INTERACTION BETWEEN SULPHITES AND NITRITES. 283 



— the minute quautity of pyrosulphite which the acid had pro- 

 duced having slowly interacted with the nitrite, but when that 

 was used up, no more action occurred and, at any time added 

 one drop of dilute acid would again remove the colour of the 

 solution. 



No further proof of the activity upon a nitrite of a normal 

 alkali sulphite is wanted, but additional evidence of the fact is 

 readily obtainable. Thus, in the case of the potassium salts, 

 while the action of pyrosulphite upon nitrite shows itself (excej^t 

 in cases of high dilution) by the formation of the insoluble 

 nitrilosulphate, no separation of this salt occurred in the above 

 experiments. Again, barium chloride, added, at any time, to the 

 mixed and to litmus very alkaline solution of normal sulphite and 

 nitrite, precipitated all the sulphur as sulphite (with also a very 

 little sulphate) and left the nitrite in solution, neutral to litmus. 

 Had sulphazotised salts been present, precipitation of the sulphur 

 would have been incomplete, and the mother-liquor would have 

 preserved a strong alkalinity to litmus and when acidified soon 

 have deposited barium sulphate in the cold and at once if boiled. 



Fremy, Claus, and Raschig all believed in the activity of di- 

 potassium sulphite upon potassium nitrite, although the last 

 named chemist recognised the value also of the pyrosulphite, as 

 Berglund had done before him. Fremy apparently used sulphite 

 neutral to litmus and took it to be the normal salt, and Claus 

 certainly did so. Since, therefore, they used sulphite which was, 

 for the most part, pyrosulphite, no evidence upon the point in 

 question can be gathered from their work. We would account 

 for Fremy's finding sodium sulphite inactive upon sodium nitrite, 

 otherwise inexplicable, by assuming that the solution of sodium 

 sulphite which he tried happened to contain no pyrosulphite. 



