190 M. Stas on the Determination of Atomic Weights. 



phate of silver. The precipitate is completely washed out, and 

 twice recry stall ized from water. In order to avoid liberation of 

 bromine during the reduction, the decomposition must be 

 effected at 0°. 



Chlorate of silver cannot be obtained pure by dissolving oxide 

 or carbonate of silver in chloric acid ; chlorine must be made to 

 act directly on oxide or on carbonate of silver. If oxide or car- 

 bonate of silver be diffused in excess of saturated chlorine-water, 

 all the silver is changed into chloride of silver, and the liquid 

 contains, along with chlorine, free hypochlorous acid without a 

 trace of chloric or perchloric acids. If during constant agitation 

 chlorine be passed into water in which excess of oxide of silver is 

 diffused, hypochlorite of silver is formed, which is very easily soluble 

 in water, and in the presence of oxide or carbonate of silver can 

 be kept several days without change. But without this admix- 

 ture it is extremely unstable ; it decomposes into chloride and 

 perchlorate of silver. Perchloric acid is not formed in this case. 



Eight pounds of pure nitrate of silver were precipitated with 

 carbonate of potassium (prepared from cream of tartar) , washed 

 with water by decantation for fourteen days, diffused in water, 

 and treated with chlorine for 1J hour in a flask which was kept 

 in constant agitation. (The manganese used for the chlorine 

 was freed from nitrates by being boiled with dilute sulphuric 

 acid.) The agitation was continued until the cessation of 

 the smell of hypochlorous acid, and the carbonate of silver was 

 now washed completely pure. Only in this way could the car- 

 bonate of silver be gradually freed from alkali. It was then dif- 

 fused in water, again treated with chlorine, whereby a solution of 

 hypochlorite of silver was obtained by decantation, which was 

 then left in the dark to spontaneous decomposition. By evapo- 

 ration, pure chlorate of silver was obtained. As the action was 

 only carried so far that not more than two-fifths of the theore- 

 tical quantity of chlorate of silver was obtained, the formation of 

 perchlorate of silver was excluded. It was only after the third 

 treatment of carbonate of silver with chlorine that the chlorate 

 of silver obtained was perfectly free from potassium. Pure 

 chlorate of silver is quite permanent in the air. It only attracts 

 moisture in case it contains some hygroscopic perchlorate of 

 silver. The reduction must be effected by a solution of sulphu- 

 rous acid at 0°. 



The Reagents. — The distilled water was freed from organic 

 substances by being distilled with manganate of potassium. The 

 first portions of the distillate were removed. If rain-water was 

 used, a considerable quantity of ammonia passed over. In that 

 case the water had to be distilled a second time, with the addition 

 of some acid sulphate of potassium or sodium. For very accu- 



