APPENDIX 



421 



It is claimed for the first pattern that the gas evolved is cooler 

 than when the water is admitted to the carbide. There does 

 appear to be some advantage in this respect, but the admission of 

 carbide, which is usually in small lumps, is difficult to control, and 

 on the whole the plan of gradually admitting water to the carbide 

 is now generally followed. 



A typical lantern generator is shown above (fig. 235). As will 

 be seen, it acts on the gasometer principle, the gas as it is evolved 

 passing into the upper bell which floats and thereby lifts the 

 carbide out of the water ; as soon as a little gas is used, the bell 

 sinks and a little more water is admitted, the whole arrangement 

 being purely automatic and requiring no attention whatever after it 

 is once started a point of 

 no little importance when 

 one has to lecture as well 

 as to manage the lantern. 



A lantern fitted with 

 an acetylene generator in 

 this way is, of course, not 

 quite so portable as with 

 oil, as the generator is usu- 

 ally as large as the lantern 

 itself; but in the opinion 

 of most operators this is 

 more than made up for by 

 the increased brilliance of 

 the light. 



A four-burner acetylene jet, as fig. 236, will well illuminate 

 a disc 12 to 14 feet in diameter. 



Saturators. The great extension of lantern demonstrations or 

 entertainments during the last ten years has greatly developed the 

 use of ether -saturators, which have gradually assumed more con- 

 venient and safer forms than either of those described in 

 Chapter VII. As anticipated on p. 101, the use of vapour from the 

 petroleum series of oils, aided by heat, has now been entirely dis- 

 continued. Only petroleum ether or sulphuric ether, which require 

 no heat, are now employed. Tanks have been discontinued, and 

 some form of porous generator has become universal. 



Safety has been gained in two ways : (1) by entirely filling the 

 cavities of the generator with porous material, so that no free space 



FIG. 236. Four-burner Acetylene Jet 



