W. E. A. Aikin on the Illuminating power of Coal Gas. 85 
enough to enable me, after a few trials, to note, very exactly, its 
true value. The results as first obtained were too startling to be 
at once believed, but subsequent repeated trials satisfied me that 
they were very close approximations to the truth. The first 
trial was with the gas from the street main, which I found equal 
to 10-71 candles. The same gas, transferred from the pipe to 
the capped receiver, and burned immediately, gave exactly the 
same power, 10°71 candles. Gas No. 1 was next used, and found 
will give the light of only 1$ candles, while the only means left 
the consumer to get the light he requires from this deteriora- 
ted gas is to burn more of it, as we have all been doing through 
the past winter. If we now take into account the well known 
ct that gas of less.illuminating power has less density, and that 
gas of less density passes more rapidly through a given aperture 
than gas of greater density, we have another cause oped to 
increase the consumption. In Hedley’s experiments e Argand 
burner which gave the light of 25 candles when supplied with 
8 cubic feet per hour of gas from Welsh cannel coal, with a spe- 
cific gravity of ‘737, required no less than 74 cubic feet per hour 
to give the same light, from the same burner, when the gas was 
~re from the Newcastle coal and had a specific gravity of only 
_ Again, as we diminish the illuminating power of the gas we 
merease its heating power, and this necessarily brings with ita 
higher temperature given to the burners, @ higher temperature 
given to the gas passing through them, and again an incr 
rapidity in the flow. It is thus manifest that the public are 
aced in a peculiarly unfortunate position, since all the mistakes 
that are likely to occur in the process of manufacture are mis- 
takes that must inevitably increase the bills of the consumer and 
the profits of the manufacturer. If the workman fails to raise 
the heat with proper rapidity, if he overlooks a retort and allows 
the heat to continue a little too long, if towards the close he al- 
lows the heat to rise a little too high, the result is inevitable the 
_— is deficient in oe power. Or if on any one 
y @ little more gas is produced than is legitimately required, 
the surplus remains in gasometer to vitiate the supply of to- 
