236 SCIENCE PROGRESS 



The work of Beans and Eastlake/ on the preparation of 

 colloidal metals in pure water by sparking, tends to show 

 that they owe their stability to certain ions formed at the 

 same time. The presence of ionic complexes was deduced 

 from the conductivity of the resulting solutions. Beans and 

 Eastlake found, moreover, that stability in such solutions was 

 increased, in some cases, by addition of very small quantities 

 of electrolytes. These results also confirm the current hypo- 

 thesis that the charge upon the colloid particle is due to adsorp- 

 tion of ions. Hardy,* as long ago as 1899, had shown that 

 albumin in acid solution was positively, and in alkaline solu- 

 tion negatively, charged. Recently, Powis ' has demonstrated 

 that ferric hydroxide, which is usually obtained positively 

 charged (as, for instance, by the dialysis of ferric chloride solu- 

 tion in the presence of positively charged ferric ions), may be 

 obtained negatively charged by running ferric chloride solution 

 into an alkaline hydroxide solution. It seems . possible that 

 this may be due in part, if not entirely, to the great mobility 

 of the H" and OH' ions, which would lead to more numerous 

 encounters between the colloid particles and these ions than 

 any others. 



Brownian Movement. — The kinetic forces of the solvent 

 molecules, the effects of which are visible in the Brownian 

 movement, seem largely responsible for maintaining the dis- 

 persoid particles in suspension. Perrin's estimation of the 

 Avrogadro constant makes use of the Brownian movement 

 in suspensions of gamboge and mastic. By extending the 

 principle of the equipartition of energy, deduced from the 

 gaseous state, to solutions, and finally to colloidal solutions, 

 he concludes that ^ " we are led to render the theory precise 

 by saying, not only that each particle owes its movement to 

 the impacts of the molecules of the liquid, but, further, that 

 the energy maintained by the impacts is on the average equal 

 to that of any one of the molecules. ..." Bancroft^ con- 

 siders that, when the size of the colloid particles is such that 

 they are sensibly affected, this energy tends to cause stability. 

 " Any substance may be brought into colloidal solution, pro- 

 vided we make the particles of that phase so small that the 

 Brownian movement will keep the particles suspended, and 

 provided that we prevent coagulation by a suitable surface 

 film." This is also another argument in favour of the uni- 

 versality of the colloid state. There seems to be an opinion 



^ Jonrn. Amer. Chem. Soc, vol. xxxvii, p. 2667, I9I5- 



^ Jonrn. Physiol., vol. xxiv, p. 288, 1899. 



^ Journ. Chem. Soc, vol. cvii, p. 818, 1915. 



* Brownian Movement and Molecular Reality, trans. Soddy, 1910. 



^ Journ. Amer. Electrochem. Soc, vol. xxvii, p. 175, 1915- 



