1824.] Mr. R. Phillips's Chemical Examination of Skorodite. 99 



yield to mechanical division parallel to the planes M M', and 

 also to the plane h of the preceding figure ; the latter being 

 parallel to the lesser diagonal of the prism ; a fragment found 

 among the crystals received from Cornwall, exhibits the latter 

 cleavage with a tolerably brilliant surface ; the former I have not 

 succeeded in obtaining, owing, perhaps, to the minuteness of the 

 crystals rendering it difficult to operate upon them, and to the 

 intermixture of the green particles. 



On subjecting these crystals to the action of the blowpipe, 

 copious arsenical fumes are given off, without altering the exter- 

 nal form, which, however, is rendered of an ochreous colour. 



Chemical Examination of the Skorodite. By R. Phillips, FRS. 



A few crystals of the skorodite were dissolved in nitric acid, 

 the solution was decomposed by potash, and after having satu- 

 rated the alkali with acetic acid, nitrate of silver was added, 

 which immediately gave the well-known red precipitate indicat- 

 ing the presence of arsenic acid. 



The precipitate separated by potash from solution in nitric 

 acid appeared to consist of peroxide of iron ; but in order to 

 ascertain whether it contained oxide of copper, it was put into 

 ammonia; this however exhibited, no appearance of having dis- 

 solved any of the oxide in question. I subsequently dissolved 

 some of the skorodite in nitric acid, and tried whether polished 

 iron would detect the presence of copper, but the attempt was 

 equally unsuccessful as the first. In order to be perfectly satis- 

 fied that the substance contained no copper, I requested Mr. 

 Children to submit it to examination ; the results of his experi- 

 ments confirmed those which I had obtained, and proved that 

 no copper was present. 



Through the kindness of Mr. Heuland, I was enabled to sub- 

 mit some crystals of foreign skorodite to examination, and these, 

 as well as some with which my brother supplied me', were totally 

 destitute of copper, and appeared to consist entirely of arsenic 

 acid and oxide of iron. 



On account of the similarity of crystalline form and measure- 

 ments in the skorodite and the martial arseniate of copper, analyzed 

 by M. Chenevix, 1 was desirous of subjecting the latter to a fresh 

 examination ; in so doing I had very satisfactory evidence that. 

 it contained a considerable portion of oxide of copper. The 

 analysis of M. Chenevix gives: 



Arsenic acid 33*5 



Oxide of iron 27 # .'j 



Oxide of copper 22-:') 



Water 120 



Silica 3-0 



98-5 

 h 2 



