General Considerations On Chemistry
( Originally Published 1913 )
WITH Chemistry we enter upon a science where the complexity of phenomena is greatly augmented, and where the nature of the phenomena is so sharply defined as to seem the result of essentially different forces, although, profoundly considered, there is no further difference than what arises from the variety of direction of the forces.
Physics treat of Masses acting at sensible distances ; Chemistry treats of Molecules acting at insensible distances.. The Telescope and the Microscope are not more obviously separated, not more identical. Indeed that conception of the German philosopher, which elevates the chemical atom, by a sort of microscopic exaggeration, into the analogue of a planet, has deep meaning in it. He compares the atoms to the heavenly bodies, which are in truth but atoms in infinite space. Innumerable suns, with their planets and satellites, move at definite distances from each other, as the atoms of terrestrial masses do. The Methods in which these masses move, Science attempts to ascertain; but in Astronomy we speak of Motion, in Chemistry of Combination : both are Methods of the unknown unknowable Force, the variety of whose directions constitutes the variety of all phenomena.
I am only hinting here at a conception which here-after will find its application ; and hint it that the reader may follow out this long chain of scientific evolution with some sense of continuity, and some sense of the grand unity of Nature. Having done so, let us open Comte's third volume, the first half of which is devoted to Chemistry.
He commences by remarking how the science of Chemistry is less advanced in its progress and more wanting in positivism than the other parts of inorganic physics. This is owing to its greater complexity, and to the fact that when the phenomena are intense in action they bear a striking resemblance to those of life, to which it is the very spirit of the Theological and Metaphysical philosophies to assimilate all phenomena. Chemistry labours also under this disadvantage, that a knowledge of its, most important phenomena is only obtained by artificial means; whereas those chemical phenomena spontaneously presented to observation, such as fermentation, are the most complicated, and the last to be analyzed.
And, first, as to its definition. The general character of its phenomena distinguishes Chemistry very distinctly from Physics and Physiology, between which it stands. A comparison of the three makes the real nature of this science very apparent. The ensemble of the three sciences can be conceived as having far its object the study of the molecular activity of matter in all the different modes of which it is susceptible. Now, under this point of view, each of them corresponds to one of the three principal and successive degrees of activity, which are distinguished from each other by the broadest and most natural differences. In chemical action we have evidently something more than simple physical action, and something less than vital action, notwithstanding the vague analogies that may be drawn between these three orders of phenomena on purely hypothetical considerations. The only molecular perturbations which physical activity, properly so called, can produce in bodies, are modifications of the arrangement of the particles ; and those modifications which are generally of no great extent are most frequently of a temporary nature ; in no case is the substance altered.
Chemical activity, on the contrary, always produces an essential and permanent change in the very composition of the particles, over and above the alterations in structure and state of aggregation : the substances originally present are not now to be recognized, so much has the ensemble of their properties been altered. Finally, physiological phenomena manifest material activity in a still greater degree of energy ; for as soon as a chemical combination is effected the bodies become completely inert ; whereas the vital state is characterized, not only by the physical and chemical phenomena which it constantly produces, but also by a double movement, more or less rapid, but always necessarily continuous, of composition and decomposition, capable of sustaining within certain limits of variation, and for a period more or less considerable, the organization of the body, by entirely renewing its substance. We thus conceive the fundamental gradation of these three essential modes of molecular activity, which true philosophy can never permit of being confounded together.
There are also two secondary considerations to be noticed respecting chemical phenomena.
First Every substance is susceptible of chemical action, and this is why chemical phenomena have been properly classed among general phenomena. They are unlike physiological phenomena, these being peculiar to certain organized substances. But still, in each case of chemical phenomena a specific difference is found. Physical properties, on the other hand, show only differences in degree.
Second—In order to produce chemical phenomena it is requisite that the antagonistic particles be brought into immediate contact. When the structure of the substance does not spontaneously permit this, it must be artificially attained by liquefaction.
The foregoing considerations may be summed up by defining Chemistry as having for its general object, the study of the laws of those phenomena of composition and decomposition, which result from the mutual molecular and specific action of different substances, natural or artificial.
There is reason to fear, from the extreme imperfection of this science, that it will not, for a long time, admit of a more exact and more precise definition, capable of characterizing plainly what are in general the indispensable data, and the final unknown terms, of every chemical problem. But the idea of science is always combined with that of prevision in true philosophy, and the final aim of Chemistry ought, therefore, to be thus conceived : Given, the chemical properties of certain substances, simple or compound, placed in chemical relation, under well defined circumstances, to determine exactly in what their action will consist, and what will be the principal properties of the new products.
We easily conceive that if such solutions were actually obtained, the three great and fundamental applications of chemical science to the study of vital phenomena, to the natural history of the terrestrial globe, and to industrial operations would be thereby rationally organized, instead of being, as at present, the almost accidental and irregular result of the spontaneous development of science : seeing that in every one of these three general cases the question immediately falls within our abstract formula, the data of which are directly furnished by the particular circumstances of each application.
