Popular Science Monthly/Volume 7/October 1875/The Artificial Preparation of Organic Bodies
|THE ARTIFICIAL PREPARATION OF ORGANIC BODIES.|
PROFESSOR OF CHEMISTRY IN WILLIAMS COLLEGE.
THE "good, old" foundation upon which our fathers stood has been sadly shaken. Its complete overthrow has at times seemed inevitable. "Scientific men" have led the attacking army, and thus gradually brought themselves into disgrace with a portion of the community. The fight has been carried on to a great extent blindly, and most attempts to establish order have only succeeded in increasing the confusion. Sorties from the camp of "the fathers" have been made, and weapons have been carried back; but, alas! the weapons were useless, or, if used, they injured the user. The conflict is still waging, and it will continue to wage. Occasionally faint promises of a better understanding are given, but some misguided enthusiast, on one side or the other, hastens to destroy the hopes of a happy issue. The frequent shocks received by "the fathers" have unduly excited them, and they look upon each advance of science as something dangerous. Often they do not stop to examine whether the movement of the hostile party is, or is not, antagonistic to their position, but blindly throw their whole force against it, and anxiously look for the results of the crash. It sometimes happens that they thus waste their force, and weaken themselves for future necessary encounters.
Dropping the figure, we may safely assert that those who are avowedly the opponents of science, though their objects may be the highest—though they may be actuated by only noble desires—have, unfortunately, from time to time brought ridicule upon themselves by upholding views which were not tenable, and which a careful examination and thorough knowledge of the subject would show to be unnecessary for the support of their theories. These somewhat trite remarks lead to a consideration of the subject embraced in the title of this paper.
There are certain chemical substances known to us which only occur in the organs of plants or animals. The number of these substances at present known is very great, and new ones are being rapidly added to the list. They consist often of but three elements—carbon, oxygen, and hydrogen; sometimes nitrogen is added to these, and, rarely, phosphorus or sulphur. Notwithstanding the fact that they are made up of few constituents, they are usually of complicated structure; indeed, the complication in some of them is so great that, with our present means of analysis, we are unable to express their composition by means of satisfactory formulæ. The substances referred to have been known by the name organic bodies.
Up to within a few years chemists were, to a certain extent, justified in drawing a line of division between two classes of bodies, both occurring in Nature: 1. Those which can be prepared in the laboratory; 2. Those which cannot be prepared in the laboratory. The second class included the so-called organic bodies. These were known to occur only in the organs of plants or animals. The two facts, taken together, were significant, and but little surprise can be expressed that a connection was traced between them. The simplest conclusion that could be drawn from the premises was drawn, and the scientific world, buoyed up by certain preconceived notions in regard to life, tacitly accepted it. Chemical substances which are produced under the mysterious influence of life, in the dark, unfathomed cavities of living organisms, cannot be produced by the hand of the mortal chemist. This was the conclusion which grew to be a dogma. and was used as a kind of ex post facto argument in favor of certain views in regard to the so-called "vital force."
But its influence did not cease here. Having worked so beneficially as an important link in a chain of retrograde logical sequences, it was afterward made a starting-point for other lines of argument. It was employed in religious and purely philosophical discussions, and assisted in the establishment of subsequent illogical conclusions.
As these discussions were taking place, the chemist quietly continued his strange dealings with the elements. Discovery followed discovery, until the fact could no longer be doubted that the dogma must fall. Its fall was, however, not the matter of a moment. It received repeated blows before it gave up its existence. Its place has been taken by an hypothetical statement founded upon a large array of facts, viz.: every chemical body, no matter of how complicated a structure, or what its nature may be, will probably, in good time, be prepared artificially in the chemist's laboratory. And this statement becomes more and more probable every day. Already a large number of the compounds, the formation of which was formerly supposed to be dependent upon the action of the vital force, have been reproduced entirely independently of any suspicion of the action of this force; and thousands of other analogous compounds which have never been found in plant nor animal are now known to us. Let us look briefly at some of the steps that were taken in this advance of opinion.
In the year 1828 Wöhler made the first observation bearing directly upon this subject. A few years earlier he had discovered cyanic acid, and he was now engaged in the thorough investigation of this acid. He prepared its ammonium salt, and, on evaporating the aqueous solution of the salt, he noticed the formation of large, well-developed crystals that in every respect resembled urea. Urea was well known, but had, up to that time, only been found among the products formed in animal bodies. Its existence was, in accordance with the then prevalent views, supposed to be due to the inexplicable action of the vital force. A careful examination failed to disclose any points of difference between the two bodies, and Wöhler was forced to the conclusion that at least one organic substance could be prepared outside of the organism.
