Biographical Meminr ofM. HttUj^ ffS 



volVcs tho former sometimes in much fi^reater qnantity, so that 

 the same mineralogical species, such as sparry iron, which is fuiu 

 damentally nothing but calcareous spar, or carbonate of lime, may 

 contain so much iron as to amount to a fourth or a third of its 

 weight, and thus l)ecome to the metallurgist, in place of a sim- 

 ple mineral, a true ore : that muriatic spar, which also h no- 

 thing but a calcareous spar, may envelope grains of sandstofne 

 to such a degree as to contain nothing else ; and all this without 

 the angles of its crystals changing a second. 



It is precisely the same in our laboratories as in the great la- 

 boratory of nature. M. Beudant, in making a mixture of two 

 salts crystallize, has seen one of the two constrain the other ta 

 mingle with its crystals, in a much greater proportion thai* 

 would have occurred in it itself. Which of the two is to character-^ 

 ize the mineral.^ Is it the most abundant? Certainly not : for, thia 

 abundance excepted, all the characters of the product are givcrt 

 by the other. 



It is not less certain that the sdme substance at the same mo- 

 ment assumes a very different form from what it commonly has 

 when it is formed into crystals, in which it is individualised, if 

 we may be permitted to employ this expression. All the effort^ 

 of chemists have been unable to find any thing essential in arra- 

 gonite, excepting the same carbonate of lime of which calcareous 

 spar is also composed ; for the small portion of strontian which 

 is discovered in it can only be considered as accidental, and yet 

 arragonite crystallizes in the octahedral form, and calcareous spat 

 in the rhomboidal. And here, also, human art is able to imfitaf^ 

 nature^ and even to make, when it pleases, what nature rarefy 

 makes. Recent exj^eriments performed by M. Mitschcrlich appear 

 to prove, that certain salts may be it)ade to assume different elfe* 

 mentary cystalline forms, according to the circumstances in which 

 they are made to crystallize. But in the small numly?r of cases 

 where nature has itself produced such differences, should We only 

 niiike a single species of these different crystallizjitions ? TheH 

 it would also be necessary to make but one of almost all ih^ 

 warm-blooded animals ; for they are as identical in the chemical 

 nature of their elements, as the two minerals which we have just 

 named. An eagle and a dog have the same fibrin in their muscles, 

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