227 



Chloride of gold was also found to be reduced by contact with the following 

 sulphides, — they include, as will be observed, all those mentioned by Mr. 

 Wilkinson — sulphides of iron (proto and bi-sulphide), sulphides of coj^per 

 (ferro-sulphide and sub-sulphide), and the sul^^hides of zinc, tin, molybdenum, 

 lead, mercury, silver, antimony, bismuth, arsenic, platinu.m, and gold ; and 

 among the arsenides, mispickel and arsenide of silver ; cubical iron pyrites is 

 rather slow in its action upon this solution of gold, while sulphide of antimony 

 scarcely affects it at all at first, but after some hours contact with it, reduction 

 goes on rapidly, perhaps by aid of some voltaic action. All these effects were 

 produced at common temperatures (with the exception of that with sulphide 

 of bismuth), while other experiments with iron and copper pyrites prove that 

 similar efiects are produced when all kind of light is excluded, so there is no 

 reason to suppose that light has been concerned in any of these re-actions. 



I should state that in the case of some of the highly-coloured minerals, 

 such as cinnibar and arsenide of silver for instance, it is necessary to 

 operate upon their streak in order to obtain a visible deposit on them, at 

 common temperatures within a reasonable time, with hot solutions ; however, 

 even these are well gilded in an hour or two. 



A portion of the metal of the sulphide operated upon was uniformly found 

 in the solution afterwai'ds, and also suli^huric acid ; the mode therefore in 

 which these effects were produced, was evidently by the oxydation of both the 

 constituents of the nucleus employed, at the expense of the chloride, or rather 

 the hydrochlorate of oxide of gold — supposing, as seems probable, an equivalent 

 of water combined with it as administered. 



Thus we have removed this singular anomaly of gold in the act of 

 precipitating, selecting as nuclei substances so diverse from it, while refusing 

 others which differ no more from such non-metallic nuclei than do these from 

 gold ; as it certainly appears from these results that whatever gold has been 

 reduced by organic matter in the experiments quoted, would never deposit 

 on these non-metallic nuclei, surface to surface, but only upon gold already 

 occupying such surfaces, reduced by the exercise of affinities far superior and 

 swifter in their action than those involved in the decay of wood or other 

 organic structiires, used by Mr. Wilkinson in the experiments alluded to. 



The question next arose, if organic matter is unnecessary, as it certainly is 

 for the commencement of gold deposits on these nuclei, is it necessary for 

 their continuance, and to give them that close coherent form obtained when 

 such matters were administered? experiment proved it to be unnecessary 

 as it was found that the solution after depositing a certain time gave films 

 towards the angles of the nuclei, which were of some thickness, and which, 

 under the mici'oscope, appeared quite continuous. 



The non-necessity of the addition of organic matter to ensure the deposition 

 of gold in. these experiments by Mr. Wilkinson, being thus shown, and the 



