18U-] On the Composition of Arragonite. 253 



contain the iron in a minimum and maximum state of oxidize- 

 ment. 



As to what Stromeyer has said in the ahove quoted letter to Pro- 

 fessor Gilbert respecting the influence of the strontian which it 

 contains upon the crystallization of arragonite so different from the 

 form of calcareous spar, I might assent to it from what I myself said 

 in your journal in my dissertation on prehnite, &c. (vol. iii. p. 19S;) 

 but the opinion being still undecided, in consequence of our igno- 

 rance of the crystalline form of carbonate of strontian, I may put 

 the question, whether, when bases and acids are crystallized, either 

 the combination of the same base with different acids, or of different 

 bases with the same acid, they do not follow the same law, according 

 to which, when the figure of certain compounds of the same base is 

 known, the still unknown figures of the other compounds may be 

 conjectured ? It were to be wished that our crystallographers were 

 more of crystallologists than they have hitherto been. 



It is of some importance to inquire into the cause why Stro- 

 meyer's method of separating strontian from arragonite failed at 

 first, both in my hands, and in those of various dexterous and 

 accurate chemists. I am not yet qualified to give an opinion on this 

 subject, as I have not yet seen Stiomeyer's paper on the subject, 

 and therefore do not know the minute details of his experiments. 

 From the columnar arragonite of Auvergne I succeeded in sepa- 

 rating strontian by means of alcohol by both processes ; and I sent 

 the matter remaining on the filter to Bucholz, for his farther satis- 

 faction. With the arragonite of Neumarkt, on the contrary, from 

 which I easily obtained strontian by Bucholz 's method, by satu- 

 rating the solution obtained from the residue after exposure to a red 

 heat, with nitric acid, and evaporating, though not in so large a 

 quantity as from the French arragonite, the treatment with alcohol 

 does not seem to answer so well. The solution indeed was opalescent 

 at first; but it did not become muddy till after an interval of some 

 days, and at last precipitated a very fine slime, by no means in 

 considerable quantity. Perhaps it is better after the evaporation of 

 the solution to dryness, which separates any excess of acid that may 

 be present, to dissolve the residuum in as much warm water as will 

 dispose the solution to crystallize on cooling, and then to treat the 

 crystallized mass with alcohol, according to Stiomeyer's method. 

 That Bucholz did not succeed in the method contrived by him 

 might be partly owing to the earthen vessel in which lie decom- 

 posed the nitrate by a red heat; for when such a vessel is employed, 

 it is obvious that a considerable portion of the matter must be lost ; 

 but his failure seems to have been principally owing to his having 

 trusted entirely to the crystallization of the strontian, obtained by 

 water from the residue exposed to a red heat, without employing 

 any other test of its presence. 



The most striking circumstance of all is, that Biot and Thenard, 

 whose apparatus for measuring and weighing was considered as very 

 complete, found the same proportion of carbonic acid in arragonite 



