ON ELECTROLYSIS IN ITS PHYSICAL ‘AND CHEMICAL BEARINGS. 139 
2. It is best to render the space above the liquid free of air. For this purpose the 
apparatus shown in Fig. 1 was used. It consisted of a glass vessel in which two 
_ platinum wires, B and C, were sealed, B being plated electrolytically with the metal 
to be separated from the solution. The latter was introduced to the level p’ n’ and 
boiled for about ten minutes, until its surface had sunk 4 or 5 mm. below the point 
of the wire Cc. While the vapour was still escaping the vessel was closed at F with 
shellac ; and, after cooling, the neck was melted off at A. The apparatus then 
appeared sufficiently free from air. 
In order to reduce the vapour-pressure, the lower part of the vessel was placed in 
ice, the upper part being freed by warming from any liquid that still clung to it. 
A battery of 1,000 Planté accumulators was then connected, the positive pole 
with B, the negative with c; upon which there appeared at c the well-known nega- 
tive glow. 
3. When the vessel contained nitrate of silver the following was observed: Soon 
after putting on the current a small round disc of bright silver was formed just 
underneath c. As the disc increased in diameter it darkened at the centre, and there 
was formed upon it a series of light and dark concentric rings, which were sometimes 
- coloured—some of these showing radial markings, which gave them the appearance 
of divided circles. The disc did not sink, provided the apparatus was kept from 
shaking. é 
4, With a solution of zinc sulphate there was no separation of metal to be seen ; 
but on looking at the surface D B from below, white Hocculent masses of zinc oxide 
were visible slowly sinking through the liquid. The zinc on separation by the current 
_ was thus immediately oxidised. 
5. For experiments with asolution of platinum chloride the apparatus in Fig. 2 
was used. In this the chlorine was collected over B. 
Fie. 1. Fie, 2. FIG. 3. 
+ 
One-third natural size. One-third natural size. One-third natural size. 
A short time after closing the circuit there was visible just opposite c a small 
lump of dead black platinum. On stopping the current this floated to the side of 
he vessel, but returned to its original position just opposite c when the current was 
in started, thus preventing the formation of a fresh lump. Very probably this 
enomenon was due to electric forces. 
__ 6. These experiments may also be carried out in air by means of an induction 
coil. The liquid is contained in a funnel, as in Fig. 3, and the discharge at ‘ break’ 
furnishes the necessary current, the spark gaps between the solution and the cathode 
being arranged to prevent a discharge at ‘make’ from taking place. In this manner 
experiments with silver, zinc, and copper solutions were carried out, with results. 
substantially the same as those described above, except that here the space flowed 
through by the current, and consequently the diameter of the silver disc was 
