72 HYPONITRITES ; PROPERTIES AND PREPARATION BY 



reducing sodium nitrite (p. 38), largely diluted and, while ice-cold, 

 nearly or quite neutralised with dilute nitric acid (mercurous 

 nitnite serving as indicator, see \^. 35), is poured into the mer- 

 curic nitrate solution, taken not in excess and containing as 

 little free acid as possihle. Very soon, the slightly turbid 

 mother liquor is decanted from the precipitate, neutralised v/ith 

 sodium carbonate, mixed with more mercui-ic nitrate, so far as 

 necessary, poured back upon the main precipitate, stirred up 

 with it, and soon again decanted. The precipitate should be 

 washed quickly by décantation, since it is liable to be soon all 

 destroyed by its slightly acid mother-liquor. 



It is a flocculent, cream-coloured precipitate, easily washed 

 on the filter, and dries up to a light buff- colon red powder, this 

 colour being due, probably, to incipient change into the mercu- 

 rous salt. Air-dried quickly, on a porous tile, it is hydrated, 

 having the formula (HgNA)2(OHo)3. Dried in the desiccator, it 

 is anhydrous. Being a little sensitive to light, it should be 

 dried in the dark. It dissolves in hydrochloric acid and in 

 sodium-chloride solution, but it is unstable, changing into mer- 

 curous salt, and therefore is liable to show turbidity in the 

 chloride solutions. The mercury precipitated as sulphide from 

 a solution of the anhydrous salt in hydrocliloric acid, proved 

 to be 76.71 per cent., while calculation for HgNA requires 

 76.92. Its solubility in excess of sodium chloride does not 

 prevent mercuric chloride giving a precipitate wnth sodium 

 hyponitrite. The solubility of the salt in sodium chloride is 

 a qualitative proof of its normal composition. The alkalinity 

 of the solution is caused by the sodium hyj)onitrite generated 

 in it. Potassium hydroxide at once decomposes mercuric hypo- 

 nitrite into oxide, without showing any tendency to produce 



