To this area may be added six square feet for every four furnaces beyond the first-named twelve, and the height need not exceed 150 feet above the furnace grates, unless the site is low compared with the district which the destructor has to serve. When using forced draught, the minimum flue area of the stack should also be 20 square feet, but in this case it will be sufficient for eighteen furnaces, and only one square foot need be added for each ad- ditional furnace. A height of 120 feet will exceed the require- ments of the furnaces, which at the furnace doors should register •25 inch water gauge, as the undergrate pressure of blast per- forms the chief duty of the hitherto extremely tall stacks. In practice it has been found that forced draught furnaces work very well with stacks 60 feet high, and the greatest possible quantity of refuse can be properly incinerated in the furnaces with forced blast and such dwarf stacks. Nevertheless as even the purest gases from the most efficient furnaces are still un- welcome in a residential district, it will be far better to continue the idea of dispersion of the gases for some time to come. 76 THE ECONOMICAL DISPOSAL OF TOWN REFUSE. Forced Draught. The pressure required for efficient working with forced draught varies according to the thickness and the density of the material on the grates, but it should not at any time exceed 1 *25 inch water gauge, and the flue dampers should be so regu- lated as to obtain not more than * 25 inch induced draught at the furnace doors, and these are the limits of pressure and draught for good working. To use a greater pressure more work is thrown on the stokers, as the fires burn hollow and blow into holes, which if not attended to allows the blast to escape, and not only reduces the pressure and rate of work, but the temperature in the flues also. Eotary blowers of the very best make should be fixed in large open places as free from dust as possible, the inlets drawing the supply either direct from the outer air or through very capacious trunks, and driven by encased engines or electric motors. The air conduits to the furnaces should be quite four times the combined area of the blast inlets in ashpits, and the exhaust steam of the engines should be mixed with the blast by means of annular nozzles, by which system the grates will be as durable as when steam-jets are used, and a similar chemical action will take place in the incandescent part of the fires. To settle the comparative efficiency of rotary versus steam- jet blowers, the author made some experiments in 1893 with a furnace of the standard type, having 25 square feet of grate surface. In each experiment the furnace was got to full heat before commencing to record the results, and every care was taken to ensure precisely similar conditions for each test. The steam pipes were well covered with hair felt, the steam pres- sure was kept at 80 lb. during each trial, and the blast mains and blower outlets were all 9 inches in diameter, which is the minimum for 25-feet grates. The first experiment was with a Korting steam-jet blower, the initial nozzle being -25 inch diameter, which gave a pres- sure of *20 inch water gauge. The second experiment was with a small high-speed engine geared direct to a Sturtevant rotary blower, and by using exactly the same weight of steam the pressure was increased to ■ 60 inch. In these two experi- ments the furnace gases passed through a multitubular boiler 10 feet long and 6 feet diameter to a stack which was 40 feet high above the grate. Two other experiments were afterwards made without the boiler, and the furnace gases passed direct to a special chimney only 12 feet high over the furnace, and it was found that with the same blast pressure the incinerating THE ECONOMICAL DISPOSAL OF TOWN REFUSE. 77 power of the furnace was as nearly as possible the same as before, which indicated the extra duty the stack has to perform when steam generators are used. A fifth experiment was made with four Korting steam-jet blowers of the same size as the one used in the first experi- ment. These were fixed to a sole-plate at the top of the chimney 12 feet above the furnace and used as exhausters. The ashpit doors being open, it was found that the in-draught at the furnace doors was only *25 inch water gauge. The power of the furnace was considerably less than in the other experiments, although using four times the quantity of steam. The result was anticipated, but the experiment was made to convince certain parties of the folly of using steam-jets to any large extent in chimneys. Boilers and Eesults. Destructor boilers have been set in many different ways, a large number of the small multitubular type having been set over the fires, without any intervening arch, and consequently the combustion was not quite perfect. Other boilers of larger