PHYSICAL CHEMISTRY 541 



/ton. — ^An interesting contribution to this subject has been made 

 by Burton and Bishop (Proc. Roy. Soc, 1921, A 100, 414), who 

 have shown that the equation derived by Perrin for the distribu- 

 tion of gamboge particles under the action of gravity, 



RX ft 



"N" ^^^ « " ^^^1 ~ ^«^^^^ " ^'^' 



does not hold for colloidal solutions of copper, where the par- 

 ticles are much smaller. They find that the colloidal particles 

 are uniformly distributed throughout a column of liquid 90 cm. 

 in height after standing for fifty days. From Perrin 's equation 

 it may be deduced that the ratio of the concentrations in such a 

 solution at any two levels i cm. apart would be given by the 

 equation — 



Log -^ = 5,000. 



The authors point out that this equation can only hold over 

 an extremely small depth of liquid, below which a uniform 

 distribution of the particles occurs. The concentration of 

 colloidal solutions of the metals rarely exceeds 10-20 mgrm. 

 per 100 cc. Attempts to increase the concentration of such col- 

 loidal solutions by slow evaporation causes settling of the metal. 



Two papers on the catalytic oxidation of carbon monoxide 

 at ordinary temperatures have appeared {J.A.C.S., 192 1, 43, 

 1973 and 1982), It is shown that mixtures of manganese 

 dioxide with other oxides are the best catalysts. The best 

 promoters appear to be the oxides of copper, cobalt, and silver. 

 For use in gas-masks it is, however, necessary to protect the 

 catalyst from moisture by means of anhydrous calcium chloride. 



Bone and Haward {Proc. Roy. Soc, 1921, [A] 100, 67) 

 have made accurate measurements of the rate of explosion of 

 mixtures of hydrogen and oxygen and carbon monoxide and 

 oxygen at high pressure. Striking differences between the 

 behaviour of the two gaseous explosives are observed. The 

 rise in pressure in the hydrogen and oxygen mixture is practi- 

 cally instantaneous, and the reaction is rapidly completed. On 

 the other hand, the explosion of carbon monoxide and oxygen 

 takes place more slowly, and the reaction continues after the 

 maximum pressure has been reached. The presence of i per 

 cent, of hydrogen in the carbon monoxide mixture, however, 

 catalyses the rate of explosion, giving an entirely different form 

 to the explosion curve. 



ORGANIC CHEMISTRY. By O. L. Brady. D.Sc, F.I.C, University 



College, London. 



Organo-metallic Compounds. — (i) Chromium. MendeMeff at 

 one time considered that it was unlikely that the metals of the 



