CHAPTER XVI.

GASEOUS AND OTHER IMPURITIES OF AIR.

Gaseous impurities of the air are very commonly associated with suspended matters, and it is often difficult to separate the effects of the two.

Different gases are also often associated, and so produce modified results. It will be convenient to consider, first of all, certain well-marked gaseous impurities, and then others in which there is a mixture of several gases, or of these with suspended solid particles.

Under the first head the most important impurity is—

(1) =Carbonic Acid.=—This is reckoned an impurity if amounting to more than 5 parts in 10,000 of air. Owing to the large amount produced in the respiration of animals, in the combustion of fires, gas, lamps, etc., and in other natural processes, it would be much greater in populous parts, were it not for the rapid diffusion occurring in the air, and the purifying action of plants. The following analyses (Angus Smith) illustrate the facts that in towns the amount rises, and is greatest in the most populous parts, while during fogs it is greatly increased.

┌──────────────────────────────────────────┬─────────────────────────┐ │ │VOLUMES OF CARBONIC ACID │ │ │IN 10,000 VOLUMES OF AIR.│ │ └─┬───────────────────────┤ │_On the mountains and moors of Scotland │ │ │ ──mean of 57 analyses_ │ 3·36 │ │_In the streets of Glasgow │ │ │ ──mean of 42 analyses_ │ 5·02 │ │_London, N., N.E., and N.W. postal districts│ │ │ ──mean of 30 analyses_ │ 4·384 │ │_London, E. and E.C.──mean of 12 analyses_ │ 4·745 │ │_Manchester streets, ordinary weather_ │ 4·03 │ │_During fogs in Manchester_ │ 6·79 │ └────────────────────────────────────────────┴───────────────────────┘

The effects of carbonic acid gas alone must be carefully distinguished from those of the same gas _plus_ the organic impurities from respiration, with which it is commonly associated. Dr. Angus Smith found that air containing 3 per cent. of carbonic acid produced difficulty of breathing, but he was able to breathe comfortably an atmosphere containing 0·2 per cent. carbonic acid. Other observers have found they could breathe without discomfort air containing 1 per cent. carbonic acid. When the carbonic acid is derived from respiration, headache and giddiness are produced in many persons when the carbonic acid amounts to 0·15 per cent. A fatal result has occasionally occurred from the inhalation of the carbonic acid at the bottom of brewing vats, or about lime-kilns. The gaseous impurity at the bottom of wells is more commonly nitrogen than carbonic acid (page 102).

The presence of an excess of carbonic acid diminishes the elimination of carbonic acid from the lungs, nutrition and muscular energy being consequently impaired. This is seen in workshops where the air is confined and gaslight is commonly employed; though the air here also contains carbonic oxide, sulphurous acid, and organic impurities, and these probably have a large share in producing the evil results.

(2) =Carbonic Oxide= in the proportion of more than 1 per cent. is rapidly fatal, and has poisoned when under 1∕2 per cent. Poisoning by its means occurs where charcoal stoves are used, and especially when the charcoal is burnt in rooms with no chimney flue. This is an occasional mode of suicide on the continent. Carbonic oxide is a much more deadly poison than the dioxide (carbonic acid); it forms a stable compound with the hæmoglobin of the red blood-corpuscles, displacing oxygen from them, and is got rid of with great difficulty. Lace-frame makers place a coke stove under their work, and thus inhale the invisible gas. Headache, giddiness, irregular action of the heart, and depression of the general health result. Carbonic oxide is the most poisonous constituent of coal-gas, and is present in much larger quantity in carburetted water-gas with which coal-gas is now commonly mixed, than in pure coal-gas (page 115).

(3) The inhalation of =Sulphuretted Hydrogen= produces headache, nausea, and diarrhœa; but in manufactures involving the inhalation of a small proportion of this gas the symptoms are much slighter.

(4) =Sulphurous Acid= is always present in small quantities in the air of towns, derived from the combustion of coal and coal-gas. Straw-bleachers and the bleachers in cotton and worsted manufactories, often suffer from severe cough and bronchitis due to inhaling its irritating vapours.

(5) =Carbon Disulphide= when vaporised and inhaled produces headache, general muscular pains, and nervous depression. It is used in the manufacture of waterproof coats, toy balloons, etc.

(6) =Ammonia= produces irritation of the eyes and bronchial irritation. Hat-makers commonly suffer from its effects, being generally pale and feeble. It is difficult to say how much is due to the ammonia, and how much to the high temperature at which they work.

