154 THE ART OF PROJECTING. 



slightly acidulated by the addition of a little sulphuric 

 acid. The terminals of the wires in the water are 

 usually made of strips of platinum to prevent other 

 chemical reactions from taking place. For projection, 

 an excellent way is to insert two test-tubes filled with 

 the acidulated water, and introduce them into the tank 

 already described, having previously fixed the two 

 platinum terminals through the rubber bottom as 



Fig. 111. 



shown in Fig. in. When the current is sent through 

 these wires the bubbles will rise rapidly and soon fill 

 the hydrogen tube. This tank is of course to be pro- 

 jected in the ordinary way, either with lantern or porte 

 lumiere, in which case the bubbles will appear very 

 large and the water will appear to be in great commo- 

 tion. 



In place of water fill the tank with a solution of 

 acetate of lead, and without the test-tubes project the 

 tank and make connection with the battery of two or 

 three cells as before : the crystallization of the lead will 

 at once begin and rapidly grow upon one of the termi- 

 nals ; reverse the current, and the formed crystals will 



