AMERICAN MARINE STEAM ENGINES FITTED TO THE SPANISH FRIGATES We had occasion, some time ago, to notice in rather unfavourable terms the steam engines manufactured in the United States for the Russian frigate Kamstchatka, which appeared to us, both in design and workmanship, much inferior to the productions of our English workshops, while they had cost a great deal more. The Spanish Government has since had two steamers, El Regent and El Congreso, (formerly the Eagle and Lion,) fitted with engines at New York by Messrs. Ward, Stillman, and Co., of the Novelty Iron Works, who have kindly enabled us to lay the accompanying engravings of them before the readers of the Mechanics' Magazine. We take pleasure in acknowledging that they fully establish the truth of the representation made to us by an American Correspondent, (vol. xxxvi. p. 222,) that the Kamstchatka's engines were by no means to be regarded as fair specimens of what his countrymen could do in this line, having been built under peculiar circumstances, which did not give fair play to their genius and skill. The engines supplied to the Spanish frigates are in every respect of a much superior character, and approach nearer to English excellence than any of foreign manufacture which have yet come under our notice. The cylinders are 42 inches in diameter; the length of stroke, 55 inches. We have not been informed of the dimensions of the Regent, but we presume they must be nearly similar to those of El Congreso, which is stated to be 154 feet in length, 30 feet 8 inches in greatest breadth, and 14 feet 8 inches in depth. The engines of both vessels have, we are assured, been in use" for a whole year without requiring any repairs whatever." We are promised a copy of "the log of several voyages;" and when we receive it shall be able to speak of the performances of the vessels in other respects. Sectional View. EL THE BUDE LIGHT. In our 849th No. (16th Nov. 1839) we gave a very full account of the Bude Light, as it existed at that time, extracted from "Minutes of Evidence taken before the Select Committee" appointed to inquire into the best means of lighting the House of Commons. The light was then stated to be produced by means of a common Argand lamp, with cotton and sperm oil, through the centre of the flame of which a stream of oxygen was passed, in place of atmospheric air, as usual. The oxygen was obtained by the dry distillation of manganese in iron retorts. After a short trial at the House of Commons, it was found "that oil lamps thus fed with vital air were expensive, and difficult to regulate." (Dr. Ure.) Mr. Gurney then substituted for the sperm oil, the naphthalized coal gas invented by Mr. Lowe, and described in our last No. (p. 392) -introducing the oxygen as before. A light of great intensity was thus obtained, but this process too was found objectionable in the long run, owing to a large portion of the naphtha becoming liquified, and depositing itself in the pipes of distribution. Mr. Gurney then devised quite a new process altogether; he obtained his flame from the ordinary coal gas in a very pure state-abandoned the artificial stream of oxygen, trusting to the surrounding atmosphere (as others do) for the requisite supply; and added a variety of mechanical contrivances for regulating the supply of gas and atmospheric air, and diffusing the light produced. For this new process he took out a patent, (25th March, 1841,) and this it is which constitutes the Bude Light of the present day, as in use at the House of Commons and elsewhere. 1. Mr. Gurney's mode of purifying the ordinary coal gas, is to pass it, as it comes from the public gas main, through a vessel similar to a common gas purifier, furnished with a mixture, either in a dry or slightly moistened state, composed of 5 parts muriate of zink, 2 parts subacetate of lead, 2 parts chloride of baryta, and parts sulphate of manganese. The muriate of zink is the principal agent, and the others seem added more for variety's sake than on any other account. "Although," says Mr. Gurney, "I prefer the above described means of applying the above-mentioned materials, I do not confine myself thereto, so long as the means resorted to are such as to bring the gas into contact with muriate of zink, with or without other suitable materials, in the passage of the gas from the gasmain to the burner or burners." Specification. Mr. Alexander Croll, the present Superintendent of the Chartered Gas Company's Works at Brick Lane, took out a patent two months before the date of Mr. Gurney's, for purifying gas by contact with muriate of zink, as it comes from the retorts, and this circumstance may serve, perhaps, to explain both Mr. Gurney's addition of the superfluous materials and the limitation of his claim to the use of the muriate of zink "in the passage of the gas from the gas main to the burner or burners." 