ioo OPTICAL PROJECTION 



gases (see same chapter). On tlio other hand, the hydrogen 

 bye-pass, when used for ether vapour, must be more free than 

 usual, and if it is a groove round the plug, as in many, this 

 may have to be filed deeper. I have seen it stated that a 

 dissolver cannot be used, but there is no difficulty if properly 

 adjusted. 



54. Cxy-Carbon Light. Mr. Albert Scott recommends 

 the use in a similar manner of benzoline, used in a porous 

 saturator which is heated by a lamp to promote volatilisation. 

 This fluid, like rhigoline or petroleum ether, belongs to the 

 paraffin series, whose formula is C n H 2n+ 2- ^ r - Scott claims 

 for this modification that a larger nipple can be used, and that 

 a better light can be obtained than with mixed gases ; also that 

 by passing even coal-gas through the fluid before burning at 

 the jet, so as to ' enrich ' the gas with hydro-carbon vapour, 

 using the mixed gases otherwise as usual, a considerable gain 

 in light is obtained, concentrated in a smaller spot. This 

 would be a very valuable gain for microscopic work, and I 

 felt much interest in the question ; but after careful trial 

 together, both Mr. Herbert Newton and myself came to the 

 conclusion that not the slightest advantage could be observed. 

 When experimenting with the oxygen passed through warmed 

 benzoline, we experienced sharp though small explosions, 

 and Mr. Scott himself writes rather flippantly of what he 

 calls ' pops.' I agree with him that these ' pops ' are of no 

 real danger with his form of generator ; but certainly no 

 audience would tolerate them, or be free from panic if they 

 occurred; and it is manifest that the need of Jieat to get 

 sufficient vapour to form a non-explosive compound, is an 

 additional item of risk about this method. I suggested to 

 Mr. Scott the use of gasoline, which is a more volatile mixture 

 than benzoline, of the same series ; and this was adopted 

 with benefit ; but I should prefer to use rhigoline' a more 

 volatile fluid still, and needing no heat, as is done by Mr. Ives. 

 I also suggested the use of benzol or benzene, as richer in 



