34^ POPULAR SCIENCE MONTHLY. 



of tlie melting point of tin, 228° C, being rarely readied in good 

 generators where these conditions are met. 



Undoubtedly the best generators, and the only ones which from 

 a scientific point of view should be employed, are those of class III, 

 in which carbide falls into an excess of water. In such generators it 

 is impossible to get a temperature higher than the boiling point of 

 water, 100° C, while with a properly arranged tank the temperature 

 never exceeds that of the air by more than a few degi'ees. Under 

 these conditions the absence of polymerization and the washing of 

 the nascent and finely divided bubbles of gas by the limewater in 

 the generator yield acetylene of a degree of purity unapproached by 

 any other form of generator. 



When acetylene is burned in air under such conditions that the 

 flame does not smoke, it has been proved by Grehant that there is 

 no carbon monoxide among the combustion products; the acetylene 

 combines with the oxygen of the air to form carbon dioxide and 

 water (C2H2 + 50 = 2CO2 + HoO). One cubic foot of acetylene 

 requires two and a half cubic feet of oxygen. Supposing a room 

 to have an illumination equal to sixty-four standard candles; this 

 amount of light from candles would use up 38.5 cubic feet of oxygen 

 from the air, and would give off forty-three cubic feet of carbon diox- 

 ide; petroleum requires, in cubic feet, twenty-five of oxygen, and gives 

 off forty of carbon dioxide; gas burned with a flat flame requires 

 about twenty-five oxygen and gives nineteen carbon dioxide — with an 

 Argand flame a little less, while* with the Welsbach burner gas re- 

 quires only three oxygen, and gives off 1.8 carbon dioxide; acetylene 

 requires five oxygen and yields four carbon dioxide. So that, light 

 for light, acetylene fouls the air less than any ordinary illuminant 

 excepting the Welsbach gas burner. (With incandescent electric 

 light there is no combustion and no fouling of the air.) 



Under the best conditions five cubic feet of acetylene give a light 

 of two hundred and forty candles for one hour, or we may speak of 

 acetylene as a two-hundred-and-forty-candle gas. Yet this statement, 

 though strictly true, may be misleading. When ordinary illuminating 

 gas is tested with the photometer, it is burned from a standard flat- 

 flame burner, burning five cubic feet per hour. Now the amount 

 of light given by such a gas flame is no greater than is pleasant to 

 the eye; it is true that if we burn five cubic feet of acetylene from 

 a suitable flat-flame burner, a light of two hundred and forty candles 

 is given, but it is unfair to take this ratio as representing the actual 

 relative illuminating value of the two lights, because we neither 

 need a light of two hundred and forty candles, nor is such an amount 

 of light issuing from one burner endurable to the eye. One-foot 

 or one-half foot acetylene burners are used for domestic lighting; 



