18 On the Serpentine Rocks of Hoboken, N. J. &e. 
and either truncated at the apex, or with an acumination so 
indistinct as to be scarcely visible. If these crystals are to 
be considered as homogeneous with the sparry mass to which 
they adhere, they are essentially crystals of carbonate of 
magnesia, but at the same time there is nothing thus far dis- 
coverable in them by which they could be distinguished 
from carbonate of lime. This white substance presents 
sometimes a singular state of disintegration, filling the cavi- 
ties of the veins with a perfectly friable and pulverulent sub- 
stance of the colour and appearance of the magnesia of the 
shops. ‘The specific gravity of this marmoraceous mineral 
taken by Nicholson’s balance was 2,880. 
Chemical characters. 50 grains of the white and sparry 
kind, possessing a splintery fracture, and giving fire with 
steel, after pulverization, and strong ignition for an hour and 
a half, came out a little tinged with brown, and had lost 25 
grains. This powder dissolved almost instantaneously in 
nitric acid, and formed a saline brown mass, which was 
evaporated to dryness, when, being diluted and filtered, itleft 
one grain of silex in a hyaline gelatinous form. 
On the addition of the prussiate of potash a deep blue 
precipitate appeared, and amounted by the usual reduction 
to a quarter of a grain of protoxid of iron. 
The whole of the earthy contents were now precipitated 
at a boiling heat with carbonate of potash, which when 
edulcorated and calcined gave 22 grains of what appeared to 
be magnesia, and which lost no appreciable portion on be- 
ing boiled in caustic potash. Its solution, however, in sul- 
phuric acid afforded 10 per cent. of gypsum, or nearly the 
proportion of three and a half grains of pure lime. From 
this experiment the magnesian marble of Hoboken appears 
to consist in the 100 parts of 
Magnesia cai ce - 44,00 
Carbonic acid and water 50,00 
Lime - - - - 3,50 
Silex -. - - - 2,00 
Protoxid of iron - - 0,50 
100,00 
The proportion of lime varies, so that in a highly colour- 
ed green and sparry specimen, scarcely distinguishable from 
serpentine, I obtained 48 per cent. of lime. 
