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 Book. _J j - • 
 
„_7. Issued February 17, 1816. 
 
 U. S. DEPARTMENT OF AGRICULTURE, 
 ^BUREAU OF ANIMAL INDUSTRY. 
 
 CHEMICAL TESTING OF MILK 
 AND CREAM 
 
 BY 
 
 ROSCOE H. SHAW, 
 
 Chemist, Dairy Division. 
 
 WASHINGTON: 
 
 GOVERNMENT PRINTING OFFICE, 
 
 1916. 
 
6 
 
 \V 
 
 D. of D. 
 WAR 17 1916 
 

 A. -7. Issued February 17, 1916. 
 
 U. S. DEPARTMENT OF AGRICULTURE, 
 BUREAU OF ANIMAL INDUSTRY. 
 
 A. D. MEL VEST, Chief. 
 
 CHEMICAL TESTING OF MILK AND 
 CREAM. 1 
 
 By Roscoe H. Shaw, Chemist, Dairy Division. 
 
 CONTENTS. 
 
 Chemical nature of milk 1 
 
 Testing for fat 3 
 
 Determination of total solids in milk 22 
 
 Determination of specific gravity of milk 26 
 
 Calculating total solids by formula 28 
 
 Determination of acidity of milk and cream 32 
 
 The detection of preservatives 34 
 
 Chemicals and apparatus used in the chemical analysis of milk 
 
 and cream 36 
 
 CHEMICAL NATURE OF MILK. 
 
 In order to follow intelligently the methods for testing 
 milk and cream some knowledge of the chemistry of milk 
 is essential. From a chemical standpoint milk is a very 
 complex substance. The component parts may, however, 
 
 1 In preparing this, bulletin free use has been made of the various 
 publications on the subject, particularly "Testing Milk and Its Pro- 
 ducts," by Farrington, E. H., and Woll, F. "W. (Madison, Wis., 1911), 
 and " Modern Methods of Testing Milk and Its Products," by L. L. 
 Van Slyke (New York, 1907). 
 15037°— 16 1 
 
be classified into a few well-marked groups, as follows: 
 (1) Water, (2) fat, (3) nitrogenous constituents, (4) sugar, 
 and (5) ash. The components other than water are col- 
 lectively known as total solids or milk solids, and the 
 solids other than fat as solids not fat. Milk serum, or 
 more properly milk plasma, is the term used to denote 
 the milk minus the fat; hence the terms serum solids and 
 plasma solids are synonymous with solids not fat. 
 
 Water. — The water in milk varies from 82 to 90 per 
 cent. The usual variation in mixed-herd milk is much 
 less and is probably covered by 84 to 88 per cent. 
 
 Fat. — The fat in milk — milk fat or butter fat — is not in 
 solution but exists as an emulsion of microscopic globules 
 so small that a single drop of average milk contains more 
 than one hundred millions of them. These globules, even 
 in milk from one cow, are not all of the same size. Some 
 may be two or three times the size of others, the average 
 size depending upon several factors, the principal one of 
 which is the breed of the animal. Chemically the fat is 
 not a single compound but a mixture of several compounds 
 known as glycerids. Some of these glycerids are common 
 to all fats, while others are peculiar to butter. This fact 
 is made use of in detecting oleomargarin or artificial 
 butter. 
 
 Cows' milk usually contains from 3 to 6 per cent of fat, 
 depending very largely upon the breed of the animal. 
 
 Nitrogenous constituents. — These are principally casein 
 and albumin, with traces of less important nitrogenous 
 compounds. The coagulum produced by rennet, dilute 
 acids, or certain other chemicals, when added to milk, is 
 chiefly casein. Albumin is the flocculent precipitate 
 produced by heating whey or skimmed milk from which 
 the casein has been removed. In constitution and be- 
 havior it closely resembles white of egg. Casein is not 
 really in solution in the milk, but exists in an extremely 
 fine colloidal condition in combination with some of the 
 ash constituents. With an appropriate filter of clay it 
 is possible to separate it from the water. Albumin is in 
 true solution in the water of the milk. Frequently, but 
 improperly, the term casein is applied to all the nitrogen- 
 ous constituents in milk. Sometimes the term total pro- 
 teins is used in referring to the nitrogenous constituents 
 
taken as a whole. The amount of casein in average 
 cows' milk varies from 2 to 4 per cent and the albumin 
 from 0.5 to 0.8 per cent. 
 
 • Sugar. — Milk sugar, or lactose, belongs to a group 
 known as carbohydrates, and is a white substance less 
 sweet in taste than cane sugar. Milk sugar is broken up 
 into lactic acid by the action of bacteria, this bringing 
 about the souring of milk. Milk sugar is in solution in 
 the water of the milk and is present to the extent of from 
 3.5 to 6 per cent. 
 
 Ash. — The ash, or the mineral part of milk, exists to 
 the amount of about 0.75 per cent and consists largely 
 of the chlorids and phosphates of sodium, potassium, 
 magnesium, and calcium. 
 
 AVERAGE CHEMICAL COMPOSITION. 
 
 The table below gives the average of more than 5,000 
 analyses of milk at the New Vork State Agricultural Exper- 
 iment Station, Geneva: 
 
 Per cent. 
 
 Water 87. 1 
 
 Total solids 12. 9 
 
 Fat : 3.9 
 
 Casein 2.5 
 
 Albumin 7 
 
 Sugar 5. 1 
 
 Ash 7 
 
 TESTING FOR FAT. 
 
 In the following remarks on the testing of milk and 
 cream the aim will be to present the subject in such a man- 
 ner that it may be followed by those who have had neither 
 chemical-training nor a course of any sort in milk testing. 
 To those who have had such training the following pages 
 will doubtless appear very elementary and overburdened 
 with detail. 
 
 TESTING MILK FOR FAT. 
 
 Preparing the sample for testing. — As before mentioned, 
 fat is not in solution in milk, but is in an emulsion of very 
 fine globules. These, being lighter than the surrounding 
 serum, tend to rise, carrying with them some of the other 
 solids, resulting in the familiar creaming of milk. Before 
 
the test can be made a homogeneous mixture must be ob- 
 tained. This can best be obtained by pouring the milk 
 several times from one vessel into another. When the 
 sample is small, beakers are convenient for this purpose, 
 and if the sample has not remained in the container more 
 than a few hours, pouring back and forth four or five times 
 is sufficient. When, however, the sample has stood for 
 some time in the container, the cream layer is liable to be 
 hard and to adhere to the walls. This is particularly true of 
 preserved samples. In such event it is well to place the 
 container in warm water until the cream has become soft- 
 ened and can then be easily removed. Care must be taken 
 that none of the cream is left on the cover of the container ; 
 if, however, any is left, a brush such as is used in cleaning 
 beakers is useful in dislodging it. 
 
 The sample must always be well mixed immediately 
 before measuring out a charge for testing. If several 
 charges are to be measured out, the sample must be mixed 
 each time. Thorough mixing is imperative for accurate 
 work. 
 
 Partially churned milk. — Milk from some cows, notably 
 of the Jersey breed, churns very easily and sometimes a too 
 vigorous agitation in the mixing of such milk results in 
 some of the fat collecting in small granules which refuse to 
 emulsify again. This also frequently happens when the 
 milk is sent a long distance in partially filled containers. 
 These granules are easily recognized, and when they are 
 present special treatment is required to prepare the sample 
 for testing. A little ether equal in volume to 5 per cent 
 of the milk may be added, and the container stoppered and 
 vigorously shaken. The ether will dissolve the granules 
 and the solution will mix with the milk. A fairly accurate 
 charge may now be quickly removed, but the percentage 
 obtained must be corrected for the volume occupied by the 
 ether. 
 
 Another and perhaps a better way to treat churned milk 
 is to place the container in hot water until the milk has 
 attained a temperature of about 110° F. In a few minutes 
 at this temperature the granules will have melted. The 
 container is then vigorously agitated and a charge for test 
 immediately measured out. 
 
The partial churning of the sample is not a frequent 
 occurrence and with proper care can always be avoided. 
 When samples are to be sent a considerable distance the 
 containers should be completely filled so that no space is 
 left at the top . A good way is to fill a bottle to overflowing 
 with the mixed sample and then to insert a rubber or cork 
 stopper having a hole about one-eighth of an inch in diame- 
 ter. As the stopper goes to its place the milk will spurt out 
 through the hole; the hole is then filled with a piece of 
 glass rod or a wooden plug. When treated in such a man- 
 ner milk will not churn. 
 
 Sour milk. — While the souring of milk does not affect 
 the fat, it is impossible to obtain a representative charge 
 from curdled milk without special treatment. , In order to 
 obtain a good mixture it is necessary to dissolve the curd. 
 This may be accomplished by adding 5 or 10 per cent by 
 volume of a strong solution of either caustic soda or potash; 
 strong ammonia water may also be used. The alkali must 
 be thoroughly mixed with the milk until it is completely 
 liquid. The charge for test must be immediately meas- 
 ured out and a correction made in the final percentage for 
 the volume occupied by the alkali solution. If desired, 
 the powdered alkali may be added directly to the milk in 
 small portions at a time, being sure that one portion is 
 dissolved before another is added, and agitating until the 
 milk has become liquid. No correction is necessary for 
 the volume occupied by the powdered lye. When making 
 a fat test on milk containing alkali, special precautions 
 must be observed in adding the sulphuric acid, as an 
 excessive amount of heat is generated and the contents of 
 the test bottle may be thrown out. When alkali is used, 
 slightly more acid is required. 
 
