ADVANCED CHEMICAL PHYSIOLOGY 331 



to Uffelmaim's reagent, 1 when the dark purple colour of the latter will 

 be changed to yellow. Test for lactic acid (see p. 230). 



III. The Fats Of Milk. Examine a thin film of milk under the 

 microscope, and note that the fat consists of small spherical bodies, 

 which are transparent and do not adhere to one another. 



The fat can be removed by shaking the milk with ether after the 

 addition to it of a few drops of weak NaOH solution. 



EXPERIMENT VII. To about 5 c.c. of milk in a test tube add two 

 drops of caustic soda (20 per cent.), and then about 5 c.c. of ether. 

 Cover the top of the tube with the thumb and shake the mixture, 

 occasionally lifting the thumb slightly to allow the vapour of ether to 

 escape. The ether will dissolve the fat, and the milk will become much 

 less opaque. By adding alkali, a certain amount of the caseinogen is 

 changed in its physical condition, so that the caseinogen films, which lie 

 between and thereby hold apart the fat globules, are diminished, and 

 consequently the fat globules are dissolved by ether. So long as they 

 are surrounded by caseinogen molecules they are not acted on by 

 ether. Not only alkalis, but also acids can effect this change. 



Colostrum. The milk which first appears during lactation is yellower 

 in colour and of higher specific gravity than that secreted later. On 

 boiling, it yields a distinct coagulum of albumin and globulin, and if 

 examined under the microscope it will be found to contain numerous 

 cells colostrum corpuscles in the protoplasm of which fat globules are 

 present. These cells are, in reality, secretory cells of the mammary 

 glands which have been extruded in the first portions of milk. 



IV. The Salts. EXPERIMENT VIII. THE DETECTION or PHOSPHATES 

 AND CHLORIDES. Add to 5 c.c. of protein-free whey half its bulk of nitric 

 acid and about twice its bulk of a solution of molybdate of ammonia 

 in nitric acid. Warm gently on the waterbath, and a yellow precipi- 

 tate of phosphate forms. In rennet or acid whey the phosphates may 

 be precipitated by ammoniated magnesium citrate. Filter. Dissolve 

 precipitate in nitric acid and heat as before with ammonium molybdate. 

 Show the presence of chlorides by means of silver nitrate test a 

 white precipitate insoluble in nitric acid, soluble in ammonia. 



EXPERIMENT IX. THE DETECTION OF CALCIUM SALTS. To some 

 whey, freed from protein by boiling, add a few drops of a solution of 

 potassium oxalate a white haze of calcium oxalate results. 



The Quantitative Determination of the various Bodies in Milk. 

 The methods here described can be employed for other fluids besides 

 milk. 



(1) The Percentage Of Water. A weighed quantity of milk is mixed 

 with a weighed quantity of fine quartz sand, which has been previously 

 heated to redness and then cooled in a desiccator. The weight of the 

 mixture is accurately determined, and it is then placed in a hot air bath 

 heated to 100 C. until all the water has been driven off and the weight 

 is constant. The amount of weight lost corresponds to the amount 

 of water which the sample of milk contains. 



(2) The Percentage Of Protein. Three gms. of milk are diluted with 

 four times its volume of distilled water, a few c.c. of a solution of sodium 

 chloride are added, and then a solution of tannic acid until all the protein 



1 This reagent is made by adding a trace of ferric chloride to a 1 per cent, 

 solution of carbolic acid. 



