ON ELEMENTARY CHEMISTRY. 
167 
ments among themselves; and lastly, the general principles 
of chemical philosophy. This arrangement is out of the 
usual course. We are accustomed, in elementary works, 
to see the laws of combination, affinity, the atomic theory, 
and the influence that electricity exerts in the composition 
and decomposition of bodies, discussed, before treating of 
the bodies themselves; so that in afterwards reading of the 
properties of substances, their relations to each other be- 
come apparent. Of the propriety of this change there may 
be a difference of opinion ; yet as most of the leading gene- 
ral laws of chemical philosophy are readily comprehended, 
and as even a partial knowledge of them adds much to the 
interest of chemical studies, some acquaintance with them 
previous to entering on a consideration of the elementary 
bodies and their compounds, seems almost indispensable. 
The third division embraces the chemistry of the metals. 
After stating the general properties of the metals, a full 
chapter on crystallography follows, which comprehends the 
subject of isomorphism, or the relation which has been 
found to exist between the crystalline form and chemical 
constitution of bodies. The grouping of bodies in their iso- 
morphous relations, is now considered the true basis of a 
natural classification ; and although all the elements have 
not been brought under the arrangement, owing to the dif- 
ficulty of discovering the crystalline structure of many of 
them ; yet sufficient has already been ascertained to give 
the subject a deep interest. The binary theory of salts is 
cursorily treated of, and is favorably viewed by the author, 
although he admits of difficulties, yet to be removed, before 
it can be unhesitatingly adopted. 
In treating of the metals and their compounds, the author 
has introduced several improvements, which add much to 
the usefulness of the work as a text-book. Among them is 
the illustration, by diagrams, of the more complex chemical 
changes, as in the rationales of the processes for making the 
mercurial chlorides, the sulphuret of antimony, and some of 
