Dr. Brown on Dr. Brett and Mr. Smith's Experiments. 389 



the latter was true paracyanogen ; and I do know that this 

 process is so difficult of performance, that it was not till after 

 long practice that my assistants, Messrs. Craig and Thomas 

 Brown, acquired facility in working it. Solubility in sul- 

 phuric acid is no test; blackened half-charred cyanide of 

 mercury, paracyanide of mercury, and most ex- organic car- 

 bonaceous substances, are all dissolved by that menstruum as 

 well as paracyanogen. It appears that "the residue was black 

 and coherent ;" it should have been extremely incoherent. I 

 do not think Mr. Smith employed the same material as I used 

 in this experiment, which is the only attempt at a literal re- 

 petition of any of mine in the whole list on free paracyanogen. 

 The paracyanogen I worked with was all prepared in the 

 hammer-iron paracyanogen-tube, which is described in my 

 paper on the production of silicon. Will neither Dr. Brett 

 nor Mr. Smith get one made? 



It appears that the next set of experiments was " On the 

 formation of compounds of silicon with copper, iron and 

 platinum by the reaction of these metals on paracyanogen" 

 (p. 300) ; but they were made with paracyanogen to which I 

 have already excepted, and that is enough. In addition to 

 that quite fatal objection, the first is equal to nothing accord- 

 ing to Dr. Brett himself; the second and third, by Mr. Smith, 

 are not performed according to my directions ; and in all the 

 three the investigation is far from being rigid. May I be al- 

 lowed to state my respectful conviction, that the authors have 

 not striven as they might? My experiments cost me eighteen 

 months' incessant labour and many a failure. Even so late as 

 last November and December I tried to effect the alleged 

 transformation before a celebrated physician and chemist six 

 weeks in vain ; but at last succeeded, or, as I must say now, 

 appeared to*succeed. 



For the next experiments (p. 301), on the ferrocyanide 

 of potassium, let such as are interested in the subject judge 

 whether they be sufficient repetitions of mine. I may men- 

 tion, in passing, that the two apparatus described in this 

 part of your Correspondents' letter, viz. an iron tube closed 

 with an iron plug, and a gun-barrel protected by luting and 

 well secured at the orifice, were the very instruments that 

 foiled me last November and December. There must be free 

 enough exit for nitrogen ; I used large crucibles of hammer- 

 iron with loose lids and porous lutes. I do not allude to the 

 first experiment of this set (p. 301), for it is original on the 

 part of Mr. Smith. This brings us down to p. 304. 



The last experiment but two (p. 304) just confirms Mr. 

 Johnstone's observation, already confirmed by myself, that 



