The Babcock Test. 67 



76. Strength of sulfuric acid. The relation between 

 the strength of sulfuric acid and its specific gravity 

 will be seen from the following table: 



Specific Gravity of Sulfuric Acid of Different Strength. 



Specific Gravity Sulfuric Acid 



(1PC, water UC). (H Z SOJ. 



1.841 97 per cent. 



1.840 96 



1.839 95 



1.837 94 



1.834 93 



1.830 92 



1.825 91 



1.820 % 



1.815 89 



1.808 88 



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

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

 acid (H 2 S0 4 ) ; 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 useless for the purpose 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 

 1.83, they would sink to a point much 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 by the color of the fat 



