Improvements in arrangement and construction may be expected, and now, in careful hands, there are several appliances which may be usefully employed. Of these, figs. 604, 605, and 606 are examples; they are well-designed and carefully-constructed ventilating gas-stoves, arranged so that the name is fed from, and the products discharged into the open air. while fresh air is separately supplied to the room through the apparatus, and warmed thereby and U pcast shafts carrying off the Vitiated Air when the gas is lighted. Pig. 604 gives the plan and section of a single apparatus: the outer case can be made of marble, faience, tiles, or mosaic, of any design or colour, in a metal framework. A double apparatus is shown in Fig. 605; in this the front has a "projecting illuminating centre", in which three gas-jets are arranged to throw light through the stained-glass panels in the projecting portion; these gas-jets are perhaps more for ornament than use, although of course they will possess a certain amount of heating power.

Fig. 607.   Plan and Section of Building showing Bruce's Radiators Wanning

Fig. 607. - Plan and Section of Building showing Bruce's Radiators Wanning the Incoming Air.

In Fig. 606 the plan, sections, and elevations of Bruce's hot-water apparatus or radiator with copper boiler are given, the water being heated by gas as in the preceding examples. The advantage of the water is that it will retain its heat for some time after the gas is turned off. Fresh air is admitted and wanned by passing over the coiled pipes.

Fig. 607 shows Bruce's gas-stoves or radiators applied to the warming and ventilation of a building, upcast shafts being provided for the vitiated air, and carried above the roof. This building, which, I understand, has been erected in Bradford, is an interesting experiment in the way of procuring warmth and ventilation by means of gas. In Fig. 608 a scheme of warmed-air ventilation is shown, having a central air-warmer in the basement, and shafts therefrom conveying the warmed air to the several rooms. The vitiated air is carried away by upcast shafts as in the previous example.

Fif.608   Plan and Section .of Building knowing Bruce's Central Air warmer and Shafts therefrom to the several Rooms, and Extract shafts for the Vitiated Air.

Fif.608 - Plan and Section .of Building knowing Bruce's Central Air-warmer and Shafts therefrom to the several Rooms, and Extract shafts for the Vitiated Air.

With respect to these radiators, my fear is that, at times, the pressure of air on the outlet for vitiated air will cause a back-draught, which may extinguish the gas-flame, and that, with the outlets from the apartments arranged as shown in figs. 607 and 608, there will not be so thorough a change of air through them as there would be with the outlets on the same side as the inlets, and with the inlets and outlets all of larger size and with the latter near the floor.

5. Hot-water Heating. - In large rooms this is a convenient method of raising the temperature, but. unless supplemented by an open fire, has many of the disadvantages of closed stoves, and, unless special means for the ingress and egress of air are provided, good ventilation is impossible. Ventilating radiators have consequently been introduced,1 by which air from the exterior is permitted to enter and pass through or around the tubes containing hot water; hut even with that provision for admitting fresh warmed air, far too little attention is generally paid to the provision of exits, with the result that change of air does not freely take place.

Low-pressure hot-water heating is the simpler method, and when properly applied secures the greater comfort in rooms. High-pressure hot water heating baa found favour because the smaller pipes are less unsightly, but they have counterbalancing disadvantages. The small volume of water they contain, and the more rapid circulation set up in the pipes, results in greater variation in temperature, and when highly heated the air is made dry.

A pernicious method of laying hot-water pipes is to place them in trenches below the floor-level, covered with gratings, through which the sweepings of the floors rind their way; the pipes thus become surrounded with filth, and when floors are washed moisture is added; the heat given off from the pipes facilitates decomposition, resulting in the contamination of the air of the room.

6. Steam, when directly used in place of water, adds to all these disadvantages, and should therefore be used with the greatest caution, if good ventilation is to be secured. Steam can, however, be more readily conveyed to greater distances than hot-water, and is therefore well adapted for large and extended buildings;

Fig. 609 steam Battery or Radiator admitting Fresh Warmed Air to a Rooms and when used in batteries to which fresh air can be admitted, such as that shown in tig. 609, ventilation may be assisted in cold weather, provided that suitable outlet Hues are properly arranged.

Fig. 609-steam Battery or Radiator admitting Fresh Warmed Air to a Rooms and when used in batteries to which fresh air can be admitted, such as that shown in tig. 609, ventilation may be assisted in cold weather, provided that suitable outlet-Hues are properly arranged.

1 For illustrations see Section on "Wanning", pp. 126-7. Vol II. - ED.

7. Hot Air. - Hot air is still more difficult to deal with effectively, unless mechanical means are employed for causing it to How where required, and when motive power is made use of, it is far more effective and reliable when used for propulsion than for extraction, because, when a propelling force is employed, the source of air-supply can be ascertained and regulated; the air can not only be tempered, bat may be cleansed and brought to a suitable hygrostatic condition, volume can be determined, and its direction can be regulated at will. The means by which air is heated may considerably affect its condition. Low-pressure steam and hot water are far more reliable than stoves or furnaces, because the latter are liable to contaminate the air, particularly in the course of time, when joints open by frequent expansion and contraction, or by the wearing away of parts, and there is a further danger from fire should the air become overheated.

Whatever methods are employed when hot air is used, all air-ducts and flues must be readily accessible, and care must be exercised to keep them clean, otherwise in its passage through them the air will be contaminated and become unpleasant, if not actually unhealthy, to breathe.

Moreover, it is as necessary to have suitably-arranged exits as it is to provide inlets for the warmed air. They also should be kept clean, and, in order to avoid irregular currents and draughts, the exits into the open must be constructed so that movement of the outer atmosphere may exercise neither a suctional not retarding influence upon the outflow.1