Part B. Composition.* 



6. (Classroom experiment.) The per cent of fat present in milk may readily be determ- 

 ined by the Babcock test. The principle of this test depends upon the fact that sulphuric acid 

 breaks up the solids of milk, other than fat. The action of sulphuric acid thus sets the fat free, 

 leaving it in such a condition that it can readily be separated by centrifugal force and col- 

 lected in the neck of a bottle, so graduated as to show by direct reading the per cent of fat 

 present. In taking a sample of milk, make sure that k is representative of the entire lot. The 

 sample may be measured with a milk pipette which holds 17.& cc. when filled to the mark on 

 the stem. After filling the pipette, place the point of it in the mouth of the test bottle, holding 

 both the test bottle and the pipette in a slightly inclined position. To the measured quantity 

 of milk in the test bottle add 17.5 cc. of sulphuric acid having a specific gravity of at least 1.8. 

 The test bottle should be held in an inclined position while pouring in the acid. This will 

 avoid having the acid drop through the body of the milk in the the bottle. By observ- 

 ing this precaution you will not char the milk or spill the acid. If the acid has been prop- 

 erly added there will be distinct layers of acid and milk in the test bottle, without any black 

 layer of partially mixed acid and milk between them. Now mix the acid and milk by giving 

 the test bottle a combined rotary and shaking motion. Do this carefully, so that no curd will 

 get into the neck of the bottle. The shaking should be continued until all particles or clots 

 of curd are entirely dissolved. The test bottles with the milk and acid properly mixed may 

 now be placed in the tester or centrifugal machine. The bottles should be arranged in pairs 

 at opposite sides of the center, so that they will balance when rotating. To produce a com- 

 plete separation of the fat. it will be necessary to whirl the bottles for five minutes. One 

 hundred revolutions of the crank per minute will run the small "Hand Tester" at about the 

 right speed. After whirling the bottles for five minutes, allow machine gradually to slow 

 down until it comes to rest. Hot water is now added to the contents of the bottles in order 

 to bring the fat up into the graduated position of the necks where it can readily be measured. 

 After adding hot water, whirl the bottles for one minute. If the test is properly made, there 

 will be a clearly defined column of fat in the necks of the bottles. If the reading is indistinct 

 on account of cloudiness of the fat, add a little hot water and whirl again. To read the per 

 cent of fat, hold the bottle up with the fat at a level with the eye and read the graduations 

 at each end of the column of fat. Each small division represents two-tenths of one per cent 



of fat. Each of the large spaces, numbered 1, 2, 3, 10, represent one per cent of fat. 



The difference between the readings indicates the percent of fat present in the milk. The per 

 cent of fat can also be read by counting .directly the number of spaces the column of fat 

 covers. 



(a) Record the per cent of fat present in the samples of milk tested. 



(b) How many pounds of fat would be present in 100 pounds of such milk as you tested? 



(c) Make a brief summary of the steps necessary in performing the test for fat present 

 in whole milk. 



Milk Use in the Body. 



1. Water 87% For water supply. 



2. Solids 13% 



1* Fat 4% For heat and fat. 



2 1 Solid, not fat 9% 



1» Sugar 5% For heat and fat. 



2' Protein 3.4% For muscle, tendon, hair. etc. 



1* Casein -....3.0% 



2* Albumen 0.4% 



3' Aih 0.6% For bone. 



159 



