of some of the Cornish Mines. 359 



to redness ; and sulphuretted hydrogen may be removed by 

 the gas being afterwards passed through a solution of chlorate 

 of lime. The nitrous gas or deutoxide of nitrogen was pro- 

 cured by the action of nitric acid in pure metallic copper, 

 collecting the gas sometimes over water, and sometimes over 

 mercury. 



The quadrisulphuret of lime was manufactured after the 

 manner recommended by Dr. Dalton. 



The samples of air taken from the different loads in the 

 mines were procured by emptying jars of water of their con- 

 tents, and four-ounce bottles of mercury from one to the other, 

 at the required spots, preserving a small portion of the water 

 or mercury, greasing the corks, driving them as tight as pos- 

 sible, and afterwards sealing them over. Both jars and bottles 

 were kept in an inverted position from this moment to that 

 of their use ; and a further proof of their security was ge- 

 nerally had by an escape of a few bubbles of air on withdraw- 

 ing the cork or stopper under water in the pneumatic trough. 



The pneumatic trough was filled with perfectly clean rain 

 water, collected from the glass roof of a green-house, and 

 renewed as frequently as opportunities would permit. 



Sample ] . One gallon. 



Wheal Vor Mine. — Tin in slate. Taken from the 250-fa- 

 thom level below the surface; fifteen fathoms west of any 

 shaft or winse, and taken a few minutes after firing a hole, 

 with two men in a core ; specific gravity of air *997. 



Oxygen. 



Average of three experiments by exposing the gasl 



to the influence of the quadrisulphuret of lime > 18*41 

 in Hopei eudiometer J 



Average of four experiments with pure hydrogen"1 „. 

 fired by electricity in Volta's eudiometer . . . 



Average of four experiments with nitrous gas . . 18*45 



One experiment with heated platina ball over mercury 18*40 



Mean . . . 18*416 



Carb. acid. 

 Average of three experiments with lime-water . . 0*06 

 Average of three experiments with solution off 



pure potash J °'° * 



Mean . . . 00*65 

 No trace of any other gas, consequently the composition 

 of this sample stands thus : — 