capacity have been set alongside the main flue not far from the destructor, but in almost every case the flue area about the boilers has been very contracted, and the heated gases could not be fully utilised. Radiation should be prevented as far as possible by building all the exterior work with a space between the inner and outer walls, a system which the author has used for nearly thirty years with great success, and which has been adopted by several engineers in plants of recent date. Experiments made by the author over twenty years ago proved that where it was impossible to obtain a temperature of 1200° F. with solid walls, a tem- perature of 2000° was easily maintained when spaces were formed in all the outer walls and coverings. It is most important that every boiler which is fired with fuel of any kind, should have a good chimney damper, and that the practice of regulating the steam supply by the opening of furnace doors or closing of ashpit doors, should not be resorted to when the use of the damper would have the same effect, as the boilers often suffer more from the want of clampers than from performing their actual work. Generally the steam generators which were used for many years after the introduction of destructors, were unavoidahlv of the multitubular type, the heated gases passing through the tubes and surrounding flues. The maximum steam pressure 78 THE ECONOMICAL DISPOSAL OF TOWN REFUSE. was for a long time only 80 lb. per square inch, and it was very seldom that any more than 60 I.H.P. was utilised from the largest installation. Lancashire boilers are now used with very fair results, and under the Meldrum system a pressure of 120 lb. can be easily maintained. The additional element in details which has led to the extended use of these boilers, is the recuperator by means of which hot air is obtained after gases have passed the boiler, and it is drawn to the ashpits by steam-jets of the Meldrum type. Within the last few years water-tube boilers have become more common, and they are no doubt the most suitable type if properly set, and when arrangements are made for catching the mud in the water and steam drum, so that the steam generating tubes may be kept perfectly clean. To back up this theory the Standard Furnace Company supplied a boiler with such improvements for the St. Pancras plant 3J years ago, which has worked continually ever since. The mud from the upper drum when dried and weighed averages 30 lb. per month (Fig. 11). The thermal storage system, as designed for Shoreditch, in connection with water-tube boilers for a maximum pressure of 400 lb. per square inch, necessitated a very heavy initial outlay, altogether out of proportion to any possible advantages, as all the pipes, valves, and fittings had to be strong enough for the full pressure, and extra covering was also necessary on all steam charged vessels and hot feed pipes to provide for increased temperature. The temperature of steam at 120 lb. pressure being 341° F., and at 400 lb. pressure 444° F., the gases leaving the boilers carry away a very high thermal value, and although an economiser may be used for utilising some part of it, most excellent results are obtained at other places without econo- misers, and it now appears that Shoreditch works very well at a pressure of 150 lb. Taking an average of several systems, it is found that 1 '26 lb. of water can be vaporised by 1 lb. of average unscreened refuse, when burnt in well-constructed furnaces, and assisted by a forced draught at a pressure of 1 * 25 inch water gauge. By the use of screened refuse, 1 ' 89 lb. of water can be vaporised per lb., but as it requires at least three tons of unscreened to produce two tons of screened refuse, there is no advantage in adopting screens, but on the contrary there is a loss of labour, as well as increased first cost and value of the extra space occupied. the economical disposal of town refuse. 79 Fire-Grates. Several systems of moving fire-bars have been used for nearly twenty years, the primary object being to break up the clinker, and open the air spaces, and thus permit of a more regular and perfect combustion of the fuel than is possible by any arrangement of firing where fixed bars are used. In the year 1881 the Galley rocking-bars were introduced, but the teeth were too short for destructors ; then came the Stevenson and the Settle rocking-bars, which had longer teeth, and also the duplex rocking-bars, which were introduced by the author in the year 1887. Of the first-named systems of bars, three were rocked from or near the centre of the webs, and they moved in one direction at the will of the operator, but the du- plex motion bars were geared so that the even number bars moved backward when the odd number bars moved forward, and the clinker was lifted and broken up (Fig. 1). All these different