

to the Contact of Gases with Liquids. 73 



If such an enclosure of electrified air as I suggest were to 

 occur at a high temperature in the upper regions of the atmo- 

 sphere, its potential would gradually rise as it cooled and 

 descended towards the earth ; for the cooling of the mass of 

 air, and the increase of pressure due to its less elevated 

 position, would cooperate to lessen its volume, and, therefore, 

 the surface of the enclosing film, while the quantity of elec- 

 tricity would remain the same. 



Up to this stage I had used glass vessels in these experi- 

 ments, but according to the view just set forth there could be 

 no reason why a metallic vessel should not behave in precisely 

 the same way. A tea-canister was accordingly filled with 

 hydrogen by displacement of water from a generator con- 

 taining zinc and hydrochloric acid. It was then placed on the 

 insulated plate, mouth upwards, and it was found that as the 

 hydrogen escaped into the air the spot moved to the left, as 

 had been expected ; and it was found on trial that everything 

 that had been done with the glass flask could be done with 

 one of metal. We have thus a condenser with only one con- 

 ductor, and apparently without a dielectric ; and, from the 

 ease with which it can be charged, and most of the properties 

 of condensers demonstrated by means of it, one which may 

 turn out useful for teaching-purposes. 



A metallic flask filled with hydrogen by displacement of 

 water from a generator containing Zn + HC1 I found very 

 instructive. It proved that hydrogen holds its charge with 

 unexampled tenacity, for the vessel could be handled or left 

 in communication with the earth for a considerable time 

 without becoming neutral. It proved that spray or vapour of 

 hydrochloric acid had nothing whatever to do with producing 

 the electrification, for these were absorbed by the water over 

 which the gas was collected. It also suggested a possible 

 means of measuring the difference of potential due to the con- 

 tact of hydrogen with hydrochloric acid. After a few trials, 

 however, I gave it up, and decided to determine the quantity 

 by Sir W. Thomson's " Water-dropper." 



A metal funnel with a long stem was fixed to the insulated 

 plate, which was as usual connected to insulated quadrants. 

 The funnel was filled with water, and a series of drops fell 

 from the nozzle of the stem. The drops broke away at a 

 distance of 6 or 7 inches from the body of the funnel. An 

 uninsulated dish 3 inches in diameter, containing Zn -f HC1, 

 was placed under the nozzle, so that the drops fell into it. 

 As the hydrogen passed into the air, enveloping tho nozzle 

 and falling drops, the spot moved rapidly up the scale to right 

 and off it. I withdrew some of the charge from the needle, 



