ledge, comes in that mighty force which we term Chemical Affinity -the power of attraction at insensible distances, uniting dissimilar particles of matter, and by its various intensity and manner of action, producing the vast assemblage of material phenomena, which we now class under a common name. Chemistry is the science which investigates this affinity, positive or relative, of the molecules of material substances-the laws which regulate their combination and separation-and the results of the actions and changes thus produced. It takes cognizance of the great imponderable elements of heat, light, and electricity, inasmuch as they are found to have most important influence on all such actions and affinities; and it may hereafter, as we have said, lead us to physical relations and laws of a higher class, in which these elements and the integral properties of matter are all concerned. The science, however, is essentially one of experiment; and its eminent progress of late years is mainly due to the closer definition of its objects, and to the enlarged methods and improved instruments with which these are pursued.

In describing it as the office of Chemistry to determine the mutual affinities of the atoms of bodies, and the results thence derived, we use the term in a sense justified by our actual knowledge. Without discussing the doctrine of atoms, as propounded either in ancient or modern philosophy, we have sufficient reason to conclude-and especially since the discovery of the law of definite proportions-that there are elementary parts or molecules of all matter-indivisible (eyeon adiαigeta)—determinate in magnitude and form, though of minuteness defying all comprehension-which affect each other under this molecular condition, and by such mutual action give origin to the incalculable variety of natural objects in the world around us, and to the changes they are incessantly undergoing. It may be the fortune of future science to carry discovery further into these elementary differences of form, or other less obvious qualities determining the mutual relations of the molecules of matter. For our present purpose it is enough to draw attention explicitly to this manner of considering the subject as the basis of all chemical inquiry.

The procedure of Chemistry, as an experimental science, may be resolved exclusively into the two great methods of analysis and synthesis; the separation of parts before united, or the union of parts before separate. No chemical operation can occur in which one or other of these changes is not concerned; and the progress and attainments of the science are best estimated by the facility and exactness with which such changes are effected. Of these two methods, both depending on the relative affinities of different kinds of matter, analysis has a natural precedence. Even

in the processes of nature the separation of compounds is more obvious than the reunion of parts. The changes and combinations upon which organic existence depends-forming the chemistry of animal and vegetable life—are slow and occult processes compared with those which dissever such combinations, and restore the parts to more elementary state. And when the subject assumed the character of an experimental science, the chemist found himself surrounded by innumerable compound bodies, readily decomposed, and suggesting that more formal analysis which might collect the parts, determine their nature, and fix the proportions in which they severally exist.

The method of synthesis comes in natural sequence to this; affording a test of the truth of analytical results, and satisfying a rational curiosity as to the effects of new combinations among the innumerable forms of matter around us. In both these operations, however, and as a first principle of all chemistry, it is to be kept in mind that no matter is either created or lost, whatever the changes or combinations taking place.. In clearly fixing this principle, which was imperfectly apprehended before, Lavoisier rendered a service to science, better deserving of record than many discoveries which have higher fame with the world.*

It may seem that we are dwelling too long on these elementary points; but in seeking to give a summary of the changes in modern chemistry, such preliminary views are essential to a comprehension of the subject. The changes in question include, not discoveries of fact only, but alterations and extensions of the methods of inquiry, sufficient to give a new aspect to the science, even apart from the great results to which they have led. This invention of new means and instruments of research is, in truth, a topic of the deepest interest to man. The sudden enlargement of power thus obtained, and the faculty of penetrating into parts of nature before hidden or obscure, place such discoveries among the highest class of human attainments, and render them epochs in the history of human knowledge. In Chemistry, especially, the reciprocal dependance and felicitous union of new facts and new methods may be said to give a geometrical power to the science; as in that eminent discovery which taught the universality of definite proportions in chemical combination; and by establishing this fact, placed instruments in our hands, wholly new as to their manner of operation, and far more powerful than any before possessed. Reverting afterwards to this subject, we must notice

*Plutarch ascribes to Empedocles a passage which is well descriptive of this great principle of Chemistry

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δυσις ουδενος εστιν εκαστού, Αλλα μονον μιξις τε διαλλαξις τε μίγεντων.

meanwhile

meanwhile some of these methods, which though not actually new, yet so greatly transcend all anterior use, that they virtually become so, and may rank among the recent revolutions of the science.

The first of these, already alluded to, is the wonderful increase of exactness in every part of chemical inquiry. Those only who are conversant with its history can form an adequate idea of the amount of this change, or of the influence it has had on the progress of the science. Pervading every part of the subject, from the simple observation of external physical appearances, to the most complex and subtle forms of experiment in the analysis and synthesis of organic bodies, its value is more especially felt in these later and higher operations. The perfection of analysis, in its compound relation to qualities and quantities, is in truth the cardinal point of all chemistry. We might give curious contrasted examples of the grossness of this operation fifty years ago, and the exactness of results it has attained at the present day. Whether it were the examination of a mineral water, or a metallic ore, or an animal or vegetable product, the older analysis seldom yielded half the ingredients which are now derived by the chemist from the same material of experiment -the greater number lying hid under the imperfection of the means used to separate them. It is true that those indicated were generally the most important, and present in largest quantity. But it often happened that the ingredients, thus latent, and yielded only to more perfect experiment, were really essential elements in the compound; modifying its physical qualities, determining its relation to other chemical agents, or providing for its uses in the economy of nature. Thus what was recorded as loss or undefined result-the mere residual dross of ancient analysis has become rich and prolific to modern research; affording those rarer products, which, while they seem to encumber our chemical tables by their number and diversity, do in effect present so many fresh objects of inquiry, and give promise of the disclosure of relations hitherto unknown.

