MIXED GASES. 409 



(/.) The last portions contain hardly any olefiant gas; they con- 

 sist of light carburetted hydrogen, and much hydrogen and carbonic 

 oxide, which is the reason that they afford so little light during their 

 combustion. 



(m.) There is great uncertainty and variety in the quantity and 

 quality of gas obtained from coal. Dr. Henry considers it as an ap- 



Eroximation to truth, to suppose, that 112 Ibs. of good coal may af- 

 >rd from 450 to 500 cubic feet of gas, "of such quality, that half a 

 cubic foot per hour is equivalent to a mould candle of six to the pound, 

 burning during the same space of time." 



(n.) I have often obtained a very bright burning gas from Rich- 

 mond (Va.) coal ; at other times a gas producing a very pale flame. 

 * (o.) Anthracite of Pennsylvania and of Rhode Island,* afford 

 much gas,f chiefly light carburetted hydrogen, but it is unfit for illu- 

 mination; most authors state that the anthracties afford little or no 

 gas. That of Wilkesbarre gave, in my trials, 40 wine pints from 

 886 grains of the coal, while the specific gravity of the coal was in- 

 creased from 1.65 to 1.77,J and several other varieties of American 

 anthracite yielded large quantities of inflammable gas. 

 II. OIL GAS. 



1. HISTORY. 



(a.) The familiar use made of animal oils, to afford by their 

 combustion, artificial light, naturally suggested the project of decom- 

 posing them to obtain gas. 



(6.) Dr. Henry, in a memoir in Nicholson's Journal for 1805, ap- 

 pears to have first brought this subject into notice, and to have proved 

 that next to the pure olefiant, the gas from oil is the best adapted for 

 artificial illumination. 



2. PREPARATION AND PROPERTIES. 



(a.) By allowing spermaceti oil, or even refuse whale oil, (as the 

 purity of the oil is not material,) to fall drop by drop, from a reser- 

 voir furnished with a stop cock, and connected by a tube with an 

 iron bottle or cylinder, upon fragments of bricks, or, as practised in 

 New York, fragments of anthracite, heated to a cherry red. 



(6.) A condensing vessel should be interposed between the fur- 

 nace and the gazorneter, to receive the undecomposed oil. 



(c.) A wine gallon of oil affords 100 cubic feet of gas, whose 

 specific gravity exceeds .900 ; more than .40 of this gas is condensi- 

 ble by chlorine ; 100 volumes require 200 of oxygen to saturate them 

 and produce 158 of carbonic acid. 



* The latter must be moist. 



t It is not easy to say how much of this gas arises from water ; the increase of sp. 

 gr. in consequence of ignition, seems however to imply that a lighter constituent of 

 the mineral has been expelled. J Am. Jour. Vol. X, p. 355, and Vol. XI, p. 78. 



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