It has been said, through all periods of combustion chemical research, that the study of Com- bustion must be the central point of the science. So it was thought in the ancient theological period of the science; and also in the more recent meta- physical stage, when combustibility was called phlogiston, and regarded as an intangible materialized entity: and the advent of the positive period of chemistry was marked by the establishment of Lavoisier's new theory of combustion. In our day it is the recognized necessity of modifying this theoi'y that has especially led to the electric conception of chemical phenomena..., The pneumatic theory of combustion of theorv Lavoisier had two entirely different objects in view; objects which are too commonly confounded, but which we must be careful to keep apart. First, the analysis of the general phenomenon of combus- tion: and, secondly, the explanation of the effects of heat and light, which is, in the eyes of the vulgar, the more im- portant of the two. Both were treated in the most ad- mirable manner possible in the existing state of knowledge; and in the characteristics of postivity and rationality La- voisier's theory has not since been surpassed. All combus- tion, abrupt or gradual, was regarded as consisting in the coml)ination of the combustible body with oxygen, whence, when the body was simjole, must result an oxide, generally susceptible of becoming the basis of a salt, and, if the oxygen THEORY OF COMBUSTION. 367 was preponderant, a true acid, the principle of a certain kind of salts. As for the disengagement of heat and light, it was attributed, in a general way, to the condensation of the oxygen, and in an accessory way, to that of the combus- tible body, in this combination.
The first part of this anti-phlogistic theory -p. i. i-.• • has a much more philosophical character than the second. It was eminently rational to analyse the pheno- menon of combustion, so as to seize whatever was common to all cases. The conclusions drawn might be too general; and were afterwards proved to be so; but Avhatever would stand the test of time miist form a body of indestructible truth, constituting an essential part of chemical science through all future revolutions. The case is different with the explanation of heat and light. The question is not, like the first, of a chemical, but a physical nature; and, whatever may be its final solution, it cannot affect chemical conceptions. It would have been wiser to abstain from offering any general explanation of the effects of heat and light through such a supposition as that of a condensation, which does not necessarily take place, and which is, in fact, found to be often absent. Lavoisier hoped to attach the therniological effect to the great law discovered by Black, of the disengagement of heat proper to the passage of any body fi'om one state to another more dense; but such a connection could not be established on the ground of phenomena not invariably present, or indisputably manifested. However, it would be too much to expect a perfect scientific reserve in discoverers who bring out scientific truths from a region of metaphysical fantasies. It is from their followers that we have a right to demand it; and we are compelled to charge upon the chemists who have been eager to substitute the electro-chemical theory for the anti- phlogistic theory, properly so called, a want of care in con- structing explanations analogous to those which are dis- missed as insufficient. To justify this charge, we must review the proofs of the imperfection of Lavoisier's theory, — still regarding it under the two divisions just exhibited. Berthollet saw presently that Lavoisier's „.i ii., method of analysis of combustion must be limitation " modified. One of the chief consequences of 368 POSITIVE PHILOSOPHY.
this analysis was that every acid and every salifiable base must be a result of combustion; that is, of the combina- tion of any element with oxygen; whereas, Berthollet dis- covered that one of the most marked of the alkalies, ammonia, is formed of hydrogen and azote alone, without any oxygen; and soon after, he proved that sulphuretted hydrogen gas, in which also there is no oxygen, neverthe- less presents all the essential properties of a real acid. These facts have since been confirmed in every possible way, and especially by the electric method; and the excep- tions, both as to alkalies and acids, have become so multi- j^lied, that the investigation and comparison of them have given that high character of generality to the study of alkalies and acids which belongs to it in our time.
Moreover, the primitive theory of combustion has been gradually modified by the discovery that a rapid disen- gagement of heat and light is not always an indication of a combination with oxygen. Chlorine, sulphur, and several other bodies, even non-elementary, have been found to occasion true combustion. And again, the phenomenon of fire is no longer attributed exclusively to any special com- bination, but, in general, to all chemical action at once very intense and vivid.
It does not follow that because Lavoisier's discoveries have parted with some of their character of generality, they have lost any of their direct value: and such altera- tion of views as there is relates chiefly to artificial pheno- mena, while the natural facts remain securely established. Thus, though there are acids and alkalies without oxygen, it is unquestionable that the greater number of them, and especially the most jjowerful, are oxygenated: and again, if oxygen be not indispensable to combustion, it remains the chief agent, and especially in natural combustions. In natural history, the theory is applicable, almost without reserve, though it is insufficient for the severe conditions of abstract science. If the universal sovereignty of oxygen has been overthrown, it will yet be for ever the chief element of the whole chemical system.
