In the case of solutions it was found that certain compounds, notably the acids, alkalies, and metallic salts, caused a depression of freezing point which was twice as great as ought to be expected. This fact was illuminated by the phenomena observed in gases, and soon it was seen that here too a splitting up of molecules, a true dissociation, occurred. These anomalous solutions, moreover, were electrolytes—that is, they conducted electricity and underwent electrolytic decompositions—while normal substances, especially solutions of carbon compounds, such as sugar, were not.
Van t’Hoff’s discoveries went far, but one more step was needed, and this was taken by Arrhenius in 1888. Electrolytic compounds, when dissolved, are actually dissociated into their ions, partially so in a strong solution, entirely so in one which is infinitely dilute, a statement which leads to some extraordinary conclusions. For instance, the ions of common salt are sodium and chlorine. In a dilute solution the salt itself ceases to exist, while atoms of sodium and atoms of chlorine wander about, chemically separated from each other but still in equilibrium. Sodium sulphate may be regarded as made up of two parts—sodium and an acid radicle which contains one atom of sulphur to four of oxygen—and these parts, its ions, are severed apart during solution to move about independent of each other.
This theory of Arrhenius, the theory of electrolytic dissociation, is supported by many facts, and fits in well with the kinetic theory of Van t’Hoff. Electrolysis is no longer to be considered as a separating process, but rather as a sorting of the ions, which receive different electrical charges and concentrate at the two electrical poles. The phenomena of freezing and boiling points in solutions, and of the absorption of heat when solid salts are dissolved, all harmonize with the conclusions which have been reached. A complete theory of solutions is yet to be proposed; but these new doctrines, which are true so far as they go, represent a long step in the right direction. A final theory will include them, but they are not likely to be set aside.
As we near the end of the century we find one more discovery to note, from a most unexpected quarter—the discovery of new gases in the atmosphere. In 1893 Lord Rayleigh was at work upon new determinations of density, with regard to the more important gases. In the case of nitrogen an anomaly appeared: nitrogen obtained from the atmosphere was found to be very slightly heavier than that prepared from chemical sources, but the difference was so slight that it might almost have been ignored. To Rayleigh, however, such a procedure was inadmissible, and he sought for an explanation of his results. Joining forces with Ramsay, the observed discrepancies were hunted down, and in 1894 the discovery of argon was announced. Ramsay soon found in certain rare minerals another new gas—helium—whose spectral lines had previously been noted in the spectrum of the sun; and still later, working with liquid air, he discovered four more of these strange elements—krypton, xenon, neon, and metargon. By extreme accuracy of measurement this chain of discovery was started, and, as some one has aptly said, it represents the triumph of the third decimal. A noble dissatisfaction with merely approximate data was the motive which initiated the work.
To the chemist these new gases are sorely puzzling. They come from a field which was thought to be exhausted, and cause us to wonder why they were not found before. The reason for the oversight is plain: the gases are devoid of chemical properties, at least none have yet been certainly observed. They are colorless, tasteless, odorless, inert; so far they have been found to be incapable of union with other elements; apart from some doubtful experiments of Berthelot, they form no chemical compounds. Under the periodic law they are difficult to classify; they seem to belong nowhere; they simply exist, unsocial, alone. Only by their density, their spectra, and some physical properties can these intractable new forms of matter be identified.
In a sketch like this a host of discoveries must remain unnoticed, and others can be barely mentioned. The isolation of fluorine and the manufacture of diamonds by Moissan, the synthesis of sugars by Fischer, the discovery of soluble forms of silver by Carey Lea—all these achievements and many more must be passed over. Something, however, needs to be said upon the utilitarian aspects of chemistry, and concerning its influence upon other sciences. Portions of this field have been touched in the preceding pages; the interdependence of chemistry and physics is already evident; other subjects now demand our attention.
Medicine and physiology are both debtors to chemistry for much of their advancement, and in more than one way. From the chemist medicine has received a host of new remedies, some new processes, and advanced methods for the diagnosis of disease. The staining of tissues for identification under the microscope is effected by chemical agents, the analysis of urine helps to identify disorders of the kidneys; nitrous oxide, chloroform, ether, and cocaine almost abolish pain. The disinfection of the sick-room and the antiseptic methods which go far toward the creation of modern surgery all depend upon chemical products whose long list increases year by year. Crude drugs are now replaced by active principles discovered in the laboratory—morphine, quinine, and the like—and instead of the bulky, nauseous draughts of olden time, the invalid is given tasteless capsules of gelatin or compressed tablets of uniform strength and more accurately graded power. A great part of physiology consists of the study of chemical processes, the transformation of compounds within the living organism, and practically all this advance is the creation of the nineteenth century. Modern bacteriology, at least in its practical applications, began with a chemical discussion between Liebig and Pasteur as to the nature of fermentation: step by step the field of exploration has enlarged; as the result of the investigations we have preventive medicine, more perfect sanitation, and antiseptic surgery. The ptomaines which cause disease and the antitoxins which prevent it are alike chemical in their nature, and were discovered by chemical methods. Physiology without chemistry could not exist; even the phenomena of respiration were meaningless before the discovery of oxygen. The human body is a chemical laboratory, and without the aid of the chemist its mysteries can not be unraveled.
To agriculture also chemistry is a potent ally, whose value can hardly be overrated. It has created fertilizers and insecticides for the use of the farmer and taught their intelligent use, and in the many experiment stations of the world it is daily discovering facts or principles which are practically applicable to agriculture. The beet-sugar industry was developed by chemical researches and chemical methods; the arts of the dairy have been chemically improved; the food of all civilized nations is better and more abundant than it was before the chemist gave his aid to its production. Adulteration, always practiced, is now easily detected by chemical analysis, and, though the evil still exists, the remedy for it is in sight. To Liebig, who gave to agricultural chemistry its first great impulse forward, mankind is indebted to an amount which is beyond all computation.
In manufactures the influence of chemistry is seen at every turn. When the century began, probably no industrial establishment in the world dreamed of maintaining a chemical laboratory; to-day, hundreds are well equipped and often heavily manned for the sole benefit of the intelligent manufacturer. Coal gas is a chemical product; its by-products are ammonia and coal tar; from the latter, as we have seen, hundreds of useful substances, the discoveries of the last half century, are prepared. Better and cheaper soap and glass owe their existence to chemical improvement in the making of alkalies; chemical bleaching has replaced the tedious action of sunlight and dew; chemical dyestuffs give our modern fabrics nearly all their hues. Metallurgy is almost wholly a group of chemical processes; every metal is extracted from its ores by methods which rest on chemical foundations; analyses of fuel, flux, and product go on side by side with the smelting. The cyanide and chlorination processes for gold, the Bessemer process for steel, are apt illustrations of the advances in chemical metallurgy; but before these come into play the dynamite of the miner, another chemical invention, must have done its work underground. For rare minerals, the mere curiosities of twenty years ago, uses have been found; from monazite we obtain the oxides which form the mantle of the Welsbach burner; from beauxite, aluminum is made. The former waste products of many an industry have also revealed unsuspected values, and chemistry has the sole honor of their discovery.
In education, chemistry has steadily grown in importance, until a single university may have need of as many as twenty chemists in its teaching staff, teaching not only what is already known, but also the art of research. As a disciplinary study, chemistry ranks high in the college curriculum, and it opens the way to a new learned profession, equal in rank with those of more ancient standing.