- CORRECT 



66 Testing Milk and Its Products. 



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 SO 4 ); slightly weaker or stronger acid than this 

 may, as previously stated, be used by adjust- 

 ing the quantity of acid taken for each test to 

 the strength of the acid, but successful tests 

 cannot be made with acid weaker than 89 per 

 cent, or stronger than 95 per cent. 

 (TOO STRONG 77. The Swedish acid tester (Fig. 24) is a 

 small hydrometer, intended to show whether 

 the acid to be used in the Babcock test is of 

 the correct strength. We have examined a 

 number of these testers, and have found them 

 practically useless for the purpose intended. 

 The reason for this is that the instrument is 

 not sufficiently sensitive; while the testers ex- 

 amined 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, 

 Swedish add than to the lines marked Too strong or Too 

 weak, respectively, when lowered into either 

 too strong or too weak acid. 



An examination of the proportionate parts of these testers 

 shows that such must be the case: The total weight of the 

 testers varies between 7 and 8 grams; the diameter of the stem 

 is nearly 5 millimeters, and the distance between the two lines 

 marked Too strong and Too weak is 13.5 millimeters. A good 

 hydrometer, such as used in chemical laboratories for determin- 

 ing the specific gravity of liquids of 1.8 to 2.0, weighs about 75 

 grams; the diameter of the stem is 6 mm., and the distance 

 between the 1.82 and 1.84 marks on the scale is 15.5 mm.; these 

 limits may be taken to represent too weak and too strong acid, 



