INTERACTION BETWEEN SULPHITES AND NITRITES. 305 



be remembered, firstly, tliat nitrous acid would oxidise liydrox- 

 imidosulpliate at once, and secondly that sulphurous acid sulplion- 

 ates the hydroximidosulphate slowly enough to allow a little of 

 it being secured in a hydrolysed state. 



IV. — a. Sulphonation of Nitrous Acid by Sulphurous Acid. 



Fremy believed that certain of his sulphazotised salts are 

 formed in the first action of sulphurous acid upon nitrous acid. 

 From this belief Clans strongly dissented, holding that the presence 

 of a base (as salt) was essential to the production of these acids. 

 Raschig considered that his experiment of treating potassium nitrite 

 with sulphur dioxide in excess (sect. III./.) proved the correct- 

 ness of Frerny's belief ; but that cannot be admitted since potas- 

 sium is present in this experiment playing the part of base. It 

 is, however, quite piacticable to establish Frerny's belief and that 

 no base wdiatever is necessarv to brino' about the formation of 

 sulphazotised acids. 



When a solution of sulphur dioxide, better ice-cold, is treated 

 with a relatively small quantity of nitrous fumes passed on to 

 its surface while it is being well agitated in a flask, and is 

 then deprived of remaining sulphur dioxide by a rapid cur- 

 rent of air, or even by quick boiling, it will give a good reaction 

 for hydroxyamidosulphuric acid with the copper test. A 

 little deviation in the composition of the nitrous gas from that 

 of nitrous anhydride is not of importance. If the object is only to 

 get amidosulphuric acid, the solution of sulphur dioxide is left 

 to stand for a day after it has received the nitrous acid without 

 expelling what is left of the sulphur dioxide. If it is then 

 evaporated on the water-bath and further concentrated in the 



