It must be observed, however, that universal and inde- finite dualism cannot be maintained unless chemists will scientifically determine the sense of the word substance; that is, restrict it to mean real cotnhhiation: for it would be easy to cite, and especially in physiological chemistry, very marked cases of the defect of dualism. But we can- not regard as a true chemical substance an accidental assemblage of heterogeneous substances, whose agglomera- MEANING OF SUBSTANCE. 343 tion is evideutly mechanical, such as sap, blood, a biliary calculus, etc., uuless we confound the notion of dissolu- tion, and even of mixture, with that of combination. If we extend in this way the use of the term substance, so valuable in chemistry, we might as well treat, as so many chemical substances, the waters of different seas, different mineral waters, soils, etc.: and even more, artificial mix- tures of a variety of salts dissolved together in water or alcohol. We shall see hereafter that all difficulties in this subject may be disposed of by our learning that they pro- ceed from our not having clearly and rigorously separated the chemical from the physiological point of view. We may be assured that the most elementary notions of chemical philosophy cannot be rationally established, in their due clearness, generality, and stability, without being founded on a full comparison with biology; a comparison which can be organized only under a complete system of positive philosophy.
Meantime, there is a marked tendency in the present movement of chemical ideas, towards a complete dualism. The increasing assimilation attempted between organic and inorganic substances is an indirect advance in that road: but much more striking, in this view, are experiments like those of M. Woehler, which I'efer the most refractory com- pounds to dualism, either by analysis or synthesis. A binary formula is adopted, too, to represent the proportion of elements proper to the most complex substances: and, though this is not a true dualism, it helps to prepare minds for the establishment of a real and general one. The sum of what has been said on this important subject of chemical dualism is this: — the real mode of agglomera- tion of elementary particles is, and ever must be, unknown to us, and therefore no proper object of our study: — our positive researches being thus circumscribed, we may rationally conceive of the immediate composition of any substance as binary; but so as to represent all the phe- nomena that chemistry can offer to us, in any future state of perfection. Thus, I do not ]>ropose universal dualism as a law of nature; for this we could never establish: but I declare it to lie a fundamental artifice of true chemical philosophy, destined to simplify our elementary concep- 344. POSITIVE PHILOSOPHY.
tious, by using our optional intellectual liberty in accord- ance with the true end and aim of positive chemistry.
These are the conditions necessary to the institution of a system of natural classification, answering in chemistry to tlie universal hierarchy of living bodies in biology, if the complication of phenomena would admit of our obtaining such a system. Up to this time, perhaps no one has formed an adequate idea of the nature and spirit of siTch an operation: but, in my view, chemical classification, thus conceived of, is the science itself, condensed into the most substantial summary. All I claim to have done is to have introduced into chemical science the special kind of philo- sophical spirit which is naturally developed by biological science, as it has been conceived of by all its great masters, from Aristotle downwards.
It is because I have high expectations of what Chemistry will become, that I attach so much importance to the pre- ceding discussion. The science is now weak and desultory, notwithstanding its rich collection of facts: but, extended and complex as it is, there is no fundamental science, except astronomy, whose phenomena are so homogeneoTis, and therefore so fit for a true systematization, in the positive spirit. Now, this future constitution of chemical science miist, it seems to me, consist in a complete system of natural classification, which cannot be obtained till all combinations, Avhatever their origin, are subjected to a fixed order of homogeneous considerations, and, on the other hand, constantly referred to a fundamental dualism.
