126 EPSOM SALTS. SODA. 
199. EPSOM SALTS, or SULPHAT OF MAGNE- 
SIA, consist of magnesia in conjunction with sulphuric acid 
(24). 
It is said that Epsom salts have been found in the 
Alps, and in Switzerland, under a powdery form, and 
sometimes even in masses, or a state of incrustation on 
stones and rocks. They are, however, chiefly found 
dissolved in mineral waters, arid particularly in those 
at Epsom in Surrey, and Sedlitz in Bohemia. Their 
taste is bitter and unpleasant. So little are they affect- 
ed by exposure to the aii'j that the Abbe Hauy kept 
some by him for more than twelve years without any 
sensible alteration. 
These salts are much used in medicine,, and are some- 
times manufactured from the waters of Epsom (290) 
and Sedlitz (289), but more frequently, and in much 
greater abundance, from sea-water. 
The magnesia of the shops is prepared by dissolving 
Epsom salts in water, and adding to the solution half 
their weight of potash (205). The substance that sinks 
to the bottom is magnesia; and this, washed with a 
sufficient quantity of water and dried, has the appear- 
ance of a light, soft, and white powder, of insipid taste. 
Magnesia is used in medicine, both in a simple state 
and when calcined or burned. It is also employed in 
some chemical processes ; and is in considerable request 
in the manufacture of enamel and porcelain. If putrid 
water be agitated with a small quantity of magnesia, it 
will lose a considerable portion of its bad taste and 
smell. 
200. SODA FAMILY. 
Soda, like potash (205), is an extremely caustic alkali (42). 
It has a greyish white colour, and agrees exactly with potash 
(205) in taste, smell, and corrosive quality, but it is not so 
heavy. 
In a mineral state soda has hitherto been found only in 
combination with some acid. 
Common salt (202) is a compound of soda with muriatic 
acid (29). 
