22 Onthe Serpentine Rocks of Hoboken, N. J. &c. 
in medicine, and imported largely into this country, could 
here be established. 
‘In England it has been found profitable to manufacture 
this salt from the calcareous magnesian minerals. In this 
process, however, it becomes necessary to saturate the use- 
less and predominating portion of calcareous ‘earth besides 
the magnesia, which in the serpentine of Hobdken, and 
probably that of Baltimore, is entirely obviated by the ab- 
sence of every soluble earth but the magnesian. 
In Salinelle, in the department of Gard in France, this 
salt is fabricated to advantage from an earth which consists 
in the 100 parts of Silex 45, magnesia 22, water 32, and a 
trace of iron. 
From such minerals and particularly from a substance so 
pure, unusually productive, and uncontaminated as that of 
the serpentine in question, the sulphate might be obtained 
in a degree of purity altogeter superior to that of commerce, 
usually manufactured from the bittern of sea-water which 
abounds in foreign ingredients. 
A pulverization similar to that which is employed in pre- 
paring gypsum for agricultural purposes is all that would be 
requisite in these serpentine rocks ; and as far as my ex- 
periments have extended in the small way, the solution of 
this mineral is more complete before than after ignition, at 
least when a moderate heat is employed. 
In the vicinity of Germantown, about eight miles from Phil- 
adelphia, a serpentine formation occurs so very similar to the 
Fahlunite of Sweden, that [ could not satisfy myself of their 
distinction in any other way than by the educts of analysis. 
Like that mineral it occurs in disseminated, but partly con- 
fluent blackish-green masses, blended with a pe tare 
confusedly laminated tremolite, closely allied to Hornblende, 
and as well as the serpentine, soft enough to be easily scrap- 
ed with a knife, and scarcely scratching glass. The frac- 
ture of this serpentine is somewhat conchoidal as in Fahlu- 
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