THE BOOK OF THE LANTERN. 85 



with a handle at the middle and a stop-cock projecting up- 

 ward at each end. A neck, like that of a bottle, projects 

 from the screw cap at the end, and is closed with a cork 

 for convenience in filling. The passage for oxygen is over 

 20 inches long, in the form of a zig-zag channel through 

 the upper surface of the roll of porous material, and 

 secures complete saturation of the gas with vapour. The 

 saturator can be filled from a bottle in one minute, and is 

 ready for use at once, or may be kept filled for any length 

 of time. Petroleum ether costs only thirty cents a pound, 

 which is less than half the price of sulphuric ether ; it also 

 vaporises at a lower temperature, so that the light can be 

 used successfully even in a very cold room, and it has 

 other advantages. It will supply a pair of lanterns con- 

 nected by dissolving key, for two hours continuously. It 

 should be stored in a cool place and kept tightly corked. 

 It is also necessary, when using it with oxygen from a 

 cylinder, to use a valve that can be opened very slowly, 

 because a very small amount of oxygen passing the satu- 

 rator will produce a very large flame at the jet. The 

 Shaw valve, manufactured by Mr. Shaw, a member of this 

 Institute, fulfils the requirements, and is already largely 

 used in this city. Some special instruction for the manage- 

 ment of the light in hot weather may also be called for. 



" In conclusion, I give it as my opinion that this im- 

 proved means for supplying the hydrogen element is so 

 much simpler and more convenient than any other, that it 

 cannot fail to entirely supersede the use of hydrogen and 

 coal-gas, when its merits shall have become generally 

 known and appreciated." 



