108 Dr. W. J. Russell. On the Action exerted by certain 



occurs on starting the experiment ; but on standing for some length 

 of time, two or three days, the water begins to rise, and after 

 a week or more it will stand at a height of four or more inches 

 above the level in tho vessel, and there it remains at least for a 

 month or more. With the thick gelatin there is no evidence of any 

 diffusion occurring. Celluloid acts much in the same way as the 

 thin gelatin, a column of water gradually rises and remains there. 

 The action of the guttapercha tissue is to absorb the hydrogen ; the 

 diffusion tube completely fills up with water and remains full without 

 showing any tendency to fall for a couple of months, and then the 

 experiment was stopped. With tracing paper diffusion occurs in 

 the ordinary manner, and the same happened in the single experi- 

 ment tried with gold-beater's skin. That the rise of the water 

 in the diffusion tubes is not owing to a mere absorption of the 

 hydrogen by the gelatin or guttapercha has been proved by placing 

 a considerable quantity of these bodies in a tube sealed up at one 

 end, filled with hydrogen and inverted over water ; after several 

 weeks no rise of the water in the tube occurred. The above experi- 

 ments have been repeated with the same results, but further trials 

 are being made. Possibly the metallic vapour is in a still finer 

 molecular state than ordinary hydrogen, and thus is able easily to 

 permeate a medium which hydrogen can only slowly get through, 

 and air cannot get through. At all events, this may be looked upon 

 for the moment as a working hypothesis. 



That the action of the metals like that of the organic bodies is 

 due to a vapour can be demonstrated by experiments exactly similar 

 to those already described. For instance, it' the thin mica plates be 

 arranged above a zinc plate, in the way already mentioned, so as to 

 cut off all direct action between the zinc and sensitive plate, a ring 

 of action is produced which can only be accounted for by supposing 

 a vapour present, which has worked its way between the sheets of 

 mica and thus gained access to the photographic plate. Again, a 

 piece of Bristol board can be made active by contact with, or mere 

 proximity to, a piece of polished zinc. A striking instance of this 

 arose in the following way : a piece of perforated zinc had lain 

 on the bottom of an ordinary plate box for a considerable length of 

 time, probably about two months ; the zinc was then taken away, 

 and a sensitive plate dropped into its place. On developing this 

 plate, a picture of the perforated zinc was obtained. Other experi- 

 ments of a similar kind have been made. If the Bristol board be 

 not in direct contact with the zinc ; if a screen, with holes cut out in 

 it, be interposed, it will be found that the Bristol board where 

 exposed to the direct action of the zinc will become active, and will 

 give an exact picture of the holes or whatever design it may be 

 which has been cut out on the screen. To produce this effect the 