designs of bars were laid across the furnaces, and con- nected by link bars to a simple knuckle attachment under the dead-plate, which was operated by a movable lever. Forwarding bars, which run from back to front of grates, and are operated by eccentrics or cams at one end only, are capable of feeding the furnace, and at the same time delivering the clinker, and by the use of such mechanical arrangements, where properly set up and attended to, the labour of working destructor furnaces is reduced very considerably, and the steam raising capacity of the plant is greatly improved (Figs. 2 and 3). The author has given special attention to this method of stoking for several years, and the only drawback against its use was the necessity of lubricating the cam shafts, which, by the use of forced blast improperly applied, wore out with twelve months' work. When forced blast is used in connection with such bars, the wall boxes and bearings should have a supply direct from the mains, so as to prevent fine dust being blown into them, in other words an equilibrium of pressure should be set up in the gearing boxes. Generally the air spaces between the fire-bars of forced-blast furnaces need not exceed one-fourth of an inch, and the spaces between the bars of natural draught furnaces should not be more than three-eighths of an inch, because an excess of width permits a large proportion of small combustible matter to pass to the ashpits unburnt. The same remarks apply with equal force to fire-grates which are used for burning coal-slack or coke, yet it is well known that many extensive users of steam, in- cluding some large engineering firms, have grates with airspaces nearly an inch in width. 80 THE ECONOMICAL DISPOSAL OF TOWN REFUSE. Kegularity of Operations. In the firing of any kind of furnace, whether by hand or by mechanical means, it is of the greatest importance to observe a regular cycle of operations, so that there shall be a continuity of work and uniformity of temperature, not otherwise obtainable but at all times possible, and which is the best way of ensuring the greatest efficiency of any plant, both as regards the quantity of refuse burnt, the thermal value of the effluent gases, and the vitreous character of the clinker. When the workmen are left to their own devices, it gene- rally means that all the furnaces are clinkered as rapidly as possible, charged up or levelled down with corresponding ex- pedition, and then there is an interval for what appears to be well-deserved rest ; but during the earlier part of that interval the furnaces may be sending forth volumes of unburnt gases, and the temperature will suddenly fall as much as 700° F., simply because all the work is allowed to be done in an inter- mittent manner, instead of making the work extend over a period which equals the time of a full cycle. Modern Furnaces. During the past seven years very considerable improvements have been made to the Fryer type of furnaces by Messrs. Boulnois, Wood and Brodie (Fig. 4), including charging appa- ratus, movable fire-bars, and setting boilers. The charging apparatus consists of a tank with several compartments, and is constructed to run upon rails over the furnaces, and provided with automatic gearing for opening and closing the furnace charging-hole. Each compartment contains sufficient refuse for a charge, and any part of the tank can be readily put into position, either to receive the refuse from the vans or to charge it into the furnace. A water-tube boiler is set between each pair of furnaces, and the effluent gases of the furnaces enter the boiler chamber through side outlets near the front, and after passing between the boiler-tubes in the usual way they escape to the chimney flue. A fire-grate is provided for each boiler, which may be used either as a cremator or to help in generating steam when refuse is scarce or when the demand for steam is suddenly in- creased. This arrangement of boiler-setting takes up more space and exposes a greater surface for radiation from one unit of plant than an overhead system of boilers. The fire-bars are of peculiar form, the upper end having a quick curve, and THE ECONOMICAL DISPOSAL OF TOWN REFUSE. 