reams of mere disputation, or a thousand groundless charges of writing under more signatures than one. Mr. Meredith, of Cambridge, as he signs himself, is very severe on Mr. Herapath for not making good the challenge given by Philo-anti-H., some time ago. In reply, I might inquire for what reason Mr. H. is to be held accountable for the rashness of every injudicious friend. You also, Mr. Editor, in some measure, join in the attack, by observing "no answer has been received certainly;" yet allow me to ask, whether if Mr. Herapath's friends have been asserting that that gentleman, some time ago, sent a full vindication to the Mechanics' Magazine, which the editor refused to print, they have been asserting a falsehood.* Although the pages of the Mechanics' Magazine have been chiefly open to one side only, on the question† at issue, between Mr. Herapath and his opponent, I hope this note will find a place in its next number, on the ground of its long reputation for impartiality. And I remain, Sir, Your most obedient, humble servant, WILLIAM COOPER. No. 17, King-street, Feb. 3, 1836. IVER M'IVER'S TABLE OF VELOCITIES. Sir, I find I wronged Iver M'Iver when I charged him with having given incorrect velocities in his table in No. 640, and I fully acknowledge it and express my regret for the occurrence. I beg to explain how I came to make this mistake. When I saw Iver M'Iver's table, the velocities struck me as being very low, and I determined to examine them, and for this purpose referred to "Dr. Gregory's Mathematics for Practical Men" on p. 238 of that work are the following equations: : v = g t sin. i = √√2 g S sin. i Now, as 2g S sin.igt sin. i, I at once substituted the one for the other, Yes; a gross falsehood.-ED. M. M. + Not true; they have been equally open to both sides.-ED. M. M. (From Mr. Gibbs' Report upon the several proposed Lines for a Brighton Railway.) An objection has been made generally to all tunnels-namely, that the air contained in them will be so contaminated by the noxious gas produced by the lo comotive-engines in passing through them. as to render it unfit for respiration. Whether this objection has ever been advanced, or at all supported, by any scientific man possessing sufficient chemical knowledge to enable him to judge correctly on the subject, is doubtful. The probability, however, is, that the fear of any injurious effects from foul air has originated in those who have witnessed the effects produced by steamengines in passing through the small tunnels on some of our canals; and if they have for a moment imagined that any similarity will be found in the effects in the two cases, their fears are quite justifiable. The tunnels on canals are commonly constructed of such limited dimensions, that it would be highly dangerous to attempt the same application of steam power as will be necessary on a railway; for instance, in the tunnel constructed by Mr. Telford on the Hare Castle Canal, the area above the water in the canal is only about one hundred feet; and even the Thames and Medway in transverse dimensions, perhaps the largest canal tunnel in England, has only an area of four hundred and fifty feet; while the smallest tunnel contemplated on the Brighton Railway, will have an area of at least six hundred feet. In order to explain to what extent the air in a tunnel is contaminated by a locomotive-engine passing through it, let us suppose a tunnel one mile in length to be traversed by a locomotive-engine, and its train of a gross weight of one hundred tons. The experience of the Liverpool and Manchester Railway has shown that the average consumption of coke is considerably less than half a pound per ton for each mile it is carried on a railway; but taking the consump tion at half a pound, the whole weight of one hundred tons will require the consumption of 50lbs. of coke. It may be calculated that every 10lbs. of coke will evaporate a cubic foot of water; so that the whole 50lbs. will convert into steam 5 cubic feet of water in the distance of 1 mile. Now to convert into steam one cubic foot of water, requires 1,950, or say 2,000 cubic feet of air, then 5 feet of water will of course require 10,000 feet; and this will be the whole amount of contaminated air in one mile in length of tunnel. To determine the proportion of such an amount of foul air, and the whole air contained in the tunnel, we may take for example a moderate-sized tunnel 30 feet high, and having an area of 800 square feet. One mile in length of such a tunnel will contain 4,224,000 cubic feet; hence the contaminated air will bear to the whole quantity in the tunnel the ratio of 10,000 to 4,224,000; or it will be as 1 to 422. It will scarcely after this appear that any valid objection to tunnels, to assert that an injurious effect must result from the contaminated air, when we find that the quantity of this description of air, produced by the passing of the whole train, will be no more than 2 part of the whole quantity in the tunnel. Let us then venture to hope, that any prejudices which may now exist against the construction of tunnels upon railways will be dispelled, when we find that no injurious consequences will ever result from the foul air, or any other of the numerous evils which have been so forcibly dwelt upon by those who affect to perceive the most unhappy consequences from their adoption. EXPERIMENTS TO ASCERTAIN THE EXISTENCE OF LEAD IN THE ATMOSPHERE OF A WHITE LEAD MANUFACTORY. BY MR. ARTHUR Dunn. (From the London and Edinburgh Phil. Mag.) Having witnessed at my manufactory the frightful effects of white lead on the workmen employed, I was anxious to determine if it was possible for lead to exist in the atmosphere, and through that medium, be absorbed into the system by the action of the lungs. For this purpose I made the following experiment, which certainly is important to the manufacturer, as it points out a serious evil to be guarded against. I shall now merely confine myself to the results obtained, and leave to some of your more seientific friends any theoretical reasoning or practical hints the experiment may suggest, provided you consider it worthy to