The Babcock Test. 5 



^ 



73. Testing the strength of acid. The strength of 

 the acid can be easily tested by the use of a balance like 

 that shown in fig. 34 (91). A dry test bottle is weighed,^ 

 and then filled with acid exactly to the zero mark, or 

 to any ether particular line of the scale. It is then 

 again weighed accurately; the difference between these 

 two weights will give the weight of the acid in the bot- 

 tle. The bottle is then emptied and rinsed thoroughly 

 with water (until the water has no longer an acid 

 taste) ; it is then filled with water to the same line as 

 before and weighed; the difference between this weight 

 and that of the empty bottle gives the weight of the 

 same volume of water as that of the acid weighed. The 

 specific gravity of the acid is obtained by dividing the 

 weight of the acid by the weight of the water. If the 

 quotient comes between 1.82 and 1.83 the strength of 

 the acid is correct. The outside of the test bottle should 

 always be wiped dry before the liquids are weighed in 

 it. Unless great care is taken in measuring the acid 

 and the water, and in weighing both these and the 

 test bottle, the results obtained will not be trustworthy. 



74. Acid that is a little too strong can be used by 

 taking less than the required amount for each test, e. g., 

 about 15 cc. Operators are warned against reducing 

 the strength of the acid by adding water to it, as acci- 

 dents may easily occur when this is done. A too strong 

 acid can, if desired, be weakened by simply leaving the 

 bottle uncorked for a time, Or by pouring the acid into 

 a bottle containing a small quantity of water. In the 

 latter case the first portions of acid should be added 

 carefully, a little at a time, shaking the bottle after 



