.c. 
 of water at between 40° and 42°, 1.5 c.c. of a 
 solution containing 10% of acetic acid by weight 
 added, allowed to stand for five minutes, washed 
 three times by decantation, pouring the washings 
 through a filter, and the precipitate transferred 
 completely to the filter. If the filtrate is not 
 clear at first, it will generally become so in two 
 or three filtrations, after which the washing can 
 be completed. The nitrogen in the .' washed 
 precipitate and filter is determined by the 
 
ANALYTIC PROCESSES 3 1 
 
 Kjeldahl-Gunning method. The nitrogen, multi- 
 pHed by 6.38, gives the casein. 
 
 In working with milk which has been kept 
 with preservatives, the acetic acid should be 
 added in small portions, a few drops at a time with 
 stirring, and the addition continued until the 
 liquid above the precipitate becomes clear or 
 nearly so. 
 
 2. Provisional Method for the Determination of 
 Albumin in Milk. — The filtrate obtained in the 
 above operation is neutralized with sodium 
 hydroxid, 0.3 c.c. of the 10% solution of acetic 
 acid added, and the mixture heated for fifteen 
 minutes. The precipitate is collected on a filter, 
 washed, and the nitrogen determined. 
 
 Van Slyke has pointed out that the casein can 
 be approximately ascertained by multiplying 
 the figure for total proteins by 0.8. 
 
 Modified Proteins, Amino-derivatives and Am- 
 monium Compounds. — The following procedures 
 are given by Van Slyke. The filtrate from the 
 albumin precipitate is heated to 70°, i c.c. of 
 5% sulfuric acid added, then solid zinc sulfate 
 to saturation. The mixture is allowed to stand 
 at 70° until the caseoses settle. The liquid is 
 cooled, filtered, the precipitate washed with 
 saturated solution of zinc sulfate slightly acidified 
 with sulfuric acid and the nitrogen ascertained 
 by the Kjeldahl method. 
 
32 
 
 MILK 
 
 For amino- derivatives and ammonium com- 
 pounds, 50 c.c. of the milk are mixed in a flask 
 marked at 250 c.c. with i gram of sodium chlorid. 
 A 1 2 % solution of tannin is added, drop by drop, 
 until no further precipitation occurs. The mix- 
 ture is diluted to the mark, shaken and filtered 
 through a dry filter. For amino-derivatives, 50 
 c.c. of the filtrate are treated for nitrogen in the 
 usual way. For ammonium compounds, 100 c.c. 
 of the filtrate are mixed with magnesium oxid 
 and about 50 c.c. distilled, the distillate being 
 received in a known volume of standard acid. 
 Large excess of magnesium oxid must be avoided. 
 
 Lactose. — For this determination, A. O. A. C. 
 employs Soxhlet's method with the following 
 reagents : 
 
 Copper sulfate solution. — 34.639 grams of pure 
 crystallized copper sulfate are dissolved in water 
 and made up to 500 c.c. 
 
 Alkaline tartrate solution. — 173 grams of pure 
 sodium potassium tartrate and 50 grams of good 
 sodium hydroxid are dissolved in water and the 
 solution made up to 500 c.c. 
 
 Sodium hydroxid /j. 
 
 25 c.c. of the sample in a 500 c.c. flask are 
 diluted with 400 c.c. of water and 10 c.c. of the 
 copper sulfate solution and 8.8 c.c. ^/^ sodium 
 hydroxid solution added. The mixture should 
 
ANALYTIC PROCESSES 33 
 
 still have an acid reaction and contain copper in 
 solution. If this is not the case, the experiment 
 must be repeated, using a little less of the 
 alkali. The flask is filled to the mark with water, 
 shaken, and the liquid passed through a dry filter. 
 50 c.c. of Fehling's solution, obtained by mixing 
 equal parts of the above copper sulfate and 
 alkaline tartrate solutions, are heated to brisk 
 boiling in a 300 c.c. beaker, 100 c.c. of the filtrate 
 obtained as above added, and boiling continued 
 for six minutes ; the liquid then promptly filtered, 
 and treated according to methods given below. 
 The amount of lactose is calculated by the table 
 on page 34 from the copper obtained by table. 
 The figures for weights of copper between any 
 two data given in the table may be calculated 
 with sufficient accuracy for practical purposes by 
 allowing 0.0008 gram of lactose for each 0.00 1 
 gram of copper. 
 
 The precipitated cuprous oxid is usually con- 
 verted into free copper and weighed as such. 
 Two methods may be employed for reduction: 
 by hydrogen or by electrolysis. 
 
 Reduction by Hydrogen. — The curpous oxid is 
 collected on an asbestos filter. This is arranged 
 most conveniently in a special filtering tube, 
 which is shown in figure 2. The wider part is 
 about 8 cm. and 1.5 cm. in diameter, the narrower 
 portion about 5 cm. long and 0.5 cm. in caliber. 
 
34 
 
 MILK 
 
 A perforated platinum disk is sealed in just 
 above the point of narrowing. The asbestos is 
 placed on this disk, washed free from loose fibers, 
 dried well, and the tube weighed. The filtering 
 tube is attached to an exhaustion apparatus by 
 passing narrower portion through the cork, and a 
 
 Copper 
 
 Lactose 
 
 Copper 
 
 Lactose 
 
 Copper 
 
 Lactose 
 
 O.IOO 
 
 0.072 
 
 0.205 
 
 O.151 
 
 0.305 
 
 0.228 
 
 0.105 
 
 0.075 
 
 0.210 
 
 0.154 
 
 0.310 
 
 0.232 
 
 O.IIO 
 
 0.079 
 
 0.215 
 
 0.158 
 
 0.315 
 
 0.236 
 
 0.II5 
 
 0.083 
 
 0.220 
 
 0.162 
 
 0.320 
 
 0.240 
 
 0.120 
 
 0.086 
 
 0.225 
 
 0.165 
 
 0.325 
 
 0.244 
 
 0.125 
 
 0.090 
 
 0.230 
 
 0.169 
 
 0.330 
 
 0.248 
 
 0.130 
 
 0.094 
 
 0.235 
 
 0.173 
 
 0.335 
 
 0.252 
 
 0.135 
 
 0.097 
 
 0.240 
 
 0.177 
 
 0.340 
 
 0.256 
 
 0.140 
 
 O.IOI 
 
 0.245 
 
 0,181 
 
 0.345 
 
 0.260 
 
 0.145 
 
 0.105 
 
 0.250 
 
 0.185 
 
 0.350 
 
 0.264 
 
 0.150 
 
 0.109 
 
 0.255 
 
 0.189 
 
 0.355 
 
 0.268 
 
 0.155 
 
 0.II2 
 
 0.260 
 
 0.192 
 
 0.360 
 
 0.272 
 
 0.160 
 
 O.II6 
 
 0.265 
 
 0.196 
 
 0.365 
 
 0.276 
 
 0.165 
 
 0.120 
 
 0.270 
 
 0.200 
 
 0.370 
 
 0.280 
 
 0.170 
 
 0.124 
 
 0.275 
 
 0.204 
 
 0.375 
 
 0.285 
 
 0.175 
 
 0.128 
 
 0.280 
 
 0.208 
 
 0.380 
 
 0.289 
 
 0.180 
 
 0.132 
 
 0.285 
 
 0.212 
 
 0.385 
 
 0.293 
 
 0.185 
 
 0.134 
 
 0.290 
 
 0.216 
 
 0.390 
 
 0.298 
 
 0.190 
 
 0.139 
 
 0.295 
 
 0.221 
 
 0.395 
 
 0.302 
 
 0.195 
 
 O.I4I 
 
 0.300 
 
 0.224 
 
 0.400 
 
 0.306 
 
 0.200 
 
 0.147 
 
 
 
 
 
ANALYTIC PROCESSES 35 
 
 small funnel is fitted tightly in the top of the tube. 
 The object of this funnel is to prevent the pre- 
 cipitate collecting on the upper part of the tube. 
 The lower end of the funnel should project several 
 centimeters below the bottom of the cork through 
 which it passes. 
 
 The filtering apparatus must be arranged 
 prior to the precipitation, so that the cuprous 
 oxid may be filtered without delay. The pre- 
 cipitate is transferred as rapidly as possible to 
 the filter, well washed with hot water, alcohol, 
 and ether successively, dried, and the cuprous 
 oxid reduced by gentle heating in a current of 
 hydrogen. When the reduction is complete, 
 the heat is withdrawn, but the flow of hydrogen 
 is continued until the tube is cold. It is then 
 detached and weighed. 
 
 Reduction of Copper by Electrolysis. — The fil- 
 tration is performed in a Gooch crucible with 
 an asbestos-felt film and the beaker in which the 
 precipitation was made is well washed with 
 hot water, the washings being passed through 
 the filter, but it is not necessary to transfer 
 all the precipitate. When the asbestos film is 
 completely washed, it is transferred with the 
 adhering oxid to the beaker; any oxid remaining 
 in the crucible is washed into the beaker by use 
 of 2 c.c. nitric acid (sp. gr. 1.42), added with a 
 pipet. The crucible is rinsed with a spray of 
 
36 MILK 
 
 water, the rinsings being collected in the beaker. 
 The liquid is heated until all the copper is in 
 solution, filtered, the filter washed until the 
 filtrate amounts to at least 100 c.c, and elec- 
 trolyzed. 
 
 Electrolytic apparatus has been constructed 
 in a great variety of forms. When the opera- 
 tion is carried out frequently, it is best to have 
 an electrolytic table. A platinum basin holding 
 not less than 100 c.c. is used. A cylindrical form 
 with fiat bottom is convenient. It should rest 
 on a bright copper plate, which is connected 
 with the negative pole of the electrical supply. 
 The positive pole should be also platinum, either 
 a spiral wire, cylinder, or fiat foil. Many 
 operators use a funnel-shaped perforated ter- 
 minal for the negative pole ; in which case a glass 
 beaker or casserole will be a suitable container, 
 the positive terminal being placed within the 
 negative. 
 
 Four cells of a gravity battery will suffice 
 for a single decomposition, and will operate 
 two, but more slowly. It is usual to arrange 
 the apparatus so that the operation may be 
 continued during the night. When the elec- 
 tricity is taken from the general supply of the 
 laboratory, it is usually necessary to interpose 
 resistance and to have some means of measuring 
 the current-flow. This is sometimes done with 
 
ANALYTIC PROCESSES 
 
 37 
 
 .A 
 
 a gas evolution cell and incandescent lamp, but 
 an ammeter and adjustable rheostat are better. 
 
 Lactose may be determined by the polarim- 
 eter after removal of the fat and proteins, 
 which is best effected, as recommended by 
 Wiley, by acid mercuric nitrate 
 solution. Wiley prepared this by 
 dissolving mercury in twice its 
 weight of nitric acid of 1.42 sp. gr. 
 and adding to the solution five vol- 
 umes of water, but Revis and Bol- 
 ton advise that mercuric oxid 
 should be used. The A. O. A. C. 
 optical method is as follows: 
 
 For polarimeters reading to 100 
 for 26.048 grams sucrose (corre- 
 sponding to 32.98 grams lactose), 
 measure, in c.c, the amount ob- 
 tained by dividing double this (i.e., 
 65.96) by the sp. gr., add 10 c.c. mercuric nitrate 
 solution, make up to 102.6 c.c, shake, filter 
 through a dry filter and examine in a 200 mm. 
 tube. Half the observed reading will be the per- 
 centage of lactose. For example, if the sp. gr. 
 of the milk is 1.030, the amount taken will be 
 65.90 -T- 1.030 = 64 c.c. 
 
 The allowance for volume of precipitate by 
 making up to 102.6 c.c. is not accurate, except 
 with closely skimmed milks. 
 
38 MILK 
 
 The correction may be made more closely by 
 calculating the actual volune of the precipitate 
 by multiplying the fat-percentage by 1.075 
 (average specific volume of fat) and the protein- 
 percentage by 0.8 (average specific volume of 
 coagulated proteins), deducting the sum of these 
 products from 100 c.c. and correcting the ob- 
 served reading by proportion. For ordinary 
 milk, the volume of the proteins from 65.96 
 grams may be taken at 1.68 c.c. Supposing 
 the sample to contain 4.0% of fat and the 
 polarimetric reading to be 10, the calculation 
 would be thus : 
 
 65 . 96 X o . 04 = 2 . 63 Amount of fat in milk taken 
 2.63 X 1 .075 = 2.82 c.c. Volume of fat in precipitate 
 
 1 . 68 c.c. Est. vol. of proteins in precipitate 
 
 4.50 c.c. Total volume of precipitate 
 100 — 4.50 = 9 . 55 c.c. Actual volume of liquid. 
 100:95-5 :: 10 19.55 9-55-^2 = 4.75, per cent, lactose. 
 
 The employment of a factor for correcting 
 for the volume of precipitate may be avoided by 
 Scheibler's method of "double dilution," in 
 which two solutions of different volume are 
 compared. The following is a summary of the 
 method given by Wiley & Ewell: For polari- 
 meters adapted to a normal weight of 26.048 
 sucrose, 65.82 grams of milk are placed in a 
 100 c.c. flask, 10 c.c. of the acid mercuric nitrate 
 
ANALYTIC PROCESSES 39 
 
 added, the flask filled to the mark, the contents 
 well mixed, filtered, and a reading taken. A 
 similar quantity of the milk is placed in a 200 
 c.c. flask and treated in the same way. The true 
 reading is obtained by dividing the product of 
 the two readings by their difference. If the 
 observations are made in a 200 mm. tube the 
 percentage is half the true reading. 
 
 The instrument should be accurate, and great 
 care taken in the work, or the results will be less 
 satisfactory than by the method first described, 
 in which an allowance is made for the volume of 
 the precipitate. 
 
 Multirotation. — When freshly dissolved in cold 
 water, lactose shows a higher rotation than that 
 given above. By standing, or immediately on 
 boiling, the rotary power falls to the point 
 mentioned. In preparing solutions from the 
 soHd, therefore, care must be taken to bring them 
 to the boiling-point previous to making up to a 
 definite volume. This precaution is unnecessary 
 when operating on milk. 
 