We cannot form any certain expectation of the fiitvire condition of Chemistry from its present state: but, before proceeding to examine the two doctrines which at this day approach nearest to positive rationality, — that of definite proportions and the electro-chemical theory, — I will indi- cate two points of doctrine which seem, by their nature, to indicate with precision the true dogmatic formation towards which the science, as a whole, must tend. Law of double First, there is the great law of double saline decom- saline decompositions, discovered by Ber- positions. thollet, and completed by M Dulong's investigations on the reciprocal action of soluble and insoluble salts. The case of double solubility, considered by Ber- CHEMICAL THEORY OF AIR AND WATER. 345 thollet, is this: two soluble salts, of any kind, mutually decompose each other whenever their reaction may produce an insoluble salt, or one less soluble than either of the two. This theorem stands first among general propositions in chemistry, and is the only one which can as yet give an exact idea of what, in chemistry, constitutes a true law. It has all the characters of a law: it relates to the proper subject of chemical science; it establishes a relation be- tween two classes of phenomena before independent; and, above all, it admits of prevision of phenomena according to their positive relations. In establishing this law, Berthollet escaped some metaphysical snares, rejecting hypotheses of affinities; but he fell into one when he attempted to explain the law which he had just discovered. No law can be exjDlained otherwise than by showing that it enters into another, more general than itself: but this law of Berthollet's is alone of its kind; and it therefore admits of no exjilanation. It may hereafter be attached to a fundamental theory of the reciprocal action of all com- pounds of the second order; and such a relation will truly explain it: but at present it is simply a general fact which, inexplicable itself, serves to explain each of the particular facts which it comprehends.
The influence of air and water in the j^ro- Chemical duction of chemical phenomena is another of theory of air the most perfect doctrines of chemistry as it ^^^^ water, stands. The importance of the action of air and water in the terrestrial economy has induced some Grerman philo- sophers irrationally to set up the system of these two fluids into a sort of third reign, between the inorganic and the organic: but abstract chemistry has nothing to do with natural history, and regards the study of air and water from a dilferent point of view, while aware of its funda- mental importance.
All chemical phenomena take place in the presence of air; and they almost invariably require the intervention of water: it is clear therefore that before we study any chemical reaction, we must be able to analyse the partici- pation of these two fluids. Thus the chemical theory of air and water is a sort of necessary introduction to the system of chemistry, properly so called, as belonging more 346 POSITIVE PHILOSOPHY.
to method than to doctrine, and as immediately following- the study of simple bodies. It is an historical fact that the double analysis of air and water marked the first great advance in modern chemistry...The influence of the air, not less important than that of water in chemical phenomena, was less difficult to characterize: for the air is simply a mixtui'e, and its chemical action is merely that of the gases which compose it, each of which acts as it were isolated, allowing for the diminution of intensity from its diffusion, and for the very few cases in which the accomplishment of the proposed phenomenon determines the combination of the gases in an accessory way. Chemistry has only to analyse it, leaving all other study of it to the cleimrtment of natural history. This analysis was effected in the early days of modern chemistry, except that there is still some uncertainty about the proportion of carbonic acid gas, and perhaps of some other more considerable principles, as, for instance, hydrogen, the existence of which begins to be generally suspected. Though no aj^preciable change in the comijosition of the atmosphere has taken place within half a century, it is impossible to conceive that some altera- tion must not happen, in some direction, in course of time, among the many perturbing infltiences which act upon the mixture. Their antagonism, and that of vegetable and animal action, partly neutralizes them: but the equilibrium cannot be precise and continuous. G-eological considerations and botanical fossils lead us to suppose that at some remote periods the composition of the air must have been sensibly different: and chemists themselves have actiially established some slight periodical variations, dependent on the propor- tion of carbonic acid at different seasons. Our analytical resources are, however, very imperfect with regard to the accessory principles of the atmosphere; for chemists can ascertain nothing of the distinctions which are proved to exist in the best-marked localities, by their influences on living beings. The study of these variations, all-impor- tant in its way, — even as possibly indicating the limits of human life in a remote future, — belongs to natural history; and that is probably the reason why chemists trouble them- selves so little about it: and if there is neglect, it should WATEK. 347 be charged upon the naturahsts. It is true that a prepara- tion is required for their order of study, like all otliei's, — a provision of knowledge, rising from physiology to as- tx'onomy itseK: but the research is not especially a matter of chemical duty.
