November 5, 19 14] 



NATURE 



253 



LETTERS TO THE EDITOR. 



The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

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» taken of anonymous communications.li 



Faraday's Views on Catalysis. 



At the present time much attention is being given, 

 both by chemists and by physiologists, to the mechan- 

 ism of catalysis in heterogeneous systems. The in- 

 terest of the question to physiologists is in connection 

 with the mode of action of those catalysts produced 

 ^v living organisms ; these are called, for convenience, 

 ■ nzymes." 



The extraordinary insight shown by Faraday into 



ti' nature of the various phenomena with which he 



td to deal is well known and needs no further com- 



:nt. But, on this ground, the paper which he pub- 



-hed in the Philosophical Transactions of the Royaf 



>i)ciety for the year 1834, entitled "'On the Power of 



Metals and other Solids to Induce the Combination 



: Gaseous Bodies," deserves more consideration by 



odern investigators than it usually receives. The 



per is also to be found in "Experimental Researches 



Electricity" (vol. i., pp. 165-94), and the references 



ven to quotations below refer to the numbered para- 



aphs in that reprint. 



Although Faraday's work was published before the 



introduction by Berzelius of the name "catalysis," the 



I combination of oxygen and hydrogen gases brought 



,|. about under the influence of platinum and other solids, 



' which is the subject of the paper before us, is clearly 



a case of this kind. In fact, the action of spongy 



rlatinum is given by Berzelius himself in illustration 



: the phenomenon. 



The chief experimental fact of importance to the 

 theor}' of the process, and demonstrated by Faraday 

 in a number of different ways, is that the only condi- 

 tion necessary is the perfect cleanliness of the surface 

 of the platinum (617). He points out that impurities 

 :' various kinds are readily condensed on the surface 

 adsorbed," as we should say), from the air and even 

 irom ordinary distilled water. The presence of such 

 I films prevents that condensation of the gases which is 

 requisite for their combination. In whatever way — 

 mechanical, as by rubbing with polishing powders 

 1591, 592, 593); chemical, by treatment with concen- 

 trated mineral acids (600) ; or by heat (596)^these 

 substances are removed, the platinum is made active. 

 Of special interest is the fact that making it either 

 anode or .kathode in dilute sulphuric acid (588) is 

 particularly effective, the formation of " nascent " 

 oxygen on the surface in the former case being the 

 more powerful, as would be expected. The difference 

 between the clean surface and the dirty surface is 

 shown by the way in which water, or gases developed 

 on the surface by electrolysis, enter into closer contact 

 with the clean surface and form uniform films, instead 

 of drops or bubbles. 



It is pointed out in paragraph 617 that the inter- 



^ention of electrical forces is excluded by the fact that 



both anode and kathode are active. Chemical reaction 



I between the platinum and oxygen is also excluded by 



i the fact that nitrous oxide and hydrogen are caused 



I to combine (572). In paragraph 618 further evidence 



I that the effect is not due to the intervention of 



! platinum in a purelv chemical way is given by the 



fact that "the effect is evidently produced by most, if 



not all, solid bodies." 



The reader will probably call to mind that it has 

 been held by some observers that this and similar 

 activities shown by platinum are to be explained by 

 NO. 2349, 'vol. 94] 



the formation of intermediate compounds of the nature 

 of oxides of platinum. The actual existence of such 

 compounds has never been demonstrated, and the 

 hypothesis did not commend itself to the acute mind 

 of Faraday, whose explanation is of much interest. 

 On account of the importance of the question I will 

 quote the actual words used : — " They " (the pheno- 

 mena under discussion) " are dependent upon the 

 natural conditions of gaseous elasticity, combined with 

 the exertion of that attractive force possessed by many 

 bodies, especially those which are solid, in an eminent 

 degree, and probably belonging to all ; by which they 

 are drawn into association more or less close, without 

 at the same time undergoing chemical combination — 

 and which occasionally leads, under very favourable 

 circumstances, as in the present instance, to the com- 

 bination of tMDdies simultaneously subjected to this 

 attraction " (619). As we might put it now, gases are 

 condensed on surfaces, losing thus the kinetic energy 

 of their molecules, and, if capable of combining 

 together, may be thus caused to do so. Could we 

 have a clearer statement of adsorption and the part 

 pla3-ed by it in catalysis? 



In further illustration of this "adsorption," Faraday 

 proceeds to give some interesting examples of the 

 condensation of water vapour and of air on the surface 

 of various powders and on glass, pointing out in the 

 latter case that there is no chemical affinity between 

 air and glass. We note also that Faraday says that 

 the vapour is condensed upon the substances. Again, 

 "The gases are so far condensed as to be brought 

 within the action of their mutual affinities at the 

 existing temperature " (630), and " The platina is not 

 considered as causing the combination of any par- 

 ticles with itself, but only associating them closely 

 around it; and the compressed particles are as free to 

 move from the platina, being replaced by other par- 

 ticles, as a portion of dense air upon the surface of 

 the globe, or at the bottom of a deep mine, is free to 

 move, by the slightest impulse, into the upper and 

 rarer parts of the atmosphere" (631). As regards the 

 adsorption of other substances on the platinum, we 

 read : " In fact, the very power which causes the 

 combination of oxygen and hydrogen, is competent, 

 under the usual casual exposure of platina, to con- 

 dense extraneous matters upon its surface, which, soil- 

 ing it, take away for the time its power of combining 

 oxygen and hydrogen by preventing their contact with 

 it " (632). We have here analogous phenomena in the 

 action of enz}mes, where an easily adsorbed sub- 

 stance, such as saponin, prevents the action of the 

 enzyme by obtaining possession of the surface itself 

 and thus excluding the condensation of the molecules 

 between which chemical action is to be brought about. 



Although Faraday evidently regards condensation on 

 surfaces as especially applicable to gases, it is clear 

 that he considers the phenomenon to be of general 

 occurrence. He does not appear to have met with 

 cases of adsorption of substances from solution in 

 liquids, but he says " an analogy in condition exists 

 between the parts of a body in solution and those of a 

 body in the vaporous or gaseous state " (657). Is this 

 statement to be looked uoon as an anticipation of 

 van 't Hoff's theon,- of solutions? 



I will conclude my quotations from the paper with 

 the following, which is worth bearing in mind at the 

 present day : — " I am convinced that the superficial 

 actions of matter, whether between two bodies, or of 

 one piece of the same body, and the actions of par- 

 ticles not directly or strongly in combination, are be- 

 coming daily more and more important to our theories 

 of chemical as well as mechanical philosophy. In all 

 ordinarv cases of combustion it is evident that an 

 action of the kind considered, occurring upon the sur- 

 face of the carbon in the fire, and also in the bright 



