THE MANAGER ON THE WORKS. 83 



nearest chemist to weigh 16 fluid ozs. (^ gallon) of the 

 sample, equal to 7,000 grains, or i Ib. avoirdupois, of clean 

 water. Since i e Twaddel = 0-005 m specific gravity, 

 each degree on 16 ozs. should increase the weight 

 7,000 x 0-005 = 35 grains. The following are the weights 

 for i to 10 liquid: 



indicates 3 strength. 



Suppose 16 ozs. of a liquor is found to weigh 7,210 

 grains. The hydrometer, if correct, should indicate 6. 

 If it registers any other figure, it is high or low, as the case 

 may be. No important decision should be based on the 

 reading of one hydrometer without corroboration. In a 

 larger works with a laboratory at command, the distillation 

 test would be used, because the specific gravity, even when 

 accurately ascertained, is not necessarily a correct indica- 

 tion of the proportion of ammonia present. 



The usual practice is to test the gas for one impurity 

 only, viz., sulphuretted hydrogen, and to leave the others 

 to take care of themselves. The gas is tested with lead 

 paper at the outlet of the purifiers, and a change is made 

 as soon as there is a sign of a foul test. The preparation 

 pf the lead solution is a simple matter, consisting of 



