METHODS OF EXAMINING MILK 247 



In the first formula W is the per cent, of water in 

 the unadulterated sample; w is the per cent, of water 

 in the adulterated sample; R is the per cent, of solids 

 not fat in the unadulterated sample ; r is the per cent, of 

 solids not fat in the adulterated sample; M represents 

 the quantity of water to 100 grammes of milk. 



In the second formula F is the per cent, of fat in the 

 unadulterated sample; f is the per cent, of fat in the 

 adulterated sample; R is the per cent, of solids not fat 

 in the unadulterated sample ; r is the per cent, of solids 

 not fat in the adulterated sample, and E represents the 

 per cent, of fat removed by skimming. 



TESTS FOR NITRATES AND NITRITES 



Soachlet's Test. One-half c.c. of a 20 per cent, cal- 

 cium chloride solution is mixed with about 30 c.c. of milk 

 and the mixture is boiled and filtered. A 2 per cent, 

 solution of diphenylamin in chemically pure sulphuric 

 acid is added in sufficient quantity to some of the filtrate 

 to make it milky. Chemically pure sulphuric acid is then 

 poured slowly down the side of the test tube so that it 

 forms a layer at the bottom. If nitrates or nitrites are 

 present a blue zone is formed at the point where the two 

 fluids come in contact. This test will detect one part of 

 nitrates in 100,000; most farm water contains one part 

 in 10,000 (Jensen). 



A modification of this test is described by Rievel as 

 follows : Place a small quantity of milk in a test tube and 

 then pour in slowly, so that the two fluids will not mix, 

 a solution of diphenylamin in chemically pure sulphuric 

 acid (1 : 10) . If minute traces of nitrites are present a 

 blue ring will form at the point of contact of the two 

 fluids. 