 THE BABCOCK TEST. 
 
 The Babcock test for fat in dairy products, named for its 
 inventor, Dr. S. M. Babcock, chief chemist of the Wiscon- 
 sin agricultural experiment station, is based upon the 
 fact that strong ,sulphuric acid will dissolve the serum 
 solids in milk and set the fat free from its emulsion. In 
 conducting the test, the charge is placed in a specially 
 constructed test bottle and mixed with the proper quan- 
 
tity of sulphuric acid. The acid performs other functions 
 than the simple solution of the serum solids. Much heat 
 is developed by its action, and this causes the fat globules 
 to lose their individuality and run together, a condition 
 which greatly facilitates the separation from the serum, 
 and this separation is still further accelerated by the 
 increase in specific gravity of the serum caused by the 
 
 f 5 ? 
 
 Fig. 1.— Old type of 
 Babcock milk-test 
 bottle. 
 
 Fig. 2.— Type of Babcock 
 ! milk-test bottle conforming 
 to the requirements of the 
 United States Bureau of 
 Standards, and showing 
 graduations. 
 
 presence of the heavy sulphuric acid. When the solution 
 of the serum solids is effected the complete separation of 
 the fat and serum is accomplished by whirling in a centri- 
 fuge. The fat is gradually driven into the graduated neck 
 of the bottle and the percentage read directly. 
 
 Test bottles. — The Babcock-test bottle for milk, as shown 
 in figure 1, consists of a body holding about 50 cubic centi- 
 
meters and the neck graduated so that the percentage of 
 fat may be read directly. Seventeen and one-half cubic 
 centimeters are used in the test, and this volume of average 
 milk weighs almost exactly 18 grams. At the temperature 
 at which the bottles are standardized the specific gravity 
 of butter fat is about 0.9. Two cubic centimeters weigh 
 twice 0.9, or 1.8 grams, which is just one- 
 tenth of the weight of the charge used in 
 the test bottle. The volume between 
 and 10 per cent in the neck should, there- 
 fore, be 2 cubic centimeters, if the bottle 
 has been correctly standardized. Each 
 unit per cent is represented by a volume 
 of 0.2 cubic centimeters in the neck. The 
 old types of bottles were 10 per cent bot- 
 tles, the smallest subdivision being 0.2 per 
 cent. In the more recent types, notably 
 those made to conform to the specifica- 
 tions of the United States Bureau of Stand- 
 ards, the necks are somewhat smaller in 
 diameter and read only to 8 per cent, and 
 the smallest subdivision is 0.1 per cent. 
 (Fig. 2.) _ 
 
 Milk pipette. — The charge for the Bab- 
 cock test for milk is measured rather than 
 weighed, the measuring instrument being 
 a pipette graduated to deliver 17.5 cubic 
 centimeters of milk . These pipettes, filled 
 to their graduation mark, hold 17.6 cubic 
 centimeters. The extra 0.1 cubic centi- 
 meter is allowed for the milk which clings 
 to the walls. Pipettes may be obtained 
 which conform to the requirements of 
 the United States Bureau of Standards. 
 (Fig. 3.) 
 
 Acid measure. — This may be either a simple glass cylinder 
 graduated to deliver 17.5 cubic centimeters, or one of the 
 more complicated devices shown in figures 4, 5, and 6. A 
 convenient little device is the small beaker with the glass 
 handle by which the proper quantity of acid may be 
 
 Fig. 3.— Pipette 
 holding 17.6 
 cubic centi- 
 meters, used 
 in measuring 
 milk in the 
 Babcock test. 
 
8 
 
 dipped out of a larger beaker and poured into the test 
 bottle. (See fig. 7.) 
 
 The centrifugal machine. — This is commonly called the 
 Babcock tester, and various types are on the market, 
 ranging from the small, two-bottle hand tester to the large 
 steam turbine or electric tester, accommodating 24 or 
 more bottles. (See figs. 8, 9, 10, and 11.) They all con- 
 sist mainly of a horizontal revolving disk or wheel provided 
 with swinging sockets to hold the bottles. At rest, these 
 
 Fig. 4.— Simple 
 acid graduate. 
 
 Fig. 5— Burette 
 for measuring 
 the acid. 
 
 Fig. 6.— A combined bottle 
 and acid measure. 
 
 sockets allow the bottles to stand upright, but when in 
 motion, the centrifugal force causes the sockets to swing 
 outward, bringing the bottles to a horizontal position, with 
 the necks toward the center. "Where steam pressure is 
 available, a steam-turbine tester is strongly recommended 
 for the reason that it maintains a uniform motion under a 
 definite pressure and at the same time the steam keeps 
 the bottles warm and supplies the hot water required. 
 Whatever kind of tester is used, it must be firmly secured 
 
to a rigid support. There must be no shaking or trembling 
 of the tester when in motion. 
 
 Acid. — The acid used in the Babcock test is the commer- 
 cial sulphuric acid, sometimes called oil of vitriol, and 
 should have a specific gravity of between 1.82 and 1.83. 
 It should be kept in glass bottles or jugs, preferably with 
 glass stoppers. Rubber stoppers will last for a time, but 
 
 Fig. 7.— A dipper made entirely of glass and holding 17.5 cubic centi- 
 meters for measuring acid in the Babcock test. 
 
 the use of cork stoppers is not permissible, as cork is rapidly 
 attacked by the acid. Owing to the property of sulphuric 
 acid of absorbing water from the air and thus diluting 
 itself, it can not be kept in open containers. 
 
 Sulphuric acid is an extremely corrosive liquid, which 
 attacks the skin, the clothing, wood, and most of the com- 
 
 Fig. 8.— A 2-bottle hand tester. 
 
 mon metals. Should the acid be spilled on the clothing, 
 it should be immediately washed off with plenty of water, 
 and ammonia water applied; this in turn must also be 
 washed off. Unless the acid is washed off immediately 
 after contact with the skin, severe burns will result. Acid 
 spilled on the table or floor may be neutralized with wash- 
 ing soda or other alkali. Lead is the only common metal 
 
 15037°— 16 2 
 
10 
 
 Fig. 9. — A hand tester for 12 bottles- 
 
 not attacked by this acid. If much testing is to be done, 
 
 it is a good plan to cover the testing table with sheet lead. 
 
 Testing strength of acid. — As already mentioned, the 
 
 specific gravity of the sulphuric acid used should be 
 
 between 1.82 and 1.83. 
 It is much better to pur- 
 chase it guaranteed of the 
 proper strength than to 
 bother with diluting the 
 stronger acid. Creamery 
 supply houses handle acid 
 guaranteed to be cf the 
 proper strength, and if 
 kept in well-stoppered 
 containers it will not 
 change. For the benefit 
 of those who prefer to test the acid themselves, the follow- 
 ing directions are given: 
 
 Use of the acid hydrometer. — This is a hydrometer de- 
 signed only for liquids having a specific gravity about 
 that of concentrated sul- 
 phuric acid. (See fig. 12.) 
 It is standardized at 60° 
 F., and for correct results 
 must be used with acid at 
 that temperature only. 
 The acid at this tempera- 
 ture is poured into the 
 hydrometer cylinder and 
 the hydrometer allowed to 
 float in it. When it has 
 come to rest, the point on 
 the scale intercepting the 
 surface of the acid indi- 
 cates the specific gravity. 
 If it is much under 1.82 
 it can not be used for test- 
 ing milk, and should be discarded and a fresh lot of acid 
 obtained. If it is above 1.83 it may be diluted with water 
 until it is of the proper strength. There are two ways of 
 doing this. The acid may be exposed to the air until it 
 absorbs sufficient water to lower its specific gravity; this is 
 
 Fig. 10.— A type of steam tester 
 with an arrangement for heating 
 the water used in the test. 
 
11 
 
 the safest and best way if the specific gravity of the acid is 
 not much above the standard . The second way is to mix the 
 acid with a small quantity of water. A small quantity of 
 water is placed in a bottle or jar and the acid poured into 
 it. Never pour water into acid, as a serious accident may 
 result. After the mixture has cooled to 60° F. it is again 
 tested with the hydrometer and the process repeated if 
 necessary. 
 
 DIRECTIONS FOR MAKING THE BABCOCK TEST WITH 
 MILE. 
 
 Measuring the charge. — Directions have already been 
 given for preparing the sample for the test. The milk is 
 poured from one beaker to another two or three times. 
 The tip of the pipette is 
 immediately inserted and 
 the milk sucked up with 
 the mouth until it reaches 
 a point well above the 
 graduation mark on the 
 stem; the dry forefinger is 
 then quickly placed over 
 the mouth of the pipette. 
 By slightly relaxing the 
 pressure of the finger the 
 milk is allowed to flow 
 down until it just reaches Fig. 11.— A type of electric tester. 
 the mark. The tip of 
 
 the pipette is now placed in the neck of the test 
 bottle and the milk allowed to flow slowly down the 
 side. The right way is to hold the pipette obliquely 
 to the mouth of the test bottle as shown in figure 13. 
 The wrong way is shown in figure 14. If the bottle and 
 pipette are held in the latter position the neck of the bottle 
 may clog up and some of the milk run over the top. 
 Care must be taken that none of the milk is lost 
 during the operation. When nearly all the milk has run 
 out of the pipette, the last drop is forced out with a puff of 
 the breath. 
 
