68 Testing Milk and Its Products. 



which separates in the neck of the test bottle when milk 

 is tested. If the directions given for making the tests 

 are carefully followed, 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 temperature, see next paragraph.] 

 The acid used in the test is not of sufficient strength 

 to appreciably attack the fat at ordinary temperatures 

 of testing, but a variation in the strength of the acid 

 or in the temperature of the milk influences the in- 

 tensity 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 into each of three bottles, A, B and C. Place A in 

 iced water, and C in warm water, leaving bottle B at 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 the tests in 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 T> (weak acid) is much lighter colored than that in C (warm 

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

 (normal temperature) and E (normal acid) is somewhere be- 

 tween that of these two series. 



