DETECTION OF ADULTERATION 49 



mining whether a given sample has been thus heated. 

 In most cases the action of the enzym is in- 

 dicated by the production of a deep blue, no 

 color change occurring when the enzym has been 

 heated. Hydrogen peroxid is commonly em- 

 ployed for furnishing the oxygen. A considerable 

 number of substances have been found to be 

 susceptible to oxidation under the influence of 

 the milk enzyms. Benzene derivatives, com- 

 monly used as photographic developers are 

 especially susceptible. Guaiacum was first used. 



Arnold's Method. — A solution of guaiacum in 

 acetone is, according to Arnold and Menzel 

 better than the ordinary tincture. The test is 

 applied by adding to a small amount of the sample 

 in a test-tube, about lo drops of the guaiacum 

 solution, to which a drop or two of hydrogen 

 peroxid solution has just been added, so that the 

 reagent will float on the milk. If the sample 

 has not been heated above 80°, the point of 

 contact of the liquids will show a deep blue ring. 



As guaiacum is liable to changes both in the 

 solid form and in solution it is important to de- 

 termine if the reagent is sensitive to raw milk, 

 hence a control test should aways be made. 

 Other reagents are now available which are, in the 

 main, more trustworthy. 



Dupouy's Method. — In this method, 1-4 diam- 

 inobenzene is used. The reagent is dissolved in 



