1821.] • Dr. Daubeny on Arragonite. 221 



discovered strontian in some of the sub-varieties, yet it still 

 remains to be proved whether this earth be an essential, or only 

 a casual ingredient." 



I imagine, from the above sentence, as well as from the silence 

 of the journals which I am in the habit of perusing, that the 

 recent experiments of ProfessorStromeyer on this subject are not 

 generally known in Great Britain ; and, under this impression, I 

 may just mention, that having visited Gottingen last summer, in 

 the course of a tour through the north of Germany, I had some 

 conversation with Prof. Stromeyer on this and similar subjects, 

 and was informed by him that he had lately analyzed no less 

 than 18 varieties of arragonite, several of them carefully selected 

 from the very localities with those which, under the hands of 

 other experimenters, had afforded results so opposite ; and that 

 all, with one exception, had yielded traces of strontian in a 

 greater or less proportion. 



This solitary exception was the " coralloidal variety," or 

 " flos ferri," in which no portion of the earth in question could 

 be detected — a fact which may be alledged in corroboration of 

 the argument adduced by Dr. Clarke to the same effect, from the 

 circumstance of this mineral appearing to result from a simulta- 

 neous process with that by which calcareous alabaster (a mineral 

 totally devoid of strontian) is deposited. 



Professor Stromeyer, therefore, I believe, proposes to separate 

 this from the crystallized varieties of arragonite, as the latter, 

 according to him, not only contain strontian as a constant 

 ingredient, but even have their form affected by the greater or 

 less proportion in which this ingredient enters into their compo- 

 sition. Nor does it appear impossible that so small a portion of 

 strontian should determine the crystallization of the mass, when 

 we consider how inconsiderable a quantity of carbonate of lime 

 will, in some instances, give itsjfbrm to the aggregate, of which 

 it forms a part, as in the instance of the Fontainbleau sand- 

 stone. 



Without, however, pretending absolutely to decide whether 

 the discovery of strontian be sufficient to remove this anomaly 

 to the general law of the correspondence of crystalline form with 

 chemical composition, it must, I think, be admitted, that unless 

 I am incorrect in considering the authority of Prof. Stromeyer in 

 those departments of Chemistry, to which he has devoted his 

 principal attention, of equal weight with that of Thenard, Four- 

 croy, and Vauquelin, who have contradicted him, the positive 

 assertion of this eminent chemist must, according to the common 

 laws of evidence, outweigh the negative testimony of the /after; 

 and if such experimenters as those above alluded to, be allowed 

 to have been mistaken, it is no disparagement of the analytical 

 skill of Mr. Holme, to whom Dr. Clarke afterwards alludes, to 

 conceive that he may have also fallen into a similar error. 



I should add that Prof. Stromeyer presented me with a paper 