 Adding the acid. — The temperature of the milk when the 
 acid is added should be between 60° and 70° F., and the 
 acid should be at about the same temperature. Seven- 
 
12 
 
 teen and one-half cubic centimeters of the acid are meas- 
 ured out, and, with the bottle held at an angle, carefully 
 poured down the side, the bottle being turned slowly at 
 the same time so that any milk adhering to the neck will 
 be washed down. For two reasons the acid must not be 
 poured into the middle of the test bottle; first, because it 
 may form a plug in the neck, which may be driven out by 
 the expansion of the air below; and second, because the 
 
 r >k 
 
 Fig. 12.— Hy- 
 drometer and 
 cylinder used 
 in testing sul- 
 phuric acid. 
 
 Fig. 13. — The right way of add- 
 ing milk to the test bottle. 
 ( Farrington and Woll, Testing 
 Milk and Its Products.) 
 
 acid may partially mix with the milk and produce black 
 particles which do not dissolve and later interfere with 
 the reading of the test. The acid and milk should now 
 be in two distinct layers without much of a dark layer 
 between them. 
 
 Mixing the acid and the milk. — The acid is now mixed 
 with the milk by giving a combined rotary motion and 
 gentle shaking with the hand grasping the neck of the 
 
13 
 
 bottle. When once commenced the mixing must not be 
 interrupted until the solution is complete . The first effect 
 of the acid on the milk is a curdling, which is subsequently- 
 dissolved. As the solution progresses the color changes 
 first to a light yellow, then to dark yellow, then through 
 various shades of violet to brown and finally to dark brown, 
 if the acid is of the proper strength and the milk and acid 
 are at the right temperature 
 when united. Too strong or 
 too warm acid produces a 
 dense black. If the milk has 
 been preserved with formalde- 
 hyde, a longer time is re- 
 quired to complete the solu- 
 tion, owing to the toughening 
 of the casein by that preser- 
 vative. Common errors of 
 beginners are failure to mix 
 the acid thoroughly with the 
 milk and to continue the shak- 
 ing until the solution is com- 
 plete . A good plan is to shake 
 the bottle for a minute or 
 so after the solution is appar- 
 ently complete. Although 
 not necessary, it is preferable 
 to centrifuge the bottles im- 
 mediately, though they may 
 be kept 24 hours if desired, 
 in which case they must be 
 placed in water from 170° to 
 180° F. for 15 to 20 minutes 
 before whirling. 
 
 Centrifuging the bottles, — The 
 bottles are now placed in 
 the sockets of the centrifuge, taking care that they are 
 equally distributed about the wheel or disk so that the 
 equilibrium of the latter is not disturbed. An even num- 
 ber of bottles should always be whirled. Should an odd 
 number of tests be made a test bottle filled with water may 
 be used to balance the machine. When the bottles are in 
 place, the tester is covered in order to keep the bottles 
 
 4 
 
 / 
 
 \ 
 
 Fig. 14. — The wrong way of 
 adding the milk to the 
 milt bottle. (Farrington 
 and "Woll, Testing Milk 
 and Its Products.) 
 
14 
 
 from getting cold and to protect the operator from flying 
 glass and acid should any of the bottles break. The tester 
 is now set in motion and the bottles whirled 4 to 5 minutes 
 at the proper speed. This will be sufficient to bring prac- 
 tically all the fat to the surface. In cold weather, if a 
 hand tester is used, it may be necessary to pour hot water 
 into the jacket of the tester to keep the bottles warm. 
 
 Speed of centrifuge. — Farririgton and Woll have calcu- 
 lated the proper speed of testers with wheels of different 
 diameters to be as follows: 
 
 Revolutions 
 of wheel 
 Diameter of wheel in inches: per minute. 
 
 10 1, 074 
 
 12 980 
 
 14 909 
 
 16 848 
 
 18 800 
 
 20 759 
 
 22 724 
 
 24 693 
 
 Adding the water. — With the pipette or with the device 
 for the purpose attached to some steam testers, or in any 
 other convenient manner, hot water is added to the bottles 
 until the contents come nearly to the lower part of the 
 neck. The cover is now replaced on the tester and the 
 whirling repeated for one minute. Hot water is again 
 added until the fat reaches a point below the highest 
 graduation mark on the neck. It must never reach the top 
 mark, or some of the fat may be lost. This time the water 
 should be dropped directly into the fat in order to clear 
 the fat of the light, flocculent material which may be 
 entangled in it and which would later interfere with the 
 reading of the test. The whirling is repeated for another 
 minute. The temperature at which the readings are 
 taken is between 130° and 140° F., and this should be 
 borne in mind when the water is added, the object being to 
 add the water at such a temperature that the temperature 
 of the fat at the close of the last whirling will be between 
 these two figures. 
 
 The water used should preferably be soft water or con- 
 densed steam. The use of hard water is liable to cause 
 trouble on account of its carbonates; these are decomposed 
 by the acid, liberating carbon dioxid, which may cause 
 
15 
 
 6. 
 c— 
 
 foam on the top of the fat column and obscure the menis- 
 cus. If soft water or condensed steam is not available, 
 hard water may be used if, before heating it, a few drops of 
 sulphuric acid are added. 
 
 Reading the percentage.— -If the test has been successfully- 
 conducted, the fat will be in a clear, yellowish liquid 
 column sharply separated from the clear and nearly color- 
 less acid solution immediately below it and with no foam 
 on top. The bottles should be kept warm either in the 
 tester or in warm water until read, and the 
 readings should always be made at be- 
 tween 130° and 140° F. The fat at this 
 temperature will, if other conditions have 
 been correct, have a well-defined menis- 
 cus at both the top and the bottom. The 
 readings are made from the extreme bot- 
 tom of the lower meniscus to the extreme 
 top of the upper meniscus. Figure 15 
 shows this graphically. An ordinary pair 
 of dividers is useful in making this read- 
 ing. The points are placed at the upper 
 and lower limits, then lowered until one 
 point is at the mark; the other point 
 will intercept the scale at the correct per- 
 centage for the sample tested. 
 
 In some steam testers where the exhaust 
 steam escapes into the jacket and no ven- 
 tilation is provided, the temperature of 
 the bottles will be too high. In such 
 case, the bottles must be allowed to cool 
 to 130° to 140° F. by placing them in 
 water at that temperature for several 
 making the reading. 
 
 Imperfect tests. — If the foregoing directions have been 
 strictly followed, a perfect test should result. It is not to 
 be expected, however, that the beginner will always meet 
 with success. The next two paragraphs may be helpful in 
 locating the trouble. 
 
 An imperfect test is caused by one of three things: 
 (1) Foam on the fat column obscuring the upper menis- 
 cus; (2) a dark-colored fat column containing dark parti- 
 cles and with dark particles obscuring the lower meniscus; 
 
 Fig. 15.— Show- 
 ing method of 
 reading fat 
 column in 
 milk testing. 
 Bead from a 
 to b, not a to 
 c, nor a to d. 
 
 minutes before 
 
16 
 
 (3) a light-colored fat column containing white, caseous 
 material obscuring the lower meniscus. 
 
 The first is caused by using hard water. Any one or a 
 combination of the following may cause the second trou- 
 ble: (a) The acid was too strong; (6) too much acid was 
 used; (c) the acid was too warm when added to the milk; 
 (d) the milk was too warm when the acid was added; (e) 
 the acid was dropped directly into the milk; (/) the mix- 
 ing of the acid and the milk was interrupted before the 
 solution was complete; or (g) the acid and milk were al- 
 lowed to stand too long in the test bottle before being 
 mixed. The third trouble is caused by one or more of the 
 following: (a) The acid was too weak; (b) too little acid 
 was used; (c) the acid was too cold when added to the 
 milk; (d) the milk was too cold when the acid was added; 
 or (e) the mixing was not continued long enough to dis- 
 solve all the serum solids. 
 
 Tested Babcoch glassware. — Babcock-test bottles and 
 pipettes should always be tested and found correct before 
 being used . It is now possible to purchase test bottles and 
 pipettes which have been tested and approved by the 
 United States Bureau of Standards. Many States also 
 have officials empowered to test and approve Babcock 
 glassware. The best way is to purchase it already tested 
 by the Bureau of Standards, or to have it made to conform 
 to the requirements of that bureau and then tested by a 
 State official. 
 
 TESTING CREAM FOR FAT. 
 
 While in a general way cream is tested by the Babcock 
 test in much the same manner as milk, there are some 
 modifications that must be observed. The range of fat in 
 cream, and consequently the specific gravity is much 
 greater than in milk, so that 17.5 cubic centimeters do not 
 necessarily represent 18 grams, as in the case of milk. 
 Cream also varies in consistency, some being thin and some 
 thick; therefore. in some cases much more would adhere 
 to the walls of the pipette than in others. For these rea- 
 sons cream can not be accurately measured. The charge 
 for the test must be weighed into the test bottle. 
 
