80 



and boiled rapidly at 189°. None of these naphthas have a 

 fixed boiling-point. In all cases the heaviest and most vola- 

 tile portions come over first in distillation, and are the most 

 valuable for the purposes here described. No dependence 

 is to be placed on high specific gravity as a test of fitness : 

 the naphtha may be heavy on account of the presence of tar 

 and naphthaline, and in this state it will not answer the pur- 

 pose. When the naphtha is colourless, heavy, and vaporiza- 

 ble from a flat open vessel, without leaving any residuum or 

 stain, it is of the best quality. 



" During the destructive distillation of common resin, a 

 naphtha is obtained which, by proper rectification, becomes 

 as pale as water, and succeeds admirably for the purposes 

 here described. Indian rubber affords a naphtha of s. g. 0-820, 

 or even 0-680 ; in which last state it boils at 98°, and answers 

 perfectly. 



" The ratio of hydro-carbon necessary for rendering a cer- 

 tain quantity of water gas luminous in burning, will depend on 

 the nature of the former. On this subject I made many ex- 

 periments. In one of them I found that two equal burners, 

 one supplied from a gasometer containing coal gas, the other 

 from a gasometer containing water gas, which was naphtha- 

 lized with Newcastle coal tar naphtha before it reached the 

 burner, afforded flames which in equal times emitted equal 

 light when the naphtha was consumed at the rate of one im- 

 perial gallon dissolved in 1000 cubic feet of water gas. It 

 was also found that the consumption of coal gas was the same 

 as that of water gas in equal times, the latter having the addi- 

 tion already mentioned ; and although the light in each case 

 was equal, as evidenced by Rumford's photometer, the water 

 gas flame was but half the volume of that from coal gas ; 

 and therefore the intensity or illuminating power of the for- 

 mer was double. This comparison only holds when the rate 

 of consumption is five cubic feet per hour ; when less, the 

 light from a naphthalized water gas flame is more than double 



