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IMPORTANT TO MANUFACTURERS OF GLASS, PORCELAIN, POTTERY, ETC.— NEW MATERIAL DISCOVERED.

Sir, It is well known that the Americans are endeavouring to supply themselves with earthenware, and that they are in possession of the materials, which at some future day may be made a greater use of. In order to retain the superiority in making pottery, porcelain, &c., that Staffordshire has hitherto had, we must not only consider the best mode of combining our earths and minerals, but also the cheapest plan of obtaining them. Under this impression I have succeeded in obtaining a material which is likely to be extensively used in the fabrication of glass, pottery, porcelain, &c. It possesses one great advantage over articles of similar properties now in extensive use, that of being cheaper. It may be obtained in any quantity, at any season of

the year, and delivered in the potteries at a less price than flint or clay. It is free from any metallic mixture, and does not contain (excepting an almost imperceptible portion of carbonate of lime,) anything but pure silica and alumina, of which there are about four-fifths of the former, and one-fifth of the latter. It would not require the expensive and tedious process of burning and stamping like flint, but merely grinding from a state of siliceous sand to powder; and containing already one-fifth of alumina, would only require an addition to be fit for the potter's use. It is difficult to meet with such a pure alumina-siliceous compound in nature. The SILICA has been extracted easily by water from the native earth and used at BIRMINGHAM and ST.

HELEN'S in the manufacture of FLINT and PLATE GLASS, and was found equal, if not superior, to the sand from the Isle of Wight, now in such general use.

Any manufacturer wishing to make a trial of this new production, may have a sample on application to the writer. SAMUEL SALT.

Liverpool, 32, Mulberry-street, Feb. 9, 1842.

PATENT FIRE-PREVENTIVE PLASTER, VINDICATED FROM THE ASPERSIONS OF COLONEL MACERONE.

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He has been bred i' the wars since he could draw a sword, and is ill schooled in boulted language; meal and bran together he throws without distinction."

Sir, I had hoped that my last communication on this subject would have sufficed to show Colonel Macerone, that he was greatly mistaken with reference to the properties of the Fire-preventive Cement; and that he had better either obtain more correct information, or be silent upon this subject.

By your last Number, however, (page 116,) I perceive that my friendly caution has been thrown away

"He winna tak the hint."

On the contrary, he continues to write most disparagingly of the "anti-phlogistic plaster," alias, "the bubble cement:" with what justice, your readers shall be enabled to determine.

The highly satisfactory experiment in Dorset-street, Clapham-road, on the 6th of June, 1838, and the (if possible) still more conclusive demonstration of the efficacy of this composition, in Traffordstreet, Manchester, on the 23rd of October following, have been duly recorded in your Gazette. Similar public exhibitions have been made in New York and St. Petersburgh. Many private experiments have also been witnessed by architects, builders, &c., and by the officers in connexion with Her Majesty's Board of Ordnance and Dock-yards, Colonel Fanshawe, Captain Jebb, Mr. Ewart, Mr. Lloyd, Mr. Sylvester, and others, who not only expressed their confidence in its properties, but have given orders for its use in the Lucifer steam ship, and the Model Prison erected under the superintendence of the Commissioners of Woods and Forests; the experiments having sa tisfactorily demonstrated that the "Patent Fire-preventive Plaster" is a com

plete protection against the spreading of fire, in all the possible casualties of ordinary conflagrations.

Witnessed, as these experiments have been, by the highest and most competent authorities, it is perfectly futile for Colonel Macerone, at this time, to misrepresent the facts, or to underrate the value of the protective powers of the composition.

