THE present director of the Physico-Chemical Institute of the University of Berlin, Prof. Henry Walter Nernst was born at Briesen, West Prussia, June 25th, 1864. He is, therefore, a much younger man than the volume and importance of his work would lead one to suspect. Intimate glimpses of a scientific man's daily life are often full of interest, especially when they reveal peculiarities or seeming eccentricicies due to the nature and intensity of his work. In the present instance, however, these peculiarities will be. left to the discussion of his intimate friends, whom, doubtless, they sometimes amuse but never offend. For the rest of us the name Nernst calls to mind chiefly a number of important contributions to the science of physical chemistry, and hence it is with these alone that the following Is concerned. In order to get a proper appreciation of Nernst contributions to human knowledge, it is necessary briefly to review the cultivation of that fertile field of science that lies midway between the chemistry of Lavoisier and the physics of Newton. As a matter of fact there is not now, and never has been, a sharp boundary between physics and chemistry. Hence a great mass of information that to-day would be grouped under the general heading, Physical Chemistry was accumulated long before any one ever thought of the above compromise title for it. Physical chemistry, then, in the sense of a knowledge of the physical properties of compounds, is not a new science. The melting and boiling points of many substances, their specific heats, atomic and molecular volumes, viscosities, spectra, powers to refract light, to rotate the plane of polarization, and the like, were long ago studied, as were also the changes in these properties owing to the addition or SUbstitution of one or more elements. The object of the earlier experimenters was exactly the same as that of the ablest of the later investigators. All •sought, as every student of nature must, to co-ordinate apparently is 0 I ate d ff1ctS through broad generalizations, or the assignment of them to a common cause. But while the experimental facts discovered by the earlier workers are of the greatest importance, only emplrI-cal and hence merely approximate relations were found. The glory of the newer physical chemistry, that which justifies its claim to a position among the sciences, is the freedom of its laws from mere empirkism, and the exactness with which it enables one to calculate results by rigid mathematical processes. It is to this branch of chemistry, the branch that might even be termed mathematical chemistrY, that Nernst has chiefly contributed. It must not be supposed, however, that he was the founder of this our newest science, for there are others, especially Ost-wald, van't Hoff, and Arrhenius, with prior claims to that honor; but he has been and still is one of its chief builders. One of Nernst's earliest contributions to physical chemistry was a rational explanation of the mutual effect of salts upon each other's solubility_ It had long been known that in many cases two salts markedly interfere with each other's solubility in water, while others do not so interfere; but no satisfactory explanation had been of'ered for this phenomenon, 10r was it pOSSible, with a knowledge of the substances themselves, to predict what effect either would have upon the solution of the other. In this case, however, as often happens, the data necessary and sufficient to a complete solution of the problem were at hand, but it was Nernst who had the inspIration and the ability to use as premises the law of mass action, as developed by Guldberg and Waage, and Arrhenius's theory of electrolytic dissociation, and from them logically to deC.uce the exact cause and numerical extent of the effect of one salt on the solution of another. Another of Nernst's many contributions to our knowledge is an explanation of why any dissolved substance, as cane sugar, for instance, gradually spreads or diffuses throughout the medium in which it is dissolved. Here use was made of the laws of osmotic pressure as formulated by van't Hof-laws that in every particular are analogous to the laws of gas pressure. Just as difference in gas density leads to gas diffusion, so does difference in concentration of a dissolved substance lead to its diffusion through the medium in which it is dissolved. Hence the distribution of osmotic pressure throughout a given solution determines both the direction and velocity of diffusion. During recent years the investigation of chemical equalibra at high temperatures has occupied most of Nernst's attention. As every one knows, the properties of substances depend upon temperature. Up to a certain temperature iron, for instance, is easily1 magnetized, while at higher temperatures it is but slightly magnetic. At ordinary temperatures rubber is exceedingly flexible and elastic, but at the temperatures of liquid air it is as brittle as glass. And so it is with other substances, their properties are profoundly modifed when the temperature is greatly changed, so that to know a SUbstance thoroughly is to know its properties at all temperatures. Nor are the physical changes with