Page:Popular Science Monthly Volume 5.djvu/52

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42
THE POPULAR SCIENCE MONTHLY.

of the human intellect, and by the instrumentality of physical forces, be formed artificially at will.

In 1828, Wöhler, a German chemist, discovered that cyanate of ammonia, a purely mineral compound, under certain circumstances became changed into urea, without either loss or gain of any foreign body, the elements rearranging themselves to form a more complex structure. But here it was claimed, by the vitalists, that urea, being an excrementitious substance, and one of the waste products of the animal system, must be considered as in reality a mineral, and only accidentally, as it were, akin to animal tissue.

There exists in the bodies of ants a secretion which apparently serves them as a weapon; it is called formic acid, and, for some years after its discovery, was universally prepared by pounding up sundry ounces of ants in a mortar, and distilling them with water, when the bodies of the insects were left in the retort, and a diluted acid was found in the receiver. Analysis showed this substance to be formed of but three elements, and which, moreover, did not appear to be united in a complex manner. From certain analogies it was inferred that the acid might be obtained by some method of gradual oxidation; at last, the right substance was found, and, by duly acting on starch by oxygen, formic acid was produced. This was considered a very great step in advance, for an animal product had been at last formed from a vegetable one; and though it is true the body in question had a simpler constitution than the starch, still the plane of possible chemical processes had been elevated into the animal kingdom.

Quite recently a method has been discovered by which formic acid may be generated directly from its elements. To do this, carbon, say a bit of charcoal or coke, is heated in a limited supply of air, and the result is carbonic oxide; this gas, if exposed for a long time over caustic potash, combines with it, and this product, if distilled with oil of vitriol, yields formic acid. Thus the body has been formed without any thing having been used which is the product of life.

From this point progress was rapid, though at first apparently it rather tended away from the matter at issue. Previous study in the department of mineral chemistry had gradually forced the conception that the position of the elements in a compound had as much to do with its properties as did their number and amount, and it also had developed the fact that certain elements might be withdrawn and their places filled by something else, without changing the general character of the substance. Indeed, a compound body was called a chemical structure, and likened to a real edifice, in which the elementary atoms were the bricks of the house, and the resulting properties constituted the shape of the building. Now, by replacing one element by another, the same kind of change was produced as would be caused by the substitution of marble for bricks, or iron for stone, in the real house. Its appearance and habitability might be greatly altered, but its general shape and character remained.