CHEMICAL TESTS OF MILK 



207 



M 



— hydrogen peroxide, and from O^l to 1 o.c. of the peroxidase 



reagent (i.e. phenol-phthalein, guaiaciim, or paraphenylenedia- 

 mine). They obtained much more rehable results with the 

 addition of the sensitising agent. 



Eaw milk gives a positive reaction with these tests at 

 once ; milk heated to boiling gives no reaction. The exact 

 temperature at which the ferments' are destroyed so that no 

 reaction is obtained is usually given at about 80° C, but 

 slightly different results are recorded by different workers. 

 The killing of the enzymes depends not only upon the tem- 

 perature, but also upon the duration of heating, although the 

 temperature reached is the most important factor. 



The following table shows results obtained by the writer 

 as the mean of a number of experiments with different samples 

 of milk, using the above four tests : 



— =no reaction. 



+ = a positive reaction. 



+ a = positive reaction very slightly delayed. 



+ b— ,, ,, after about 30 seconds. 



p = a, partial and indefinite reaction : no reaction at first, but after 

 standing a few minutes some colour alteration occurs, but not the 

 true tint. 



Experiments were also carried out to ascertain what pro- 

 portion of raw milk must be present, added to the cooked milk^ 

 to cause the mixture to give the reactions of raw > milk. A 

 quantity of milk was heated to 80° C. for five ; minutes, and 



