onent elements them-selves."
Our former illustration of letters may help us to an explanation of isomerism, which is erroneously supposed to depend on a simple difference in the grouping of the elementary atoms, and not on a difference also of synthesis. Thus, in Stoekhardt's work on Chemistry we see isomeric diagrams, in which the, atoms are differently arranged, to explain all the differences of phenomena; as if a difference to the eye carried with it all other differences !
Isomeric bodies, properly, defined, are bodies having similar elementary composition with dissimilar immediate synthesis; and in proof thereof, they not only form different compounds when united with similar bodies, bases or acids, but also it is now found they give different products when analyzed with sufficient precaution.* It is to be further noted that all these isomeric bodies are bodies having an organic origin ; many of them are actually organic, i. e., they are formed of several proximate principles.
There is another difference of composition, and one which demarcates Chemistry from Anatomy with sufficient precision to form of itself a ground for denying the propriety of such a science as Organic Chemistry. The difference I refer to is this : Inorganic substances are definite in their composition. Water, for example, whether as water, steam, or ice, is uniformly composed of 122 ounces of hydrogen to 100 ounces of oxygen. Quicklime, however prepared—from marble, limestone, chalk, or oyster-shells—uniformly contains 250 ounces of calcium to 100 ounces of oxygen. It is on this fact rests the brilliant atomic theory of definite proportions.
Not so Organic substances. Those which are specially Organic—those, I mean, which are not crystallizable are uniformly indefinite or indeterminate in their composition, That is one of their definitions. No chemical formula, precise in its equivalents, will serve to characterise absolutely an organic substance.
Not only is the elementary composition of organic substances very complex, the immediate composition is so likewise. This immediate composition is not formed of proportions fixed, determinate, invariable, and de-fined, as in inorganic substances. The organic substance, without losing its distinctive characters of coagulation, &c., may possess a little more or a little less of the elements of water, for example. Elementary analyses do not always give one constant result, as they do in the reduction of inorganic substances ; showing that the composition is not definite.
It is because the composition of organic substances oscillates between certain limits (limits, it is true, not very distant) that we are unable to foretell with any absolute certainty what are the molecular acts of combination or of double decomposition which will occur in any given ease, as we can. with urea, for example. The instability which accompanies this complexity of composition prevents our being certain, after having combined any organic substance with an acid, of finding it precisely as it was before, when we remove the acid by means of a base ; as we can with urea and nitric acid. The composition being indeterminate, it is possible the substance may have lost some of its elements, or its immediate molecular composition may have been modified.
How much of this indeterminateness may be mere mixture, I do not pretend to say. The distinctive fact is all needed for my purpose. The differences resulting from different immediate composition may be seen in Albumen and Fibrine, two substances having exactly the same elementary composition, and yet two substances so different that no one could confound them. Yet by reagents, or by heat, we can change Albumen into a solid and Fibrine into a liquid, so that the two may be indistinguishable one from the other ; and this without altering their elementary composition. Indeed, to use the language of the chemist I have been following, " Ces éléments varient constamment de quantité entre certaines limites pour une même espèce anatomiquement identique, mais prise chez des individus différents, 