UXiMlDUöULl'UUXATEt; OK SULPHAZUTATES. 4^ 



KON(S03lv), + iMvOH = H.Ü + KNO,+ 2K2S03; 



but the reversäion is attended Avith some other changes resuhiiiü; in the 

 escape of nitrous oxide and perhaps nitr()<ien, a consideration of which 

 will be found following the paragraphs on hydrolysis (}>. 42). 



The normal salts in solution, or as solids not quite free from 

 moisture, soon suffer s(jnie reversion in the cold, and very much more 

 when the solutions are boiled, without any alkali being added : — 



The tive-sixths normal potassium salt, althougli when well 

 prepared and preserved in a dry atmosphere it can be kept for months 

 without suffering noticealjle change, is when damp unstable, as found 

 by Claus and Raschig. But even the best preparations of it prove at 

 last unstable, and we have found that this is due to the reversion 

 which slowly goes on in it : — 



K5H(X8,0,), = K,HXS,U7 + KN(J, + K,.S,0, 



Such a mixture of salts must be very unstable, liable to hydrolysis and 

 other changes, sufficient to account for that entire break-up of the salt 

 which finally hapjjens. Even l^efore the cViange has proceeded far 

 encjugh to aff'ect the appearance of the cryst;ils, the reversion can be 

 detected by the presence of sulphite. For this detection direct acidi- 

 fication of the salt is hardly effective, because of sec(mdary relictions 

 which then consume the sulphurous acid. But by dissolving the 

 salt, thus slightly decomposed, in water, adding barium chloride, and 

 acidifying the washed precipitate, the sulphite can be readily found. 



The disodium and di potassium salts should, as neutral or nearly 

 neutral salts, be liable to neither reversion nor hydrcjlysis, but their 

 equilibrium is so unstable that the fact is that they are especially 

 prone to rapid change. It is probable that they do really suffer no 



