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XI. Chemical Examination of Lettsomite^ {Velvet Ore). 

 Bj/ John Percy, M.D., F.R.S.f 



A T the requestor Mr. Brooke and Professor Miller(ofCam- 

 "^^ bridge), I have examined chemically some minerals, of 

 which the composition has not hitherto been satisfactorily 

 ascertained. 



The first which I have analysed is the velvet copper ore, 

 Mr. Brooke having supplied me with a specimen containing an 

 unusually large proportion of the mineral, yet weighing only 

 12-8 grs. 



First analysis. — The quantity employed, after separating 

 extraneous matter by the aid of a lens, weighed 2*99 grs. 



On adding hydrochloric acid, slight effervescence occurred, 

 due to the presence of some minute particles of blue carbonate 

 of copper : only a trace of matter was left undissolved. The 

 whole was then evaporated to dryness. The residue consisted 

 of brown interlacing acicular crystals. Hydrochloric acid 

 was added, and after some time water, when a pale greenish- 

 blue solution was obtained. This was passed through a very 

 small filter, which, being washed and incinerated, gave only 

 O'Ol grain, its own ash included. The filtrate was treated 

 with sulphuretted hydrogen, which produced a brown-black 

 precipitate. This was washed with water containing hydro- 

 chloric acid and sulphuretted hydrogen, and then digested 

 with dilute nitric acid. The solution was boiled with potash. 

 The precipitate (CuO), vtashed and ignited, weighed 1'44 gr. 



The last filtrate was reduced by evaporation and treated 

 with chloride of barium. A white precipitate (BaO, SO^) was 

 obtained, which, washed and ignited, weighed 1'34 gr. 



The excess of baryta was separated by sulphuric acid, and 

 ammonia added, when flocculent white matter, like alumina, 

 was precipitated, which, by the addition of hydrosulphate of 

 ammoni^, became greenish-black. It was redissolved in hy- 

 drochloric acid, boiled with nitric acid, and again precipitated 

 by ammonia. Washed and ignited it ( Al^ O^ and Fe^ O'^) 

 weighed 0*35. 



The filtrate, after separation of the alumina and peroxide 



* The name Lettsoniite has been assigned to this mineral at the request 

 of Mr. Brooke, as an acknowledgement of the interesting and useful mine- 

 ralogical assistance he has received from W. G. Lettsom, Esq., whose ex- 

 tensive practical knowledge of minerals, and ample collection of specimens, 

 have enabled him to supply information which Mr. Brooke would have 

 found it difficult otherwise to obtain. 



t Communicated by the Author. 



