HEATING EFFECTS OF THE DISCHARGE, 629 



l mm apart. The outer ends of the wires are bent into 

 rings. The cavity being filled with the mixture, one 

 end of a small chain is sus- 

 pended to the left ring and 

 the other end is held in con- 

 tact with the outer coating 

 of the jar, the knob of which 



FIG. 327 (i real size). 



is rapidly brought near to 



the ring on the right-hand side. At the instant when 

 the spark passes between the ring and the knob, and 

 between the two wire points in the mixture, the latter is 

 ignited, the combustion taking place with almost as 

 great rapidity as that of gunpowder. 



Into a small block of wood, 5 cm long and wide and 4 cm high, a 

 hole is bored 2 cm deep with a centre-bit 12 mm wide ; 15 mm below 

 the top of the block a hole is bored horizontally right throngh the 

 block with a fine gimlet. Wires of the form shown in the figure, 

 and stout enough to fit tight into the holes and to sit firmly, are 

 pushed in from either side. The ends of the wires are previously 

 filed round. 



The easy inflammability of the mixture depends entirely on the 

 fact that both ingredients have been reduced to a very fine powder, 

 and on account of its being so inflammable not more of it should 

 be prepared than is required each time ; for two experiments, 2 

 grammes of each substance is sufficient. Potassic chlorate is a white 

 salt, sold in the form of flat crystals or a rough powder; it is not 

 inflammable by itself, but mixed with other inflammable substances 

 it is apt to cause dangerous combustions and explosions ; it should 

 therefore be kept in a stoppered glass bottle to keep out impurities 

 such as dust, splinters of wood, etc. The quantity required is weighed 

 out and ground in a very clean porcelain mortar until it feels like 

 fine flour, not in the least gritty. The powder is then in the mean- 

 time placed on a piece of paper, and the mortar and pestle care- 

 fully cleaned and dried. The sulphide of antimony is a native ore of 

 antimony. It is sold as a dark grey crystalline powder (called crude 

 antimony), but not sufficiently fine for our purpose ; it should 

 therefore also be rubbed down in a mortar until it is like fine flour, 

 and no longer shows lustrous points. The polassic chlorate is now 