In order to show his intimate knowledge of the ingredients of which the firepreventive plaster was composed, Colonel Macerone says, "I took a portion of it home, and found it to consist of Roman cement, size, and alum." The mode of chemical analysis by which the Colonel can resolve one composition into another must be a very singular process. Unfortunately, however, either for Colonel Macerone's honesty, or for his chemical skill, no such matters as Roman cement or alum enter into the composition of the article in question; and I am the more surprised at the temerity of Colonel Macerone, in venturing to put forth such mistatements upon this subject, because the actual components of this plaster are no secret. The specification of the patent, duly enrolled, gives the public free access to all the information they can desire upon this head. The basis of the fire-preventive cement or plaster is, slate and calcined river sand. The refuse pieces of slate are ground to a fine powder, and with the sand are boiled with a small quantity of tar, rosin, and the strongest glue, or other animal gelatinous substance. When brought to the required consistence, the mixture is dried, powdered, and packed in casks for sale. When required for use, it is tempered with water, as in mixing common

mortar.

Colonel Macerone further states, that at the house in Dorset-street, he saw "the tubs of Roman cement, those of size, and others, which, not being opened, I cannot swear that they contained the alum." No such materials as Roman cement, size, or alum, were on the premises; the "preventive cement" was delivered in tubs ready for use, requiring nothing but the addition of a proper quantity of water. Indeed it is necessary to mention, by way of caution to par

Surely if such ingredients composed the plaster, they would have been combined in the manufacture, not in the using!

MECHANICAL-CHIMNEY SWEEPING.

ties using the preventive plaster, that Roman cement, if mixed with it, spoils it. Such a mixture greatly impairs its antiphlogistic powers, and never hardens properly; I have seen specimens which remained soft and friable, while the cement alone attained a stone-like hardness.

The determined hostility with which Colonel Macerone has all at once attacked the fire-preventive plaster-professing as he does, to be a fellow labourer in the cause of "fire prevention"-is most surprising. Nor will I pretend to explain the wherefore. Neither can the materials, of which the fire-preventive cement is composed, be of any very great consequence, so long as it retains the remarkable fire-resisting properties, which every trial has hitherto proved it to possess. Without pursuing the subject further, I beg to remain,

Sir, yours respectfully.
WM. BADDEley.

February 14, 1842.

MECHANICAL CHIMNEY SWEEPING.

Sir,--On reference to page 337, vol. ii., of your instructive Magazine, you will find fully described by G. W. T., with drawings, the first and best of the plans suggested by your correspondent, Mr. Emslie, in a recent Number. An improvement upon this plan I first made public in 1837, the object of which was to obviate the necessity of going on to the top of the house every time a chimney required cleaning. A model of my improvement is exhibited in the Polytechnic Institution, Regent-street, and may be described as follows:-Across the top of the chimney or chimney-pot, rather to one side, is placed a round bar of iron, over which runs a small endless chain, (jack-chain,) or incombustible rope, descending to the fire-place, where it passes under another round bar, placed in any convenient corner at the bottom of the chimney, to prevent the chain from twisting. A whalebone brush, or wisp of heath, &c., is to be attached to any part of the chain or rope, and by moving

it up and down, it will effectually bring down all the soot, however crooked the chimney may be. This accomplished, detach the brush, clear away the soot out of the grate, and place the lower end of the chain at the side of the chimney. It

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will be necessary to have a chain or rope hung in each chimney. The only objection I can see to this plan is, that in the course of time the chain or rope will be apt, in rubbing against any acute angles, to work into the joints of the bricks, as chimneys are now constructed. To obviate this, I propose to insert in the chimney, where any very acute angle occurs, a metal brick, with one of its corners well rounded, which would form an easy surface for the chain or rope to pass over.

To all straight chimneys, the jointed rods, (Glass's machine,) are well adapted, and as one set will answer for many chimneys, they will on that account be found the most economical. If the above plan were generally adopted, it would only be necessary for adult sweeps to go about in the morning with brushes of two or three sizes to attach to the chain or rope, and a bag to carry away the soot.

Should you think the above worthy of insertion in your valuable Magazine, you will further oblige, Sir,

Your most obedient servant,
A. M'GILLIVRAY.

38, Clarendon-square,
Feb. 1, 1842.

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Sir, I feel assured you will do me the justice to give early insertion to a few words in reply to the strictures of Mr. Baddeley, on my plans for mechanical chimney-sweeping, published in your 964th Number.

