236 Dr Fyfe on the Illuminating and Heating Power of 



on an average, 18 feet would be required to boil off 1 gallon, 

 i. e. 10 lb. of water. In this town 1000 feet cost 9s., 18 feet 

 would therefore cost 1.9 of a penny, say 2d. 



It is generally allowed, that 1 lb. of coal, were the heat gene- 

 rated during its combustion all applied, would evaporate about 

 14 lb. of water, but this is never done in practice. It is con- 

 sidered as a good result when it evaporates from 6 to 8 lb. 

 Now, suppose a ton of coal to cost 128., 1 lb. will cost about 

 the fourth part of a farthing, so that a quantity of coal which 

 costs little more than a fourth of a farthing will evaporate as 

 much water as gas which cost 2d. Perhaps the same proportion 

 will be found to hold at other places, for where coal is dearer 

 gas is also more expensive. But though gas, as a source of 

 heat, is much more expensive than fuel, yet there are occasions 

 where it may be applied where the expense will not be found 

 to be very great ; indeed, in some instances not more than 

 would be requisite were coal used, besides having many advan- 

 tages. When it is required to warm water when there is no 

 fire at hand, a gallon may be boiled by the consumpt of about 

 3 feet of gas, at a cost, therefore, of little more than a farthing. 



With regard to the use of gas for cooking, we are, of course, 

 enabled so far to judge of its expense. In the paper pub- 

 lished in the Edinburgh New Philosophical Journal, and in 

 the Transactions of the Society, by Sir J. Robison, already 

 alluded to, it is proposed to burn the gas on gauze of from 3 

 to 4 inches in diameter ; the flame being larger or smaller ac- 

 cording to circumstances. Suppose a pot is used holding a 

 gallon of water, and it is wished to bring this to boil in half 

 an hour, and to keep it boiling, then the gauze will consume 

 6 feet per hour ; so that, for each hour the gas is in use, each 

 gauze-burner will cost a little more than a halfpenny, and we 

 may perhaps consider this as an average ; the gas being at the 

 rate of 9s. per 1000 feet. Suppose a larger consumpt of gas 

 required, then each burner would cost, say about Id. per hour ; 

 but this is, I believe, beyond what a burner of the kind men- 

 tioned is capable of consuming, without waste of gas from 

 smoke, or from part of it escaping without being burned. If 

 six of these burners are in use, say for three hours at a time, 

 then the expense would range from 9d. to Is. 6d. : say, on an 



