DR. ARNOTT ON HEALTHFUL WARMTH AND VENTILATION. * TEE laws of

combustion and ventilation applied to the pur- poses of health and life in a civilized state are the subjects of this volume. Particular topics, indeed, wear a smaller appear- ance, and take upon themselves a very housewife kind of look ; the two most important -being a fireplace which shall consume its own smoke yet retain the bright and cheerful fireside oha- meter which an Englishman loves, and the knocking out a brick in the chimney-wall towards the top of the room to insert a Little machine that acts by means of a nicely-adjusted valve. The practical effects which these things produce, the laws by which they operate, and the easy simplicity by which those laws are ex- pounded and applied, not only redeem the treatise from anything like technical mechanics, but render it an interesting and instruc- tive essay, apart from its immediate bearing on comfort and health.

The great object in domestic " combustion " is of course to get

• On the Smokeless Fireplace. Chimney-Valves, and other Means. Old and 'New, of obtaining Healthful Wartnth and Ventilation. By Neil Arnett, M.D., &c., Phy- sician Extraordinary to the Queen; Author of "The Elements of Physic," &c. Published by Longman and Co. .

all the heat you can oat of your fuel. The common iron stove ac- complishes this to a great degree ; but it barns the air, is disagree- able and is admittedly unwholesome. Our author's invention,

well known as "Arnotes stove," when properly made and fitted, obviated these -evils; but Englishmen do not like stoves, and very

probably not the monotony of a uniform temperature regulated by thermometer. It is of no use pointing to the Continent and Ame- rica, where people do not like fireplaces : " de gustibas non eat," and indeed in some spots, as at St. Petersburg, they cannot be warmed by them. Of as little use is it to appeal to futurity—to urge upon a Briton that the coal-mines are exhaustible, and that posterity some centuries hence will have to shiver if he goes on wasting fuel in

open grates at the rate he does. "Beef and a sea-coal fire" are national tastes ; an Englishman will have an open fire as long as he can get one, without pinch respect to his own pocket, much less to future ages. To meet this state of public opinion is an object of Dr. Arnott's open smoke-consuming grate, and at the same time to save a large portion of the four or five sixths of the heat given out by the fuel which is now wasted by going up the chimney.

"Is it possible to avoid or to consume smoke—in other words, to produce a smokeless coal-fire ?_ "Common coal is known to consist of carbon and bitumen or pitch; of which pitch, again the chief element is still carbon, joined then with hydro- gen, a substance Which, when separate, exists as an air or gas.

"When the coal is heated to a temperature of about 600' Fahrenheit, the bitumen or pitch evaporates as a thick, visible smoke which, as it after- wards Cools, assumes the form of a black dust or flakes called blacks, or smut or soot. If pitchy vapour, however, be heated still more than to 600°, as it is in the red-hot iron retorts of a gas-work, or while rising through a cer-

tain thickness of ignited coal in an ordinary fire, its elements combine in a new way, and are resolved in great part into invisible carburetted hydrogen gas, such ail we burn in street-lamps. "Now, when fresh coal is thrown upon the top of a common fire, part of it is soon heated to 600°, and the bitumen of that part evaporates as the visible

smoke immediately rising. Of such matter the great cloud over London con-

sists. Whatever portion of the pitchy vapour, however' is heated to the temperature of ignition by the contact of flame or ignited coal suddenly be-

comes gas, and itself burns as a flame. This is the phenomenon seen in the flickering or irregular burning of gas, which takes place on the top of a common fire.

"But if fresh coal, instead of being placed on the top of a fire, where it must emit a visible pitchy vapour or smoke, be introduced beneath the burn-

ing red-hot coal, so that its pitch, in rising as i vapour, must pass through

the burning mass, this vapour will be partly resolved into the inflammable coal-gas, and will itself burn and inflame whatever else it touches. Persons may amuse themselves by pushing a piece of fresh coal into the centre of the i

fire n this way, and then observing the blaze of the newly-formed gas. "Various attempts had been made to feed firep always from below, and so to get rid altogether of smoke. One of the grit recorded was made by Dr. Franklin. He placed the buriiing fuel in a cage of iron bare supported on pivots ; and when part of the fuel was consumed, leaving the upper part of the cage empty, he filled the vacant space with flesh coal, and immediately turned the cage upside down, so that the new smelting coal was underneath, sending its pitchy vapours upwards through the mass of ignited coke. Another attempt was made about thirty years ago, by an ingenious manufac-

turer in London, Mr. Cutler. He platted a box filled with coal under the fire, in which box there was a moveable bottom, by raising which the coal was lifted gradually into the grate to be consumed. The apparatus for lift- ing, however, was complicated, and liable to get out of order ; which, with other defects, caused the stove to be little used." .