In examining more profoundly this rational definition of chemical science, and carrying out the principle of it another step, we shall find it susceptible of an important transformation ; for all the fundamental data of Chemistry could thus be reduced to the knowledge of the essential properties of simple substances solely, which would lead to that of the different immediate or primary combinations, and thence to the most complex and most remote. We should then have to make each simple substance the direct object of experimental. study by itself. It may be that there is a certain general and necessary harmony between the chemical and physical properties of each chemical substance ; but we canpot go the length of saying that this harmony would ever dispense with a distinct and independent chemical examination of each of these substances. But if once our knowledge of the chemical qualities of each simple substance were completed, by observation and experiment, all the other chemical problems, notwithstanding their immense variety, would become susceptible of purely deductive solutions, by means of a small number of invariable laws, established by the true genius of Chemistry for the different classes of ,combinations.
Under this point of view compounds naturally present two general modes of classification, both of which necessarily require marked notice.
First, the simplicity, or the greater or less degree of composition of the primary combinations.
Second, the number of the combined elements.
Now, observation has shown that the higher the order of composition of any substances, the more difficult does chemical action between them become : the majority of compound atoms belong to the two first orders, and beyond the third their combination seems almost impossible ; while, under the second point of view, compounds very rapidly lose their stability, in proportion as the number of elements is increased. Most frequently there is only a simple dualism, and scarcely any body is more than a quaternary. Hence the number of general chemical classes to which this two fold and necessary distinction can give room can never be much extended. To each of them there would correspond a fundamental law of combination, which, when applied to any case in hand, would deductively make known the result from the elementary data. It is to our own radical feebleness, and partly to the vicious direction of our intelligence, much more than to the peculiar nature of the subject, that we must specially attribute the cause of our being yet so very far from such a method of philosophizing. However difficult it may appear at present, we ought not to forget that we find it realized to a certain extent, in a very important though secondary category of chemical researches the study of proportions. By the aid of a chemical coefficient, evalued empirically for each simple substance, we are able, in numerous cases, with sufficient exactness, to determine deductively, from a small number of general laws, the proportion according to which the compounds previously known unite in each new product. Why should not all the other branches of chemical study allow in the end of a perfect analogy ?
We may sum up these observations by defining Chemistry as having this for its ultimate object : Given, the properties of all simple substances, to find those of all the compounds which they can form.
Chemistry, when compared with the preceding sciences, affords a strong verification of the law that the complexity of the sciences, and their means of exploration, increase together.
It is here that the first and the most general of the three essential modes of investigation, which we have distinguished in Natural Philosophy, begins to receive its integral development ; until arrived at this science, observation is in fact always more or less partial. In Astronomy, it is necessarily limited to the exclusive employment of a single sense ; in Physics, hearing, and particularly touch, come to the aid of sight ; but taste and smell remain essentially inactive. In Chemistry, on the contrary, all the senses simultaneously concur in the analysis of its phenomena. We can form a correct idea of the increase of power which results from this convergence, by trying to picture what would become of Chemistry if it were necessary to renounce the use of smell and taste these very often furnishing us with the only characteristics by which we could recognize and distinguish the different effects produced. But what the philosophical mind ought especially to observe on this subject is, that in this correspondence there is nothing accidental, nor even empirical. Because the true physiological theory of sensation clearly shows that the apparatus of taste and smell, unlike those of the other senses, acts in an eminently chemical way, and that, consequently, the nature of those two senses specially adapts them for perceiving the phenomena of composition and decomposition.
With regard to experiment, Comte repeats that the part it plays in Chemistry is altogether overrated, great though its efficacy undoubtedly is, and greater though it will be when the science is cultivated more philosophically; for chemical effects usually depend on too great a concurrence of different influences to make it easy to throw light on their production by true experiments. We should have the difficult task of instituting two parallel eases, exactly identical in all their characteristic circumstances, save in that one of which we desire to find the value; this being the fundamental condition of all unexceptionable experiment. The nature of philosophical investigations presents a complete obstacle to the purely experimental method, the use of which is almost always illusory there ; and it is in Chemistry, owing to the complication of its phenomena, that we first meet with this same impediment, although to an infinitely less extent.
In a passing note I venture to question Comtés assertion as regards this peculiarity of Taste and Smell; the phenomena of Vision are quite as much dependent on chemical action.
Finally, with regard to the third fundamental mode of rational exploration, comparison, properly so called, the least general of all; it is of importance to consider here, that if this process is essentially destined for physiological studies, its employment first begins to acquire a real efficacy in chemical researches. The essential condition of this precious method consists in the existence of a sufficiently extended series of analogous but distinct cases, where a phenomenon common to them all is more and more modified, both by simplifications and by a successive and almost continuous decrease in the degree of its manifestation. Evidently, physiological phenomena can alone give complete scope for the employment of this method. But the admitted existence of natural families in Chemistry makes it probable that, in the future progress of this infant science, a corresponding classification will yet be made, which will lead to the use of the comparative method in Chemistry, both being founded on the common considerations of uniformity in certain preponderating phenomena displayed in a long series of different bodies.
Chemical investigations enjoy the advantage of a verification by means of the double process of analysis and synthesis. Strictly speaking, the process of synthesis, though useful, may be dispensed with when the object of the experiment is to discover the simple elements of a given substance ; whereas, when the experiment is made to find out what are the compounds which immediately form the given substance, we may in appearance obtain them, but have in reality got compounds produced by new combinations in the course of the process. In the latter case, therefore, synthesis is generally indispensable to ensure certainty. As the higher its order the more does the stability of a compound decrease, and conversely, the facility of recomposition increase, it follows that we can most easily apply the synthetical method where it is most needed.