 Acidity. — Milk being often amphoteric to lit- 
 mus, that indicator cannot be employed in 
 estimating acidity. Phenolphthalein is usually 
 employed. Several methods differing in details 
 have been proposed. Probably the best is that 
 of Thorner. In this, 10 c.c. of milk are diluted 
 with 20 c.c. of water, a few drops of a dilute 
 4 
 
40 MILK 
 
 alcoholic solution of phenolphthalein added and 
 the titration made with standard alkali. Thorner 
 proposes that the number of c.c. required should 
 be multiplied by lo and the result termed the 
 "degree of acidity." Fresh normal milk will 
 show figures ranging from i6 to i8. When the 
 degree of acidity is 23 or over, the sample will 
 coagulate on heating. 
 
 The process involves a slight error, in that the 
 addition of a notable amount of water to a milk 
 sample disturbs somewhat the relation of the 
 phosphates and diminishes the acidity. It may 
 be advisable to titrate the undiluted milk. If 
 the number of c.c. used is multiplied by 0.9 the 
 lactic acid equivalent to the acidity of the sample 
 is given in grams per 1000 c.c. 
 
DETECTION OF ADULTERATION 
 
 By far the larger part of the laboratory work on 
 milk is for assistance in the sanitary control of the 
 supply, and the analyses are principally directed 
 to the detection of the ordinary forms of adultera- 
 tions. The most important of these are: skim- 
 ming, watering and use of coloring, thickening 
 and preserving agents. Skimming and watering 
 are detected by determining fat and total solids; 
 from these data the solids not fat are calculated. 
 For the ordinary purposes of milk control, fat 
 can be estimated with quite sufficient accuracy 
 by centrifugal methods. The total solids may be 
 estimated directly as described on page 12, or 
 calculated from the sp. gr. and fat as indicated on 
 page 21. 
 
 Judgment whether a given sample has been 
 skimmed or watered depends in many cases upon 
 the standard for whole milk. Some irregularity 
 of standards for fat and solids not fat exists, and 
 the opinion of the analyst will be determined, 
 therefore, by the standard of the locality. In 
 most cases the standard for fat is between 3 and 
 4%, and that for total solids about 8.50%. 
 
 As fat diminishes the sp. gr. of milk, and the 
 
 41 
 
42 MILK 
 
 other solids increase it, it is possible to take off 
 a small amount of the former and add some 
 water without disturbing the sp. gr., but, of 
 course, the above analytical methods will detect 
 this procedure. It is now admitted that, except 
 in cases of wide departure from the usual limits, 
 the adulteration of milk cannot be detected by 
 the sp. gr. alone but the employment of a care- 
 fully graduated lactometer is of use in routine 
 milk inspection. 
 
 Direct Detection of Added Water. Serum-refrac- 
 tion. — Of late years several methods have been 
 proposed for this purpose but most of them have 
 no positive value and have not come into general 
 use. The refractive index of the whey (milk- 
 serum) offers a rapid and satifactory method for 
 detecting watering. Several methods of pre- 
 paring this whey have been proposed, but 
 Lythgoe has found, as the result of extended 
 experience, the following to be satisfactory. 
 
 Dissolve 7.25 grams of crystallized copper sulfate 
 in water and dilute to 1000 c.c. If this solution 
 does not refract 36 on the scale of the immersion 
 refractometer at 20°, add water or copper sulfate 
 until the desired result is obtained. To 8 c.c. 
 of the copper solution add 32 c.c. of milk. Shake 
 well and pour upon a dry filter. When the filtrate 
 begins to come through clear, change the receiver, 
 pour the small quantity of cloudy filtrate upon 
 
DETECTION OF ADULTERATION 43 
 
 the filter and continue the filtration as usual. 
 Refract the clear filtrate at 20°, by means of the 
 Zeiss immersion refractometer. A reading below 
 36 indicates added water. The advantages of 
 this method over the acetic acid method are as 
 follows: It is quicker, heating of the samples is 
 unnecessary, consequently there is no error due 
 to evaporation. The range of differences in the 
 refraction of pure milk is less. 10% of added 
 water will reduce the refraction of high-grade 
 milk below the minimum, but it takes 15 % in the 
 acetic acid method. Lythgoe made analyses 
 of 150 samples of milk of known purity by this 
 method. The total solids ranged from 17.17 to 
 10.40%, the fat from 7.7 to 2.45%, the solids not 
 fat from 10.50 to 7.5% and the refraction of the 
 copper serum from 36.1 to 39.5. These refrac- 
 tions were distributed as follows: 
 
 Refraction 
 
 Number 
 
 OF Samples 
 
 39.0 to 39.5 
 
 
 6 
 
 38.0 to 38.9 
 
 
 66 
 
 37oto37.9 
 
 
 65 
 
 36.1 to 36.9 
 
 
 13 
 
 150 
 
 See also table of refractions on page 7 . 
 
 As a result of extended experience, Lythgoe 
 has recently given the following applications 
 of some of the methods of milk analysis. 
 
 The least variable constituents of milk are 
 
44 MILK 
 
 lactose and ash, both of which are valuable data 
 in detecting added water. It is possible within 
 reasonable limits to indicate by the total solids 
 and fat whether a given sample has been watered 
 or skimmed. 
 
 No relation exists between the refraction of 
 the (sweet) serum and the ash of the sour serum 
 (see page 66), therefore, if both these data are 
 below those of normal milk, added water is 
 positively indicated. 
 
 The ratio of protein to fat in normal milk 
 is always less than i. If the ratio exceeds i, 
 skimming is indicated. If the protein-fat ratio 
 is less than 0.7, or the percentage of fat to 
 total solids is over 35, in samples having a low 
 serum refraction, these may be declared watered, 
 the refraction being not necessarily below the 
 minimum for all samples of known purity. 
 
 The sp. gr. of the sweet serum or its total 
 solids may be used as a datum in place of the re- 
 fraction; either will be a safe guide. 
 
 Lowering of Freezing-point. — Several observers 
 have shown that watered milk has a lower freezing- 
 point than pure milk, and that the amount of 
 depression has a definite relation to the amount 
 of water added. One of the most recent state- 
 ments on the subject is by J. W. Leather, who 
 found the procedure very satisfactory for de- 
 tecting watering in cows' milk and that of the 
 
DETECTION OF ADULTERATION 45 
 
 India buffalo. He states that one observer 
 has found that a depression to 0.537° indicates 
 2.3% of added water. The procedure requires 
 special apparatus and careful manipulation; data 
 from testing samples of known composition should 
 be obtained before relying on it in important 
 cases. 
 
 Thickening Agents. — To conceal skimming 
 and watering many thickening agents have 
 been used. At least two instances of the use 
 of brain matter have been reported. Dextrin, 
 starch, sugar, salt, gelatin and agar have all 
 been used. 
 
 Brain matter can be easily detected by the 
 microscope, starch jelly by the iodin test, 
 dextrin by increased polarimetric reading, sodium 
 chlorid by the increased chlorids in the ash. 
 Agar is frequently used in certain milk products, 
 especially the cheap ice-cream sold in American 
 cities. 
 
 Gelatin. — Stokes detects the presence of gelatin 
 in cream or milk as follows : 10 c.c. of the sample, 
 20 c.c. of cold water, and 10 c.c. of acid mercuric 
 nitrate solution (page 37) are mixed, shaken 
 vigorously, allowed to stand for five minutes, 
 and filtered. If much gelatin is present, it may 
 be difficult to get a clear filtrate. A portion 
 of the filtrate is mixed with an equal bulk 
 of saturated aqueous solution of picric acid. 
 
46 MILK 
 
 Gelatin produces a yellow precipitate. Picric acid 
 will detect the presence of i part of gelatin in 
 10,000 parts of water. The picric acid solution 
 should not give a precipitate with the nitrate 
 solution. 
 
 For sucrose Cotton devised the following tests : 
 10 c.c. of the sample are mixed with 0.5 gram 
 of powdered ammonium molybdate, and 10 c.c. 
 of dilute hydrochloric acid (i to 10) are added. 
 In a second tube, 10 c.c. of pure milk or 10 c.c. 
 of a 6 % solution of lactose are similarly treated. 
 The tubes are then placed in the water-bath and 
 the temperature gradually raised to about 80°. 
 If sucrose is present, the milk will become blue, 
 while genuine milk or milk-sugar remains un- 
 altered unless the temperature is raised to the 
 boiling-point. According to Cotton, the reaction 
 is well marked in the presence of as little as i 
 gram of sucrose to 1000 c.c. of the milk. For 
 the detection of other organic thickening agents, 
 such as pectoses, agar and mixtures of agar and 
 gelatin, see under ''Cream," page 67. 
 
 Calcium Saccharate (Saccharate of Lime). — A 
 compound produced by the action of lime on 
 sucrose has been used as a thickening agent. A 
 test due to Bauer and Neumann is recommended 
 by Ly thgoe, from whose description the following 
 is taken : 
 
 To 25 c.c. of milk (or cream) add 10 c.c. of 
 
DETECTION OF ADULTERATION 47 
 
 5 % solution of uranium acetate, shake well, al- 
 low to stand for five minutes and filter. To lo c.c. 
 of the clear filtrate (in the case of cream use the 
 total filtrate, which will be less than lo c.c.) add a 
 mixture of 2 c.c. saturated ammonium molyb- 
 date and 8 c.c. dilute hydrochloric acid (i part 
 25% acid and 7 parts water), and place in a 
 water-bath at a temperature of 80° for five minutes. 
 If the sample contains sugar the solution will 
 have a prussian blue tint. This should always 
 be compared in a colorimeter with the standard 
 Prussian blue solution prepared by adding a few 
 drops of potassium ferrocyanid and 5 drops of 
 10% hydrochloric acid to a solution of i c.c. of 
 0.1% ferric chlorid in 20 c.c of water. 
 
 It has been claimed that pure milk will give 
 this test. Occasionally samples of pure milk will 
 give a pale blue, but this can be entirely removed 
 by filtration, and the filtrate will be green; while 
 the color due to sucrose will pass through the 
 filter, giving the blue solution characteristic of 
 adulterated samples. The color is due to re- 
 duction of molybdic acid, and is caused by 
 levulose and dextrose as well as by sucrose. 
 Solutions of I gram of lactose, levulose, dextrose 
 and sucrose in 35 c.c of water were used in com- 
 paring the amount of color produced when heated 
 with the molybdenum reagent for five minutes. 
 Lactose produced no color, levulose gave a heavy 
 
48 MILK 
 
 blue, sucrose a weaker blue and dextrose the 
 weakest blue, corresponding in intensity as 
 lo 13 : 1. 
 
 Stannous chlorid and ferrous sulfate give this 
 color, but the reaction takes place in the cold, 
 and with small quantities the color disappears on 
 heating. In order for the color to persist after 
 heating the sample of cream must contain these 
 substances to the extent of i % calculated as the 
 metal. In this case the sample will be completely 
 coagulated and the taste will be disagreeable. 
 Hydrogen sulfid will also give the blue, but it will 
 disappear on heating. If the solution does not 
 show blue before heating, it is free from hydrogen 
 sulfid, ferrous sulfate or stannous chlorid. 
 
 As a confirmatory test for sugar, the resorcinol 
 test may be applied to the serum prepared with 
 uranium acetate as described. This test is given 
 by sucrose and levulose, but not by dextrose or 
 lactose. 
 
 The quantitative estimation of sucrose in milk 
 is given under Milk Products (page 74). 
 
 Detection of Heated Milk. — Fresh milk con- 
 tains one or more enzyms of the ' ' peroxydase " 
 type, that is, having power to bring about 
 transfer of oxygen from peroxids to oxidable 
 substances. As the function of these enzyms 
 is destroyed by temperatures near 100°, it be- 
 comes possible to utilize the reaction for deter- 
 
DETECTION OF ADULTERATION 49 
 
 mining whether a given sample has been thus heated. 
 In most cases the action of the enzym is in- 
 dicated by the production of a deep blue, no 
 color change occurring when the enzym has been 
 heated. Hydrogen peroxid is commonly em- 
 ployed for furnishing the oxygen. A considerable 
 number of substances have been found to be 
 susceptible to oxidation under the influence of 
 the milk enzyms. Benzene derivatives, com- 
 monly used as photographic developers are 
 especially susceptible. Guaiacum was first used. 
 
 Arnold's Method. — A solution of guaiacum in 
 acetone is, according to Arnold and Menzel 
 better than the ordinary tincture. The test is 
 applied by adding to a small amount of the sample 
 in a test-tube, about lo drops of the guaiacum 
 solution, to which a drop or two of hydrogen 
 peroxid solution has just been added, so that the 
 reagent will float on the milk. If the sample 
 has not been heated above 80°, the point of 
 contact of the liquids will show a deep blue ring. 
 
 As guaiacum is liable to changes both in the 
 solid form and in solution it is important to de- 
 termine if the reagent is sensitive to raw milk, 
 hence a control test should aways be made. 
 Other reagents are now available which are, in the 
 main, more trustworthy. 
 
 Dupouy's Method. — In this method, 1-4 diam- 
 inobenzene is used. The reagent is dissolved in 
 
50 MILK 
 
 water (a weak solution will suffice), a few drops 
 added to the sample, then a few drops of hydrogen 
 dioxid solution, and the liquids shaken gently. 
 Milk that has not been heated above 80° gives 
 immediately a bright blue. Milk that has been 
 heated above this temperature shows no color 
 change at first but may slowly acquire a bluish 
 tint. This test is much in favor, but it is open 
 to the objection that the solution of the reagent 
 does not keep more than few hours, and even in 
 the solid state some commercial samples soon 
 decompose. 
 
