70 THE BOOK OF THE LANTERN. 



has a removable perforated shelf fitted to it, and the box 

 itself is so arranged that it can be wedged tightly in its 

 place. The shelf is to hold the necessary supply of 

 scrap zinc, and as . the acidulated water attacks the 

 metal, hydrogen is rapidly given off, until the water is 

 forced by the pressure of the gas below the shelf, and 

 the action ceases. It is again renewed when gas is 

 drawn off from the tap, for then the water again rises 

 to the zinc, and a fresh supply is generated. This 

 apparatus is clearly a modification of the Dobereiner 

 lamp, in which the gas generated in this manner impinges 

 upon and renders red-hot a -pellet of spongy platinum. 

 At a recent lantern exhibition at the Crystal Palace, where 

 a 30-foot screen was used, pure hydrogen from a bottle 

 fed the lime-light. On one occasion ordinary coal-gas was 

 substituted, with a loss of light which was estimated by 

 those well qualified to form a judgment, at no less than 

 25 per cent. 



