554 ACCOUNT OF A REPETITION OF SEVERAL OF DR SAMUEL BROWN'S 



We heated the paracyanogen in tubes of glass, of brass, and of iron, alone and 

 mixed with spongy platina, and at various temperatures from 600 up to a white 

 heat. The tubes were of small bore, and the included air was expelled as much 

 as possible by a gentle heat, before they were raised to the temperature at which 

 the paracyanogen decomposed. In spite, however, of every precaution calculated 

 to prevent the paracyanogen coming in contact with any source of oxygen, we 

 invariably procured carbonic oxide and carbonic acid. 



The black matter left after the gases had been evolved, which should have 

 been silicon or a siliciuret, in all the cases where it was examined, except in one 

 very remarkable one which will be mentioned hereafter, was found to diminish 

 rapidly in bulk and weight before the blowpipe, and to consist chiefly of carbon. 



Later researches have shewn us, that it was useless to look for quantitative 

 results from so impure and variable a body as crude paracyanogen. As it comes 

 from the iron tubes, it contains, according to Dr BROWN, absorbed cyanogen, and 

 frequently also silicon. We have always found metallic mercury present in a state 

 of very fine division, a soluble salt of mercury (which is not the cyanide, but, per- 

 haps, as Professor JOHNSTON has suggested, the cyanate), and often also carbon. 



We have lately attempted to purify the paracyanogen so procured, by boiling 

 it with water for several hours to aggregate the mercury ; washing it on a filter to re- 

 move the soluble salt of that metal; and, according to the process given by Dr BROWN, 

 for depriving paracyanogen of its absorbed cyanogen,* afterwards boiling it with 

 carbonate of potass and water. From paracyanogen purified in this way, and heated 

 in brass and iron tubes, we procured nitrogen, carbonic acid, and carbonic oxide; and 

 the residue (carbon) was almost entirely dissipated before the blowpipe. In one ex- 

 periment, 3-3 grains of crude paracyanogen heated in an iron tube, gave off 5*75 cubic 

 inches of gases, of which 66 per cent, was absorbed by potass ; the remainder 

 burned with the blue flame of carbonic oxide, and was not farther examined as to 

 the presence of nitrogen. The potass, when examined by SCHEELE'S test, gave much 

 Prussian blue, shewing that the absorbed gas was chiefly cyanogen. In another 

 experiment 3 grs. of purified paracyanogen gave 6 cubic inches of gas, whereof 

 potassa absorbed 20 per cent., which, on examination, proved to be carbonic acid 

 with a trace of cyanogen. The residual gas, which burned with the characteristic 

 flame of carbonic oxide, was mingled with an equal volume of oxygen, and ex- 

 ploded by the electric spark. After the carbonic acid had been withdrawn, and 

 phosphorus had ceased to cause contraction, there remained 65 per cent, of nitro- 

 gen, shewing, of course, 15 per cent, of carbonic oxide. 



Unable to confirm Dr BROWN'S results with paracyanogen heated alone, we 

 turned to his experiments on the fusion of that body with carbonate of potass. 

 Crude paracyanogen, when fused with that substance in a closed platina crucible 



* Trans, of Royal Soc., vol. xv. p. 168. 



