446 MODERN CHEMISTRY. 



together, the two bases exchange acids by an exact compensa- 

 tion ; the original compounds are altogether lost and two new 

 salts evolved, without either loss or addition of any kind in the 

 process. So numerous are the facts and tables illustrating 

 this doctrine of chemical equivalents, and so various the 

 forms under which the subject may be viewed, that we must 

 rest on this exposition of the principle, and proceed to other 

 results from the law which is the basis of the whole. 



One of the most curious of these has been derived from 

 the researches of Berzelius into the chemical relations of the 

 molecules of matter. This has received the name of 

 Isomerism, as expressing the fact that in certain cases the 

 same elements may be combined in exactly the same pro- 

 portions, yet produce compounds having very different 

 chemical properties. Two conditions of Isomerism may be 

 noted; one in which the absolute number of atoms and 

 consequently the atomic weight of the compound is the 

 same : the other, where, though the relative proportions 

 of the elements are the same, the absolute number of atoms 

 of each is different. But taking the simplest expression of 

 the phenomenon, it necessarily implies a difference in such 

 cases, in the mode of grouping together of atoms absolutely 

 alike in nature, number, and relative proportion a circum- 

 stance conceivable indeed, but never before proved. The 

 whole investigation, still in its infancy, and perplexed by 

 ambiguities, is of singular importance to the theory of com- 

 pound bodies and to every part of organic chemistry. It 

 promises for the future deeper insight into those primary 

 atomic conditions of matter, which have yet been approached 

 only by the rash speculator or imaginative poet. 



The same may be said of another great discovery, ana- 

 logous in kind, of Mitscherlich of Berlin ; and to which the 

 name of Isomorphism was applied, to express the fact it 

 discloses ; viz. that the chemical elements of certain bodies 



