MECHANICS AND USEFUL ARTS. 95 



cone for the high-pressure steam-jet at the end of it, which jet was 

 placed at the proper striking distance from a cylinder of sheet-iron one 

 foot in diameter and about nine feet long. The cylinder was the pas- 

 sage between a coke furnace and the downcast shaft, through which 

 the air was driven by the force of the steam-jet, and, by a simple con- 

 trivance, we were able to blow in either the air passed through the fur- 

 nace, or fresh, at pleasure. 



When the preparations were completed, a party descended into the 

 mine, Mr. Gurney blowing them in fresh air from above, and there 

 cleared away two old iron doors into the waste, and knocked a hole 

 through an old puddle-wall, and then, hearing a good deal of rumbling 

 and rushing, as if the roof were falling, they thought it more prudent 

 to retreat, as they had effected their object of opening a passage for the 

 gases into the burning waste. The heat at the bottom of this shaft 

 was 100 F. at this time. These obstacles having been cleared away 

 and a free passage obtained, the shaft was covered with iron plates 

 and clayed over, so as to render it air-tight, and the chokedamp was 

 turned on. The extinguishing gas was made by passing the atmos- 

 pheric air through an intense coke fire in a brick furnace, which 

 deprived it of all its oxygen, or rather the oxygen combined with the 

 carbon of the coke, and formed carbonic acid, which gas, in mixture 

 with the nitrogen left, was forced through the furnace, along the iron 

 cvlinder, down the shaft and into the burning waste ; the quantity of 

 coke consumed being a sufficiently accurate measure of the air passed. 



The remainder of the process is thus described by one of the assistants 

 of Mr. Gurney : After blowing in about 8,000,000 cubic feet of choke- 

 damp, (at the rate of about 7,000 cubic feet per minute,) which we 

 calculated to be about the contents of the waste, (allowance having 

 been made for falls of the roof,) we found the upcast or high level 

 shaft or drift was full of it to the mouth, flowed over, and ran along 

 the ground, extinguishing lights if held near the surface of the earth 

 at some distance from the spot. We found when we ceased blowing 

 in gas that after a time the chokedamp receded in the upcast, and that 

 whenever we blew it into the downcast, it poured out of the upcast in 

 volumes, being thus a perfect measure of the quantity of chokedamp 

 in the mine, and giving us a proof that it had passed completely 

 through it. After keeping the mine full for upwards of three weeks, 

 it was thought advisable to blow in chokedamp at a lower tempera- 

 ture than we had been previously doing, which we believed to have 

 been about the temperature of 250. In order to effect this, Mr. Gur- 

 ney used a very beautiful contrivance, by which, by the power of the 

 steam-jet, water was driven into the shaft along with the chokedamp 

 in the form of the finest spray. This process Mr. Gurney thought very 

 important, as he considered the difficulty of cooling the immense mag- 

 azine of heat, after the fire was extinguished, to prevent reignition on 

 the admission of fresh air, to be the most uncertain part of the whole 

 experiment. That he could extinguish the fire he had no doubt what- 

 ever, but to cool down the waste against the existing conditions of non- 

 conduction and non-radiation, he considered far more difficult. The 

 water being so minutely divided by the immense force of the jet, was 



