Page:Nature - Volume 1.pdf/36

22 spontaneous motions of particles of matter, whether in the state of gas or in the liquid state.

It was known that 1 part by weight of hydrogen occupies the same volume as 16 parts by weight of oxygen when measured at like temperature, and under like pressure. Chemical investigations prove that these equal volumes of the two gases contain the same number of atoms. also know that the atoms in such a gas are in rapid motion, and resist the pressure to which the gas is at any particular time exposed, by striking against the surface which presses them together with force equal to that which presses them together.

Thus a given volume of hydrogen is maintained against the atmospheric pressure by an energy of atomic motion, Each atom equal to that of the same volume of oxygen. of hydrogen accordingly exerts a mechanical energy equal to that of each atom of oxygen; but we have seen that the hydrogen atom is much lighter than the oxygen atom, and accordingly it must move with much greater velocity than the oxygen atom.

Now Graham allowed hydrogen to escape through a very small hole in a plate of platinum and allowed oxygen to escape under similar circumstances. He found that each hydrogen atom moves out four times as fast as each oxygen atom. His experiments were so arranged as to enable him to measure the relative velocities of certain motions of the atoms—motions not imparted to them by any peculiar or unnatural conditions, but belonging to them of necessity in their natural state. He found, moreover, that heat increases the velocity of these atomic motions, whilst increasing the force with which a given weight of the gas resists the atmospheric pressure.

The study of the condensation of gases by solids, and the combination of soluble compounds with membranes led him to discoveries which are likely to be of great value to physiologists in explaining processes of absorption and secretion.

Thus he found that oxygen is absorbed to a greater than nitrogen by caoutchouc, and that when a bag made of a thin membrane of this substance is exhausted by means of a good air-pump, the oxygen and nitrogen diffuse through it (probably as condensed liquids), and evaporate inside the bag in different proportions from those in which they are present in air the oxygen rising to over 40 per cent. of the diffused air. Again, a mixture of hydrogen and oxygen was separated almost completely by the action of palladium, which condensed the hydrogen in very large quantity, and the oxygen very slightly.

Perhaps the most remarkable substances discovered in the course of his experiments on diffusion, were the soluble modifications of tungstic and molybdic acids, ferric oxide, &c., and the process by which these bodies were obtained was, perhaps, the most instructive part of the result proving, as it docs, that in their salts, these bodies have properties different from those which they normally possess in the free state and retain them when the other constituent is removed by a sufficiently gentle process.

Another remarkable fact which bears on a most important theory, is the separation effected by Graham of potassic hydrate and hydric sulphate, by diffusion of potassic sulphate in aqueous solution—a fact which requires us to admit that the solution of the salt in water contains those just as much as the products mixed with one another experiment of diffusing air through a porous clay pipe, and getting its constituent in a different proportion from that of the original air, proved that air is a mixture and not a compound of the two gases.

In his later researches, Graham was assisted by Mr. W. C. Roberts, and cordially acknowledged the zeal and efficiency displayed by that able young chemist. Graham's scientific influence extended beyond his researches for, on the one hand, his lectures for 18 years at University College were remarkable for logical accuracy and clearness of exposition, and were highly valued by those who had the privilege of hearing them. On the other hand, his "Elements of Chemistry" is a masterly exposition of the best known facts of the science and of chemical physics. It was translated into German, and afforded at that time the most philosophical account of the working and theory of the galvanic battery.

In many of his ideas Graham was in advance of his contemporaries, and it might be difficult to find a chemist who has dealt more cautiously with general questions and delicate experimental operations, or one whose results, in each direction in which he has worked, may more safely be expected to stand the test of future investigations.

ROM the 18th to the 24th of September last the little air of unwonted bustle and excitement. Its population, already augmented by the usual throng of summer tourists, was swelled by the advent of somewhere about 800 additional visitors professors, doctors, directors, men of all sciences, often with their wives and daughters, who had come from all parts of Germany to attend the forty-third Meeting of the German Naturalists and Physicians. These meetings resemble those of our own British Association, though they differ in several veiry characteristic respects. One of the first contrasts to strike an Englishman is the entire absence of private hospitality. Everybody, so far as we can learn, is in private lodgings or in a hotel and there are no such things as dinner-parties. Although our own customs in these respects are certainly very pleasant, there can be no doubt that the German fashion leaves the visitors more freedom, and allows them much more opportunity of seeing and talking with the friends they most wish to meet. With us it is no easy matter to get together a party of chemists, or geologists, or physiologists, to hold a social gathering after the labours of the sections are over. We are all either staying with friends, or invited to dinner, or engaged in some way. But at the German meetings such social reunions are one of the distinguishing features. One o'clock in the day brings with it the necessity for dining, and numerous dinner parties are improvised there and then friends of like tastes, who have not met perhaps for a year before, adjourn to a restauration or kaffee-haus, and while eating the meal have a pleasant opportunity of comparing notes, and discussing questions which have in the interval arisen.

Another feature of contrast is in the length of time devoted to the sitting of the sections. At the British Association the sections open their sittings at eleven in the forenoon and the work goes on steadily all day without intermission till four or five o'clock in the afternoon. But, in Germany, the sittings commence sometimes as early as 8 A.M., and are frequently over by ten or eleven o'clock, leaving the rest of the day for some short after-dinner excursion, or for general miscellaneous intercourse among the members. In fact, the German meetings are designed less for the purpose of bringing forward new scientific work, than with the view of affording to men of science opportunities of becoming personally acquainted with each other, and of discussing the value and bearing of recent contributions to knowledge. Hence, the papers which arc brought before the sections, contain, to a large extent, outlines, summaries or notices of recent researches, and exhibitions of books, maps, memoirs, specimens, experiments, t:c., which have recently attracted notice.

In our British Association gatherings, there is probably more hard work than in those of our German brethren, and I daresay there is as much opportunity for sociality as suits our national temperament. For our Association