Composite Samples of Milk. 169 



milk is added day by day, its color will become lighter 

 yellow. The complete sample should have a light straw 

 color; such samples are most easily mixed with acid 

 when tested. If more bi-chromate is used, the solution 

 of the casein in the acid is rendered difficult and re- 

 quires persistent shaking. Bi-chromate can be bought 

 at drug stores or from dairy supply dealers at about 30 

 cents a pound. Powdered bi-chromate of potash should 

 be ordered, and not crystals, as the latter dissolve only 

 slowly in the milk. Bi-chromate tablets containing the 

 correct quantity of preservative for a quart or pint sam- 

 ple have also been placed on the market and will be 

 found convenient. 



193. Corrosive sublimate tablets for composite 

 samples. During late years corrosive sublimate tablets 

 have come into general use in factories. These contain 

 mercuric chlorid with anilin color (rosanilin). 1 The 

 coloring matter is added to give a rose color to the sam- 

 ple preserved, thus showing that the milk is not fit for 

 consumption; the bi-chromate giving naturally a yellow 

 color to the milk, renders unnecessary the addition of 

 any special coloring matter. 



Compounds containing corrosive sublimate are violent 

 poisons and must always be handled with the greatest 

 care, lest they get into the hands of children or persons 

 not familiar with their poisonous properties; they will 

 preserve the milk longer than bi-chromate when applied 

 in sufficient quantities. 



Among other substances recommended for use in but- 

 ter or cheese factories as milk preservatives for com- 



1 Iowa experiment station, bulletins 9, 11, 32. 



