For some six months of the year in this country artificial heat is a necessity in our homes. At such times the outer atmosphere is too cold for the comfort of occupants when little exertion is being made. Various methods are consequently employed for raising the temperature of dwellings, such as open fires, closed stoves, gas-fires, gas-stoves, hot water, steam, and hot air. These systems of warming houses are dealt with in the Section on "Warming", and therefore they will only here be referred to as regards the effect they may respectively have on the ventilation of houses.

1. Ventilating Fire-grates. - The open fireplace has previously been referred

1For further information on this important subject see the "General Introduction", by Dr. Andrewes, pp. 20-23, VoL I.-ED.

to and the value of smoke-flues discussed, but in addition to the simple Open fire, which undoubtedly is cheerful and pleasant under ordinary circumstances, although wasteful and frequently the cause of cutting draughts, there are more complicated forma specially designed to secure comfortable ventilation, the idea being to impart to the necessary incoming air. which must replace that ascending the Hue, a portion of the heat given out by the fire.

Theoretically the idea is excellent, but unfortunately the difficulties which have to be overcome in the construction of the grate are considerable. and.

although I have tried many forms, I cannot say that any are permanently satisfactory, the principal reason being that metal (generally iron) 1- employed, which must be jointed, and the constant variation in temperature alternately expands and contracts the parts, so that in time the joints open, and smoke is drawn into the fresh-air channels, vitiating the atmosphere of the apartments. One common fault they nearly all have, viz. the passage of cold air abstracts heat from the hot gases, given off at the top of the tire, to such an extent that soot is quickly deposited, and the temperature of the flue is proportionately reduced, frequently resulting in a clogging of the mouth of the flue and a lifeless fire.

I have obtained better results by utilizing the heat of the body of the tire, instead of abstracting it from the gases given off. Nevertheless I am inclined to think that in rooms of moderate dimensions it is better to be content with the radiant heat of the fire, in a well-constructed grate in which the fire is well surrounded with firebrick, and to admit a reasonable amount of fresh air by suitably-placed openings in the upper portion of the room as previously described; a further reason in favour of this opinion is that, as the air-inlet channels around the fire-grate cannot be easily got at and periodically cleaned, in time they must become fouled by the large quantity of air, which passes through and necessarily brings with it a considerable proportion of dust and dirt. and. to ground-floor rooms, the air-inlets are frequently too near the surface of the outer ground

2. Closed Stoves. - Better heat-value in proportion to the amount of fuel used can be obtained from these than from an open fireplace, but generally at the expense of change of air, beause the sectional area of the flue is less, and consequently the amount of air extracted is reduced

Another result arising from the use of many closed stoves, particularly those principally constructed of iron, is that the metal becomes overheated; this causes a rapid circulation of air in the room, and large volumes of air are brought into contact with the overheated surfaces. Much of the dust floating about in the atmosphere consists of particles of organic substances; these either burn and give off carbonic acid, or are charred and cause an offensive odour. Those heated surfaces also dry the air and make it unpleasant to breathe; to mitigate this evil, vessels of water should be placed upon or near closed stoves, and care should be taken to have the vessels and water clean.

3. Gas-fires. - If properly constructed, gas-fires are convenient and cleanly, and, as regards ventilation, might be expected to act in a similar manner to an open coal-fire, hut in two important particulars they are less satisfactory: - 1. The heat from a gas-fire has a decided tendency to over-dry the air of an apartment, so that, unless a pan of water or other suitable appliance be

used to supply sufficient moisture, the air becomes unpleasant if not actually unhealthy to breathe. 2. In setting grates for gas-fires it has become a custom to very considerably reduce the area of the flue, and in consequence change of air cannot take place so frequently within the room.

Fig. 604   plan and section of Bruce's singgle Apparatus fur Warning Incoming Air by Gas.

Fig. 604 - plan and section of Bruce's singgle Apparatus fur Warning Incoming Air by Gas.

4. Gas Stoves, as far as our subject is concerned, may be divided into two classes, viz. those that are intended to assist ventilation, and those which make no attempt in that direction. As regards the latter, they should only be used when efficient means of ventilation can otherwise be secured.

Of those designed to assist ventilation, there are several varieties and forms, the object principally aimed at being to impart a portion of the heat, evolved from the burning of gas, to the incoming air of the apartment, and to convey the products of combustion into a flue or more directly to the open. A difficulty which the writer has experienced is to prevent back-draughts extinguishing the

flame, and thereby causing an escape of gas. Moreover, the working parts of such gas-stoves are principally of metal and have to be jointed; variation in temperature, arising from being at times highly heated and then allowed to cool down, causes varying expansion and contraction of parts, and ultimate breaking

of the joints, and the products of combustion also cause corrosion, so that any degree of permanence can scarcely be expected.

Fig. 605, Plan, Section, and End Elevation of Bruce's Double Apparatns for Warming Incoming Air by Gas.

Fig. 605,-Plan, Section, and End Elevation of Bruce's Double Apparatns for Warming Incoming Air by Gas.

Fig. 606  Plan, Section, and Elevations of Bruce's . Hot wafer Apparatus or Radiator, heated by Gas.

Fig. 606 -Plan, Section, and Elevations of Bruce's . Hot-wafer Apparatus or Radiator, heated by Gas.