DESCRIPTION OF MR. WHITE'S PATENT BRICK AND TILE-MAKING MACHINE. In the summer of 1839 I was requested to examine a pug-mill at Brixton, then in operation, supplying clay to a brick machine invented by the Marquis of Tweeddale, whose success in drain tile making establishes an early claim to the art of moulding clay for agricultural purposes by machinery. The parties at whose request I attended were licensees of the Tweeddale patent, and the object they had in view, was to be furnished with some plan whereby the pug-mill might produce a continuous stream of clay to the brick machine. The defect in this respect of the Tweeddale apparatus proceeded from the under knives only expelling the clay as they passed the port, or aperture where it escaped, which was about 10 inches long, and 6 inches deep; when they were not in a position to effect this, the clay made a stop, the top knives in their turn being too distant to produce a similar result. At these intervals, with the brick machine in motion, the clay parted, and the bricks at such places were generally spoiled. To remedy this evil, I proposed making each knife a regular segment of a circle, and fixing them at the bottom of the pug-mill on a round shaft, with iron collars between them, so that the edge of the one segment should begin its evolution where the former left off, and a uniform pressure on the clay be thus kept up as the shaft revolved. But this arrangement, both in principle, and form, approached the screw so closely, that it was almost immediately abandoned for the latter. With the screw as a propelling instrument, I next proposed converting the pug-mill into a brick machine, by contracting the aperture the clay escapes from, to the form and size transversely of a brick, and giving the screw sufficient power to expel the clay through it. At this proposition the licensees of the Tweeddale patent got alarmed, supposing if bricks were so formed, draining tiles might also be protruded through a suitable orifice, and to protect their own interests, they entered into arrangements, in pursuance of which a patent was obtained for my invention in the following autumn. I have explained these facts, from observing in a late number of the It is Bricks which are moulded by pressure, either by the Tweeddale apparatus, or by my screw machine, must of necessity have more solidity than bricks formed by hand-and this is a property which builders are not likely to appreciate from its adding weight to its bulk, and consequently increasing the expense of conveyance; from being heavier to handle too, they may also possibly add to the charge in building. I have considered this subject well, and recommend machinemade bricks to be moulded of the form represented in fig. 1, and fig. 2, the latter of which is an end view. Bricks of this form are well adapted to partitions, and all sorts of building intended to be plastered over. The quantity of clay removed by the grooves a a, would reduce their weight to that of common bricks, and give additional facility to drying and burning them. For ornamental cottages, a brick of the form of fig. 3, might be used as a binder; fig. 4 is a side view of it. Bricks of this form would be bedded so close, as to leave the joints hardly perceptible, the mortar being retained in the recesses, the work would be stronger than usual; and from the solidity of the bricks, impervious to water, which is not the case with hand-made bricks, although of the very best description. In cases of cottage building, where design is unfettered by the close grip of economy, pipe clay might be introduced in forming the bricks, and give to them a new and elegant appearance. I shall now proceed to describe the machine. Fig. 5, a, is a driving shaft; b, vertical shaft in gear with the former, by two bevelled wheels; c, spur-wheel; e, large pinion on the shaft, f; on the lower end of this shaft a screw of one turn is formed, and fitted to the cylinder g, in which it revolves; h, cylindrical chamber into which the clay is pressed by the inclined surfaces of the screw on the shaft, f, and out of which it exudes at the moulding aperture, represented by a curved dark line in form of a draining tile. The clay is supplied at the top of the cylinder, g, by engine power, or manual labour, as circumstances may determine. The cutting apparatus receives motion from two inclined planes on the circular plates, ii. As the plates revolve, the inclined planes alternately strike the roller, j, on the upper and under side; when the roller is depressed, the lever k is moved to the right, and when it is raised it is moved to the left. The cutting frame is attached to the lever, k, by a connecting rod, , and supported from four levers, two of which are only seen, marked mm. There are also two cutting wires, to divide the clay as it exudes from the moulding orifice, one of which is only seen, represented by a sharp dark line near the orifice. The cutting wires are the exact distance apart from each other, required by the length of the moulded articles, and for each revolution of the screw, a sufficient quantity of clay is moulded to make two, (and a little more,) one on each side of the machine, its operation being double, the overplus falls down, and is thrown back and re-moulded. The object of cutting with two wires is to produce all the articles of the same length. When the shaft b makes ten revolutions per minute, the shaft, f, makes twenty, consequently, forty bricks or tiles are moulded in the same time. The cutting wires and frame have a sawing motion, from being sustained on the levers, mm, which is preferable to moving them in a straight line. As the