81 alternate bars are rocked at intervals by means of toggle-gear and a cataract arrangement, which feeds the charge forward and at the same time opens the air spaces. The combustion is assisted by forced draught obtained from rotary blowers of the Sturtevant type, and altogether very satisfactory results have been obtained, both as regards the quantity of refuse burnt and the steam produced. A great many authorities have adopted the Horsfall furnace, the gases from which have never caused any serious nuisauce, and for which no form of cremator has ever been required to deal with them. The outlet flues are in the roof near to the front and the effluent gases pass over the furnace crown, and then through down-flues to the main flue which leads to the boiler and chimney. The improvements made by Mr. G-eorge Watson allow of the charging holes being arranged centrally, so that each charge can be pushed fairly down the slope with- out much side work in spreading the same. For a plant of, say, four to eight furnaces, a steam generator is set alongside the main flue not far from the last furnace, and up to this point the flues are generally at a red heat, but so far the generating power has not been fully used. Cast-iron boxes are built in the side walls of the furnace above the fire-grate, through which the air blast is led to the underside of the grate, and the cooling* effect of the air prevents the clinker adhering, as it generally does, to the sides of brick-lined furnaces, and makes the clinkering far less laborious. A special design of steam -jet apparatus is used for forcing the draught, which is conveyed in very large flues to the furnaces, but the use of these flues was known before the date of Mr. Watson's patent, and he has been good enough to inform the author that his claim is narrowed down to the com- bination of the air ducts. Generally this furnace has a broad likeness at first sight to the design which was patented by the author some years prior to that date, and there is no reason why both designs should not give equally good results (Figs. 5 and 6). The Warner furnace has been adopted to a very large extent, and is now combined with steam generating (Fig. 7). It has an inclined grate and back hearth, and over the latter are charging hoppers which are fitted with falling flaps, so as to drop the charge upon the hearth. The flue outlets to the boiler are at the sides, and when the heat is not required for the boiler, the effluent gases pass oft' through an outlet at the back end of the furnace. By the use of forced draught from rotary blowers the combustion of the refuse is rapid and perfect, and there is a simplicity in the working of this apparatus which 82 THE ECONOMICAL DISPOSAL OF TOWN REFUSE. is commendable. One boiler and two furnaces form one Unit of plant, and below the boiler there is a good dust pocket. Hocking bars are used for the fire-grates of the type indicated by Fig. 1, and the complete apparatus is thoroughly reliable. The Beaman and Deas furnace is very similar in its general outline to the furnace introduced by the author in conjunction with water-tube boilers in 1880, which were set between the furnaces for the first time as a combined apparatus (Figs. 8 and 9). The method of feeding the refuse is more laborious than for any other system at present in use, partly in conse- quence of the furnace doors being at the sides, whereas for all other systems the designers have put the doors at the front. Forced draught is obtained from rotary blowers, and the com- bustion of the gases is completed at a very high temperature, and the latter is taken advantage of for generating steam in water-tube boilers. The boilers are set on the same level as the furnaces, but on the opposite side of the main flue, and the outlet end of the boilers rests over the chimney flue. This class of plant is not as compact as some of the others, and the loss of heat by radiation and absorption is unavoidably greater. The Meldrum recuperative furnace is associated with hand- firing and Lancashire boilers, but remarkable results have been obtained, and it must now rank as a destructor (Fig. 10). The furnace gases from four grates pass into one combustion cham- ber, and the latter also traps the greater part of the fine dust. Thence the gases pass into the tubes and through the flues of a Lancashire boiler, and on emerging from the boiler they are further utilised for heating the incoming air for the furnace. Steam-jet blowers are used for the forced draught, and there is the unavoidable noise which even the late Sir William Siemens failed to suppress. From the results of independent experi- ments already named, this system of drawing hot air from the recuperator must be a great waster of steam. The combustion of the gases is perfect, and the labour of charging is not greater than usual. In front of the furnace, at a convenient distance and level, is a deep hopper for the daily supply of refuse, and there is no nuisance from this system of storage. The furnace, which was designed by the author in 1896 (Fig. 11), is constructed by the Standard Furnace Company, and has the main flue above it, so that the effluent gases can be passed to any of the boilers which are set over it, and any boiler or furnace can be shut off without interfering with the remainder. Any kind of fire-grates may be used, although the author has a preference for mechanical ones, and if properly fitted up, they are undoubtedly the most suitable. In adopting water-tube boilers as at present working at St. Pancras, the author makes the width of the setting much THE ECONOMICAL DISPOSAL OF TOWN REFUSE. 