154 CALORIFIC POWER OF FUELS. 



must increase and the effective suction in C' must decrease,, 

 and in consequence the velocity of the air thiough A will 

 increase and the velocity of the air through B will decrease, 

 until the same quantity of air again flows through both aper- 

 tures. Thus every change of temperature in the air entering 

 through the aperture A will cause a corresponding change of 

 suction in the chamber C. If two manometer-tubes/ and q, 

 Fig. 38, communicate respectively with the chambers C and 

 C' ', the column in tube q will indicate the constant suction in 

 C' and the column in tube/ will indicate the suction in the 

 chamber C, which suction is a true measure of he tempera- 

 ture of the air entering through the aperture A. 



DETERMINATION OF THE CARBON IN SMOKE. 



SOOT or black forms from quick cooling of the hydro- 

 carbons, temporarily dissociated by high temperatures. Fuels 

 having no hydrogen as hydrocarbons, never produce smoke ; 

 pure charcoal, coke, or graphite never smokes. Soft coal, on 

 the contrary, produces more as the air-supply grows less. 



Sainte-Claire Deville proved that a compound gas when 

 heated sufficiently separates into its elements ; a sudden cool- 

 ing now will give a simple mixture instead of the original 

 combination. A slow cooling, however, reproduces the 

 original gas. Berthelot proved, on the other hand, that new 

 compounds are formed on heating the hydrocarbons to high 

 temperatures, a part of the carbon being deposited as soot. 

 These two phenomena undoubtedly go on together in smoke 

 production.* 



If a metal tube be put in the gas current over a grate at 

 a short distance from the fire, the hottest gases will be col- 



* Bunte gives some analyses of smoke-black: 



C H 



I *... 97.2 2.8 



2 97-3 2.7 



3 98.5 1-5 



