630 HEATING EFFECTS OF THE DISCHARGE. 



added to the powder in the mortar, and intimately mixed by con- 

 stant stirring with the soft tip of the finger. The hard pestle must 

 on no acconnt be nsed for this operation, as combustion might 

 take place and the hand be severely burnt. 



The cavity is filled loosely with the mixture up to 2 or 3 mm above 

 the wires. The cavity must not be closed by a plug, or the block 

 will burst. The burning mass shoots upwards as a vivid jet of 

 fire ; the discharge should therefore be made with the outstretched 

 arms, lest anything should fly into the face of the experimenter. 

 After the experiment, the cavity should be well scraped with an 

 old knife to remove any residue of the combustible mass. 



Of liquids, ether is most easily ignited by the 

 electric discharge; it evaporates as quickly and is as in- 

 flammable as disulphide of carbon, 

 but has not the unpleasant smell of 

 the latter. The handle of the flat 

 vessel represented in fig. 328 is 

 clamped in the retort-stand; a 

 small chain is suspended by the 

 ring at the end of the handle, a 

 few drops of ether are poured into 

 the shallow dish, the free end of 

 the chain is placed in contact with 

 the outer coating, and the knob 

 quickly brought close to the raised 

 portion in the middle of the dish ; 

 a spark will pass, which is pretty 

 certain to set fire to the ether. 



The dish consists of a disc of thin sheet- 

 328 brass soldered to the lower side of a ring 



made of brass wire, 2* thick, which forms 



the side of the vessel and is continued into a handle. The elevation 

 in the middle of the vessel is made before the disc is soldered on ; the 

 disc is softened in the flame, laid upon a support of lead, a piece of 

 iron or brass, which has been filed round at one end, is placed in 

 the centre, and a depression is made by a very moderate blow of the 



