192 THE BOOK OF THE LANTERN. 



descend and immediately break out into a number of 

 branches. These branches will on the screen appear to rise 

 rapidly upwards after the manner of a number of coloured 

 rockets, and by varying the colours of the dyes and putting 

 one or two drops into the tank simultaneously, a most lovely 

 effect on the screen is obtained. 



The decomposition of water is another experiment which 

 has a most curious effect. For this experiment a small electric 

 battery is necessary, and the most convenient form to use is 

 a single bichromate cell, say of one pint capacity. This can 

 be hidden away in a box beneath the lantern, and as it 

 gives off no fumes, there is nothing disagreeable in its use ; 

 moreover its action, if freshly charged, is energetic, and this 

 action can be stopped when required by lifting the zinc 

 plate from the solution in which it is immersed. The wires 

 from the poles of the battery must be long enough to reach 

 the lantern stage ; the slide for this experiment being simple 

 in the extreme. The tank to be used shyuld be of rectangular 

 form, and as a matter of convenience, it should be furnished 

 with two binding screws on one of its outer sides, so that 

 the wires from the battery can be readily connected with 

 them. These screws should be in connection with two 

 gutta-percha covered wires, which proceed to the bottom of 

 the tank, where their ends are bare and turned upwards for 

 about a quarter of an inch. These ends may be so fixed 

 that they are about half an inch apart. The tank is pre- 

 viously filled with diluted sulphuric acid (one part of acid 

 to eight of water), and is then ready for action. Directly 

 connection is made -with the battery, the two wires will 

 rapidly give off bubbles of gas, one being hydrogen and 