the explanation or fare, — it was destroyed by the first direct examination of it. No new facts were re- THEORY OF COMBUSTION. 369 quired for its overthrow, but merely a more scientific appreciation of common phenomena. It will not even serve naturalists for their concrete purposes in any degree, having never really explained the most ordinary effects. The required condensation is found to be only occasionally present, and often absent in the most important cases; so that if it were not for the connection of this aspect of the theory with a sounder one, it would be inconceivable how it could have held its ground up to a recent period, — busy as the chemists were with other theoretical speculations. After finding that in cases where condensation was sup- posed, expansion exists instead; and that where we find vivid combustion, there should, by the theory, be a great cooling, we are brought to the reflection that if the fire on our hearths was not a matter of daily fact to us, its exis- tence must become doubtful, or be disbelieved, through those very explanations by which the phenomenon has been proposed to be established. To my mind, this is a clear indication that the chemical production of fire does not admit, in a general way, of any rational explanation. Otherwise it appears incomprehensible that men of such genius and such science, at a time so near our own, should have been so deluded. The electric fire, now proposed for an explanation, must have been sufficiently known to La- voisier, Cavendish, Berthollet, and others, to have served as a basis to their theory, if its preponderance over the merits of their hypothesis had been so great as is now commonly supposed. This consideration however, striking as it may be, is no dispensation from the duty of examin- ing the electro-chemical conception, for which we have been prepared by this short account of its antecedents.
According to this theory, the fire produced in the greater number of strong chemical reactions must be attributed to a real electric discharge which takes place at the moment of combination (by the mutual neutralization, more or less complete, of the oi:»posite electric conditions) of the two substances under consideration, — one of which must be electro-positive and the other electro-negative. There is every reason to fear, however, that when this theory has been effectually examined, it will be found as defective in rationality as its jjredecessor. If electric effects are I. B B 370 POSITIVK PHILOSOPHY.
concerned in all chemical phenomena, as seems to be now agreed upon by most chemists and jihysicists, they must oftener be supposed than found: and the electric symptoms are most impossible to detect in precisely those chemical phenomena which have been most relied on for overthrow- ing the old theory. And in the cases in which electriza- tion is evident, its chemical influence is so equivocal that some regard it as the cause, and others as the effect, of the combination. The explanation is not yet positively estab- lished for any phenomenon whatever that has been duly analysed: while its vague nature leaves room for fear that it will not be so radically or so speedily destroyed as its predecessor. It could be plainly shown whether the requisite condensation did or did not exist: but there is always a resource, in the more recent case, in the faint or fugitive character of the electric condition, which defies our means of positive exploration, — qualities which are far from being a ground of recommendation of a theory which is to account for very striking and intense effects. I do not desire to say that the disengagement of light and heat can never have an electric origin, any more than that it can never proceed from the condensation proposed: but 1 think an impartial observation woi;ld decide that in most cases of combustion there is neither condensation nor electriza- tion. My own view is that these vain attempts to explain the chemical production of fire jDroceed from the lingering metajihysical tendency to penetrate into the nature and mode of being of phenomena: and that chemical action is one of the various primitive sources of heat and light, which cannot, from their nature, usually admit of any positive explanation; that is, of being referred, in this relation, to any other fundamental influence.
If our chemical science were more advanced than it is, we should not have to point out that the consideration of fire, which, however important, is only a physical accessory of chemical phenomena, cannot afford a rational ground for a radical change in our conceptions of chemical action. When our predecessors regai'ded heat as the tlie theorv^ chief physical agent in composition and de- composition, they did not pervert such a consideration to the point of assimilating chemical to DIFFICULTIES OF THE THEORY. 371 thermological effects. We are less cautious at the present day: we confound the auxiliary, or the general physical agent of the jjhenonienon, with the phenomenon itself, and pervert chemistry by confounding it with electrology, by irrationally assimilating chemical to electrical properties, as is seen especially in the theory of M. Berzelius. How can there be any scientific comparison between the tendency of two bodies to a mechanical adhesion after a certain mode of electrization, and the disposition to unite all their mole- cules, external and internal, by a true chemical action? M. Berzelius has frankly declared that cohesion, properly so called, admits of no electric explanation. Nothing is gained towards explaining the molecular connection, in- dissoluble by any mechanical force, in contrast with the magnetic union so easily overcome, by talking of voltaic elements with their positive or negative pole, and their connection by the electric antagonism of the opposite poles. Such inventions give no idea whatever of molecular co- hesion. Nor is affinity, or the tendency to combination, any better explained by the electro-chemical theory. Elec- trical phenomena, in physics, are eminently general, offering only differences of intensity in different bodies; whereas, chemical phenomena are essentially special or elective: and therefore every attempt to make chemistry, as a whole, enter into any branch of physics, is thoroughly anti- scientific. This would be enough: but we see besides that the smallest changes in the mode of electrization reverse the electric antagonism, and destroy the proposed electrical order of elementary bodies: we find ourselves \anable to deduce the new electric properties which the theory bids us look for in the compounds of different orders; we do not know by what laws they derive their positive or nega- tive character from the electric condition of each of the two elements; nor are we able to approach the great end of chemical science, — the prevision of the qualities of com- pounds by those of their constituent elements. Moreover, in any case, the great body of chemical phenomena opposes insurmountable obstacles; as when oxygen, the most nega- tive element, when entering largely into certain oxides, finds them positive towai'ds certain acids, into which it enters much more sparingly, — the radicals of the first 372 POSITIVE PHILOSOPHY.
