HYGIENE OF GAS.

New Zealand Herald, Volume XLIV, Issue 13625, 19 December 1907, Page 8

HYGIENE OF GAS.

"■USE OF GAS FROM A HYGIENIC" STANDPOINT. Extract from lecture by Professor Vivian li. Lewis, F.1.C.. F. 0.5.. Professor of Chemistry at the Royal Naval College, Greenwich The effect of burning coal gas as an illuminant on the air of our dwelling-rooms and the health of its occupants is as old a subject as the uso of coal gas > itself ; and in tho early days of the gas industry it threatened to wreck its future for indoor illumination, as tho crude gas then" sent out, rich in sulphuretted hydrogen, gave rise to such discomfort when consumed that ventilating burners of clumsy device had to be employed for its use, while badly-made and leaky fittings gave at all times an aroma which suggested to the nose and mind of tho householder a doubt as to tho sanitary condition of tho drainage. A very short period, however, served to convince the gas manager that the purity of tho gas was a matter of even greater importance to him than to the public, as the latter could escape the effects of the sulphurised products of combustion by adopting other illuminants; while the gas manager's livelihood depended on keeping his customers. As a result, purification from sulphuretted hydrogen was adopted, and the use of coal gas increased with enormous rapidity; tho public being convinced by experience that, properly used, coal gas in no way injuriously affected their health. With the advent of the electric light as an illuminant great stress was laid upon its enormous advantages from the hygienic point of view; and its supporters still make the claim that it must of necessity be far more healthful to use as an illuminant than coal gas. It lias not unnaturally been assumed that, owing to incandescent electric lighting adding nothing to the impurities in the atmosphere, and —what is quite as important —withdrawing no oxygen from it, it must be the most hygienic form of illumination to employ ; but in the years which have elapsed since electricity was pressed into tho service of man for illuminating purposes, it has become perfectly clear that, though it is inactive as regards vitiation of the atmosphere, a gas-lighted room will nearly always be more pleasant and healthy to live in than one lighted by the newer form of illuminant. I have in my mind at the moment a ball, which in the old days was lighted by gas, and in which a large audience could with comfort sit through an hour's lecture or with pleasure through a three hours' dinner, but which, with the march of civilisation, had its illumination changed from gas to electricity; the latter being employed with all the latest refinements to effect the lighting under the best conditions, with the result that any large gathering within its walls leads to a state little short of asphyxiation. It is with factors that lead to this anomaly that I now desire to deal. THE CONSTITUENTS OF THE ATMOSPHERE. The atmosphere is composed mainly of two elementary gases—oxygen and nitrogen. The oxygen is the great supporter of life and combustion, and is the agent employed by Nature in those cleansing: processes, chief among which is "decay;" while tho nitrogen serves to dilute the oxygen and keep its action within the proper limits. These two gases are present in tho air in the proportion of. 20.9 per cent, of oxygen to 79.1 per cent, of nitrogen by volume, or, roughly, 1 volume of oxygen to 4 volumes of nitrogen. Besides these, however, we find in tho atmosphere traces of other bodies, some of which, like water vapour, carbon dioxide, and ammonia, are necessary for the carrying on of Nature's processes; while others are the true impurities, and generally have a local origin.

The oxygen used up daily by the processes of animal life, combustion, and decay, amounts, according to tho calculations of Faraday, to no less than 3i million tons; and it is replaced in the atmosphere by the products evolved by these actionsnamely, water vapour and carbon dioxide. Yet analyses continued over the past hundred years have failed to detect any diminution in the quantity of oxygen or increase in the amount of carbon dioxide bo that it is manifest that Nature must have at hand some method not only for the removal of carbon dioxide from the air, but also for the production of oxygen, as otherwise the atmosphere would rapidly deteriorate and become unfit to support life.

The main factor in this marvellous natural work is to be found in vegetation; the waste products from tho animal world being utilised for building up the vegetable kingdom —an action by which the oxygen is replaced in the atmosphere, and keeps it in a condition fit for breathing, while other impurities aro partly washed out from the air by lain, and partly oxidised and destroyed by ozone. Tho wonderful power of diffusion possessed by gases is the chief factor in keeping the composition of the atmosphere constant, as, aided by air currents and wind, it keeps the whole of the. gases present so thoroughly intermixed that it took scientific observers half a century to discover whether these gases were really only mixed together in tho atmosphere or in chemical combination.

In the open air these provisions of Nature are ample to maintain tho air in a healthy condition for breathing; but it is when we are in an enclosed space, such as a room, that we interfere with tho work of purification, so that tho air in the room rapidly becomes fouled by the products of respiration, and unless wo take, special means to aid Nature in tho revivification of the air, it rapidly becomes unfit to bo re-breathed, and our health suffers in consequence.

