45 



specific gravity is 30'GOO : its hardness just sufficient to scratch 

 calcareous spar. Its crystals, which are tolerably transparent, are 

 of a dark green colour, with sometimes a brownish tinge ; and when 

 a decomposition takes place, the crystals pass into the state of a 

 pulverescent oxide of a fine reddish yellow colour. 



The 2nd species is denominated cupro-martial arseniate. Its 

 crystals are of an uncommon brilliancy, and perfectly transparent : 

 their form is a rhomboidal tetraedral prism. Its specific gravity is 

 34'003 : its hardness rather greater than that of the arseniate of 

 iron ; the colour, a very faint sky-blue, sometimes a little deeper. 

 Hitherto this ore has not been met with in any form but that of a 

 perfect crystal. 



Analysis of the Arseniates of Copper, and of Iron, described in the pre- 

 ceding Paper ; likewise an Analysis of the red octaedral Copper Ore 

 of Cornwall ; with Remarks on some particular Modes of Analysis. 

 By Richard Chenevix, Esq. M.R.I. A. Communicated by the Right 

 Hon. Sir Joseph Banks, Bart. K.B. P.R.S. Read March 5, 1801. 

 [Phil. Trans. 1801, p. 193.] 



After having perused the accurate detail of the external characters 

 and crystalline varieties by which Count de Bournon, in a paper he 

 lately communicated to the Society, identified the several species of 

 the ores mentioned in the title, the mineralogist will surely be grati- 

 fied to find in this, which may be considered as a continuation of the 

 Count's treatise, an elaborate analytical investigation, whereby not 

 only the above-mentioned classification is fully confirmed, but also 

 some progress is made jn the theory of the docimastic art. After 

 pointing out the principal imperfection of this art, and in what 

 manner more precision is likely to be obtained, both as to the pro- 

 cesses and the terms used in describing them, Mr. Chenevix enters 

 into a full detail of the mode in which he proceeded in his inquiry, 

 and of the many precautions he used in order to obviate every pos- 

 sible deception. The results, he repeatedly declares, have been to 

 him singularly satisfactory, as they fully evince that great confidence 

 can be placed in the crystallographical arrangement, and that in fact 

 the evidence obtained by the two modes reciprocally contribute to 

 confirm the inferences derived from each. 



These results, as far as they relate to the arseniates of copper, are 

 briefly these : 



The natural arseniate of copper exists in three different states of 

 combination ; the first containing 14, the second 21, and the third 

 28 per cwt. of the arsenic acid. 



Each of these may contain different proportions of water, either as 

 constituting a hydrate, or as water of crystallization. 



Upon losing their water they generally pass from a blue to a pale 

 green colour, and finally to brown. 



One species only, being the first of the Count's classification, can 

 be considered as a real arseniate of copper ; the others, from the 



