572 Dr. George Senter. The~Role of Diffusion in the [Mar. 7, 



in motion may not be so readily detected as stationary particles,* yet 

 the uncertainty from this cause would be least in the case of large 

 particles, so that it seems very improbable that particles of the 

 diameter //. could escape detection under the above conditions. 



Zsigrnondy and Siedentopf f have investigated the magnitude of the 

 particles in colloidal solutions of gold prepared by reduction ; they find 

 many particles of the diameter 1/100//, and others still smaller. Stockl 

 and VaninoJ have independently arrived at the same result. So far as 

 I am aware, colloidal solutions, prepared by Bredig's method, have not 

 been examined by Zsigmondy and Siedentopf's method, but it does not 

 seem probable that such solutions would differ markedly, as regards the 

 magnitude of the particles, from those prepared by reduction. 



It may, therefore, be concluded that the want of agreement between 

 K D and K cannot be accounted for by too low a value having been 

 taken for the magnitude of the particles. 



(3) Tlie suggested inactivity of part of the platinum surface towards hydrogen 

 peroxide. Equation (7) has been derived on the assumption that all 

 the particles are active towards hydrogen peroxide. If only some of the 

 particles are thus active, the total reacting surface, which is proportional 

 to v for equal particles, would be diminished, and thus K D would attain 

 a value more nearly coresponding to K. (It should also be noted that 

 v and consequently K D would be diminished by the process discussed 

 under the third heading in the section on convection, p. 570, but this 

 effect would, in any case, be small and would completely disappear for 

 solutions in which oxygen is not evolved in bubbles, so that we cannot 

 account in this way for the difference between K D and K). Nernst has 

 already suggested the possibility that part of the platinum is inactive, 

 and some positive evidence to this effect is to be found in papers by 

 Bredig and Fortner|| and by Liebermann.H The first two investigators 

 found that the palladium catalysis of hydrogen peroxide is greatly 

 accelerated by previous treatment of the palladium with hydrogen, and 

 the same is true, though to a much smaller extent, of the platinum 

 catalysis. The latter result has been confirmed by Liebermann. 

 Bredig** has also found that platinum which has been poisoned with CO 

 is more active after recovery from the poison than platinum which has 

 not been so treated. 



* The limit of visibility under the microscope will probably depend upon the 

 number of the particles present in a given volume, as well as on the nature and 

 magnitude of their motion. 



t ' Zeit. fur Elektrochemie,' vol. 8, p. 686, 1902. 



J ' Zeit. fur physikal. Chemie,' vol. 30, p. 99, 1899. Compare also Lobry de 

 Bruyn, ' Keceuil Travaux Chim. Pays-bas,' vol. 19, p. 251, 1900. 



Loo. tit., p. 55. 



11 'Berichte d. deut. chem. Ges.,' vol. 37, p. 805, 1904. 



IT ' Berichte d. deut. chem. Ges.,' vol. 37, p. 1519, 1904. 



** ' Anorg. Fermente,' p. 79. 