 Cream-test bottles. — The cream-test bottles used in the 
 Babcock test are of various designs, as shown in figures 16, 
 17, 18, and 19. Those conforming to the requirements of 
 
17 
 
 the United States Bureau of Standards differ from milk 
 bottles only in the graduations and in the length and diam- 
 eter of the neck. Test bottles are made for both an 18- 
 gram and a 9-gram charge. 
 
 Cream-test balances. — Several types of balances designed 
 for weighing cream charges are on the market (figs. 20, 21, 
 and 22). The small torsion balances prove to be very sat- 
 isfactory if care is taken that the important metal parts 
 
 sr3o 
 
 g-25 
 g-20 
 
 g-10 
 
 £-5 
 
 5^0 
 
 g-50 
 |-45 
 f-40 
 §-35 
 §-30 
 §-25 
 §-20 
 
 r is 
 
 §-10 
 
 1-5 
 =-0 
 
 Fig. 16.— 9-gram, 6- 
 inch cream bottle. 
 
 Fig. 17.— 18-gram 6- 
 inch cream bottle. 
 
 are not allowed to rust. Balances should be tested for 
 sensitiveness from time to time and should always be kept 
 in perfect condition. 
 
 Preparing cream, for testing. — The point never to be lost 
 sight of in testing cream or milk is that the small quantity 
 taken for the test must be truly representative. No matter 
 how carefully the test is carried out, if the charge taken 
 does not accurately represent the cream or milk to be 
 
 15037°— 16 3 
 
18 
 
 ^ 
 
 =-30 
 
 1-25 
 
 ^20 
 
 tested, the results will be worthless. The preparation of 
 cream for testing does not differ materially from that of 
 milk. The fat must be evenly distributed, and if there are 
 no lumps this can be accomplished by 
 pouring from one receptacle to another, 
 warming the cream slightly if cold. If 
 lumps are present, it has been advised 
 to pass the cream through a fine sieve, 
 rubbing the lumps through with the 
 fingers and then mixing as usual. If 
 the cream has stood for some time in the 
 sample jar, the top may have become 
 hard, leathery, and difficult to remove. 
 In this case, the jars should be set in 
 warm water until the contents have 
 reached 100° to 110° F., when the cream 
 will be soft and can be easily removed. 
 Weighing the charge. — After the sam- 
 ple has become homogeneous through- 
 out, the charge is quickly weighed into 
 the test bottle. The weight of the 
 charge depends upon the style of bottle 
 used . For this purpose the 9-gram bottle 
 is recommended . A pipette is useful in 
 conveying the cream to the test bottle, 
 as the flow can be easily controlled and 
 checked on the drop when the pointer 
 of the balance indicates that the correct 
 quantity has been run in. This weight 
 must be exact, and some experience is 
 necessary before the charges can be 
 quickly and accurately weighed. 
 
 Completing the test. — Instead of add- 
 ing a measured quantity of sulphuric 
 acid to the cream in the test bottle, as is 
 done with milk, the best way is to add the acid until the 
 mixture assumes the color of coffee to which cream has 
 been added. 1 The quantity of acid required to produce 
 this color varies with the percentage of fat in the cream. 
 If the cream and acid when mixed are about 70° F., from 
 
 i O. F. Hunziker and H. C. Mills, Testing Cream for Butter Fat, Indi- 
 ana Agricultural Experiment Station, Bui. 145. June, 1910. 
 
 Fig. 18.— 18-gram 9- 
 inch cream bottle. 
 
19 
 
 9Gr 
 
 Fig. 19. — Types of cream bottles conforming to the requirements of the 
 United States Bureau of Standards. 
 
20 
 
 4 to 8 cubic centimeters of acid (specific gravity 1.82 to 
 1.83), depending upon the percentage of fat, will be re- 
 quired for a 9-gram charge. After adding the acid to the 
 cream, the procedure up to the reading of the percentage 
 
 Fig. 20.— Type of knife-edge cream balance. 
 
 is exactly the same as in the milk test. After the final 
 whirling, the test bottles are submerged to a point above the 
 fat column in water at 135° to 140° F. in a suitable tank. 
 After remaining in this tank for about 15 minutes they are 
 
 Fig. 21. — Type of torsion balance for single bottle. 
 
 removed and the readings quickly made. The important 
 difference between reading the cream test and the milk 
 test is that in the cream test the fat column included is 
 from the bottom of the lower meniscus to the bottom, not 
 the top, of the upper meniscus. (See fig. 23.) It is advised 
 
21 
 
 to destroy the upper meniscus by dropping into the bottle 
 at this point a few drops of a liquid in which the fat is 
 not soluble. Glymol (petrolatum liquidum, U. S. P.), 
 known commercially as white mineral oil, gives satisfac- 
 tory results and may be purchased at almost any drug store. 
 If desired it may be colored with alkanet root. 1 If glymol 
 is used, the fat column included in the reading is from the 
 bottom of the lower meniscus to the line between the fat 
 and the glymol. If the fat column is read with the upper 
 meniscus intact, care must be taken that the eye is on a 
 
 Fig. 22.— Type of torsion balance for several bottles. 
 
 level with the points on the scale at which the readings 
 are made; otherwise an error will be introduced. 
 
 PRESERVING SAMPLES. 
 
 If, for any reason, it is desired to keep a sample of milk 
 or cream for a few days before testing it, a preservative 
 should be added to prevent decomposition. Formalin 
 (which is a 40 per cent solution of formaldehyde), corrosive 
 sublimate (mercuric chlorid), or potassium bichromate 
 are used for this purpose. Formalin has the advantage of 
 being a liquid and easily handled; on the other hand, it 
 
 1 Hunziker and Mills, loc. cit. 
 
has the property of toughening the casein and rendering it 
 more difficult to dissolve later in the sulphuric acid. One 
 cubic centimeter should keep a pint or a quart of milk cr 
 cream for two weeks or more. Corrosive sublimate, while 
 the most powerful of the three, is a deadly poison. Sam- 
 ples preserved with it should be colored in some way to 
 indicate the presence of the poison. Tablets of corrosive 
 sublimate containing coloring matter are 
 V/~v- on the market. If potassium bichromate 
 
 is used, the samples should be kept in a 
 dark place; 15 to 20 grains is sufficient 
 to preserve a pint for a reasonable length 
 of time. 
 
 & 
 
 'td 
 
 Fig. 23— Show- 
 i n g method 
 of reading fat 
 column in 
 cream testing. 
 Read from a 
 toc,notato6, 
 nor a to d. 
 
 CLEANING THE TEST BOTTLES. 
 
 After the test, and before the test bot- 
 tles have become cold, they should be 
 emptied with a shake or two to loosen 
 the deposit of calcium sulphate which 
 accumulates on the bottom. A conven- 
 ient device is shown in figure 24. This 
 consists of a 5 -gallon stone jar with a 
 wooden cover in which one - half - inch 
 holes have been bored. After the test 
 the necks of the bottles are placed in the 
 holes and the contents allowed to run 
 out, giving each bottle an occasional 
 shake. The bottles should then be rinsed 
 out twice with boiling water and, after 
 the outside has been rinsed off, placed 
 in a suitable rack and drained. At fre- 
 quent intervals the bottles should also be 
 given a bath in a dilute solution of lye, 
 or a solution of soap or cleansing powder. 
 
 DETERMINATION OF TOTAL SOLIDS IN MILK. 
 
 As brought out earlier in this circular, milk is composed 
 of water and the various solids collectively known as total 
 solids or milk solids. Manifestly the simplest way of 
 determining the amount of total solids in a given quantity 
 of milk is to separate them from the water and weigh them. 
 
23 
 
 This is precisely the manner in which the total solids in 
 milk are determined in the laboratory. A small quantity 
 of milk is weighed into a shallow, flat-bottomed dish, and 
 then heated until all the water is driven off. During this 
 evaporation the milk must not be heated more than a 
 degree or so above the boiling point of water, because at a 
 higher temperature some of the solids are decomposed. 
 
 Ovens.— Several types of ovens are used for holding the 
 milk at the right temperature during the evaporation. 
 The simplest type is perhaps the so-called double-walled 
 drying oven (fig. 25) . This piece of apparatus is really one 
 oven inside of another, the space between the two being 
 partly filled with water. A burner placed under the oven 
 boils the water, and the remaining space 
 between the walls is filled with steam, 
 maintaining a constant temperature in 
 the inner compartment which holds the 
 milk dishes. Unless carefully watched, 
 the oven will "boil dry," to prevent 
 which it is a good plan to attach some 
 sort of condenser. The type of condenser 
 known as the globe condenser is very sat- 
 isfactory for this purpose. Some ovens 
 are constructed with a constant-level at- 
 tachment. 
 
 Balance. — Nice weighings are required 
 in the determination of total solids in milk, and it is nec- 
 essary to use the type of balance known as the analytical 
 balance (fig. 26), the cream-test balance not being sensi- 
 tive enough for this purpose. On the other hand, the 
 analytical balance can not be used with advantage in 
 weighing cream charges. Both balances are required. An 
 analytical balance sensitive enough for the purpose can be 
 purchased for from $30 to $40. A set of accurate analytical 
 weights will also be required. Space does not permit di- 
 rections for using the analytical balance. If the operator 
 is not familiar with its use, he is advised to consult some 
 elementary treatise on quantitative chemical analysis. It 
 must be borne in mind that the analytical balance is a very 
 delicate instrument and should be treated accordingly. 
 