(7) =Acid Fumes= are very irritating to the lungs, and in the case of alkali manufactures, they destroy all vegetation for considerable distances. _Hydrochloric acid_ produces great irritation, and chlorine even more so. The fur-dyer is not only subject to the dangers of dust, but also of the fumes of _nitric acid_, used to remove fat and give certain shades of colour to the fur.

(8) =Other Vapours= evolved in various processes produce special symptoms. House-painters suffer from the inhalation of _turpentine vapour_, headache and loss of appetite commonly resulting. The symptoms from the commonly coexistent lead-poisoning are distinct. Brush-makers have a persistent cough, due to the inhalation of _resinous fumes_, evolved in making brushes.

_Workers in paraffin_ are liable to an irritative disease of the hair-follicles of the body, followed by the formation of scars, almost like small-pox marks.

_Workers in quicksilver_, as those engaged in making mirrors or thermometers, are prone to suffer from mercurial poisoning. The gums become spongy, and there is profuse salivation, also generally alimentary disturbance; and in some cases nervous affections, resulting in persistent muscular tremblings, etc.

Under the second head—cases of inhalation of mixed gaseous and particulate contamination—we must consider

(1) =The Effects of Air Rendered Impure by Respiration.=—It has been already stated that an amount of carbonic acid which could easily be borne alone, is intolerable when other products of respiration are mixed with it. These are chiefly organic gases and solids, which (unless removed quickly) render the atmosphere close and “stuffy”—an effect which is readily perceptible by the sense of smell of those entering an occupied room immediately from the outer air. When such a room is inhabited for a few hours, headache, langour, drowsiness, and yawning (which is really a cry for purer air) result. The soporific effects so commonly produced in churches, etc., are commonly due to the vitiated atmosphere, rather than as is supposed to the soothing effects of the sermon.

When the exposure to foul air is _more chronic_, and occurs day after day, there results a general lowering of strength and vigour—both bodily and mental—even where no actual disease is set up. Oxidation processes are retarded; the consequence is an anæmic sallow complexion, which compares badly with the ruddy complexion of those spending a great part of the day out of doors.

The prolonged breathing of air, foul from the products of respiration, is perhaps more common in workshops and schools than in private houses; but in both, a faint smell is commonly perceptible on entering from the open air, indicating imperfect ventilation and accumulation of organic putrescible matter. The preceding remarks are left as in the last edition. It must be noted, however, that recent research attaches more importance to the particulate matter (dust) in the atmosphere than to the amount of gaseous impurity, though the latter remains a convenient index of impurity. Experiments made by Drs. Haldane and L. Smith on themselves negative the older conclusion that a special organic poison exists in expired air. They were able without any appreciable effect on themselves to breathe air which was vitiated to such an extent as to completely prevent a match from burning; and they conclude that excess of carbonic acid and deficiency of oxygen are the sole cause of danger from breathing air highly vitiated by respiration. This conclusion may be accepted under the conditions of these experiments. Under ordinary conditions, however, the evil effects produced by breathing the air of crowded rooms, are due not only to the excess of carbonic acid and deficiency of oxygen, but also to the dust which is usually associated with them. This dust, which may be derived from handkerchiefs of patients suffering from influenza, consumption, sore throat, &c., or from other sources, is apt to be inhaled by the persons occupying such rooms.

The =tendency to catarrhs= is greatly increased by living in a vitiated atmosphere. In the causation of “colds” two elements are concerned, the infective agent, and the condition of the patients. “Colds” are caused primarily by infection from previous patients. The nasal discharge of a “cold in the head” contains the contagium. This is dried on handkerchiefs, and is subsequently scattered as dust, and thus conveyed to others. Ordinarily there is considerable resisting power against such catarrhs. When, however, the general vitality or the local vitality of the mucous membrane of the nose, throat, and lungs is impaired by the breathing of impure air or by sitting in wet clothes after exposure to wet and cold, a catarrh is produced.

The close connection of =phthisis= (consumption) with overcrowding and the breathing of a vitiated atmosphere will be discussed hereafter (page 313). The polluted air acts in producing consumption by depressing vital functions, and diminishing the powers of resistance against the actual contagium of the disease, which is inhaled as dust, produced by the drying of the expectoration of consumptive patients.

The germs of infectious diseases are propagated very rapidly in an impure atmosphere; and typhus fever occurs almost solely in conditions of overcrowding.

