54 Dr Fyfe on the Prevention of Smoke ^ Sfc. 



According to Despretz, when 1 of oxygen enters into union 

 with other substances, heat is given forth sufficient to boil off 

 4.6 of water from 32. Now 1057 x 4.6 = 4862, which mul- 

 tiplied by 1.6 = 7779. In my trials the consumpt of 1.6 of 

 gas boiled off 7000, and consequently there was, by this mode 

 of calculation, a loss of about one-tenth of the evaporative 

 power in my trials. 



It is generally allowed that 112 lb. of coal will yield 500 

 feet of gas, consequently 1 lb. will yield 1.46, or very nearly 

 4^ feet. It has been shewn that in my trials 1.6 of gas eva- 

 porated 7000 of water, and according to the consumpt of oxy- 

 gen, it should evaporate 7779, and as 1.6 : 7779 : : 4.6 : 22,362, 

 and 22,362 -r- 7000 = 3.19. Accordingly th^ gas from each 

 pound of coal should, by its combustion, and provided there 

 were no loss of the heat evolved, evaporate 3.19 of water 

 from 32. 



The average quantity of fixed carbon in Scotch coal amounts 

 to 50 per cent., consequently it ought to boil off 6.15 of water 

 from 32 ; now adding this to the 3.19 formerly mentioned, 

 1 lb. of coal should evaporate 9.34, provided the whole of the 

 fixed carbon, and of the gas given off from it, as in the ma- 

 nufacture of coal-gas, were completely consumed ; but this is 

 short of what a pound of coal ought to do, supposing the whole 

 of its inflammable ingredients were consumed, and provided 

 also the whole of the heat evolved were taken up by the 

 water. 



In the table given by Mr Richardson, Lond. Phil. Mag., 

 1838, the average quantity of oxygen necessary for the com- 

 bustion of 1 of Scotch coal is 2.47, which would make 1 lb. 

 evaporate 11.3 of water. Now, deducting 9.34 from this 

 gives a deficiency of 1.96, which must be accounted for by 

 the formation of the tar and volatile oil, also produced in the 

 manufacture of coal-gas, by the elements entering into a new 

 state of combination, and which, if burned along with the 

 fixed carbon and gas, should make up the evaporative power 

 to 11.3, or thereabouts. If we deduct the 6.15, representing 

 the evaporative power of the fixed carbon, from the total 

 amount, the deficiency is 5.15. Now, allowing that, by the 



