156 Intelligence mid Miscellaneous Articles, 



ACTION OF CHLORIDE OF TIN ON SULPHUROUS ACID. BY 

 M. HERING. 



It is well known that sulphurous acid, although one of the most 

 powerful reducing bodies, is nevertheless inferior to chloride of tin 

 in this respect, for a solution of sulphurous acid is completely re- 

 duced by this chloride ; it is on this energetic reducing property 

 that is founded the known method of trying whether the muriatic 

 acid of commerce contains sulphurous acid. In fact, if to a solution 

 of sulphurous acid, mixed with a large quantity of hydrochloric acid, 

 a small quantity of solution of chloride of tin be added, the liquor 

 though at first perfectly clear becomes turbid after some time, and 

 then assumes, at first a sulphur yellow colour, and afterwards a 

 deeper one. This action of chloride of tin is almost instantaneous 

 when the mixed liquors are slightly heated, and then the odour of 

 sulphurous also ceases. 



The yellow precipitate has usually been considered as a mixture 

 of oxide of tin and sulphur ; according to this opinion, an equivalent 

 of chlorine must be displaced by two equivalents of oxygen ; and 

 there would occur at the same time the separation of an equivalent 

 of sulphur and the formation of chloride of tin. 



It was nevertheless natural to presume that the precipitate in 

 question might also be a peculiar sulphuret of tin. In order to 

 determine this, a portion of a solution of sulphurous acid was mixed 

 with hydrochloric acid, and reduced in the manner stated by 

 chloride of tin, with the aid of heat. The precipitate obtained, after 

 being well washed and dried at a gentle heat, was subjected to the 

 following experiments. 



Put into caustic potash, it completely dissolved after some time, 

 and the solution assumed a yellow colour ; the acetic and hydro- 

 chloric acids produced in it a yellow precipitate without any 

 evolution of sulphuretted hydrogen; after remaining some time in 

 ammonia it was completely dissolved, with the exception of a slight 

 trace, and the solution was of a deep yellow colour; the solution 

 was decomposed by the addition of acetic or hydrochloric acid ; when 

 agitated and left for a long time in contact with sulphuret of carbon, 

 no change occurred either in colour or bulk ; the solution, which 

 was separated by filtration, left but slight traces of sulphur by spon- 

 taneous evaporation ; the precipitate dissolved readily and without 

 residue in sulphuret of ammonia ; acids precipitated yellow sulphuret 

 of tin and sulphur, accompanied with the disengagement of sulphur- 

 etted hydrogen. 



Hydrochloric acid dissolved it gradually with the assistance of 

 heat, and gave out a great quantity of sulphuretted hydrogen, but 

 slight traces of sulphur were separated ; the solution with potash 

 and ammonia yielded white precipitates, soluble in an excess of these 

 alkalis. 



According to these researches, the substance produced by the re- 

 action of chloride of tin on sulphurous acid is a sulphuret of tin. M. 

 Hering, conceiving that he should arrive at a more perfect knowledge 

 of its composition by combustion, heated 228 parts in the air a small 



