42 MR JOHNSTON ON PARACYANOGEN 



4. These paracyanates are soluble in hot dilute nitric acid, from which they 

 are again partially separated on cooling, or on the addition of water. By pro- 

 longed boiling in the acid, not only the salt, but the paracyanic acid itself, is in a 

 great measure decomposed. 



5. Concentrated sulphuric acid dissolves them slowly in the cold, giving a pale 

 yellow solution ; when heated, they, dissolve more rapidly, in larger quantity, and 

 with evolution of carbonic and sulphurous acids and nitrogen. On cooling, crys- 

 tals are deposited, which are a mixture of bisulphate and paracyanate. From the 

 liquid portion water separates a brownish precipitate, and the diluted superna- 

 tant liquid gives a white with a nitrate of mercury. Sulphm-ic acid, therefore, 

 partly decomposes the salt, and retains the acid in solution, which it resolves into 

 cai'bonic acid, nitrogen, and perhaps ammonia, when raised to the boiling tempe- 

 rature. 



6. Muriatic acid dissolves them by the aid of heat, but if diluted with water a 

 portion is again thrown down. 



7. Solutions of caustic potash or ammonia immediately blacken the protox- 

 ide salts, especially if newly precipitated, forming a yellow solution, and leaving 

 protoxide of mercury. Neutralized or rendered acid by nitric acid, the solution 

 again gives a copious precipitate with nitrate of mercury. 



8. The newly precipitated salt suspended in water is also rendered dark grey 

 by binoxide of nitrogen and sulphurous acid. The latter forms a yellow solution 

 containing a little mercury, and a considerable quantity of the paracyanic acid, 

 which, when the excess of sulphurous acid is driven off by heat, again falls as a 

 yellow paracyanate on the addition of a salt of protoxide of mercmy. 



9. Diffused through water, the salts of mercury are blackened by hydrosul- 

 phuret of ammonia, or by hydrosulphuric acid, without, however, being wholly 

 decomposed, the black sulphuret, when sublimed, still leaving a residue of para- 

 cyanogen. Even when the salt is dissolved in muriatic, and precipitated by ex- 

 cess of hydrosulphuric acid, the sulphuret of mercury is apt to carry down with 

 it a portion of the paracyanic acid, so powerfully do these compounds resist the 

 decomposing action even of the mineral acids. 



10. A current of chlorine gas causes a very interesting reaction when passed 

 through water, holding the salt in suspension. It decomposes both the salt and 

 the acid, causing the evolution of carbonic acid, and forming bichloride of mer- 

 cury, sal ammoniac, and carbonate of ammonia, which remain in solution. The 

 action in this case is represented by the following formula : — 



(C8N,0 + Hg 0) + 4 CI + 14 HO = HgCla -f- 2 (NH^ CI) + 2 (NH3 -I- CO^) + 6C0, 



11. When a solution of iodide of potassium is digested on a protoxide salt, 

 the latter becomes dark green, grey, and finally black, from the separation of me- 



