POWDERED LITMUS MILK 



A PRODUCT OF CONSTANT QUALITY AND COLOR WHICH CAN 

 BE MADE IN ANY LABORATORY 



HERBERT W. HAMILTON 



Sanitary Research Laboratories, Massachzisetts Institute of Technology 



Received for publication June 7, 1920 



The wide use of litmus milk as a culture medium, due to its 

 great value in the differentiation of bacteria, has led to the 

 development of various casein media as substitutes. Canned 

 milk has also been used with varying degrees of success. This 

 paper presents a formula which insures a standard product. 



Present practice requires the purchase of milk, whole or 

 skimmed. In the former case the fat has to be removed. When 

 the milk is finally prepared it is often found to be too acid and 

 readjustment is required. After such a readjustment is made 

 the effect of sterilization of the milk is often detrimental. But 

 what is more important is the varying color of the milk with 

 every batch. It was with this fact in view that the present 

 foraiula was developed. 



PREPARATION OF THE INDICATOR 



1. The dye should be a blue azolitmin, as free as possible 

 from the red dye. This may be prepared by extracting litmus 

 cubes with boiling distilled water and decanting off the clear 

 solution. The liquid is evaporated to a thin paste over a free 

 flame and treated with an excess of glacial acetic acid. The 

 evaporation is now carried to dryness on a water bath. A 

 quantity of 95 per cent alcohol is added and the whole trans- 

 ferred to a filter. The residue is washed several times with 

 alcohol. The filtrate is discarded. Should the residue be left 

 reddish a drop or two of sodium hydroxide solution will restore 



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