1895.] in the Flames of Hydrocarbon Gases. 453 



These results show that the diameter of the wire seriously affects 

 the temperature recorded under these conditions by the thermo- 

 couple, the same degree of heat being recorded by the fine wire as 

 being 248 hotter than is shown by the thickest wire employed, this 

 discrepancy being probably chiefly due to loss by conduction. 



In taking the temperature of heated gas flowing through a tube 

 this source of error is but small, as some considerable length of wire 

 being heated on each side of the twist, conduction has but little effect 

 on the thermo-couple itself, but in determining the temperature of 

 flames it is manifest that the finest usable wire must be employed in 

 order to reduce the error from conduction. Test experiments also 

 showed that no part of the thermo-couple must project beyond the 

 flame, as if it did a considerable diminution in the recorded temperature 

 took place. 



For these reasons it was manifestly best to use the finest wire 

 which could be employed without the risk of fusing at the tempera- 

 tures existing in the flames to be tested ; and all temperatures 

 recorded in this paper were made with wire 0*011 in. in diameter, 

 the twist being as short as possible, so that it is probable that, 

 although the temperatures may be from 100 to 200 too low, yet the 

 results are strictly comparable. 



Experiments which I have lately made with pure acetylene, prepared 

 by the action of water upon calcic carbide, show it to be the most 

 powerful illuminant to be found amongst the gaseous hydrocarbons, 

 as when burnt in a small flat flame burner under the most suitable 

 pressure, and its illuminating power calculated to a flow of 5 cubic ft. 

 an hour, its value is equal to about 240 candles. 



The colour of the flame is pure white, and an ethylene flame beside 

 it looks yellow and dull the purity of the light at once suggesting 

 a very high condition of incandescence in the particles of carbon 

 present in the flame. 



On now taking the temperature of the various portions of the 

 flame, and comparing these with the temperatures obtained in the 

 same way with the ethylene flame and a coal-gas flame of the same 

 size, the following results are obtained : 



Portion of flame. Acetylene. Ethylene. Coal gas. 



Non-luminous zone 459 C. 952 C. 1023 C. 



Commencement of luminosity. . 1411 3340 1658 



Near top of luminous zone .... 1517 1865 2116 



whilst the illuminating values of the gases calculated to a flow of 

 5 cubic ft. an hour in the burners best suited for their consumption, are 



Acetylene 240'0 



Ethylene 68'5 



Coal gas 16*8 



