Skey. — On Cyanogen, 579 



to avoid producing them I used the protochloride in place of 

 the bichloride of mercury ; and I may further state that the 

 solution of this cyanogen kept persistently acid, even when it 

 was three weeks old and much of the gas decomposed ; and, 

 what is more singular still, the solution was far more solvent 

 of gold at that time than just after it had been made. It was 

 therefore apparent to me that it is not any degree of acidity 

 in a cyanogen solution that does, as is now supposed, con- 

 serve this gas — it is not a mild acidity that is always effective 

 for this purpose. So I increased the acidity of the cyanogen 

 solution by adding to it a few drops of hydrochloric acid, and 

 tried another gold test-paper therein, when I was unable to 

 detect, even after the lapse of seven days, the slightest change 

 of tint had been produced upon that test-paper. Hydro- 

 chloric acid had not any retarding effect upon the dissolu- 

 tion of gold in weak solutions of bromine. 



For supplementary and confirmative evidence on this point 

 I next passed cyanogen gas through a weak solution of nitrate 

 of silver to wash out any ammonia, hydrocyanic and hydro- 

 chloric acids contained therein, and the purified gas was then 

 iillowed contact with the gold test-paper both as gas and as 

 aqueous solution of it, when I got results altogether confirma- 

 tory of those obtained in the previous experiment — that is, 

 no perceivable effect was produced on the test-papers by 

 seven days' contact. 



The results of these various experiments, taken collec- 

 tively, appear to be positively overwhelming in favour of the 

 correctness of the assertion I made before the Society last 

 month — that aqueous solutions of free cyanogen have not the 

 least solvent power upon gold ; consequently they support 

 the old contention of mine cited in the former paper, and 

 alluded to here — that cyanogen does not, as is now generally 

 supposed, compare with the haloids, chlorine, bromine, and 

 iodine, chemically — that, in fact, except that it appears to be 

 a monad with these and a dozen or so more of the elements, 

 it has no chemical relations to any of them. 



I should inform you that the gold I used for the experiments 

 here detailed, also for those for my former paper to the Society, 

 was practically pure ; at least, it only contained minute traces 

 of copper. Argentiferous gold, of which class most or all our 

 native gold is, would, of course, if possible, be still less 

 amenable to solutions of cyanogen than the gold I used, and 

 for the reason that argentic cyanide, if formed at all, would 

 always remain as a product quite insoluble in such cyanogen 

 solutions. 



That cyanogen would have very little tendency to form by its 

 decomposition solvents for gold as used upon quartz, &c., at 

 the gold-mines appears to me absolutely certain, as both air 



