Pollution from Gas Works.

119

a site in a thinly-populated place, and as far from the town as possible.

When the gases and vapours issue from the retorts they are subjected to the action of water and lime. The tarry liquid, nearly all the ammonia, and some of the sulphurous and carbonic acids, and sulphuretted hydrogen, are retained by the water. The lime takes up the rest of the sulphurous acid, sulphuretted hydrogen, and carbonic acid, and the traces of prussic acid which escape solution. The gases that remain pass into the gas-holders, and from thence to the points at which they are to be consumed for illuminating and heating purposes. Unless great care is taken in purifying the gas before it is delivered to the consumers, it is certain to contain sulphuretted hydrogen. Impure gas is most injurious to the health of inmates of rooms where it is burnt. Ammonia is never absent; but it cannot be regarded as an injurious impurity. Disulphide of carbon is a most objectionable impurity, and is invariably present. When burned it produces an acid, which acts corrosively on the leather binding of books and on many other articles. When coal gas contains an injurious amount of impurities it becomes a nuisance, and the manufacturer may be compelled to abate it.

The lime used in purifying coal gas is a nuisance when it is allowed to remain in large quantities exposed to the atmosphere, into which it abundantly exhales sulphuretted hydrogen gas. Oxide of iron is now very generally substituted for lime as a coal gas purifier. The oxide, mixed with sawdust, is placed in layers. ten or twelve inches deep on perforated trays or shelves, through which the gas passes. So soon as the absorption of sulphuretted hydrogen gas is complete, the sulphide (into which the oxide has been converted) is exposed to a current of air, which reproduces the oxide, and sets free the sulphur. This purifier can, therefore, be repeatedly used, until it becomes mixed with too much sulphur; even then it is valuable to the sulphuric acid manufacturer. The drainage from gas works should never be allowed to mix with sewage from chemical works, the acid contained in the one setting free the sulphuretted hydrogen and prussic acid dissolved in the The gases evolved from such a mixture have destroyed

other.

the lives of workmen.

Coke works and lime kilns discharge enormous quantities of carbonic acid and carbonic oxide into the air. They should not be tolerated within the limits of towns. Carbonic acid, carbonic oxide, and traces of sulphuretted hydrogen gas are given off during the manufacture of bricks and cements.

Artificial manure works in general throw out sulphurous acid gas. Sometimes the odours of decomposing animal matter and of hydrofluoric acid are very perceptible at and near these works ; but in general they do not affect the atmosphere to a greater

extent than alkali works.

Private slaughter-houses are amongst the greatest nuisances

from which the inhabitants of towns suffer. The atmosphere of those places is highly tainted with putrescent matters; and the exhalations from them caunot but seriously affect the public health.

Bone-boiling, tallow-melting, and glue-making are processes during which are evolved vapours of no very pleasant odour. If the nuisance be very sensible, it admits of a remedy either by an action at common law or by the interference of the public health authority.

The air of towns is tainted with the products of the combustion of fuel. Carbon constitutes the great bulk of ordinary fuel: at a high temperature it unites with atmospheric oxygen, and produces carbonic acid. The quantity of heat evolved during combustion depends upon the amount of oxygen consumed by the fuel. Carbon unites with oxygen in two proportions, forming carbonic acid and carbonic oxide: the centesimal composition of these compounds is shown in the table :

Carbonic acid is carbon in a perfectly oxidised or mineral state but carbonic oxide is charcoal imperfectly burned, and it is a highly combustible body. When carbon is converted into carbonic oxide instead of carbonic acid, sixty-seven per cent. of the fuel is wasted; and it is owing to the defective construction of furnaces that a large quantity of the fuel used in manufactories is lost, because its carbon is converted into carbonic oxide. The pale flame which is sometimes seen emerging from high chimneys is produced by highly heated carbonic oxide, combining with the atmospheric oxygen.

