386 Dr. Turner's Chemical Examination of the Fire Damp 



of purity from coal, wholly free from admixture with hydrogen, carbonic 

 oxide, or olefiant gases, and but rarely 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 ratio is favourably adjusted for combus- 

 tion. The most explosive mixture, as Davy correctly states in his " Essay on 

 Flame," is formed of one measure of pure fire damp, and about seven 

 measures 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 in contact 

 with flame, and detonates readily with the electric spark. As the propor- 

 tion of pure fire-damp rises above a sixth, the mixture burns less and less 

 readily, and the tint of the flame changes at the same time from blue to 

 yellow or brown. These phenomena receive a ready explanation from the 

 well-known principles established by Davy. 



The analysis of fire-damp was performed by detonation with oxygen gas 

 over mercury. In successful analysis with all the gases, the diminution in 

 volume subsequent on detonation with the electric spark and due to 

 gaseous matter condensed as water, was precisely twice the volume of car- 

 bonic acid gas which was generated, and equal to the oxygen gas which 



* 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 re- 

 gards Wallsend Pit they are important, and to me conclusive. 1 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. Respecting the Wallsend 

 gas he says — " 1 received your letter and bottles of gas safely, 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 hydrogen 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, sul- 

 phurous acid, sulphuretted hydrogen and lime." 



