SECOND REPORT - 1832 . 
436 
Polymeric are those which contain the same relative hut not 
the same absolute number of atoms of the same elements , and 
whose atomic weights are consequently unlike. 
To this class belong olefiant gas (2 C+2 H) and oil of wine 
(4C-f4H), in which the relative proportions of the two ele¬ 
ments is the same, but the weight of the atoms as one to two. 
Metameric are those which while they contain the same 
absolute and the same relative number of atoms of the same 
elements yet constitute substances belonging to an entirely 
different class of bodies, or a different order of chemical com¬ 
pounds. 
It is not easy to express this definition clearly, but it will be 
understood from the following examples. Sulphate of protoxide 
-9 ti« •• • r 
of tin (Sn-f S), and sulphite of peroxide (Sn-f S) if it exist, 
contain the same absolute and relative number of atoms of the 
same elements,—but they are not isomeric. If by heat or 
by any other process one of these compounds could be made 
to change entirely into the other, we should not have two iso¬ 
meric compounds, but two salts belonging to entirely different 
classes, distinguishable by their appropriate designations. But 
similar changes may occur among compound bodies ; and it is 
to distinguish such from really isomeric changes, that the term 
metameric is employed. One beautiful example of this kind 
is exhibited in the cyanuric and hydrous cyanic acids. The 
former, without giving off or absorbing anything, is wholly con¬ 
verted by heat into the latter,—that is, it is changed from a 
compound atom of the first order, or from an oxide of a ternary 
radical J (Cy -f 2 O -f H), into a compound atom of the second 
• • 
order,—-into an acid chemically combined with water (Cy + H). 
These two substances Berzelius calls metamei’ic modifications 
of each other *. 
Isomeric bodies .—The followinglists comprise nearly all that 
is at present known on this interesting subject. 
I. List of Isomeric Bodies. 
1°. The phosphoric and parapliosphoric f acids and their 
salts. 
2°. The tartaric and paratartaric acids. 
3 °. The two states of the peroxide of tin 
* See Berzelius, Arsberattelse, 1832, p. 66, from which the illustration of 
these terms is taken. 
f When two acids differ as these do, Berzelius proposes for the second the 
prefix 7ra^ci, as denoting change. 
t See Berzelius, Traite de Chimie, iii. p. 162. 