occupy a space in your valuable magazine : An evaporating dish, containing about twenty-eight pounds of moist carbonate of lead, was placed in a sand-bath, and heated to about the same temperature as the dryingstove commonly used, never exceeding 1500 Fahrenheit; over this was fixed, at the distance of from eight to twelve inches, a pair of common bellows, with a glass tube attached to the pipe, which pipe was introduced into a green glass bottle, containing twelve ounces of distilled water, acidulated with two drachms of nitric acid. The apparatus being thus arranged, the bellows were set in action, by which means the atmosphere, loaded with the moisture from the lead, was made to pass in a continued current through the liquid; this was continued for six hours. The whole was then transferred into a platina dish, and evaporated to perfect dryness. The residue was dissolved in one ounce of distilled water, with two drops of nitric acid, to insure the solution of the lead, should any be present. A current of sulphuretted hydrogen was next passed through the solution, which immediately gave a minute dark precipitate; this being collected on a filter, and washed, was transferred to a watch-glass, and treated in the usual manner with nitric acid to decompose the sulphuret, which gave, on the application of hydriodate of potash, the most unequivocal proof of the presence of lead. Another experiment was conducted at the same time, with similar vessels, in the same room, but the current of air was not passed through the liquid. This, on the application of sulphuretted hydrogen, gave not the least indication of lead; but, on evaporating the whole to dryness, and treating the residue, in the manner before described, with hydriodate of potash, the slightest possible trace of the yellow iodine of lead was perceptible. The nitric acid and distilled water were separately tested with great care, but were found perfectly free from lead, so that, no doubt, the trace of lead must have been absorbed from the atmosphere, as the bottle containing it stood beside the one through which the current of air was passed. I ought to have mentioned before, that the temperature of the laboratory during the experiment, was from 700 to 800 Fahrenheit, and that the door was kept closely shut, that the air might be loaded as much as possible with the vapour. EASY METHOD OF FILLING LONG SYPHON TUBES. BY WILLIAM FOSTER, ESQ. (From Silliman's American Journal.) The application of the syphon upon a large scale, for the purpose of drawing water from distant places, may not be new; but I do not remember to have seen it in this, or any other country, before I tried the experiment. The ancients, we know, brought water for the supply of their cities, by means of costly aqueducts, over hills and valleys, without ever using the fountain principle. Some years ago Mr. Chapman, proprietor of a distillery in Charlestown, requested me to describe my plan for carrying water through a syphon several hundred feet in length, and drawing water from one well into another; and with the instruction I gave him, he employed a plumber to lay a leaden tube of three-quarter inch bore, from a well twenty-five feet deep, several hundred feet distant from the well of his distillery, which was about thirty feet deep, and where he wanted a greater supply of water. The operation failed. He then came to me, and told me that I had led him into an expensive error. I told him that, had he communicated to me his intentions, I would, with great pleasure, have superintended the work; but now, not knowing what defects there might be in the tube, I could not answer for his success. However, I consented to assist him, but my first essay was unsuc cessful. The power of the syphon to overcome an eminence is limited to about thirty-two feet, answering to the column of water which the pressure of the atmosphere can raise; or that any defect in the syphon, or any air confined in it, would be fatal to its operation. The usual mode of charging a syphon is by exhausting it partially by inspiration at the longer end. But this was not possible with a tube several hundred feet long, and the expense of a pneumatic apparatus, to procure a vacuum, would have been too great; therefore, I had determined to put it in operation by filling it with water, both ends being stopped; this was done by a small branch at the summit of the tube; and, when filled, this branch was well corked, and the cork pressed down hard on the water, so as to exclude all the air at the surface. It was to be apprehended that some undulations might exist in the horizontal part of the tube, and afford a receptacle for air, which would there be confined without a possibility of escaping, and also prove fatal to the success of the experiment; but of this I could know nothing, as I had not seen the tube laid. In this state of uncertainty, I began the operation, and filled the syphon; but, as I said before, it failed. On the second trial, I observed that, when the syphon was full, the water in the filling branch rose and fell alternately, and so much, that as water has but little elasticity, I concluded that there was air in the tube, and it was, therefore, emptied. Then, to charge it anew, and, at the same time, to exclude the air, it was proposed to perforate the lower end of the long branch, at the bottom of the receiving well, with a fork, just above the cork which closed it. These small holes allowed the air to escape as it was driven before the water, without losing enough water to prevent the filling the tube with ease. Thus was the air excluded, and the syphon put into operation, and continued for a long time, with some occasional obstruction, arising from the smallness of the tube, and the want of water at the source. I should suppose that there were many situations where water might be brought from one valley to another, over any hill not exceeding thirty-two feet, or which could, without too much expense, be reduced to that point, for the purposes of irrigation, or manufacturing. Large quantities of water, as well as small, may be raised by means of iron mains of large