22 DAIRY CHEMISTRY 



all of the foam and light material, as leaves, collect 

 in the center. 



22. The Acid. Commercial sulphuric acid (sp. 

 gr. 1.82), about 90 per cent strength, is used. 

 One pound of acid will make about twenty tests. 

 When the acid is too strong, the fat presents a 

 blackened and charred appearance ; if too weak, par- 

 ticles of undissolved casein appear immediately 

 below the fat line. When just right, the fat sepa- 

 rates in a distinct and well-defined layer and looks 

 like butter. If the acid is too strong, and chars the 

 fat, use a smaller amount in making the test. In 

 that case, if the test is not satisfactory, the acid 

 should be exchanged for a new lot. Do not attempt 

 to dilute the acid with water. If the acid is too 

 weak, a larger amount than 17.6 cc. may give satis- 

 factory results. The strength of the acid can be 

 determined by using a hydrometer for heavy liquids, 

 and noting the depth to which the spindle sinks in 

 the acid. To obtain the best results, the acid should 

 vary but little from 1.82 specific gravity or 90 per 

 cent strength. 



STRENGTH OF ACID SPECIFIC GRAVITY 



88 1.808 



89 1.815 



90 1.820 



91 ; 1.825 



92 1.830 



93 1.834 



94 1.837 



95 1.839 



