26 Discovery of the Composition of the Arragonite. 
with that of baryta, and hence supposed that, if the arra- 
gonite contained strontia, it must infallibly be precipitated 
from the solution in muriatic or nitric acid, by the sulphuric 
acid, or by a salt contaming it, when the solution was only 
diluted in such a degree that the lime would not be separated 
from it.. This supposition is however not true, as I have 
formerly had occasion to remark in my analysis of the sul- 
hate of strontia from Suntel. 
There is in general a great resemblance in the chemical 
relations of strontia and lime. It is therefore very difficult 
to separate them, and I have only been able to do it effec- 
tually, by dissolving the arragonite in pure nitric acid, eva- 
porating the solution to crystallization, and treating the 
crystalline mass with alcohol, in which the nitrate of 
strontia is not soluble. In the evaporation of the solution, 
we may be convinced that it contains strontia. If we carry 
the evaporation nearly to the point of crystallization of the 
nitrate of lime, the nitrate of strontia is deposited while it 
3s cooling, and often during the evaporation, if it was nearly 
neutral, in small octabedral crystals which are left unaltered 
when alcohol is poured on the mass. 
You will naturally ask if this quantity of the carbonate 
of strontia can be sufficient to produce the striking pecu- 
Jiarity of the appearance of the arragonite ; and I believe £ 
may safely answer that itcan, Many experiments which 
I have made in analysing the natural magnesian limestones, 
seem to show that even small proportions of substances 
possessed of strong powers of crystallization may cause 
other substances to assume their form. For example, I 
have analysed a specimen of perfectly rhomboidal magne- 
sian spar from St. Gothard, which contained only 7 per 
cent. of carbonate of lime. In the same manner I have 
found reason to think that many of the sparry iron stones 
derive their rhomboidal fora trom the carbonate of lime 
which they contain. May it not therefore be imagined, 
that the crystalline form of the arragonite depends on that 
of the carbonate of strontia, which has certainly stronger 
powers of crystallization than the carbonate of lime? As 
far however as I know, the strontianite has not yet been found 
perfectly crystallized; hence its proper structure is unknown, 
and nothing can be decided positively respecting it. But 
may not the circumstance of the frequent confusion of the 
arragonite with strontianite be considered as favouring my 
opinion ? 
My experiments on the magnesian limestones were un- 
dertakcn with a view to investigate whether the laws laid 
down 