2. Mr. Gurney regulates the supply of gas and atmospheric air by the following means. He uses a burner consisting of two or more hollow concentric rings, perforated with a great many small holes on their upper surfaces, the atmospheric air being admitted to flow freely up between the rings; and the flame is enclosed within two conical chimneys, which are also concentric (as it were) to one another; only, that there is a small space left between the top of the one and bottom of the other, which admits air to the exterior of the flame. 3. To reflect or diffuse the light, there are two circular concave reflectors, placed back to back, which project from the upper chimney at a point nearly coincident with the middle of the flame, to a distance all round more than equal to the diameter of the chimney; one reflecting the light downwards, and the other upwards. A second upper chimney is also occasionally used, called by Mr. Gurney "a refracting zone," which is "cut on the outside into prismatic projecting rings at such angles as to direct the light in the desired directions," and rests on the twin reflectors. A ground glass shade may be added or not, according to the brilliancy of illumination desired. Dr. Ure calculates that the Bude Light, as thus improved, gives as much light as the best Argand gas flame, with only half the expenditure of gas; and he ascribes this, first, to Mr. Gurney's burner giving, by means of its concentric rings, a compound flame, (like that of the flames of two candles brought into close contact,) the circles of which "mutually enhance each other's temperature," and consequently illuminating power; and, secondly, to the circumstance that by means of Mr. Gurney's concentric series," the prejudicial excess of atmospheric air is prevented, and only so much permitted to come into contact with the gas, as will effect the due separation and ignition of its carbon, even at the origin of the flame."-(Lond. Jour.) With great respect, however, for Dr. Ure's authority, we must confess that his two reasons appear to us far from being sufficient to account for the great superiority ascribed to this new light. The flame produced from any burner whatever, of more than one hole, as long as the holes are close together, is just as much a "compound flame" as that of Mr. Gurney's. The twelve columns of flame rising in a single ring from a twelve-hole Argand burner of the common sort, do just as much "mutually enhance each other's temperature," and consequently illuminating power, as if they were arranged in two rings. The admission of the atmospheric air to the flame, in the exact quantity requisite to "effect the due separation and ignition of its carbon," would be something more to the purpose, if this could be really shown to be effected by Mr. Gurney's plan; but in what respect is this admission more exactly regulated in his lamp than in others? He gives no proportions for his apertures of admission, and places them just where others do. The bottom apertures which admit the air into the interior of the flame, are smaller than usual -that is all; but this seems rather an accidental consequence of the concentric ring construction, than an antecedent condition of it. We are confirmed in this view of the matter by Mr. Gurney's claim on this head, which is simply to the "lighting apartments or rooms by means of burners composed of concentric rings of tubes, combined with suitable glass chimneys”—not a word of suitable apertures. We should have thought something might be due to the process of purifying, but this appears to count with Dr. Ure for nothing; and if it be true, as is currently reported, that the process of purification has been abandoned at the House of Commons, he may not be far wrong in this respect. After all, there seems to be good reason for concluding that the reflectors and refractors, combined with Dr. Reid's better system of ventilation, have more to do with the superiority of this light at the House of Commons than any thing else. The Bude Lamp which was set up at the bottom of Waterloo-place, where the ventilating system could not be so well brought into play as at St. Stephen's, has never been of the extraordinary brilliancy represented in newspaper paragraphs, and gives ordinarily no more light than would be afforded by an equal body of common gas flame surrounded with reflectors. The Trinity House gave Mr. Gurney a commission to fit up the Orford Lighthouse according to his views; but after a brief trial, the Bude apparatus has been entirely removed from that establishment; and the cause is unreservedly stated