As an example of this class of syntheses, the alcohols may be cited. Ordinary or wine alcohol is one of a large class of bodies which have similar features, and to which the same general name has been given; they constitute a series: thus, we have methylic alcohol, vinic alcohol, tetrylic alcohol, and so on. Now, in most of these we can substitute certain metals for hydrogen; for instance, metallic zinc can be thus inserted, and hydrogen removed, yielding zinc-ethyl, and, with the addition of oxygen, zinc-alcohol, and we get a colorless, fragrant liquid, in which, singularly enough, the zinc has so far lost its usual characteristics as to be both invisible and volatile. By carrying on the steps of this process still further, several metals may be introduced leading to the production of bodies of great resultant complexity, but which, through all their metamorphoses, are yet true members of the alcohol family.
In this sense the artificial processes may be said to surpass the natural ones; for man is able to add many individuals to a series of which Nature presents us with only scattered terms; and, in addition, in this particular group, he is able to form some of the natural members, such as wine alcohol and glycerine, by a direct process of construction, starting with the free elements, carbon, hydrogen, and oxygen. The method is briefly as follows: Carbon, in the form of black-lead, and therefore strictly a mineral substance, is heated intensely between the poles of a galvanic battery; when it is brilliantly incandescent, hydrogen gas is made to pass over its surface, in a suitable apparatus, the sides of which are kept comparatively cool, and the result is the formation of an invisible but extremely irritating gas, known as acetylene. Now, if acetylene is brought into a solution of copper, it combines with it, forming a dark-red explosive compound, and, if we act upon this body by hydrogen, the copper will be expelled, and olefiant gas, a sweetish ethereal substance, is obtained; and, finally, by distilling this last with sulphuric acid, alcohol is one of the products. Thus, in the several steps leading to this result, only mineral matter and ordinary chemical forces have been employed.
It must not be inferred, from the above meagre examples, that the number of syntheses is equally limited. Already there have been formed several natural vegetable acids, many of the alcohol family, some of the sugars, a whole host of ureas, a multitude of bodies analogous to the vegetable alkaloids, as well as many of the natural flavoring and coloring agents; these last, indeed, on an extended commercial scale.
So far as the evidence of experience goes, there seems no limit to the possible production of organic bodies which possess a definite chemical structure, at least of those which have the power of crystallizing, for the number, even now beyond the powers of an ordinary memory, is constantly increasing in an accelerating ratio, and already, as has been referred to, in some instances exceeds the range of Nature herself.