THE REDUCTION OF XITROSOSULPHATES. 28 3 



ing to the contents of the first note by one of us to the Royal Society on 

 the Formation of salts of nitrous oxide, the presence of hyponitrite should 

 have interfered, but thanks to Thum's valuable contribution (1891) to 

 the knowledge of hyponitrous acid, in which it is correctly pointed out 

 that hyponitrous acid does not act upon iodine (evidence to the 

 contrary having been due to presence of acid silver hyponitrite in the 

 crude solution), we had learned that it was without influence. In 

 titrating-, the solution was poured at once into the iodine solution, and 

 the excess of this measured by sodium thiosulphate. One other point 

 about the sulphite is that, after precipitating from the alkaline solution 

 sulphate and sulphite by barium nitrate in bare excess, the solution, 

 with more barium nitrate added to it, continued, for a day or two, to 

 deposit barium sulphite, as well as the sulphate already mentioned. 



Amidosulphonate. — The sulphur not precipitated by barium nitrate 

 remains in solution as amidosulphonate. The precipitate also contains 

 some amidosulphonate, although its barium salt is soluble in water. 

 This can be extracted from the precipitate by washing it with water. 

 Having added a small excess of barium nitrate and filtered off the 

 precipitate, after two or three days standing, the mother-liquor, slightly 

 acidified with nitric acid, is poured into a moderate excess of mercuric 

 nitrate solution, in order to precipitate oxymercuric amidosulphonate 

 (see our paper on Amidosulplionic acid, this vol., p. 242). This is collect- 

 ed and washed, and decomposed by hydrogen sulphide. The mercuric 

 sulphide requires much washing in order to extract all amidosulphonic 

 acid from it. The filtrate and washings evaporated to dryness in a 

 desiccator, leave the acid in an impure form, but it can be purified, 

 without much loss, by washing it with dilute sulphuric acid. Another 

 way of examining the mercury precipitate is to boil it with hydro- 

 chloric acid and potassium chlorate, or to hydrolyse it at 150°, and 

 then precipitate sulphate by barium chloride. By working in these 



