250 CHLORIMETRY. 



to ebullition for a quarter of an hour, the flask closed 

 air-tight, and allowed to cool; the solution is poured 

 off, the residual copper washed, first with very dilute 

 hydrochloric acid, then with pure water, dried, and 

 weighed. 2 equivs. of copper = 63.4 parts, require for 

 their conversion into subchloride, 1 equiv. = 71 parts 

 of chlorine. 



Then 63.4 : 71 as the amount of copper dissolved is 

 to x (the amount of chlorine sought). 



1.22 grms. of pure binoxide of manganese evolve 

 1.00 grm. of chlorine, and therefore are capable of 

 effecting the solution of 1.78 grms. of copper. 



123. CHLORIMETRY. 



The "bleaching powder'' 1 of commerce is a variable 

 mixture of bypochlorite of lime and chloride of cal- 

 cium, with hydrate of lime. When treated with an 

 acid, it evolves the whole of the chlorine in a free 

 state. In order to determine its value, i. e., the amount 

 of available chlorine which it contains, different 

 methods are employed. 



I. Fourteen grms. of pure arsenious acid are dis- 

 solved in solution of potassa, and so much water added 



Fig. 35. 



