Dr Fyfe on the Illuminating Power of Coal-Gas, &c. 229 
and supposing candles to be 73d. per pound, then the cost for 
each candle is 5 farthings. Suppose the gas to cost 8s. 4d. per 
1000 feet,* then six feet will cost 23 farthings, or very nearly 
so; accordingly, for half the expense, 3.75 times the amount of 
light is obtained; in other words, for the same light, the expense 
of tallow candles is 73 times that of gas. The gas I employed 
in these trials contained, on an average, 12 per cent. of con- 
densible matter. Should the gas contain more or less, then 
the comparative expense would be greater or less just accord- 
ing to the quantity. In Edinburgh I have found the chlorine 
test to indicate from 11 to 14, and 15, very rarely is it up to 
the latter ; of late [have rarely found it to go beyond 13. Con- 
sidering the foregoing calculation as applying to the gas now 
supplied to Edinburgh, and presuming it to contain 12 per 
cent. of matter condensible by chlorine, then the expense of 
tallow candles is 74 times greater for the same light than that 
of gas consumed by jet burners. 
In England, where the gas is generally manufactured from 
English caking-coal, the illuminating power is inferior to that 
of gas got from parrot-coal, or from a mixture of it and com- 
mon Scotch coal. Now, suppose the price of the gas the same, 
and that the condensation by chlorine amounts to 6, then the 
comparative expense of candles and of gas for the same light 
would be 3.75 to 1. 
Similar trials were made with the other candles mentioned. 
Double-wicked tallow, 1s. per pound.—This candle burns for 
53 hours at a cost of 8 farthings; the light compared to that of 
the jet is as 1 to 2.1, making the expense as 7.1 to 1. This 
candle has the advantage of not requiring to be snuffed. 
Cocoa candle, 11s. per pound, will burn for nine hours, at 
a cost of 7.3 farthings ; the light compared to the jet is as1 to 
3.6, or the same as that of the common tallow candle ; thus 
making the expense as 7.3 to 1. 
Palm candle, 1s. 2d. per pound, will burn for 6.6 hours, ex- 
pense 9.3 farthings, light 1 to 3, expense as 10.5 to 1. 
* I have taken this as being easy for calculation. It is not far from the 
price of gas in Edinburgh, and in other towns in the neighbourhood of the 
coal districts. 