The study of water requires much more ex- „.
tended and complex researches than that of the air; and it is indispensable to the general system of chemical science: for water being a real combination, and perhaps the most perfect known to us, ma.y exercise chemical effects proper to itself, independently of those attributable to its elements, and apart from its imj^ortance as a solvent, — to say nothing of it as a simple mixture. Thus there are three aspects under which water must be considered by chemists, all distinct and all essential; and the appreciation of them has been slow and difficult, if even we may say that this fundamental examination is yet complete.
The analysis of water, represented by a quantity of hydro- gen double in volume that of oxygen, and unquestionably confirmed by synthesis, is the finest of the early discoveries of modern chemistry, not only from the light it casts upon the whole of chemical phenomena and the general economy of nature, but also from its conquest of prodigious difficul- ties. In regard to the first view, chemical science leaves nothing to desire. Yet, a notion has arisen, in recent times, of the existence of a new and more highly oxy- genated combination between the two elements of water, which may raise some interesting questions, not about the irreversible composition of water, but about the kind of chemical influence which is taken for granted in its decom- position and recomposition in a multitude of phenomena; and especially, about the true mode of union of oxygen and hydrogen in all substances, and above all in liquids, which cannot be obtained without water. Some doubts have lately been proposed about this, which seem to me to deserve mature examination.
The dissolving action of water has been the subject of a long series of laborious researches, much less difficult, and not far from complete. Yet more attention ought to be paid than is paid to the first experiment of Vauquelin, in 348 POSITIVE PHILOSOPHY.
which it is shown that watei*, saturated with one salt, remains capable of receiving another, and even acquires by that the singular property of dissolving a new quantity of the first. This experimeiit, which has been in a manner desi^ised, seems to me of the first order in its way, and a fit basis of a series of interesting researches about the apparently capricious laws of solubility, the study of which is yet essentially empirical.
Chemists were long in conceiving that water, besides being a solvent, might act in a really chemical manner, otherwise than by its elements. It seemed as if a combination so eminently neuter must be inoffensive, and inoperative, ex- cept by its decomposition. It was Proust who thought that this neutrality itself afi^orded a presumption of certain chemical affections, independently of its composition. This was the rational consideration which led him to create the important study of the hydrates, regarded as a sort of new salts, in which water plays the part, with regard to the alkalies, of a kind of hydric acid.
The examination of these combinations, and of all others that water can form with any substances without being decomposed, constitutes the thii'd and last jDart of the fun- damental study of water, regarded as an indispensable preliminary to the general system of chemical studies.
349 CHAPTER III.
DOCTRINE OF DEFINITE PROPORTIONS.
THERE are two general doctrines in chemistry, as it now exists, which present a systematic appearance, and invest the science with such rationality as it has at- tained. The first of these is the important doctrine of Definite Proportions.
Even if this doctrine were complete, it could exert only a secondary influence on the joctHne solution of the great problem of the science, — the study of the laws of the phenomena of composition and decomposition. The essential question is, what separa- tions and new combinations must take place under deter- minate circumstances; and the theory of definite propor- tions affords no assistance to this kind of prevision. It proceeds, indeed, on the supposition that the question is already solved; and that it is to be taken as the point of departure for the estimate of each of the new products, — of their quantity and the j^roportion of their elements. Thus, the theory of definite proportions presents the singular scientific character of rendering rational, in its numerical details, a solution which usually remains empi- rical in its most important aspect.
It was natural that the founders of modern chemistry should have attended to the laws of composition and de- composition, in preference to a study which they regarded as subordinate; and it was natural also that, as the ad- vance of science disclosed to them the vast difficulties of the main problem, they should attend more and more to the secondary study, which promised an easier and more speedy success. But the most important office of this sub- ordinate theory, — that of supplying the defect of imme- diate experiment, — can be but very imperfectly fulfilled, while it is regarded apart from the principal theory; and 350 POSITIVE PHILOSOPHY.
thus, the doctrine of definite proportions will never acquire its iull scientific value till it is connected with an unques- tionable basis of chemical laws, of which it will be the in- dispensable numerical complement.
