RECENT ADVANCES IN SCIENCE 205 



being in Bodenstein's favour, and the theory of false equilibria 

 came to be regarded as disproved. 



The question has, however, been reopened recently by 

 Bancroft (6), who has pointed out that in heterogeneous re- 

 actions we must expect in general to find selective adsorption 

 or condensation of certain of the reactants or resultants upon 

 the surface of any solid or liquid material present even in 

 the case in which the solid or liquid material is itself taking 

 part in the reaction, i.e. the surface of the sulphur or selenium. 

 Owing to the specific nature of adsorption certain substances 

 are adsorbed to a greater extent than others, and as a result 

 of this the surface of the reacting solid or liquid may be so 

 completely covered that the solid or liquid can take part no 

 longer in the reaction, and hence the reaction is brought to 

 a standstill prematurely, i.e. before a true equilibrium point 

 has been attained. This view is a great deal more definite 

 and clear than any based upon the rather hypothetical viscous 

 or frictional forces referred to above. Obviously the " poi- 

 soning " effect of adsorption, as far as the solid or liquid is 

 concerned, will be relatively greater the smaller the total 

 amount of solid or liquid present. As Bodenstein's experi- 

 ments have shown, the selenium acts as a catalyst for the re- 

 action in which it itself participates, and it is reasonable to 

 expect that sulphur acts in a similar manner. If the hydrogen 

 sulphide or hydrogen selenide, produced as a result of the re- 

 action, is very strongly adsorbed upon the sulphur or selenium, 

 as Bancroft supposes, a phenomenon quite analogous to false 

 equilibrium is to be anticipated, for the hydrogen sulphide or 

 selenide will thereby " poison " the condensed reactant and 

 prevent the reaction occurring further. As Bancroft says : 

 I It is possible though not proved, that the discrepancy be- 

 tween Pelabon's and Bodenstein's results is due to Bodenstein 

 having used relatively more sulphur and more selenium than 

 Pelabon did, just as was claimed by Duhem. With varying 

 amounts of catalytic agent to be ' poisoned ' one may get all 

 possible false equilibria between the limit of no reaction and 

 the limit of reversible equilibrium. The theory of false equili- 

 brium outlined is in harmony with all our thermodynamical 

 relations." Analogous effects to those mentioned above have 

 been observed in reactions which involve enzymes (hetero- 

 geneous reactions). The whole question of false equilibria 



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