MECHANICS AND USEFUL ARTS. 95 



cent., is a little over six-tenths of a candle (.Gil exactly) ; above 

 that quantity the ratio of loss ftills to one-half a candle power for 

 each additional one per cent, up to about 12 per cent, of air ; above 

 which, uf) to 25 per cent., the loss in illuminating 2^ower is as 

 shown by column 12 of the table, nearly four-tenths of a candle 

 for each one per cent, of air added to the gas. In column 11 of 

 Table 1, the ratio of loss in candle power is given in percentages 

 for the several volumes, while in column 10 the destructive effect 

 of air upon the illuminating power is most conspicuously exhibited, 

 12 per cent, of air destroying over 40 per cent, of the illuminating 

 power. In the diagram this loss of power is represented by the 

 numerals in the right-hand column, which are inverse to those in 

 column 10, and stand with the maximum intensity =:: 100. 



2d. With less than one-fourth of atmospheric air, not quite 15 

 per cent, of the total illuminating power remains ; and with between 

 30 per cent, and 40 per cent, of air it totally disappears. 



In large gas works the liability to contamination by air acci- 

 dentally introduced by various causes diminishes in proportion to 

 the total make of gas, and an amount of air which, when diffused 

 in a very large volume of gas, becomes insignilicant, if confined 

 to 10,000 or 15,000 feet daily product, will become a most serious 

 injury to its illuminating power. This cause of deterioration in 

 gas has been overlooked almost entirely by gas engineers ; but in 

 small gas works it deserves special attention, and we have m) 

 doubt that the low illuminating power too often obtained in such 

 works is largely due to this cause. 



llesults of Messrs. Audouin and Berard. — We have already al- 

 luded to the results obtained by Messrs. A. and B., which form 

 part of an important memoir published in 1860, under authority 

 of the French Government, " upon the various burners employed 

 in gas-lighting and researches on the best conditions for the com- 

 bustion of gas." Their table shows *' a considerably higher ratio 

 of loss than we have obtained, being rather more than 6 per 

 cent, loss for each one per cent, of air added to the gas, reaching 

 a total loss of 80 per cent, with 15 per cent, of air added ; while we 

 obtain 57.53 per cent, loss with 16 per cent; and 93 per cent, loss 

 with 20 per cent, air, while with the latter volume of air added 

 we get 72.90 per cent. loss. These differences may be accounted 

 for by the French trials being made upon a gas of not more than 

 12 candle-power, our trials being made on a gas averaging nearly 

 15 candles ; also, by the fact that in the French experiments the 

 gas was burned from a batswing burner, purs from a standard 

 Argard. 



It appears that the introduction of 6 to 7 per 100 of air suffices 

 to diminish the intensity by one-half, and a mixture of 20 of air 

 with 80 of gas leaves almost no illumination. Unfortunately 

 Messrs. A. and B. do not record the actual illuminatin*^ power of 

 their standard gas, which, however, we are led to believe cannot 

 be more than 12 candles of the English and American standard. 



For a fuller discussion of this subject the reader is referred to 

 the memoir of Prof. Silliman and Wurtz. 



