HEATING EFFECTS OF THE DISCHARGE. 631 



hammer. It will be more easy to solder the ring to the disc if the 

 latter is first cut square ; it may then be conveniently heated by 

 beino- held at one corner with the flat pliers. When the ring is 

 fixed on, the projecting portions of the disc may be removed with 

 the shears and the file. 



The small elevation in the middle is necessary in order to assign 

 a definite path along which the spark has to pass ; otherwise the 

 spark spreads itself in a radiating manner over the surface of 

 the liquid, and its heating effect is then obviously less than when 

 it forms a single straight line. If the vessel were deep it would be 

 very difficult to ignite the ether. The reason is that the vapour 

 of ether formed at the temperature of the room is heavier than air, 

 as may be proved by holding the dish, filled with ether, against 

 the light of the window, and looking along the sides of the vessel, 

 when the heavy vapour of ether will be seen to flow downwards 

 over the sides. A deeper vessel, in which there is some ether, is 

 thus quickly filled with its vapour, which forms a layer above 

 the liquid, and when the knob is brought close to the liquid the 

 spark passes entirely within the vapour of ether, where there is no 

 air ; hence no combustion can take place, since the free access of 

 the oxygen of the air is an absolute necessity for combustion. 



The ether is poured into the dish after the jar is charged, or the 

 liquid would all evaporate while the jar is being charged, especially 

 if this is done with the electrophorus. If an electrical machine is. 

 used, the jar is really not required for this experiment ; the vessel 

 is placed near the conductor, a chain is hung to the ring which 

 reaches to the ground, one knob of the discharger is placed upon 

 the conductor of the machine, and the other knob is held 1 or l cm> 5 

 above the elevation in the middle of the dish. 



Ether cannot be preserved under 'water like carbon disulphido ; 

 it is lighter than water, and mixes with it gradually when in contact 

 with it. It should be preserved in a glass bottle closed with a well- 

 fitting soft cork, and the bottle should always be closed and 

 placed aside before the quantity in the dish is inflamed. If a little 

 of the burning ether should flow over the edge of the vessel and 

 upon the retort-stand, it may be blown out by a vigorous blow or 

 rather a strong puff, provided that not too much ether has been 

 unnecessarily used. 



Combustible gases may be ignited even by a weak 

 electric spark. A jet of illuminating gas issuing from 

 a Bunsen burner may very frequently be inflamed by 