But this by no means brought about a change of views. The upholders of the old dogma immediately found relief which was apparently satisfactory. Cyanogen compounds, of course including cyanic acid, had only been prepared from substances which had had their origin in the organs of animals, and, although these original substances had been subjected to purely chemical influences, and thus another animal substance produced, the vital force had nevertheless played its part as an essential agent in the formative process. This argument seemed plausible, and could hardly be objected to. Other and more decisive experiments were necessary.
In 1841 Fownes succeeded for the first time in preparing cyanogen directly from its elements. He passed nitrogen-gas over a mixture of charcoal and hydrate or carbonate of potassium at a red heat, and obtained a salt of cyanogen and potassium—cyanide of potassium. From this salt it was a comparatively simple matter to prepare all the other cyanogen compounds, and, finally, urea. Thus, then, there could be no doubt that a direct construction of some organic bodies from their elements was possible.
But urea, in comparison with most animal or vegetable products, is of simple structure. It contains but one atom of carbon in each molecule, whereas many others contain a very large number of carbon-atoms. The transformation of cyanate of ammonia into urea, which took place so readily, was a very simple one, if we consider merely the relation of the two bodies to each other. They have exactly the same composition. They contain the same percentages of carbon, hydrogen, nitrogen, and oxygen. A change of the arrangement of the atoms was necessary, but this was all—no addition of material, no building up, no binding together of a large number of atoms into one compound. There was still left something which could be ascribed to the influence of vital force, and this fact was seized upon and made to do service. It was now stated that, although it might be possible to prepare artificially some of the simpler organic bodies, the vital force was necessary to bring about the complicated form of union found in the greater number of the products of the life-process. This statement held its own for a number of years. In the mean time a series of brilliant experiments by Berthelot had established the fact that a large number of organic bodies could with ease be prepared artificially. In 1856 this chemist published the first results of his investigations. He had effected a direct union of carbonic oxide with hydrate of potassium, and thus obtained the potassium salt of formic acid. Later he showed that a direct union of carbon with hydrogen was possible; using carbon-poles, he passed a current of electricity through them in an atmosphere of hydrogen; he thus obtained acetylene, a hydrocarbon made up of two atoms of carbon and two of hydrogen. He also produced marsh-gas, ethylene, and a number of other hydrocarbons from inorganic materials which, in their turn, could be obtained from the elements. It was shown that marsh-gas could be converted into methyl alcohol; ethylene into ethyl alcohol; and from these alcohols it was an easy step to formic and acetic acid; to the aldehydes, amines, acetines, etc., etc. These results, although startling when viewed from the oldest stand-point. could still be reconciled to these views as necessarily modified subsequently to Wöhler's discovery. The compounds thus formed artificially were still of comparatively simple structure; and, in the numerous transformations effected by Berthelot, in no case was the passage from a compound of a lower to one of a higher order. Marsh-gas, methyl alcohol, and formic acid, each contained but one atom of carbon; ethylene, ethyl alcohol, and acetic acid, each contained two atoms of carbon. Surely the vital force alone could build up more complicated bodies.
Not so. The series of advances in the new doctrine, thus so propitiously begun, did not stop. New methods of investigation were introduced. Questions of a different character were put to chemical substances, and answers were not wanting. The interest in chemical science increased, and the army of those who were to carry it forward also increased. The growth of the science became proverbially rapid, and, during the excitement attendant upon this development, the last of the old landmarks between inorganic and organic bodies was swept away; vital force, as far as it was directly concerned in the formation of organic bodies, lost prestige. Both classes of bodies were found to be subject to the same fixed laws, A chemical substance is a chemical substance, look at it as we will. Its constituents, in one case as in the other, are bound together by chemical affinity, simply and alone. Whatever the conditions may be which surround the formation of organic bodies in the animal or vegetable organism, the final combination of the atoms, necessary to the formation, is brought about by chemical affinity. Although we cannot reproduce these conditions outside of the body, we can in so far imitate them that the same kind of combination will take place. We have a-t our command at present many means for the building up of the most complicated organic bodies from the simplest. Some of these are easily understood, and were discovered as the result of strict logical deduction; others are still inexplicable, and were discovered by accident. We can pass readily from one hydrocarbon to another, adding carbon-atoms to an extent which, theoretically at least, is unlimited; from one acid to another of higher order; from alcohol to alcohol; from alcohol to acid; from acid to hydrocarbon; from hydrocarbon to acid, through all the normal series of organic compounds. So great is our power in this direction, that it is possible to produce any member of any regular series of organic compounds from marsh-gas as a starting-point, or from any other member whatsoever. But marsh-gas can be indirectly produced from its elements, carbon and hydrogen; hence, we have the possibility given of preparing artificially by far the greater number of organic compounds. This number includes many of those substances which are formed in the animal or vegetable organism.
