mixture of one part nitric acid, two parts sulphuric, and one hundred water; he also stated that the acid in practice could be always renewed by having a constant dropping of fresh acid liquor into the trough, while a similarly gentle discharge of the spent acid from the trough could be kept up. He stated, that a numerical comparison of the economy of this mode of producing motive power with that depending upon the agency of steam, would give a vast preponderance in favour of this method, while the part of the power consumed in working the machine itself might be left entirely out of account, since the apparatus which changed the poles in his model, would equally suffice in a machine capable of working with the power of one hundred horses. In his model he only worked one of the two soft iron magnets, and its power was only that of lifting seven pounds, and yet this appeared to be sufficient to overcome all the friction, inertia, and other impediments to motion, of the several parts of

MR. HALL'S STEAM-ENGINE IMPROVEMENTS.

Sir, Although it is long since I expressed my opinions on this subject, I trust I shall not be considered either out of time or place in again recurring to a "matter (as you truly say) confessedly of some public importance."

No sooner was my first letter (commencing with the truism," that in these days of quackery, extraordinary announcements are most certain to create suspicion" se -see p. 156, vol. xviii.) before the public, than I was most unmercifully attacked by Mr. Hall-no, I ask pardon, not by Mr. Hall (for, by the advice of his professional and confidential friend, Mr. A. Rosser,* p. 278, last volume, he has

Had it not been for the P. S. to this gentleman's letter, I should never have believed it possi ble, that the liberal-minded adyocate, and great

long since determined never to appear in a controversy on the subject of his own inventions), but by the unpresuming "Audax," and his coadjutor, Mr. J. Ride.

In 1832, Mr. Hall, be it remembered, published a particular and detailed ac count of "the five parts of his invention, all mutually assisting each other, and con stituting a perfect whole;" which perfection, it was stated, was, and could only be obtained by his "particular mode of using metallic surfaces," viz. "by keeping them full of the water resulting from the condensation of the steam, which becomes the internal condensing water," for want of which, all previous attempts to attain this desideratum had proved abortive. All this was strenuously upheld and insisted upon by " Audax" and Mr. J. Ride; the latter even went a step fur ther, and vouched for it as the "" great principle," which, in fact, formed "the substratum of the whole invention." I should think there is not one among your innumerable readers, who, having witnessed the contumely with which I was treated in vol. xviii.-particularly for say ing that the water confined in the refrigerating pipes, by means of the caps, could be of no other use than to reduce their "sectional area"-I say, no one could possibly imagine, that that hint should have been made the basis of Mr. Hall's last patented improvements, the most prominent feature of which improvement on perfection itself, consists of getting rid of the internal condensing water by doing away with the wonder-working caps, and fixing the pipes vertically instead of horizontally, and, finally, by reducing them to about 3ths of their original" sectional area!!" Thus at once upsetting in toto that most beautiful and scientific " great principle," " the substratum of the whole invention."

Again, in the item of fuel Mr. Hall first stated the saving to amount to twothirds, but how stand his testimonials? "Audax" does not mention any saving. Mr. J. Ride would have said a great deal, but was forced to acknowledge he knew nothing about it. Mr. J. Wright says, that on board the Prince Llewellyn

champion of the emancipation of the junior class of chimney-sweepers, conld give publicity to such illiberal sentiments, which, if carried into effect, must clap the padlock on the minds of more than half your correspondents.

he "

can fully testify the saving is fully one-third of the fuel formerly consumed." Captain K. B. Martin's statement is still more vague-"he is convinced that in smooth water, &c., the vessel is rather faster, and the saving of fuel is about a ton per average passage." Messrs. Lloyd and Kingston, in their Report to the Lords' Commissioners of the Admiralty, say not one word of any saving in fuel, but give it as their opinion that "the power of the engines is not diminished;" the total silence of these gentlemen as to fuel may perhaps in some measure be accounted for by an experiment which I have heard confidently spoken of, wherein the saving amounted, not to upwards of 60, as at first stated by Mr. Hall, nor to 30, as fully testified by Mr. J. Wright, nor yet to either 20, 10, or 5, but posi tively to no more than 24 per cent. !!!

The following is an extract from the evidence given by J. Field, Esq., before the Select Committee on Steam Navigation to India, p. 253 :

"886. Are you aware of the improvement introduced into some steam-vessels, to condense the steam in the pipes, without admitting the jet of water into the aperture?— I am.

"888. Do you think it likely that this will be brought to perfection? I do not know; IF IT SUCCEEDS, it will be a very great advantage."

To appreciate justly the value of this evidence to the public at large, it must be remembered, that Maudsley and Field stand first on Mr. Hall's list of "eminent engineers," who, “having fully investigated the matter," have taken licenses under the patent.

Surely, Mr. Editor, there never was such vague, negative, and inconclusive evidence before published in support of an invention with such extraordinary pretensions.

