Smells are conveyed about a house by the flow of air to feed the fires, and they nearly always find their way from all parts of the house to the ground-floor sitting-rooms when the doors are left open and the fires are burning. On their way they pass through passages and are therefore nearly ubiquitous. The air of any room in the house is in communication with that of every other room, and it is only by the nature of the smell that we can tell its probable source. There are people who like when they open the bedroom door in the morning to know that coffee and bacon await them downstairs, or on coming into the house from a cold winter’s walk to meet a “delicious 90 smell of Irish stew.” To other people all smell of cookery is abhorrent, and they feel a sense of irritation that their guests should on entering the house be regaled with the odour of the preparation of food. To many mistresses the only remedy that suggests itself is a message to the cook, who is powerless in the matter and returns an answer that she is sorry, but that she doesn’t know why there should be a smell of cooking upstairs as there is none in the kitchen. A visit to the kitchen will generally confirm the cook’s statement as to that particular spot, but a considerable smell will be encountered on the kitchen stairs. We may inquire into the cause of this. The usual equipment of the kitchen includes a closed range, supplemented in many cases by a gas stove. The kitchen fire draws a plentiful supply of air from casual openings, and this air for the most part passes with the smoke up such flues as are open. The oven is provided with a ventilator, which carries off the odour of baked or roasted meats. The odour in the hot air over the closed range has no escape except into the kitchen—the cook says that ever so slight an opening in the top of the range will prevent the oven from heating. This odour-laden air therefore comes directly into the kitchen, and being hot is directed to the ceiling, thus escaping the cook who is in the draught of the fresh air supply. Travelling along the ceiling the hot air passes through the opening at the top of the door and mingles with the fresh air on its way upstairs. The same thing happens when the 91 gas stove is in use. The only remedy is to provide some exit for the hot air of the kitchen which will be more easily accessible than that by way of the door, for the hot air will travel by the easiest path. A considerable knowledge of science is required to achieve this object.
Fig. 2.
Closely allied with the smell of cookery is the smell of the gas stove. Many persons consider that the use of a gas stove either in the kitchen or in a bedroom is inseparable from the peculiar odour of partially consumed gas. It may therefore be useful to consider how the gas supplied to stoves and incandescent lights differs from that of an open gas fire or that of an ordinary burner. Gas stoves and incandescent lights get their supply of gas through what are known as Bunsen burners, so called after the German chemist whose invention they are. In an ordinary burner the gas mixes with atmospheric air at the opening at which it burns; the supply of air obtained in this way is insufficient for complete combustion until the outer layers are reached; the interior part of the flame is bright and smoky. In the Bunsen burner the gas issues from the main through a nozzle which opens inside a bulb. The bulb is perforated to allow of the ingress of atmospheric air; the gas and air mix in the tube which is a prolongation of the bulb, and the mixture is lighted at the top of the tube. Fig. 2 shows a representation of the Bunsen burner as applied to a gas stove. In this the gas escapes from the main at the nozzle n, into a bulb of which the tube A is a prolongation, 92 air is admitted to the bulb at the openings a a, and the mixed gas and air is burnt at the openings in the tube A. The amount of air supplied is regulated by the size of the openings a a and the holes where the gas is lighted. The gas thus supplied with air is completely consumed where combustion begins, and a clear, blue, non-luminous flame is the result. If the holes through which the mixture of gas and air issues are partially closed by rust or by accretions from the “boiling over” of saucepans it is evident that, the gas supply being unchanged, less air can be drawn through them; consequently the gas will not be entirely consumed, and acetylene (C2H2, one of the products of partially consumed coal gas) will pass into the atmosphere and will give rise to the peculiar odour associated with gas stoves. This product of partially consumed gas is very poisonous, and all gas stoves should be furnished with chimneys to carry off the fumes to the open air. The phenomenon known as “burning back,” that is, the ignition of the gas at the nozzle in the bulb, is caused by the pressure of gas being too small for the supply of air. The gas should at once be 93 turned out and relighted till it burns at the proper places. The simple remedy for smell from a gas stove is the cleansing of its burners, unless indeed the kettle is too close to the holes from which the gas issues for complete combustion to be possible.
There is another winter phenomenon which is very disagreeable—the presence of fog in the house; and the perplexed housewife asks, Where does the fog get in when all outside doors and windows are closed? We have already pointed out that the sitting-room fires must have air, and that that air will be drawn from casual openings. Among these openings are the chimneys of fireless grates; the greater part of the fog in the house comes down these chimneys. On a foggy day it is wise to close the chimneys of fireless grates and provide some other opening for the supply of air; but all air from the outside is full of fog. The problem of how to let in air and keep out fog suggests the question, What is fog? Fog consists of material particles (dust or smoke) on which vapour has condensed; if these particles can be removed the air will be clear. The problem for the housewife is how to free a sufficient quantity of air from these particles.
A smell of gas in any part of the house may be very dangerous if no one on the premises has any scientific knowledge, for it may be premised that the escape of gas is not where the smell is first perceived. Gas being lighter than air is carried upwards, and the smell is at first above the place of escape; it may even be in a room over where 94 the gas is escaping. The only safe detector of the source of mischief is the nose; the mixture of coal gas and atmospheric air is explosive, and no light must be struck. The upper sash of the window should be pulled down to allow the gas to escape, and if the accident is at night time must be allowed before searching for the source of escape further than can be done by feeling the taps in the dark or following the scent by the nose.
Further illustration of the effect of convection currents in the air of a dwelling-house are needless, but the student may profitably spend time and thought in considering how fresh air may be introduced into a room without causing cold air to lie on the floor or hot, vitiated air to cling to the ceiling. It is the old problem (with a difference) of teaching a grandmother to suck an egg. He may also interest himself in seeking answers to the questions (1) What action is expected to take place when a poker is placed against the bars of a grate to make the fire draw? and (2) Does the sun put the fire out, and if so how? In connection with the expansion of air with heat he may consider the popular fallacy that an inverted empty pot in a pie keeps in the juice.
EFFECT OF CHANGES OF TEMPERATURE ON WATER
Accidents have occurred in houses owing to ignorance of the full effects of heating or cooling water from its ordinary temperature. Water at 95 any ordinary temperature expands when subjected to the action of heat; it contracts on cooling till it reaches a temperature seven degrees above the freezing point; from this temperature it expands until it becomes a solid mass of ice. At still lower temperatures ice contracts.