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



is to have proved an unequivocal anomalous appearance or production of the latter 

 body. Our experiments, moreover, throw no light on the source of that silicon. 

 Taking the experiment with the iron crucible as the simplest in its conditions of 

 all those we have made, and not multiplying hypotheses unnecessarily, we shall, 

 nevertheless, be obliged to admit as equally tenable three views of the origin of 

 the silicon. 



Paracyanogen, a compound of carbon and nitrogen, disappeared, and was re- 

 placed by' silicon. 



We may say with Dr BROWN, that the latter came from the carbon ; or with 

 Mr KNOX,* that it came from the nitrogen ; or, for anything the experiment be- 

 trays to the contrary, that it came partly from both. Great difficulties lie in the 

 way of all of these hypotheses, which we feel it quite unnecessary to discuss, un- 

 less so far as to acknowledge that Mr KNOX'S theory stands on a broader basis of 

 alleged fact than either of the others, as he professes to have established his view of 

 the relation of silicon to nitrogen both by analytic and synthetic proofs. No one, 

 however, has repeated or confirmed his experiments. 



We have, in the meanwhile, relinquished the farther trial of Dr BROWN'S pro- 

 cesses, because the experience of four months' failure has satisfied us that his ex- 

 periments cannot be repeated at will j that the conditions essential to their success 

 have not been satisfactorily ascertained ; and that none of his processes are suffi- 

 ciently wrought out in detail, to afford the means of establishing the transmuta- 

 bility of carbon into silicon on quantitative grounds, the only grounds on which such 

 a proposition can be based. 



In particular, we have been deterred from farther trial, by finding that para- 

 cyanogen which, according to Dr BROWN, is a " true cyanide of cyanogen, decom- 

 posed neither by heat, because its constituents are equally volatile, nor by elec- 

 trolysis and reagents,"f is in reality susceptible of such a decomposition. 



This is not the place or time for entering on this matter. But we may men- 

 tion, that paracyanogen, purified from adhering or absorbed cyanogen with the 

 utmost care, has been found by us to pass back or revert into cyanogen.J Fused 

 with carbonate of potass, or heated with potassium, it has given cyanide of potas- 

 sium abundantly. In one case where two grains of paracyanogen were heated with 

 potassium, and precipitated by nitrate of silver, acidulated with nitric acid, they 

 gave 4'4 grs. of cyanide of silver, containing of cyanogen 0'86 gr., and there re- 



* An abstract of Mr Knox's paper, which has not, so far as we know, yet been published, will be 

 found in the London and Edinburgh Philosophical Magazine for 1843. 



f Trans, of Royal Soc., vol. xv. p. 175. 



J We offer no opinion as to the constitution of paracyanogen. By the substance which we so de- 

 signate, we mean the black powder obtained by heating cyanide of mercury ; and in speaking of its re- 

 version into cyanogen, we purposely use the language of Dr BROWN, who supposes it to be a combina- 

 tion of two atoms of cyanogen. 



