Experiments on the Gas from Coal. 167 



nufactorv*,) it will be important to select that gas, which in a 

 given volume has the highest illuminating power, and which 

 therefore requires vessels of the smallest capacity for its convey- 

 ance. Having, I hope, furnished documents for solving ques- 

 tions of this sort, I shall proceed to describe in what manner the 

 facts were ascertained. 



Method of Analysis. 



1 . Determination of the proportions of carloiiic acid and sul- 

 phuretted hydrogen gases in coal gas. In experiments formerly 

 made on this subject, I employed the agency of chlorine to con- 

 dense both these impurities, and estimated how much of the ab- 

 sorption was due to each, bv a rule which I have stated f. Re- 

 cent experience, however, has led me to distrust this method ; 

 and after comparing the effects of several other agents, by expe- 

 riments on mixtures of known composition, I now prefer the 

 white carbonate of lead, precipitated from acetate of lead by car- 

 bonate of ammonia without heat, and therefore fully saturated 

 with carbonic acid. This precipitate it is better not to dry, but, 

 after washing it sufticiently, to leave it under as much water as 

 will give it, when wanted for use, a due degree of fluidity. This 

 mixture may be applied by means of a tube of the capacity of a 

 cubic inch, divided into 100 equal parts, and accurately ground 

 into a short and wider piece of tube, which ought not to contain 

 more than three or four tenths of that quantity. The wider tube 

 being filled with the fluid carbonate of lead, and placed with its 

 mouth upwards under water, the graduated measure full of gas 

 is fitted to it ; and the gas and liquid are brought into contact 

 by alternately inverting the two tubes, all violent agitation being 

 carefully avoided. The sulphuretted hvdrogen is thus absorbed, 

 and the carbonic acid, being left untouched, is afterwards taken 

 out from the same portion of gas by a similar use of solution of 

 pure potash. 



2. To ascertain the proportion of olefiant gas in the residue 

 left by potash. From 25 to ;)0 hundredths of a cubic inch of 

 chlorine gas are passed into a tube of the diameter of about f^ths 

 of an inch, accurately divided into hundredths of a cubic inch; 

 and the volume of the chlorine is noted when actually in the tube, 



• A small carriaj^e upon springs conveys two square close gasometers 

 made of uTought iron plates, and each containing 50 cubic feet of pei'fectly 

 purified gas, e(iuivalent together to about (ilbs. of talloiv. Each gasometer 

 weighs about UiO pounds; and lias a valve at the bottom, whicli is opened 

 by the upright main pipe, the moment the gasometer is immersed in the 

 pit. The strength of one man is found to be sufficient for the labour of re- 

 moving the gasometer from the carriage to its place. 



t I'hil. Trans. IHOS page 21)5. 



L4 to 