Meanwhile, however, it affords a real, though secondary assistance to chemists, in renderino- their analyses more easy and more precise. Moreover, it restricts the number of cases of combination logically possible, by exhibiting the very small number of distinct proportions; and by thus diminishing the uncertainty in cases of chemical action, it is, in fact, a natural preliminary to the establish- ment of those chemical laws to which it will be, under another view, a necessary supplement.
.,, ^. In regard to doctrine, this theory offers a perfect type of the precise kind of rationality which must hereafter belong to Chemistry as a whole. In .,, regard to method, the inquirers who have devoted themselves to establish the theory have advanced chemical science while appearing to diverge from it; simplifying the vast problem which their suc- cessors will solve, and preparing for the disclosure of the great laws of composition and decomposition, which would be undiscoverable amidst the infinity of products, if sub- stances could combine, within certain limits, in all ima- ginable proportions. Such are the claims of this theory, as to doctrine and to method. J-,. It assumed its existence and present form during the first quarter of this century: and it arose from a phenomenon discovered by Richter, and a speculative discussion established by Berthollet. — During the latter half of the last century, several chemists had observed that, in the mutual decomposition of two neutral salts, the two new salts thus formed are always equally neuter. Bergmann, among others, had steadily and spe- cially dwelt upon this. Yet the fact was neglected or underrated till Richter, at the end of the century, gene- ralized the observation, saw what it imported, and derived from it the fundamental law which bears his name. The J,..,, law is this: that the ponderable quantities of the different alkalies requisite to neutralize a given weight of any acid are always proportionate to HISTORY OF THE THEORY. 351 those required for the neutralization of the same weight of every other acid. This is, in fact, evidently the imme- diate consequence of the maintenance of neutrality after the double decomposition. Such a transformation would appear almost spontaneous if it related to a simpler and more developed science than Chemistry; but amidst its complications and the imperfection of our intellectual habits, the closest deductions are difficult if they have anv character of generality, and therefore of abstraction; and this achievement of Eichter's is, in consequence, eminently meritorious, on other grounds than its high utility.- — His law, with the complements it has since received, is the original basis of the general doctrine of definite propor- tions. It exhibited, in the case of a considerable number of compounds, the great end of this doctrine; viz. the assignment to every substance of a certain chemical co- efficient, invariable and specific, indicating the proportions in which it can combine with each of those that have been similarly characterized. When it had been determined, by a double series of trials, what was the numerical composi- tion of all the salts that may be formed by any one acid with the different alkalies, and any one alkali with the different acids, Richter's law enabled us to deduce imme- diately the proportions relating to all the compounds that can result from the binary combination of these two orders of substances. Richter himself brought his discovery up to this result, and prepared (but on a basis of experiment too narrow and imperfect) the first table of what were afterwards called chemical equivalents.
These neuti-al salts constituted a particular case, which could hardly have led on to a extenSo?'^ general theory of definite proportions. The idea of perfect neutralization must probably, at all times, have suggested to chemists that of a single proportion, on either side of which the neutrality must be destroyed; and thus the neutral salts were a natural first stage of the general theory; but they could not in themselves involve such a theory. It was Berthollet who extended the con- sideration of proportions to the whole of chemical pheno- mena. Some years after Richter's discovery he established as a fundamental principle, in his " Chemical Statics," the 352 POSITIVE PHILOSOPHY.
necessary existence of definite proportions for certain com- pounds of all orders; and he assigned the essential con- ditions of this characteristic property, which he attributed to all causes which can release the product of chemical reaction, as it forms, from the ulterior influence of the primitive agents. He thus added to Richter's restricted case the idea of a great number of cases subjected to the same principle, and able to lead on to its entire generaliza- tion. It is assigning much too little honour to Berthollet to recognize only the influence of his controversy with Proust, eminent as was the service rendered by Proust in that conflict, in establishing directly the general principle of determinate and invariable proportions.
Such was the double origin, experimental and specula- tive, of numerical chemistry. The next development had also a double character, arising fi'om the extension ^^ ^^^ harmony between the conception of Dr.
