Mercury Films hy an Electrical Process. 75 



In this way I have deposited mercury-films upon such 

 different substances as filter-paper, plaster-of-paris, Wood- 

 bury-type-gelatine, porous earthenware, asbestos-paper, and 

 sheep's skin. As a rule, the only preparation of the sub- 

 stances is damping with distilled water. Asbestos mill-board 

 is one of the best materials to operate upon. 



The coating of mercury formed by this electrical process is 

 far more perfect than any I have been able to obfain by the 

 methods of " pickling " or contact-pressure. I have no defi- 

 nite views as to the cause of the phenomenon, but I am 

 inclined to regard it as a secondary action, the result of elec- 

 trolysis, aided to some degree by electric osmosis. The 

 experiments of Mr. 0. K. Falkenstein* upon the electric 

 tanning of leather are evidence in favour of the osmosis 

 theory. I understand also that electric osmosis has lately 

 been used for administering cocaine, replacing the ordinary 

 hypodermic injections. 



It will be remembered that in some experiments | I recently 

 described to the Physical Society a globule of mercury, elec- 

 trified in a partially conducting liquid, sent forth a tentacle 

 in a direction towards the positive electrode. It is perhaps 

 significant that in the present experiments the film is always 

 on the positive surface. In the case of liquid "coherers" it 

 is possible to conceive that, under the influence of steady or 

 transitory currents, mobile conductors attempt to creep in 

 this fashion through the dielectric films. And, again, though 

 the effect is probably very slight and entirely masked by 

 electrolytic disturbances, sea-water may thus penetrate the 

 dielectric at a "fault'" in a cable. The film-forming process 

 may be of practical utility where large surfaces are required 

 to be coated with mercury, as in gold extraction ; and pos- 

 sibly in the preparation of plates for primary or secondary 

 batteries. 



The following experiments are given in illustration of the 

 action : — 



(1) A sheet of filter-paper, damped with distilled water, is 

 folded upon itself four or five times. It is then laid flat upon 

 a conducting surface. An indiarubber ring is pressed down 

 on the folded paper, and mercury is poured in to fill the ring. 

 A battery of 200 volts is then connected for about three 

 minutes between the mercury and the lower conducting plate, 

 the mercury being positive. After stopping the current the 

 ring is removed from the filter-paper and superfluous mer- 



* Journ. Inst. Elec. Engineers, vol. xxii. p. 225 (1893). 



t "Liquid Coherers and Mobile Conductors," Phil. Mag. May 1897. 



