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 
Sowvhlet’s Test.—One-half ¢.c. of a 20 per cent. cal- 
cium chloride solution is mixed with about 380 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. 
