S25 
Sulphat of Lime, 
I procured 150 grains of gypsum from 100 of pure limestone^ 
when the gypsum after being carefully washed in a moderate pro- 
portion of water was dried for an hour on the top of a ten plate stove* 
on which I could just bear my hand. But when I calcined it for 
an hour in a full red heat, I procured from 100 grains of carbonat 
of lime, but 1 30 grains of gypsum. 
I took a well characterized piece of compact gypsum from a 
ton that lay for sale in the street here ; and reducing it to fine pow- 
der, I calcined it in a crucible in a full red heat for an hour. I 
drove olf 2 1 i parts : this occurred to me three times. 
I took from a lump of the same gypsum (Nova Scotia, import- 
ed to Baltimore and thence sent to Carlisle) some of the semi-trans- 
parent chrystals of a vein that ran through the lump. Exposed to 
heat in the same manner, the result was the same. 
Hence I conclude ; that 100 parts of pure carbonat of lime, will 
yield 1 30 parts of anhydrous gypsum (from which the water has 
been expelled) and from 151 to 152 parts of gypsum as it is com- 
monly found. 
In the spring of 1809, I went into the Genesee country, and 
brought with me to Northumberland several specimens of gypsum 
which I had found there. I have since understood that Mr. Church 
of Angelica in that country, had previously discovered and used 
some gypsum, as a stucco. 
The country adjoining the waters of the north east branch of Sus- 
quehanna, are now supplied with gypsum from the Genesee. This 
commerce began in 181 1. A set of people in the neighbourhood 
of Pine creek in 1812, sold great quantities of common limestone 
for gypsum, and deceived many farmers, and injured many mill- 
stones by the deception. It may be worth while to give a few 
characters of gyfisum that may prevent a similar imposition. 
First. When a piece of stone is presented to you as gypsum, 
try to scratch it with your nail, and to chew it between your teeth. 
You may thus scratch and pulverize gypsum, but you cannot ea- 
sily do so with limestone, which is much harder. 
Secondly. Drop on it, a drop of spirit of salt, or of aqua forth. 
If an effervescence, a bubbling, and extrication of air ensue, the 
stone is probably limestone ; for no such effervescence takes place 
on a piece of gypsum, but the acid spreads evenly upon the surface 
as a drop of water would do. Now and then indeed, a specimen of 
gypsum may contain a small portion of limestone, but this does not 
occur often. 
