the subject, it does seem remarkable that so little has been done in this direction. Of the different fire-feeding machines, as they have been called, that have been employed at different times, I think I am correct in stating that, excepting the one I wish to bring under your notice, Juckes' Endless Chain Grate is the only one that has received any considerable amount of approval. Of the performance of this furnace very conflicting accounts are given; but I believe that under favorable conditions as to fuel, management, and work to be done, when applied to externally fired boilers the performance of this furnace has been found satisfactory. Although the Juckes' grate does, under favorable circumstances, prove the superiority of mechanical over hand stoking, yet it does not, I think, sufficiently meet the engineering requirements of the present time; it has one serious defect: it is only applicable to externally fired boilers, and is very cumbrous. Before describing particularly our furnace, I will speak of what I conceive ought to be aimed at in constructing a mechanical stoker.

"The late Mr. Charles Wye Williams, who has done so much to diffuse and popularize correct views on the subject of furnace management, writes, in his work on the combustion of coal and the prevention of smoke: The facility with which the stoker is enabled to counteract the best arrangements naturally suggests the advantage of mechanical feeders. Here is a direction in which mechanical skill may be successfully employed; the basis of success, however, should be a sustaining at all times the uniform and sufficient depth of fuel on the bars.' This is correct so far as it goes, but a mechanical stoker, to be successful, must do more than this: it must preserve the air spaces of the fire grate uniformly open, be self-cleansing by discharging the ashes, slag, or clinker as formed; and, in addition, I think it is important that the fuel should be introduced at the front of the furnace, and should have a progressive motion towards the bridge. The advantage of introducing the fuel at this part, as a means of insuring economy and preventing smoke where bituminous fuel is used, has been proved conclusively by numerous experiments. I suppose the cause of this is the long run of the volatile hydrocarbons over the incandescent fuel that fills the bridge part of the furnace. It is also important that the machine stoker should be easily regulated and controlled for the purpose of adjusting the supply of fuel to the work to be done, and that it should be very little liable to derangement, or wear and tear. I think our apparatus fulfils all these conditions. Like all fire-feeding machines, it is provided with a hopper or fuel receptacle; the fuel is forced into the furnace by two plungers or pushers (having an alternate motion) at a level of about 6 inches above the bars. In very wide furnaces we use 3 plungers, and the shaft that works the plungers is moved by a ratchet. A very simple arrangement enables the attendant to vary the rate of feed by causing the diving eccentric at each stroke to take a lesser or greater number of teeth. Progressive motion is given to the fire by causing the bars to move forward en masse, and bringing them back in detail. The

cleansing of the bars is also effected by this motion: the bars have a stroke of about 3 inches, and we find in the average of cases that a complete stroke about every 2 minutes is sufficient to give the progressive motion necessary to maintain a proper thickness of fire. As the bars themselves form an important part of the machine, we have found it necessary to make special provision for their preservation. Each movable bar is provided with a trough containing water, and there is a centre rib cast on each bar which is immersed in the water. The other part of the bar forms a perfect cover for the trough to exclude ashes, etc.; these troughs are supplied with water from a small cistern, and the level is maintained by a very sensitive float and valve. In conse quence of the slow motion of the machine, very little wear and tear occurs in the working parts. There is no part of the apparatus exposed to any injurious action of fire except the upper surface of the bars, and these are effectually protected by the trough arrangement. Our experience shows that with moderate care the amount of wear and tear is not greater than what occurs in most ordinary furnaces.

