514 



NATURE 



{Oct. 5, 1876 



hydration of the outer surface extends through the thickness of 

 the membrane and reaches the inner surface, it there receives a 

 check. . . . The contact of the saline fluid is thus attended by 

 a continuous catalysis of the gelatinous hydrate, by which it is 

 resolved into a lower gelatinous hydrate and free water. Now 

 this question of hydration is perhaps the most remarkable in- 

 stance of the persistent continuity of Mr. Graham's work, as 

 Dr. Odling has pointed out,^ — "it is noteworthy that for him 

 (Mr. Graham) osmosis became a mechanical effect of the hydra- 

 tion of the septum ; that the interest attaching to liquid trans- 

 piration was the alteration in rate of passage consequent on an 

 altered hydration of the liquid, and that the dialytic difference 

 between crystalloids and colloids depended on the dehydration 

 of the dialytic membrane of the former class of bodies only." 



I must now direct your attention to a section of Mr. Graham's 

 work, which, although it was the last, was a reverrion to f ome 

 of his very eailiest experiments. In 1829, under the title, 

 "Notice of the Singular Inflation of a Bladder," he described the 

 following experiment : — A bladder two-thirds filled with car- 

 bonic acid was introduced into a bell jar filled with carbonic acid 

 gas ; alter the lapse of some hours the bladder was found to 

 contain 35 per cent, of carbonic acid, and to have become dis- 

 tended. Mr. Graham observes : — " M. Dutrochet will probably 

 view in these experiments the discovery of endosmose acting 

 upon aeriform matter as he observed it to act on bodies in a 

 liquid state. Unaware of the speculations of that philosopher 

 at the time the experiment was made, I fabricated the following 

 theory to account for them : — The jar of carbonic acid standing 

 over water, the bladder was moist, and we know it to be porous. 

 Between the air in the bladder and the carbonic acid without 

 there existed capillary canals through the substance of the blad- 

 der, filled with water. The surface of the water at the outer 

 extremities of these canals being exposed to carbonic acid, a 

 gas soluble in water would necessarily absorb it. But the gas 

 in solution , , . permeated the canal, and passed into the blad- 

 der and expanded it." 2 



You will remember that in the concluding experiments on the 

 diffusion of gases Mr. Graham employed a tube, closed with a 

 graphite disc (Fig. 2), in which a Torricellian vacuum could be 

 produced. In his experiments on the penetration of different 

 gases through membranes the same apparatus was employed, 

 only the disc of graphite was replaced by a film of india-rubber. 

 He found that gases penetrated to the vacuous space at the rates 

 given in the last column of the table (p. 512). You will observe 

 that the gas which penetrates most rapidly is carbonic acid, and 

 you will also see that the rates of passage are in no way connected 

 either with those of diffusion or transpiration. 



A comparison of the relative rates of passage of oxygen 

 and nitrogen led to a most remarkable experiment. Oxygen 

 penetrates 2J times as fast as nitrogen, therefore by dialysing 

 air ,Mr. Graham actually increased the quantity of oxygen 

 from 20"8 to 41 per cent., just as he had effected, by the aid 

 of a tobacco-pipe, a partial separation of oxygen from air by 

 the slightly greater diffusion velocity of nitrogen. The Torri- 

 cellian vacuum was ill adapted for the experiments, and Mr. 

 Graham gladly availed himself of the mercurial exhauster devised 

 by Dr. Hermann Sprengel, and he considered that without the 

 aid of this instrument it would have been impossible to conduct 

 certain portions of the research. He was thus able to use larger 

 septa of india-rubber, bags of waterproof silk being found to be 

 most convenient (Fig. 8). The vacuum was not even absolutely 

 necessary, for the penetration of the nitrogen and oxygen of air 

 through rubber into a space containing carbonic acid could be 

 readily effected, the gas being absorbed by potash at a certain 

 stage of the operations. 



Mr. Graham considered this penetration to be due to an actual 

 dissolution of the gas in the substance of the india-rubber, for, 

 as he observes, " gases undergo liquefaction when absorbed by 

 liquids and by soft colloids like india-rubber," words I think of 

 interest, when we remember that the sentence only marks a slight 

 extension of the view he expressed in his first paper in 1829. 



These discoveries led Mr. Graham to inquire whether it was 

 probable that the discovery of MM, Troost and Deville of the 

 penetration of red-hot platinum and iron tubes by hydrogen, 

 could be due to an actual absorption and liquefaction of the gas 

 in the pores of the metal, and by submitting the question to the 

 test of experiment it was proved that such an absorption did take 

 place. 



' Lecture on "Prof. Graham's Scientific Work," Royal Institution, 

 January, 1870. 