Dalton and the ex2:)eri mental reseai'ches of Berzelius, Gay-Lussac, and Wollaston. The inquiry was in a nascent state when Dalton's philosophic mind dis- cerned its i^ossible generality. He proposed the great . ^. ^, Atomic theory, under which the doctrine of dennite proportions was developed to the whole extent that it has reached, and which serves as the basis of its daily application. The general jjrinciple of the theory is this: all elementary bodies are conceived of as formed of individual atoms, the different species of which unite, generally by twos, in a small number of groups, constituting compound atoms of the first order, always mechanically indivisible, but thenceforth chemically di- visible, and, in their turn, constituting all the other orders of composition by a series of analogous combinations. The principle is in such harmony with scientific conceptions in all departments, that it appeared like a hapi)y generaliza- tion of the most familiar ideas of scientific men in every province of natural philosophy; and its universal and immediate admission took place as a matter of course.
It was observed by Berzelius that the deduction of the existence of definite proportions from this principle would be illusory if the combinations were not restricted to a very small number of atoms: for otherwise, — if the number THE ATOMIC THEORY. 353 was, though limited, very great, — the binary assemblages would be so multiplied that we might as well have combi- nations in any proportions whatever; and then the atomic theory might almost equally well represent the opposite doctrines of definite and indefinite proportions. Dalton was well aware of this; and the restrictions that he enun- ciated were presently declared too narrow by his successors, who found that they would not comprehend all existing combinations. His assertion was, that, in every combina- tion, one of the immediate principles always enters for a single atom, and the other generally for a single atom also, and always for a very small number, rarely exceeding six. Taken with the exj^ansion proposed by his successors, the atomic conception evidently represents the entire doc- trine of definite proportions. But it is the theory of suc- cessive multi])les, derived from the primary doctrine, which especially distinguishes Dr. Dalton's influence upon nu- merical chemistry. From the ground of his doctrine he easily saw that if two substances can combine in various distinct proportions, the ponderable quantities of the one which correspond, in the diffei-ent compounds, to the same weight in the other, must naturally follow the series of whole numbers, since these compounds will have resulted from the union of one atom of the second substance with one, two, three, etc., of the first: and this constitutes a principal element, then perceived for the first time, of the theory of chemical proportions.
Berzelius followed, with his vast experi- mental study of the whole of the important jjerzriius" ^^ points concerned in numerical chemistry, the diiferent parts of which he has done more than any other chemist to develope and systematize. He first perfected Richter's law, so as to connect it closely with the atomic theory; by which it became susceptible of the extension given to it by Berzelius himself, to all compounds of the second order. But the most important new knowledge has arisen from his numerical study of compounds of the first order. By comparing the composition of the metallic sulphurets and that of the corresponding oxides, he dis- covered a law, analogous to Richter's in regard to the salts. This law, — that the quantity of sulphur of the first 354 POSITIVE PHILOSOPHY.
is always proportionate to the quantity of oxygen com- bined with a Kke weight of the base in the second, — is now regarded, by induction, as appKcable to all the com- pounds of the first order to which the same degree of chemical neutrality is assignable. And again, the luminous series of the analyses of Berzelius have precisely verified in another direction the law of successive multiples dis- covered by Dalton in pursuance of his atomic theory.
Gay-Lussac followed, with the valuable Gav-Lussac numerical analyses he eftected by having recourse to gaseous combinations, considered, not as to weight, but to volume. He thus not only verified, in a special manner, the general principle of definite pro- portions, but j^resented it under a new aspect, which, by a wise induction, comprehends all possible cases, — showing that all bodies in a gaseous state combine in invariable and simple numerical relations of volume. An accessory advantage of this achievement was that the specific gravity of the gases might be obtained with a precision often com- parable to that of experimental estimate. It is necessary however to warn inquirers not to be led away, in their application of the theory of volumes to substances which have never been vaporized, from the point of view which in Gay-Lussac's aj^jilication is equivalent to Dalton's, as adopted by Berzelius.
, The labours of Wollaston bore a great