REPORT ON CHEMISTRY. 
435 
Dr. Dalton, in liis reasonings on atomic arrangement, had 
early shown that the atoms of compound bodies might be 
supposed to group themselves in one of several different ways ; 
—Berzelius in 1814 had proved, by his experiments on Tin, 
that there existed two chlorides and two oxides of that metal, 
having the same atomic constitution but possessing unlike pro¬ 
perties ;—and Dr. Thomson, in his First Principles , in treating 
of the then supposed identical composition of the acetic and 
succinic acids, had made it exceedingly probable that there did 
actually exist very unlike chemical compounds, in which the 
same elements in the same relative proportion were so grouped 
together as to produce the same atomic weight;—but it was 
not till the appearance of an admirable paper by Berzelius, on 
the Composition of the Tartaric and Paratartaric (Racemic) 
Acids, that the doctrine was fully established. In this paper * 
he showed that these two acids on the one hand, and the phos¬ 
phoric and paraphosphoric on the other, are identical in com¬ 
position, and for such bodies die proposed the term Isomeric 
(kto's equal , psgog part). The able and interesting researches f 
of MM. Wohler and Liebig on the acids of cyanogen, added 
to the list, by showing that the soluble and insoluble cyanuric 
acids § (Cy + 2 O + H)-the cyanic and fulminic acids were 
also isomeric. Many other examples have since been brought 
forward, and the investigation of organized compounds is daily 
adding to our knowledge on this important subject. The doc¬ 
trine itself has likewise met with general reception ; and in ad¬ 
verting to the enlarged ideas it has already given birth to, we 
cannot help regarding the establishment of it as a new bound 
the science has taken towards that vast extension it is destined 
to attain. 
Polymerism and Metamerism. —Since the introduction of the 
term Isomeric, it has sometimes been misapplied by chemical 
writers fromnotproperly understanding the exact meaning it was 
intended to convey. To prevent such mistakes in future, and 
to designate compounds approaching in atomic constitution very 
nearly a to those properly called Isomeric, Berzelius has proposed 
the introduction of two new terms, polymeric and metameric. 
The distinction between the three terms is as follows. 
Isomeric bodies are those which contain the same absolute 
and relative number of atoms of the same elements , and have 
consequently the same atomic weight. Of this kind are the two 
oxides of tin, the two phosphoric acids, &c. 
* Kong. Vet. Acad. Handl'ingar 1830, p. 49. 
f Annates de Chimie, xlvi. p. 25. 
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