articles are cut they are removed by hand, or conveyed away on an endless belt supported on rollers, one of which is seen below the moulding orifice, and one at each side for lateral protection. In moulding tiles from an orifice, the edges are slightly turned up, which prevents the tiles from slipping after they are laid, an accident of frequent occurrence, and not unfrequently accompanied with a complete destruction to the drain. On the end of the driving shaft, a, a small crank, n, is fixed, which works the force-pump, o, in the cistern, p; this pump supplies water to the moulding orifice by a small pipe, q, and within the cistern there is a cock to regulate the supply. The orifice being lubricated in this way, the movement of the clay through it is made easy, and whatever be the figure of the mould, the clay exudes with a smooth unbroken surface. In moulding draining tiles, the clay is cut in motion, the small angle thereby produced being of no consequence, but when the articles require to be cut at right angles, the clay stops at that moment, by a contrivance added to the wheel c, for that purpose. JAMES WHIte. 11, East-place, Lambeth, October, 1841. MR. PARKES' THEORY OF THE PERCUSSIVE FORCE OF STEAM. Sir, I have to-day read the paper, (From the Minutes of the Transactions of Civil Engineers,) contained in No. 946, page 247 of your very useful work, "On the Percussive Action of Steam, and other Aeriform Fluids." By Josiah Parkes, M. Inst. C. E., in which, illustrative practical proofs are furnished of the percussive effect of steam upon the piston of the steam engine, as a motive power, and that the impulse furnished is due to percussive power rather than to expansive, but without any attempt to elucidate the theory of such force. As the effects described appear to me to corroborate very strongly the theory which I have, from time to time, endeavoured to inculcate in your pages relative to the law of equal diffusion to which heat is subject, I cannot refrain from attempting (with your permission) to point out, what appears to me to be the theory of the percussive power of steam, as well as its expansive. It will perhaps be remembered by some of your readers, that in a former communication I pointed out, that not only is heat subject to the law of equal diffusion, but that the rapidity of its diffusion is in the reverse ratio to the difference in the thermometric temperature of the impartive and receptive substances, and that, therefore, the greater that difference the more rapid will be the transition of heat, and the greater its repelling or impulsive force. It will also probably be remembered that I expressed the opinion, that the hermometric temperature of steam cannot be increased beyond 212°, and that the superior impulsive power of high-pressure steam above that of low pressure, is due to the accumulation of heat in the metal composing the boiler, instead of to its accumulation in the steam within the boiler, and that the immense power exerted by such steam on its egress from the boiler is not innate in the steam while within the boiler, but is derived from the thermometric heat of the metal of the boiler in which it is accumulated, and from which it is rapidly transmitted to the water in the boiler-creating additional volumes of steam, on the opening of the eduction valve, as induced by the law of equal diffusion, and thereby imparting to such steam both its percussive and expansive power, the former in the inverse ratio of the difference between the amount of accumulated thermometric heat in the steam within the boiler, and the metal of which the boiler is composed. To illustrate more clearly the principles of the theory which I advocate, I will first suppose, that thermometric heat is imparted to water in a boiler, until the temperature of both is raised to 212°, and if the valve communicating with the cylinder of the engine is opened as suddenly as possible, it will be found that such steam does not possess a sufficient percussive power to raise the piston, and the effect will be, that as much heat will be abstracted from the steam emitted, by the metal of the cylinder and piston, as will reduce the temperature of the one, and raise the temperature of the other to a state of equality; and such a reduction in the temperature of the steam will cause its condensation, or, in other words, will cause its component ponderable atoms to unite and be reconverted into water. But should the piston in such cylinder be raised by adventitious means, the moment the steam valve leading to the cylinder is opened, the steam will enter, and although not of sufficient volume to fill the cylinder in its natural state, yet will it expand and fill the space for a short period, as induced by the law of equal diffusion, to which the heat of the steam is subject, and such steam being decomposed by the removal of its caloric beyond its constituent limits, its ponderable atoms will be released from their component position, and fall to the bottom of the cylinder as induced by the law of gravity. As the generation of steam, under such circumstances, will not furnish a sufficient motive power, it becomes necessary to resort to those means which are adequate to the purpose, and the rationale of such means appears to me as follows: The safety-valve of the boiler is loaded to an amount more than equal to the intensity of the force required to raise the piston of the steam cylinder, in order to prevent the escape of the steam within the boiler; and the moment the space above the water is completely filled with the indestructible and incompressible constituent atoms of steam, it becomes impossible that