Proceedings of the British Association. 99 



Section B. — Chemistry and Mineralogy. — Thursday. 



1 Notice of some Experiments upon a new Compound, called lodosul- 

 phuric Acid, upon the true constitution of Chlorochromic Acid, and up- 

 on Chromamide,' by Mr. Lyon Playfair. — The object which I proposed 

 to attain (said the writer) in commencing these experiments, was to dis- 

 cover some mode of isolating hyposulphurous acid. The experiments 

 are still unfinished, but I will here notice the results already obtained. 

 The best method of studying this subject appeared to be, to examine 

 the characters of those compounds which have an analogous constitu- 

 tion. Chlorochromic acid, according to MM. Walter and Regnault, 

 may be viewed as a compound of a hypothetical radical, " chromous 

 acid," united with an atom of chlorine. If hyposulphurous acid also be 

 considered as a combination of sulphurous acid with sulphur, both of 

 these acids would belong to the same class. But as the opinions of 

 chemists are much divided respecting the true rational composition of 

 chlorochromic acid, Mr. Playfair was anxious to ascertain which view 

 was the most correct. For this purpose, the behaviour of the solid com- 

 pound of chlorochromic acid and ammonia was examined. By various tests 

 applied to it, it did not appear to contain chromic acid. Now, if chlo- 

 rochromic acid be really a salt, the bichromate of the perchloride of 

 chromium, it ought to contain chromic acid ; in short, it seems to be 

 a peculiar compound, chromamide united with muriate of ammonia, and 

 analogous to the sulphamide of Regnault. Chlorosulphuric acid is 

 a compound which did not suit my purpose, on account of its never be- 

 ing obtained free from a foreign substance — the liquor of the Dutch 

 chemists. It therefore became necessary to discover a substance of an 

 analogous constitution, and which might be obtained with more ease, 

 and with more purity. For this purpose, two equivalents of iodine 

 were mixed with one of sulphite of lead, and the mixture was subjected 

 to distillation : a dark red fluid passed over. This method, however, does 

 not yield it of sufficient purity, being contaminated with iodine, which it 

 retains in solution. A better method, therefore, consists in dissolving 

 iodine in pyroxylic spirit, and sending a steam of sulphuric acid through 

 the solution until it be completely saturated. By evaporation, distilla- 

 tion, and allowing the substance thus procured to remain over sulphuric 

 acid, it may be obtained in a state of absolute purity ; its taste is ex- 

 tremely acid, and when it is dropped upon the cuticle, a disagreeable 

 obstinate sore is occasioned. I hoped that hyposulphurous acid might be 

 isolated in a similiar manner, and, upon trying the experiment, with the 

 substitution of sulphur for iodine, a yellow liquid of an acid taste, dis- 

 tilled over ; but it speedily decomposed with the deposition of sulphur. 

 A sufficient quantity was not obtained for analytical investigation. There 

 are many other modes suggested by the properties of iodosulphuric acid, 

 some of which I hope may succeed. I have merely stated the method 

 of obtaining iodosulphuric acid, but the same process is applicable to 



