Purrot Coal for yielding Gat, 



221 



Tahular View of the Illuminating Power of the Gases, as proved hy the 

 Shadow, hy the Chlorine Test, and hy the Time for Consuming a Cubic 

 Foot hy the 6~inchjet. The gas from Skaterigg heing taken as unity. 



The foregoing observations apply solely to the comparative 

 value of the gas for the purposes of illumination, as found by 

 the methods described ; but it will be seen by inspecting the 

 table, that not only is the time required for consuming equal 

 volumes of the gases different, but that the quantity of gas 

 given off, though generally nearly the same, yet in some cases 

 is higher than in others ; of course, these must be taken into 

 account in fixing the comparative value of the gases, and con- 

 sequently in enabling us to ascertain the comparative value of 

 the coals for the manufacture of gas. 



The following table shews the comparative illuminating 

 power for equal consumpts of gas, as proved by the shadow- 

 test. Skaterigg being taken as unity. 



In addition to the above, if we take into account the quan- 



