carefully-conducted experiments of Sir Humphry Davy, there cannot exist a doubt as to the necessity which exists for preventing a surcharge of cold air acting upon the furnace. Its high temperature is essential to its efficiency, either as regards economy in the use of the fuel, or the equivalents of ignition with atmospheric air.

The question of temperature applied to combustion is therefore one of great interest. It involves many considerations, both mechanical and chemical; and although apparently of easy attainment, it is, nevertheless, surrounded with many difficulties. Our knowledge of high temperatures, as well as our instruments for measuring their intensities, are far from perfect; and we have yet to learn at what temperature the gases unite, or, as Mr. Williams calls it, ignite 'in a series of electric explosions,' with atmospheric air. This temperature, or rather the lowest temperature at which the gases and atmospheric air will unite, has not yet been ascertained: some fix it at 800°, and some others at 1000° of Fahrenheit. These degrees of temperature are, however, highly problematical, as Sir H. Davy's experiments seem to prove that a white heat is necessary to produce the phenomena of combustion; and as atmospheric air seldom exceeds from 80° to 90° of temperature, it is evident, that when air of this temperature is poured upon the incandescent fuel, it will rob the evolving gases of a portion of the heat essential to combination, and thus reduce the temperature in many cases below the point of ignition.

The combustion of fuel is to all appearance an easy as well as a natural process; but on mature consideration it will be found that before we can arrive at sound practice, we must have some knowledge of science; and before we can make a single step in advance, it must be done through those laws which the Great Author of Nature has so bountifully and so invitingly supplied for our guidance.

195

LECTURE IX.

ON THE ECONOMY OF FUEL, CONCENTRATION OF HEAT, AND PREVENTION OF SMOKE.

IRRESPECTIVELY of the intensity of heat, form of boilers, and quality of fuel, as described in the last Lecture, there are other conditions connected with the phenomena of combustion which require attentive consideration before that process can be called perfect, or before economy or the prevention of smoke can be attained. It is perfectly clear, that although we may possess abundance of excellent fuel, and a perfect knowledge of all the elements necessary for its combustion, yet we are still far short of attaining our object, unless due regard to economy is strictly kept in view. A manufacturer may have well-proportioned boilers, excellent furnaces, and good fuel; but with all these advantages he will not succeed, unless the whole of the elements at his command are properly and economically combined, and that upon fixed laws already determined for his guidance. Count Rumford, in his admirable Essays on the Economy of Heat,' truly observes, that No subject of philosophical enquiry within the limits of human investigation is more calculated to exite admiration and to awaken curiosity than fire, and there is certainly none more extensively useful to mankind. It is owing, no doubt, to our being acquainted with it from our infancy that we are not more struck with its appearance, and more sensible of the benefits we derive from it.

Almost every comfort and convenience which man by his ingenuity procures for himself is obtained by its assistance, and he is not more distinguished from the brute creation by the use of speech than by his power over that wonderful agent.'

Such was the opinion of one of the most eminent philosophers of his time, and such were the pertinency of his remarks and the depth of his researches, that had he lived in the present instead of at the close of the last century, he would not only have extended and enlarged our views on the management and economy of heat, but he would have expressed astonishment at the increase, the immense extent of expenditure, and the lavish and culpable waste of fuel by which we are surrounded on every side. It is true we have some exceptions to this rule, such as the engine boilers in Cornwall and some parts of the Continent, where fuel is expensive; but taking the aggregate, it might be said, without fear of contradiction, that if onehalf of the fuel now used were properly applied, it would perform the same service, and afford the same comforts, as we now derive from the whole consumption of our mineral products. This is a great reflection upon the philosophy and the economy of the age, and I think it can be shown that one-half the fuel now wasted might be saved with great advantage to individuals, and with increased benefit as well as comfort to the public. The wasteful expenditure which exists does not arise so much from ignorance as from prejudice, and a close adherence to old and imperfect customs. We all, more or less, venerate the works of antiquity, but unfortunately we forget to draw the distinction between what is really ancient and sound in principle and what is imperfect in practice. Hence follows a blind adherence to established usage, and the consequent propagation of all the defects as well as the

perfections of the system. Now this state of things should not exist, as we have the experiments of Watt, Rumford, Davy, Parkes, and many others, before us; and adding to these the excellent treatise of Mr. C. W. Williams on the combustion of coal and prevention of smoke, we are enabled by these means to establish a sound and much more perfect and economical system of combustion. Keeping these objects in view, we shall endeavour to determine some fixed principle on which may be founded the prevention of smoke, concentration of heat, and economy of fuel.

It is well known that in practical operations there is no combustion without oxygen as its supporter: and as that important element cannot be procured for general purposes without the other constituents of atmospheric air, it follows, that in order to effect combustion, a regular supply of this compound must be constantly at command. Now it is not the facility, but the control and regulation, of the supply of air which requires attention, and on this point of the inquiry we must refer to the researches of Mr. C. W. Williams, where, in speaking of gaseous combinations,' he shows that much depends upon the conditions and proportions in which the gases evolved during the process of combustion combine with the oxygen of the air. And in order to effect this it is necessary for those entrusted with the management of furnaces to know the 'equivalents' or definite proportions under which these combinations take place. On this head it will be sufficient to observe, that the principal gases evolved from coal in a state of combustion, are light carburetted hydrogen, heavy carburetted hydrogen or olefiant gas, and some others, such as carbonic acid gas, carbonic oxide, &c., the properties of which it is not requisite on this occasion to investigate, but to confine the enquiry to the union of

light carburetted hydrogen and heavy carburetted hydrogen with the oxygen of the atmospheric air. Following, therefore, the Daltonian theory, it will be found that the constituents of one atom of light carburetted hydrogen or bicarburetted hydrogen, consists of the following symbols, each representing an atom, and the figures the weight:

Bicarburetted hydrogen is therefore composed of 2 equiv. hydrogen and 1 equiv. carbon=1 equiv. bicarburetted hydrogen. In weight 2 hydrogen+6 carbon=8 bicarburetted hydrogen. The constituents of heavy carburetted hydrogen are, 2 equiv. hydrogen and 2 equiv. carbon=1 equiv. heavy carburetted hydrogen. In weight, 2 hydrogen and 12 carbon, or 2+12=14 heavy carburetted hydrogen.

These are the two principal gases which require attention, and as the oxygen of the air is an element that cannot be dispensed with, the object of our next enquiry will be the quantity and constituents of atmospheric air.

According to the best authorities, atmospheric air is found in the proportion of 1 equiv. of oxygen to 2 equiv. of nitrogen, or, according to Mr. Williams (and adopting the figures as representing the weights as before):