ON MILK AND MILK-TESTING 49 



2. Small quantities are used. 



3. Can be secured in a convenient tablet form. 



What are the disadvantages of corrosive sublimate? 



1. It is a deadly poison. 



2. In excess it hardens milk casein so that the 

 acid does not dissolve it so readily. 



How much preservative should be used? 



Enough to keep milk or cream sweet until tested. 

 Usually one to two tablets of mercuric chlorid will 

 preserve one-half pint for two weeks. Of formalin 

 one-half c. c. should preserve the same sample for 

 two weeks. If bichromate of potash is used, add 

 enough of it to give the milk a lemon-yellow color. 

 About 15 grains is usually sufficient to keep a pint 

 of milk for two weeks. 



What are the advantages of formalin? 



1. It is a good antiseptic. 



2. It is in liquid form. 



3. It is not a violent poison. 



What are the disadvantages of formalin? 



It tends to harden casein so that sulphuric acid 

 does not readily dissolve it. 



What are the qualities of potassium bichromate as 

 a preservative? 



1. It is inexpensive. 



2. It is not a violent poison. 



3. It colors the milk yellow and the quantity 

 necessary to add can be determined by the depth 

 of color of the solution. 



