68 Testing Milk and Its Products. 



lowed, the fat separated out will be of a golden yellow 

 color. If the fat is light colored or whitish, it generally 

 indicates that the acid is too weak, and a dark colored 

 fat, with a layer of black material beneath it, shows that 

 the acid is too strong, provided the temperature of both 

 milk and acid is about 70. [For influence of tempera- 

 ture, see next paragraph.] 



The strength of the acid used in the test is not suf- 

 ficient at ordinary temperatures of testing to appreciably 

 dissolve the fat, but a variation in the strength of the 

 acid or in the temperature of the milk influences the 

 intensity of the action of the acid on the fat, as shown in 

 the color of the fat obtained. 



The following experiment shows the relation between 

 the strength of the acid, the temperature of the milk, 

 and the color of the fat: 



First: From a sample of milk, measure the usual quantity 

 for testing iuto each of three bottles, A, B and C. Place A in 

 ice water, and C in warm water, having bottle B at the ordi- 

 nary temperature. After the bottles have been left for ten min- 

 utes under these conditions, add the normal quantity of acid 

 to each and proceed with the test in the ordinary manner. 



Second: Measure some of the same milk into three other 

 bottles, D, E and F. Into test bottle D pour the usual amount 

 of rather weak acid; add the same amount of acid of normal 

 strength (1.82-1.83) to bottle E, and add 17.5 cc. of a still 

 stronger acid (concentrated sulfuric acid, sp. gr. 1.84), in test 

 bottle F; complete these tests ill the usual way. 



On the completion of the preceding six tests the operator will 

 notice that the fat in the necks of test bottles A (cold milk] and 

 D (weak acid] is much lighter colored than that in C (warm 

 milk] and F (strong acid], and that the color of the fat in B 

 (normal temperature} and E (normal acid] is somewhere 

 between that of these two series. 



