Different kinds of Coal for tlie purpose of Illumination. 275 



square roots of the pressures, and the times, for equal con- 

 surapts being inversely as the square roots, while the spe- 

 cific gravities are also inversely as the square roots of 

 the pressures, the following table will give the consumpt 

 of gases in 60 minutes, the time for the consumpt of a 

 foot; and the specific gravity, at 60", and barometer 30, calcu- 

 lated from the square roots of the pressiu'cs, the gases being 

 consumed, with a flame of 5 inches from the jet 40 ; taking, 

 as I have already stated, a gas of specific gravity 6026, burn- 

 ing under a pressure of J^l^ths, 1 foot in 64' 41" ; the square 

 root of pressure 117 being 108166. 



Should any other jet be found preferable, the quantity of 

 gas consumed by it, with a flame of a fixed height, must be 

 ascertained by repeated trials, with an accurate experi- 

 mental metre ; taking the pressure accurately each time. 

 The average consumpt and pressure being thus fixed on, the 

 specific gravity is to be taken by expei'iment in the usual 

 way ; then the consumpts and specific gravity of other gases 

 with the same burner and height of flame, will be found, as al- 

 ready directed, with jet 40 ; and for which the table has been 

 constructed. 



Table, shewing the Times for Equal Consumpts, the Consumpts 

 in Equal Times, and the Specific Grravities of Gases, requir- 

 ing the following Pressures to burn them, from Jet 40, with 

 a 6-Inch Flame. 