 Benzidin Method. — Wilkinson and Peters sug- 
 gested this reagent, employing a solution of it 
 with a few drops of acetic acid followed as usual 
 by the oxidizing agent. Leffmann finds that 
 the commercial benzidin hydrochlorid (furnished 
 for volumetric estimation of sulfates) acts satis- 
 factorily without acetic aicd. 
 
 Wilkinson and Peters' test is performed simi- 
 larly to those just described, and has a similar 
 significance. They give experiments to show 
 that the method is rather more delicate than 
 with diamino-benzene or guaiacum. The solu- 
 tion of the benzidin compound keeps better. 
 They found that milk heated to 77° had lost its 
 reactivity to guaiacum but retained reactivity 
 to the other two reagents. Heated to 78° the 
 reactivity was also lost to these. 
 
DETECTION OF ADULTERATION 5 1 
 
 Leffmann has found that several commercial 
 photographic developers, e. g., amidol, are ap- 
 plicable in this test with about the limitations 
 above noted. 
 
 At critical temperatures, however, the results 
 with all the reagents depend materially on the 
 length of the heating. 
 
 Colors. — Annatto, turmeric, and some coal-tar 
 colors are much used. Caramel is occasionally 
 used, saffron and carotin but rarely. Annatto 
 may be detected by rendering the sample 
 slightly alkaline by acid sodium carbonate, im- 
 mersing a slip of filter-paper, and allowing it to 
 remain over night. Annatto will cause a reddish- 
 yellow stain on the paper. 
 
 Leys gives the following method for detecting 
 annatto; 50 c.c. of the sample are shaken with 
 40 c.c. of 95% alcohol, 50 c.c. of ether, 3 c.c. of 
 water, and 1.5 c.c. of ammonium hydroxid 
 solution (sp. gr. 0.900), and allowed to stand for 
 twenty minutes. The lower layer, which in pres- 
 ence of annatto will be greenish-yellow, is tapped 
 off and gradually treated with half its measure of 
 10% solution of sodium sulfate, the separator 
 being inverted without shaking, after each addi- 
 tion. When the casein separates in flakes that 
 gather at the surface, liquid is tapped off, strained 
 through wire gauze, and placed in four test- 
 tubes. To each of these amyl alcohol is added, 
 
52 MILK 
 
 and the tubes shaken and immersed in cold 
 water, which is gradually raised to 80°. The 
 emulsion breaks up, and the alcohol, holding 
 the annatto in solution, comes to the surface. 
 The alcoholic layer is separated from the lower 
 stratum, evaporated to dryness, and the residue 
 dissolved in warm water containing a little 
 alcohol and ammonium hydroxid. Clean white 
 cotton is introduced and the liquid evaporated 
 nearly to dryness on the water-bath. The 
 cotton, which is colored a pale yellow, even with 
 pure milk, is washed and immersed in a solution 
 of citric acid, when it will be immediately red- 
 dened if the milk contains annatto. Saffron, 
 turmeric, and the coloring-matter of the marigold 
 do not give a similar reaction. 
 
 Coal-tar colors may often be detected by dyeing 
 wool, but Lythgoe has devised the following 
 method, which is satisfactory: 15 c.c. of the 
 sample are mixed in a porcelain basin with an 
 equal volume of hydrochloric acid (sp. gr. 
 1.20), and the mass shaken gently so as to break 
 the curd into coarse lumps. If the milk con- 
 tains an azo-color, the curd will be pink; with 
 normal milk the curd will be white or yellowish. 
 
 General Method for Colors in Milk. — Leach 
 devised a general method. 150 c.c. of the 
 sample are coagulated in a porcelain basin, 
 with the addition of acetic acid and heating, 
 
DETECTION OF ADULTERATION 53 
 
 and the curd separated from the whey. The 
 curd will often collect in a mass; but if this does 
 not occur, it must be freed from whey by straining 
 through muslin. The curd is macerated for 
 several hours in a closed flask, with occasional 
 shaking, with ether to extract fat. Annatto 
 will also be removed by it. The ether and curd 
 are separated and treated as follows: 
 
 The ether is evaporated, the residue mixed 
 with a little weak solution of sodium hydroxid, 
 and passed through a wet filter; and when this 
 has drained, the fat is washed off and the paper 
 dried. An orange tint shows annatto, which 
 may be confirmed by a drop of solution of 
 stannous chlorid, which makes a pink spot. 
 
 If the curd is colorless, no foreign coloring- 
 matter is in it; if orange or brown, it should be 
 shaken with strong hydrochloric acid in a test- 
 tube. 
 
 If the mass turns blue gradually, caramel is 
 probably present. The whey should be ex- 
 amined for caramel (see page 95). 
 
 If the mass turns pink at once, an azo-color 
 is indicated. 
 
 Falsification of the ''Cream-line.'^ — The use of 
 glass bottles for retail delivery of milk enables 
 purchasers to make approximate estimations of 
 the richness of the sample by the depth of cream 
 formed after standing for some time, this being 
 
54 MILK 
 
 of distinctly different tint from the milk below it. 
 Deception has of late been extensively practised 
 by a treatment of milk which breaks up the fat 
 globules and increases the volume of cream 
 formed, so that a slightly skimmed milk will yield 
 a fair volume of cream. Determination of fat by 
 the usual methods will show the fraud. See 
 page 65. 
 
 It has been found that many of the bottles 
 used for distribution of milk are not of the capac- 
 ity designated on them, but this is a matter of 
 police regulation. 
 
 Perservatives. — These are largely used, es- 
 pecially in the warmer season, as a substitute for 
 refrigeration. Many of them are sold under 
 proprietary names which give no indication of 
 their composition. Preparations of boric acid 
 and borax were at one time the most frequent 
 in use, but at present formalin, a 40% solution 
 of formaldehyd, has come into favor. Sodium 
 benzoate is now in common use as a preservative 
 of cider, fruit- jellies, and similar articles, and 
 may, therefore, be found in milk. Salicylic 
 acid is not so much employed. Sodium car- 
 bonate is occasionally used to prevent coagula- 
 tion due to slight souring. Fluorids and abrastol 
 may be used. A mixture of boric acid and borax 
 is more efficient than either alone. The quantity 
 generally used is equivalent to about 0.5 gram of 
 
DETECTION OF ADULTERATION 55 
 
 boric acid per looo c.c. Formaldehyde is an 
 efficient antiseptic. In the proportion of 0.125 
 gram to 1000 c.c, it will keep milk sweet for a 
 week. Hydrogen peroxid, ozone and dichro- 
 mates have been used. The almost universal 
 decree of sanitary authorities is that milk 
 must be free from any added material, but 
 owing to its comparatively high cost, liability 
 to decomposition and the marked characters 
 of even incipient decomposition, great tempta- 
 tion to use preservatives exists and any anti- 
 septic, not actively poisonous, may be used. It 
 has been, found that milk drawn and marketed 
 under strict sanitary precautions will keep for 
 a considerable time, even at moderate tempera- 
 tures. The only permissible method of pre- 
 serving milk is by refrigeration. 
 
 In addition to the descriptions of the detec- 
 tion and estimation of preservatives given below, 
 see also under ''Cream." 
 
 Formaldehyde. Hehner's Test. — Hehner found 
 that when milk containing formaldehyde is 
 mixed with sulfuric acid containing a trace 
 of a ferric compound, a distinct blue appears. 
 Richmond and Boseley showed that the delicacy 
 of the test is much increased if the milk is 
 diluted with an equal volume of water and 
 sulfuric acid of 90 to 94%, added so that it 
 forms a layer underneath the milk. Under 
 5 
 
56 MILK 
 
 these conditions, milk, in the absence of for- 
 maldehyde, gives a slight greenish tinge at 
 the junction of the two liquids, while a violet 
 ring is formed when formaldehyde is present 
 even in so small a quantity as i part in 200,000 
 of milk. The color is permanent for many 
 hours. In the absence of formaldehyde, a 
 brown ring may form in the course of a few 
 hours, but it is below the junction line of the 
 two liquids. 
 
 Phenylhydrazin Test. — The following test 
 avoids the fallacy of some other tests. A pinch 
 of phenylhydrazin hydrochlorid is added to a 
 few c.c. of the sample, the liquid shaken, then a 
 drop of a fresh solution of sodium nitroprussid 
 and a few drops of sodium hydroxid solution. 
 A greenish tint is at once produced if formalde- 
 hyde is present. If the test is applied to the 
 liquid obtained by distilling milk the color will be 
 deep blue. 
 
 Phloroglucol Test. — A small amount of a 1% 
 solution of phloroglucol is added to the sample 
 and then a considerable volume of sodium 
 hydroxid solution. In the presence of formalde- 
 hyde a distinct rose tint will be produced. It 
 is best to add the phloroglucol by means of a 
 tube passed to the bottom of the test-tube. 
 
 Bonnet's test utilizes the vapor of formalde- 
 hyde, and avoids the fallacies of some of the 
 
DETECTION OF ADULTERATION 57 
 
 older tests. A solution is made by dissolving 
 0'035 gram pure morphin sulfate in lo c.c. of 
 sulfuric acid. This solution does not keep well. 
 A convenient amount of the sample is placed in 
 a dish or beaker, a watch-glass containing i c.c. 
 of the above solution is floated on it, and the dish 
 covered with a glass plate. The materials are 
 allowed to remain undisturbed at room-tempera- 
 ture for several hours. Formaldehyde is in- 
 dicated by the development of a color ranging 
 from pink to dark blue. A black discoloration 
 is disregarded. Bonnet found that with i part 
 of formaldehyde to 25,000 parts of sample a 
 distinct color appeared in one hour. 
 
 In testing ice-cream and similar articles it 
 must be borne in mind that some of the flavor- 
 ing materials being aldehydic in nature may 
 simulate formaldehyde. La Wall has found 
 that vanilHn may act thus. The phenylhydrazin 
 and Bonnet tests are least liable to fallacy in this 
 respect. 
 
 Nitrites and Formaldehyde. — Mixtures of these 
 substances are now sold under fanciful and mis- 
 leading names, for milk preservatives as a 
 nitrite prevents the reactions of formaldehyde 
 with some of the tests. 
 
 Leffmann has found that the phenylhydrazin 
 test will react promptly with formaldehyde in 
 presence of notable amount of nitrite and also 
 
58 MILK 
 
 that the well-known test for nitrites (sulfanilic 
 acid and alphanaphthylamine) reacts in the 
 presence of formaldehyde. The reactions are 
 obtained in fresh samples and in those that have 
 stood for twenty-four hours. 
 
 Determination of Formaldehyde. — In the case 
 of milk the proportion of formaldehyde is almost 
 always small and it may be in great part removed 
 from milk by distillation especially in a current 
 of steam. B. H. Smith found that if loo c.c. 
 of the sample are distilled with i c.c. of dilute 
 sulfuric acid (1:3), one-third of the formaldehyde 
 present will come over with the first 20 c.c. 
 Distillation of milk is troublesome owing to 
 bumping, but Smith found that it could be safely 
 conducted with a flat evaporating burner. It is 
 advisable to put a few pieces of pumice into the 
 flask. 
 
 Shrewsbury and Knapp recommend the fol- 
 lowing method for estimation of formaldehyde. 
 An oxidizing reagent is prepared by mixing o.i 
 gram of pure nitric acid (sp. gr. 1.52) with 100 c.c. 
 of strong hydrochloric acid are mixed. This 
 mixture should be freshly made. 
 
 5 c.c. of milk are treated with 10 c.c. of the 
 reagent, the mixture well shaken and kept for ten 
 minutes in a water-bath at 50°. The depth of 
 color is proportional to the amount of formalde- 
 hyde present and by means of milk containing 
 
DETECTION OF ADULTERATION 59 
 
 known amounts of the preservative estimations 
 may be made. 
 
 Hydrogen Peroxid. — Many tests have been 
 devised for detection of this substance. Among 
 the most convenient and satisfactory is the 
 reaction with vanadic acid first given by Werther. 
 It may be carried out by adding to lo c.c. of the 
 milk, lo drops of a i% solution of vanadic acid 
 in dilute sulfuric acid. This solution may be 
 conveniently made by dissolved commercial 
 sodium orthovanadate in the dilute acid. 
 
 In the presence of hydrogen peroxid a distinct 
 red will appear promptly. Barthel states that a 
 proportion of o.oio gram of the peroxid in loo 
 c.c. of milk can be detected positively using only 
 lo c.c. of the sample. 
 
 Benzoates and Salicylates. — The following 
 method covers both these preservatives. 
 
 lo c.c. of dilute sulfuric acid (5%) are added 
 to 20 c.c. of 95% alcohol and into this 50 c.c. of 
 the milk are poured in a fine stream with constant 
 stirring. After a few moments, the mixture is 
 filtered, the filtrate being returned until it passes 
 clear. A sufficient volume of the filtrate is 
 extracted in the usual manner with an equal 
 volume of ether or similar solvent. The solvent 
 is divided into two portions that are separately 
 evaporated and tested for benzoic and salicyHc 
 acids respectively as given below. 
 
6o MILK 
 
 Benzoates. — This is detected by a modification 
 of Mohler's method by Von der Heide and 
 Jakob as given by U. S. Bureau of Chemistry. 
 
 The residue that is to be tested for benzoic 
 acid is dissolved in a little water, the solution 
 mixed with from i to 3 c.c. of normal sodium hy- 
 droxid and evaporated to dryness. To this resi- 
 due is added from 5 to 10 c.c. of concentrated sul- 
 furic acid and a small crystal of potassium nitrate 
 and the mixture heated either for ten minutes 
 in a glycerol bath between 120° and 130° or for 
 twenty minutes in boiling water. If heated in 
 the glycerol bath the temperature must not be 
 permitted to go over 130°. Metadinitrobenzoic 
 acid is formed. After cooling i c.c. of water is 
 added, the liquid made decidedly ammoniacal, 
 boiled to break up ammonium nitrite, and some 
 fresh colorless ammonium sulfid solution added 
 so that the liquids do not mix. A brown ring at 
 junction indicates benzoic acid. The liquids 
 being mixed, the color diffuses and on heating 
 changes to greenish-yellow. The last reaction 
 distinguishes benzoic acid from salicylic and 
 cinnamic acid as these latter form amino-deriva- 
 tives which are not destroyed by heating. 
 Phenolphthalein interferes with this process. 
 