dimensions; and the cutting down hills to procure levels, or surrounding them, and thus increasing the length of aqueducts, at a great expense, and loss of water by percolation and evaporation, may be avoided. Mountain swamps may be drained, or any swamps, where a lower level is not too far distant for the place of issue, or even in a level country, provided some vein of loose gravel can be found, into which a place of discharge may be dug below the surface of the swamp. The ingenuity of our countrymen will, I am confident, yet find many other useful purposes to which the principle may be applied. NOTES AND NOTICES. Architectural Prize. -The honorary premium of the Institute of British Architects, for the best essay on "Concrete," has been awarded to Mr. George Godwin, junior, architect, of Brompton. Patents taken out with economy and despatch; Specifications, Disclaimers, and Amend. ments, prepared or revised; Caveats entered; and generally every Branch of Patent Business promptly transacted. Drawings of Machinery also executed by skilful assistants, on the shortest notice. The Supplement to the last volume, containing title, index, &c. and portrait of Charles Vignoles, Esq., C. E., is just published, price 6d. Also, the volume complete, in boards, price 9s. 6d. LONDON: Published by J. CUNNINGHAM, at the Mechanics' Magazine Office, No. 6, Peterborough-court, between 135 and 136, Fleet-street. Agent for the American Edition, Mr. O. RICH, 12, Red Lion-square. Sold by G. G. BENNIS, 55, Rue Neuve, Saint Augustin, Paris. CUNNINGHAM and SALMON, Printers, Fleet-street. DESCRIPTION OF NICKOLL'S PATENT CONDENSING-STEAM FIRE-ENGINE AND RAILWAY CONDENSING-LOCOMOTIVE. (Communicated by the Inventor.) The distinguishing feature of these inventions consists of an apparatus for cooling the water that has been heated in, or by, the condenser of a portable condens ing steam-engine. The apparatus in question, alias the refrigerator, is constructed of several series of layers of any kind of cloth, or metal, arranged on metal wires or rods, horizontally, and at such a distance apart, one above the other, that currents of air from the surrounding atmosphere may pass freely and continually through and among its various strata. The refrigerator may in some cases be open to the wind on all sides; or it may be enclosed in a box or carriage, having an induction and eduction air-chamber, perforated with numerous apertures to effect a more equal distribution of the air in the refrigerator, with or without a pipe to conduct the air and vapour from the refrigerator to the furnace. The water that it is intended to cool, is discharged by the engine upon the upper layer of the refrigerator; from whence descending by its gravity through the inferior layers of the refrigerator to the cold-water reservoir, it (i. e. the remainder of the water) suffers from the evaporation of a portion such a reduction of its temperature, as to be again adapted to supply the condenser. The refrigerator must be made very rough, and not too porous, lest the water which has been transmitted into the refrigerator to be cooled should not be long enough exposed to the refrigerating process. The superficial area of the refrigerator that I should recommend, when a smart breeze could be always at command, would be about 100 square feet per horse-power. The second feature of these inventions consists in connecting the piston-rods of two steam engine cylinders and the piston-rods of the air-pump, and of such other pump or pumps as may be required to the same cross-head. The object of this arrangement of steam-machinery is to render condensing steam-engines lighter, and more compact, and, consequently, more suited for various useful purposes; to wit, for locomotive purposes on railways, in working fire-engines, and in propelling vessels, &c., the power, in the case of steam-vessels, being immediately applied, through the medium of two forked connecting-rods, to two cranks on the shaft of the paddle-wheels. Now, as in the descending stroke, with the present arrangement of the steam-engine, the weight of the pistons, rods, and crosshead, would occasion a very great momentum, the air-pump is made to perform its greatest labour in the descending stroke; i. e. the air-pump, as used solely to exhaust the condenser, ejects in its descending stroke the principal part of its hot water; its piston being furnished with one or two very small valves, merely to permit the passage of the incondensible gas, and a small quantity of the hot water above the piston, to be ejected at the upward stroke of the air-pump into the main ejection-pipe. But in the construction of my portable condensing steam-engines, as used in extinguishing fires and for some other purposes, I make the air-pump not only to exhaust the condenser, but also to operate as an ordinary suction and force pump; i. e. it has a solid piston, and is supplied from the condenser, as in the diagram, fig. 2, at the aperture A, through the medium of a pipe B, which, from the action of the pump, is alternately above or below the level of the water in the condenser C; and which pipe B, consequently, alternately admits the incondensible gas, or hot water of the condenser, into the airpump D. E, the hot water and incondensible gas ejection-pipe of the airpump D, terminating in the air-vessel F. R, the suction-pipe, by which water that is acted on by atmospheric pressure enters at the base of the air-pump D; this water, by the descending stroke of the air-pump, is ejected through G into the base of the air-vessel F. To work the steam-valves of my portable condensing-steam fire-engine, I connect the rods of the two ordinary slidevalves to the same cross-head K (see side-view, fig. 3). K is connected by the rod L to the oscillating-lever M, externally to the carriage-floor N; and the lever M is worked by the tappet-rod O from the engine's cross-head P.. Fig. 1 represents a section of a railway condensing locomotive steam-engine, with the refrigerator A, placed in that part of the ordinary locomotive tender which at present constitutes the reservoir. TT are the air induction and eduction passages. |