The ash-base of this beater is provided with an ash-pan, the convenience of which will at once appear. In connection with the fire-pot, the makers draw attention to "a very ingenious contrivance, by which a most perfect combustion is secured, without the use of non-conducting material between the fire and water-surfaces. This is by the use of broken lines, both horizontal and vertical. The horizontal lines are secured by the surface being larger at the grate than just above. there being three distinct steps. These several steps are crossed by broken vertical ribs, which seeure the most perfect results. . . . The products of combustion are passed through oval holes 'staggered', until the final delivery to a warm chamber at the top of the heater, and so finally to the exit-flue."

At first sight the heater seems somewhat complicated, but it appears to give extremely good results. There will, of course, be loss of heat from the exterior, and this cannot well be counteracted by the application of non-conducting composition, as it would interfere with the joints. A boiler of this kind, measuring 42. inhes in height and 22 inches in diameter, is rated to be capable of heating al>out 170 square feet of radiating surface, and as this is the rating used in Canada, it is considered well within the mark for the much more temperate climate of the British Isles.

Fig 512   View .of fire pot ,of the   Oxford Boiler showing circulation of water.

Fig 512 - View .of fire-pot ,of the " Oxford Boiler showing circulation of water.

The Defiance Boiler, by the same makers, is intended for small powers, and is shown in Fig. 513.

The l)oilers made by Mr. James Keith are also of cast-iron. The type known as the "Viaduct" Boiler is illustrated in Fig. 514. These require no brick-setting whatever, the cast-iron exterior has a fire-brick lining, which is, in my opinion, a distinct advantage over the Canadian form, as the heat will be radiated from the glowing surface, and it is practically impossible for the exterior of the heater to become red-hot, as may easily happen in the case of the Canadian type. The shell is made in two pieces, which are held together by bolts. The stoking-door is immediately under the crown of the arched water-way, and consequently a large amount of fuel can be inserted, and the fire will burn for a long time without attention. A clinker-door is provided immediately over the grate-bars, and an ash-door below. There are in the figure two outlets for the flow-pipes, and two inlets for the returns. This type is made in sizes with heating capacities up to 1500 square feet of radiating surface.

The surface required in an ordinary house will not usually exceed this figure, but if it does, another more powerful boiler by the same maker may be used; it is known as the "Challenge" Boiler, and is illustrated in Fig. 515. This boiler has horizontal or nearly horizontal sections, somewhat similar to the Gurney boiler, but, instead of horizontal baffle-plates, cross tubes run from back to front. It does not appear to me to be designed so as to baffle the upward currents of heated gases as effectually as the Canadian type, but the deposition of soot upon horizontal surfaces must always be very considerable, even when the boiler is cleaned out frequently, and this would detract from the value of the Gurney Boiler.

Fig 513  View of the   Defiance  Cast Iron Boiler.

Fig 513 -View of the " Defiance" Cast Iron Boiler.

An interesting type of boiler, resembling the boilers used for high-pressure hot-water heating, is made by Messrs. Renton Gibba & Co., Ltd., and is illustrated in Fig. 516. It will be observed that the boiler really consists of a series of coils of pipe, placed in a fire-brick chamber; part of the tubes form the grate-ban, and the flame plays directly on to the upper tubes. The flow of water produced in the tubes is, of course, extremely rapid.

Fig. 514   View of  Viaduct  cast lron Boiler, with the Front Half of the Outer Case Removed.

Fig. 514 - View of "Viaduct" cast-lron Boiler, with the Front Half of the Outer Case Removed.

Korting's Boiler is shown in figs. 517 and 518. It is designed for low-pressure steam heating, but we describe it here, as a very similar type is also used for hot-water heating. The following description is taken from the maker's list

"As the boiler is provided with an open stand-pipe st, there is absolutely no risk of explosion,1 and the position occupied by the boiler may be decided without reference to the question of safety. As furnace, which serves at the same time as hopper and as fire grate, we have adopted our patent cast-iron ring tubes (see d, Fig. 518), which are filled with water, and are connected at the bottom and top to the water space of the boiler. By removing the cover f on the top of the boiler, the hopper and furnace may be filled with fuel. It is preferable that, where possible, coke or anthracite coal should be used. Tin-air for combustion pas through the draught-regula-tor, and a flue in the setting of the boiler, to the front of the furnace. As the furnace-door is kept closed, except when the ash is removed, and with closed door the connection between the front of the furnace and the ash-pit is hermetically sealed, the air on its way to the boiler must pass between the water-tubee of the grate, and through the fuel inside the grate. When the furnace-door is opened for the removal of ash, cold air passes direct through the ash-pit to the boiler, checking the draught, and diminishing rather than increasing the combustion in the furnace during the time the door is open.

Fig  515.   Sectional View of the  Challenge  cast iron Boiler.

Fig- 515. - Sectional View of the "Challenge" cast-iron Boiler.

1 But suppose that the water in this is frozen (as may readily happen if the apparatus is only used on certain days of the week), and the water in the circulation-pipes is also frozen, so that relief cannot be obtained through the sir-pipes, then an explosion will be almost a matter of certainty if the fire is lit.-ED.

Fig. 516. Section of the   Ronton Gibbs  Tubular Boiler.

Fig. 516.-Section of the " Ronton Gibbs" Tubular Boiler.