1 MILK 99 



in the presence of casein, that is in milk, the colour is a beautiful 

 indigo blue. 



To carry out the test about 5 c.c. of milk are put into a test- 

 tube and one drop of a 0'2 per cent, solution of hydrogen 

 peroxide is added from a dropping bottle, also two drops of a 



2 per cent, solution of paraphenylene diamine, also from a 

 dropping bottle. 1 The test-tube is then well shaken, and if 

 the milk has not been heated above 78 C.. or if not heated at 

 all, then an intense blue coloration is produced. If at once 

 or after half a minute 



the milk becomes t . 



bluish-grey, it indi- f *< 



cates that it has been 



*> * i * **% S\rfw * 



heated to a tempera- , s l " 1% J - \ % j ** *^ * * 



ture of 78-80 C. ^ 'I* +"i* '.*' 



When the colour of * ^* * f*lf 



the milk is un- "?/-* f**^- ****> h 1 ** A 

 changed after addi- w - %! *>'< ^. I v * **'* v ** * r * - 



tion of the reagents, '\;J**^ A- 



it may be concluded * t * * * 



that the heating has >f * * $. 



exceeded 80 C. : ^ '\ fr 



Storch's test has . _ * / ^* fyjf * "^ \ 

 shown itself to be 

 the most reliable of 



all the methods pro- FIG. 48. 1 : 80. Barthel photo. Microphotograph 

 posed for distinguish- of Leucocytes in Separator Slime. 



ing heated from tin- 

 heated milk. All the so-called improvements which have been 

 advocated by other chemists have proved to be of no benefit, 

 often indeed the opposite. 



If during the pasteurisation of the milk the temperature 

 falls below 80 C. for a time, then the whole of the milk 

 after being mixed reacts to Storch's test. The sensibility of 

 the test is so great that the admixture of 10 per cent, of milk 

 which has only been heated to 78 C., suffices to make the whole 

 volume of milk react to the test. 



Reference will be made to the use of this test for proving 

 whether cream which is to be used in making butter has been 



1 Paraphenylene diamine solution does not usually remain active for longer 

 than two months, so it must be renewed within that time. 



H 2 



