246 On the Composition of Arragonite. [Oct. 



But is not the fact, that arragonite and strontianite have been often 

 confounded tog-ether, in favour of my supposition? 



I shall conclude by remarking, that I have found some per cents, 

 of carbonate of lime both in the Saxon strontianite, from Braunsdorf. 

 near Freiberg, and in the Scottish strontianite, which Pelletier and 

 Klaproth analysed. It was this mixture of a little carbonate of 

 lime with the carbonate of strontian which led me to the analysis of 

 arragonite. The result has been the discovery which I have the 

 happiness to communicate in the present letter. 



II. 



On Arragonite, and the Chemical Difference lehveen it and CaU 

 carenus Spar. By Stromcyer, Professor of Chemistry at Got- 

 tingen.* 



The history of the author's examination of this problematic body 

 is as follows : — As he was engaged last winter in the analysis of a 

 mineral discovered at Braunsdorf, near Freiberg, which some consi- 

 dered as a strontianite, and others as an arragonite, it occurred to him 

 that it would be worth while to subject arragonite itself to a new 

 chemical analysis. He found the mineral in question a strontianite, 

 containing some per cents, of carbonate of lime. On analysing 

 again the Scottish strontianite, examined by Klaproth and Pelletier, 

 he found that it likewise contained some per cents, of carbonate of 

 lime. Hence he was led to suspect that some of the native carbo- 

 nates of lime might also contain some carbonate of strontian. The 

 great external resemblance between arragonite and strontianite led 

 him to pitch upon that mineral as most likely to verify his sus- 

 picion. 



Kirwan had already conjectured, from the similarity between ar- 

 ragonite and strontianite, that the former contained a portion of 

 strontian. But Bucholz and Thenard, who examined arragonite 

 expressly to determine whether it contained any strontian, could 

 not detect in it the smallest traces of that earth. But their experi- 

 ments did not appear to the author sufficiently decisive to demon- 

 strate the absence of strontian in arragonite. Besides, various 

 analyses of bitterspar, and of the mineral called steelstone, had 

 satisfied him that the acute notion of Professor Haussman, respect- 

 ing the influence of the power of crystallization of certain sub- 

 stances in determining the crystalline form of other substances, 

 was not without foundation ; and that substances which possess a 

 very strong tendency to crystallization, even when mixed in very 

 small proportions with other bodies, may yet he able to impress 

 upon them their own determinate crystalline form. It was therefore 

 pot very unlikely that the crystalline form of arragonite might de- 

 pend upon the presence of strontian. 



* Gilbert's Annalcn dcr Phjsik, xU. 217. October, 1813. 



