CIRCULATING PIPES, DAMPERS, &c. 15 



revolutions per minute in most cases, it will be seen that the demand for steam is wonderfully 

 less in the latter, than in the former case. There being two engines employed, and each 

 making two strokes to effect a revolution of the wheel, four cylinders full of steam are consumed 

 in the same time, though of a pressure less than that on the safety-valve : independently of 

 expansion, the pressure of the steam is diminished by condensation in the passage through the 

 steam pipes and jackets, which, by the bye, is very considerable in those vessels fitted with 

 the cylinders forward. Now, the loss of heat by radiation from the steam pipes, cylinders, 

 and slide casings being constant at all speeds, the saving, by dispensing with the use of one 

 or more furnaces, will fall short of the expectations raised by their temporary disuse, 

 inasmuch as the remaining furnaces require to be urged. A furnace cannot be thrown out of 

 use with economy, when the fuel contained in the remainder must be disturbed often before 

 it is fairly consumed ; and this must be the case, unless the mouth of the furnace unemployed 

 be closely covered in, the in-draught of cold air through the same being a great drawback on 

 the effect of the other furnaces : hence the greatest effect will be produced when an entire 

 boiler is thrown out of use. When one furnace only of a boiler could be dispensed with, I have 

 often found it most economical to burn the ashes of the rest therein, mixed with a little coal ; 

 and when too dirty, or the draught too much impeded by clinker, another furnace performed 

 the same office, while it was thoroughly cleared out, and became an active furnace ; and so on 

 in turn with the rest. 



26. Since it has been shown that the consumption of fuel, on principle, should be expected 

 to be in proportion to the revolutions of the wheel, but that in practice it is found to be much 

 greater, the masses of the boilers, cylinders, pistons, &.c. &c. having at all speeds to be 

 maintained by the steam at its own temperature, it follows that the less these parts are 

 exposed, the better ; and if radiation were prevented by completely covering the boilers, steam- 

 pipes, and cylinders with non-conducting materials, the saving of coals only would soon amply 

 return the cost, particularly in sea-going vessels, where gain cannot at all times be effected 

 by bearing up for a port, but where the gale must be struggled with for many days together, 

 not to mention the constant injury sustained by bulk-heads, comings, and decks, by the 

 overpowering heat to which they are submitted. The frequent repairs and renewals of these 

 parts only, amount to no small cost per annum in Her Majesty's steam vessels on foreign stations. 

 Economy of fuel on long voyages has not, I am prepared to say, met with the attention it 

 deserves: stokers consult their own convenience ; and as long as they keep plenty of steam 

 flying off to waste, they are seldom called to account : as to myself, I have found the greatest 

 difficulty in obliging them to keep the fires uniformly. In a gale of wind, and then only, when 

 the labour was little on the fires, and when it became a consideration with every one, both on 

 deck and below, to eke out the means of arriving at the destined port in safety, the fires were 

 minutely attended to, and the fullest effect obtained at the least possible expense : a few 

 clinkers only, and no ashes, which should never, in iron boilers, be allowed to remain 

 longer than two hours in the ash-pits, or in contact with the boilers on the stoke-hole 

 plates, were thrown overboard twice in twenty-four hours, when such discipline was 

 observed, and this with the Welch coal. How much greater would the gain be at all times, if 

 the oppressive heat, which drives the fireman from his quarters now, were removed, so as 

 to permit him to dispose a less portion of fuel to a wonderfully increased advantage ? These 

 considerations are by no means visionary ; the people in Cornwall understand them well, and 