Limited oxidation is a cause of the evolution of carbonic oxide from furnaces, stoves, and fire-grates. Sometimes the carbon of the fuel is at once converted into carbonic oxide; at other times carbonic acid, formed where the air is abundantly supplied to the fuel, is afterwards converted into carbonic oxide by contact with red hot carbon. The greater part of the fuel in furnaces is in a state of incandescence, but not of combustion—that is, it is so highly heated by the burning part of the fuel that it becomes luminous. Carbonic acid gas, passed over incandescent charcoal, combines with it, and forms carbonic oxide; and in this way the products of the perfect oxidation of one part of the fuel carry off, imperfectly oxidised, another portion of it.

The imperfect oxidation of fuel produces two bad resultsfirstly, a waste of heat; secondly, the vitiation of the air. Carbonic oxide is a highly poisonous compound; and, as it does not contribute to the growth of plants, its presence in the atmosphere subserves no useful purpose.

Dense fuels such as, for example, anthracite, or smokeless coal

Smoke Consuming Furnaces.

121

-produce during their combustion more carbonic oxide than lighter fuels-wood and peat more especially. Carbonic oxide is at least four times more poisonous than carbonic acid. The headache, giddiness, and severer symptoms produced by the gases evolved from stoves, braziers, and chafing-dishes appear to be due much more to the influence of carbonic oxide than of carbonic acid.

The cause that produces carbonic oxide in furnaces also gives rise to smoke from them. On an average nearly one per cent. of bituminous, or flaming coal passes of in the form of soot—a mixture of tar, charcoal, coal ashes, and a few other substances. Smoke, hanging like a pall over a town, acts injuriously by partially excluding light; and air containing sooty particles is likely to affect the respiratory organs. Whether or not the more serious affections of the breathing organs are produced by the respiration of smoky air, exact evidence is wanted to determine.

The evolution of smoke and the production of carbonic oxide might be considerably lessened by careful stoking. If too much air be admitted, the temperature of the fire is lowered below the point of perfect combustion; but the great and usual defect is a deficiency of air. Coal contains carbon and hydrogen, and when highly heated yields carburetted hydrogen gas. When a fire is lighted, coal gas begins to be produced, and the hydrogen of it is oxidised. The carbon also, if there be abundance of air, is burned; but if the supply of oxygen be inadequate, part of the carbon, or charcoal, is converted either into carbonic oxide or smoke, or both. To prevent smoke, the fire should be maintained at a high and nearly equable temperature, so that the gases may not be cooled. The fuel should be added frequently and in small quantities and pieces, and care must be taken not to choke the furnace. Fresh fuel should be placed at the door of the furnace, the red coal being pushed back. A common mistake is to do exactly the reverse, whereby the fresh coal is, to a great extent, converted into unoxidised gases, which escape up the chimney. The openings through which the air is admitted to all places where fuel is burned should be kept free from cinders and ashes. There are several kinds of furnaces which are said to emit no smoke, but the best of them permit unoxidised matters to escape. Jucke's chain furnace is very costly, but it effects great economy of fuel. The fire bars consist of a series of "endless" chains, set in motion by means of two wheels furnished with teeth. A hopper is placed in front of the furnace, and from it the fuel is delivered through an opening, the size of which regulates the supply of fuel to the furnace. By these means the supply of fuel is regular, and every part of it is equably exposed to the air. Hill's furnace is intended to prevent smoke, by mixing highly-heated air with the unburnt gases as they pass from the furnace to the flue. Prideaux's smoke-prevention furnace is mentioned favourably by several authorities on this subject. The 108th section of the

I

122 Influence of Chemical Works on Health, &c.

Towns Improvement Clauses Act (1847) enables municipal authorities to prosecute those who permit black smoke to escape from the chimneys of manufactories.