 Salicylic Acid. — The other portion of the 
 ether-extract may be evaporated and tested for 
 
DETECTION OF ADULTERATION 6 1 
 
 salicylic acid in the usual manner with a ferric 
 compound. 
 
 Saccharin. — ^A suitable amount of the sample 
 (50 or 100 c.c.) is acidified with dilute (25%) 
 sulfuric acid and extracted with a mixture of 
 equal parts of petroleum spirit (boiling below 60°) 
 and ether. The solvent is evaporated at a gentle 
 heat. The presence of saccharin in the residue 
 may be detected by the taste. 2 c.c. of a 
 saturated solution of sodium hydroxid are added 
 and the dish heated until the residue dries and 
 then to 2io°-2i5°, and maintained thus for half 
 an hour. The saccharin is converted into salicylic 
 acid, which may be detected in the residue by 
 acidulating it with sulfuric acid and applying the 
 ferric chlorid test. If salicylic acid be present 
 originally in the sample, the residue from the 
 petroleum spirit and ether solution is dissolved 
 in 50 c.c. of dilute hydrochloric acid, bromin 
 water added in excess, the liquid shaken well, 
 and filtered. Salicylic acid is completely removed 
 as a brominated derivative. The filtrate is made 
 strongly alkaline with sodium hydroxid, evapo- 
 rated, and fused as described above. 
 
 Sodium Carbonate and Sodium Acid Car- 
 bonate. — These substances are occasionally added 
 to milk to prevent acidity due to decomposition. 
 Barthel recommends a test devised by Hilger. 
 50 c.c. of the milk are diluted with 250 c.c. of 
 
62 MILK 
 
 water, the mixture is heated, precipitated with a 
 small amount of alcohol and a convenient 
 volume filtered. The filtrate is evaporated to 
 half its bulk. The presence of an alkali-carbon- 
 ate is easily ascertained by the usual tests. 
 
 Borates. — Jenkins' method is convenient and 
 reasonably delicate. lo c.c. of milk are mixed 
 with 7 c.c. of hydrochloric acid, filtered, a strip 
 of turmeric paper dipped in the filtrate, and then 
 dried on a watch-glass on the water-bath. The 
 paper becomes red in the presence of borates. 
 
 A simple test is to mix in a porcelain basin a 
 drop or two of the milk, a drop of hydrochloric 
 acid and a drop of alcoholic solution of turmeric 
 and evaporate to dryness on the water-bath. 
 The residue touched with ammonium hydroxid 
 will show a distinct greenish stain in the presence 
 of very small amounts of borates. 
 
 It is obvious that the delicacy of both these 
 tests may be materially increased by concen- 
 trating the sample. As boric acid is volatile 
 with steam it is best to render the sample slightly 
 alkaline with sodium hydroxid before evaporating. 
 
 Abrastol (Asaprol). — This is a calcium beta- 
 naphthol-sulphonate that has marked antiseptic 
 powers and has been used as a food preservative. 
 The following test suggested by Leffmann will 
 detect very small amounts. lo c.c. of the 
 sample are mixed with 0.5 c.c. of the solution of 
 
DETECTION OF ADULTERATION 63 
 
 mercuric nitrate described on page 37. In 
 the presence of abrastol a distinct yellow tint is 
 produced in a few minutes. Greater delicacy- 
 can be obtained by using the same proportion 
 of the reagent with 10 c.c. of milk known to be 
 pure. 
 
 Organic Contamination. — Sanitary control of 
 market-milk also involves tests for animal prod- 
 ucts, such as pus cells, and the identification 
 of specific microbes, such as those causing tuber- 
 culosis and typhoid fever. These investiga- 
 tions, however, are mostly outside of the scope 
 of a work on chemical analysis. For informa- 
 tion concerning these recourse must be had to 
 works on pathology and bacteriology. 
 
 Several chemical tests have been published 
 by which it is claimed that approximate deter- 
 mination of these contaminating organisms and 
 substances can be made but they are not capable 
 of replacing the exact methods of the pathologic 
 and bacteriologic laboratory. One of these is 
 the following. A dilute solution of methylene 
 blue is prepared by adding 5 c.c. of a saturated 
 alcoholic solution of the dye to 200 c.c. of water. 
 0.5 c.c. of this solution is added to 10 c.c. of 
 the sample. If the color is discharged promptly, 
 the sample contains over 100,000,000 bacteria 
 per c.c. 
 
 Hydrogen dioxid has been shown by the in- 
 
64 MILK 
 
 vestigations of Rentschler to kill quickly many 
 forms of microbes, and may be applicable to the 
 purification of milk, when, as in war, systematic 
 protection and inspection are not possible. 
 
 Preservation of Samples. — For the preservation 
 of milk samples for a day or two, refrigeration 
 is the best method. Sterilization in the ordinary 
 steam sterilizer used in preparing culture-media, 
 will enable milk to be kept for a considerable 
 time if in a flask closed with a cotton plug. 
 Several preservatives have been proposed for 
 keeping samples. Richmond found small amounts 
 of hydrofluoric acid effective, but it has been but 
 little used. Formaldehyde is very efficient; in 
 large amount it increases the total solids, inter- 
 feres with the reactions of the proteins and simu- 
 lates some of the reactions of the carbohydrates. 
 A couple of drops of commercial formalin to 25 
 c.c. will preserve a sample for several days. 
 
MILK PRODUCTS 
 
 CREAM 
 
 Cream differs from whole milk principally in 
 the fat-content; the analytic procedures, there- 
 fore, follow those indicated under ' ' Milk, ' ' except 
 that the high fat may render some modifica- 
 tions advisable. It is better, for instance, to 
 weigh rather than measure cream, and it is 
 often advisable to dilute it with a known 
 weight of water. For the determination of fat 
 the Rose- Gottlieb method is much in favor 
 (see page 72). The following are some special 
 procedures. 
 
 Imitation Cream. — By means of special ma- 
 chinery, the fat globules of milk may be broken 
 into very small portions without causing them 
 to coalesce. This is termed ''homogenizing" 
 and will give to poor cream an appearance of 
 richness. It is also possible to incorporate 
 butter with skim-milk, producing an article 
 resembling cream. Of course, unsalted, un- 
 colored butter must be used. As butter made 
 in the usual manner, always contains water, the 
 
 65 
 
66 MILK PRODUCTS 
 
 adulteration may be detected by the change 
 in the refractive power of the serum as described 
 on page 42. H. C. Lythgoe, who has investi- 
 gated this question, finds that samples adulter- 
 ated with butter will give a refraction below 36.0. 
 Results may be confirmed by taking the ash 
 of the sour serum. A large amount of the 
 sample is taken (as the yield of serum is small), 
 soured with a pure culture of lactic acid bacillus, 
 or with a little sour milk, shaken in a bottle 
 until the fat and curd have separated, the serum 
 drawn off and the ash of 25 c.c. taken. It 
 should not be below 0.73%. The homogizing 
 of cream without the addition of fat can be 
 detected by microscopic examination. 
 
 Formic Acid. — ^Revis and Bolton state that 
 glucose containing this may be found in cream 
 and give the following method for its detection. 
 
 100 grams are diluted with an equal weight of 
 water, 20 c.c. of a 20% solution of phosphoric 
 acid added, and 100 c.c. distilled, the end of the 
 condenser dipping below the surface of milk of lime 
 containing at least i gram of calcium hydroxid 
 and 2 c.c. of 3% acetic acid, free from formic. 
 The distillate is evaporated to dryness, sealed 
 in a small tube of hard glass, drawn out at one 
 end that dips into a small U-tube containing 
 2 c.c. of water, arranged so that none of the water 
 can be drawn into the tube, and heated until 
 
CREAM 67 
 
 distillation ceases. The water in the U-tube is 
 mixed with 2 c.c. of Schiff's reagent. If formic 
 acid was present, the mixture will become violet 
 within a half hour. 
 
 SchifE's reagent is obtained by dissolving i 
 gram of rosanilin hydrochlorid in 10 c.c. of 
 water, adding a mixture of 2 c.c. saturated 
 solution of sodium acid sulfite and 0.5 c.c. strong 
 hydrochloric acid, then water to make 100 c.c. 
 The solution keeps for some time in the dark. 
 
 j[gar. — This is now often used as a thicken- 
 ing agent. Although characteristic diatoms are 
 found in it, the detection of the substance by 
 isolation of these has not been practically 
 successful. Revis and Bolton recommend the 
 following method. 
 
 50 grams of the sample are diluted with 100 
 c.c. of water, heated in boiling water and cleared 
 with 5 c.c. of 10% calcium chlorid solution. 
 The mixture is filtered, preferably in a hot-water 
 funnel, cooled and mixed with about two-thirds 
 its volume of strong alcohol. The precipitate 
 (containing any agar that may have been in the 
 sample) is separated, and boiled with 5 c.c. of 
 water until dissolved. If it contains agar, the 
 solution will gelatinize on cooHng. To detect 
 the presence of gelatin in association with agar, 
 the procedure is the same, except that when the 
 precipitate is dissolved, a few c.c. of the solution 
 
68 MILK PRODUCTS 
 
 are treated with picric acid solution. A pre- 
 cipitate indicates gelatin. In this case, the re- 
 mainder of the solution is evaporated to small 
 bulk, and mixed with a io% solution of tannin 
 until no more precipitate is produced. The 
 liquid must in this treatment not have a tem- 
 perature of over 60°. To it a few c.c of white of 
 egg are added and the mixture heated to boiling 
 for thirty minutes, filtered hot, concentrated 
 to small bulk on the water and allowed to cool 
 and gelatinize. 
 
CONDENSED MILK 
 
 Commercial condensed milks present two prin- 
 cipal forms, sweetened and unsweetened. In the 
 latter sucrose is generally used. Often consti- 
 tuting more than half the soUds of the product. 
 Up to recent years, unsweetened condensed milk 
 was largely sold in the United States as ** evapo- 
 rated cream" but this is now forbidden by the 
 federal food law and by many State enactments. 
 Dried milk has also been manufactured but 
 does not seem to have met with much favorable 
 reception. Commercial evaporation of milk is 
 conducted at a low temperature so that less 
 modification of the ingredients is produced than 
 in ordinary boiling, but some modification of the 
 lactose may occur which will make polarimetric 
 readings less accurate than with unheated milk. 
 
 The analysis of unsweetened condensed milk 
 can be conducted along the same lines as those 
 for ordinary milk and cream, the sample being 
 diluted about three times by adding a known 
 volume of water. It must not be forgotten, that 
 lactose may crystalHze from condensed and dried 
 milks, and excessive polarimetric rotation occur in 
 recently made dilutions, unless these are heated 
 to brief boiling and cooled (see page 39). Com- 
 
 69 
 
70 MILK PRODUCTS 
 
 mercial condensed milks usually represent whole 
 milk concentrated to about one-third or two- 
 sevenths of its original volume. A small amount 
 of invert-sugar may be present. The most com- 
 mon defect in condensed milks is deficiency 
 in fat, due to preparation from closely skimmed 
 milks. Preservatives (other than sucrose) and 
 coloring-matters are rarely used, nor is it likely 
 that foreign fats will be present. 
 
 The fat of unsweetened condensed milk can be 
 readily determined by the L-B method (page i8). 
 
 In a recent publication, Bigelow andPitzgerald 
 give the following detailed description of the 
 application of the Leffmann and Beam method 
 to the examination of unsweetened condensed 
 milk: 
 
 Weigh 9 grams of evaporated milk into an 
 8% Babcock milk bottle. Add lo c.c. of water. 
 Thoroughly mix by shaking and add 3 c.c. of a 
 mixture of equal parts of amyl alcohol and con- 
 centrated hydrochloric acid. Shake thoroughly 
 and add 10 c.c. of concentrated sulfuric acid 
 (1.84 sp. gr.) in three or four portions, mixing 
 after each addition. If too much heat develops 
 the bottle may be cooled somewhat in water 
 during the addition of the acid. 
 
 Fill the bottle to near the base of the neck with 
 a hot fresh mixture of equal parts of sulfuric 
 acid and water. Thoroughly mix the contents 
 
CONDENSED MILK 7 1 
 
 of the bottle by shaking. Raise the fat column 
 to the top of the scale by means of the acid and 
 water mixture, and whirl for five minutes. 
 Read promptly (see page 20) from the extreme 
 bottom of the fat column to the bottom of the 
 upper meniscus. Multiply the reading by 2, and 
 deduct 0.25; the remainder is the per cent, of 
 fat. 
 
 If an electric centrifuge without heat has been 
 employed, the fat column will be somewhat cool 
 and should be heated, before reading, in a water- 
 bath about 60°. 
 
 The same authors give the opinion that the 
 centrifugal methods are not sufficiently accurate 
 to be depended upon for determining if evapo- 
 rated milk is up to standard. The Rose-Gottlieb 
 method is best for this purpose. If the centrif- 
 ugal methods are employed, considerable allow- 
 ance must be made for inaccuracies. Results 
 obtained are inaccurate unless the fat column 
 is clear, with the meniscus at the bottom of the 
 column perfect and not distorted by either char 
 or milky appearance. 
 
 The percentage of solids as calculated from 
 the sp. gr. is not sufficiently accurate to 
 determine whether the milk complies with the 
 standard unless the correction factor for the for- 
 mula of calculation is ascertained frequently by 
 the determination of solids by drying. 
 
 6 
 
72 MILK PRODUCTS 
 
 The full analysis of sweetened condensed milk 
 is difficult, and many of the published figures are 
 erroneous. The sucrose interferes with the ex- 
 traction of the fat by solvents. The same 
 difficulty occurs in the analysis of some prepared 
 infant-foods, such as mixtures of milk with malt 
 and glucose. 
 
