300 Dr. R. H. Brett and Mr. J. D. Smith's Experiments 



tate : this acid solution, evaporated to dryness, ignited, and 

 again treated with hydrochloric acid and water, left no per- 

 ceptible residue; whereas, from the statement of Dr. Brown 

 (p. 236), if rightly understood by us, we ought to have ob- 

 tained at least 1 1 grs. of silicic acid from this quantity of 

 paracyanogen. — (J. D. S.) 



We may here be allowed to remark, in explanation of the 

 circumstance which seems to Dr. Brown so difficult to account 

 for in the experiments just described, viz. " the disappearance 

 of the carbon" of the paracyanogen when ignited with carbo- 

 nate of potash, that it is probable that one portion of the 

 paracyanogen decomposes the carbonate of potash forming 

 carbonic oxide, mixed perhaps with carbonic acid, azote and 

 potassium, and that the last-named substance combines with 

 that portion of paracyanogen which is decomposed by heat 

 into cyanogen, forming cyanide of potassium, a portion of 

 which is volatilized, whilst, as we have seen, the remainder is 

 found mixed with the excess of carbonate of potash used in the 

 process : other explanations may be given, but this appears 

 to us to be both the most feasible and the most in accordance 

 with the facts we have noticed. 



Although the foregoing experiments were as direct and, to 

 us, as decisive as we could desire respecting the alleged trans- 

 formation of carbon, we nevertheless determined to pursue 

 the investigation further, so as to render it complete ; we there- 

 fore turned our attention to the experiments of Dr. Brown 

 (p. 236-7) on the formation of " compounds of silicon with 

 copper, iron, and platinum, by the reaction of paracyanogen 

 on these metals." 



Three grains of paracyanogen from decomposed prussic 

 acid were tightly wrapped up in platinum foil and placed in 

 a porcelain crucible, the bottom and sides of which were lined 

 with platinum foil, so as to prevent the foil containing the pa- 

 racyanogen from coming in direct contact with the glazed 

 lining of the crucible ; a cover was placed over the crucible, and 

 the whole imbedded in plaster of Paris paste contained in a 

 Hessian crucible ; when dry, the apparatus was exposed to a 

 white heat for two hours. The plaster of Paris had become 

 vitrified by heat, and a portion of this vitrified matter found 

 entrance into the porcelain crucible ; the latter, however, when 

 broken up, displayed the platinum of a brilliant colour, and of 

 softer texture than foil not previously exposed to so high a 

 temperature. It could hardly therefore be supposed that the 

 platinum had been acted upon by silicon, which renders it 

 brittle, and does not render the metal more brilliant ; it was 

 obviously useless to act upon the platinum by aqua regia for 