 Fig. 24. — Jar 
 with per- 
 forated cover 
 for use in 
 emptying test 
 bottles. 
 
24 
 
 Desiccators. — Dishes that are warm can not be accurately 
 weighed on the balance because air currents are created 
 which will buoy up the scale pan sufficiently to make the 
 object appear Lighter than it really is. Again, many sub- 
 stances can not be exposed to the air without absorbing 
 atmospheric moisture and in this way introducing an error 
 into the weighing. For these reasons it is customary 
 always to cool the dishes in a device known as a desiccator 
 (fig. 27) before weighing them. A desiccator is a specially 
 
 Fig. 25. — Double-walled drying oven. 
 
 constructed covered jar containing a substance like cal- 
 cium chlorid, which attracts to itself all the atmospheric 
 moisture in the inclosed space surrounding it. The desic- 
 cator, containing no moisture, will, of course, permit a sub- 
 stance to be kept in it without absorbing any. The cal- 
 cium chlorid, which forms a layer about 1 inch deep on 
 the bottom of the desiccator, should be renewed as soon as 
 it shows any signs of moisture. The cover of the desiccator 
 should be removed only as often as is necessary, and then 
 for the shortest possible time. 
 
25 
 
 Milk dishes. — These are best made of aluminum and 
 should be from 2 to 2 \ inches wide and about one-half inch 
 deep (fig. 28). Each dish should bear a number by which 
 
 Fig. 26. — Analytical balance. 
 
 it can be identified; this number may be scratched or 
 punched on the side. 
 
 Preparing the dishes. — After the dishes are clean and dry 
 they should be placed in the drying oven for half an hour, 
 then removed and placed in the 
 desiccator until cool. They 
 should be handled with forceps or 
 crucible tongs, and as soon as they 
 are cool they are weighed on the 
 analytical balance. 
 
 Weighing the charge. — After. the 
 milk has been thoroughly mixed, 
 it is drawn up in a pipette and 
 allowed to flow into the dish until 
 a thin film just covers the bottom; 
 the dish and milk are then 
 quickly weighed. The weight of the empty dish sub- 
 tracted from the last weight is the weight of the charge, 
 and should be about 2 grams. 
 
 Fig. 27." — Desiccator. 
 
26 
 
 Fig. 28.— Milk dish. 
 
 Evaporating the water. — The dishes containing the milk 
 are now placed in the oven, dried for about four hours, and 
 then placed in the desiccator until cool, when they are 
 weighed. They are then returned to the oven for 30 min- 
 utes, after which they are cooled and weighed as before. 
 
 If there is no loss in weight, 
 or if there is a slight gain in 
 weight during the 30 
 minutes, it indicates that all 
 the water is driven off, and 
 this last weight minus the 
 weight of the empty dish is 
 the weight of the total solids 
 in the charge taken. This multiplied by 100 and divided 
 by the weight of the charge gives the percentage. If there 
 was a loss in weight during the 30 minutes, the dishes are 
 returned to the oven and 
 dried for another period or 
 until they cease to lose 
 weight. 
 
 Determination of solids 
 not fat. — The percentage 
 of solids not fat, or serum 
 solids, is found by sub- 
 tracting the percentage of 
 fat from the percentage of 
 total solids. 
 
 DETERMINATION OF 
 SPECIFIC GRAVITY 
 OF MILK. 
 
 For exact work the spe- 
 cific gravity of milk is de- 
 termined by comparing the weight of a volume of milk with 
 that of an equal volume of pure water under controlled- 
 temperature conditions. For inspection work an instru- 
 ment known as the Westphal balance or the special 
 lactometer described in Bulletin 134 of the Bureau of Ani- 
 mal Industry, United States Department of Agriculture, 
 is sufficiently accurate. 
 
 Fig. 29.— Westphal balance. 
 
27 
 
 r\ 
 
 
 \ 
 
 Westphal balance. — This instrument (fig. 29) consists of 
 a pivoted beam graduated on one arm and bearing a 
 plummet or float. The weights in terms of specific gravity- 
 represent unity, tenths, hundredths, thousandths, and 
 ten-thousandths. With no weight on the beam it balances 
 when the plummet floats in air. When the unit weight 
 is in position, it balances when 
 the plummet floats in pure water 
 at the proper temperature. 
 When the plummet is submerged 
 in a liquid heavier than water, 
 such as milk, additional weights 
 are required to bring the instru- 
 ment to equilibrium. The spe- 
 cific gravity is read off directly 
 from the value of the weights 
 and their position on the beam. 
 Detailed directions usually ac- 
 company the instrument. 
 
 Lactometers. — Most lactome- 
 ters are not sensitive enough for 
 determining the specific gravity 
 of milk if more than approxi- 
 mate figures are required. The 
 use of either the Westphal bal- 
 ance or the special lactometer, 
 previously mentioned, is ad- 
 vised. If, however, only ap- 
 proximate results are required 
 the ordinary lactometer, of 
 which there are several types on 
 the market, will suffice. 
 
 The lactometer (figs. 30 and 31) 
 is used exactly in the same man- 
 ner as is the hydrometer in test- 
 ing sulphuric acid, directions for which are given on page 
 10 . Care must be taken that the milk is at the temperature 
 at which the lactometer is standardized and that the lac- 
 tometer floats freely in the cylinder. The specific gravity 
 of milk can not be taken until the milk is three or four 
 hours old . The point on the scale of the lactometer where 
 the surface of the milk intercepts represents the specific 
 
 Fig. 30.— Types of ordinary 
 lactometers. 
 
28 
 
 gravity which is usually expressed in 
 Quevenne^ degrees. 1 A slight meniscus 
 will obscure the surface line, and it is neces- 
 sary to estimate its depth. This will cause 
 no error if it is remembered that the point 
 to be read is at the surface of the milk and 
 not at the top of the meniscus. 
 
 A type of lactometer known as the New 
 York board of health lactometer is in 
 somewhat general use. The scale of this 
 instrument does not give the specific 
 gravity directly, but is so arranged that 
 milk having a specific gravity of 1.029 
 (at 60° F.) will read 100°. As the zero 
 mark is the point to which it will sink 
 when immersed in pure water, 100° on the 
 scale corresponds to 29° on the Quevenne 
 scale. New York board of health lactom- 
 eter degree may be converted into Que- 
 venne degrees by multiplying by 0.29. 
 
 CALCULATING TOTAL SOLIDS BY 
 FORMULA. 
 
 When the percentage of fat and the spe- 
 cific gravity of the milk are known and 
 only the closely approximate percentage 
 of total solids is wanted, it should be cal- 
 culated by the Babcock formula. The 
 following table and directions for using it 
 are taken from Bureau of Animal Industry 
 Bulletin 134: 
 
 1 Quevenne degrees are converted into specific 
 gravity by dividing by 1,000 and then adding 1 to 
 the quotient. This is done at a glance. For ex- 
 ample, if the Quevenne reading is 32.5, the specific 
 gravity is 1.0325. 
 
29 
 
 Table for determining total solids in milk from any given , 
 cific gravity and percentage of fat. 
 
 [Per cent total solids.] 
 
 Per- 
 cent- 
 age of 
 fat 
 
 Lactometer reading at 60° F. (Quevenne degrees). 
 
 26 27 28 29 30 31 32 33 34 35 36 
 
 2.00 
 2.05 
 2.10 
 2.15 
 2.20 
 2.25 
 2.30 
 2.35 
 2.40 
 2.45 
 
 8.90 
 8.96 
 9.02 
 9.08 
 9.14 
 9.20 
 9.26 
 9.32 
 9.38 
 9.44 
 
 9.15 
 9.21 
 9.27 
 9.33 
 9.39 
 9.45 
 9.51 
 9.57 
 9.63 
 
 11.41 
 11.47 
 11.53 
 11.59 
 11.65 
 11.71 
 11.77 
 11.83 
 11.89 
 11.95 
 
 2.50 
 2.55 
 2.60 
 2.65 
 2.70 
 2.75 
 2.80 
 2.85 
 2.90 
 2.95 
 
 9.50 
 9.56 
 9.62 
 9.68 
 9.74 
 9.80 
 9.86 
 9.92 
 9.98 
 10.04 
 
 9.75 
 9.81 
 9.87 
 9.93 
 9.99 
 10.05 
 10.11 
 10.17 
 10.23 
 10.29 
 
 10.75 
 10.81 
 10.87 
 10.93 
 10.99 
 11.05 
 11.11 
 11.17 
 11.23 
 11.30 
 
 12.01 
 12.07 
 12.13 
 12.19 
 12.25 
 12.31 
 12.37 
 12.43 
 12.49 
 12.55 
 
 3.00 
 3.05 
 3.10 
 3.15 
 3.20 
 3.25 
 3.30 
 3.35 
 3.40 
 3.45 
 
 10.60 
 10.66 
 10.72 
 10.78 
 10.84 
 10.90 
 10.96 
 11.03 
 11.09 
 11.15 
 
 11.10 
 11.17 
 11.23 
 11.29 
 11.35 
 11.41 
 11.47 
 11.53 
 11.59 
 11.65 
 
 12.61 
 12.68 
 12.74 
 12.80 
 12.86 
 12.92 
 12.98 
 13.04 
 13.10 
 13.16 
 
 3.50 
 3.55 
 3.60 
 3.65 
 3.70 
 3.75 
 3.80 
 3.85 
 3.90 
 3.95 
 
 10.95 
 11.02 
 11.08 
 11.14 
 11.20 
 11.26 
 11.32 
 11.38 
 11.44 
 11.50 
 
 12.72 
 12.78 
 12.84 
 12.90 
 12.96 
 13.02 
 13.08 
 13.14 
 13.20 
 13.26 
 
 13.22' 
 13.28 
 13.34 
 13.40 
 13.46 
 13.52 
 13.58 
 13.64 
 13.70 
 13.77 
 
 4.00 
 4.05 
 4.10 
 4: 15 
 4.20 
 4.25 
 4,30 
 4.35 
 4.40 
 4.45 
 
 12.06 
 12.12 
 12.18 
 12.24 
 12.30 
 12.36 
 12.42 
 12.48 
 12.54 
 12.60 
 
 12.81 
 12.87 
 12.93 
 12.99 
 13.05 
 13.12 
 13.18 
 13.24 
 
 13.3013.55 
 13.3613.61 
 
 13.83 
 13.89 
 13.95 
 14.01 
 14.07 
 14.13 
 14.19 
 14.25 
 14.31 
 14.37 
 
30 
 
 Table for determining total solids in milk from any given spe- 
 cific gravity and percentage of fat — Continued. 
 
