Mode of analijzing and testing Gypsum, 105 



in 1812, sold great quantities of common limestonr for 

 gypsum, and deceived many farmers, and injured ma- 

 ny millstones by the deception. It may be worth white 

 to give a few characters of gypsum 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 pul- 

 verize gypsum, but you cannot easily do so with lime- 

 stone, which is much harder. 



Secondly. Drop on it, a drop of spirit of salt, or of 

 aqua fortis. If an effervescence, a bubbling, and ex- 

 trication of air ensue, the stone is probably limestone ; 

 for no such effervescence takes place on a piece of gyp- 

 sum, 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. 



Thirdly. If the preceding tests do not give satisfac- 

 tion, then take 100 grains of the stone : reduce it to a 

 fine powder : grind up with it 250 grains of common 

 pearl ash, boil them in a tin or earthen vessel, with 

 half a pint of water, to dryness. Wash what remains 

 by three separate affusions of half a pint of boiling wa- 

 ter : dry the sediment at the bottom. If the stone be 

 gypsum, that sediment will weigh 77 or 78 grains ; it 

 will have all the properties of common limestone redu- 

 ced to powder, it will effervesce with, and totally dis- 

 solve in a mixture of one part of spirit of salt to two 

 parts of water, added by degrees till the wliole be dis- 

 solved. 



VOL, III. o *" 



