ITD Professor Thomas Thomson <m Coal Gas. 



Nine-elevenths of the hydrogen and seven- ninths of the oxygen 

 go to the formation of water and various other compounds. The 

 ammonia formed amounts to about one per cent, of the liquor obtained 

 during the distillation of the coal. 



When gas works wore first established, the coal was distilled in iron 

 retorts ; but it has been found more economical to substitute vessels 

 of stoneware, or rather, indeed, ovens of fire brick made air-tight. 

 These, I believe, have every where superseded the iron retorts. 



During the course of last winter, I made thirty-five analyses of gas 

 from different gas works, but most commonly Glasgow gas. The gas 

 which I used was taken from a pipe at some distance from the gas 

 work, because the gas required to be washed and purified before it 

 was examined. After turning the stop-cock, the gas was kindled and 

 allowed to burn for several minutes before I began to collect it. In 

 every case it contained a mixture of common air, which varied in dif- 

 ferent specimens of gas from 4 per cent, to 28 per cent. The mean 

 quantity was 12^ per cent. The specimen containing 28 per cent, of 

 common air was brought up from Greenock, and though very great 

 care was taken in packing it, it is possible that at least a portion of 

 this air might have made its way into the bottles during the transit. 

 If we omit this specimen, the average quantity of common air in the 

 Greenock gas was \0\ per cent. : the average quantity in the Glasgow 

 gas was 12i per cent. 



I think it most likely that the common air which forms a constant 

 ingredient in all gas from gas works that I have examined, had made 

 its way into the pipes, which it must be very difiicult to make air- 

 tight ; and when the pressure is removed, common air will undoubtedly 

 enter wherever it can find access. The Greenock gas was collected 

 in an apartment very near the gas works : the Glasgow gas was col- 

 lected in my laboratory, which may be about a furlong from the gas 

 works. Now, the average quantity in the Greenock gas was 10|, and 

 in the Glasgow 12 J. 



The highest specific gravity of the Glasgow gas was 0*582, and the 

 lowest 0*463 : the average was 0*502. 



The quantity of olefiant gas in Glasgow gas varied from 11*77 per 

 cent, to 17*83 per cent: the mean quantity was 13*52 per cent. 



I got gas made at Greenock with as much care as possible, from 

 each of the three varieties of cannel coal found in the neighbourhood 

 of Glasgow, namely, Skaterig, Lesmahagow, and Monkland. The 

 specific gravity of these gases were, 



These are the specific gravities after the air was extracted. 