 ^ Quart. Journ. Sci., 1829, P- 88. 



For instance, palladium was found to act as platmum only in 

 a more marked manner. A tube of palladium when attached to 

 the mercurial exhauster did not allow hydrogen to pass in the 

 cold, but when heated to redness in an atmosphere of hydrogen 

 the gas passed through the walls of the tube at the rate of 4,000 

 cubic centimetres per square metre in an hour (Fig. 9). This led 

 to the remarkable discovery of the absorption or occlusion of 

 gases by metals. It was found that nearly all metals appear to select 

 one or more gases. Silver, for instance, absorbs many times its 

 volume of oxygen, and under certain circumstances gives it out 

 again on cooling. Iron is specially characterised by its absorp- 

 tion of carbonic oxide, but it also retains hydrogen, and this fact 

 led Mr. Graham to extract from meteoric iron, the gas that 

 probably affected its reduction to the metallic state, and which 

 certainly exists in the atmosphere of certain stars. 



The most remarkable results v/ere obtained with palladium. I 

 celled your attention at the beginning of the lecture to the index 

 which you will observe has moved six inches. 



I will now describe the apparatus ; it consists of a tall jar 

 filled with acidulated water ; at the bottom of the jar two wires 

 are fixed, and these wires are parallel throughout the entire 

 length of the jar. Each is attached to the short arm'of a lever, 

 the longer arms of which are about five feet long. One wire is 

 of palladium, the other of platinum, and they form the electrodes 

 of a small battery capable of decomposing the water. The 

 palladium now forms the negative electrode, and is freely 

 absorbing hydrogen, the excess of which is escaping from its 

 surface. The absorption of hydrogen has been attended by a 

 considerable expansion, as is shown by the fall of the index. 

 The index attached to the platinum wire has of course remained 

 stationary. 



This expansion enabled Mr. Graham to calculate the'density of 

 the gas in its condensed form, and for reasons which I cannot 

 give you now he was led to believe that hydrogen gas is the 

 vapour of a white magnetic metal of specific gravity o"j. 



Now by taking palladium which has been charged in the 

 manner you have seen, and heating it hi vacuo, I can actually 

 extract and show you the hydrogen it contained. This little 

 medal of palladium contains an amount of gas condensed into 

 it which would be equivalent to a column of gas more than a 

 yard high, and of the diameter of the medal. 



The story of Mr. Graham's work has been much better told 

 by Odling, Williamson, Hofmann, and Angus Smith, but what 

 does it teach us from a point of view of a collection of scientific 

 apparatus ? Surely that, although in certain researches or for 

 accurate observation and measurement, delicate and complicated 

 instruments may be necessary, the simplest appliances in the 

 hands of a man of genius may ;' give the most important results. J 



Thus we have seen that with a glass tube and plug of plaster of J 

 Palis, Mr. Graham discovered and verified the law of diffusion " 



of gases. With a tobacco-pipe he proved indisputably that air 

 is a mechanical mixture of its constituent gases. With a tam- 

 bourine and a basin of water he divided bodies mto crystalloids 

 and colloids ; and obtained rock crystal and red oxide of iron 

 solttble in water. With a child's indiarubber balloon filled with 

 carbonic acid he separated oxygen from atmospheric air, and 

 established points, the importance of which, from a physiological 

 point of view, it is impossible to overrate. And finally, by the 

 expansion of a palladium wire, he did much to prove that 

 hydrogen is a white metal. 



GERMAN EXPEDITION TO SIBERIA''- 



" ^A/E stayed in I^psa until May 17. We obtained some 

 ' ^ varieties of lizards, one kind of frog, and a toad, a kind 

 of fish like the barbel, and all sorts of varieties of cobitis, but 

 no salmon. We obtained only a few beetles and butterflies, but 

 we had a rich collection of the flora. On May 13 and 14 we 

 made a short excursion into the mountains and found several 

 new kinds of birds differing decidedly from the European kinds, 

 e.g., the Chiclus leucogaster, with the white belly, ^the MotactUa 

 fcrsonata, the Pica leticoptera, a fine Carduelis, and a splendid 

 specimen of the red-finch. 



" On May 15 we made a long excursion to the Dschasyl Kul 

 (green lake), 6,000 feet above the level of the sea. The abun- 

 dance of trees and bushes has a most agreeable effect, and above 

 all is the mild red and pink of the wild apple-tree (Pinis Sieve- 

 rianus) pleasing to the eye. The lake, lying amongst high 



» The second letter dates from Saissan, in Russian Turkestan, May 27, 

 1876. Continued from p. 359. 



