^g90.1 Accum on Coal Gas. 287 



rontains a portion of that gas ; but I have never met with any 

 coa oa consisting of pure carburetted hydrooen. It has always 

 nro ve'd ui the cases x4ere I had an opportunity of examnrnrg it, 

 rmivtuve of carburetted hydrogen, carb<.u|c oxide and hydrogen 

 Ja" the proportions of which vary according to the nature of the 

 foal and of the process. When the heat is applied suddenly, 

 and when it amomits to a good red heat, the pix.poit.on ot car- 

 buretted hydrogen is greatest, and when the heat ,s low, the 

 pronoi'ion^of Jure hydrogen is greatest. Olefiant gas and 

 Siffetted hydrogen are probably likewise present ; though in 

 sma 1 and variable^ quantity. There is another circumstance 

 cminected with this gas, which has not hitherto been not.ced ; 

 but wdrich must hav^'e some influence upon the ight wmch it 

 vSds Coal o-as has always the very same smell as the oil or 

 naphtha which coal yields when distilled ; theretore, it obvious y 

 contams a certain portion of naphtha mixed with it in the state 

 of vapour. When naphtha is put m contact w.th a quantity of 

 common air, or indeed of any gas whatever, a portion of it 

 ires with the gas m the state of vapour, and commumcates to 

 k the peculiar smell by which it is distingu.shed. Gas thus 

 contaminated wi^h the Vapour of naphtha -^ »f -f y P»f ^^^ 

 again. It may be allowed to remain in contact ^yth water, or 

 efen passed throudr water without losing any of the naphtha 

 vapour. The quantity of this vapour contained in coal gas 

 depends upon the temperature of the "aphtha and gas when 

 plTced in contact. At the temperature of o5° the bulk of ai , 

 £n placed in contact with naphtha, '%-^^7;'.^'^.^P5^ 7"^: 

 I find that the specific gravity ot vapour of naphtha is 2 25, that 

 of common air being 1^00. From this it will not be difficult o 

 determine the quantrty of naphtha with which coal gjis is usual y 

 contaminated.^ One Volume of vapour of naphtha for complete 

 combustion requires rather more than 2-4 volumes ; but not 

 quite so much as 2-5 volumes of oxygen gas. 

 ^ As carburetted hydrogen gas, carbonic oxide, hydrogen, and 

 olefiant -ases, are all destitute of smell, and as coal gas has 

 aWs a'stroi g smell of naphtha from which it cannot be, or at 

 Sas neve? yet been deprived, I conceive, that the presence 

 of the vapour of naphtha in it will not admit of a doubt. 



In the third paA our author gives a classification of pit-coal 

 as far as the production of coal gas is concerned. I need 

 scarcely remaii, that our author's division - JJT -^P^/f^^^ 

 indeed ; and that, as he gives no description o^^he varieties 

 which he names, the division, imperfect as it is^ is of little or no 

 „sr. For an idea of the composition, which will enable the 

 reader to form some accurate ideas on the subject 1 refer to a 

 paper of mine on the coal found near Glasgow, published in the 

 ^Znah of Philosophy, xiv. 81. Mr. Accum divides coal into 

 three classes : 