Quo of tho most wonderful of the many marvellous processes taking place in our bodies is that which really forms the great mainspring of life. We build up our bodies from the foods and liquids winch wo assimilate, and the tissuo so produced is then consumed in tho body by a process of slow combustion taking place at the' expense of tho oxygen, which, inhaled into the lungs, is carried by the circulation of the blood throughout tho body, and, burning up the tissue, generates the energy needed for very action, voluntary or involuntary, and gives the warmth to the body which exists while life lasts. HOW AIR IS CONTAMINATED. The products given off during the process of respiration are carbon dioxide, exhaled from the lungs as we respire, water vapour, and traces of organic matter; and air which has been once breathed is unfit for further respiration until Nature has dealt with it by her cleansing processes. The air in the country contains on an average three parts of carbon dioxide in 10,000, while in towns the proportion is generally four parts in 10,000; and the latter figure is usually taken as the proportion present in normal air. In a room, however, in which people are breathing the air, the amount of carbon dioxide will increase; and when it has reached six parts in 10,000, the atmosphere of the room will become noticeably fouled to the nose of an observer entering from tho fresh air, and is what we call. " stuffy." This is due to tho presence of organic matters evolved from the skin and lungs during respiration, and not to the slight excess of carbon dioxide, which is absolutely harmless but the organic matter is excessively deleterious to health, and, moreover, often contains the germs of disease. When prodioxide and organic matter increase at the ;same ratio ; and as it is fairly easy to cstL-.

mate the amount of carbon dioxide in the air, and extremely difficult- to determine the organic matter,-the condition of the atmosphere in enclosed spaces is generally investigated by determining the percentage of carbon dioxide present. Tito sanitary limit allowable, has been taken at six volumes of carbon dioxide in 10,000 of air. Put though this is perfectly correct when the source of pollution is respiration, vet the proportion may bo far higher when the carbon dioxide is generated by processes of combustion without- injuriously affecting health.

In tho ordinary dwelling house, the attempts at ventilation are of the most primitive and inefficient character; indeed, m the majority of households the efforts of tho inhabitants seem to be directed to getting tho rooms as nearly air-tight as possible, in order to make them warm. This, however, soon serves to render tho air so vitiated as to be unfit for breathing. In the course of ten hours a man breathes out six cubic feet of carbon dioxide; and as tho air already in the room contains four parts of this gas in 10,000, in order to reach the sanitary limit ho can only add two parts more to each 10,000 parts of air. In the ten hours, therefore, he must be supplied with 30,000 cubic foot of fresh air. In other words, if tho air of a room be not changed, it must bo of sufficient size to contain 3000 cubic feet if it is to bo inhabited by him for one hour; while in the case of a bedroom in which ho is to spend seven hours, it would have to be of 21.000 cubic feet capacity. This is manifestly an impossibility ; therefore arrangements are made by which the air in'a room can be constantly changed. As this can l>e done three or lour ' times an hour without creating draughts, the air supply can l>o diminished to from 750 to 1000 cubic foot per inhabitant per hour in rooms which are to be occupied for any length of time; and this is tho basis on which the ventilation of properly constructed buildings is arranged. It is the organic matter given off from the lungs and tissues during respiration that it is essential to remove from the air; and before one can condemn the atmosphere in an enclosed space by mere analysis, the source from which the* carbon dioxide was produced must be known, as without the presence of the organic matter it. is possible to live in an atmosphere containing 20 parts of carbon dioxide in 10,000 without injury to health.

In all processes of ventilation, the great factors which enable us to change tlie atmosphere in our dwelling-rooms are the air currents set up by alterations in temperature and inter-diffusion between volumes of air at different temperatures; and it is this which gives coal gas its great advantages as an illuminant over electric lighting. The combustion of one cubic foot of coal gas will use up six cubic feet of air; giving approximately half a cubic foot of carbon dioxide ami nearly 1£ cubic feet of water vapour. Using an incandescent mantle on an atmospheric burner, about four cubic feet of gas per hour are consumed; and this gives two cubic feet of carbon dioxide, which would very soon suffice to raise the proportion of carbon dioxide above the sanitary limit of six parts in 10,000. But though everything be done to render the room as air-tight as possible, it will be found that the proportion of carbon dioxide is enormously less than it should be by theory ; this being due to the-fact that alterations in tho temperature of tho air of tho room set up currents and actions which tend to bring about a change of the atmosphere.