 [Per cent total solids.] 
 
 Per- 
 cent- 
 age of 
 fat 
 
 Lactometer reading at 60° F. (Quevenne degrees). 
 
 26 27 28 29 30 31 32 33 34 35 36 
 
 4.50 
 
 4.55 
 
 4.60 
 
 4.65 
 
 4.70 
 
 4.75 
 
 4. 
 
 4.85 
 
 4. 
 
 4.95 
 
 12.91 
 12.97 
 13.03 
 13.09 
 13.15 
 13.21 
 13.27 
 13.33 
 13.39 
 13.45 
 
 13.92 
 13.98 
 14.04 
 14.10 
 14.16 
 14.22 
 14.28 
 14.34 
 14.40 
 14.46 
 
 14.43 
 14.49 
 14.55 
 14.61 
 14.67 
 14.73 
 14.79 
 14.85 
 14.91 
 14.97 
 
 5.00 
 5.05 
 5.10 
 5.15 
 5.20 
 5.25 
 5.30 
 5.35 
 5.40 
 5.45 
 
 13.51 
 13.57 
 13.63 
 13? 69 
 13.75 
 13.81 
 13.87 
 13.93 
 14.00 
 14.08 
 
 5.50 
 5.55 
 5.60 
 5.65 
 5.70 
 5.75 
 5.80 
 5.85 
 5.90 
 5.95 
 
 13.11 
 13.17 
 13.23 
 13.29 
 13.35 
 13.41 
 13.47 
 13.53 
 13.59 
 13.65 
 
 14.12 
 14.18 
 14.24 
 14.30 
 14.36 
 14.42 
 14.48 
 14.54 
 14.60 
 14.66 
 
 14.27 
 14.33 
 14.39 
 14.45 
 14.51 
 14.57 
 14.63 
 14.70 
 14.76 
 14.82 
 
 15.03 
 15.09 
 15.15 
 15.21 
 15.27 
 15.33 
 15.39 
 15.45 
 15.51 
 15.57 
 
 14.88 
 14.94 
 15.00 
 15.06 
 15.12 
 15.18 
 15.24 
 15.30 
 15.36 
 15.42 
 
 15.63 
 15.69 
 15.75 
 15.81 
 15.87 
 15.93 
 15.99 
 16.06 
 16.12 
 16.18 
 
 6.00 
 6.05 
 6.10 
 6.15 
 6.20 
 6.25 
 6.30 
 6.35 
 6.40 
 6.45 
 
 13.96 
 14.02 
 14.08 
 14.14 
 14.20 
 14.26 
 14.32 
 14.38 
 14.44 
 14.50 
 
 4714. 
 53 14. 
 5914. 
 65,14. 
 71 1 14. 
 77:15. 
 83'15. 
 90' 15. 
 9615. 
 02115. 
 
 14.98 
 15.04 
 15.10 
 15.16 
 15.22 
 15.28 
 15.34 
 15.40 
 15.46 
 15.52 
 
 16.24 
 16.30 
 16.35 
 16.42 
 16.48 
 16.54 
 16.60 
 16.66 
 16.72 
 16.78 
 
 6.50 
 6.55 
 6.60 
 6.65 
 6.70 
 6.75 
 6.80 
 6.85 
 6.90 
 6.95 
 
 14.82 
 14.88 
 14.94 
 15.00 
 15.06 
 15.12 
 15.18 
 15.24 
 15.30 
 15.36 
 
 15.83 
 15.89 
 15.95 
 16.01 
 16.07 
 16.13 
 16.19 
 16.25 
 16.31 
 16.37 
 
 16.84 
 16.90 
 16.96 
 17.02 
 17.08 
 17.14 
 17.20 
 17.26 
 17.32 
 17.38 
 
31 
 
 Table for determining total solids in milk from any given spe- 
 cific gravity and percentage of fat — Continued. 
 
 PROPORTIONAL PARTS. 
 
 
 Fraction 
 
 
 Fraction 
 
 
 Fraction 
 
 Lactom- 
 
 to be 
 
 Lactom- 
 
 to be 
 
 Lactom- 
 
 to be 
 
 eter 
 
 added to 
 
 eter 
 
 added to 
 
 eter 
 
 added to 
 
 fraction. 
 
 total 
 
 fraction. 
 
 total 
 
 fraction. 
 
 total 
 
 
 solids. 
 
 
 solids. 
 
 
 solids. 
 
 0.1 
 
 0.03 
 
 0.4 
 
 0.10 
 
 0.7 
 
 0.18 
 
 .2 
 
 .05 
 
 .5 
 
 .13 
 
 .8 
 
 .20 
 
 .3 
 
 .08 
 
 .6 
 
 .15 
 
 .9 
 
 .23 
 
 Directions for using the table. — If the specific gravity as 
 expressed in Quevenne degrees is a whole number, the 
 percentage of total solids is found at the intersection of 
 the vertical column headed by this number with the 
 horizontal column corresponding to the percentage of fat. 
 
 If the specific gravity as expressed in Quevenne degrees 
 is a whole number and a decimal, the percentage of total 
 solids corresponding to the whole number is first found, 
 and to this is added the fraction found opposite the tenth 
 under "Proportional Parts." Two examples may suffice 
 for illustration: (1) Fat, 3.8 per cent; specific gravity, 32. 
 Under column headed 32, 12.57 per cent is found corre- 
 sponding to 3.8 per cent fat. (2) Fat, 3.8 per cent; specific 
 gravity, 32.5. The percentage of total solids correspond- 
 ing to this percentage of fat and a specific gravity of 32 is 
 12.57. Under "Proportional Parts" the fraction 0.13 
 appears opposite 0.5. This added to 12.57 makes 12.70, 
 which is the desired percentage. 
 
 An inspection of the table shows that the percentage 
 of total solids increases practically at the rate of 0.25 for 
 each lactometer degree and 1.2 for each per cent of fat. 
 This gives rise to Babcock's simple formula: Total solids= 
 \ L+1.2 F. (L=lactometer reading in Quevenne degrees 
 and f=percentage of fat.) 
 
 To illustrate the, use of the formula the following example 
 is given: Fat, 4 per cent; specific gravity, 32. In this case 
 one-quarter of 32 is 8; 1.2 multiplied by 4 is 4.8; 8 plus 
 4.8 equals 12.8, which represents the percentage of total 
 solids. 
 
32 
 
 This simple formula can be used in cases not provided 
 for in the table. 
 
 DETERMINATION OF ACIDITY OF MILK AND 
 CREAM. 
 
 Acidity in milk is attributable to two causes, (1) the pres- 
 ence in milk of acid phosphates and perhaps of carbon 
 dioxid, and (2) lactic and other acids produced by the 
 decomposition of the milk sugar by bacterial action. 
 When freshly drawn milk is acid to phenolphthalein, this 
 acidity is from 0.07 per cent to 0.08 per cent and is owing 
 to causes given under (1). Lactic acid is not present in 
 freshly drawn milk; it develops only on standing. Milk 
 is not sour to the taste until it has a total acidity of at 
 least 0.3 per cent. 
 
 For convenience the total acidity of milk is usually 
 calculated as lactic acid. The principle upon which the 
 determination of acidity is based is the well-known 
 chemical action of acids upon alkalies. To illustrate, the 
 action of hydrochloric (sometimes called muriatic) acid 
 on a solution of caustic soda may be taken. This acid 
 has a sharp and very sour taste, while caustic-soda solu- 
 tions have a soapy feel and a peculiar odor, and if suffi- 
 ciently strong will attack the skin. If the solution of 
 caustic soda is slowly added to the hydrochloric acid, the 
 sour taste will gradually disappear until the exact point of 
 neutrality is reached, when a new substance is produced — 
 sodium chlorid, or common salt, which has neither the 
 acid properties of the one nor the alkaline properties of 
 the other. The sense of taste, however, is not sufficiently 
 sensitive to determine when the exact point of neutrality 
 has been reached. Phenolphthalein is an organic com- 
 pound, having the property, when in solution, of turning 
 pink with alkalies and remaining colorless with acids. 
 Such a substance is called an indicator because it indicates 
 by a color change when a certain chemical reaction has 
 taken place. 
 
