The Babcock Test. 67 



It will be noticed that the sulfuric acid to be used in 

 the Babcock test should contain 90 to 92 per cent, of 

 acid (H2SO4) ; slightly weaker or stronger acid than 

 this may, as previously stated, be used by varying the 

 quantity of acid taken for each test according to the 

 strength of the acid, but successful tests cannot, as a 

 rule, be made with acid weaker than 89 per cent, or 

 stronger than 95 per cent. 



77. The Swedish acid tester is a small hydrometer, intended 

 to show whether the acid used in the Babcock test is of the cor- 

 rect strength. An examination of these testers will show that 

 they are practically useles.i for the piirpose intended, from the 

 fact that they are not sufficiently sensitive; while the testers 

 examined were found to sink to the line marked Correct on the 

 scale, when lowered into sulfuric acid of a specific gravity of 

 l.^.'l, they would sink to a point duch nearer the same 'mark, 

 than to the lines marked Too strong or Too weak, respectively, 

 when lowered into either too strong or too weak acid. 



78. The color of the fat column an index to the 



strength of the acid used. The strength of the acid 



is indicated to a certain extent bj' the color of the fat 



which separates in the neck of the test bottle when milk 



is tested. If the directions given for making the tests 



are carefully followed, the fat separated out will be of 



a golden yellow color. If the fat is light colored or 



whitish, it generally indicates that the acid is too weak, 



and a dark colored fat, with a layer of black material 



beneath it, shows that the acid is too strong, provided 



the temperature of both milk and acid is about 70°. 



[For influence of temperature, see next paragraph.] 



The acid used in the test is not of sufficient strength 



to appreciably attack the fat at ordinary temperatures 



of testing, but a variation in the strength of the acid 