To refer to particular instances of this great change might detract from what we wish to convey of its universality. A single illustration may be taken from the history of Iodine and Bromine -substances discovered some thirty years ago in the waters of the sea, and in certain sea plants-remarkable as new and elementary forms of matter to our present knowledge- and possessing properties so peculiar, as to make it certain that they fulfil definite, though unknown, purposes in the economy of the globe. The exceedingly minute proportion in which they are found in nowise disproves this. Chemical energy is only partially dependent

on

on quantity; but were the latter alone concerned, it would be enough to estimate the enormous mass of ocean waters of which they form a part, to convince us that they cannot be inert or indeterminate in the objects of creation. To the new substances, so discovered, the refinements of modern chemistry have been incessantly directed. By delicate and beautiful experiments they have been detected in numerous mineral waters and brine springs, and even in certain metallic ores-they have been brought into close relation of analogy with other great chemical agents, as oxygen and chlorine, and into artificial combinations of endless variety-and these combinations have already yielded new remedies to the physician, new agents in experimental research, and the most refined methods wherewith to determine the chemical actions of light, and to give them their happiest application in photography. In the progress of these researches tests have been attained so delicate, that iodine may be detected in a liquid containing much less than its millionth part by weight; the familiar substance of starch affording this subtle test, by the chemical relation it bears to the element in question.

Without protracting this illustration by further details, we may briefly state that the same exactness and completeness of inquiry has been carried into every part of Chemistry. Chance, vague hypothesis, and crude results, are altogether excluded from the science. Weight and proportions, numerically expressed, form the basis and test of experiment; and exact cognizance must be had of every quantity gained, or lost, by the substance operated upon. No conclusions are deemed perfectly valid unless so substantiated. This higher principle of research-mainly due in its origin to the genius of Lavoisier, but extended and fortified by later discoverers-has given such perfection to chemical theory as applied to analysis, that the chemist can often foretel results, even before entering his laboratory; and experiment comes rather as fixing and completing the deductions from general laws, than as disclosing facts previously unknown.

The relative affinities of the particles of bodies give foundation to this refined analysis, as they did to the earliest and rudest operations of Chemistry. The progress described has been gradual, but accelerated of late by the facilities which every increase of knowledge affords to its further advancement. In our own country Dr. Wollaston contributed, perhaps, more than any other to the cultivation of this exactness of experiment. If we name Berzelius, Mitzcherlich, Liebig, and Dumas, in the same light abroad, it is with some hesitation, lest we should seem to disparage the other great Continental chemists, whose labours have tended to this perfection of the science they profess.

While referring to the increased exactness of all chemical knowledge, we must give the statement a more particular application to that part of it which relates to the influence of small quantities in composition. We have already adverted to the frequent case of an ingredient existing in very minute proportion, yet conveying important, or even essential, chemical properties to the compound of which it forms a part;-or what is an analogous case, to the effect of a slight change in the proportions of one ingredient in altering the qualities of the whole. Modern chemistry is replete with instances of such facts; the proper estimate of which, though only of late duly made, is indispensable to the perfection of the science. It has belonged to the refinements of recent analysis to detect, and assign their proper value, to these more minute ingredients not merely discovering many new and rare elements, but also indicating purposes which they fulfil in the economy of nature, even by virtue of their diffusion and minuteness. In organic chemistry, whether of animal or vegetable life, we find this admirably exemplified; and to the consummate skill with which such small quantities have been estimated, we owe some of the most striking discoveries in physiology, agriculture, and the arts of life.

We have cause, indeed, to presume, that whenever a particular element is generally present in a compound, and in definite proportion to the other ingredients, such element is essential to its nature, however small the proportion may be. This principle has been continually extended and confirmed as chemical knowledge advanced; and becomes now the expression of phenomena, which may well astonish those not familiar with the subject. It is exemplified by the carbonic acid present in the atmosphere, in a proportion not exceeding To part of its weight-and presumably also by the iodine and bromine in the waters of the sea, though here the proportion is yet infinitely smaller. The iron existing in a portion of the blood-the phosphorus found in the medullary substance of the brain and nerves-the fluoric acid in bones-the sulphur in albumen, fibrin, and certain other animal matters-and the silica, sulphur, phosphorus, and the metallic oxides or alkalis, found in different vegetable substances-are a few among the many examples which organic chemistry furnishes of the influence of minute quantities in combination. They are relations of deep interest to us, as wonderful and exquisite provisions of Providence for the purposes of life, and for the mutual dependance of the several parts of creation. What they present in natural combinations has its counterpart in the artificial chemical union of different substances, where we still find under various forms this marvellous influence of small quantities, pervading and changing the sensible properties