 There are several so-called acid tests before the public. 
 The one known as Manns' s acidity test is widely used and 
 is conducted as follows: 
 
33 
 
 MANNS'S ACIDITY TEST. 
 
 Apparatus required : 
 One 50 cubic centimeter glass burette graduated to 
 
 tenths, with stopcock. 
 One 50 cubic centimeter pipette. 
 One 250 cubic centimeter beaker, or a white teacup. 
 One support for burette. 
 Glass stirring rods. 
 
 One-tenth normal solution of caustic soda , each cubic 
 centimeter of which will neutralize 0.009 gram of 
 lactic acid. 
 An alcoholic solution of phenolphthalein made by 
 dissolving 10 grams in 300 cubic centimeters of 90 
 per cent alcohol. 
 One who has not had training in chemistry should not 
 attempt to make the tenth-normal solution of caustic soda, 
 as it can be purchased to better advantage from any 
 chemical supply house. 
 
 Conducting the test. — With the pipette 50 cubic centi- 
 meters of the milk or cream is measured into the beaker or 
 cup. If the cream is thick, it may be slightly warmed. 
 The burette is filled with the tenth-normal caustic-soda 
 solution so that the lowest part of the meniscus is level 
 with the zero point on the graduations. The solution is 
 now run slowly from the burette into the milk or cream, 
 stirring with a glass rod at the same time. It will be 
 noticed that the alkali at once produces a pink color where 
 it strikes; this, however, disappears on stirring. As more 
 and more of the alkali is added, it will be noticed that the 
 pink color is slower in disappearing until finally it becomes 
 permanent for a time. Toward the end, the alkali should 
 be added drop by drop and the very first appearance of a 
 permanent faint pink is the signal that the neutral point 
 has been reached. This color, on account of absorption 
 of carbon dioxid from the air, will disappear after standing 
 a short time. The number of cubic cenlimeters of alkali 
 used can be learned by referring to the burette, remember- 
 ing that the reading is taken from the lowest point of the 
 meniscus. 
 
34: 
 
 The percentage of acidity is calculated by multiplying 
 
 the number of cubic centimeters of alkali solution used 
 
 by 0.009 and dividing by the number of cubic centimeters 
 
 of milk or cream taken, the quotient being multiplied by 
 
 100. Thus: 
 
 -d 4- t -jv c. c. alkaliX-009 K '' nn 
 
 Percentage of acidity = c . c , sample test ea X 100. 
 
 If 50 cubic centimeters of the sample required 10 cubic 
 centimeters of the alkali to neutralize, the percentage of 
 acidity would be 
 
 10> ^ 009 X100, or 0.18 per cent. 
 
 THE DETECTION OF PRESERVATIVES. 
 
 The preservatives usually met with are formaldehyde, 
 borax, and boric acid, and these are not difficult to 
 detect if care is used in conducting the tests. Until one 
 is thoroughly familiar with the tests it is a good plan to 
 run three samples together, one being the suspected 
 sample, one which is known to contain the preservative 
 looked for, and one known to be free from that preserva- 
 tive. 
 
 Formaldehyde. — There are two well-known tests for 
 detecting formaldehyde, one known as the Hehner test 
 and the other ?s the Leach test. 
 
 In the Hehner test, about 5 cubic centimeters of the 
 milk is placed in a 6 by \ inch test tube, and then about 
 the same quantity of concentrated sulphuric acid to which 
 a trace of ferric chlorid has been added. The acid is 
 allowed to run down the side of the test tube so as not to 
 mix with the milk. In a few minutes the presence of 
 formaldehyde will be indicated by a violent coloration at 
 the juncture of the milk and the acid. This must not be 
 confused with the charring of the milk by the acid. A 
 modification which avoids this charring is in use in the 
 dairy laboratory of the Bureau of Chemistry, United 
 States Department of Agriculture, the only difference 
 being that the sulphuric acid used is diluted with water 
 until it has a specific gravity of 1.8. 
 
 The Leach test, which is the more delicate test of the 
 two, is conducted as follows: To 10 cubic centimeters of 
 
35 
 
 the milk in a white teacup, 10 cubic centimeters of con- 
 centrated hydrochloric acid (specific gravity 1.2) contain- 
 ing one part by volume of a 10 per cent ferric-chlorid 
 solution per 500 parts is added and the mixture brought 
 slowly to a boil over a Bunsen burner. Formaldehyde 'is 
 indicated by a violent coloration varying in intensity with 
 the amount present. 
 
 Borax and boric acid. — Twenty-five cubic centimeters of 
 the milk is treated with limewater until a piece of red 
 litmus paper when immersed in it turns distinctly blue. 
 The mixture is evaporated to dryness in a small platinum 
 or porcelain dish and then burned to an ash. A few drops 
 (not too much) of hydrochloric acid are added to the ash, 
 and then a few drops of water. A strip of turmeric paper 
 is then dipped in the solution. When the turmeric paper 
 becomes dry, it will be of a cherry-red color if borax or 
 boric acid is present. The test is still more certain if , 
 when the paper is moistened with an alkaline solution, it 
 turns a dark-olive color. 
 
 A test for the detection of borax or boric acid which is in 
 use in the dairy laboratory of the Bureau of Chemistry, 
 United States Department of Agriculture, and by which 
 the ignition of the milk is avoided, is conducted as follows: 
 Ten cubic centimeters of the milk is mixed with 5 cubic 
 centimeters of hydrochloric acid in a white cup. A strip 
 of turmeric paper about 3 inches long is suspended in the 
 mixture so that at least 2 inches of the dry strip remain out 
 of the liquid. The dry portion of the paper will gradually 
 become moist by capillarity, and if borax or boric acid is 
 present the paper will take on a reddish-brown tint. If 
 only a trace of the preservative is present, several hours 
 may be required for this color to develop. A drop of am- 
 monia water on the red portion will produce an olive- 
 green color, which becomes lighter, and finally disappears 
 as the ammonia evaporates. 
 
36 
 
 CHEMICALS AND APPARATUS USED IN THE 
 CHEMICAL ANAYLSIS OF MILK AND CREAM. 
 
 Chemicals: 
 
 Ammonia water. 
 
 Borax or boric acid. 
 
 Caustic soda. 
 
 Caustic soda, tenth- 
 normal solution. 
 
 Caustic potash. 
 
 Corrosive sublimate. 
 
 Ether. 
 
 Ferric chlorid. 
 
 Formaldehyde. 
 
 Hydrochloric acid, con- 
 centrated. 
 
 Potassium bichromate. 
 
 Phenolphthalein. 
 
 Sulphuric acid, com- 
 mercial. 
 
 Sulphuric acid, pure 
 concentrated. 
 
 Litmus paper, blue. 
 
 Litmus paper, red. 
 
 Turmeric paper. 
 Apparatus: 
 
 Balance, analytical , 
 with weights. 
 
 Balance, cream test. 
 
 Balance, Westphal. 
 
 Babcock tester. 
 
 Beakers, 250 c. c. and 
 500 c. c. 
 
 Burner, Bunsen. 
 
 Burette, 50 c. c, gradu- 
 ated to tenths, with 
 i stopcock. 
 
 Apparatus — Continued . 
 
 Cylinder, for acid hy- 
 drometer. 
 
 Cylinder, for lactome- 
 ter. 
 
 Condenser for oven. 
 
 Desiccator. 
 
 Dishes, milk. 
 
 Dishes, evaporating, 
 either porcelain or 
 platinum. 
 
 Drying oven, double- 
 walled. 
 
 Forceps. 
 
 Hydrometer, acid. 
 
 Jars, sample. 
 
 Jars, stoneware. 
 
 Lactometer. 
 
 Measure, acid, 17.5 c. c. 
 
 Pipette, 17.6 c. c. 
 
 Pipette, 50 c. c. 
 
 Stirring rods, glass. 
 
 Support for burette. 
 
 Test bottles, Babcock, 
 for milk. 
 
 Test bottles, Babcock, 
 for cream. 
 
 Tongs, crucible. 
 
 Test tubes, 6 by inch. 
 
37 
 
 Comparison of metric and customary weights and measures. 
 
 Customary 
 
 weights and 
 
 measures. 
 
 Equivalents in 
 metric system. 
 
 Metric 
 
 weights and 
 
 measures. 
 
 Equivalents in 
 customary system. 
 
 
 2.54 centimeters. 
 0.3048 meter. 
 
 1 meter 
 
 39.37 inches. 
 
 lfoot 
 
 1.0936 yards. 
 0.155 square inch. 
 
 1 square inch. . 
 
 6.452 square centi- 
 
 1 square cen- 
 
 
 meters. 
 
 timeter. 
 
 
 1 square foot . . 
 
 9.29 square deci- 
 
 1 square met- 
 
 10.764 square feet. 
 
 
 meters. 
 
 er. 
 
 
 1 cubic inch... 
 
 16.387 cubic centi- 
 
 1 cubic centi- 
 
 0.061 cubic inch. 
 
 
 meters. 
 
 meter. 
 
 
 1 cubic foot . . . 
 