I remain, Sir, very respectfully yours, T. V. ROBSON. Sept. 3, 1835.

MR. GALT'S SUBSTITUTE FOR STEAMPOWER.

Sir,-Seeing in your last Number, under the title of "Substitute for SteamPower," a plan by which Mr. Galt proposes to avail himself of the power of a Bramah's hydrostatic-press in producing motion, I am induced to trouble you

with a few remarks on the subject, the same idea having occurred to myself not many days previously to my seeing the article on the subject, but which, on consideration, I believe not to be applicable.

It is evident that if a cylinder, in which a piston is made to move air-tight, and the upper surface of which is exposed to the atmosphere, be filled with water so as to exclude all the air, and that then this water be allowed to escape by an orifice at the bottom, a vacuum will be produced beneath the piston, which consequently will be pressed down with a force proportionate to the surface exposed. Here, then, we would seem to have a determinate moving-power, but it is evident that the motion produced would be but slow, as it would require a certain time for the water to escape even from a considerable orifice. Mr. Galt proposes, if I mistake not, that this motion be ap. plied to work a forcing-pump, or some other contrivance by which a certain quantity of water is to be raised so as to exert a pressure on the bottom of the piston in the large cylinder, as soon as it has reached the bottom, and thus raise it: but here comes the difficulty. The power of Bramah's hydrostatic-press is known to depend on the relative diameters of the two pistons. Suppose the piston in the large cylinder to be one foot in diameter, and that of the forcing-pump to be half an inch, then the pressure of the water on the bottom of the large piston will be to the pressure of the smaller piston as a square foot to a quarter of a square inch (the areas of circles being as the squares of their diameters), that is, as 144 square inches to 4th of a square inch, or as 576 to 1; and, therefore, if the pressure of 1 lb. weight be given to the water in the forcing-pump by means of its piston, the larger piston will be moved upwards with a force of 576lbs.; hence the smallest given quantity of a fluid may be made to produce an unlimited pressure, either by diminishing the diameter of the column, and increasing its height, or by increasing the surface which supports the weight: but it is evident that the motion produced by such pressure upon the piston in the large cylinder will be but through an indefinitely short space, as it would require a column of water in the small cylinder of the forcing-pump to be raised to a prodigious height in order to equal the contents of the larger cylinder; consequently,

the length of stroke of the large piston must be very short, while that of the small piston must be a proportionately long one. The impelling power produced, in the first instance, by the descent of the large piston, must act, then, at a great mechanical disadvantage in raising the weight at the end of a long lever, by means of a power at the end of a very short one; and here, I conceive, that instead of motion being produced, there would, on the contrary, be an equilibrium between the weight and power.

Such was the view that I had taken of this subject before I saw the article in your last Number. I may be mistaken in that view, and if so, should be glad to be corrected. If the object could be attained of applying the power of the hydrostaticpress in producing an effective movingpower, it would certainly be a important addition to the present state of mechanical knowledge,

most

Should these remarks appear to you to be worthy of insertion,

You will oblige, &c.,

Sept. 2, 1835.

HYDRAULICUS.

P. S.-Mr. Galt, in the article I allude to, mentions the application of his pressure-syphon to the propelling of vessels. Not being acquainted with the principle of this machine, 1 should feel particularly obliged to you, or to any of your correspondents, to explain it in a subsequent number of your valuable Magazine.

PERKINS'S HOT-WATER HEATING SYSTEM.

[We copy the following judicious remarks from an article in the last Number of the Architect. Mag., on the "Comparative Advantages and Disadvantages of the various Hot-Water Systems." The author lays it down as a general rule, which he supports by many cogent arguments, that the hot-water system, now so much in vogue, is only properly applied where great uniformity of temperature is important, and where, at the same time, ventilation or change of the mass of the air heated is unnecessary, and rapidity in increasing the temperature, is not required. He objects, therefore, altogether to its use in airing rooms, churches, theatres, &c.EĎ. M. M.]

The advantages attributed to this mode of warming by hot water may, I think, be re

duced to the following:-that, by closing the apparatus altogether, the temperature of the included water may be raised to any required amount; that, therefore, in proportion as the temperature of the surface of the tubes is higher, their superficies may be diminished, and that this will enable tubes so small to be used, that they can be bent, accommodated, and placed in situations where large ones would be impracticable; that the cost of the apparatus is thus much reduced; that no fresh supply of water is ever needed, and, therefore, no deposit of sediment can take place in the tubes; that the higher temperature enables the fire to be raised proportionably in intensity, and, therefore, to burn less to waste, or to a more advantageous use of fuel; and that less weight of water and apparatus is placed on the floors, &c. This, I think, is a pretty fair statement of all that can be reasonably alleged in favour of the pressure system. Let us now see how far the allegations are borne out. First, it will be advisable to see what increase of temperature we shall get, in proportion to the increase of pressure on the apparatus, over and above 2120 Fahr.; accordingly, from Dulong and Arago's tables of elasticity and temperatures, the latest and probably most accurate that have been formed, we extract the following, omitting decimals:

