116 



CONTRIBUTIONS TO THE KNOWLEDGE 



The per centage amount of olefiant gas contained in the 

 Pelton gas and the gases marked B and C in the above table, 

 all of them coal gases, would lead us to infer that their illu- 

 minating power is much lower than is really the case, for 

 according to the experiments upon cannel gases, it appears 

 that when a consumption of 5 feet per hour produces a light 

 equal to 20 candles, the gas contains 13.12 per cent, of 

 olefiant gas, or its equivalent in richer hydrocarbons; and, 

 hence, we should expect that a gas containing only half this 

 amount would, when burnt at the same rate, produce a light 

 equal only to 10 candles, instead of 13, as is found to be the 

 case. This excess of illuminating power in the case of coal 

 gases over that indicated by analysis, is probably owing to 

 the presence of luminiferous constituents not condensible 

 either by fuming sulphuric acid, or by chlorine. The nature 

 of these constituents, and the cause why they cannot be 

 detected by our present methods of gas analysis, I have 

 already pointed out, (Journal of Chemical Society, vol. iii. 

 p. 42.) The following table exhibits this difference between 

 the value of olefiant gas in coal gas, compared with that in 

 cannel gas, and shows also, that in the case of the latter 

 the illuminating power is always directly proportional to the 

 amount of olefiant gas to which the per centage of condensible 

 hydrocarbons is equivalent. The establishment of this rule 

 with regard to gases having such different per centages of 

 light carburetted hydrogen as the Boghead gas, with and 

 without water gas, I hold to be conclusive evidence that light 

 carburetted hydrogen has no higher illuminating power than 

 hydrogen or carbonic oxide* 



Value of 1 cubic foot of the olefiant gas, contained in the 

 following gases, expressed in sperm candles, each burning 

 10 hours, at the rate of 120 grs. per hour. 



