396 INCANDESCENT MANTLES. 



Assuming, for the sake of simplifying* the calculation, that all the car- 

 bon of the benzene and half that of the ethjdene is separated and 

 hcatod to incandescence in the flame, it may he calculated that about 

 54 milligrammes of carbon arc separated from a liter of good coal gas 

 (23.6 grains from 1 cubic foot). Thus 4 per cent of ethylene and 1 

 per cent of benzene gives per liter of gas 00 cubic centimeters of car- 

 bon vapor from the henzene and 4(» cubic centimeters from the eth}^!- 

 ene, in all 100 cubic centimeters, which is equivalent to about 54 

 milligrammes of carbon. The volume of the luminous portion of a 

 flame having a consumption of 5.297 cubic feet per hour and an illumi- 

 nating power of 17.5 candles is about 2 centimeters at 32° F. There 



2 X 54 . 



is, therefore, in it l . y niilligranmies, or O.i milligrammc=().O015 



grain of incandescent carbon. Such an extremely small quantity of 

 incandescent carbon as 0.0015 grain gives the luminous surface to the 

 gas flame and emits a light of 17.5 candlepower. Now. the 1 per cent 

 of ceria in the Wels})ach mantle amounts to about 4milligranmies (0.06 

 grain) per mantle, or about forty times the quantity of incandescent 

 carl)()n in an ordinary flat flame. The quantity is, therefore, quite 

 suflicient to explain why tlie WelsV)a('h burner may give a light of 60 

 candles while the flat Hame. or Argand hurner, furnishes only 17.5 

 candles." 



The only other legalized mantle at present before the pu})lic is the 

 Sunlight, the ingredients of which consist of alumina and the oxides 

 of chromium, and it is interesting to see how far the light yielded by 

 this mantle can b(> attril)uted to the same action as in the ease of the 

 Welsbach. If a mixture of alumina or alumina and zirronia with 

 aver}' small percentage of chromium be employed, a very high eandle- 

 power is produced, Avhich, however, soon dies away, owing to the 

 volatilization of the chromium compound, while if the amount of 

 chromium present be increased, the mantle acquires a more ruddy 

 light and retains its illuminating power for a much longer period, so 

 that, with a proper percentage of chromium, a candlepower of 10 to 

 11 candles per cubic foot of gas can be obtained for a period of 400 

 to 500 hours, and it is noticed that the chromium, which on first burn- 

 ing shows as green chromium oxide, rapidly combines with the alu- 

 mina to form a pink compound which has much the same composition 

 as the ruby, and it is quite probable that the increased life given by 

 the larger quantity of chromium is due to the fact that the lighting 

 power of the mantle is really dependent on small traces of the oxide 

 of chromium, and that as this gradually volatilizes off from the sur- 

 face of the mantle some of the pink compound gets dissociated by 

 heat and supplies a fresh portion of chromium oxide to the surface of 

 the mantle, this pink compound being far less volatile than the chro- 

 mium oxide itself. 