The formation of urea and formic acid has been alluded to. Without reference to the historical order, a few of the achievements of chemists, which have from time to time astonished and delighted the world, may here be briefly noted. Among vegetable products are oxalic acid, which was formed directly from carbonic acid, a combination of two carbon-atoms being necessary in the process; valeric acid, containing five carbon-atoms; malic acid, with four carbon-atoms, one of the most widely-distributed acids of the vegetable kingdom, being contained in a large number of unripe fruits; cinnamic acid, containing nine atoms of carbon; tartaric acid, the acid of grape-juice. Wintergreen oil, obtained from Gaultheria procumbens, has been found to consist mainly of an organic ether, which can be, and has been, prepared artificially. The oil of garlic (Allium sativum) contains carbon, hydrogen, and sulphur. It can be prepared with all its properties without the plant. The oil of mustard, with its peculiar arrangement of carbon, hydrogen, nitrogen, and sulphur, is now manufactured on the large scale by a patented process, the mustard-plant being outrivaled by the chemist. The deadly poison conine, and the beautiful colors alizarine and indigo, finally, belong in the same list. In regard to alizarine or Turkey-red, it may be remarked that the discovery of the methods for its artificial preparation has led to the establishment of an important branch of industry of far-reaching influence. It is doubtful, however, whether as much will ever be said concerning the preparation of indigo. Among animal products that have yielded up the secrets of their internal structure to the chemist are the simple fats and the lactic acids. In a great many portions of the animal organism, as the brain, pancreas, liver, lungs, the thyroid and thymoid glands, is found a substance, containing six atoms of carbon, which has been called leucine. This substance is also a frequent product of the decomposition of organic bodies. Leucine is obtained more readily by artificial means than it can be extracted from the tissues in which it exists ready formed. A constant ingredient of the juice of flesh is creatine; and one of the products of decomposition of creatine is sarcosine. Both creatine and sarcosine can be constructed from the elements by purely chemical processes. Taurine, which occurs in the bile, in the contents of the alimentary canal, in the lung-tissue and the kidneys, and contains carbon, hydrogen, nitrogen, oxygen, and sulphur, can be prepared by a very simple process.
These examples suffice to indicate the character of the results already achieved, and furnish justification for the hope now entertained by chemists that in good time it will be possible to produce all chemical substances in the laboratory. No one who has given the subject a sufficient amount of attention to enable him to form an opinion can for a moment feel a doubt on this subject.
The old dogma no longer exists. There are those who sigh at its death; who consider that the sacrilegious step of Science which annihilated it has, in some way, tended to lessen the mystery of life, and to embolden the votaries of science to look for, work for, further disclosures which may threaten some favorite view—it may be one of more importance than that which we have considered. But others, supporting themselves on the basis that truth can never be dangerous to the right, see no cause for alarm in such advances. They hail them with pleasure, and encourage the spirit which hastens their arrival. In regard to the special question treated in this paper, arguments are hardly necessary to show that the results of investigation, as we have stated them, could not materially modify any time-honored, fundamental views. Is life less of a mystery? Has the question concerning the nature of life been even approached in these researches? We think not. That chemical substances of peculiar structure are found in the living organism is true. That these substances are formed by the action of the force called chemical affinity is just as surely a truth. Do these two truths mutually detract from the importance of each other? When the active agent in the formation of the so-called organic bodies became known, a thousand questions could be proposed to one that could be proposed previously. The conditions for its working became subjects of inquiry, and an almost endless series of possibilities presented itself. From what substances have the new ones been formed? What chemical processes have brought about the final formation? Years—ages must elapse before our knowledge on these points can begin to be exhaustive. And then what? Is the mystery solved? No.
We are ascending a mountain of great light. Our views are becoming more and more extended as we reach higher and higher positions. Should we ever be enabled to reach the summit, there would be found a pleasant harmony in the broad panorama, and our eyes would rest in delight upon it; but the most extensive view has its horizon, the barrier between the visible and the invisible.