Variable Illuminating Power of Coal Gas. 137 



How far any neglect in the observance of the precautions re- 

 quired to produce a proper illuminating gas, may explain the 

 result the public have no means of knowing. All that we know 

 is that the manufacturers furnish an article which they say is the 

 right article and prepared in the right way, and possessing an 

 illuminating power varying from 14 to 17 candles. That is, their 

 engineer reports, that on trial with a photometer, at stated times, 

 the gas burning from a jet, consuming five cubic feet per hour, 

 gives ?n amount of light equal in the average to that of 15 patent 

 candles six to the pound. The patent candle being ostensibly a 

 mixture of spermaceti and wax. Assuming as true all that is 

 claimed by the manufacturers, it can still be shown that the gas 

 even if properly made and correctly tested may be and is fur- 

 nished to the consumer in a condition of greatly diminished illu- 

 minating power, compelling the consumption of a greater bulk to 

 obtain the required light and consequently swelling the record of 

 the meter and the sum total of the quarterly bills. In my trials to 

 determine the specific gravity of our gas by weighing a globe 

 previously exhausted and then filled with it, I obtained a result 

 ranging from 5*70 to 580 somewhat below that giveu as charac- 

 terizing good gas. But in reality I attach very little importance 

 to this result since the mere specific gravity of such a complex 

 mixture as coal gas can hardly be relied upon to determine its 

 commercial value. 



Although good gas certainly has a higher specific gravity than 

 poor, yet the difference could not be taken to represent the true 

 difference in value since the principal components of the mixture 

 hydrogen, carbonic oxyd, light carburetted hydrogen, defiant gas 

 and other still heavier hydrocarbons having specific gravities, 

 widely different, might vary somewhat in their relative proportions 

 sufficient to affect the illuminating power, without at the same 

 time and to the same extent affecting the specific gravity. The 

 action of chlorine in removing the olefiant gas and other more 

 dense hydrocarbons, the principal light giving materials of the 

 coal gas, showed a per centage of these substances never exceed- 

 ing 10 per cent. But not having time at the moment to guard 

 against all sources of error in the process, laid it aside. My atten- 

 tion was principally directed to the simple inquiry to what extent 

 will the illuminating power of the gas be impaired by keeping it 

 in contact with water for noted periods. That it does deteriorate 

 when thus kept, or when kept in contact with oil or even close 

 vessels has been long known. 



