IMIDOSULPHONATES. 65 



by us, are so similar to those we record of the sodium salt, as to make 

 it profitless to give ])articulars of them. 



Tripotassiuiii imidosidpliofitik'. — Tripotassium imidosulphonate was 

 prepared by Berglund, and again by Haschig, by dissolving the 

 dipotassium salt in solution of potassium hydroxide, evaporating, and 

 crystallising. 



Sodium imidosidp honates. 



Disodiiim iiiiidosidplwnate. — The preparation of this salt depends 

 upon the same changes as those which give the potassium salt by 

 Fremy's method, but the details of working differ materially. Sodium 

 nitrite, as nearly pure as possible, and sodium carbonate in crystals, in 

 the proportion of two molecules of nitrite to three molecules (six 

 equivalents) of carbonate are, with twice their weight or more of water, 

 treated freely with sulphur dioxide in a capacious flask, better fitted 

 with cork and gas tubes. After the carbonate crystals have dissolved, 

 and acid-carbonate has been precipitated and redissolved with con- 

 tinuous effervescence, the liquor, still quite alkaline to litmus, begins 

 to grow warm when more sulphur dioxide enters it. To prevent 

 any considerable rise of temperature, which might cause premature 

 hydrolysis and spoil the operation, the flask is, from this point, 

 kept in motion in cold water, and the stream of sulphur dioxide 

 somewhat lessened and held under watchful control. Neutralisa- 

 tion of the alkaline liquor by the sulphur dioxide entering it is 

 markedly retarded by the action of the nitrite, in the presence of 

 which neutral sulphite cannot continue to exist. When, at length, 

 neutrality to lacmoïd paper is almost reached, the flask is actively 

 agitated without intermission, and the flow of gas first made quite 



