1820.] -D/-. Clarke on Cadmium. 275 



the inner surface of the glass ; but which may, perhaps, be due 

 to lead contained in the glass itself. 



At another time, liaving ihYOwn down \\\\\\ sulphuretted hydro- 

 gen the sulplnnet of cadmium, and observing that its fine o/owge 

 colour was darkened by the presence of lead, I endeavoured ta 

 ascertain the quantity of lead present by reviving it in a crucible 

 with xuda. iu this manner 1 obtained globules of pure lead^ 

 which had separated from other bronze-looking globules that 

 were brittle, and these after solution, &c. in muriatic acid gave 

 an oraiigc-co/oured precipitate to sulphuretted hijdrogen, and a 

 white precipitate to hi/drate of potass, which was redissolved in 

 liquid ammouia. It is evident, therefore, that they contained 

 Cadmium, and were, perhaps, alloyed with copper; but the heat 

 necessary for melting copper would volatilize cadmium, if Stro- 

 mei/er's observation be correct, as stated in p. 274, vol. xiv. of 

 your Aituals. 



Having now exhausted my materials, I went to London to see 

 if I could procure any more of the dark Jibrous silicate of zinc. 

 At Mr. Mawe's shop in the Strand, I was shown something of 

 a similar nature, although not agreeing as to colour. This was< 

 the Derhi/shire silicate of' zinc, having a greenish colour, vvith a 

 radiated structure, like wacellite, and containing in cavities the 

 reddish-hrown, or orange-coloured earth before-mentioned. The 

 specific gravity of the pure fibrous part equals 3'6767, but it is a 

 very impure mineral, containing, as well as the preceding silicate, 

 both copper and iron, besides a considerable quantity of wiflgz/es/ffrt- 

 carljonate of lime andfuor spar. Mr. Mawc furnished me with 

 several of these specimens, and our professors of chemistry and 

 geology, Cumming and Sedgewich, have kindly added more. Inali 

 of them 1 have found Cadmium: and the quantity of this metal ia 

 the ore may be, perhaps, ascertained; because 540 gr. of the mine- 

 ral, by the process 1 have already described, yielded 3-j-\~ths of 

 sulphuret if cadmium, allowing rather less than -puths of a grain 

 per cent. I have sent the carbonate of cadmium and the sulphuret 

 to you for examination ; and you have confirmed what I have said 

 as to tiieir real nature. The truth of the foregoing observations 

 respecting the presence of Cadmium in our English ores o^ zinc 

 has also been since confirmed by Dr. Wollaston and by i\Ir. 

 Children, who have examined the Derbyshire silicates whence I 

 obtained the metal, and obtained Cadmium, from them. 



Since making- the foregoing observations, I began the exami- 

 nation of other English ores of zinc, and especially of an ochreous 

 eartliy-lfjoking carbonate of zinc, irom Aldstone Moor, in Cum- 

 berland. This ore is dug near the house of a dealer in minerals^ 

 of the name of./. Cov.per, who resides in the town of Aldstone. 

 After its solution in sulphuric acid, when a stream of sulphuretted 

 Aj/drugcn gas is sent through the solution, it assumes a vivid 

 orange colour, and a precipitate is thrown down, which has the 



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