202 EDWARD DIVERS AND MASATAKA OGAWA : 



free sulphur dioxide. It is insoluble in ether, soluble in 

 alcohol without change, and recoverable from its solution by 

 evaporation unchanged, provided every trace of water is kept 

 away. It is also in part precipitated from its concentrated 

 solution in alcohol, by saturating this with ammonia at a 

 low temperatui'e. It is exceedingly deliquescent and is im- 

 mediately decomposed by water, in which it dissolves. Its 

 alcoholic solution at once crusts over when exposed to the 

 air, ammonium pyrosulphite being produced. The aqueous 

 solution or deliquesced salt smells strongly of sulphur dioxide 

 and gives the reactions only of a sulphite in its fresh state ; 

 but from the tendency of pyrosulphite to change into trithionate, 

 it becomes a little yellow on standing and its silver precipitate 

 slowly changes colour. Hydrochloric acid gives no precipitate 

 of sulphur in its fresh solution, and the acid solution loses 

 all its sulphur as sulphur dioxide, when quickly boiled. 



Szarvasy found it necessary, in preparing methyl magne- 

 siumsulphite, to saturate the alcoholic solution with sulphur 

 dioxide, while, for the reason above given, we found it ad- 

 vantageous to saturate the alcohol with sulphur dioxide in 

 preparing the ethyl ammoniumsulphite. Rosenheim and Lieb- 

 knecht, on the other hand, state that the use of any excess of sul- 

 jjhur dioxide in making the alkyl alkalisulphites is most carefully 

 to be avoided, since otherwise these salts decompose into " acid " 

 alkalisulphites. This difference between closely allied salts 

 would be remarkable and not easy to understand if its existence 

 could be confirmed. In absence of water, pyrosulphites, rather 

 than acid sulphites, alone can form. But, if the unknown 

 ethyl sodiumpyrosulphite had been the salt formed, these 

 chemists would, presumably, not have failed to indicate the 



