Calibrating the Glassware 99 



the fat is measured. With this last it is possible 

 to read easily to .01 of 1 per cent. 



The fat in the solid milk products, as butter and 

 cheese, may also be conveniently determined by the 

 Babcock test. Since butter or cheese cannot be 

 measured, it is necessary that the sample to be 

 tested be weighed. Balances sensitive to .1 of a 

 gram are sufficiently delicate. Either 18 grams of 

 the substance may be weighed, in which case the 

 percentage of fa,t is read directly from the bottle ; 

 or, what is more convenient, any amount from 4 to 

 8 grams may be taken. In the latter case, the 

 observed reading of fat bears the same proportion 

 to the percentage of fat in the substance taken that 

 the weight of the sample taken bears to 18 ; and the 

 percentage is found by multiplying the observed read- 

 ing by 18 and dividing the result by the weight of 

 the sample taken. 



In testing butter and cheese, it is convenient to 

 use the bottles with detachable necks. A little 

 water should be added to the bottle before the 

 acid is put in, to aid in the solution of cheese. 



Calibration of glassware. The correctness of the 

 graduation of the glassware may be tested with more 

 or less accuracy according to the means at hand. 

 The bottles are all graduated on the assumption 

 that the tubes are of uniform caliber. The and 

 10 points are determined experimentally, and the in- 

 tervening space equally divided into 50 divisions 

 with a dividing engine. The spaces should, there- 

 fore, be of uniform size, and if the eye can detect 