temperature more pronounced than are ·the chemical. Substances that combine at 'ne temperature decompose at another, and qualities that are in a state of chemical equilibrium at one temperature are thrown out of balance by heating or cooling. Hence change in temperature furnishes unlimited studies for the physical chemist-studies to which Nernst and his students have given the most attention, but with results which, while valuable, necessarily are still incomplete. The subject is so vast and so diff,cult that it will require years of work approximately to complete it. Probably the general public, since it cares more for an art that serves its needs than it does for the science tlat rendered the art possible, knows of Nernst chiefly, if not solely, as the inventor of the electric glower that bears his name. This, however, like practically all other discoveries worth while, was the outcome, or, more exactly, a by-product of a purely scientific investigation, a careful study of the electrical conductivity of solid electrolytes. In the course of this work it was found that the oxides of certain rare elements possess properties that adapt them to economical use in electrical illumination. This was the always necessary discovery; the rest, in rendering the glower practicable, was but the ingenious combination of things already known. To the scientific world, however, Nernst is best known as the man who first developed a satisfactory theory of the action of the primary electric cell; a theory that enables one to calculate beforehand just what electro-motive force will be generated by a given combination of elements and solutions. The theory in question is based on three things, namely: (a) van't Hof''s laws of osmotic pressure, or tendency of a dissolved SUbstance to move from places of greater to places of less concentration. (b) The electrolytic dissociation theory' of Arrhenius, which accounts for certain properties of dissolved salts on the assumption that they are morc or less broken down into their constituent parts and that these individual parts are electrified. (c) Nernst's theory of solution tension, or the assumption that any metal, when placed in a liquid, even a solution of one of its own salts, dissolves to a certain extent, just as a liquid evaporates. The theory of the action of primary cells not only accounted for the actions of all known cells of this nature, but even suggested previously untried combinations and foretold their action. An exceedingly simple cell, but one that illustrates the theory, consists of two zinc rods dipping, the one into a concentrated, the other into a dilute water solution of zinc chloride. The tendency of the zinc to dissolve into the water-its sol uti0 n tension -is the same in the two cases, but the osmotic pressure of th,) zinc ions furnished by the zinc chloride is greater in the concentrated than in the dilute solution. Hence, since the osmotic pressure and the sohltion tension are in opposite directions, a state of equilibrium requires a larger number of zinc particles to be dissolved from the zinc bar in tae wt:k solution than from the one in the strong solution. But each zinc particle carries with it a definite charge of positive electricity, and consequently both zinc rods are left negatively charged, though the one in the dilute solution is more strongly charged than is tho one in the concentr<ted sol ution. Therefore, when the two zinc rods are connected by means of an electrical conductor, and the circuit is otherwise properly completed, a current flows from the less negatlvely to the more negatively charged rod outside the solutions , and in the reverse direction within the solutions. This, of course, destroys the balance, in both solutions, between the solution tension and osmotic pressure. In the diluted solution the advantage, after the balance is destroyed, is on the side of the solution tension, while in. the more concentrated solution it is with the osmotic pressure. Hence, zinc is dissolved and added to the dilute solt!tion from the rod that is in it, and at the same timf an equal amount removed from the other solution and deposited on the rod it contains, till,, in the end , the two solutions are of equal strength. At all times, and in all similar ceUs, the electromotive force is directly proportional to the logarithm of the difference between the two osmotic pressures, and is numerically calculable. Such, then, are some of Nernst's important contributions to science, and there is every reason, judging from his industry, ability and pOSition, to expect still others of great value. New Life Preserver RECENT consular reports describe a new form of life preserver, which it is proposed to introduce into the German Navy. It consists of two swimming cushions bound together by straps and arranged to lie upon the breast and back. The novel feature of the apparatus is an electric lamp, which is worn on the forehead. The lamp burns 3 or 4 hours, and is provided with a reflector, which throws its light for a distance of several hundred yards at night. The life preserver can be buckled on in 5 seconds
This article was originally published with the title "Henry Walter Nernst"