bein^ often as negative as those of the last. According to M. Berzelins's own frank declaration, organic compounds cast insuperable difficulties in the way of his arrangement of electric relations; and he alleges the transience of the combinations in that class of cases as an explanation of the anomaly: but chemical science would be impossible if compounds were not throughout considered stable till causes of decomposition arise: and if organic compounds are guarded from these, they remain chemically stable, like inorganic substances. The fundamental obstacle of the whole case, — the identity of the elements, in opposition to the electric variety, — cannot by any means whatever be got over.
Leaving all these difficulties on one side, we learn nothing about chemical phenomena by likening them to electrify action, for we establish thus no harmony between the pre- tended causes and the real eifects. Every attempt seems to prove simply the auxiliary influence of electricity on chemical effects, — acting as heat does, only with a different intensity. In fact, there are scarcely any electro-chemical combinations which caimot be effected by ordinary chemical processes, without any electric indications; and the few exceptional cases still existing may, by analogy, be expected to be brought under the rule. If, in the face of all this, we were to persist in investing the electrical influence with the specific and molecular attributes of chemistry, we shovild merely be restoring the old entity of affinity, decked out with some hypothetical material attributes, which would be far from rendering it more positive: and such a pro- cedure would be as hurtful to jjhysics as to chemistry, by infusing new vagueness into our notions of electricity, which are at present far from being sufficiently distinct. And then might follow, as likely as not, the founding on electrology, not only the whole of chemistry, but the theories of heat, of weight, and probably, as a consequence, that of celestial mechanics. And then, if we added to this heterogeneous assemblage a confounding of the supposed nervous fluid with the pretended electric fluid, we should have attained to the show of an universal system, devoid of all scientific use, which would fall to pieces as soon as tested by real study, parting off into RESULTS OF THE THEORY. 373 categories of independent doctrine, and encumbering natural philosophy with insoluble questions, which must be dis- carded, to enable us to begin afresh.
Thus, to sum up, the great chemical influence of elec- tricity, like that of weight, and yet more of heat, is un- questionable; and I have endeavoured to exhibit the high imjiortance of electro-chemistry to the improvement of chemical science, of which it is one of the essential elements. But I must, once for all, reject the conception through which it has been attempted to transform all chemical into electrical phenomena. In a philosophical point of view, Lavoisier's theory appears to me, notwith- standing its serious imperfections, very superior as a scientific composition to that to which it has given j^lace. It related directly to the aim of chemical science, — the establishment of general laws of composition and decom- position; whereas the newer theory draws attenticm away from it, in a vain inquiry into the intimate nature of chemical phenomena. Thus the anti-phlogistic conception has suggested numerous and important chemical dis- coveries, while it is very doubtful whether as much will ever be said for the electric theory. In an indii-ect way however it may operate favourably for..
chemical science, by its binary antagonism amUKnvers^ suggesting the extension of dualism among compounds which are as yet supposed to be more than binary. Berzelius appears to have felt this connection; and he would probably have erected dualism into a funda- mental principle, but for his subjection to the old division of chemistry into organic and inorganic. Others, who are free from this entanglement, may be prepared by the electro-chemical theory for general dualism; though it is not, in principle, desirable to recur to faulty means to attain good results in an indirect way. In another view, this theory may be useful, — in fixing the attention of chemists on the influence of time in the production of chemical effects; — an influence remarkably manifested by many phenomena, but not, as yet, directly analysed. Not only does time naturally increase the mass of the products of chemical re-action; it also causes formations which 374 POSITIVE PHILOSOPHY.
would not otherwise exist. The chemical theory of time is at present a blank in science; and the phenomena of electro-chemistry seem likely to enlighten us on this head, ■ — so all-imjiortant in its connection with chemical geology, while constituting an indispensable element in the concep- tions of abstract chemistry.
To complete our survey of the |>hilosophy of Chemistry, we must turn to some considerations already suggested, on the subject of what is commonly called Organic Chemistry.
375 CHAPTER V.
ORGANIC CHEMISTRY.
