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the Institution. It is very effective as a smoke preventer, and it promises also to be economical in fuel. Welsh dust, which is difficult fuel, is successfully burned on this grate.

Economy of fuel, it should be kept in view, may be effected in two forms: by reducing the rate of consumption of the same fuel for the same duty, or by the substitution of a cheaper fuel, as the various coal slacks. There the mechanical stokers operate with good effect. With the Vicars' stoker, which has recently been tested by the Institution, a large degree of economy has been effected in the substitution of slack for Welsh coal, whereby the cost for fuel to evaporate 1,000 gallons of water was reduced from 10s. 74d. by the ordinary furnace, to 7s. 74d. by the Stoker, showing 28 per cent. economy.

The recent advances made in the practice of coal burning in steam boilers, above indicated, according to the test trials made by the National Smoke Abatement Institution, are the more remarkable when contrasted with the results of professedly smoke-preventing furnaces tested in connection with the Smoke Abatement Exhibition in 1881-82. These were directed, for the most part, to the prevention of smoke, irrespective of economy, and the only systems in which the prevention of smoke was absolutely complete, Blocksage's and Barber's, depended upon a highly heated reverberatory furnace of fire-brick, enclosing the burning fuel, for completely burning the fuel and preventing smoke. But these were not economical of fuel. They evaporated a mean of 6·65 pounds of cold water per pound of Yorkshire slack; while, in the recent performances of Thompson's and Ashworth's furnaces, a mean of 9.64 pounds of cold water was evaporated per pound of Yorkshire slack. Taking the cost of the slack at 10s. per ton delivered, the contrast stands as follows:

Coal consumed per 1000 galls. 1881-82

of water evaporated.

1886-87

... 13 cwt. 48 lbs. 9 cwt. 29 lbs. Cost of fuel per 1000 galls........ 6s. 8d. 4s. 7d.

Here is an apparent economy of 31 per cent. in 1886-87 as against 1881-82, combined with complete combustion.

The result of the year's testing has been to show that further improvement has taken place, both in the furnaces designed to substitute mechanical stoking for hand-stoking, and in those wherein ordinary hand-firing is employed.

[For discussion on this paper see page 335.]

On "Smoke Abatement," by ORLAND D. ORVIS, Chicago, Ü. S. A.

MR. PRESIDENT, MEMBERS, AND GENTLEMEN,

One of the greatest blessings which nature can confer upon mankind is good health. Every thing which can affect this priceless boon is of the most vital importance. How necessary then that we look carefully to the purity of the air we breathe, to the great supporter of life, oxygen, which we constantly inhale into our lungs. Air is a more indispensable agent than water or food. We cannot exist many moments without air. Water can be purified by boiling, by filtering, and by chemicals. But it would be practically impossible to effect a thorough filtration of the air before we inhale it.

The average composition of atmospheric air, according to Regnault, Bunsen, Dalton, and others, is in volumes :

[blocks in formation]

The purity of the air is more or less affected by other substances, such as the products of combustion of coal, vapour of water, ozone, ammonia, organic and inorganic dust, and the decomposition of organic matter.

One of the chief reasons why the atmosphere of cities is not so pure and healthful as it is found to be in the country, is because the enormous volume of coal-gas and smoke emitted from thousands of chimneys in large cities pollutes the air with noxious vapours destructive alike to animal and vegetable life.

From the vast forests of chimneys in all the great manufacturing towns in England, there arises a dense exhalation of inky blackness, which envelopes these cities in a pall of gloom from Monday morning until Saturday night. It is only on the Sabbath that we are permitted to catch a glimpse of clear blue sky, and breathe the pure air, so essential to health and comfort. The sooty vapour finds its way to our food and drink, it is

inhaled into the lungs, impairs the health, stains and discolours the walls of public and private buildings, soils the face and clothing, penetrates houses, smears carpets and furniture, almost destroys oil paintings, soils books and engravings and whatever precious objects of art or utility we try to preserve. Indeed it is difficult to say in what particular we are not harmed by the all-persuasive soot and smoke. However much opinions may have differed, there is little doubt now that the cause of the London fogs can be traced to the smoke. The infinitesimal particles of water-vapour floating in the atmosphere, become coated with the volatile products of combustion-the sooty particles of carbon which float in the hydrogen,-and these countless myriads of molecules or atoms, impervious to the sun's rays, envelope the great Metropolis in impenetrable gloom.

The highest medical authorities attest the injurious effects on the respiratory organs, and on the body generally, from living in a smoke-laden atmosphere. The fatal consequences of the fogs to which London and other great towns are periodically subjected are shown by a marked increase, on these occasions in the Registrar General's returns of mortality.

The prevention of smoke is the great want of the age.

In this era of invention and progress, when the fertile brain of the scientist and the inventive genius of the skilled mechanic are achieving such marvels of invention, it is almost a wonder that the great problem of abating the "smoke nuisance" of large cities should have remained so long unsolved. The secret art of burning bituminous coal without allowing a large part of its carbon to escape in a cloud of smoke, seems to have baffled the wits of inventors during the past 200 years. The alchemists, in 1685, tried various devices for the purpose of consuming the smoke in their furnaces. In 1785, Watt patented an apparatus for consuming smoke. His process consisted in feeding the coal in a hopper, and forcing the gas and smoke to pass through a body of hot coal.

