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SELECTED ARTICLES. 
their ova, which settling into the lowest parts of the atomic 
atmosphere, are equally defended from heat and cold. This 
substance, he conceives, gives rise to the miasmata of marshes, 
to infectious effluvia, and other concomitant exhalations: chlo- 
rine, acids, and other substances, owe their disinfecting 
qualities to their power of absorbing this substance into their 
atmospheres. If its existence should be ascertained, Microgen 
might be deemed an appropriate name. 
Athenaeum — Tra?isaction of the British Association. 
ART. LIII.— NOTE ON THE CONSTITUTION OF SALTS. 
By Professor Graham. 
The author hoped to be excused for drawing the attention 
of chemists to a distinction in saline combinations, which is, 
at present, too often overlooked, and confusion thereby occa- 
sioned. The orders of monobasic, bibasic, and tribasic salts, 
of which the phosphates proved types, have lately been greatly 
enlarged by the discoveries of Liebig and Dumas, respecting 
vegetable acids, and the distinctive characters of these orders 
are w T ell understood. The best proof of an acid being bibasicor 
tribasic is, its combining at once with two bases which are iso- 
morphous or belong to the same natural family, as phosphoric 
acid does with soda and ammonia in microcosmie salt, and tar- 
taric acid with potash and soda in Rochelle salt. Water and mag- 
nesia, water and barytes, water and oxide of lead, are also 
constantly associated as bases in bibasic and tribasic salts, 
but never in true double salts, or combinations of two or more 
salts with each other, with which salts of the preceding orders 
are apt to be confounded. But it is too generally supposed 
that a metallic oxide cannot exist in a saline combination, ex- 
cept in the capacity of base, although in most of those bodies 
which are at present termed sub-salts, the whole or a portion 
of the metallic oxide is certainly not basic, but is attached to 
a really neutral salt, in a capacity similar to that of constitu- 
tional water, or water of crystallization. Oxide of copper, 