83 greater and the height proportionately less than for solid fuel firing. There is only one bridge over which the gases have to pass to the chimney outlet, and this ensures the lowest velocity of current whilst giving the maximum flue area. Under this system the loss by radiation is absolutely irreducible, and a maximum efficiency is always obtainable, as the generating tubes are kept constantly clean. A most serviceable steam generator for combination with any type of furnace, or, better still, for setting between two common flues, is built up with vertical tubes and top and bottom headers, whilst the latter are connected to opposite ends of an upper drum (Fig. 12). The author's arrangement for drawing off all sediment from the overhead drum will perform the most valuable duty in this modification by keeping the generating tubes clean inside, but in addition they have to be kept clean on the outside, and by the use of scrapers this can be done more effectually than by any other means. This paper would not be complete without a reference to the work of Pickard, Kichmond, Pease, Lupton, Kidd, and Whiley, each of whom has made some discovery in the adaptation of general principles which has since been perfected and adopted by later inventors with more or less success. At1 the end of the paper will be found a Table of results showing the comparative efficiency of working of the modern systems referred to by the author. He suggests the following method of standardising the results of official and other trials. Its object is to enable fair and reliable comparisons of different systems to be made. The various results should be arranged in accordance with the tabulated statement just referred to. In recording temperatures they should be taken hourly for a whole day and then averaged. Injectors should be used for feed water supplied from measuring tanks. Wages to be rated uniformly at sixpence per hour per man. Duration of trial not less than one full week, day and night. The annual amount of sinking fund required to pay off the capital cost and royalties in twenty years, allowing for 3 per cent, interest, should form an item in the table of results. The unit of plant operated upon should be as nearly as possible of the capacity shown in the Table of results. The author uses the following formula for calculating the efficiency of capital and revenue accounts referred to at X as capital outlay, in Table of results. C = Sinking fund for plant of given capacity. W = Net cost of destruction per annum. R = Tons of refuse incinerated per annum. S = I.H.P. per hour of steam generated. X = Coefficient for comparing various systems. 84 THE ECONOMICAL DISPOSAL OF TOWN REFUSE. fl c3 eS © CO *C ^0o£ § O .3 • COOIN h >-< t>- 2 •* • '-, r_l 2 pH;cca ft lO r-l T* CO CO CO O CM ^^lO 0 ° OO^f^^ ^ g.®Tf(0^ -C ,_l re © ft a s^ s^ >« fe rvT fc.S-S la's % o oo ©^Sjo 02 -do^o O Jh t-h o.PQ © . X • C5 JO »0 © <M CO <M CO rt< S o o o ^oS © £2 t~»o O a c fc.S.H £rH ©^ S >ooo5 o m u o ""0. © Hb.SO ' I-H -H CM CO CO o o i-i CO -+■ g lO IO o • 2 OtH o fc.2.2 ^col ©^ o gg O CO CO CO .. 1* © 2 -S'-'COO Hfa _ cm <M CO lO <M CO tH § <=> ° v o o 200<N ©epeo d0gn o ,_, © .£ o © U CO oo ft gw CM IQ • * . CO fe .2 .2 ■! 13 o o ^ a 9 .? ^ •"hoij o ^ &C| cs a ft O Q} » *-< *-• *-l (D oj is s-s a £0£ •^3 «® © ~ cr1 © ~ © j. — g««.a ft 5 m © p e3 £ © ^H © « CJDt,., ft ft O d c >* Sm © o si^B SHWcoh o t3 »13 ,5 ® * S © (« o " ° fttH -IJ ^ CD 5$ © !- H O O W)£ S s © s_. -w e<-i S 02 O ft 03 a : 0 <d ja .- 3 s 2 2 , o o) ^ 2 j © « ft_, p «t3 ^f i, . © .^ 5 m ft eS o O «9 te^ g S © ti_ 2 +e ft © TJ ft © a 9 o & fl © © -5 a 2 S S. 5 ££ SW <j pqOQHfeeW^^^^g^; OPhC?« 3D H P }> »< J* nj THE ECONOMICAL DISPOSAL OF TOWN REFUSE. 85 Then— B + S = x 30 (0 + W) The value of the steam has been based upon coal or slack, which costs 4s. 2d. per ton, and produces 784 I.H.P., or say, 1 lb. evaporates 7 lb. of water, and its equivalent is *0b'35 of a penny per I.H.P. By adopting this rate, the cost of wages and the value of steam, shown in column 1 of the Appendix, are exactly the same. Throughout the paper 20 lb. of steam is allowed per I.H.P. In conclusion the author desires to thank all those who have kindly afforded him information upon which the statistical portion of his paper has been based. DISCUSSION. The President said that one of the points in Mr. Healey's paper which had particularly struck him was the varying nature, both from the calorific and the carbon point of view, of the refuse with which the destructor had to deal. That would cause very great difficulty in standardising the results which came from different parts of the country. Again, the quantity of moisture in the refuse would make a very con- siderable