86 Proceedings nf the Royal Irish Academij. 



XIT. — Ox THE YoLL'iTETErc EsTiMATiox OF CHROiirrir. By Thomas 



Batlet. 



[Read, June 25, 1877-] 



The well-known property possessed, by the peroxides of Mckel and 

 Cobalt, of decomposing Sodic Hypochlorite with evolution of oxygen, 

 can be made nse of for the estimation of Chromium, as follows : — 



The Chromium salt is mixed with -1 or "2 gram, of Cobalt in solu- 

 tion, and then with excess of Potash or Soda. To this mixture, excess 

 of cold NaClO, free from Chlorate, is added. On warming the solution, 

 the whole of the Chromium is at once oxidised to the state of Chromate, 

 and peroxide of Cobalt (C03O0) is formed at the same time. The solu- 

 tion is then allowed to stand in a warm place for a few hoiirs, in order 

 that the excess of Hypochlorite may be [decomposed by the Cobaltic 

 peroxide. Hydrochloric acid is afterwards added until a few drops 

 only are in excess ; the solution is then boiled until all the Chlorine 

 is expelled. The solution then contains the Cobalt as protochloride, 

 and the Chromium as alkaline Chromate ; when cold it is mixed with 

 Potassic Iodide and Hydrochloric acid, and the liberated Iodine is esti- 

 mated by Soclie Thiosulphate solution. 25 cc of a standard solution of 

 Bichromate of Potassium, equivalent to ■?A'll gram, of Iodine, were 

 reduced to Chromous Chloride by Hydi'ochloric acid and Alcohol, and 

 then estimated by the above method. The following results were ob- 

 tained : — 



Of Iodine. 



Theory. Found. 



•3171 gram. -3212 gram. 



In a second experiment : 



•3171 „ -3171 „ 



The results contained in this Paper were obtained in the Laboratory 

 of the Eoyal College of Science. 



