422 
STEPHENSON’S PATENT 
cleaning out the fire-box and removing the sediment that is deposited from the water. 
Two mud holes, at opposite corners of the fire-box, are usually opened twice a 
week, and the deposit washed out by directing a stream of water into them; each 
pair of opposite holes being opened alternately. The boiler does not often require 
cleaning, but it is occasionally washed out by putting the water hose in at the man 
hole, and washing all the sediment into the fire-box ; this is found to be quite suf 
ficient to keep it clean. 
Blow-off Cocks.—R R are two cocks, one inch in diameter, fixed one in each 
side of the fire-box, close to the bottom, for the purpose of emptying the boiler; 
this is called blowing off, as it is done just after the engine has left work, and the 
water is blown out with great force by the pressure of the steam. This blowing 
off serves to cleanse the boiler, and the whole water has to be thus emptied out 
two or three times a week when the engine is in full work, as it gets foul after 
remaining in the boiler for some time. 
Fire and Heating Power.—The fuel used is coke, and is that most generally 
used in locomotives; coal was employed in the first ones, and is now made use of 
on railways in the collieries and where passengers are not carried; but on the 
large public railways it is inadmissible on account of the smoke that is produced. 
Coke has an advantage over coal in being very light in substance and not caking 
together, but allowing the draught of air to pass freely through the fire; it is also 
capable of attaining a very intense degree of ignition ; but its lightness renders it more 
liable to be drawn through the tubes by the draught, and the fine dust or ashes, pro 
duced by its combustion, is very annoying to outside passengers. The coke used is 
of the best quality; and the operation of coking the coal is performed only with a 
view to the abstraction of the volatile parts, as the hydrogen, and the losing as little 
as possible of the carbon; gas coke or the remains of the coal used in gas works is 
very inferior, being overburnt and having lost a good deal of its carbon to form the 
gas, carburetted hydrogen; it also contains a good deal of sulphur, which is very in 
jurious to the metal of the boilers; this causes also the principal objection to the 
use of coal. The coke used in the locomotives on the London and Birmingham 
Railway is made upon the works, and is very nearly pure carbon. Welsh stone 
coal or anthracite has been also tried ; it produces no smoke or flame, being almost 
pure carbon, like coke; but it appears to be not suited to locomotives, from its den 
sity and flying into small pieces, so as to form a close mass on the fire-grate, and not 
allow a sufficiently free passage for the air through the fire. 
The fuel is carried in the tender behind the engine and immediately contiguous to 
the fire-door, so that it can be readily shovelled into the fire when required; it is sup 
plied on an average in quantities of about half a cwt. at intervals of from five to ten 
minutes. The heating the water in the boiler and getting up the steam takes about