 For the general operations, a portion of the 
 well-mixed contents of a freshly opened can 
 should be accurately weighed, diluted with a 
 known amount of water, and well mixed, from 
 which mass the portions for analysis may be 
 taken and the results calculated to the original 
 sample. 50 grams mixed with 150 c.c. of water 
 will be a convenient quantity. For the polar- 
 imetric determination of lactose, a special pro- 
 cedure will be necessary ; but for determination of 
 solids, ash, total proteins, and total reducing 
 sugars, the examination may be made as with 
 ordinary milk upon this diluted sample. 
 
 Fat. — The Adams method is not satisfactory 
 under ordinary conditions, owing to the sucrose. 
 The Rose-Gottlieb method is now largely used 
 and generally approved. The following descrip- 
 tion is given by Bigelow and Fitzgerald : 
 
 Weigh from 4.5 to 5.0 grams evaporated or 
 condensed milk into a Rose-Gottlieb tube, add 
 water to make about 11 grams and i3^ to i3^ 
 
CONDENSED MILK 73 
 
 c.c. concentrated ammonium hydroxid, and thor- 
 oughly mix by shaking. 
 
 Add lo c.c. 95 % alcohol and shake thoroughly. 
 Fill up to the level of the side tube with water, if 
 necessary, and shake. Add 25 c.c. ether and 
 shake well for one minute. Add 2 5 c.c. petroleum 
 spirit (b. p. below 65°) and shake well for one 
 minute. 
 
 Allow tube to stand until layers separate 
 well. Draw off ether-fat solution as completely 
 as practicable and run it through a small quick- 
 acting filter into a weighted flask (weighted by 
 counterpoising, if the test is not finished the day 
 it is started.) 
 
 Re-extract the liquid in tube as before with 
 15 c.c. of each of petroleum spirit and ether, 
 shaking after each is added. Before the addition 
 a little alcohol may be added and the contents 
 of the tube mixed by shaking, to bring the layer 
 of ammoniacal liquid close up to the outlet tube, 
 for by repeated extractions the surface of sepa- 
 ration is lowered. 
 
 Run the solution from the second extraction 
 through the filter into the flask, and wash end of 
 spigot, filter paper, and lower surface of the 
 funnel with ether; or, better, with a mixture of 
 equal parts of ether and petroleum spirit which 
 has been allowed to stand for separation of 
 water. 
 
74 MILK PRODUCTS 
 
 In the examination of cream a third extraction 
 is necessary, but with evaporated and condensed 
 milk the third extraction does not recover more 
 than 0.02 or 0.03 % of fat, and may be omitted. 
 
 Evaporate the liquid slowly on a steam bath 
 and dry the fat in steam oven until its weight is 
 constant . Weigh after one hour and then at half - 
 hour intervals. As soon as the fat begins to gain 
 in weight stop drying and take the next previous 
 weight. Increase of weight is due to oxidation 
 after all moisture and alcohol are gone. In all 
 cases the drying should be completed the day it 
 is begun. 
 
 Double Extraction. — The following is given as a 
 provisional A. O. A. C. m.ethod: Extract with 
 ether, as usual, about 5 grams of a 40% solution, 
 dry, leave the tubes in a dish containing at least 
 500 c.c. of water, dry, extract again with ether for 
 four hours. 
 
 Sugars. — If regard is to be given to the 
 presence of invert-sugar, a special method must 
 be followed. The processes first given consider 
 lactose and sucrose only. The heating employed 
 in the manufacture of condensed milk may 
 reduce the rotatory power of lactose sufficiently 
 to cause error in the polarimetric method. The 
 reducing power with alkaline copper solutions 
 is not seriously affected. 
 
 Determination of sucrose may be made by 
 
CONDENSED MILK 75 
 
 difference; that is, subtracting the sum of the 
 other ingredients from the total soHds. This will 
 serve for ordinary inspection purposes, since 
 the amount present is almost always large, gener- 
 ally more than the total of milk-solids, and a 
 slight error does not affect the judgment as to 
 the wholesomeness of the sample. Exact work 
 requires, however, that the sucrose be de- 
 termined directly. Several processes have been 
 devised for the purpose. Sucrose exerts but 
 little action on Fehling's solution, but invert- 
 sugar acts powerfully, and some processes depend 
 on determining the reducing power before and 
 after inversion. Since the polarimetric reading is 
 also markedly changed by the inversion, the 
 difference in polarization may be employed. 
 Fermentation may be so conducted as to re- 
 move the sucrose (also any form of glucose) while 
 the lactose is unaffected. This method is chiefly 
 valuable for recognizing invert-sugar or either of 
 its constituents. 
 
 Inversion Methods. — These must be such as to 
 secure prompt inversion of the sucrose without 
 affecting the lactose. Experiment shows that 
 citric acid and invertase are the most suitable 
 agents. Stokes & Bodmer have worked out the 
 citric acid method substantially as follows: 
 
 25 c.c. of the diluted sample are coagulated by 
 addition of i% of citric acid, without heating, 
 
76 MILK PRODUCTS 
 
 and made up to 200 c.c. plus the volume of the 
 precipitated fat and proteins (see page 38). The 
 liquid portion, which now measures 200 c.c, is 
 passed through a dry filter. The reducing power 
 with alkaline copper solutions is determined at 
 once upon 50 c.c. of this filtrate. To another 
 50 c.c, 1% of citric acid is added, the solution 
 boiled at least thirty minutes, and the reducing 
 power also determined. The increase over that 
 of the first solution is due to the invert-sugar 
 formed by the action of the citric acid on the 
 sucrose. It is necessary to bear in mind that the 
 reducing equivalents of lactose and invert-sugar 
 are not the same. Volumetric methods may be 
 employed. 
 
 The following method is based on the difference 
 in polarimetric reading before and after action of 
 invertase. 75 cc of the diluted milk are placed 
 in a loo-cc flask, diluted to about 80 c.c, 
 heated to boiling, to correct birotation, cooled, 
 and 10 c.c. of acid mercuric nitrate solution 
 (page 37) added. The mixture is made up to 100 
 cc, well shaken, filtered through a dry filter, and 
 the polarimetric reading taken at once. It will 
 be the sum of the effect of the two sugars. The 
 volume of the sugar-containing liquid is calcu- 
 lated by allowing for the precipitated proteins 
 and fat, as described on page 38. 
 
 50 c.c. of the filtrate are placed in a flask 
 
CONDENSED MILK 77 
 
 marked at 55 c.c, a piece of litmus paper dropped 
 in, and the excess of nitric acid cautiously neu- 
 tralized by sodium hydroxid solution. The 
 liquid is then faintly acidified by a single drop of 
 acetic acid (it must not be alkaline), a few drops 
 of an alcoholic solution of thymol are added, 
 and then 2 c.c. of a solution of invertase, prepared 
 by grinding half a cake of ordinary compressed 
 yeast with 10 c.c. of water and filtering. The 
 flask is corked and allowed to remain at a tem- 
 perature of 3 5° to 40° for twenty -four hours. The 
 cane-sugar will be inverted, while the milk-sugar 
 will be unaffected. The flask is fllled to the mark 
 (55 c.c.) with washed aluminum hydroxid and 
 water, mixed, filtered, and the polarimetric 
 reading taken. The amount of cane-sugar can 
 be determined from the difference in the two 
 readings by the formula 
 
 ^^ _ 100 a -\- b 
 
 t 
 
 142.08 
 
 2 
 
 in which 5 is the percentage of sucrose; a, the 
 reading before, b, after inversion; t, the 
 temperature. 
 
 Lactose, Sucrose and Invert-sugar. — Bige- 
 low and McElroy propose the following routine 
 method to include invert-sugar. The reagents 
 are: 
 
78 MILK PRODUCTS 
 
 Acid Mercuric lodid, — Mercuric chlorid, 1.35 
 grams; potassium iodid, 3.32 grams; glacial acetic 
 acid, 2 c.c. ; water, 64 c.c. 
 
 Alumina- ere am. — A cold saturated solution of 
 alum is divided into two unequal portions, a 
 slight excess of ammonium hydroxid is added 
 to the larger portion and the remainder added 
 until a faintly acid reaction to litmus is obtained. 
 
 The entire contents of the can are transferred 
 to a porcelain dish and thoroughly mixed. A 
 number of portions of about 25 grams are 
 weighed carefully in 100 c.c. flasks. Water is 
 added to two of the portions, and the solutions 
 boiled. The flasks are then cooled, clarified by 
 means of a small amount of the acid mercuric 
 iodid and alumina cream, made up to mark, 
 filtered, and the polarimetric reading noted. 
 Other portions of the milk are heated in the 
 water-bath to 55°; one-half of a cake of com- 
 pressed yeast is added to each flask and the 
 temperature maintained at 55° for five hours. 
 Acid mercuric iodid and alumina-cream are 
 then added, the solution cooled to room tem- 
 perature, made up to mark, mixed, filtered, and 
 polarized. The amount of sucrose is determined 
 by formula given above. Correction for the 
 volume of precipitated solids may be made by the 
 double-dilution method. The total reducing 
 sugar is estimated in one of the portions by one of 
 
CONDENSED MILK 79 
 
 the reducing methods, and if the sum of it and 
 the amount of sucrose obtained by inversion is 
 equal to that obtained by the direct reading of 
 both sugars before inversion, no invert-sugar is 
 present. If the amount of reducing sugar seems 
 to be too great, the lactose must be re-determined 
 as follows: 250 grams of the condensed milk are 
 dissolved in water, the solution boiled, cooled to 
 80°, a solution of about 4 grams of glacial phos- 
 phoric acid added, the mixture kept at 80° for 
 a few minutes, then cooled to room temperature, 
 made up to mark, shaken, and filtered. It may 
 be assumed that the volume of the precipitate 
 is equal to that obtained by mercuric iodid solu- 
 tion. Enough sodium hydroxid is then added to 
 not quite neutralize the free acid, and sufficient 
 water to make up for the volume of the solids 
 precipitated by the phosphoric acid. The mixture 
 is then filtered and the filtrate is measured in 
 portions of 100 c.c. into 200-c.c. flasks. A 
 solution containing 20 milligrams of potassium 
 fluorid and half a cake of compressed yeast is 
 added to each flask, and the mixture allowed to 
 stand for ten days at a temperature between 25° 
 and 30°. Invert-sugar and sucrose are fermented 
 and removed by the yeast in the presence of a 
 fluorid ; lactose is unaffected. The flasks are filled 
 to the mark and the lactose determined either 
 by reducing or by the polariscope. The amount 
 
8o MILK PRODUCTS 
 
 of copper solution reduced by the lactose and 
 invert-sugar, less the equivalent of lactose re- 
 maining after fermentation, is due to invert- 
 sugar. 
 
BUTTER 
 
 Butter is a mixture of fat, water, and curd. 
 The water contains lactose and the salts of the 
 milk. Common salt is usually present, being 
 added after the churning. Artificial coloring 
 is frequently used. 
 
 Butter-fat is distinguished from other animal 
 fats in that it contains a notable proportion of 
 acid radicles with a small number of carbon atoms. 
 Thus, about 91% consists of palmitin and olein 
 and the remainder of butyrin and caproin, along 
 with small amounts of caprylin, caprin, myristin, 
 and some others. According to the experiments 
 of Hehner & Mitchell, stearin is present only in 
 very small quantity. The exact arrangement of 
 the constituents is unknown. 
 
 The composition of good commercial butter 
 usually ranges within the following limits: 
 
 Fat 78% to 94% 
 
 Curd i%to 3% 
 
 Water 5% to 14% 
 
 Salt 0% to 7% 
 
 Butter containing over 40% of water is some- 
 times sold. Such samples are pale and spongy, 
 lose weight, and become rancid rapidly. 
 
 81 
 
82 MILK PRODUCTS 
 
 The official methods of the A.O.A.C. for the 
 analysis of butter are as follows: 
 
 Preparation of the Sample. — If large quantities 
 of butter are to be sampled, a butter trier or 
 sampler may be used. The portions thus drawn, 
 about 500 grams, are to be perfectly melted in a 
 closed vessel at as low a temperature as possible, 
 and when melted the whole is to be shaken vio- 
 lently for some minutes until the mass is homo- 
 geneous and sufficiently solidified to prevent 
 the separation of the water and fat. A portion 
 is then poured into the vessel from which it is 
 to be weighed for analysis, and should nearly or 
 quite fill it. This sample should be kept in a 
 cold place until analyzed. 
 
 Water. — From 1.5 to 2.5 grams are dried to 
 constant weight at the temperature of boiling 
 water, in a dish with flat bottom, having a surface 
 of at least 20 sq. cm. The use of clean dry sand 
 or asbestos with the butter is admissible, and 
 is necessary if a dish with round bottom be 
 employed. 
 
 Fat. — The dry butter from the water deter- 
 mination is dissolved in the dish with absolute 
 ether. The contents of the dish are then trans- 
 ferred to a weighed Gooch crucible with the aid 
 of a wash-bottle filled with the solvent, and are 
 washed until free from fat. The crucible and 
 
BUTTER 83 
 
 contents are heated at the temperature of boiling 
 water till the weight is constant. 
 
 The fat may also be determined by drying the 
 butter on asbestos or sand, and extracting by 
 anhydrous alcohol-free ether. After evaporation 
 of the ether the extract is heated to constant 
 weight at the temperature of boihng water and 
 weighed. 
 
 Casein, Ash, Chlorin. — The crucible con- 
 taining the residue from the fat determination is 
 covered and heated, gently at first, gradually 
 raising the temperature to just below redness. 
 The cover is removed and the heat continued until 
 the material is white. The loss in weight rep- 
 resents casein, and the residue mineral matter. 
 In this mineral matter dissolved in water slightly 
 acidulated with nitric acid, chlorin may be 
 determined gravimetrically with silver nitrate, 
 or, after neutralization with calcium carbonate, 
 volumetrically, using potassium chromate as 
 indicator. 
 
