410 -Dr. Thomson on [June, 



Gehlen, are of such a nature as to exhibit the real composition 

 of this substance. Indeed a good analytical result was at that 

 time unlikely ; not merely because we were ignorant of the true 

 nature of the compound, but because the curious suite of changes 

 which it undergoes, when left in contact with water, could not 

 be understood till the nature and properties of hyposulphurous 

 acid had been investigated. 



Before proceeding to the analysis of chloride of sulphur, 

 which is to constitute the subject of this paper, I beg leave to 

 return my thanks to Mr. Herschell for his paper on the hyposul- 

 phurous acid, published in the first volume of the Edinburgh 

 Philosophical Journal. It is an excellent paper, and does great 

 credit to the author both as an experimenter and a philosopher. 

 I was myself aware of a good many of the facts contained in 

 that paper before its publication, but by no means of the whole 

 of them. Indeed it was a fact contained in it, new to me, that 

 suo-o-ested to me the new analysis of the chloride of sulphur 

 which I am going to describe. The fact to which I allude is the 

 gradual decomposition of hyposulphate of silver, when left in 

 solution in water, and its conversion into sulphuret of silver. 

 This put me in mind of a phenomenon which I had observed in 

 my former rude attempts to analyze the chloride of sulphur, and 

 which I was unable to account for — I mean the change of 

 colour which the precipitate (from water in which the chloride 

 of sulphur has been agitated), by means of nitrate of silver, 

 tmdergoes from white to brownish-black. The knowledge of the 

 spontaneous change of hyposulphite of silver into sulphuret of 

 silver suggested the cause of this change, and induced me to 

 repeat my old analysis with the requisite attention to precision ; 

 so true is it that no addition can be made to any part of che- 

 mistry, which has not a tendency to throw hght upon other parts 

 of the science apparently totally unconnected with the new dis- 

 coveries. 



42-9 grs. of chloride of sulphur were dropped into about eight 

 ounces of distilled water contained in a common phial. The 

 phial was immediately corked tightly, and it was agitated 

 violently at intervals for several weeks. The chloride at first fell 

 to the bottom of the liquid. It was partially decomposed, and 

 flocks of sulphur separated by the agitation ; but the decompo- 

 sition was very slow, and at 'least six weeks elapsed before all 

 traces of the chloride disappeared. There was then a quantity 

 of sulphur collected at the bottom of the phial, and the water 

 had a considerable opalescence, owing apparently to a portion of 

 sulphur suspended in it in the state of a very minute ])0wder. I 

 allowed it to remain at rest for a week to give the sulphur time 

 to subside ; but finding it continue as opalescent as ever, I 

 poured into it a quantity of ammonia rather more than sufficient 

 to saturate all the acid which it contained, and threw the whole 

 upon a filter. The liquid passed through colourless; and the 



