AND THE PARACYANIC ACID. 35 



tion of black matter ceases, and the thick treacly fluid separates into a black pow- 

 der, and a transparent and nearly colourless supernatant liquid. 



16. It is unnecessary at present to inquire minutely into the nature of the 

 complicated changes which take place during the mutual reaction of cyanogen and 

 alcohol on each other. To this subject I shall have occasion to revert, in a future 

 memoir, when describing certain new substances produced, partially at least, by 

 this reaction, but of which the investigation is still incomplete. Ammonia and hy- 

 drocyanic acid are formed in considerable quantity, and probably more than one 

 ethereal substance. The greater number of these appear to be decomposed in 

 their turn, and the black powder is the ultimate and chief result. >: 



17. When the thick alcoholic solution is thrown on the filter, and the sub- 

 stance dried without washing, it gives a mass, having a deep black colour and 

 shining fracture ; washed with hot water, it is of a brown, more or less dark, and 

 if boiled in repeated portions of water, as long as any thing is dissolved and dried 

 at 212° F. it is of a dark olive-brown colour. Heated over a lamp in a close tube, 

 it gives off, like the substance deposited in prussic acid, water, carbonic and hy- 

 drocyanic acids and ammonia, leaving a black residue, which, at a dull red heat, 

 gives off cyanogen, and slowly disappears. 



The black residue burned with oxide of copper, gave a mixture of carbonic 

 and nitrogen gases, of which 



88.5 vols, left 80 of nitrogen. 



85.5 — 29 — 



This is as near the ratio of N : Cg as can generally be expected. 



18. When dry cyanate of silver is heated in a close tube, it is decomposed, 

 giving off nitrogen and carbonic acid in the proportion of 1 : 2 by volimie, and 

 there remains behind a black matter mixed with metallic silver. This black sub- 

 stance has the same composition as that left by bicyanide of mercury, and its for- 

 mation is accounted for by the following formula — 



2(NC20 + AgO) = NC2 + 2Ag + N + 2C02 



19. Rectified wood-spirit (bihydrate of methylene) also absorbs cyanogen 

 rapidly and in large quantity. When it has absorbed upwards of thirty times its 

 volume of the gas, it begins to be coloured, and the absorption goes on tUl it be- 

 comes dark brown and opaque, and begins to deposit a dark brown powder. In 

 the course of an hour the quantity of gas taken up amounts to thirty or forty 

 volumes, after the lapse of two days it has increased to between fifty and sixty 

 volumes, and a portion of the deposit was observed. If the wood-spirit be not 

 saturated with the gas, it exhibits no change of colour for some days, but ulti- 

 mately assumes a reddish-brown colour, more or less dark, and gives a brown 

 deposit. 



20. When the ferro-cyanides, Prussian blue and prussiate of potash, are de- 



