SODIUM OR POTASSIUM : EDWARD DIVERS. 73 



basic salts. In very dilute alkali the precipitate is slightly 

 soluble. 



What makes this salt so remarkable, not only as a hypo- 

 nitrite but as a mercuric salt, is the nature of the decomposition 

 which it undergoes. Slowly or quickly, it decomposes into 

 mercurous hyponitrite and nitric oxide, — some of the latter, 

 oxidised by the air, converting some hyponitrite into nitrate. 

 No other mercuric salt decomposes into mercurous salt, while 

 many cupric salts change into cuprous. Ferric oxalate shows 

 just the same kind of change, namely, into ferrous oxalate and 

 carbon dioxide. The most closely related change, however, is 

 that of sodium (hypo)uitrososulphate into sulphite and nitric 

 oxide, the very 2:)lienomena being similar, so that, except for 

 the colour-change, I might describe my experience wdth this 

 salt in the words of the paper by Haga and me on sodium 

 (liypo)nitrososulphate {J. CL Soc, 1895, 67, 1095). Thus, 

 having, on one occasion, left some grams of the salt all night 

 in the desiccator, in form of a pressed cake, just as removed 

 from the filter, then taken it out, and w^eighed it between 

 watch-glasses, I noticed that it was losing weight on the balance- 

 pan. AVhen the glasses were opened, a strong nitrous odour 

 was observed, the cake soon became grey-white on the surface 

 and, being left loosely covered, grew very hot, and gave out 

 torrents of nitric oxide. It then cooled and underw^ent no 

 further change, even in the course of months. The whitish 

 colour of the cake was found not to penetrate beyond a 

 millimetre into it, the inside of it being of a uniform yolk- 

 yellow and consisting of mercurous hyponitrite. The surface- 

 coating proved to be mercurous nitrate, largely soluble in water, 

 and had evidently been produced with the assistance of the 



