434 
SECOND REPORT— 1832. 
Isomerism .-—The differences in chemical and mechanical pro¬ 
perties among simple and compound bodies, were the first to 
attract the attention of the early chemists. When methods 
were discovered in more recent times by which the elements of 
compound bodies could be separated from each other, it was 
natural to expect that those which were possessed of unlike 
properties should also prove unlike in composition. Nor did 
the results of analysis disappoint this expectation. It was 
found that substances differing in properties were composed 
either of unlike elements or of the same elements in unlike pro¬ 
portion ; and if results of a contrary character were at any time 
obtained, they were at once set down as erroneous, and further 
research generally proved them so. But as the art of analysis 
improved, and the chances of error were confined within nar¬ 
rower limits, the views of chemists in regard to the composition 
of bodies became more extended. The vast variety of organic 
compounds which Nature, by her mysterious processes of ela¬ 
boration, has formed out of the same four simple elements, taught 
them that the characteristic properties of different compound 
bodies depended less on the presence of unlike elements than 
had hitherto been supposed.—The near approach to equality 
in the proportions of the elements of many widely different ve¬ 
getable products, showed them how closely substances might 
stand to each other in composition, while they were far sepa¬ 
rated in properties and when at length it was proved by con¬ 
vincing experiments, that the elements may be the same, and 
their proportions identical, and yet different compounds result, 
it became necessary to recognise the mode of grouping or ar¬ 
ranging these elements, as alone sufficient to produce the most 
striking sensible differences. This last conclusion was first 
distinctly pointed at by the compounds of carbon and hydro¬ 
gen ; it has been confirmed and established by many more re¬ 
cent investigations. 
Until lately the atomic weights of compound substances con¬ 
taining the same elements in the same relative proportion were 
always found to differ, and in this difference there appeared 
still a sufficient reason for their unlike nature. It was conceiv¬ 
able that in bodies differing as to their atomic constitution in 
this one point only, the elements might be more or less con¬ 
densed, or otherwise so differently grouped as to give rise to 
the observed difference in their properties. But the progress 
of the science has removed this distinction also, and made us 
acquainted with instances in which like elements grouped to¬ 
gether in like number and proportion, constitute unlike com¬ 
pounds having the same atomic weight. 
