Blake — Behavior of Bed Colloidal Gold Solutions. 436 



affairs never changes in the arm of the U-tube carrying the 

 cathode. But the gold particles at first concentrated around 

 the anode by the action of the current give up their negative 

 charge to that pole, and, being for some reason unable to 

 remain in contact with it (except to a slight extent in the for- 

 mation of the dark-colored slime), depart laden with a positive 

 charge. Hence the surface of demarcation at first formed 

 above the asbestos plug soon settles back to its original posi- 

 tion, causing the plug to become positively charged, which 

 then acts as the anode to the particles below it. The posi- 

 tively charged particles repelled from the lower end of the 

 asbestos plug, or from the anode if no ping is present, meet- 

 ing the negatively charged particles from the cathode, form 

 some sort of a union, possibly by mutual attraction without 

 disruption of the water envelopes with which they are sur- 

 rounded, thus producing the red cloud at the bend of the U- 

 tube. The fact that the gold in this cloud was ultimately car- 

 ried into the asbestos plug in the one experiment continued for 

 a week shows that the positively charged particles present in 

 the cloud must slowly lose their charge ; and both that fact 

 and the fact that diffusion restores the original conditions* 

 indicate that the union of positively and negatively charged 

 particles in the red cloud is very feeble. The fact that the 

 gold above the plug does not settle, on the other hand, is a 

 further indication that some kind of aggregation of oppositely 

 charged particles must take place to form the red cloud in the 

 bend of the U-tube. 



The formation of the red cloud midway between the elec- 

 trodes in these experiments closely resembles the formation of 

 a precipitate similarly situated observed by Lehmannf in his 

 study of suspensions made viscous by gelatine. A dark- col- 

 ored corona gradually extended from the anode • and a light- 

 colored corona from the cathode. Midway between the elec- 

 trodes the coronas met with the formation of a precipitate and 

 the liberation of heat. So, also, the reverse or " secondary 

 movement " noticed by Hardy:}: in the case of egg-albnmen, as 

 well as the reverse movement of haemoglobin noticed by 

 Gamgee,§ must be closely similar in their nature to the back- 

 ward movement of the gold here described. 



II. Behavior toward Electrolytes. 

 Bodlanderii and Spring*|f have each insisted that in studying 

 the action of electrolytes on pei'manent suspensions it is neces- 

 sary to distinguish two phenomena : (1) Coagulation ; (2) Pre- 



* Cf. post, p. 441. t Wied. Ann., lii, 455. 



:}:Loc, cit. gProc. Eoy. Soc, Ixx, 79. 



II Neues Jahrb. f. Mineral., ii, 156. ^Loc. cit. 