I am, indeed, much obliged to Mr. Baddeley for giving me credit for motives of humanity in submitting these plans to the public; but, after showing himself so strenuously adverse to the employment of little children in the sweeping of chimneys, I think he might have left his mind open for the unprejudiced consideration of every variety of suggestion for the introduction of mechanical means, instead of so strenuously advocating one invention, to the exclusion of all others.

Could I have persuaded myself that Mr. Glass's machine was a perfect instrument for the purposes in question, I should not have troubled myself to devise new means. I uphold, however, and shall demonstrate thisthat the rope, weighted brush, pulley, and flue-door mode is much superior to Mr. Glass's, in many instances. It is all very well for Mr. Baddeley to say, "There is no chimney in existence, capable of being swept

by the weighted brush, that could not be swept far better, and with less injury, by Glass's machines." But where is the proof of this? Mr. Baddeley cannot expect that the public will take his mere assertion of the thing as an absolute fact. I may with more

reason, I think, ask-Can a single flue be pointed out, which Glass's machine is capable of cleansing, that the weighted brush mode is not equally able to effect? I am sure that all those who understand the respective properties of both methods, and are disinterested as to the success of either, will answer in the negative. Suppose the question reversed, what do we arrive at? Why, at this; that by numerous soot-doors the most perversely constructed chimney may, by Glass's machine, be swept; but that by many fewer contrivances, and much more easily, the same construction of chimney may be effectually cleaned by the weighted brush. The following sketch will illustrate the difference :

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BURSTING OF PIPES.

IMPROVED GREASE CUP FOR STEAM

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Sir,-A few days ago as I was viewing the operation of a newly-erected steamengine, I thought proper to open the cock in order to empty the grease cup into the cylinder. But instead of doing this during the ascent of the piston, that is, when the space above the piston was void, I unthinkingly did it during the descent; the consequence was, that the steam blew out the contents of the greasecup with very considerable force, and scattered them all over me. To save others from being exposed to such accidents, I beg to suggest that the cup should be formed in the manner represented in the prefixed sketch. It will be advisable, previous to allowing the oil or tallow to enter the cistern C, to extract the air therefrom, by closing the cock D, when a vacuum will be produced immediately beneath: also to make the cistern C a little larger than A, in order to preserve a small portion of air above the tallow, after the cock B is closed, the expansion of which would, on opening the cock D, cause the oil or tallow to leave the cistern more freely. I am, respectfully, yours, &c. FRANCIS HAROLD.

BURSTING OF PIPES.

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Sir,-In No. 966, Mr. Baddeley has given an account of the bursting of a pipe under peculiar circumstances, which he designates a " Singular Phenomenon." I was surprised that Mr. Baddeley, with his stock of general knowledge, should find the solution difficult.

My explanation is this:-That part of the pipe situated outside the house being colder than the portion which is inside, acted as a condenser to the vapour rising from the surface of the water in the shorter leg of the syphon. The vapour, as it became condensed upon the sides of the colder parts of the pipe, would descend to the stop-cock at the lower end, and would accumulate there. The frost would perform the remainder of the operation.

By the rising and falling of the water in the cistern, and consequently, in the shorter leg of the syphon, the inclosed air would be alternately compressed and dilated, which would increase the evaporation, as the variable density of the air I would give it different capacities for retaining the aqueous vapour; and, by the falling of the water in the shorter leg, the sides of the pipe would be left wet, and thus the evaporating surface would be much increased, forming a complete distilling apparatus upon a small scale. It may be asked, why the pipe should burst at a distance of 9 inches above the cock? The answer would be, that the water is supposed to have stood at that height, and the upper surface becoming frozen first, would strain the pipe in that part, and the condensation still going on, would cause the ice to accumulate there and complete the fracture.

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If this view of the case should be deemed satisfactory, perhaps it may assist in the explanation of the bursting of gas pipes, for they are subject to accumulations of a fluid, more or less watery, in the lower situations, and are liable at times to be frozen.

Yours respectfully,

T. CLAXTON.

29, Harrington-street North, Hampstead-road, February 14, 1842.

[Somewhat similar explanations have been furnished by S. E. A., and An Old Subscriber.-ED. M. M.]

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