Chapter II · (continued 2)

The importance of having a definite language in every science is apparent at each step of advance. Lavoisier found great difficulty in making his opinions clear because he was obliged to use a language which had been introduced by the phlogistic chemists, and which bore the impress of that theory on most of its terms. About the years 1785-1787, Lavoisier, Berthollet, Fourcroy and De Morveau drew up a new system of chemical nomenclature. The fundamental principles of that system have remained as those of every nomenclature since proposed. They are briefly these:—

An element is a substance from which no form of matter simpler than itself has as yet been obtained.

Every substance is to be regarded as an element until it is proved to be otherwise.

The name of every compound is to tell of what elements the substance is composed, and it is to express as far as possible the relative amounts of the elements which go to form the compound.

Thus the compounds of oxygen with any other element were called oxides, e.g. iron oxide, mercury oxide, tin oxide, etc. When two oxides of iron came to be known, one containing more oxygen relatively to the amount of iron present than the other, that with the greater quantity of oxygen was called iron peroxide, and that with the smaller quantity iron protoxide.

We now generally prefer to use the name of the element other than oxygen in adjectival form, and to indicate the relatively smaller or greater quantity of oxygen present by modifications in the termination of this adjective. Thus iron protoxide is now generally known as ferrous oxide, and iron peroxide as ferric oxide. But the principles laid down by the four French chemists in 1785-1787 remain as the groundwork of our present system of nomenclature.

The antiphlogistic theory was soon adopted by all French chemists of note. We have already seen that Black, with his usual candour and openness to conviction, adopted and taught this theory, and we are assured by Dr. Thomas Thomson that when he attended Black's classes, nine years after the publication of the French system of nomenclature, that system was in general use among the chemical students of the university. The older theory was naturally upheld by the countrymen of the distinguished Stahl after it had been given up in France. In the year 1792 Klaproth, who was then Professor of Chemistry in Berlin, proposed to the Berlin Academy of Sciences to repeat the more important experiments on which the Lavoisierian theory rested, before the Academy. His offer was accepted, and from that time most of the Berlin chemists declared themselves in favour of the new theory.

By the close of last century the teaching of Lavoisier regarding combustion found almost universal assent among chemists. But this teaching carried with it, as necessary parts, the fundamental distinction between element and compound; the denial of the existence of "principles" or "essences;" the recognition of the study of actually occurring reactions between substances as the basis on which all true chemical knowledge was to be built; and the full acknowledgment of the fact that matter is neither created nor destroyed, but only changed as to its form, in any chemical reaction.

Of Lavoisier's other work I can only mention the paper on "Specific Heats" contributed by Laplace and Lavoisier to the Memoirs of the Academy for 1780. In this paper is described the ice calorimeter, whereby the amount of heat given out by a substance in cooling from one definite temperature to another is determined, by measuring the amount of ice converted into water by the heated substance in cooling through the stated interval of temperature. The specific heats of various substances, e.g. iron, glass, mercury, quicklime, etc., were determined by the help of this instrument.

As we read the record of work done by Lavoisier during the years between 1774 and 1794—work which must have involved a great amount of concentrated thought as well as the expenditure of much time—we find it hard to realize that the most tremendous political and social revolution which the modern world has seen was raging around him during this time.

In the earlier days of the French Revolution, and in the time immediately preceding that movement, many minds had been stirred to see the importance of the study of Nature; but it was impossible that natural science should continue to flourish when the tyrant Robespierre had begun the Reign of Terror.

The roll of those who perished during this time contains no more illustrious name than that of Antoine Laurent Lavoisier. In the year 1794 Lavoisier, who had for some time acted as a fermier-général under the Government, was accused of mixing with the tobacco "water and other ingredients hurtful to the health of the citizens." On this pretext he and some of his colleagues were condemned to death. For some days Lavoisier found a hiding-place among his friends, but hearing that his colleagues had been arrested, he delivered himself up to the authorities, only asking that the death sentence should not be executed until he had completed the research in which he was engaged; "not" that he was "unwilling to part with life," but because he thought the results would be "for the good of humanity."

"The Republic has no need of chemists; the course of justice cannot be suspended," was the reply.

On the 8th of May 1794, the guillotine did its work; and in his fifty-first year Lavoisier "joined the majority." To the honour of the Academy of which he was so illustrious a member it is recorded that a deputation of his fellow-workers in science, braving the wrath of Robespierre, penetrated to the dungeons of the prison and placed a wreath on the grave of their comrade.

The period of the infancy of chemical science which I have now briefly described is broadly contemporaneous with the second half of the eighteenth century.

At this time the minds of men were greatly stirred. Opinions and beliefs consecrated by the assent of generations of men were questioned or denied; the pretensions of civil and ecclesiastical authorities were withstood; assertions however strongly made, and by whatever authority supported, were met by demands for reasons. In France this revolt against mere authority was especially marked. Led by the great thinker Voltaire, the French philosophers attacked the generally accepted views in moral, theological and historical matters. A little later they began to turn with eager attention and hope to the facts of external Nature. Physical science was cultivated with wonderful vigour and with surprising success.