From this we perceive, that, to increase the temperature of the included water in the tubes, only one-half more than in any com. mon open vessel, namely, to raise it from 2120 to 318°, we must produce a pressure on every part of the surface of the apparatus of six atmospheres, or of ninety pounds, to the square inch, nearly; and that, to raise this temperature again by one-half, or to 4770, we must increase the pressure to nearly forty atmospheres, or to the enormous amount of six hundred pounds on the square inch.

To this latter temperature and pressure I believe Perkins's tubes never have been attempted to be raised, for the best of reasons, that they would not stand it: to the former they, perhaps, occasionally may. But, supposing that the temperature of the included water is actually doubled, or 424o, and, consequently, the surface of the pipe also doubled in heat; as the heating power of every body

that radiates is, cæteris paribus, directly as the temperature and surface of radiation, so here, the temperature being doubled, we may reduce the surface by one-half, and have the same heating power; in other words, the entire gain is, that the diameters of the pipes may be reduced by one-half. This, however, is not exactly the way in which the reduction is made; for the diameters of the pipes are kept always of the same dimension (about one inch), and the variation of surface is produced by lengthening or shortening them.

This, certainly, is no sufficient inducement for incurring the danger of having a network of tubes running in all directions about a building, charged with an intensely heated fluid, at so enormous a pressure. But the advocates of the system contend that there is no danger whatever, and that tubes, charged to six, eight, ten, or a dozen atmospheres, with water and highly elastic steam, are perfectly safe and innocuous; for that the tubes are proved, before they are used, to bear one thousand pounds to the square inch; that they are so small, that, even if burst, no danger can arise; that high-pressure steam will not scald, &c. &c.: all which, let those believe who can, I, for one, cannot; and I do not believe any twelve intelligent engineers (I do not mean hotwater engineers) can be found who will agree in a verdict of "safety."

To give my own particular notion, however, of why this mode of heating is unsafe: -The tubes used are what are called strong "rolled gas tubing," which is made of thin plate iron, with the edges united, without any lap, by pressure between the rolls, at a welding heat; and I never yet have seen a piece of it that would stand five hundred pounds to the inch, much less a thousand; to which latter amount I do not believe they are subjected, notwithstanding what is asserted; and any one who knows the difficulty of making and keeping in order a pump and valves, with other apparatus, &c., capable of forcing pipes to that pressure, will, probably, agree with me. Secondly, when gas. pipes burst, they almost always rip open at the usually imperfect weld, and that, too, for a good length; the result of which would be, in this case, that a gush of a fluid, half water and half steam, would rush out, and continue to do so until it had completely emptied the whole apparatus: and, supposing it were true that steam only made its way out, although, under certain circumstances, high-pressure steam will not scald close to the issuing orifice, yet when two, or three, or more feet distant from it, it will scald as well as the most vulgar steam in the world; but, in this case, it would be steam and hot water mixed, which, together, will scald, and scald horribly, at any distance from the is

suing aperture within its range. Thirdly, it is apparently kept carefully in the back ground, that what is called the expandingtube is usually one of about three inches in diameter, and, therefore, that it, which, from its size, is the most likely to burst, has no plea to put in on account of its small size. Farther, I should like to know how Mr. Perkins, or any of his deputed engineers, can tell to what amount of pressure they subject their tubes; for the only way it can be regulated, apparently, is so to apportion the cooling surface of the pipes to the surfaces receiving heat, that it shall, after a certain temperature, be carried off as fast as generated: but, even if this were accomplished, if the temperature of the air around the tubes rises or falls, or the fire burns better by change of fuel or weather, that moment the temperature of the included water rises with it, and the pressure increases likewise. So that there appears, thus, in principle, the utmost uncertainty, both in the application and management of the apparatus. In fact, I am inclined to believe that, in most cases, it is only a mode of heating by high-pressure steam, and that at no very great pressure either (care being taken that the coil in the fire shall not be able to burst the pipes), which goes by the title of "the patent hot-water apparatus."

I have not had much opportunity of observation of this system myself; but two facts I feel it most important to state, which I have on, I think, excellent authority; and, should it become necessary, I can give name and place for both cases and authority. First, the apparatus nominally called "hermetically sealed " is found almost, if not wholly impracticable to be kept so. The result is, that a small escape of steam at the joints, or at the top-feeding screw or airscrew (I know not what name the inventors give it), is continually taking place; so that, instead of its being never necessary to add fresh water, it is obliged to be poured in every twenty-four hours or so. Hence arises

a very formidable consideration: every quart of water so added lays on a coat of sediment all over the inside (and especially over the parts in the fire) of the apparatus; and this coat of sediment is not deposited over a large boiler and large tubes, but confined to those the majority of which are only one inch in diameter; so that the first one-eighth of an inch in thickness, which is deposited in the pipes, will stop up about one-fourth of their area, and nearly destroy their power of conducting heat to the outside; and the second eighth in thickness will stop up a much greater proportion, and injure the conducting power to a greater amount also.

