50 MILK 



water (a weak solution will suffice), a few drops 

 added to the sample, then a few drops of hydrogen 

 dioxid solution, and the liquids shaken gently. 

 Milk that has not been heated above 80° gives 

 immediately a bright blue. Milk that has been 

 heated above this temperature shows no color 

 change at first but may slowly acquire a bluish 

 tint. This test is much in favor, but it is open 

 to the objection that the solution of the reagent 

 does not keep more than few hours, and even in 

 the solid state some commercial samples soon 

 decompose. 



Benzidin Method. — Wilkinson and Peters sug- 

 gested this reagent, employing a solution of it 

 with a few drops of acetic acid followed as usual 

 by the oxidizing agent. Leffmann finds that 

 the commercial benzidin hydrochlorid (furnished 

 for volumetric estimation of sulfates) acts satis- 

 factorily without acetic aicd. 



Wilkinson and Peters' test is performed simi- 

 larly to those just described, and has a similar 

 significance. They give experiments to show 

 that the method is rather more delicate than 

 with diamino-benzene or guaiacum. The solu- 

 tion of the benzidin compound keeps better. 

 They found that milk heated to 77° had lost its 

 reactivity to guaiacum but retained reactivity 

 to the other two reagents. Heated to 78° the 

 reactivity was also lost to these. 