In some parts of England chemical and smelting works are so numerous that the gases evolved from them have almost annihilated the vegetation of considerable tracts of country. In the spring of 1874 I was employed by the Chamber of Agriculture of Lanca shire to inspect the manufacturing districts of that county-Wid ness, Warrington, St. Helens, &c.—and to deliver a lecture upon the results of my observations at Newton-le-Willows. I found many tracts of land, several thousands of acres in extent, so much affected by the noxious vapours, and gases, and smoke that they only produced very poor crops. I found that on some farms close to alkali and copper smelting works whole crops had utterly failed. For miles not a healthy tree was visible. In some places the trees and bushes were utterly destroyed, blackened stumps alone remaining of them. I readily detected acid liquid on the leaves of such plants-hardy bushes-as had survived. Cows kept near these works were, I was informed, peculiarly liable to abort; and the condition of all kinds of stock was very unhealthy. On close inquiry I found that the death rate was very high for semirural districts.

The factories which give forth the gases that have effected so much injury to vegetation and to health in Lancashire and other places are salt-cake, soda ash, copper smelting, and glass works. They evolve sulphur acids, hydrochloric acid, and metallic vapours, besides enormous volumes of black smoke. The numerous collieries, too, blacken the atmosphere with volumes of smoke.

The Alkali Nuisance Prevention Act was amended in 1874, and it now includes sections prohibiting the escapement of sulphurous acids and other deleterious gases from alkali and acid works. The chief inspector of alkali works is Dr. Angus Smith, of Manchester, who, as well as one of the Assistant Inspectors, Dr. Blatherwick, periodically visit Ireland to examine into the condition of the chemical works. Although alkali and acid factories are placed under the supervision of special inspectors, they are not outside the jurisdiction of the local sanitary authorities. Should they produce a nuisance, either by permitting the escape of black smoke or of an undue amount of acid vapours or gases, their owners can be proceeded against under the common sanitary laws.

Influence of Elevation on Health.

CHAPTER XIII.

123

METEOROLOGY AND TOPOGRAPHY IN RELATION TO HEALTH.

The highest inhabited part of the world is the Buddhist Convent of Hanle in Thibet, 10,000 feet above the level of the sea. Mr. Glaisher ascended in a balloon to a height of 38,000 feet, at which altitude his heart fluttered rather than beat, and his hands were benumbed. The huge condor may be observed flying 500 feet higher than the summits of the Andes, five miles above the sea level.

The physical condition of the atmosphere is a point of considerable hygienic importance. At great heights above the surface of the ocean the pressure on the body is much diminished, the circulating fluid is impelled with greater rapidity through the vessels, and the respirations are proportionately increased. A pleasurable excitement is experienced, and the desire for muscular exercises is exalted. The advantages of mountain air are many. The light is less obscured in passing through it; the quantity of moisture in it is small; there is the merest trace of organic matter; and no infusorial animals occur in it. The air of upland regions -say from 3,000 to 7,000 feet elevation-has been found most useful in the treatment of dyspepsia, anæmia, or wasting of the body, gout, and scrofula. At a height of from 5,000 to 7,000 feet rheumatic patients often find their painful malady ameliorated. Inflammation of the lungs and acute bronchitis do not appear to be removed by mountain air. There is some doubt as to the efficacy of mountain air in the treatment of pulmonary consumption; but it is remarkable that persons who live in very elevated regions rarely suffer from this disease. Malarious fever is seldom, if ever, contracted at great heights.

According to Toner, the greatest number of deaths from phthisis in the United States occur in the parts least elevated, and in which there is much water. Perhaps as the cold in the United States is intense in winter that it is the conjoined influence of cold and damp that is productive of thoracic complaints. In some moist but mild climates pulmonary consumption is rare. Tubercular diseases are said to occur very rarely in the highest parts of the inhabited Alps.

Dr. M'Nab' has directed attention to the remarkable immunity from pulmonary phthisis enjoyed by the Highlanders of Scotland, and more especially by the natives of the Hebrides. In one dis

trict inhabited by 2,500 persons there were but five well defined cases of pulmonary consumption during a period of nine years. In the peninsula of Dingle the infrequency of phthisis is equally remarkable.

The Immunity from Consumption in the Hebrides. By John M'Nab, M.D. Edinburgh, 1869.