Magnesian Limestone . 321 
filter and washed, dried and weighed. The solution was then preci- 
pitated by hot carbonat of potash which threw down the magnesia 
and the lime ; and filtered. This precipitate was re-dissolved in sul- 
phuric acid, and left to stand. The sulphat of lime (generally about 
one sixth) separated spontaneously, fell down and was added to the 
first portion. 
The whole of the magnesia was then thrown down by carbonat of 
potash, well washed, dried over a charcoal fire in the heat of about 
160* and then weighed. 
The sulphat of lime, or gypsum, was exposed in a crucible for 
2 hours to a red heat, and the lime calculated on the proportion of 
100 parts limestone to 130 of the anhydrous gypsum. A propor- 
tion, for which I will assign my reasons in a supplement to the 
present paper. 
Secondly. I proceeded in another way. 
I treated the finely powdered limestone with strong sulphuric 
acid (oil of vitriol of commerce) ; triturating them together in a 
glass mortar. I then added four times the quantity of water. The 
clear liquor was decanted from the sediment which was washed 
with another portion of water, and the liquors added together. 
The sediment (gypsum) was rendered anhydrous by exposure to 
a red heat in a crucible for 2 hours, and the limestone calculated 
on the proportion of 10 parts limestone to 13 of anhydrous gyps: 
deducting the silex previously found. The filtered solution to 
which the washings were added, was concentrated by evaporation, 
which occasioned a slight precipitate (about ^-th) of sulphat of lime : 
it was then treated with carbonat of ammonia for the alumina, and 
with carbonat of potash for the magnesia as before. 
The component parts of the stones sent to me, were ascertain- 
ed on the average of these two methods. 
The limestones transmitted to me, bore evident marks of conti- 
guity to primitive strata. The colouring matter was black horn- 
blende, sometimes in streaks or veins, sometimes minutely divi- 
ded and mixed with the limestone, giving the greyish tinge to the 
stone. The 9th specimen was intermixed with mica ; the insole 
ble residuum of the four first specimens in dilute marine acid con- 
tained a small portion of matter, silky to the touch. I believe all 
the limestones connected with the range of primitive formations on 
the seaboard of our country from Boston to Virginia contain more or 
less of magnesia. They are in the immediate neighbourhood of the 
steatite and other magnesian strata, that envelope as a matrix, the 
S s 