As far back as 1306, the smoke of burning sea coal was considered to be so injurious to public health, that King Edward I. issued an order forbidding its use. It is alleged that one man who disregarded the King's order, was tried, convicted and executed for burning sea coal in London.

Much might be said relative to the history of the various fuels used by civilized man during the past few hundreds of years. It is a curious history, the progress from wood to coke, and from coke to coal. Wood and coke are now little used for steaming purposes in this country, and King Coal is the present ruling monarch on the throne of fuels. Anthracite is the most condensed form of mineral coal, and the richest in carbon. All

coals, including naphtha, petroleum, asphaltum, &c., are but representatives of the change from vegetable to mineral matters. Anthracite is the condensed coke of bituminous coal. American anthracite possesses from 85 to 92 per cent. carbon, and 21⁄2 to 4 hydrogen. South Wales and Russian anthracite have been found to possess as high as 95 per cent. carbon. Bituminous coal possesses about 80 per cent. carbon and 5 hydrogen, and from 10 to 50 per cent. bitumen, from which smoke is produced.

Concerning the origin of coal, its connection with the vegetable kingdom is too distinctly traced to admit of any reasonable doubt that this fuel once formed parts of growing plants, requiring in its geological transformation many thousands of years. The coal, then, which we see burnt in our furnaces to-day liberates the heat and light of the sun's rays which have been stored in the coal through countless ages.

The total amount of coal consumed annually in the United States now exceeds 100,000,000 tons. The annual consumption of coal in Great Britain is now not far from 150,000,000 tons. The entire annual product of the world is estimated at 300,000,000 tons.

Should the coal supply ever become exhausted, Nature, in her bounteous wisdom, has provided us with a still better fuel, viz., Petroleum, which is now quite extensively used as fuel in the United States and in Russia. Liquid fuel, however, would prove to be rather an expensive luxury in England at the present low price of coal.

Some of our ablest scientists maintain that the area of the subterranean seas of petroleum is even greater than that of the coal beds of the world, and that petroleum distillation in Nature's vast laboratory is still going on as rapidly as ever.

It is only by the light of modern science that we are enabled to explain the meaning of the heat given off in the act of chemical combustion. Fifty years ago we possessed no knowledge of chemical dynamics.

Combustion consists in the oxygen of the air uniting (forming a chemical union) with the constituents of the combustible substance.

The chemical combination of atmospheric oxygen with the carbon of coal is always accompanied by the production of more or less heat, but it is only when the action is so rapid as to evolve intense heat, accompanied by light that the process is called burning or combustion. A few substances burn at ordinary temperature, such as phosphorous, which glows when exposed to the air. While the absolute amount of heat evolved during the combustion of any burning body is the same, yet the

sensible heat may vary according to the rapidity of the process. Thus, when phosphorous is exposed to the air at ordinary temperature it very slowly combines with oxygen, and gives out little heat at any one moment, but it is diffused over a great length of time, while if the phosphorous is set fire to in the air, it burns vividly, and gives out much heat and light for a short time, and still further, if the burning phosphorous be placed in pure oxygen, it enters into most vivid combustion, and evolves a most intense heat and brilliant light for a still shorter time. The same remarks apply to the coal consumed in a furnace. So long as the furnace-door is left open, and there is little draft of air through the fuel, a moderate amount of heat is evolved, which may last for several hours; but when the door is shut, and much air is drawn through the coal, the latter is more quickly burned, and more heat is evolved during a shorter period of time than before, but in the long-run there is the same amount of heat evolved.

A fresh charge of coal thrown upon a fire absorbs heat which liberates the gas from which flame is produced. This gas is composed of hydrogen and carbon-carburetted hydrogen. Coal gas will ignite only as it combines with the oxygen of air. The hydrogen then separates itself from its fellow-constituent, carbon, and unites with atmospheric oxygen producing steam. Carbonic acid is the result of perfect combustion, and is a compound of one atom of carbon with two atoms of oxygen. Carbonic oxide is composed of one atom of carbon and one atom of oxygen, only half of the required amount of oxygen to produce perfect combustion. The air in passing through the grate bars, gives out its oxygen to the incandescent carbon, producing intense heat, in the formation of carbonic acid. This acid passing upwards through the body of unconsumed coal, absorbs an additional portion of carbon and becomes carbonic oxide. This carbonic oxide, of which smoke is the visible part, inflames at a lower temperature than ordinary coal gas, and is often ignited at the top of the chimney, on meeting the air, as seen in the chimneys of blast furnaces, and steam vessels.

It requires, chemically, the oxygen of 152 cubic ft. of air to consume one pound of coal. The gas requires 45 and the coke 107 cubic ft. A furnace charged with fresh coal, generates a large volume of gas (about four cubic ft. to each pound of coal), requiring an equivalent quantity of pure air for its combustion. Now, by reason of the mass of fresh fuel thrown in, the passage of air through it is necessarily the most restricted. Thus the smallest quantity of air will be enabled to gain admission simultaneously with the greatest demand for it, and the largest generation of gas simultaneously with the most restricted means

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