54 QUESTIONS AND ANSWERS 



What character of water should be used? 



Soft water should be used when possible, but any- 

 ordinary good water will serve. One or two cubic 

 centimeters of sulphuric acid added to the water 

 used for the final filling will aid materially in giv- 

 ing a clear fat column, especially if the water is 

 hard. 



Why does the mixture of milk and acid become 

 hot? 



Sulphuric acid, combining with the water of 

 milk, generates most of the heat. Some heat is 

 developed by the action of the acid on the milk 

 solids. 



Why does the mixture turn dark? 



The acid burns or oxidizes the milk solids, which 

 contain carbon. The darkening process is similar 

 to burnt wood, becoming dark when burned in air. 



If the acid does not completely dissolve the casein 

 in composite samples, how may the difficulty 

 be overcome? 



1. Have the acid and milk at a slightly higher 

 temperature than usual at the time of mixing. 



2. Use a larger amount of acid than ordinarily. 



3. Shake the samples for a longer time than 

 usual before placing them in the machines. 



If the temperature of the fat is not right when 

 through whirling, how may it be corrected? 



1. If too hot, allow the bottles to stand a short 

 time at room temperature. 



2. If too cold, place the bottles in hot water. 