difference in the results. It seemed to him, there- fore, that the author's suggestion as to some means of standard- ising the tests was a very admirable one, and it was admirable as regarded not only destructors, but every other form of test which could be made. That was a point which had not been sufficiently thought about and cared for in the past. One was struck with the enormous difference between the results ob- tained from different places. Presumably the plant was of the best description that could be used in each of those places, and therefore the greatly differing results should not appear. But if one came to examine the results very carefully, it would be found that in different parts of the country different rates of wages were paid, and different values for the carbon had been chosen, and in every case a different standard had been used in making the test. If some standard could be adopted a very distinct step forward would be taken in the matter of combining the results of tests. Another point which had struck him was that the author H 86 THE ECONOMICAL DISPOSAL OF TOWN EEFUSE. had not confined himself to any one special form of destructor in which he might be personally interested, but had taken the trouble to obtain the working results of various forms of such apparatus, and had given a useful general review of the whole subject. The waste which had been shown by the author in connection with many destructors which were not used for the purpose of raising steam, seemed to be a point that should be carefully considered at the present time when fuel was rising rapidly in price every day. Any means of raising steam for power ought to be thoughtfully examined. The use of clinker in concrete was a matter with which he had been very familiar for many years, and he was very glad to find that the author gave a table of results showing that clinker — a material which had always been considered in gas- works to be as good as any other for concrete — had been proved by tests to be as good as, if not better than other materials which were commonly used for concrete. The author had spoken of a furnace in which the bars lasted on an average for about twelve months. Had the author had any experience of those bars when they were partly immersed in water ? He (the President) knew a system of forced draught in which the bars were made very deep, and were fitted so that the lower portion of them was in an ash-pit containing water, which helped very considerably to keep the bars cool. He would propose a cordial vote of thanks to Mr. Healey for his interesting and valuable paper. The vote of thanks was unanimously carried. Mr. George Watson said that Mr. Healey had raised a number of important points. Mr. Healey was well known as one of the pioneers of refuse destructors, and therefore they would expect to hear from him nothing but practical common sense, and figures based upon personal knowledge. He had been extremely moderate in what he had said as to the possi- bilities of destructors. A great deal of harm had been done in the past by overrating the value of destructors as steam generators. The author spoke of indicated horse-power avail- able from a ton of refuse. He (Mr. Watson) thought that that should be indicated horse-power hours, because the horse-power obtained depended upon the rate of burning. He did not agree with the author in putting the boilers between or over the furnaces. It was quite true that there was a loss of radiation if the boilers were put at the end of the block of furnaces, but there was a great saving in other ways. For instance, the boilers could be cleaned, and the tie bolts of the furnaces would not be interfered with ; also long steam pipes would be avoided, and that was very important. THE ECONOMICAL DISPOSAL OF TOWN REFUSE. 87 A good deal of money had been spent upon mechanical furnaces, but up to now they had not been able to compete with hand -fired furnaces. The late Mr. Whiley, of Manchester, put up a number of mechanical furnaces, but no one in Man- chester regarded them as satisfactory. The input was only about three tons of refuse in twenty-four hours. The clinker formed such a very large proportion of the total refuse that the employment of mechanical fire-bars in destructors was attended by very great difficulties. Whiley's fire-bars did not break up the clinker. They shifted it forward, but so slowly that the results were quite inappreciable. He agreed with Mr. Healey as to the importance of charging at one end and clinkering at the other. It seemed quite a wrong principle to try to work with a single-ended furnace. In a furnace of that kind there was a danger of mixing unburnt refuse with the clinker which was being drawn. The only reliable dust-catcher which he had found up to the present time was one which depended on the principle of