xalic acid. Oxalic acid, however, is not regarded as a binary compound of carbon and oxygen ; the fact that it undergoes decomposition when its water of crystallization is extracted is no proof to the contrary, for nitric acid is decomposed by the extraction of the last portion of its water. Woehler also finds, that urea is obtained in place of cyanide of ammonia when a solution of chloride of ammonia is poured over freshly precipitated cyanide of silver, chloride of silver being formed at the same time. Urea is also formed in the decomposition of cyanide of lead by solution of ammonia. The solution at first contains cyanide of ammonia; but by evaporation of the fluid this salt is converted into urea. In the same way, also, whet cyanous acid is mixed with water or liquid ammonia cyanide of ammonia is first formed, and thence urea.
The point is worth consideration. If you analyse an organic substance into its elementary parts, you cannot again reconstruct the original substance from those elements. True. But the reason is that you have made an elementary analysis, and the synthesis required is not elementary, but immediate. The substance was not formed of the four organogens and some mineral elements it was not formed directly of the elements into which it is decomposed it was formed of proximate' principles, and these proximate principles were formed of the elements: In inorganic substances precisely the same difficulty meets us. We can decompose saltpetre into its elements oxygen, nitrogen, and potassium. But we cannot recompose saltpetre by the direct combination of these elements, any more than we can so recompose organic substances ; because saltpetre is formed by a synthesis of nitric acid with potass, and not directly. Thus, as Comte remarks in his chapter on Chemistry, Wöhler would never have succeeded in producing urea if he had endeavoured to combine the elements which compose it; he succeeded because he combined its proximate principles.
An illustration : There is a favourite game in which a number of letters forming a word to be guessed are thrown together pell mell. These letters may represent the elementary atoms. According as they are arranged in sequence they form the word intended, or some other word. My own name, for example, will form Lewes, Sewel, Elwes, Wesel, Weesl, Leews ; in a way analogous to that in which the organogens form isomeric bodies. All depends on the arrangement, sequence, synthesis.
Further, be it remarked that among the proximate principles of organic substances there are many of what may be termed mineral origin, whose part is accessory but indispensable ; and experiment justifies à priori deduction in asserting that in proportion as organic substances contain a large percentage of these principles, the more do they approach those substances which can be artificially formed; and vice versa. Urine, for example, is formed of a larger proportion of water and salts than of other principles, and contains more than other organic products.
" Thus, then, we see that elementary analysis can teach us little or nothing of organic substances formed of proximate principles. The value of the elements varies with their varying positions.
As Mulder says, this synthesis is all important : " if we pass in review the substances present in the organic kingdom, we perceive an endless series of combinations from either two, or three, or four elements only. This is enough to show that there is an indefinite capacity for modification in the primary forces which operate in the elements. The influence of one upon another is thus unlimited also. A slight difference in the state of an element is sufficient to give it the appearance of a new, an entirely peculiar, substance, as compared with the other elements. Let us take, for example, starch, gum, sugar, acetic acid, glucic acid, inuline. All these are composed of the same elements, taken in the same proportions. Thus they consist severally in equivalents of "The carbon of one of these substances is no doubt equal to the carbon of any of the others, in so far 