 Salt. — About 10 grams are weighed in a beaker 
 in portions of about i gram at a time taken from 
 different parts of the sample. Hot water (about 
 20 c.c.) is now added to the beaker, and after 
 the butter has melted, the mass is poured into 
 the bulb of a separating funnel, which is then 
 closed and shaken for a few moments. After 
 standing until the fat has all collected, the water 
 
84 MILK PRODUCTS 
 
 is allowed to run into an Erlenmeyer flask, with 
 care not to let fat globules pass. Hot water is 
 again added to the beaker, and the extraction 
 is repeated from ten to fifteen times, using each 
 time from lo to 20 c.c. of water. The resulting 
 washings contain all but a mere trace of the salt 
 originally present in the butter. The chlorin is 
 determined volumetrically in the filtrate by 
 means of standard silver nitrate and potassium 
 chromate indicator and calculated to sodium 
 chlorid. 
 
 Butter -substitutes. — The chief adulteration of 
 butter consists in the substitution of foreign fats, 
 especially the product known as oleomargarin. 
 
 When fats are saponified and the soap treated 
 with acid, the individual fatty acids are obtained. 
 It is upon the recognition of the peculiar acid 
 radicles existing in butter that the most satis- 
 factory method of distinguishing it from other 
 fats is based. Since the relative proportion of 
 these radicles differs in different samples, the 
 quantitative estimation cannot be made with 
 accuracy; but when the foreign fats are substi- 
 tuted to the extent of 20% or more, the adultera- 
 tion an be detected with certainty and an 
 approximate quantitative determination made. 
 
 The detection of adulteration of butter-fat by 
 other fats is generally carried out by the deter- 
 
BUTTER 85 
 
 mination of the volatile acid, but some other 
 confirmatory processes are occasionally employed. 
 
 Qualitative Tests. — Two tests are convenient 
 for preliminary examinations, especially for sort- 
 ing out, when many samples are to be tested. 
 The experience of Dr. William Beam and myself 
 in testing many hundred samples for the Dairy 
 and Food Commissioner of Pennsylvania showed 
 that the methods are satisfactory and useful. 
 
 Heating test. — When butter is heated in a 
 small tin dish directly over a gas flame, it melts 
 quietly, foams, and may run over the dish. 
 Oleomargarin, under the same conditions, sput- 
 ters noisily as soon as heated and foams but little. 
 Even mixtures of butter and other fats show this 
 sputtering action to a considerable extent. The 
 test is not applicable to butter which has been 
 melted and reworked (renovated or process 
 butter) . 
 
 Saponification test, — An alcoholic solution of 
 sodium hydroxid, boiled up with butter, and then 
 emptied into cold water, gives a distinct odor of 
 pineapples, while oleomargarin gives only the 
 alcoholic odor. 
 
 Quantitative Methods. Volatile Acids. — 
 This method, suggested by Hehner & Angell, 
 systematized by Reichert, is generally called the 
 Reichert process. In this form it is carried 
 out by saponifying 2.5 grams of the fat, adding 
 
86 MILK PRODUCTS 
 
 excess of sulfuric acid, distilling a definite portion 
 of the liquid, and titrating the distillate with 
 ^/lo alkali. The number of c.c. of this solution 
 required to overcome the acidity of the distillate 
 is called the Reichert number. E. Meissl sug- 
 gested the use of 5 grams, and the number so 
 obtained is called the Reichert-Meissl number. 
 Alcoholic solution of potassium hydroxid was 
 originally used for saponification, but the solu- 
 tion devised by Leffmann & Beam, namely, 
 sodium hydroxid in glycerol, is more satisfactory. 
 This procedure is now official in the U. S. and 
 several European countries. The reagents and 
 operation are as follows : 
 
 Glycerol-soda. — 100 grams of good sodium 
 hydroxid are dissolved in 100 c.c. of distilled 
 water and allowed to stand until clear. 20 c.c 
 of this solution are mixed with 180 c.c. of pure 
 concentrated glycerol. The mixture can be con- 
 veniently kept in a capped bottle holding a 10- 
 c.c. pipet, with a wide outlet. 
 
 Sulfuric Acid. — 20 c.c. of pure concentrated 
 sulfuric acid, made up with distilled water to 
 100 c.c. 
 
 Sodium Hydroxid. — An approximately ^/lo, 
 accurately standardized, solution of sodium 
 hydroxid. 
 
 Indicator. — Solution of phenolphthalein. 
 
 A 300-c.c. flask is washed thoroughly, rinsed 
 
BUTTER 87 
 
 with alcohol and then with ether, and thoroughly- 
 dried by heating in the water-oven. After 
 cooling, it is allowed to stand for about fifteen 
 minutes and ' weighed. (In ordinary operation 
 this preparation of the flask may be omitted.) 
 A pipet, graduated to 5.75 c.c, is heated to about 
 60° and filled to the mark with the well-mixed 
 fat, which is then run into the- flask. After 
 standing for about fifteen minutes the flask and 
 contents are weighed. 20 c.c. of the glycerol- 
 soda are added and the flask heated over the 
 Bunsen burner. The mixture may foam some- 
 what; this may be controlled, and the operation 
 hastened by shaking the flask. When all the 
 water has been driven off, the liquid will cease 
 to boil, and if the heat and agitation be continued 
 for a few moments, complete saponification will 
 be effected, the mass becoming clear. The whole 
 operation, exclusive of weighing the fat, requires 
 about five minutes. The flask is withdrawn from 
 the heat and the soap dissolved in 135 c.c. of water. 
 The first portions of water should be added drop 
 by drop, and the flask shaken between each 
 addition in order to avoid foaming. When the 
 soap is dissolved, 5 c.c. of the dilute sulfuric acid 
 are added, a piece of pumice dropped in (this 
 must not be omitted), and the liquid distilled 
 until no c.c. have been collected. The con- 
 densing tube should be of glass, and the distilla- 
 7 
 
88 
 
 MILK PRODUCTS 
 
 tion conducted at such a rate that the above 
 amount of distillate is collected in thirty minutes. 
 The distillate is usually clear; if not, it should 
 be thoroughly mixed, filtered through a dry 
 filter, and loo c.c. of the filtrate taken. A little 
 of the indicator is added to the distillate, and the 
 standard alkali run in from a buret until neutrali- 
 
 FiG. 3. 
 
 zation is attained. If only 100 c.c. of the dis- 
 tillate have been used for the titration, the c.c. 
 of alkaU used should be increased by one-tenth. 
 The distilling apparatus shown in figure 3 is 
 that recommended by the A. O. A. C. (and since 
 adopted in Great Britain), and the directions for 
 
BUTTER 89 
 
 preparing the flask are also from the same 
 source. 
 
 When it is intended merely to distinguish 
 butter from oleomargarin, it will be sufficient to 
 saponify 3 c.c. of the clarified fat, dilute, acidify, 
 distil 100 c.c. in the ordinary manner and titrate 
 as directed. "Straight oleos," that is, samples 
 containing inappreciable amounts of butter, will 
 give a distillate requiring only a few c.c. of alkali. 
 
 Butter (5 grams) yields a distillate requiring 
 from 24 to 34c. c. of ^/lo alkali. Several instances 
 have been published in which genuine butter has 
 given a figure as low as 22.5 c.c, but such results 
 are uncommon. The materials employed in 
 the preparation of oleomargarin yield a distillate 
 requiring less than i c.c. of alkali. Commercial 
 oleomargarin is usually churned with milk in 
 order to secure a butter flavor, and, thus acquiring 
 a small amount of butter-fat, yields distillates 
 capable of neutralizing from i to 2 c.c. of alkali. 
 
 If coconut oil has been used in the preparation 
 of the oleomargarin, the figure will be higher, but 
 there will still be no difficulty in distinguishing 
 pure butter. 
 
 The determination of the Reichert number will 
 usually give sufficient information as to the 
 nature of a butter sample. In doubtful cases it 
 may be of advantage to apply other tests as 
 corroborative evidence. 
 
go MILK PRODUCTS 
 
 Index of Refraction. — This datum differs nota- 
 bly in different oils, but it is not of much value 
 in detecting adulteration unless considerable of 
 the adulterant be present. Several instruments 
 have been devised for making refraction de- 
 termination; a familiar one is the butyrorefrac- 
 tometer of Zeiss. 
 
 The butyrorefractometer has been strongly 
 recommended for the examination of butter. 
 It is equally adapted for the general examination 
 of fats and oils, and may be used for the de- 
 termination of the index of refraction as well. 
 As these instruments are made by only one firm 
 and are furnished with directions for use, further 
 description will not be required. 
 
 Renovated Butter. — So-called ''process" or 
 "renovated" butter, made by melting old or in- 
 ferior samples, purifying the fat, coloring and 
 salting, is now a familiar article. When heated in 
 a dish such butter sputters, with but little foam- 
 ing as does oleomargarin, but yields with alcoholic 
 solution of sodium hydroxid the pineapple odor. 
 The fat or process butter gives refractometric 
 data and Reichert-Meissl data similar to ordinary 
 butter. Hess and Doolittle state that the curd 
 of process butter has characteristic qualities, and 
 propose the following method for detecting it. 
 
 50 grams of the sample are melted in a beaker 
 at about 50°. Ordinary butter yields a clear 
 
BUTTER 91 
 
 fat almost as soon as melted, while with process 
 butter the fat may remain turbid for a long while. 
 When the curd has largely 1 settled, as much of the 
 fat is poured off as possible, and the remaining 
 mixture is thrown on a wet filter, by which the 
 water will drain away, carrying the soluble 
 proteins and salt. A few drops of acetic acid 
 are added to the filtrate and the mixture is 
 boiled. The filtrate from ordinary butter gives 
 a slight milkiness, but that from process butter 
 gives a flocculent precipitate. Quantitative ex- 
 amination is made by dissolving 50 grams of the 
 sample in ether; if it is ordinary butter, the curd 
 is so finely divided that it remains suspended for 
 some time. As much as possible of the solution 
 is decanted and the mass transferred to a sepa- 
 rator, the casein, water, and salt removed, and the 
 remainder washed three times, at least, with 
 ether to remove the fat. The curd is collected 
 on a filter, washed with water, and the nitrogen 
 determined by treating the precipitate with the 
 filter by the Kjeldahl-Gunning method. The 
 filtrate from the curd is made sHghtly acid with 
 acetic acid, boiled, the precipitated proteins 
 collected on a filter, and the total nitrogen de- 
 termined. The factor 6.38 may be used in each 
 case for converting the nitrogen into proteins. 
 
 A distinction between ordinary and process 
 butter may often be made by microscopic ex- 
 
92 MILK PRODUCTS 
 
 amination under polarized light with crossed 
 nicols (i. e., dark field), when the process buttet 
 appears mottled, owing to the presence of 
 crystals. 
 
 Butter Colors. — Butter and butter-substitutes 
 are usually artificially colored. Turmeric and 
 annatto or azo-colors allied to methyl-orange are 
 used. 
 
 Azo-colors. — These may be detected by the 
 test devised b}^ Geisler. A small amount of the 
 sample, or, better, the fat filtered from it, is mixed 
 on a porcelain plate with a little fullers' earth. 
 Azo-colors give promptly a red mass; if they are 
 not present, the mixture becomes only yellow or 
 light brown. All samples of fullers' earth are 
 not equally active, and tests should be made with 
 different samples by using fat known to contain 
 the azo-compound until a good specimen of the 
 earth is secured. 
 
 For the detection of very minute quantities of 
 the color, the sample may be dissolved in light 
 petroleum, and the fullers' earth added to the 
 solution, when the pink color will appear as a 
 distinct ring or zone at the edge of the deposited 
 layer of the reagent. 
 
 Low has proposed the following test for the 
 yellow azo-color: A few c.c. of the filtered 
 fat are mixed in a large test-tube with an 
 equal volume of a mixture of one part strong 
 
BUTTER 93 
 
 sulfuric acid and four parts glacial acetic acid. 
 The contents of the tube are then heated almost 
 to boiling and thoroughly mixed by violently 
 agitating the bottom of the tube. When now 
 allowed to stand and separate, the lower layer of 
 mixed acids will be strongly colored wine-red if 
 the azo-color be present. Pure butter-fat im- 
 parts no color to the acids, or, at most, only a faint 
 brownish tinge. 
 
 Turmeric and Annatto. — Martin's test will 
 usually be satisfactory: 2 c.c. carbon disulfid 
 are mixed with 15 c.c. of alcohol, by adding small 
 portions of the disulfid to the acohol and shaking 
 gently; 5 grams of the butter-fat are added to 
 this mixture in a test-tube and shaken. The 
 disulfid falls to the bottom of the tube, carrying 
 with it the fatty matter, while any artificial 
 coloring-matter remains in the alcohol. The 
 separation takes place in from one to three 
 minutes. If the amount of the coloring-matter 
 is small, more of the fat may be used. If the 
 alcoholic solution be evaporated to dryness and 
 the residue treated with concentrated sulfuric 
 acid, annatto will be indicated by the production 
 of a greenish-blue color. With many samples 
 of oleomargarin, a pink tint will be produced, 
 which indicates an azo-color. 
 
 Palm oil has been used as a coloring agent in 
 butter-substitutes. Crampton & Simons have 
 
94 MILK PRODUCTS 
 
 found that two tests devised for detection of 
 rosin-oil can be satisfactorily adapted to detec- 
 tion of palm oil. Success depends on several 
 points. The sample must be kept in a cool 
 dark place until used, filtered at a temperature 
 not above 70°; the heating as brief as possible, 
 and promptly tested. The reagents must be 
 pure and colorless. Cochran finds that annatto 
 will simulate palm oil in these tests, and hence 
 the absence of the former must be assured 
 (see above) before inferring the presence of the 
 latter. 
 
