Chemical Examination of the Fire-Damp. 203 



containing a trace of carbonic acid gas.* The sole difference in 

 the explosive gas of different mines must hence be referred to the 

 degree of admixture with air. If diluted with nineteen or twenty 

 times its volume of air, the mixture does not detonate or take fire 

 at all ; on diminishing the proportion of air below this term the 

 mixture becomes inflammable, and on the approach of a lighted 

 candle, a pale blue flame appears, which passes slowly through 

 the mixture when the air is in large excess ; rapidly when the ra- 

 tio is favorably adjusted for combustion. The most explosive 

 mixture, as Davy correctly states in his " Essay on Flame,"f is 

 formed of one measure of pure fire-damp, and about seven meas- 

 ures of air. Such mixture, unlike an explosive mixture made 

 with air and hydrogen or carbonic oxide gas, is not kindled by 

 incandescent solid matter, such as a mass of hot iron ; but it 

 burns rashly [rapidly?] in contact with flame, and detonates 

 readily with the electric spark. As the proportion of pure fire- 

 damp rises above a sixth, the mixture burns less and less read- 

 ily, and the tint of the flame changes at the same time from 

 blue to yellow or brown. The phenomena receive a ready 

 explanation from the well known principles established by Davy, 



sonal services in collecting the specimens of gas, and making such arrangements 

 as will secure their conveyance to London unadulterated. 



" I have the honor to be, &c. &c. 



" William Hutton, Secretary. 



" To Robert William Brandling, Esq." 



The Coal Trade Committee immediately adopted the suggestion, and appointed 

 John Buddie, George Johnson, and Nicholas Wood, Esq'rs,to make the necessary 

 arrangements, for collecting the specimens of gas. 



* Extract of a letter from Major Emmett, Royal Engineer, to Mr. Hutton, dated 

 Hull, 19th February, 1836. 



" I send you the following extracts from a letter from Dr. Dalton of the 13th. As 

 regards Wallsend Pitt, they are important, and to me conclusive. I sent him three 

 bottles Mr. Buddie had collected for me about three months ago, also one of water 

 from the old working at Gateshead Park Pit, forwarded to me by Mr. Wood. Re- 

 specting the Wallsend gas he says : ' I received your letters and bottles of gas safe- 

 ly, and soon after opened the bottles under water. The air in each bottle was very 

 much alike. It was constituted of some two or three per cent, of carbonic acid, 

 about one tenth common air rather short of oxygen, and the rest, about eighty-five 

 per cent., was pure carburetted hydrogen, or pond gas, without a trace of either 

 pure hj^drogen or olefiant gas.' Respecting the Gateshead water he says, " The 

 bottle of water from the old waste I also examined ; it contained about one per cent, 

 of soluble matter, chiefly common salt, with some carbonic acid, sulpluuoua acid, 

 sulphuretted hydrogen and lime.' " 



[t See Phil. Mag. First Series, vol. xlvi, p. 448.] 



