G32 HEATING EFFECTS' OF THE DISCHARGE. 



bringing the charged cover of the electrophorus near to 

 it, especially if the burner be held horizontally or 

 nearly so. To render the ignition of a gas by a 

 weak spark more certain, the small contrivance re- 

 presented in fig. 329 may be used. It consists of a 

 cork which carries a jet-tube and two insulated wires, 

 between which the spark passes. The cork is clamped 

 in the retort-stand, the jet-tube being connected by an 

 india-rubber tube with a gaspipe or the generating 

 apparatus for hydrogen. By means of a pinchcock 

 placed upon the india-rubber tube the quantity of gas 

 which issues is so regulated that the flame is not- 

 larger than indicated in the figure. Placing one hand 

 on the ring of the left wire, and bringing the charged 

 cover of the electrophorus near to the ring on the right, 

 the gas is inflamed each time with certainty. 



The upper ends of the two wires are at first left quite straight. 

 The wires are heated about the middle until sealing- wax melts upon 

 them, and then surrounded by a cylinder of sealing-wax of about 

 the thickness of a pencil. When cold they are pushed into holes 

 suitably bored in the cork, and are bent above into the required 

 shape, and then the jet-tube is set in its place ; the opening at the 

 point of the jet-tube should be from 0*5 to l mm wide. Wires and 

 tube must fit tight in their holes so as t6 remain firmly fixed. The 

 distance between the ends of the wires, which should be filed round, 

 is 3 mm ; their height above the end of the jet-tube l lum '5. When 

 hydrogen is used its purity must first be examined in the manner 

 explained on page 380 before lighting it by the electric spark. 



That even good conductors are heated by the electric 

 discharge may be shown by the apparatus fig. 330. A 

 small wide-necked glass bottle is closed by a cork, 

 through, which two wires pass and also a glass tube, 

 which is drawn to a point, about l mm - 5 wide, and benthori- 

 ; the wires .ar-e connected by a long, very narrow 



