

GAS, COAL 571 



mixed constituents, condensible by anhydrous sulphuric acid, has been found to vary 

 from 2'54 to 4'36 volumes, it is clear that this amount of carbon-vapour must be accu- 

 rately determined for each specimen of gas, if we wish to ascertain the value of that 

 gas as an illuminating agent. Fortunately this is easily effected ; for if we ascertain 

 the amount of carbonic acid generated by 100 volumes of the gas in its original con- 

 dition, knowing from the preceding analytical processes the percentage of illuminating 

 hydrocarbons, and also the amount of carbonic acid generated by the non-luminiferous 

 gases, we have all the data for calculating the illuminating value of the gas. For 

 this purpose a known volume of the original gas (about one cubic inch) is introduced 

 into the explosion eudiometer, and mixed with about five times its volume of oxygen ; 

 the electric spark is passed, and the volume of carbonic acid generated by the explo- 

 sion ascertained as above directed. If we now designate the percentage of hydro- 

 carbons absorbed by anhydrous sulphuric acid by A, the volume of carbonic acid 

 generated by 100 volumes of the original gas by B, the carbonic acid formed by the 

 combustion of the non-luminous constituents remaining after the absorption of hydro- 

 carbons from the above quantity of original gas by C, and the volume of carbonic 

 acid generated by the combustion of the luminiferous compounds (hydrocarbons) by 

 x, we have the following equation : 



and therefore, the amount of carbonic acid generated by. one volume of the hydrocar- 

 bons is represented by 



B-C 

 A ' 



But as one volume of carbon-vapour generates one volume of carbonic acid, this 

 formula also expresses the quantity of carbon-vapour in one volume of the illumi- 

 nating constituents. For the purpose of comparison, however, it is more convenient 

 to represent the value of these hydrocarbons in their equivalent volume of olefiant gas, 

 one volume of which contains two volumes of carbon- vapour ; for this purpose the 

 last expression need only be changed to 



B-C 

 ~2AT' 



Thus, if a sample of gas contain 10 per cent, of hydrocarbons, of which one volume 

 contains three volumes of carbon-vapour, the quantity of olefiant gas to which this 10 

 per cent, is equivalent, will be 15. 



By the application of this method we obtain an exact chemical standard of com- 

 parison for the illuminating value of all descriptions of gas ; and by a comparison of 

 the arbitrary numbers thus obtained, with the practical results yielded by the same 

 gases when tested by the photometer, much valuable and useful information is gained. 



Analysis of Coal-gas with Frankland and Wards apparatus. Introduce a few cubic 

 inches of the gas into the tube i, fig. 1025, and transfer it for measurement into F, by 

 opening the cocks I V and placing the tube F in communication with the exit pipe h, 

 the transference being assisted, if needful, by elevating the trough c. When the gas, 

 followed by a few drops of mercury, has passed completely into F, the cock I is shut, 

 and f turned, so as to connect F and H with h. Mercury is allowed to flow out until 

 a vacuum of two or three inches in length is formed in H, and the metal in F is just 

 below one of the divisions ; the cock / is then reversed, and mercury very gradually 

 admitted from G, until the highest point in F exactly corresponds with one of the 

 divisions upon that tube ; we will assume it to be the sixth division. This adjustment 

 of mercury and the subsequent readings can be very accurately made by means of a 

 small horizontal telescope placed at a distance of about six feet from the cylinder, 

 and sliding upon a vertical rod. The height of the mercury in H must now be accu- 

 rately determined, and if from the number thus read off, the height of the sixth division 

 above the zero of the scale on H be deducted, the remainder will express the true 

 volume of the gas. As the temperature is maintained constant during the entire 

 analysis, no correction on that score has to be made; the atmospheric pressure being 

 altogether excluded from exerting any influence upon the volumes or pressures, no 

 barometrical observations are requisite ; and as the tension of aqueous vapour in F is 

 exactly balanced by that in H, the instrument is in this respect also self-correcting. Two 

 or three drops of a strong solution of caustic potash are now introduced into i by 

 means of a bent pipette, and mercury being allowed to flow into F and H by opening 

 the cock g, the gas returns into i through 1 1', and there coming into contact with an 

 extensive surface of caustic-potash solution, any carbonic acid that may bo present 

 will be absorbed in two or three minutes, and the gas being passed back again into H 