In the sciences of heat and light we have at this time the all-important works of Fourier, Prévost and Fresnel; in geology and natural history we have Buffon and Cuvier; the name of Bichat marks the beginning of biological science, and chemistry takes rank as a science only from the time of Lavoisier.

From the philosophers an interest in natural science spread through the mass of the people. About the year 1870 the lecture-rooms of the great teachers of chemistry, astronomy, electricity, and even anatomy were crowded with ladies and gentlemen of fashion in the French capital. A similar state of matters was noticeable in this country. Dr. Black's lecture theatre was filled by an audience which comprised many young men of good position. To know something of chemistry became an essential part of the training of all who desired to be liberally educated.

The secrets of Nature were now rapidly explored; astonishing advances were made, and as a matter of course much opposition was raised.

In this active, inquiring atmosphere the young science of chemistry grew towards maturity.

Priestley, ever seeking for new facts, announcing discovery after discovery, attacking popular belief in most matters, yet satisfied to interpret his scientific discoveries in terms of the hypothesis with which he was most familiar, was the pioneer of the advancing science. He may be compared to the advance-guard sent forward by the explorers of a new country with orders to clear a way for the main body: his work was not to level the rough parts of the way, or to fill in the miry places with well-laid metal, but rather rapidly to make a road as far into the heart of the country as possible.

And we have seen how well he did the work. In his discovery of various kinds of airs, notably of oxygen, he laid the basis of the great generalizations of Lavoisier, and, what was perhaps of even more importance, he introduced a new method into chemistry. He showed the existence of a new and unexplored region. Before his time, Hooke and Mayow had proved the existence of more than one kind of air, but the chemistry of gases arose with the discoveries of Priestley.

Although Black's chief research, on fixed air and on latent heat, was completed fifteen or twenty years before Priestley's discovery of oxygen, yet the kind of work done by Black, and its influence on chemical science, mark him as coming after Priestley in order of development. We have seen that the work of Black was characterized by thoroughness and suggestiveness. The largeness of scope, the breadth of view, of this great philosopher are best illustrated in his discourses on heat; he there leads us with him in his survey of the domain of Nature, and although he tells us that hypotheses are a "mere waste of time," we find that it is by the strength of his imagination that he commands assent. But he never allows the imagination to degenerate into fanciful guesses; he vigorously tests the fundamental facts of his theory, and then he uses the imagination in developing the necessary consequences of these facts.

To Black we owe not only the first rigorously accurate chemical investigation, but also the establishment of just ideas concerning the nature of heat.

But Lavoisier came before us as a greater than either Priestley or Black. To great accuracy and great breadth of view he added wonderful power of generalizing; with these, aided by marked mental activity and, on the whole, favourable external circumstances, he was able finally to overthrow the loose opinions regarding combustion and elementary principles which prevailed before his time, and so to establish chemistry as one of the natural sciences.

At the close of the first period of advance we find that the sphere of chemistry has been defined; that the object of the science has been laid down, as being to find an explanation of the remarkable changes noticed in the properties of bodies; that as a first step towards the wished-for explanation, all material substances have been divided by the chemist into elements and compounds; that an element has been defined as any kind of matter from a given weight of which no simpler forms of matter—that is, no kinds of matter each weighing less than the original matter—have as yet been obtained; that the great principle of the indestructibility of matter has been established, viz. that however the properties of matter may be altered, yet the total mass (or quantity) remains unchanged; and lastly, we find that an explanation of one important class of chemical changes—those changes which occur when substances burn—has been found.

And we have also learned that the method by which these results were obtained was this—to go to Nature, to observe and experiment accurately, to consider carefully the results of these experiments, and so to form a general hypothesis; by the use of the mental powers, and notably by the use of the imagination, to develop the necessary deductions from this hypothesis; and finally, to try these deductions by again inquiring from Nature "whether these things were so."

Before the time which we have been considering the paths of chemical science had scarcely yet been trodden. Each discovery was full of promise, each advance displayed the possibility of further progress; the atmosphere was filled as with "a mighty rushing wind" ready to sweep away the old order of things. The age was an age of doubt and of freedom from the trammels of authority; it was a time eminently suited for making advances in natural knowledge.

In the unceasing activity of Priestley and Lavoisier we may trace the influence of the restlessness of the age; but in the quietness and strength of the best work of these men, and notably in the work of Black; in the calmness with which Priestley bore his misfortunes at Birmingham; in the noble words of Lavoisier, "I am not unwilling to part with life, but I ask time to finish my experiments, because the results will, I believe, be for the good of humanity"—we see the truth of the assertion made by one who was himself a faithful student of Nature—

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