DR BROWN ON THE PRODUCTION OF SILICON FROM PARACYANOGEN. 235 



supplies the desideratum in the first three, and establishes the conclusion that 

 the silicon, which appears in these experiments, is produced from the para- 

 cyanogen itself, and is not extracted from any part of the apparatus in which it 

 is conducted through the steps of the operation ; and abundant additional evi- 

 dence of this will be adduced in the progress of the investigation. 



The success of these last two experiments, however, does not provide us with 

 the means of determining with exactitude that the nitrogen of a given weight of 

 paracyanogen is wholly dispelled, and that the four equivalents of carbon are the 

 sole factors of the silicon which remains ; for they were made with crude paracy- 

 anogen, which, as has been already observed, always contains both cyanogen and 

 traces of silicon itself, previously produced by the transformation of carbon. Here 

 it is worthy of remark, as a criticism on the manner of analysis followed by Mr 

 JOHNSTONE in his examination of this substance, that a specimen might contain 

 both of these impurities in any proportion, and yet yield to the reaction of oxide 

 of copper, or chromate of potassa, carbonic acid and nitrogen mingled in the 

 ratio of 2 to 1 ; and this both explains and reconciles his results with the seem- 

 ingly incongruous observation of GAY-LUSSAC, that the cyanogen, driven by high 

 temperatures from the bicyanide of mercury, always contains traces of nitrogen, 

 and my own, that paracyanogen, prepared by fire, almost invariably contains 

 appreciable traces of free silicon.* It is equally deserving of observation, how- 

 ever, as a comment on the great process of the history of sciences, that, but for 

 the partial and consequently erroneous procedure of the distinguished analyst in 

 question, the isomerism of cyanogen and paracyanogen might not have been yet 

 discovered. 



At first I thought that the difficulty resulting from the presence of silicon 

 and cyanogen in crude paracyanogen might be overcome by having recourse to 

 the purified substance ; but, in fact, paracyanogen which has been subjected to the 

 process of purification, by sulphuric acid and exposure of the solution to the damp of 

 the atmosphere, is no longer one of the most attenuated of solid forms, but a pretty 

 dense powder, intermediate in character between the crude and the ignited prin- 

 ciples, which cannot be reduced by any elevation of temperature, however pro- 

 tracted, short of that of ignition ; and the objection to such a temperature has 

 already been stated. An accident, the investigation of which forms the subject 

 of the next section, eventually led to a method which will be described in the 

 third part of the present inquiry. 



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. As the nu- 



* Op. cit. sect. i. compared with the results given in this section of the present paper. 