 0.0283 cubic meter. 
 
 1 cubic centi- 
 meter. 
 
 0.0338 fluid ounce. 
 
 1 fluid ounce . . 
 
 29.57 cubic centi- 
 
 1 cubic deci- 
 
 61.023 cubic inches. 
 
 
 meters. 
 
 meter. 
 
 
 1 quart 
 
 0.9464 liter. 
 
 lliter 
 
 1.0567 quarts. 
 
 
 3.7854 liters. 
 
 1 dekaliter . . . 
 
 2.6417 gallons. 
 
 
 64.8 milligrams. 
 
 
 15.43 grains. 
 
 1 ounce (av.).. 
 
 28.35 grams. 
 
 1 gram 
 
 0.035274 ounce. 
 
 1 pound (av.). 
 
 0.4536 kilogram. 
 
 1 kilogram. . . 
 
 2.2046 pounds (av.) 
 
 Comparison of Fahrenheit and Centigrade thermometer scales. 
 
 Fah- 
 
 Centi- 
 
 Fah- 
 
 Centi- 
 
 Fah- 
 
 Centi- 
 
 heit. 
 
 grade. 
 
 heit. 
 
 grade. 
 
 heit. 
 
 grade. 
 
 212 
 
 100. 00 
 
 183 
 
 83.89 
 
 154 
 
 67.78 
 
 211 
 
 99.44 
 
 182 
 
 83.33 
 
 153 
 
 67.22 
 
 210 
 
 98.89 
 
 181 
 
 82.78 
 
 152 
 
 66.67 
 
 209 
 
 98.33 
 
 180 
 
 82.22 
 
 151 
 
 66.11 
 
 208 
 
 97.78 
 
 179 
 
 81.67 
 
 150 
 
 65.55 
 
 207 
 
 97.22 
 
 178 " 
 
 81.11 
 
 149 
 
 65.00 
 
 206 
 
 96.67 
 
 177 
 
 80.55 
 
 148 
 
 64.44 
 
 205 
 
 96.11 
 
 176 
 
 80.00 
 
 147 
 
 63.89 
 
 . 204 
 
 95.55 
 
 175 
 
 79.44 
 
 146 
 
 63.33 
 
 203 
 
 95.00 
 
 174 
 
 78.89 
 
 145 
 
 62.78 
 
 202 
 
 94.44 
 
 173 
 
 78.33 
 
 144 
 
 62.22 
 
 201 
 
 93.89 
 
 172 
 
 77.78 
 
 143 
 
 61.67 
 
 200 
 
 93.33 
 
 171 
 
 77.22 
 
 142 
 
 61.11 
 
 199 
 
 92.78 
 
 170 
 
 76.67 
 
 141 
 
 60.55 
 
 198 
 
 92.22 
 
 169 
 
 76.11 
 
 140 
 
 60.00 
 
 197 
 
 91.67 
 
 168 
 
 75.55 
 
 139 
 
 59.44 
 
 196 
 
 91.11 
 
 167 
 
 75.00 
 
 138 
 
 58. 89 
 
 195 
 
 90.55 
 
 166 
 
 74.44 
 
 137 
 
 58.33 
 
 194 
 
 90.00 
 
 165 
 
 73.89 
 
 136 
 
 57.78 
 
 193 
 
 89. 44 
 
 164 
 
 72.33 
 
 135 
 
 57.22 
 
 192 
 
 88.89 
 
 163 
 
 72.78 
 
 134 
 
 56.67 
 
 191 
 
 88.33 
 
 162 
 
 71.22 
 
 133 
 
 56. 11 
 
 190 
 
 87.78 
 
 161 
 
 71.67 
 
 132 
 
 55.55 
 
 189 
 
 87.22 
 
 160 
 
 71.11 
 
 131 
 
 55.00 
 
 188 
 
 86„67 
 
 159 
 
 70.55 
 
 130 
 
 54.44 
 
 187 
 
 86.11 
 
 158 
 
 70.00 
 
 129 
 
 53. 89 
 
 186 
 
 85.55 
 
 157 
 
 69.44 
 
 128 
 
 53.33 
 
 185 
 
 85.00 
 
 156 
 
 68.89 
 
 127 
 
 52.78 
 
 184 
 
 84.44 
 
 155 
 
 68.33 
 
 126 
 
 52.22 
 
88 
 
 Fahrenheit and Centigrade thermometer scales — Continued. 
 
 Fah- 
 
 Centi- 
 
 Fah- 
 
 Centi- 
 
 Fah- 
 
 Centi- 
 
 ren- 
 heit. 
 
 grade. 
 
 ren- 
 heit. 
 
 grade. 
 
 ren- 
 heit. 
 
 grade. 
 
 125 
 
 51.67 
 
 82 
 
 27.78 
 
 39 
 
 3.89 
 
 124 
 
 51.11 
 
 81 
 
 27.22 
 
 38 
 
 3.33 
 
 123 
 
 50.55 
 
 80 
 
 26.67 
 
 37 
 
 2.78 
 
 122 
 
 50.00 
 
 79 
 
 26.11 
 
 36 
 
 2.22 
 
 121 
 
 49.44 
 
 78 
 
 25.55 
 
 35 
 
 1.67 
 
 120 
 
 48.89 
 
 77 
 
 25.00 
 
 34 
 
 1.11 
 
 119 
 
 48. 33 
 
 76 
 
 24.44 
 
 33 
 
 0.55 
 
 118 
 
 47.78 
 
 75 
 
 23.89 
 
 32 
 
 0.00 
 
 117 
 
 47.22 
 
 74 
 
 23. 33 
 
 31 
 
 - 0.55 
 
 116 
 
 46.67 
 
 73 
 
 22.78 
 
 30 
 
 - 1.11 
 
 115 
 
 46.11 
 
 72 
 
 22.22 
 
 29 
 
 - 1.67 
 
 114 
 
 45.55 
 
 71 
 
 2L67 
 
 28 
 
 - 2.22 
 
 113 
 
 45.00 
 
 70 
 
 21.11 
 
 27 
 
 - 2.78 
 
 112 
 
 44.44 
 
 69 
 
 20.55 
 
 26 
 
 - 3.33 
 
 111 
 
 43.89 
 
 68 
 
 20.00 
 
 25 
 
 - 3.89 
 
 110 
 
 43.33 
 
 67 
 
 19.44 
 
 24 
 
 - 4.44 
 
 109 
 
 42.78 
 
 66 
 
 18.89 
 
 23 
 
 - 5.00 
 
 108 
 
 42.22 
 
 65 
 
 18.33 
 
 22 
 
 - 5.55 
 
 107 
 
 41.67 
 
 64 
 
 17.78 
 
 21 
 
 - 6.11 
 
 106 
 
 41.11 
 
 63 
 
 17.22 
 
 20 
 
 - 6.67 ' 
 
 105 
 
 40.55 
 
 62 
 
 16.67 
 
 19 
 
 - 7.22 
 
 104 
 
 40.00 
 
 61 
 
 16.11 
 
 -18 
 
 - 7.78 
 
 103 
 
 39.44 
 
 60 
 
 15.55 
 
 17 
 
 - 8.33 
 
 102 
 
 38.89 
 
 59 
 
 15.00 
 
 16 
 
 - 8.89 
 
 101 
 
 38.33 
 
 58 
 
 14.44 
 
 15 
 
 - 9.44 
 
 100 
 
 37.78 
 
 57 
 
 13.89 
 
 14 
 
 -10.00 
 
 99 
 
 37.22 
 
 56 
 
 13.33 
 
 13 
 
 -10.55 
 
 98 
 
 36. 67 
 
 55 
 
 12.78 
 
 12 
 
 -11. 11 
 
 97 
 
 36.11 
 
 54 
 
 12.22 
 
 11 
 
 -11.67 
 
 96 
 
 35.55 
 
 53 
 
 11.67 
 
 10 
 
 -12.22 
 
 95 
 
 35.00 
 
 52 
 
 11.11 
 
 9 
 
 -12.78 
 
 94 
 
 34.44 
 
 51 
 
 10.55 
 
 8 
 
 -13.33 
 
 93 
 
 33.89 
 
 50 
 
 10.00 
 
 7 
 
 -13.89 
 
 92 
 
 33.33 
 
 49 
 
 9.44 
 
 6 
 
 -14. 44 
 
 91 
 
 32.78 
 
 48 
 
 8.89 
 
 5 
 
 -15.00 
 
 90 
 
 32.22 
 
 47 
 
 8.33 
 
 4 
 
 -15.55 
 
 89 
 
 31.67 
 
 46 
 
 7.78 
 
 3 
 
 -16. 11 
 
 88 
 
 31.11 
 
 45 
 
 7.22 
 
 2 
 
 -16.67 
 
 • 87 
 
 30.55 
 
 44 
 
 6.67 
 
 1 
 
 -17.22 
 
 86 
 
 30.00 
 
 43 
 
 6.11 
 
 
 
 -17.78 
 
 85 
 
 29.44 
 
 42 
 
 5.55 
 
 - 1 
 
 -18.33 
 
 84 
 
 28.89 
 
 41 
 
 5.00 
 
 - 2 
 
 -18.89 
 
 83 
 
 28.33 
 
 40 
 
 4.44 
 
 - 3 
 
 -19. 44 
 
 o 
 
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