centrifugal force. Many engineers advocated large flues, which made the gases travel slowly. They were certainly effective to a certain extent, but only a portion of the dust was caught, while practically all of it was caught by a centrifugal appa- ratus. As regarded dampers, those of steel plate were most un- satisfactory. One of the greatest difficulties of destructors had been the high temperature. Dampers buckled in high tem- peratures, and they ought to be always either full in or full out. A damper suspended from above, and specially cooled by means of water, was the only thing that would answer in a high tem- perature. He was glad to find that Mr. Healey did not advocate high stacks. If a stack was built 300 feet high, all the people in the neighbourhood could see it, and, if they smelt anything within a radius of three miles of the stack, they would put it down to the destructor. He knew of instances in which com- plaints had been made even before the fires had been lighted. 31 r. \V. Worby Beaumont asked Mr. Watson if he would explain the method of application of the centrifugal principle to the collection of the dust. Mr. Watson said that the apparatus was known as the Centrifugal Dustcatcher. It is shown in plan in the annexed engraving, and the fol- lowing is a description of it. The apparatus consists of an outer annular chamber and an inner circular chamber or well. The inlet Hue is so arranged u 2 88 THE ECONOMICAL DISPOSAL OF TOWN REFUSE. that the gases enter the outer annular chamber tangentially and swirl rapidly round it, thereby throwing up the greater part of the suspended dust against the outer wall. The bottom of this chamber is divided by the walls of the flue entrance and exit, and also by several * special walls into pockets which serve to collect and retain the dust. These pockets are each provided with a cleaning door so that the dust can be removed without special use of the apparatus. As the gases swirl round the outer annular chamber they gradually rise to the roof of the chamber, where they can pass over the wall of the inner circular chamber or well, and then they pass downwards to the bottom of the well and out through an outlet flue provided near the bottom of the well, which passes to the chimney. Centrifugal Dustcbtcher Thus the dust which has not been caught in the outer annular chamber by the centrifugal action of the swirling gases is cast downwards in this well into the pit at the bottom of it, from whence it can be withdrawn through an opening and cleaning door. The exit flue is placed slightly above the dust-pit at the bottom of the well. Mr. Beaumont said that the centrifugal method appeared to be very suitable for effecting the deposition of the dust. As to the expression " horse-power " in the paper, it would be better if the quantity of water evaporated per pound of refuse were stated. The author made a statement as to the number of furnaces connected with one boiler, and mentioned that four furnaces produced 101*05 indicated horse-power, and that six THE ECONOMICAL DISPOSAL OF TOWN BEFUSE. 89 furnaces working to the same boiler produced only 100 indicated horse-power. That was only 1 ■ 05 per cent, difference between the two. One per cent, was extremely little when they con- sidered not only the great difference between the heat value of the material from clay to day, but the way in which it varied in different places. He should like to know whether the four and the six furnaces worked under precisely the same condi- tions, and whether that one per cent, as printed was what the author meant to put in the paper. With regard to the use of the jet and the fan, he was glad to see that it had been recognised that a good fan was so very much more economical for moving air than steam-jets could possibly be. The author stated that the opening of furnace doors to regulate the steam supply should not be resorted to when the use of a damper would have the same effect. That was a point which one was always washing to insist upon, but he (the speaker) was afraid that, so long as it was easier to open a fire door than to manipulate a damper, the lire door would be used. Keferring to the average value of materials, the author said that, " taking an average of several systems, it is found that 1 * 26 lb. of water can be vaporised by 1 lb. of average un- screened refuse, when burnt in well constructed furnaces, and assisted by a forced draught at a pressure of 1 ■ 25 inch water- gauge. By the use of screened refuse, 1 * 89 lb. of water can be vaporised per pound ; but, as it requires at least three tons of unscreened to produce two tons of screened refuse, there is no advantage in adopting screens." On that point he would ask the author whether the whole of the tailings, or that part of the material which was rejected by the screen, was useless for heating