THE BOOK OF THE LANTERN. 



is shown at fig. 29. A is the loose nut by which it is 

 attached to the gas-bottle ; B, the 

 valve proper, which is governed 

 by the spring lever D. The 

 tendency of this spring is to keep 

 the bag shut, and when in that 

 position the tap is open. The 

 gas pressure, however, quickly 

 inflates the bag, and turns off the 

 gas supply. The delivery pipe, 

 E, is connected with the lantern. 

 The. apparatus is small and com- 

 pact, and works well. 



It may be noted here, that there is a distinct gain in 

 using pure hydrogen, instead of the carbureted gas 

 from the main, although its employment undoubtedly 

 leads to extra trouble and ex- 

 pense. The most convenient 

 way of making this gas in small 

 quantities is by treating scrap 

 zinc with dilute acid. A con- 

 venient apparatus is that shown 

 in the diagram, fig. 30. It was 

 devised some years ago by Mr. 

 Pumphrey, and published in one 

 of the Photographic Annuals. 

 It consists of a copper container, 

 in which is an inverted box with 

 a delivery tube and tap attached 

 to it for drawing off the gas as 

 it is generated. This inner box 



Fig. 30. 



