360 FOOD AND NUTRITION 



18 to 45 per cent. fat. Much attention is given to the amount 

 of fat in milk, and it is commonly supposed to be a safe guide 

 in judging the quality of the milk. But it must be remem- 

 bered that there are other food materials in milk besides fat. 

 Milk also contains about 3.2 per cent, protein and 5 per cent, 

 carbohydrate, MILK SUGAR (see Pig. 248) . But in general, if the 

 fat percentage is low, the other constituents are likely to be low 

 also. But there is much food value in SKIM MILK. Skim milk 

 contains the valuable protein. One might purchase skim 

 milk and make up for the fat it lacks by purchasing a cheaper 

 fat as oleomargarine. Most states and cities have laws fixing 

 the lowest amount of fat that milk can contain to be sold as 

 whole milk. These laws usually place the lowest limit at 3 per 

 cent, or 3.5 per cent, of fat. 



401. The Babcock Method of Determining Fat in Milk. 

 The method of the test is as follows: A certain amount of 

 milk is placed in a test bottle having a graduated neck. Con- 

 centrated sulphuric acid is then added to the milk and the 

 mixture is well shaken. The sulphuric acid dissolves all of 

 the constituents of the milk except the fat. The bottle and 

 the mixture are then placed in the Babcock machine in which 

 they are whirled at a high rate of speed. The fat, being the 

 lighter, rises to the surface of the mixture in the bottle and by 

 getting the fat into the graduated neck the percentage of fat 

 may be read directly. 



Exercise 81. The Babcock Test 



(1) Mix the milk to be tested by pouring it from one bottle to 

 another several times. This mixes the cream with the remainder 

 of the milk. (2) By means of a milk pipette (Fig. 250) draw 

 17.6 c.c. of the mixed milk and place it in an 8- or 10-per cent, milk 

 bottle (Fig. 250). Do not insert the tip of the pipette so far into 

 the milk bottle that the milk is spilled as the air escapes from the 

 bottle. Draw out another 17.6 c.c. portion and place it in another 

 bottle. (3) Place 17.5 c.c. of concentrated sulphuric acid in the acid 

 measure (Fig. 250) using care to avoid spilling any of* the acid on the 

 hands or clothing. Now carefully pour the concentrated acid into 

 the test bottle of milk containing the 17.6 c.c. of milk allowing the 