In the cattle-plague of 1866, it was found that nearly all the cows died when crowded together in unventilated sheds, while only a third died when there was free ventilation.

The effects of air containing the products of respiration in a _concentrated condition_, and of a deficient supply of air, have been shown only too well in the oft-quoted case of the Black Hole of Calcutta. In this case, 146 persons were confined in a space eighteen feet every way, with two small windows on one side. Next morning 123 were found dead, and the remaining 23 were very ill.

In the experience of this country, the highest death-rates are in the most densely populated districts. The death-rate from phthisis, childbirth, and typhus fever for instance, is far higher in cities than in country-places. The fact may be explained in various ways. Density of population commonly implies insufficient or unwholesome food, unhealthy work, and poverty; but especially impurity of the air, uncleanliness, and imperfect removal of excreta. Of these factors, the vitiated air is probably the most powerful for evil. Children suffer more than adults from close aggregation of population, largely owing to the greater ease with which infectious diseases spread in towns.

(2) =Coal-gas= is obtained by the destructive distillation of coal, free from access of air. The average composition of London coal-gas is hydrogen 50 to 53, saturated hydrocarbons 33 to 66, unsaturated hydrocarbons 3·5 to 3·6, carbonic oxide 5·7 to 7·1, carbonic acid 0 to 0·6, nitrogen 2·5 to 4·1, and oxygen 0·2 to 0·3 per cent. Of these the illuminants are olefiant gas (C₂H₄) and the higher hydrocarbons. Sulphuretted hydrogen and other sulphur compounds are present in small quantities, averaging 12 grains of sulphur per 100 cubic feet of London gas.

The inhalation of coal-gas, even in small quantities, is liable to produce headache, and may lead to chronic poisoning if allowed to continue. Where the escape of gas is more extensive, as when a tap is left turned on accidentally during the night, two dangers may arise. If a light is struck in the room an explosion occurs; or persons may be poisoned in their sleep by inhalation of the gas. The most poisonous gas in coal-gas is the carbonic oxide. The _chief product of the combustion_ of coal-gas is carbonic acid. Some sulphurous acid is also produced, which is irritating to breathe, and injurious to bookbindings, picture-frames, etc. If the flame is imperfect, as when the pressure of gas is too great, some carbonic oxide may also escape.

In recent years =Carburetted water-gas= has been largely mixed with coal-gas in certain districts. This is made by passing steam over heated coke. Thus

C + H₂O = CO + H₂ (coke) (steam) (carbonic oxide) (hydrogen)

The product is water-gas which burns with a non-luminous flame and has no smell. For illuminating purposes it is enriched with vaporised paraffin oil, which gives it a high illuminating power, and a smell rather like that of coal-gas. In some towns as much as 60 per cent. of this carburetted water-gas is mixed with 40 per cent. of coal-gas. Now as the former contains about 30 per cent. of carbonic oxide, and the latter only 7 per cent., a mixture of equal parts of the two gases would contain 18·5 per cent. of carbonic oxide, and would therefore be much more dangerous than coal-gas. This has been found to be so in actual experience of escapes of gas.

In speaking of these products of different illuminants, it is necessary to adopt a =standard of light=. In this country the standard has hitherto been a light known as “one-candle power” which is given by a sperm candle burning 120 grains per hour, or in V. Harcourt’s standard flame by a mixture of air and pentane (C₅H₁₂). A good fish-tail or bat’s wing burner for coal-gas gives an illuminating power equal to 16 candles, and burns from 4 to 5 cubic feet of gas per hour. Most flat flame burners known as 4 or 5, and supposed to burn that number of cubic feet of gas per hour, really consume nearly double this amount of gas. In the following table the amount of various products produced and of vitiation of air caused by various forms of illuminants is compared, when an illumination equal to 16 candles is produced in each instance:—

┌────────────────────┬───────────┬─────────┬─────────┬─────────┬─────────┐ │ │ │CARBONIC │ │ │AMOUNT OF│ │ │ AMOUNT │ ACID │MOISTURE │ OXYGEN │VITIATION│ │ │ BURNT. │PRODUCED.│PRODUCED.│ REMOVED.│PRODUCED[a]│ ├────────────────────┼───────────┼─────────┼─────────┼─────────┼─────────┐ │_Sperm candles_ │1740 grains│6·6 c.ft.│ 6·6 c.ft│9·6 c.ft.│ 11 │ │_Paraffin oil_ │992 „ │4·5 „ │ 3·5 „ │ 6·2 „ │ 7 │ │_Coal gas burned in │ │ │ │ │ │ │ Argand burner │4·8 c. ft. │2·5 „ │ 6·4 „ │ 5·8 „ │ 4 │ │ Flat-flame burner_│5·5 „ │3·5 „ │ 7·4 „ │ 6·5 „ │ 6 │ └────────────────────┴───────────┴─────────┴─────────┴─────────┴─────────┘ [a] Stated in terms of the number of adults who would cause an equal vitiation.

