are sat rendered more powerful a 
is farther combined with an acid. The mildest preparation of mer- 
cury, for example, is that prepared by trituration merely, in which _ 
the mercury approaches nearest to the metallic state, and the most 
virulent preparation of that metal is the corrosive page in which 
it is very highly oxydated. 
The last class of simple substances is the EARTHS. They hee 
usually been.defined substances, insipid, infusible, having little solu- 
bility, uninflammable, having a specific gravity, compared with water 
as a standard, always less than 5 to J, and combining with acids to 
form neutral salts. Of these characters some apply only to some 
earths ; that of insipidity, for instance, is confined to two or three 5 
others, as lime and barytes, being considerably sapid. 
These characters too are understood as applying to pure earths ; 
substances which, so far as has been discovered, are absolutely simple. 
These by combination, or intimate mixture with each other, and with 
other bodies, give rise to a vast variety of compounds, still distin- 
guished by the title of earths, but to which these characters are only 
in part applicable. Such compounds are not the objects of pharma-~ 
ceutic investigation, it being only the pure earths, or commas 
of them effected by art, that are usedin medicine. 
The principal earths are six; silex, i 
_ and strontites. Of. two or shies others hate eet g 
but in quantities so 1 as not to require notice in this eeu: 
/Sinex, though an abundant ingredient in stones, scarcely exists 
pure in nature. When obtained by a chemical process, it is in the 
form of a light white powder. Its chemical character is its little 
susceptibility of combination. It unites with none of the acids, the 
fluoric excepied. Itis dissolved by potash and soda ; and by fusion 
it combines with the earths and metallic oxyds. 
Areu. is distinguished by insipidity, infusibility by heat, insolubili- 
ty im water, and by forming a ductile paste with that fluid, but more 
completely by the compounds which it forms with acids. It is never 
used in medicine ia its pure state ; but some of its ier gare ee 
cially that resulting from its union with sulphuric acid, are employ-— 
ed. The salts formed by its combination with acids, have one 
-neral medicinal character, that of ning enemas a 
of a 
MM. s5 pure, is siwayer in pres form of a fine white a : 
light fwiekee _ It is infusible ; insoluble in less than 2000 parts of 
water, and does not form with it a ductile paste ; is somewhat sapid ; 
changes the colours of vegetables:to a green, and forms with the acids" 
peculiar neutral salts. It is never found in a~ pare. ne: im neteet 
but is always the produce of art. © > ik 
Magnesia, in its pure state, is extensively anid in lisedhctegis 2 
also several of its compounds. It is given as an antacid, a 
_ Salts:it forms with the acids bave all a cathartic power. 
~ Lime is distinguished by its disagreeable, penetrating, styptiet 
Bewttencta: water rapidly from the atmosphere; it is heated 
water is poured ‘on it, and falls into a dry white powder ; 
ia about 700 parts of that. fai: and its = ha 
i 
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