MILK INSPECTION 189, 



shaking gently with a mixture of- ether and petrolic ether. The 

 mixture is made of equal parts of ether and petrolic ether and 

 equal volumes of acidulated milk and ether mixture are taken. 

 Then, after standing for several hours, the upper ethereal solution 

 is poured off and the remaining liquid is evaporated in a porcelain 

 evaporating dish. Add, to the residue on the white evaporating 

 dish, a few drops of water and, if salicylic acid is present, a drop of 

 ferric chloride solution will produce a violet or purple color on being 

 added to the solution. 



It sometimes happens that it is desirable to determine whether 

 milk has been heated to 176 F. or over. To test this (Storch's. 

 test), add to 5 cubic centimeters of milk 2 drops of a freshly pre- 

 pared 2 per cent, solution of Paraphenylenediamine hydrochloride 

 or meta-di-amido-benzene chloride, and then one drop of a 2 per- 

 cent, solution of hydrogen peroxide. Unheated milk gives a blue 

 color when thus treated, but milk heated to 176 F., or over, gives 

 no color.* This test depends upon the action of the ferments or- 

 peroxidases, normally present in milk, inducing oxidation of meta- 

 di-amido-benzene by means of hydrogen dioxide with the production. 

 of a blue color. 



When milk is heated to, or over (8o° C.) 176 F., the ferments.- 

 are killed and the blue color is absent. 



According to different authorities the temperature of the milk, . 

 at which the blue color disappears, varies from 75" C. (176 F.) 

 for 2 minutes (Storch), to 8o° C. (see p. 216). 



The simplest test for preservatives is to place some milk in a 

 warm place (at temperature of 8o u to 90 F.) in a corked, clean 

 bottle for 24 hours. If it does not sour or curdle, the addition of 

 a preservative may properly be suspected, unless the milk has been 



* If the milk at once becomes indigo blue, or the whey violet or reddish brown, 

 then the milk has not been heated — or not heated above 172.5° F. If the milk 

 ■turns bluish gray immediately, or within one-half minute, it has been heated to. 

 174. 2° F. The test should be done on an unheated specimen along with that on L 

 the suspected sample. 



