434 Blake — Behavior of Red Colloidal Gold Solutions, 



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poles, thus showing that the effect is not due to gravity. The 

 red cloud may at any time be readily diffused throughout 

 the liquid by gentle agitation or warming, and slowly diffuses 

 spontaneously when the current is broken. By withdrawing 

 the clear liquid and dissolving the red cloud in pure water a 

 purihed red colloidal gold solution may be obtained. 



This experiment becomes still more instructive if an asbes- 

 tos plug be placed in one arm of the U-tube, just below the 

 anode, as shown in the cut. If the plug is tight, the electrical 

 osmosis of the liquid carries the gold with it to some extent. 

 If the plug is loose, no movement of the liquid is observable 

 and the gold moves in obedience to the 

 current. 



When the plug is loose the gold moves 

 toward the anode as soon as contact is made, 

 settling from around the cathode in exactly 

 the same manner as in the former experi- 

 ment ; simultaneously a little gold is car- 

 ried into the lower part of the asbestos 

 plug below the anode, while that above the 

 plug rises a little way, leaving the- color- 

 less liquid clearly defined. By the end of 

 half an hour this latter surface of demarca- 

 tion settles back to the asbestos plug, and 

 thereafter for a long time (a week in one 

 experiment, with interruption of the cur- 

 rent over night) the o^old solution above 

 the plug remains unchanged, except that a dark-colored slime 

 in slight amount forms on the anode, as in the former experi- 

 ment. The gold below the asbestos plug not carried into it 

 during the first half hour gathers in a red cloud at the bend of 

 the IJ-tube as in the experiment wdiere no plug was used. In 

 the one experiment which was continued for a week, this red 

 cloud practically all disappeared, and the gold which it con- 

 tained was deposited in the lower end of the asbestos plug for 

 a distance of I''"', coloring the asbestos red. 



It was found that when the hydrochloric acid formed in the 

 reduction of the gold chloride was removed from the colloidal 

 gold solution by dialyzing the liquid until it became neutral to 

 litmus, the electrical movements of the gold were not notice- 

 ably different from those given above. Also, when a red col- 

 loidal gold solution was prepared without the presence of 

 ether, by the action of a dilute aqueous solution of gold chlor- 

 ide on acetylene water, the results were still the same. 



These various occurrences may, perhaps, be explained as 

 follows : All of the gold particles are originally negatively 

 electrified and hence start toward the anode. This state of 