to be, that the Gurney light was found to possess no more illuminating power than any other light, while his system of reflectors was not nearly so good for maritime purposes as others previously in use. The Northern Light Commissioners had given an order for a Bude apparatus to be applied to one of the lighthouses under their management; but on hearing of the Orford failure, that order has been countermanded. GLEANINGS OF A TRAVELLER IN AMERICA -EXPEDITIOUS BISCUIT BAKING—SIMPLE HOT WATER APPARATUS. Sir,-Some years since I saw, in New York, a very simple mode of baking, which I shall endeavour to describe from recollection. It may furnish to biscuit and small cake-makers some useful hint in the construction of the oven on a scale of economy. The inventor was Mr. George Dencale. In the middle of the shop was erected, of brick work, an oven, about 4 feet high, 12 feet long, and 6 feet wide. The upper surface, or top, of brick and mortar, had no opening whatever. The end, which constituted the front, had, near the ground, an opening with a metal door, like that of any common furnace, through which the fuel was introduced, and thence pushed forward so as to cover the entire of the floor within the walls of this oven. Above the furnace door, some 12 inches, MR. WALKER'S PUMP AND THE CENTRIFUGAL COMPARED. the brick-work had an opening of 6 or 8 inches height, the entire width of the front; an equal opening was in the opposite end. Outside, and immediately facing each opening, a wooden cylinder was affixed, that at the front having a winch; the length of each cylinder corresponded with that of the opening. A piece of wire lattice-work, the width of the cylinders' length, passed over the cylinders, was continued underneath both, so that the ends met, and were so tightly united that on turning the winch the wire-work revolved freely (like an endless chain or strap, similarly circumstanced,) lengthways through the oven over the ignited fuel. The dough-cakes being brought to the fireman, he placed a row on the wirework, then gave the winch a turn; next these a second row was placed, and the winch again turned; and thus in succession until the first row had arrived at the remote opening, where the cakes fell over its cylinder into a basket, completely baked. I noticed also an economical method of supplying a house with hot water day and night. Four old gun-barrels were connected with leaden pipe so as to form one gridiron-shaped tube, by which there were three necks and two ends of leaden pipe. The ends of the barrels were laid on brick-work six inches from the ground, and the leaden necks covered with mortar: the four barrels lay in the same horizontal plane: under and over these the fire was placed. From each of the unconnected ends of the gun-barrels proceeded a piece of lead pipe, which entered a wooden chest or barrel with a steam-tight lid. The pipes entered the barrel, one much higher than the other, in order that the cold or heavier water in the wooden vessel should descend through the lower, and the heated water in the barrel ascend into the water vessel through the upper pipe, and thus facilitate the circulation, which is productive of a roaring noise, the degree of which indicates the temperature of the water. The water vessel may be in one kitchen, the gun-barrels in a different, or in a bathing-room adjoining, according to the length of pipes and convenience required. When the water is boiling in the covered tub, it is surprising the very few hot ashes, round the barrels, required to keep it so all night. For bathing at night, on 421 an emergency, and in hospitals, the plan T. H. P. MR. WALKER'S PUMP AND THE CEN- SIR,-Mr. Walker's pump appears to be 1st. Although by overcoming the inertia of the pipes, &c. at the beginning and end of every stroke, there is not, from the nature of the crank, any loss of power, yet power must be wasted in friction from the pressure on the crank-shaft bearings, &c. in overcoming the inertia of the pipes and other parts twice in each stroke, and the inertia of the water in each pipe, once in each stroke. In the centrifugal pump, the motion of the pipe and arms, not being reciprocating, but continually rotary, there is is no strain or friction on any part of the machinery, to overcome their inertia and change the direction of motion. 