purposes or for any purpose. Of course the screen must reject a very considerable proportion of that which it received, but the tailings might not be useless, though the author had treated them as of no value. That had the effect of giving to the three tons of unscreened and screened refuse values of 3 ' 75 and 3 ■ 78 according to the author's figures. One would like to know what was done with the screenings, and what was the character of the screen and the separating tackle that was used for the purpose. Vibromotor screens had been used successfully for that purpose, and he would like to know why it was that, according to the author's figures, separation did not pay. Towards the end of the paper the author gave, in ;i bandy form, the results of his experience with regard to the economical 90 THE ECONOMICAL DISPOSAL OF TOWN REFUSE. value of the furnaces and destructors, as destructors and as steam-giving apparatus. If the author, instead of putting in- dicated horse-power, would allow the expression to be, so much evaporation per ton of materials used, the table would have a rather wider application than it could have in its present form. Mr. W. N. Blair said that he agreed with previous speakers as to the value of 31 r. Healey's paper, and also as to the modesty he had exhibited in speaking of arrangements with which he had been himself connected. The author had dealt most fairly with svstems which were rivals to his own. Many of the points raised in the paper were of great interest, but without some systematic preparation it was scarcely possible to deal with them as thev deserved. One of the most important things with which anyone constructing a system of destructor furnaces had to deal, was the extreme differences in the character of the refuse. The differences in that respect between one town and another were phenomenal. He did not know of any place in this country the refuse from which would not burn without the addition of fuel ; but it was a fact that in Berlin the refuse was so devoid of carbonaceous matter that the authorities were obliged to actually add fuel to it to get it to burn at alL His experience was that where the carbonaceous properties of a refuse were low, greater intensity of fire, or, in other words,, a stronger draught, was needed to make it burn than would be needed in the case of material which was fairly rich in carbon. The draught of a furnace must be varied to meet the character of the material. He did not agree with the author's statement that the draught should not exceed 1 J inch water gauge. Many of those present would be familiar with Beaman and Deas's furnaces., where the draught quoted in the table at the end of the paper was 1 * 7 inch. He had seen those furnaces burning with 5 inches of pressure indicated by the water gauge, and the normal pres- sure being admittedly 3 inches or a little over. It was only where those large draughts existed that a large consumption was obtained. For instance, if they took the average con- sumption of destructor furnaces generally to be between six and seven tons, they would get ten or eleven tons with some forced draught furnaces, that was to say, with something under 2 inches of draught-pressure; but where they had the higher pressure of Beaman and Deas's, they would get 16 or 20 tons con- sumption per cell per day. It was true that where there was an increased consumption there was an increased cost per ton, but that, he thought, was almost to be expected. They could THE ECONOMICAL DISPOSAL OF TOWN REFUSE. 91 not put through the furnaces a larger quantity of material with- out having more labour upon it. In connection with that point there had arisen in his mind a criticism on the author's statement as to regulating the work of feeding and clinkering the fires through the whole cycle of operations. The author had pointed out that it was often the practice for the men to feed as quickly as they could, and get round and have a rest. Anyone who was familiar with the work in a destructor establishment would not by any means wonder at a man desiring to get done with his job and sit down and have a rest. It was not light work to clinker in front of a furnace with a temperature of from 1600 to 2000 degrees. To begin with, a man did not want much clothing on, and when he had finished he would be almost sorry that he had any on at all. That being so, he did not think there was much hope of getting the men to work slowly at each furnace, so that when they had got from three to six furnaces to attend to they would occupy an hour and a half or two hours in one cycle of operations. The effect must be that a larger proportion of fire-grate area was covered with fresh material, and, that being so, the tem- perature of the effluent flue must be lower than if there was a greater proportion of fire at its maximum temperature. 