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With regard to the economical results obtained, you will find some particulars given in our circular. As compared with the best hand-firing, where ordinary fuel is used, the results do not exceed 10 to 12 per cent. We find that the system adopted by the careful stoker and the machine system are very similar. In both cases frequent charges at short intervals are adopted instead of heavy charges at longer intervals; but, in the case of handfiring, the incessant opening of the doors, and the interruptions caused by cleaning the bars, are drawbacks that are avoided in the machine. Of course, when the machine is compared with ordinary random hand-firing, its economical superiority is very decided; but the chief source of economy arises from our being able to use the smallest and cheapest fuel, fuel much of which cannot be used at all in ordinary hand-fire furnaces. The saving from this cause varies in different districts, and will range from 20 to 100 per cent. In most cases, perhaps, the appreciation that leads to the adoption of any machine or system is the most satisfactory evidence of its value; yet this is not a rule without numerous exceptions, and on no subject is there more reasonable ground for a justifiable scepticism as to the merits of any remedy that may be propounded than that of smoke prevention. many years the public have had plans constantly brought under their notice that were to end the nuisance arising from smoke, but it still continues a very substantial nuisance, and appears to have a very wonderful vitality. As evidence of approval of the furnace, I may state that since we commenced manufacturing this form of furnace, about 18 months ago, we have fixed and put to work more than 120, with the most satisfactory results, and approval of the furnace is extending. We are at present sending out more than 20 per month; in the town of Bradford alone, which appears to be taking the lead in the enforcement of sanitary improvements we have orders for between 50 and 60 furnaces in a single street or road, Thornton Road.

For

"To prevent misapprehension it is as well to state that we have been, for a period of 5 or 6 years, engaged perseveringly in efforts to perfect mechanical stoking, but our first attempts were only partially successful. Our first grate was a modified Juckes; but we soon found the wear and tear so considerable that we had to turn our attention to discover some means of remedying these very serious defects, and for more than 3 years we were engaged in extensive experiments involving much thought and money expenditure. The result is the machine I have the honor to bring under your notice."

Mr. Lavington E. Fletcher, C.E., said he had witnessed some very carefully conducted trials with this apparatus used against careful hand-firing, and the results were very satisfactory. The chairman said there was no doubt that mechanical stoking must be superior to hand stoking. Such an apparatus as had been described by Mr. Smith was wanted, and it was only a question of cost. Mr. Smith then thanked the chairman and gentlemen for their attention, and said he would be glad to show any gentleman the furnace at work who would favor Messrs. Vicars with a visit to their works, Seel Street, Liverpool.

EFFICIENCY OF FURNACES AND MECHANICAL FIRING.

Having for some time past given a large share of my attention to the subject of the efficiency of furnaces, I have to bring before you a few results of my experience in this most interesting and important inquiry.

Since the time in which Wye Williams lived and labored, Professor Tyndall and Dr. Frankland have shown that the energy of combustion is within wide limits independent of the density of the air, the natural inference at first sight being that in furnaces the temperature of the air does not affect the efficiency. One of Wye Williams' well-known experiments was to introduce a bent plate perforated with 56 half-inch holes into the centre of a furnace where one or two bars had been removed for its reception. "Adequate mixture," says Mr. Williams, "was thus instantly obtained, as in the argand gas-burner; the appearance, as viewed through the sight-holes at the end of the boiler, being even brilliant, and as if streams of flame instead of streams of air had issued from the numerous orifices. It is needless to add that nowhere could a cooling effect be produced, notwithstanding the great volume of air introduced."

Now I cannot at present do more than state the simple fact that I have tried similar arrangements in many different instances and under several different conditions, and that I have rarely failed to produce a cooling effect. The arrangement by which the results have been arrived at may be thus described: A few of the ordinary fire-bars are removed from the centre of the flue. A pair of longitudinal bearers about 6 inches apart are then introduced, their upper surfaces being level with the common firebars. On these bearers are placed small arched transverse bars, each about 1 inch thick, in contact with one another. Semi-circu

lar holes are cast in the transverse surface of these bars, so that when placed together on the bearers they present the appearance of a tunnel about 9 inches high pierced with numerous small holes, an arrangement not differing widely from that of Wye Williams, except that the tunnel, being of loose cast-iron pieces, is no more liable to deterioration by heat than common fire-bars. If the mere fact of admitting air to the hydrocarbons at the moment of their generation, and in minutely divided lines, is sufficient to insure their combustion, surely nothing could do so more effectually than this arrangement. But the result.