ORGANIC Chemistry comprehends, it cannot be denied, two kinds of researches, chemical and physiological, which are perfectly distinct. For instance, the study of organic acids, and especially the vegetable Confusion of acids, and alcohol, ethers, etc., has a character two kinds of as purely chemical as that of any inorganic *^^*- substances whatever; and, on the other hand, there is no doubt of the biological character of inquiries into the com- position of sap or blood, and of the analysis of the products of respiration, and many other matters included in organic chemistry. The confusion of the two orders is prejudicial to both sciences, and especially to physiology. The division of Chemistry conceals or violates essential analogies, and hinders the extension of dualism into the organic region, where it is seldom found, though, as I have shown, it is optional, in fact, throughout the whole range of chemistry; and thus the arbitraiy arrangement is the chief obstacle in the way of the entire generalization of the doctrine of de- finite proportions. And whenever a true chemical theory shall fitly replace the anti-phlogistic conception, it must necessarily comprehend all organic, as well as inorganic compounds. The most philosophical chemists are tending more and more to a recognition of the identity of the two departments; and there can be no doubt that the establish- ment of that identity will be an immediate conseqxience of a rational classification of chemical knowledge.
The confusion is more mischievous, but less felt by chemists, under the other view, — the comprehension of biological phenomena among those of organic chemistry. The confusion arose from the need of chemical researches in very many physiological questions; and these chemical researches, being usually extensive and difiicult, were out 376 POSITIVE PHILOSOPHY.
of the range of the jihysiologists, aucl were taken posses- sion of by the chemists, who annexed them to their own domain. Both classes were to blame for the vicious arrangement, and both must amend their scientific habits before a division can be effected in entire conformity to natural analogies. The physiologists have the most difficult task before them, having to qualify themselves for inquiries from which the chemists have only to abstain.
It is scarcely possible to characterize or to circumscribe the physiological part of organic chemistry, formed as it is by successive encroachments. It comjirehends the chemical analysis of all the anatomical elements, solid or fluid, and that of the ^ro(^Mc/s of the organism; and if its usurpations remained unchecked, it would soon include the phenomena of Avhat Bichat called the organic life; that is, the functions of nutrition and secretion, the only ones comiuon to all living bodies, and in which the chemical point of view might well appear the natural one. In such a state of" things, physio- logy would be reduced to the study of the functions of animal life, and to that of the development of the living- being. It is easy to see what would become of biological science, if it were reduced to this fragmentary state. Chemists cannot but be unfit for the rational examination of the important questions of anatomy and physiology, vegetable and animal, because the research requires that comprehension of view which their studies, as chemists, preclude them from obtaining. In the anatomical relation, they are perpetually overlooking the fundamental division, established by M. de Blainville, between the true elements of the organism, and its simple products; and they take for one another, almost indifferently, the tissues, the paren- chyma, and the organs. The spirit of biological investiga- tion being unknown to them, they can neither choose their subject well, nor direct their analysis wisely. If these are grave inconveniences in anatomical questions, they are much more serious in physiological problems, properly so called, the essential conditions of which are not understood by chemists. The rational direction of physiological analysis can take place only by the subordination of the chemical to the physiological view; and therefore by the employment of chemistry by the physiologists themselves, as a simple RELATION OF CHEMISTRY TO AXATOMY. 377 means of investigation. It is an analogous case to that before exhibited, of the application of mathematical analysis to physical questions. If it is important that physicists should emj)loy the instrument of analysis, instead of de- livering over physical subjects to the mathematicians, to be a mere theme for analytical exercises, much more im- portant is it that the greater diversity of view in chemistry and physiology should not be lost sight of. The irrational and incoherent studies comprised in the organic chemistry of our day give us no idea of the true nature of the aids that biology may derive from chemistry. A few instances will show the high im]>ortance of an improved organization of scientific labour.
In the anatomical order, almost all the re- Kelatiou of searches of chemists have to undergo an Chemistry to entire revision by the physiologists, before Anatomy, they can be applied to the studies of the elements or the products of the organism. The fine series of researches of M. Chevreul on fatty bodies are ])erhaps the only important chemical study immediately applicable to biology, animal or even vegetable. In the chemical analysis of blood or sap, or almost any other element, a single case, taken at hazard, is usually presented as a satisfactory type, without any comparative investigation either of each species of organism in its normal state, or of the degree of develop- ment of the living being, — its sex, its temperament, its mode of alimentation, the system of its exterior conditions of existence, etc., and other modifications which physio- logists alone can duly estimate. Such analyses correspond to nothing in anatomy but the single case observed; and even that is seldom sufficiently characterized. Hence inevit- able divergences among chemists, who choose different types, and discussions of no scientific use, as the discor- dance is attributed to the diiferent analytical methods em- ployed, instead of to the variations which physiology would