The principle of Dr. Arnotes open smokeless stove is founded on that of Cutler, but is more simple in its mechanical action,

While it is constructed with a stricter reference to the laws both

of combustion and Ventilation or draught. A fuel-box is attached to the grate, which, by a simple contrivance set in motion by the

poker, feeds the fire without trouble ; the wide chimney-aperture of common stoves is considerably narrowed by a metal covering, to stimulate the draught, which admits of regulation by "a blower." There are also other contrivances to influence the heat of the room, or which are necessary to the practical erection of the stove, or to a complete understanding of its nature ; and these are all explained at length, and by means of diagrams, in the volume. The main objects, however, are to consume nearly all the smoke of the fuel, and to turn nearly all the heat to account, by feeding the fire from the bottom and regulating the draught. The invention may be ap- plied to a common grate by a competent workman. Immediately connected with combustion is ventilation. "We think our fathers fools, so wise we grow." What more outré than the oldfashioned lofty chimneypiece and the high-set stove ? Tasteless as they were, however, they were more comfortable and wholesome than the modern low grate and corresponding chim- neypieoe. Heat radiates. If the centre of a wheel were a fire,

the heat would be given off equally along the line of spokes all round. Heat does not warm the cur it passes through, but any

opposite body on which it impinges. Thus the heat given off in

front of a fire does not directly warm the air of the room, but first warms some opposing body—a wall, a screen, a table, &c. A good

portion of the heat from the top of the fire radiates up the chim- ney, in a ratio proportioned to the faulty construction of the fire- place. In an oldfashioned high-set stove a large part of the warmth

from the bottom radiated into the room on to-the floor. In a low- set modern stove it radiates into the hearth, leaving the bottom of the room a species of cold-air bath. • "As would be anticipated by a person understanding the subject aright,

low fires occasion coldness of the feet to inmates, unless when they sit near the fire with their feet on the fender : but many of these, deceived by their fallacious reasoning, are disposed to blame the state of their health or the

weather as the cause, and they rejoice at having the low fire, which can quickly warm their feet when placed near it. A cotnpany of such persons seen sitting close around their fire with thankfulness for its warmth near their feet, might suggest the case of a party of goodnatured people duped out of their property by a swindler and afterwards gratefully accepting portion of it from him as a charitable contribution." As rooms are constructed and generally used, a greater evil than even cold feet, or waste of fuel, attends low chimneypieces, or rather low chimney-openings. Heated air or gas ascends. The vitiated air we expire, and any impurities from lights, dishes, &c., rise to the top of the room. These strata of vitiated airs, so to speak, get lower and lower, contaminating the atmosphere as they descend. It is of small use to open the top of the windows; that does little more than admit cold air. The only escape for the contaminated at- mosphere is by the chimney-opening. When this is very high, the air may be comparatively pure for persons sitting down, though that above their heads is vitiated. In the case of low modern ohim- neypieces the air below the mouth is vitiated. Dr. Arnott's plan of ventilation in connexion with his open smokeless-grate, but applicable with any stove, is to make a small aperture in the chim- ney just below the ceiling, and fix therein a small ventilator, which carries off the foul air as it arises. The principles just indicated are fully explained by Dr. Arnett, as well as the nature and mechanism of his invention. The truth of the principle is also shown by cases from which we take one illustration.

"The wretched sleeping-rooms resorted to by mendicants and other vagrants in great towns have their inmates often lying on the very floors, and so thickly crowded as completely to cover the floors. Yet it has been remarked that in these houses disease was less frequent and destructive than in some others which were not so crowded, and where there were raised benches or bedsteads for the sleepers. The explanation is, that in the first. mentioned rooms the heads of the sleepers were considerably below the level of the chimney-openings or fire-places, and had therefore more free ventila- tion than the others."

Other inventions already before the public, and partially re- duced to practice—as the celebrated Arnett stove, and the ven- tilating pump—are more fully and systematically explained and il- lastrated than they have hitherto been. Dr. Arnott says in a notice, that his "professional engagements did not allow him at that time [when he first called attention to "Warming and Venti- lating to publish more on the subject, and he waited until his intended retirement from active professional duties should enable him to repeat and extend his lesson. This work is his present offering."

His lesson cannot be said to have fallen on barren ground ; for his name is an authority, and " Arnott's stove" is in compara- tively extensive use. It is probable, however, that all inventions would be more quickly adopted did their authors turn them into monopolies and endeavour to introduce them to the world as a mat- ter of mercantile profit. Like Franklin, Dr. Arnett takes out no patents ; yet the personal exertions of an inventor as a monopo- list may be necessary to the quick establishment of his inven- tion, for two reasons. The world is charitably apt to suppose that what is given away is not worth having ; no one is so interested in the success of a design as the designer himself, or is indeed so qualified to carry it out. Manufacturers who undertake from a printed description to execute a new invention without a sufficient knowledge of the principles on which it is based are liable to fail. Till the practice is thoroughly established, unforeseen difficulties arise, which not only require a mastery of the principles to over- come, but adiscoverer's invention to boot. Had Watt, instead of *oinii3g with Bolton to sell improved steam-engines, merely pub- halted his theory and constructed some models, it is probable that, instead of having very soon to contend at law with invaders of his patent, he might have been denounced, by " parties " whom his discovery had led into expensive and vain experiments, as a visionary projector, whose notions could not be reduced to prac- tice; and the theory of the "separate condenser" remained for a long time:barren.