Thus as an adult expires 0·6 cubic feet of carbonic acid per hour, it follows that the amount of carbonic acid produced in one hour by the various illuminants named in the above table, burning so as to give a light equal to 16 standard candles, varies from 4 to 11 times the amount produced by the adult. Candle and oils possess the advantage over coal-gas that no sulphurous acid is produced in combustion. If the pressure in the mains is excessive, some gas may escape through the burner unburnt or carbonic oxide may escape.

In England the flashing-point of mineral oils has been fixed at 73° Fahr. The material of which the reservoirs of lamps are composed should not be glass or other breakable material, and the wick should be contained in a small wick chamber extending nearly to the bottom of the reservoir. Only a tight fitting wick must be used.

The best illuminant for domestic purposes is incandescent electricity, in which no products of combustion are formed, and only a comparative small amount of heat is produced. Electrical illumination possesses the further advantages that there is no blackening of ceilings and no damaging of other decorations as in illumination by gas.

(3) =Air Rendered Impure by Exhalations from the Sick.= In addition to the ordinary impurities of occupied rooms, special impurities are produced, varying with the character of the disease. They may include infectious particles from the sick. In wards for consumptives and for diphtheria, dust in the room has been found to contain the special microbes of these diseases. Making beds, sweeping floors, &c. may help to scatter infectious dust; hence the importance of adopting means of cleansing which will not scatter dust, and of keeping sick-rooms spotlessly clean. In many diseases _e.g._ consumption, a patient may re-infect himself with such infectious dust, and thus diminish his own chance of recovery (see page 311). Hospital wards can scarcely be too freely ventilated; but even more important than ventilation is the strictest cleanliness in every minute detail.

(4) =The Air of Sewers, Cesspools, etc.=, may contain the products of decomposition of sewage, such as volatile fœtid organic matter, carbo-ammoniacal substances, sulphuretted hydrogen, carbonic acid, etc. The amount of these various products varies greatly under different circumstances, such as dilution of the sewage, ventilation of sewers, temperature, etc. The effluvia from cesspools are usually more concentrated than those from sewers. It appears fairly certain that the emanations from sewers or drains may give rise to diarrhœa and gastric disturbances, and to certain forms of sore throat, which favour the production of diphtheria. On the other hand, there is much evidence showing that the danger from sewer-emanations has been exaggerated. Carnelley and Haldane found that the air of the sewers of the Houses of Parliament and of certain sewers of Dundee was not very impure, containing a smaller number of bacteria than external air. There is reason to believe that the emanations from well-ventilated sewers, possessing a good gradient, so that the contents of the sewers are hurried away to the outfall, are free from danger. The chief source of possible danger would be the escape of the bacteria of such diseases as enteric fever or diphtheria, which had been discharged into the sewer from patients suffering from these diseases. But, in the absence of splashing, these bacteria could not escape from a liquid medium. Their escape could only occur when the sewer became dry, and the dust was carried up by rapid currents of air, a very improbable occurrence in sewers. Hence in the majority of instances sewer emanations must be freed from the accusation of producing infectious diseases. Sewer-men usually enjoy good health, and there is no excess of infectious diseases among them.

The emanations from _obstructed drains or sewers_ may cause serious mischief, similarly to that occasionally produced by the emanations from cesspools. Under such conditions, sulphuretted hydrogen, carburetted hydrogen, and other gases are evolved, and fatal asphyxia has been caused by these. In other instances acute sewer-gas poisoning, without pneumonia, has followed.

The exhalations from cesspools or privies while cleaning them out, may produce severe disorders, which are sometimes fatal. When a drain is newly opened or sewer gas gets into a house, a less marked form of poisoning sometimes occurs, chiefly characterised by languor, headache, vomiting, and diarrhœa. In some cases there may be febrile attacks lasting a few days. Children are especially sensitive to such conditions and quickly fall into ill health.