 Halphen method. — 100 c.c. of the filtered fat 
 are dissolved in 300 c.c. petroleum spirit and 
 shaken out with 50 c.c. of potassium hydroxid 
 solution (o. 5 % of hydroxid) . The water is drawn 
 off, made distinctly acid with hydrochloric acid, 
 and shaken out with 10 c.c. of carbon tetrachlorid. 
 This solution is drawn off, and part of it tested 
 by adding to it 2 c.c. of a mixture of i part crys- 
 tallized phenol in 2 parts carbon tetrachlorid. To 
 this add 5 drops of hydrobromic acid (sp. gr. 1.19). 
 The test is best performed in a porcelain basin and 
 the contents mixed by agitating gently. Palm oil 
 gives almost immediately a bluish-green liquid. 
 
 Liebermann-Storch method. — 10 c.c. of the 
 filtered fat are shaken with an equal volume of 
 acetic anhydrid, one drop of sulfuric acid (sp. 
 gr. 1.53) is added and the mixture shaken for 
 
BUTTER 95 
 
 a few seconds. If palm oil be present, the heavier 
 layer separating will be blue with a tint of green. 
 
 Egg-yolk has been proposed as a color for 
 oleomargarin, and although its use is unlikely, 
 the possibility of it should be borne in mind. 
 To detect it, about lo grams of the filtered fat 
 should be shaken with warm alcohol, the liquid 
 drawn off as closely as possible and evaporated 
 to dryness. The coloring matter of egg-yolk 
 is soluble in alcohol, but insoluble in water. It 
 may be distinguished from turmeric by moisten- 
 ing it with a few drops of a mixture of boric and 
 hydrochloric acids, and drying at a gentle heat. 
 Turmeric becomes brown ; egg-color is not affected. 
 Egg-yolk contains considerable lecithin, a phos- 
 phoric acid derivative. Pure fats contain no 
 phosphorus compound. If, therefore, a few 
 grams of the fat, carefully freed from water or 
 curd, are charred and the mass extracted by 
 boiling with nitric acid, the filtered solution 
 should not give an appreciable precipitate with 
 ammonium molybdate. 
 
 Vegetable colors may be detected by boiling 
 up the filtered fat with water, drawing off the 
 watery liquid, adding a few drops of hydrochloric 
 acid and heating the mixture with a piece of clean, 
 undyed wool. True butter colors will not dye 
 wool under these circumstances. 
 
 Caramel may be detected by shaking the 
 
g6 MILK PRODUCTS 
 
 watery solution with fuller's earth and filter- 
 ing. The filtrate is notably paler if caramel is 
 present. Fuller's earth differs in efficiency, and 
 each sample should be tested on known solutions. 
 
 Preservatives. — The preservatives used in milk 
 may be found in limited amount in butter, but a 
 mixture of boric acid and borax is often added as 
 a substitute for salt. 
 
 Glucose is sometimes used as a preservative, 
 especially in butter intended for export to tropical 
 countries. Crampton found as much as io% 
 in a sample of highly colored butter intended 
 for exportation to Guadeloupe. For the de- 
 tection of glucose the phenylhydrazin test might 
 be used. For determination Crampton used the 
 following method: lo grams of the sample were 
 washed with successive portions of convenient 
 bulk, the solution made up to 250 c.c, and an 
 aliquot portion determined, as given for lactose 
 on page 32. The solution may also be clarified 
 by alumina-cream or acid mercuric nitrate and 
 examined in the polarimeter. 
 
 Boric Acid. — 25 grams of the sample are melted, 
 the watery portion separated and tested as de- 
 scribed on page 62. 
 
Cheese is the curd of milk which has been 
 separated from it, pressed, and undergone some 
 fermentation. The precipitation is produced 
 either by allowing the milk to become sour 
 — when the lactic acid is the agent — or by rennet. 
 The first-named method is mainly applied to the 
 manufacture of so-called Dutch or sour-milk 
 cheese, green Swiss cheese, and cottage cheese. 
 More commonly cheese is obtained by means of 
 rennet derived from the fourth stomach of the 
 calf. The action is due to an enzym which 
 acts directly on the proteins and does not pro- 
 duce its affect through the intervention of acids. 
 The curd (cheese) undergoes, by keeping, various 
 decompositions, some essentially putrefactive, 
 and due to the action of microbes. The de- 
 composition of the cheese is termed "ripening." 
 
 In the sour milk cheeses, ripening is restricted 
 intentionally, since there is liability to an irregular 
 and miscellaneous bacterial growth by which the 
 fermentations may be carried too far, undesirable 
 and even harmful products being formed. Such 
 cheeses are intended for prompt use. 
 
 Cheese contains no casein, if by this term 
 
 97 
 
98 MILK PRODUCTS 
 
 is meant the protein as it exists in milk, or as 
 precipitated from milk by acids. When milk 
 is coagulated by rennet, only a part of the 
 proteins enter into the curd; true casein contains 
 about 15.7% of nitrogen, but the protein matter 
 of cheese contains about 14.3%. Under the 
 process of ripening this is further decomposed, 
 amino- and ammonium compounds, peptones 
 and albumoses being formed. 
 
 The following figures, obtained by Van Slyke, 
 will serve to give some idea of the extent to which 
 the curd is changed in ripening. The figures 
 represent average percentage on the total nitrogen. 
 The cheese was an American cheddar: 
 
 Green After Five 
 
 Cheese Months 
 
 Soluble nitrogen compounds ... 4.23 35-52 
 
 Soluble amino compounds none 11 .66 
 
 Soluble ammonium compounds none 2.92 
 
 Van Slyke 's experiments seem also to indicate 
 that the cheese ripened more rapidly when the 
 curd was precipitated by a larger quantity of 
 rennet and, especially, that cheese rich in fat 
 ripened more rapidly than skim-milk cheese. 
 
 In addition to the fat and nitrogenous com- 
 pounds just mentioned, cheese may contain a 
 small amount of lactose and of lactic and other 
 organic acids. There is present also a certain 
 proportion of mineral matter, alkaline and earthy 
 
CHEESE 99 
 
 phosphates, along with any salt that has been 
 added. Traces of nitrates have been found. 
 
 Skimmed milk is not infrequently used for the 
 production of cheese. Partially-skimmed milk is 
 used in the preparation of certain Dutch cheeses. 
 Foreign fats, such as are used in the manufacture 
 of oleomargarin, are sometimes incorporated, the 
 article being known as "filled cheese." 
 
 The common American cheese is known as 
 Cheddar. According to Van Slyke, this has, 
 when ripe, the following average composition: 
 
 Water 3 1 • 50% 
 
 Fat 37-oo% 
 
 Proteins 26.25% 
 
 Ash, sugar, etc 5 • 25 % 
 
 The ash of cheese consists largely of calcium 
 phosphate and salt. Mariani & Tasselli de- 
 termined the total ash, chlorin, calcium, and 
 phosphoric acid in 15 samples of cheese. The 
 amounts of salts (calculated from the chlorin) 
 depend on the mode of salting. The proportion 
 of phosphoric oxid was always greater than that 
 necessary to form tricalcium phosphate, ranging 
 from 1.07 and 1.08 equivalents of phosphoric 
 anhydrid to calcium oxid in cheese made from 
 sour milk to 1.56 to i in Gorgonzola, 1.67 to i 
 in skim-milk cheese, and 1.75 to i in Edam cheese. 
 The largest quantities of calcium and phosphoric 
 oxid were found in sheep 's-milk cheese and in 
 
lOO MILK PRODUCTS 
 
 cheese made from sour milk, whence it follows 
 that acidity does not prevent the precipitation of 
 calcium phosphate in the curds. The excess of 
 phosphoric oxid obtained was attributed to acid 
 phosphates. 
 
 The salt in cheese usually ranges between i and 
 
 4%. 
 
 Analytic Methods. — ^The analytic points usu- 
 ally determined in regard to cheese are water, fat, 
 casein, ash, the presence of fats other than 
 butter-fat, and coloring-matters. 
 
 In addition to this, especially in comparing the 
 qualities of genuine cheeses, the proportion of 
 proteic, aminic, and ammoniacal nitrogen is of 
 value. 
 
 Care should be taken to select for analysis a 
 sample which represents the average composition 
 of the entire cheese. 
 
 The following methods for the determination 
 of water, fat, ash, total nitrogen, and acidity 
 have been adopted by the A. O. A. C. : 
 
 Sampling. — When the cheese can be cut, a 
 narrow wedge-shaped segment, reaching from 
 the outer edge to the center of the cheese, is 
 taken. This is to be cut into strips and passed 
 through a sausage-grinding machine three times. 
 When the cheese cannot be cut, samples are taken 
 by a cheese trier. If only one plug can be 
 obtained, this should be perpendicular to the 
 
CHEESE lOI 
 
 surface, at a point one-third of the distance from 
 the edge to the center of the cheese. The plug 
 should reach entirely through, or only half-way 
 through, the cheese. When possible, draw three 
 plugs — one from the center, one from a point 
 near the outer edge, and one from a point half- 
 way between the other two. For inspection 
 purposes, the rind may be rejected; but for 
 investigations requiring the absolute amount of 
 fat in the cheese, the rind is included in the 
 sample. It is preferable to grind the plugs in a 
 sausage machine, but when this is not done, 
 they should be cut very fine and carefully 
 mixed. 
 
 Water. — Between 2 and 5 grams of the sample 
 should be placed in a weighed platinum or 
 porcelain dish which contains a small amount of 
 material, such as freshly ignited asbestos or sand, 
 to absorb the fat that may run out. This is then 
 heated in a water-oven for ten hours and weighed ; 
 the loss in weight is considered as water. If 
 preferred, the dish may be placed in a desiccator 
 over concentrated sulfuric acid and dried to con- 
 stant weight, but this may require many days. 
 The acid should be renewed when the cheese 
 has become nearly dry. 
 
 Fat, — The extraction-tube described on page 16 
 is prepared as follows : The perforations in the 
 bottom of the tube are covered with asbestos, 
 
I02 MILK PRODUCTS 
 
 on which is placed a mixture containing equal 
 parts of anhydrous copper sulfate and pure dry 
 sand to the depth of about 5 cm., packed loosely, 
 and the upper surface covered with a film of 
 asbestos. On this are placed from 2 to 5 grams 
 of the sample, the mass extracted for five hours 
 with anhydrous ether, then removed and ground 
 to fine powder with pure sand in a mortar. The 
 mixture is replaced in the extraction tube, the 
 mortar washed free from all matters with ether, 
 the washings being added to the tube, and the 
 extraction is continued for ten hours. The fat so 
 obtained is dried at 100° to constant weight. 
 
 Here, as in most extractions, carbon tetra- 
 chlorid can be substituted for ether, but the 
 results obtained are not necessarily equivalent, 
 and in official analyses the official method must 
 be used. 
 
 Total Nitrogen. — This is determined by the 
 Kjeldahl-Gunning method, using 2 grams of the 
 sample. The percentage, multiplied by 6.38, 
 gives the nitrogen compounds. 
 
 Ash. — The dry residue from the water de- 
 termination may be taken for the ash. If the 
 cheese is rich, the asbestos will be saturated there- 
 with. This mass may be ignited carefully, and 
 the fat allowed to burn off, the asbestos acting as 
 a wick. No extra heating should be applied 
 during the operation, as there is danger of spurt- 
 
CHEESE 103 
 
 ing. When the flame has died out, the burning 
 may be completed in a muffle at low redness. 
 When desired, the salt may be determined in 
 the ash by titration with silver nitrate and potas- 
 sium chromate. 
 
 Provisional Method for the Determination of the 
 Acidity on Cheese. — Water at a temperature of 
 40° is added to 10 grams of finely divided cheese 
 until the volume equals 105 c.c, agitated 
 vigorously, and filtered. Portions of 25 c.c. of the 
 filtrate corresponding to 2.5 grams of the cheese 
 are titrated with decinormal solution of sodium 
 hydroxid, using phenolphthalein as indicator. 
 The amount of acid is expressed as lactic acid. 
 
 The above processes may be advantageously 
 modified in some respects. The determination 
 of water may be made by the extraction of the 
 cheese with alcohol and ether and drying of the 
 alcohol-ether extract and fat-free solids sepa- 
 rately. Blyth recommends this method as more 
 accurate and less tedious than the direct drying. 
 In the determination of ash it will be better to 
 extract the charred mass with water and pro- 
 ceed as described in the determination of the ash 
 of milk. 
 
 The fat extracted by ether may be examined 
 
 for other than butter-fat by the distillation 
 
 method in the usual way. When the composition 
 
 of the fat is alone desired, it may often be ex- 
 
 8 
 
I04 MILK PRODUCTS 
 
 tracted by simple methods. Pearmain & Moor 
 recommend that 50 grams be chopped fine and 
 tied up in a musHn bag, which is placed in a water- 
 bath. When the water is heated, the fat will 
 generally run out clear. If not clear, it can be 
 filtered through paper. 
 
 Henzold suggests the following: 300 grams 
 of the powdered cheese are agitated in a wide- 
 neck flask with 700 c.c. of 5% solution of potas- 
 sium hydroxid previously warmed to 20°. In 
 about ten minutes the cheese dissolves, the fat 
 floats, and by cautious shaking may be col- 
 lected in lumps. The liquid is diluted, the fat 
 removed, washed in very cold water, keaded 
 as dry as possible, melted, and filtered. It is 
 claimed that the fat is not altered in composition 
 by the process. 
 
 The fat of cheese may be estimated by the 
 centrifugal method, as follows: 
 
 About 3 grams of the mixed cheese in small 
 fragments are weighed and transferred to the 
 bottle, the last portions being washed in with the 
 acid of water. A few drops of ammonium hy- 
 droxid are added, and suflicient water to make 
 the liquid about 15 c.c. The liquid is warmed 
 with occasional shaking until the cheese is well 
 disintegrated, and then treated as a sample of 
 milk. The percentage of fat is found by mul- 
 tiplying the percentage reading by 15.45 and 
 
CHEESE 105 
 
 dividing by the number of grams of cheese taken 
 for analysis. 
 
