234 REPORT — 1872. 



The way in wliicli wasto arises from these causes is, that unnecessary air is 

 introduced into the fire at a temperature of, say, G0°, and that this air has to be 

 heated, and then (even if the lieat he abstracted from it, as far as practicable by 

 the boiler) it will escape up the chimney at a temperature of from 200° to 300° in 

 excess of that which it had; and the whole of this excess represents wasted coal. 

 Thus, on the one hand, it is of importance that there should bo a proper amount of 

 air to secure the perfect conversion of the carbon into carbonic acid ; and, on the 

 other hand, it is most desirable that this amount should not be exceeded, involving 

 the necessity of uselessly heating air not wanted for combustion. Such a happily 

 balanced state of things it is almost impossible to secure by hand-tiring-, almost 

 impossible, but not absolutely impossible, though only attained at competitive trials, 

 and when these trials are conducted by highljr skilled men. 



In such trials of portable engines before the judges of the Eoyal Agricultural 

 Society of England, the firemen will put coals upon the fire as frequently as forty- 

 five times in an hour, the quantity put on at each time being, as may be supposed, 

 little more than a spoonful. 



Writers on the management of the steam-engine usually advise that the fire-doors 

 should be opened as little as possible, and that the firing should take place about 

 every quarter of an hour. 



Under ordinary circumstances they may be right ; but when it is desired, regard- 

 less of the amount of manual labour, to obtain every particle of useful eft'ect out of 

 the fuel, it is then found to be remunerative to open the door, not four times an 

 hour, but more than forty times an hour, taking care, however, that it is only 

 opened for the fr.action of a second. It is by this frequent feeding of a small 

 quantity of coal, distributed over the fire, that the competitors are enabled to 

 insure a uniforin condition of that fire to receive the action of the air. They know 

 precisely the amount of draught they have got, and by experience they also know 

 what thickness of tire will exactly balance, as it were, the <air that comes through, 

 so that the combustion may be perfect, and yet there may be no free air. But in 

 ordinary hand-tiring, done at intervals of a quarter of an hour, it is obvious that tlie 

 thickness of the tire at the end of such an interval nnist be very difterent from that 

 which it was at the beginning of it, and thus if that thickness be right in relation to 

 the draught at one time it must be wrong at another. At one time, immediately 

 after tiring, there may be a distillation of the coal, producing blaclc smoke 

 and carbonic oxide ; this will go on till the fire burns thin and burns into holes, 

 when there will be a passage of free air. I do not wish to be understood that 

 I am advocating the attendance of skilled firemen to fire forty-five times in an 

 hour. Coal must be far dearer than it now is to make it pay so to occupy a man, 

 or rather watches of men ; for no one man could submit to such continuous labour 

 for more than from four to five hours. But my observations tend to call your attention 

 to the subject of mechanical tiring. I believe that the high evaporative duties that 

 have been obtained by the use of liquid fuel, duties approaching very closely 

 indeed to the theoretical power of that fuel, are largely due to the fact that the 

 air and lic[uid can be injected in definite and regular proportions, insuring perfect 

 combustion. 



Again, in the use of powdered fuel bj' Mr. Crampton, where the powder is blown 

 into the furnace by the very air which is there to enter into combustion with it, 

 ver)' high evaporative results have been reached even under tlie disadvantageous 

 circumstances attendant upon earlj' experiments ; and this also I believe to be due 

 to the power of accurately adjusting the quantity of air to the fuel to be burnt. 



The same power of adjustment may be obtained in those instances where the 

 fuel is previously converted into gas, as practised by Mr. Siemens ; and nearly 

 similar control can be got with ordinary fuel by reverting to some of those systems 

 of mechanical fire-feeding which were in use from twenty-five to thirty years ago, 

 but which have been to a great extent abandoned in consequence of the more 

 general adoption of internal fires and high-pressure boilers. The fires of such 

 boilers are in furnaces of small diameters, which do not admit of the introduction of 

 the apparatus, for which room was readily found below the bottoms of the waggon- 

 shaped boilers fornrerly used for low-pressure steam. Qther modes of fire-feeding, 

 however, have been devised, and have come, to a certain extent, into use. It is 