A large quantity of fuel being placed upon the incandescent carbon in the furnace, we have, after the expiration of a few seconds, a splendid display of white flame, not entirely smokeless, but comparatively smokeless, unless the quantity of air admitted is very large; white flame and intense heat, - evidence of the precipitation of the carbon particles and of their combustion after precipitation; smoke-burning, -not smoke-prevention; greatly increased temperature of the furnace-door, - evidence of increased radiation of heat. But, as I said before, in almost all cases a loss of efficiency in the furnace, ―a reduction in the absolute temperature of the flame. Was Mr. Williams deceived by that radiant heat? I cannot avoid the conclusion that he was in some cases at least. But the furnaces adopted with economical results contained elements not yet described. The ash-pit was divided into 3 chambers by 2 vertical sheet-iron partitions, made fast to the longitudinal bearers in such a manner that all air entering it at the central chamber must pass through the arched bars, while that entering by the two side chambers reaches the fuel in the ordinary manner. Now, observe the difference: Here we have a long central fire-chamber open to the air only at one end. The air before entering the fire-chamber passes over the surface of highly heated sheets of iron, traverses in turn the cross-pieces of the little arched bars and the heated surface of the ribs. Even with this simple change the results are, I believe, in all cases, altered from failure to success. A heating effect has been obtained where a cooling effect only could be produced before.

To sum up my own observations on this subject, I find: (1.) That the admission of cold air in quantities sufficient for the complete combustion of the gases in ordinary furnaces is attended with a loss of efficiency in all cases, even if that admission takes place in finely divided streams immediately over every portion of the fuel from which the gases are rising. Radiant heat, and consequent temperature of the furnace door, are enormously increased; smoke, however, is considerably reduced. (2.) That by the comparatively slow motion of air over heated surfaces, and its consequent rarefaction and increase of velocity when issuing from the orifices of the arched bars, a much more perfect chemical union is insured. The flame is not so luminous, but a higher rate of efficiency is obtained. Radiant heat is decreased, the furnace door is rendered less hot, and smoke is more perfectly prevented. The old Cornish system of dead-plate firing, when conducted very carefully, and in such a manner that the incan

descent fuel at the back of the furnace is never allowed to burn into holes, has, as we all know, certain advantages. But when the back of the furnace is left to itself, I believe it to be a most difficult matter to avoid the admission of cold air en masse, a condition which cannot but be attended with loss of efficiency; and in my attempts to discover the best method of mechanical firing, I could not find that those systems in which the coal had a progressive motion from the front to the back were free from these defects. Such methods appear to me to owe their advantages, for no doubt they have advantages, to other causes than that of the perfect combustion of the hydrocarbons; and is not the comparative freedom from smoke in this system of firing the result, in a great measure, of that union of carbon from the front with carbonic acid from the back, producing carbonic oxide, and inevitable loss of heat, the pernicious principle resorted to by a whole army of smoke-burning patentees? The apparatus which appears to me most correct in principle does not profess to compete with the more perfect mechanical stokers, inasmuch as the clinkers are removed by the firemen in the ordinary manner. In short, since my attention was drawn to the subject, I have come to the conclusion that the principle of what was probably the first attempt ever made in mechanical firing - I speak of Stanley's patent is capable of the highest possible efficiency. Twenty years ago nearly every furnace in Lancashire was fed by the apparatus popularly known as the "hopper." In a box on the front of each furnace 2 fans revolved horizontally. Fuel was drawn from a hopper by rollers which crushed and let it fall on to the 2 fans, which in their turn propelled it into the furnace. It was possible to adjust the speed in such a manner that the fuel was spread uniformly over the whole surface of the bars. I would merely add that when the 2-flued Lancashire boiler replaced the wagon and egg-ended boilers then in use, the hoppers were taken down, possibly in some places applied to the new flue boilers, found not to throw the fuel evenly over the bars, and discarded. In Leeds, however, they are still in use to a considerable extent, probably because some makers there took the trouble to adjust them to their altered circumstances. For a single 2-flued boiler the hopper, as now in use at Leeds, requires about 20 toothed wheels, and at least 2 worms to drive the crushers and other portions; and notwithstanding the fact that the teeth of those wheels are constantly breaking, and that the whole apparatus trembles under the sudden check caused by a large lump of coal falling between the small crushing rollers, manufacturers who have tried it for so many years give universal testimony as to its economy. I understand that one engineer in Leeds still makes a considerable number of them. This apparatus does not, of course, prevent smoke, but it distributes the smoke from a given quantity of fuel over a longer period than in hand-firing, and reduces its blackness in the same proportion.

Now, does it not appear that if we can retain the manner of throwing on the fuel, very considerably simplify the means, and use it in conjunction with the fire-bar arrangement already de