 Chattaway, Pearmain & Moor use the follow- 
 ing modification: 2 grams of the cheese are 
 placed in a small dish and heated on the water- 
 bath with 30 c.c. of concentrated hydrochloric 
 acid until a dark, purpHsh-colored solution is 
 produced. The mixture is now poured into 
 the test bottle, portions of solution remaining in 
 the dish rinsed with the hydrochloric acid fusel- 
 oil mixture into the bottle, and, finally, enough 
 strong hot acid added to fill the bottle up to the 
 mark. It is then whirled for about a minute. 
 The difficulty in this method is to get all the fat 
 into the bottle. It is best to weigh the cheese 
 in the bottle. 
 
 For accurate determination of fat, Revis and 
 Bolton recommend the Schmid-Bondyzynski 
 method, as follows: About 1.5 grams are weighed 
 in a small flask, 5 c.c. of hydrochloric acid and 
 a little powdered sulfur added and the mixture 
 boiled gently. (For dry cheese, acid of sp. gr. 
 1. 12 5 is best, for moist cheese, sp. gr. 1.19.) 
 The mixture is cooled, transferred to the appara- 
 tus used for Rose-GottHeb method, by the use of 
 two portions of 2.5 c.c. each of alcohol and then 
 small quantities of ether until 12.5 c.c. have been 
 used. The contents are mixed, 12.5 c.c. light 
 
Io6 MILK PRODUCTS 
 
 petroleum added and the analysis carried out 
 as described on page 72. 
 
 Lactose. — This may be estimated by boiling the 
 finely divided cheese with water, filtering, and 
 determining the reducing power of the filtrate 
 on Fehling's solution. 
 
 Determination oj Albuminoid Nitrogen (Stutzer's 
 Method). — 0.7 to 0.8 gram of the cheese are 
 placed in a beaker, heated to boiling, 2 or 3 c.c. 
 of saturated alum solution added to decompose 
 alkaline phosphate, then copper hydroxid mix- 
 ture (see below) containing about 0.5 gram of 
 the hydroxid, and stirred in thoroughly; when 
 cold, the mass is filtered, washed with cold water, 
 and, without removing the precipitate from the 
 filter, the nitrogen determined by the Kjeldahl- 
 Gunning method. Before distillation, sufficient 
 potassium sulfid solution must be added to pre- 
 cipitate the copper. 
 
 The special reagent is prepared as follows: 
 100 grams of copper sulfate are dissolved in 5000 
 c.c. of water, 25 c.c. of glycerol added, and then 
 a dilute solution of sodium hydroxid until the 
 liquid is alkaline. The mass is filtered, the 
 precipitate is mixed well with water containing 
 5 c.c. of glycerol per liter, and washed until the 
 washings are no longer alkaline. It is then 
 rubbed up with a mixture of 90% water and 10% 
 glycerol in sufficient quantity to obtain a uniform 
 
CHEESE 107 
 
 magma that can be measured with a pipet. The 
 quantity of copper hydroxid per c.c. should be 
 determined. It should be kept in a well-closed 
 bottle. 
 
 Ammonium compounds. — ^About 5 grams of 
 cheese are rubbed up in a mortar with water, 
 transferred to a filter, and washed with a liter 
 of cold water. The filtrate is concentrated by 
 boiling (if alkaline, it must be neutralized before 
 heating), barium carbonate added, the liquid 
 distilled, and the ammonium hydroxid in 
 the distillate estimated by titration with stand- 
 ard acid. 
 
 According to Stutzer, magnesium oxid or 
 magnesium carbonate (the latter usually contains 
 some oxid) should not be used as some of the 
 amino-compounds may be decomposed. 
 
 Amino-compounds. — The nitrogen as amino- 
 compounds is estimated by subtracting from 
 the figure for total nitrogen the sum of the 
 protein and ammoniacal nitrogen. If nitrates 
 are present, the nitrogen as such should also be 
 determined and subtracted. 
 
 Van Ketel & Antusch propose the following 
 methods for estimating the nitrogen compounds: 
 
 Ammonium compounds. — The sample, pow- 
 dered with the addition of sand, is distilled with 
 water and barium carbonate, and the distillate 
 received in a measured quantity of standard 
 
I08 MILK PRODUCTS 
 
 sulfuric acid, and, after boiling, the excess of acid 
 is neutralized with standard sodium hydroxid, 
 using rosolic acid as indicator. 
 
 Amino-compounds. — These are determined by 
 macerating the powdered cheese in water for 
 fifteen hours at the ordinary temperature. After 
 adding a little dilute sulfuric acid (1:4), the pro- 
 teins and peptones are precipitated by phospho- 
 tungstic acid. The precipitate is filtered off and 
 washed with water containing a little sulfuric acid. 
 The filtrate is made up to a definite bulk, and the 
 nitrogen is determined in an aliquot portion of 
 the liquid by the Kjeldahl-Gunning process, 
 allowance being made for the nitrogen existing as 
 ammonium. 
 
 Peptones and Alhumoses. — These are deter- 
 mined jointly by boiling the powdered cheese 
 (mixed with sand as before) with water and 
 filtering from the undissolved casein and albumin. 
 In an aliquot portion of the filtrate the peptones 
 and albumoses are precipitated by adding dilute 
 sulfuric acid and phosphotungstic acid. After 
 washing with acidulated water the nitrogen in 
 the precipitate is determined by the Kjeldahl- 
 Gunning process. 
 
 The total nitrogen of the cheese is also deter- 
 mined, and after allowing for the nitrogen ex- 
 isting as other forms, the remainder is calculated 
 to casein. 
 
CHEESE 109 
 
 Poisonous Metals. — Lead chromate has been 
 found in the rind of cheese, and finely divided 
 lead in a number of Canadian cheeses. In 
 England zinc sulfate has been employed under 
 the name of cheese spice to prevent the heading 
 and cracking. Arsenic has also been found; it 
 may be detected by Reinsch's test. Lead, zinc, 
 and chromium may be detected by ashing a 
 portion of the sample in a porcelain crucible and 
 applying the usual tests. 
 
FERMENTED MILK PRODUCTS 
 
 The usual fermentation of milk is the con- 
 version of the lactose into lactic acid, but by 
 special methods other changes may be substituted. 
 These modified fermentations are of rather 
 ancient origin, and being produced by mixture 
 of organisms, the products are complex and 
 irregular. The proteins are more or less changed 
 into proteoses and peptones. 
 
 Kumiss is milk which has undergone alcoholic 
 fermentation. The inhabitants of the steppes 
 of Russia prepare it from mares' milk. When 
 cows' milk is used, sucrose must be added. It 
 is often made by adding sucrose and yeast to 
 skim-milk. 
 
 Vieth gives the following analysis of kumiss at 
 successive stages of fermentation : 
 
 Kumiss from Cows' Milk 
 
 One One One Three 
 
 Day Week Month Months 
 
 Alcohol I.I 0.9 i.o I.I 
 
 Solids 1 1. 3 8.9 8.6 8.5 
 
 Fat 1.6 1.4 1.5 1.5 
 
 Casein 2.0 2.0 1.9 1.7 
 
 Albumin 0.3 0.2 0.2 o.i 
 
 Carbohydrates 6.1 3.1 2.2 1.7 
 
 Lactic acid 0.2 0.9 1.3 1.9 
 
 Lactoprotein and peptone. 0.3 0.5 0.7 0.9 
 
 Soluble ash o.i 0.2 0.2 0.2 
 
 Insoluble ash 0.4 0.3 0.3 0.3 
 
 IIO 
 
FERMENTED MILK PRODUCTS ill 
 
 The item ' ' lactoprotein and peptone" refers 
 to the substance precipitated by tannin after 
 removal of the casein and albumin. 
 
 Kumiss from Mares' Milk 
 
 At the Alco- Nitrogenous Lactic Lac- 
 
 End of: hol Fat Matters Acid tose Ash 
 
 I day 2.47 1.08 2.25 0.64 2.210.36 
 
 8 days 2.70 1. 13 2.00 1.16 0.690.37 
 
 22 days 2.84 1.27 1.97 1.26 0.510.36 
 
 Kefyr. — This is usually made from cows' milk. 
 It has been used in the Caucasus for centuries. 
 For its preparation a peculiar ferment is used, 
 which is contained in the kefyr grains. These 
 are first soaked in water, by which they are 
 caused to swell and rendered more active, and 
 then added to the milk. If taken out of the milk 
 and dried, the grains may be used repeatedly. 
 
 The following are analyses of kefyr: 
 
 KONIG Hammarsten 
 
 Alcohol o • 75 o . 72 
 
 Fat .. 1.44 3.08 
 
 Casein 2 . 88 2 . 94 
 
 Albumin 0,36 o. 18 
 
 Hemialbumose 0.26 0.07 
 
 Peptone o . 04 
 
 Lactose 2.41 2 . 68 
 
 Lactic Acid i . 02 o . 73 
 
 Ash 0.68 0.71 
 
 According to Konig, good kefyr will not 
 contain more than i % of lactic acid. 
 
 Analytic Methods. — Solids and ash are deter- 
 
112 MILK PRODUCTS 
 
 mined by evaporation as described on page 13. 
 Acidity is determined by titration with ^/jo 
 alkali, using phenolphthalein or methyl-orange as 
 an indicator. The amount of acidity is expressed 
 in terms of lactic acid. The Kjeldahl-Gunning 
 method will give the total nitrogen. For further 
 examination of the nitrogenous bodies, the 
 methods given on pages 106 to 108 may be applied. 
 Total reducing carbohydrates may be estimated 
 as given on page 32. If sucrose and common 
 yeast have been added, the fermented material 
 will be likely to contain invert-sugar, with un- 
 changed lactose and sucrose, and the method of 
 examination of sweetened condensed milk may 
 be applicable. Fat can, probably in all cases, 
 be determined with sufficient accuracy by the 
 L-B. process. If it be desired to make polari- 
 metric readings, the liquid should be clarified 
 with acid mercuric nitrate solution (page 37), as 
 some partly hydrolyzed proteins which have 
 rotatory power may not be precipitated by other 
 reagents. The determination of alcohol accu- 
 rately is difficult, as the quantity is usually 
 small. The cautious distillation of a consider- 
 able volume of the material previously neutral- 
 ized with a little sodium hydroxid will yield 
 a distillate in which alcohol may be detected 
 and determined by the usual methods. 
 
FERMENTED MILK PRODUCTS II3 
 
 Preservatives are not likely to be used, since 
 they would interfere with the fermentation, but 
 attempts may be made to secure better keeping 
 by adding some preservative after the fermenta- 
 tion has occurred. In some cases, therefore, tests 
 for boric acid, formaldehyde, and salicylic acid 
 should be made, as these will be most likely to be 
 used. 
 
INDEX 
 
 Abrastol, 62. 
 
 Acidity, 39. . . 
 
 Acid mercuric iodid, 78. 
 
 nitrate, 37. 
 
 Adams' method, 14. 
 Agar, 67. 
 
 Albumin, 2, 28, 31. 
 Aldehyde number, 27. 
 Almen's reagent, 29. 
 Alumina-cream, 78 
 Amphoteric milk, 39. 
 Annatto, 51, 53, 93. 
 Asaprol, 62. 
 Ash, 3, 13. 
 
 Babcock's method, 16. 
 Benzoates, 59. 
 
 Boiled milk, detection of, 48. 
 Borax and boric acid, 62. 
 Butter, 81. 
 
 colors, 92. 
 
 fat, 81. 
 
 , process, 90. 
 
 renovated, 90. 
 
 Butyrorefractometer, 90. 
 
 Calcium saccharate, 46. 
 
 Calculation methods, 21, 28. 
 
 Caramel, 95. 
 
 Casein, 28, 30. 
 
 Cheese, 97. 
 
 Citric acid, 2. 
 
 Colors in butter, 92. 
 
 milk, SI. 
 
 Colostrum, 7. 
 Condensed milk, 69. 
 Cream, 65. 
 
 , evaporated, 69. 
 
 Cryoscopy, 44. 
 
 Egg-yolk in oleomargarin, 95. 
 Enzyms in milk, 2. 
 Evaporated cream, 69. 
 
 Pat of milk, i. 
 Fehling's solution, 32. 
 Fermented milk, no. 
 Filled cheese, 99. 
 Formic acid, 66. 
 Formaldehyde, 55. 
 Formalin, 55. 
 
 Gelatin, detection of, 45. 
 Globulin, 2. 
 
 Glucose, detection of, 96. 
 Glycerol-soda, 86. 
 
 Hydrogen peroxid, 59- 
 
 Imitation cream, 65. 
 
 Kefyr, iii. 
 
 Kjeldahl-Gunning method, 22. 
 Kumiss, no. 
 
 Lactose, 2, 32. 
 
 Lecithin, 3. 
 
 LefJmann-Beam method, 19, 86. 
 
 Mercuric iodid, acid, 78. 
 
 nitrate, acid, 37. 
 
 Metals in cheese, 109. 
 Milk-sugar, 2, 32. 
 Multirotation, 39. 
 
 Nitrites in milk, 57. 
 
 Oleomargarin, 84. 
 
 Palm oil, detection of, 93. 
 Preservation of samples, 64. 
 Process butter, 90. 
 Proteins, determination of, 22. 
 
 Recknagel's phenomenon, 4. 
 Refraction index, 42. 
 Refractometer, 90. 
 Reichert-Meissl number, 86. 
 Renovated butter, 90. 
 Roese-Gottlieb method, 72. 
 
 Saccharin, 61. 
 Saccharate of lime, 46. 
 Salicylic acid, 61. 
 Separated milk, 5. 
 Serum-refraction, 42. 
 Sodium carbonate, 61. 
 
 benzoate, 59. 
 
 Soxhlet's method, 32. 
 Specific gravity, 8. 
 Sucrose, 46, 74. 
 
 Turmeric, 93. 
 
 Volatile acids, 85. 
 
 Whey, 6. 
 
 115 
 
QOOOB'^ 
 
 B55H2 #