The direct origin of acute infectious diseases from the effluvia from drains or cesspools has occasionally occurred. Leaky and choked drains under a house are especially dangerous. The subsoil becomes contaminated more and more as time goes on; foul gases are aspirated into the house, owing to its interior being warmer than the subsoil; and finally infectious matter may find its way into the house, or carried by insects or vermin, through cracks in the earth.

_Diphtheria_ has been ascribed to emanations from drains and sewers. There is reason to believe that a non-specific form of sore throat may originate in this way; but diphtheria is generally, if not always, spread by personal infection. _Diarrhœa_ has been occasionally ascribed to sewer-emanations. It chiefly occurs in hot weather, and is usually associated with a foul condition of the surface soil, and speedily ceases after this has been scoured by copious rain.

_Enteric or typhoid fever_, has been frequently ascribed to drain and sewer effluvia. It was formerly thought that putrefactive changes alone, under certain conditions of temperature, etc., would produce it, and Dr. Murchison, one of the greatest authorities on the subject, who adopted this view, proposed for enteric fever the name “pythogenic fever” (_i.e._ filth-produced). Isolated cases of enteric fever, occurring where there is no system of drainage, support the same view, as does also the fact that, with the adoption of drainage, the enteric mortality has steadily diminished. On the other hand, numerous cases can be quoted to show that emanations from excreta have been breathed, and sewage-contaminated water drunk, for years, without the production of a single case of enteric fever—until a case is accidentally imported. The weight of evidence is clearly on the side of the view that only emanations from the liquid or solid dejecta of previous enteric patients will produce enteric fever, and that it is the solid particles of the urine or fæces, either inhaled as dust or carried on to food by flies, &c., or mixed with food by contaminated water, &c., which cause infection. Furthermore, modern investigation shows that infection by dust is the exception in England; and that the enteric infection is usually swallowed and not inhaled, being taken in infected water or milk or other food.

(5) =Effluvia from Decomposing Organic Matter.=—(_a_) =The air of marshes= contains an excess of carbonic acid, marsh gas, etc., in addition to other organic matters. Malarial diseases are commonly ascribed to the inhalation of the marsh effluvia under certain conditions, though the recent proof of the part played by the mosquito in spreading malaria, puts the inhalation of such effluvia in the background as cause of this disease (page 307). Some forms of diarrhœa and dysentery have been ascribed, with a less degree of probability, to the same cause. In this case, as in that of emanations from other organic sources, the impurities received by the air are both gaseous and particulate.

(_b_) =The Air of Graveyards= contains an excess of carbonic acid. The older intramural graveyards appear to have been a cause of illness; but modern graveyards, kept under good regulations have never been shown to cause illness.

(_c_) =The Effluvia from Decomposing Carcases=, especially of horses on the battle-field, have led to outbreaks of diarrhœa and dysentery among the soldiers.

(_d_) =The Effluvia from Manure and Similar Manufactories= do not seem to injure the workmen as a rule, but attacks of diarrhœa have been produced in the neighbourhood when the wind has wafted the effluvia towards any particular part. Sore throat, and occasionally diphtheria, have been ascribed to the inhalation of London manure taken into Essex.

(6) =The Effluvia from Certain Manufacturing Processes= seem to be rather nuisances than actually productive of ill health. The vapours given off by _tallow-making_ and _bone-burning_ processes are most disagreeable, but there is little or no positive evidence of their direct insalubrity.

The air of _brickfields_ and cement works is peculiarly disagreeable.

=The Degree of Moisture and the Temperature= of air are of great importance in relation to health. Air which is unduly moist or dry, hot or cold, may be injurious apart from any foreign matters it contains.

The _relative amount of moisture_ is of greater importance than its actual amount. An atmosphere which contains aqueous vapour up to the point of saturation is very oppressive; the normal evaporation of insensible perspiration (and with it of the organic impurities removed from the skin) is interfered with; and consequently the “oppressiveness of the day” is complained of.

_An unduly hot air_ is generally productive of pallor and ill health, though it is difficult to know how much to ascribe to the high temperature, and how much to the commonly coexistent vitiated atmosphere. The temperature of living-rooms ought not to be over 60° to 65° Fahr., and of bedrooms not over 60° Fahr.

The devitalising influence of extreme _cold_ is well known. Its effects are more particularly seen in young children and the very old, who require to be carefully tended during severe and long-continued cold weather. Dry, cold weather, with the temperature near the freezing point of water, and a cutting east wind prevailing, is not uncommonly described as “bracing.” This is so far from being the case, that it requires all the vital powers of the strong and healthy to resist its depressing influence, and the feeble of both extremes of age succumb.