Now, the friction of the water in tubes of one inch diameter, and the immense resistance

occasioned by the vast number of bends and turns necessarily given to accumulate the required length of pipe into rooms, &c., is such, that I am strongly disposed to doubt whether, if a common apparatus of the sort were left open, and kept under the boiling point, the water would circulate in it otherwise than very languidly indeed; but when the bore comes to be reduced from one inch to three quarters of an inch, and from that to half an inch (for the second thickness will be laid on in much less time than the first), the friction would be so immense, and the heat given out so little, that the apparatus, before long, would be worse than useless. Time, as yet, has not been sufficient, probably, to develop this in any particular apparatus; but I am inclined to think it will be the fate and exit of many an one yet.

The other fact is this, and it is at once curious and important. One of the patent apparatuses had been at work some time successfully, when it ceased to give heat, and the pipes were found nearly cold, although the furnace was lighted. On examination, and taking out the top screw, the water was found to have wholly disappeared; and, on applying a lighted candle to the screw aperture, the tubes were found full of hydrogengas, which ignited at the aperture, and burnt away with a lambent flame.

There are but two ways to account for this: either the apparatus was not staunch, although "hermetically sealed," and the water had all boiled away, so that the tubes became red hot, and decomposed the last portions; or wrought-iron possesses the pro perty of decomposing water at a lower temperature, namely, at that due to the pressure on the apparatus; and if so, in every one that has ever been put up the water is thus slowly (perhaps I should rather say rapidly) decomposing, and thereby destroying the tubes. This, I confess, I think the most probable solution; and, if so, it is a confirmation of what has been predicted of the thing in the Mechanics' Magazine. Which ever horn of the dilemma is taken, it is cogent againt the apparatus, and adds for midably to the danger of bursting.

I must again repeat, that the recommendation given of them, that they are quickly heated, and hold little water, is, like in the case of the flat pipes, an argument against them, as they, also, cool quickly (although not so fast as the flat pipes), and, therefore, give no uniformity of heat.

Still, I freely admit that, for some purposes, where uniformity of heat is no object, they may be advantageously applied; but in those purposes I never could include heating the air of apartments; and, least of all, heating horticultural buildings.

COOKING BY GAS.

(From the New York American.) This new application of gas seems to us of great promise for economy, comfort, and safety. We had heard nothing of it until a few evenings ago, on the invitation of Mr. L. Suydam,* President of the Manhattan Gas-Works, we had an opportunity, at his house, both of seeing the process of cooking, and verifying the fact, that what was thus cooked was " well done," even though not quickly done."

The apparatus is of great simplicity. A circular or elliptical burner of such dimen sions as may be needed-in a large family several of different dimensions would be required is constructed, pierced with numerous and very small apertures, so that all the gas that passes may certainly be consumed. In the centre of the circle is a permanent perpendicular spit, on which the joint to be roasted is impelled, a sheet-iron funnel-shaped chimney, large enough at the bottom to include the lights, and tapering upwards so as to concentrate and reflect the heat, is then placed over the whole, and the cook may go about any other business for the next two or three hours, fully assured on coming back at the end of that time, of finding the meat well cooked. But this is not all. Over the funnel-shaped chimney is placed a large tin vessel, divided horizontally into two compart ments-the lower one serving as a kettle to boil water, the upper as a vessel in which to boil meats or vegetables; and the same fire and the same time required for roasting will also suffice for boiling the water, and cooking the vegetables. The cost for fuel of such a fire as we saw, by which a 121b. piece of beef was roasting, was stated by the superintendent, Mr. Barlow, at two cents an houror six cents for the whole period for cooking dinner-add to this the further economical advantage, that you only light your fire when you want it, and extinguish it the moment it has fulfilled its purpose, and we have a strong argument on the score of cheapness.

It is obvious that any number of these burners may be arranged-all to be supplied by one main leader-and as the cost of these fixtures is small, and only the gas actually used is paid for, it would be expedient always to have several of them.

Of course, the value of this new application of gas depends upon proper care in the use of the apparatus, and on the part of the Company, in the preparation and purification of the gas. As to the first, the whole thing is so simple, that except through wilfulness there could be no mistake; and as to the puri

* The gentleman alluded to in Mr. Barlow's letter in the last Number of the Mechanics' Magazine. -ED. M. M.