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



In page 235 Dr. Brown observes, that " before leaving the 

 production of silicon from uncombined paracyanogen, there 

 is another mode of operating to be mentioned, and it is equally 

 remarkable for simplicity and freedom from any intelligible 

 source of fallacy." " Triturate crude paracyanogen with an 

 excess of carbonate of potash, and fuse the mixture two hours 

 at a full white heat in a closed platinum crucible. Paracy- 

 anogen disappears ; there is no free carbon in the white saline 

 product; but it yields a conformable proportion of silicic acid 

 when treated in the ordinary method of analysis for that com- 

 pound." " This process is more striking when subborate of 

 soda is substituted for potassa ; for when the product is treated 

 with acids, there is no effervescence of carbonic acid ; and 

 it must be remembered, once for all, that in every professed 

 process of transformation, the disappearance of carbon has 

 to be accounted for as well as the new formation of silicon." 

 Dr. Brown further states, that his crude paracyanogen con- 

 tains " nearly a third of its own weight of condensed cyano- 

 gen," and " that it yields a weight of silicon never less than an 

 eleventh, and never more than a twelfth, under the calculable 

 weight of the constituent carbon, the cyanogen of absorp- 

 tion being dissipated in the course of the processes;" by which 

 we presume is meant, that from crude paracyanogen he always 

 obtained between 21'5 and 28 per cent, of silicon, a propor- 

 tion so large that, when converted into silicic acid, it is im- 

 possible it could escape observation, even when the quantities 

 of paracyanogen subjected to experiment are very small. 



As the two processes just quoted are strongly recommended 

 by Dr. Brown for their " simplicity and freedom from any in- 

 telligible source of fallacy," and as they appeared to us to 

 bear so directly upon the question of transformation as to be 

 absolutely crucial experiments, we have followed the formula 

 detailed by Dr. Brown with the greatest exactitude and care 

 in the following experiments : — 



Fifteen grs. of paracyanogen were mixed with 100 grs. of 

 carbonate of potash prepared from the bitartrate : the mixture, 

 placed in a closely covered platinum crucible, and this put 

 into an earthen one, which was covered and carefully luted, 

 was ignited at a full yellow heat for two hours ; on examina- 

 tion when cold, a portion of the salt, probably cyanide of po- 

 tassium, was found to have volatilized, cementing the cover 

 to the platinum crucible, and the residual salt was white; 

 this, treated with distilled water, gave a slightly opalescent so- 

 lution, which, when a small portion was treated with a mixture 

 of per- and protosulphate of iron and hydrochloric acid, gave 

 an abundant precipitate of Prussian blue; to the solution, 



