522 



NATURE 



[Al'KIL 3. 1902 



now appears that the three rivers flow on the surface of the 

 12,000 feet high Tibet plateau, and are separated — not by fan- 

 like radiating mountain ranges, but by ranges of mountains 

 rising some 3000 feet above tlie plateau and all running parallel 

 to each other, N.W. toS.E. In its western portion, the high 

 plateau, deprived as it is of the rains of the monsoon region, 

 is a dreary desert, covered with shingle ; but in its south-eastern 

 portion, the character of the plateau changes entirely. A deep 

 erosion makes of it an alpine mountain region. Wide valleys 

 and deep gorges alternate with stony ridges ; the routes and the 

 footpaths go down to a deep level, or lead to great relative and 

 absolute altitudes. Regions of soft and of rough climate, of rich 

 and extremely poor vegetation, rapidly alternate. This alpine 

 character already appears in ihe basin of the Blue River, but it 

 is still more evident in the basin of the Mekong, where the valleys 

 are still deeper and their vegetation still more varied. Forests 

 of fir and of a tree-like Juniperus make their appearance, as 

 also growths of birch, wild apricots, apple trees and a variety 

 of bushes. In the thickly wooded gorges, the expedition also 

 found the conspicuous white Tibet pheasants (Crossopftlon thihet- 

 anum), the green Ilhaginis Gcoffyoyi, the Telraof'hasis ohsciiriis, 

 Telrastes Sewertzowii, several species of blackbirds and a good 

 number of the smaller birds of the Passeres group. On a 

 bright clear day the forests and the meadows are full of bird- 

 life. Small colonies of monkeys stay in close proximity to the 

 Tangute encampments. 



On June 13 the expedition reached at last the two lakes 

 Orin-norandjarin-nor, whence it proceeded to Tsaidam, and then 

 once more across the Gobi, back to Kiakhta. It appeared that 

 everything was in order at the meteorological station, where 

 regular observations were made for a full year. As to the collec- 

 tions made in Tibet, they were very rich and contained no less 

 than 120 mammals, 600 birds, moie than 600 species of plants 

 (10,000 specimens) and about 300 specimens of rocks. Lati- 

 tudes and longitudes were determined in thirteen different spots. 

 The expedition is now back at St. Petersburg. P. K. 



T 



CATALYSIS} 



HE idea and name of catalytic action were introduced into 

 science by Berzelius in 1S35, apropos of Miischerlich's 

 work on the formation of ether. Berzelius pointed out that the 

 action of sulphuric acid in this case was analogous to the action 

 of dilute acids on starch, to the similar action of malt extract, 

 to the decomposition of hydrogen peroxide by metals and oxides, 

 and to the action of platinum on combustible mixtures of gases. 

 According to Berzelius, catalytic force appeared to consist 

 essentially in this, " that substances by their mere presence and 

 not by their afiinity have the power to rouse latent affinities, 

 so that compound substances undergo reaction and a greater 

 electrochemical neutralisation occurs." Berzelius made no 

 attempt to explain the phenomenon ; on the contrary, in a 

 subsequent discussion with Liebig, he insisted on the great 

 danger of attempting to explain incompletely understood pheno- 

 mena by hypothetical assumptions, lest experimental investiga- 

 tion should thereby be hindered. Berzelius' warning was not 

 heeded, and the neglect of it is felt to the present day. 



Catalytic actions may be divided into four cla.sses : — (l) Re- 

 lease in supersaturated systems. (2) Catalysis in homogeneous 

 mixtures. (3) Heterogeneous catalysis. (4) Enzyme actions. 



(I) This first division includes phenomena which may be 

 regarded as fundamentally explained. The best-known case is 

 the crystallisation of a supersaturated solution, for example, of 

 Glauber's salt, by the admission of a very small trace of the 

 solid substance with respect to which the solution is super- 

 saturated. We notice here in the first place the characteristic 

 disproportion between the quantity of the acting substance and 

 the quantity of substance changed by its influence. By a 

 particle of dust far below the limit of what is ponderable, it is 

 possible to bring an indefinitely large quantity of supercooled 

 solution 10 congelation. The smallest particle which suffices 

 is between io~'" and io~'- gramme. The processes are not 

 limited to supersaturated solutions of solids ; they are applicable 



' The phenomena of catalytic action have been the chief subject of 

 investigation by Prof. Ostwald and his pupils during the p.ist f?iv years. 

