384 Mr Anderson on the Illuminating Poxoer of Coal-Gas. 
for the purpose of extending them to streets where they are not 
yet laid. 
This result, which greatly exceeds what has been obtained by 
means of an equal number of retorts ^ at any coal-gas work in 
the kingdom, I ascribe much less to the quantity of gas which is 
decomposed from a given weight of coal, than to the processes 
of purification by which the gas is prepared for consumption, in 
consequence of which, it retains nearly the same proportion ofsu- 
per-carburetted hydrogen, as the best oil-gas. In fact, the quan- 
tity of gas procured at the Perth Gas- work, from a certain weight 
pf coal, differs little from that which is usually stated to be ob- 
tained at ether coal-gas establishments, from the same species of 
coal ; being, when the coal is carbonized for three hours, about 
four cubic feet from the pound, and, consequently, about 9600 
cubic feet from the quantity of coal daily subjected to distilla- 
tion. 
This quantity of coal-gas, according to the report submitted 
by Taylor and Martineau to the Dundee Gas Company, would 
not give a light equal to that which is in reality afforded by the 
burners used in Perth above two hours daily, which is only about 
a third part, at an average, of the time they actually burn. We 
are thus compelled to admit, either that these individuals have 
grossly underrated the illuminating powers of coal-gas in general, 
or that the gas manufactured in Perth, possesses nearly three times 
the illuminating quality of the coal-gas to which they refer. The 
former of these conclusions, notwithstanding the obvious interest 
which Taylor and Martineau have to undervalue the properties 
of coal-gas, cannot, in justice to their characters, be admitted ; 
and, on the other hand, the alternative would imply, that the 
Perth coal-gas is of a quality so superior to the ordinary kind 
* In the report furnished by Mr Tait to the Dundee Gas Conopany, the quan- 
tity of gas requisite to maintain 700 burners is estimated at 6,336,^50 cubic feet 
annually; and the quantity of coal necessary for its production, at 528 chaldrons, 
or 71^1 tons. By the mode of decomposition and purification practised at Perth, 
the same extent of illumination will be procured from 180 tons of coal. Mr Neil- 
son of Glasgow', in his report to the same company, estimates, that a gas esta- 
blishment, supplying 5000 jets, would require 3^ tons of coal daily. The Perth 
gas-w'ork now' supplies about 80QO jets, by means of less than a third -part of that 
quantity of poal. 
