70 Testing Milk and Its Products. 



bubbles that sometimes obscure the upper line (menis- 

 cus) of the fat, making indistinct the point from which 

 to measure it, is generally caused by the action of the 

 acid on the carbonates in hard water. The carbonic 

 acid gas liberated from such water by the sulfuric acid 

 is more or less held by the viscid fat and produces a 

 layer of foam on its surface. If clean soft water cannot 

 be obtained for this purpose, hard water may be used, by 

 adding a few drops of sulfuric acid to the water before 

 it is heated, thus causing the carbonic acid to be ex- 

 pelled. By simply boiling, many hard waters will be 

 rendered soft and adapted to use in the Babcock test, 

 as most of the carbonates which cause this foaming are 

 thereby precipitated. 



If the test has been completed, and a layer of foam 

 appears over the fat, it may be destroyed by adding a 

 drop or two of alcohol. If this is done, the fat column 

 should be read at once after the alcohol is added, as 

 the latter will soon unite with the fat and increase its 

 volume. 



81. Reservoir for water. When only a few tests are 

 made at one time, hot water can be added with the 17.6 

 cc. pipette. If many tests are made, the water is more 

 conveniently and quickly filled into the test bottles by 

 drawing it from a small copper reservoir or tin pail 

 suspended over the testing machine. 1 The flow of water 

 through a rubber tube connected with the reservoir, is 

 regulated by means of a pinch cock. The water must 

 be hot when added to the test bottles so as to keep the 



1 Ordinary tinware will soon rust when water is left standing in 

 it, and copper reservoirs are therefore more economical. 