 ... . ^f (j,^ chief results .so far obtained, together with a statement 



of the_ general character of catalytic phenomena. 



NO. 1692, VOL. 65] 



also to solutions of gas. In these cases a trace of a gas may 



cause the liberation of an entirely disproportionate amount of 

 another gas. Then again, supersaturation is not limited to the 

 liquid state. X'apours can be supersaturated in respect to 

 liquids and solid bodies, and even in the case of .solids, cases are 

 known where they are supersaturated in respect to liquids, that 

 is to say that when they are in contact with a small quantity 

 of liquid in question they are converted into liquid. Super- 

 saturation on the part of solid bodies in respect to the solid 

 bodies which can he produced from them are very common. 

 On the contrary, supersaturation of a liquid in respect to another 

 liquid has not been observed and would be difficult to obtain. 



The theory of all these phenomena is known. In all cases we 

 have the formation of a system the stability of which is not the 

 greatest possible under the given conditions of temperature and 

 pressure. There are, on the contrary, other more stable conditions 

 which are characterised by the fact that in them anew phase, that 

 isa physically different component with other properties, makes its 

 appearance. In the case of a supersaturated solution of Glauber's 

 salt, this is the solid salt ; in supersaturated soda-water, it is car- 

 bonic acid gas. As a rule such a new phase does not appear 

 spontaneously if the supersaturation is not too great, and the 

 system behaves as if it were in equilibrium ; but if a small quan- 

 tity of the absent phase comes in contact with the metaslable 

 system, the action is set going and the new phase increases until 

 equilibrium is reached. 



If the new phase is a solid substance, the releasing action is 

 associated with a solid nucleus of the same composition. Iso- 

 morphous substances have also the property ; other solid bodies, 

 on the other hand, are without action. There is here opened a 

 wide field for investigation, since isomorphous substances 

 probably act by the formation of solid solutions, and it is to be 

 ascertained whether solid substances which are not isomorphous 

 with the substance concerned, but are capable of forming solid 

 solutions with it, are active. Further, there are cases where 

 solid bodies act without being isomorphous or without forming 

 solid solutions. Such artificial nuclei can be prepared, for 

 example, by allowing silicic acid to deposit in presence of a 

 crystal and then dissolving the crystal by means of a suitable 

 solvent. This subject has not been fully investigated, but it 

 explains many apparent contradictions that have occurred in the 

 investigation of this difficult subject. Whilst the nuclei in cases 

 of supersaturation in reference to a solid phase must be of a 

 specific nature, in the case of supersaturation with gases any gis 

 whatever will act as a nucleus. This is in consequence of the 

 fact that every gas dissolves without limit in every other gas, 

 that is, forms a homogeneous mixture with it. 



A given liquid can be simultaneously supersaturated with 

 respect to different phases, for example, one can easily melt 

 together sodium acetate and sodium thiosulphate to form a 

 liquid, from which, by the addition of a nucleus of either salt, 

 that salt is separated, whilst the other remains dissolved. 



Supposing we had such a liquid flowing through a tube at 

 one point of which w.as a nucleus of acetate and at another of 

 thiosulphate, then each nucleus would continue to grow in its 

 own way as Ihe liquid circulated. We have here an example of 

 the physicochemical possibility of certain organic processes to 

 which Berzelius alluded, such as the formation of the most 

 different substances in the animal body from one and the same 

 liquid, namely the blood. If we might consider the blood as a 

 supersaturated solution in respect to all these substances, it 

 would be intelligible that every organ could increase its sub- 

 stance from one and the same liquid. It would be inadmissible 

 to suppo.se that we have here a general theory of animal 

 secretion, for the consideration only applies to heterogeneous 

 phases. 



Again, there is the question as to whether a compound which 

 does not preexist in the liquid, but can only come into exist- 

 ence by the action of contained substances, is capable of 

 exhibiting supersaturation in regard to other phases in contact 

 with it. There are phenomena of supersaturation known to us 

 in connection] with calcium sulphate, solutions of which are so 

 dilute that the salt must be almost entirely in the form of its 

 ions. Since there are no ions in the solid .salt there must be 

 here a chemical change. Dilute solutions of lead salts and 

 thiosulphates dikewise show a supersaturation in respect to 

 le.ad .sulphide, which is formed from them by complicated 

 chemical ilecomposition. Finally, the " physical development " 

 in photography affords exampleiof such phenomena. 



Further examples of possible physiological applications can- 



