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 



