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. 
