344 POPULAR SCIENCE MONTHLY. 



as traces of tar are usually fuuiid in the residual lime, in some cases 

 in sufficient quantity to make the lime yellow and pasty, while vapors 

 of benzene and other polymerization products pass off with the gas. 

 Leaving the question of temperature in this type of generator, another 

 important question is the leng-th of time during which the generation 

 of gjis continues after the water supply is automatically cut off. It 

 is found that gas is evolved with increasing slowness sometimes for 

 an hour and three quarters after the water supply has ceased, the 

 total volume of gas so evolved being large. 



The experiments showed that in any automatic generator of this 

 type the cut-off should be so arranged that one quarter of the total 

 capacity of the gas holder is still available to store the slowly generat- 

 ing gas. 



The second class of generators bring about contact either by water 

 rising from below to the carbide suspended in the cage (II, A), or by 

 a cage of carbide suspended in a movable bell which, as it falls, dips 

 the carbide into water, withdrawing the carbide from the water as the 

 excessive generation of gas lifts the bell (II, B). Lewes found that 

 under certain conditions generators of the type II, B were far worse 

 than those of type I. 



The trials were made with a movable glass bell, with counter- 

 weights, containing a half-pound of carbide. The maximum temper- 

 atures reached in four trials were 

 703°, 734°, 754°, and 807° C. 

 Excessive heating took place in 

 every case; in the last mentioned 

 the temperature was far above the 

 ■]"1"r?'i";"*r'~i^;""'Ti'' I point at which acetylene is decom- 

 "^ ^ ■ posed into carbon and hydrogen, a 



thin black smoke being formed 

 immediately around the carbide 

 while tar vapor poured out. On 

 removing tlie residue aiter coo lino- 



Tyi"K of Generator. . c ^ ^ ^ i • i 



it was lound to be coated with soot 

 and loach'd with tar. On several occasions the charge was removed 

 from the generator just after the maximum temperature was 

 reached, and was found to be at a bright red heat. 



These experiments are of the greatest practical importance. At 

 600° acetylene begins to polymerize — i. e., to form more complex 

 hydrocarbons, which are liquid, or solid, at ordinary temperatures. 

 Probably in the generator acetylene is first given off so rapidly that 

 the heat does not act on it, but as decomposition advances into the 



NoTK. — We are in(leV)tf(l to the courtesy of tlic !'rof;re?sive Age for cuts sho\viii<: types 

 of geiierntori'. 



GAS 



