INTERACTION BETWEEN SULPHITES AND NITRITES. 287 



sul^jkazate, also used precipitation of alumina as tlie indication to 

 stop the process while yet alkali remained. 



Thus, then, it would seem, Fremy, Claus, and Raschig, the 

 last in less degree, have all prepared sulphazoiised salts without 

 difficulty, under conditions which we pronounce to be in- 

 compatible with their production. To remove this apparent 

 contradiction in results it is sufficient to assume, for one thing, 

 that, in Fremy's way of working, success followed only because, 

 temporarily and locally, the point of saturation of the alkali 

 was reached and exceeded again and again where the gas entered 

 the solution, — a state of things, never avoidable altogether, above 

 all at the time when the potassium hydroxide is nearly exhausted- 

 There is nothing to show that, to check this, he kept his solu- 

 tion well agitated. Secondly, we can assume, with great proba- 

 bility that his solution often lost its alkalinity between the additions 

 of the hydroxide which he made. Working as we believe he 

 actually did, we have found it easy to get results such as his. 

 So far as Claus and Raschig followed Fremy's method, their 

 results are equally open to objection, while it is to be remarked 

 of tlieir alumina indicator that, not only is normal sulphite 

 alkaline to litmus but, as we have found, any aluminium present 

 is precipitated as hydroxide just when the sulphur dioxide has 

 converted all alkali into normal sulphite. They will, therefore 

 in their experiments have preserved none of the alkali unchanged 

 and most probably have generated also some pyrosulphite. There 

 is besides indirect evidence in Claus's work that normal sulphite 

 is either inactive or only very slowly active upon nitrite, for when, 

 having taken no excess of this salt, he stopped the process just 

 after precipitation of alumina, much of this nitrite remained in 

 the solution, while, as we have just pointed out, much normal 