more can enter, other than to supply the place of those atoms of heat which permeate the metal of the boiler, and escape by radiation. At the time such space is filled, the thermometric temperature of the steam within is about 212, and no subsequent addition of heat, or further retention of such steam within the boiler, will ever cause an increase of its thermometric temperature. Now having endeavoured to show that steam of such a temperature does not possess sufficient power to raise the piston within the cylinder, it next devolves on me to attempt to show what additional power is required to effect the purpose-whence that power is derived-where collected-and the way in which it is applied. The source from which the power is derived, is the fuel in a state of combustion in the furnace; the magazine in which it is stored is the metal of which the boiler is constructed; and the mode of application is by the law of equal diffusion to which heat is subject. The transmission of heat from the burning fuel to the boiler, and from the boiler to the lower stratum of water therein, is induced by the law of equal diffusion; and from the lower to the upper surface by the same law in the first instance, but subsequently by the secondary law of recession from the earth; the thermometric temperature of the upper surface ever exceeding that of the lower, until the whole mass is raised to about 212°. The impartation of heat being continued, its atoms are transmitted from the lower to the upper surface, and every interstice furnished by the position of the spherical ponderable atoms of the water being completely filled, a definite and proportionate amount of such ponderable atoms are raised from the mass of water in combination with a definite and proportionate amount of the atoms of heat-the admixture constituting the fluid termed steam, which gradually expels the air from the space between the water and the dome of the boiler, and occupies its place, remaining there until mechanically released, or until the accumulated power resulting from the continued impartation of heat, exceeds the restraining power, and the raising of the safety-valve or the disruption of the boiler, and the liberation of the imprisoned steam ensues. The whole of the interior of the boiler, being completely filled with solid and incompressible atoms, and the interstices presented by the union of the ponderable atoms being filled to repletion with the atoms of heat, and the thermometric temperature of the whole mass being about 212°, I have yet to learn how it is possible, that the density of the steam within the boiler, or its thermometric temperature, can be increased by the continued impartation of heat, or in other words, how the atoms of such additional heat can find access to, that which I conceive to be, a perfect plenum, except as to the interstices which must be presented by the union of the atoms of heat. In short, unless any one is prepared to prove the existence of a more subtle fluid than heat-that the atoms of such fluid are smaller than the atoms of heat, and that their introduction can raise the thermometric temperature of the steam within the boiler,-I must ever remain sceptical as to the possibility of compressing a volume of steam into a space less than that which it naturally occupies at a temperature of 212°, or to increase the thermometric temperature assigned to it. I am finally, therefore, constrained to reject the com monly-received notion, that the force of steam is due to an increase of its density, or thermometric temperature. As little can I assent to the alleged elasticity of steam. For if, then, the limits of the receptive capacity of the water for heat, and the steam within the boiler is such as will admit of no greater increase of its thermometric temperature than to the extent of 212°; if steam is composed of a large amount of the atoms of heat, and a small amount of the ponderable atoms of water;-if those atoms of heat in their passage through water, are enabled to raise from its surface those ponderable atoms which were closely or proximately united, with a force superior to the power of gravity, and to place them widely distant in position, as a necessary condition to the formation of a fluid of much less specific gravity than the water from whence derived; - if there is no contradiction in the laws of nature, and the impartation of heat to water decreases its density as a liquid, and infinitely decreases its density as vapour;—if there exists no such anomalous contradiction in the execution of those laws, as that a moderate impartation of heat is absolutely necessary to expand water and steam, and decrease their density, and that an excessive impartation is necessary to compress and increase their density, then steam cannot be elastic, nor can it possess any innate motive power. What then is this stupendous power? Equal diffusion of heat, subject to a celerity of transmission in the inverse ratio of the difference in the thermometric temperature of the impartive and receptive substances. And where is its source at the time of action? In the metal of which the boiler is constructed, which becomes a receptive magazine for the imparted heat which emanates from the burning fuel, and which (the steam not being able to receive beyond its constituent limits,) is therein stored to any extent within the limits of its receptive capacity, or cohesive tenacity, ready to obey the law of equal diffusion to which it is subject, with a force and rapidity of transmission, proportionate to the ratio of difference between the amount of atoms therein collected, and which may be possessed by the receptive sub |