2nd. The centrifugal pump is far more simple, as it has only one main pipe, the weight of which, with the water in it, rests in the best manner possible, on a pivot; besides this, there is no need of a flywheel, beam, three connecting rods, and frame-work, all which serve to render the machine bulky and unportable, increase the prime cost, and produce friction to some extent at least. Again, ceteris paribus, the main pipes of Walker's pump must be much larger than that of the centrifugal pump, on account of the uninterrupted and more rapid flow of water through the latter. A Walker's pump of the dimensions given in No. 971 of the Mechanics' Magazine, namely 30 ft. lift, interior diameter of pipes 3 inches, length of stroke 3 inches, rotation of crank say 300 times per minute, with two pipes would, according to calculation, discharge 10 cubic It could not well be worked quicker, the strain on the crank, and for the most part on the other bearings, at 300 times per minute, would be about 7 times the weight of the water in one pipe. Both the pipes themselves, with their connecting-rods and working beam, would at 600 times per minute be 30 times the weight of the above-mentioned parts. feet of water per minute: (if the rotation of the crank were 227 times per minute no discharge would take place.) Now with a centrifugal pump, having the same distance of lift 30 feet, and same discharge 10 cubic feet of water per minute, with arms of 2 feet radius, and orifices at the ends 0:36 inch diameter, the interior diameter of its single main pipe need be less than 14 inch, and the rotation of the arms would be 600 times per minute, being the velocity at which only 3 per cent. of the total power employed would be wasted, owing to the water having some velocity after quitting the arms; (if the rotation were 208 times per minute no discharge would take place.) In short, if this centrifugal pump had its orifices 0-8 inch, and its pipe of the same diameter as in the Walker's pump, it would, with proportionate power, perform five times the work, besides being simpler, as shown. I am, Sir, yours, W. P. April 26, 1842. [It would be unfair to discard so old and well-tried a friend, as "Centrifugal," without giving him a fair hearing; but we dare say Mr. Walker will have something to say in reply.-ED. M. M.] IMPROVED PLATE DIE FOR MAKING SCREWS. Sir,-Having made an improvement in the plate-die for making screws, I send you a description of it, and should you think it worth notice, I shall feel obliged by your noticing it in your valuable work. The hole must be made and tapped in the usual way, and then cut into the shape represented in the prefixed figure, leaving the thread full only at AA. I have made one, and I find that it cuts easier than any plate I ever used before. On the old plan the thread is formed more by compression than any thing else. On mine, it results naturally from the form of the die, and is produced without any difficulty. I remain, yours, R. HAMMOND. P.S. The writer of this is now out of employment. Any one desirous of the services of a person of good practical knowledge of mechanics, and accustomed to the vice and lathe, may address to R. H., 8, Southampton-terrace, Southamptonstreet, Pentonville. ON THE TRUE PRINCIPLES OF VELOCITY IN STEAM NAVIGATION-BEING A SUPPLEMENT TO SPECIFICATION OF JOEST'S IMPROVEMENTS IN PROPELLING VES SELS (MECH. MAG. VOL. XXXV. p. 386. BY MR. A. W. BEYSE, ARCHITECT AND ENGINEER. Whenever we shall arrive at that point where the speed of a steam vessel is equal to the velocity of the circumference of the paddle-wheels in the middle of the floats we shall have attained perfection. But it is obvious, that such perfection is unattainable in actual practice, and that all we can hope for is a near approximation to it. We must mark well the first beginning of the motion of a propelled steam-boat, and the moment when the power of the engines and the circumferential velocity of the wheels are in equilibrium, as also the resistance to propulsion offered by the vessel and floats. At first, every float drawn through the water acts with all its power, as a skull or oar, and the ship resists with all its power. But after the two forces have become equal, the striking float alone propels the vessel, and is but little assisted by the others, which are incumbered by back-water, work in broken water, and experience only the difference of resistance betwixt their own velocity and that of the fluid in which the steam boat moves. Again, the resistance of the vessel itself should also increase in the ratio of the square of its velocity, and so also the resistance of the floats drawn through the water; but this is not the case, because, after the vessel has attained a certain speed its resistance goes on in a decreasing proportion, and the floats find almost no resistance, because they escape before the broken water can detain them. Let fig. 1 be the transverse section under the water line of a well-built steamer in its greatest width, where also the engines and paddle-wheels are placed; its keel and bow as sharp as the materials of which it is constructed will permit. The |