106 REPORT — 1844. 



On a comparison of the above table, it will be seen that the generative 

 powers of a boiler do not depend upon its cubic contents, nor yet upon the 

 quantity of water it contains, but upon the area of flue surface exposed to 

 the action of heat ; and that the nearer the area of the flue surface approaches 

 the cubic contents, the greater the ceconomy and more perfect the boiler. 



This has been proved by experiment, and also by practice in the use of 

 No. 6 and 7 boilers, where the generative powers have been much increased, 

 and where they approach nearer to the maximum than any other, excepting 

 probably those with a number of small tubes, such as the locomotive, and 

 the present construction of marine-boilers. These latter are however not so 

 well adapted for stationary purposes, nor yet are they calculated for the at- 

 tainment of other objects contemplated in this report. 



It has already been stated that the relative areas of fire-grate and fine 

 surface, taken from a series of observations, are as 1 to 11*, and in the 

 average of Cornish boilers as 1 to 25. Now, if we take the mean of these 

 two, and fix the ratio at 1 to 18, we shall have a near approximation to a 

 maximum eft'ect; and, for general practice, it will be found that such a pro- 

 portion will better serve the interests of the public, and of parties employing 

 steam-boilers, than the extreme of 1 to 25, or 1 to 30, where a great increase 

 of boiler power must be the result. In many situations, such as the large 

 manufacturing towns, this cannot be accomplished, and to enforce such a 

 regulation by legislative or municipal enactments would be, to say the least, 

 inexpedient and oppressive. Taking, therefore, the experiments, observa- 

 tions and other circumstances bearing upon these points into consideration, 

 it will appear that the circular boiler, with an enlarged and extended flue 

 surface, and accurately proportioned furnaces of about 1 to 18, is the best 

 calculated under all circumstances for the ceconomy of fuel, and those objects 

 which have yet to be considered. 



III. The Temperature of the Furnace and the surrounding Flues. 



It is a difficulty of no ordinary description to ascertain with sufficient ac- 

 curacy the temperature of a furnace. In fact every fire and every furnace is 

 continually changing its temperature, as well as the nature of the volatile pro- 

 ducts as they pass off during the process of combustion. When a furnace is 

 charged with a fresh supply of fuel, its temperature is lowered, and that from 

 two causes : first, by the absorption of heat which the cold fuel takes up when 

 thrown upon the fire ; and, secondly, by a rush of cold air through the open 

 door of the furnace. Attempts have been made to remedy these evils by 

 the aid of machinery and continuous firing, but taking the whole of the exist- 

 ing schemes into account, and bestowing upon them the most favourable 

 consideration, it is questionable whether they are at all equal (either as re- 

 gards efficiency or ceconomy) to the usual way of working the fires by hand. 

 I am persuaded the latter plan is the best ; and provided a class of careful 

 men were trained to certain fixed and determined regulations, and paid, not 

 in the ratio of the quantity of coals shoveled on the fire, but in proportion to 

 the saving effected, we should not then have occasion for the aid of machinery 

 as an apology for ignorance. 



Operations of this kind require but a small portion of physical strength in 

 supplying a furnace with fuel (which a machine can do), but some measure of 

 intelligence is necessary to watch over and assist nature in the development 

 of those laws which regulate as well as govern the process of combustion. 



* Since the above was written, I have received from my friend Mr. Andrew Murray of tlie 

 Royal Dockyard, Woolwich, a series of experimental researches, some of which will be found 

 at the close of the report. 



