It a revolution in the world of art. Certain it is, that the invention could not be in better hands, so far as the bringing it fairly before the public is concerned; Mr. Knight is not the man to sleep on his post, and, should the new process of "illuminated engraving" fail at last, it will assuredly be for no want of effort to give the world an opportunity of judging of its capabilities. Two or three series of coloured engravings, portraits and historical pieces, are already announced, as well as two series of maps, a species of illustration for which the new process is said to be peculiarly fitted. As the specification is not yet enrolled, it is not known in what way Mr. K. proposes to effect his object, but that it must be rapidly and easily attained is evident from the low prices at which these commencing series are to bé published,-two or three large coloured maps, for instance, at ninepence, or of the largest size for a shilling. is conjectured that the whole of the colours are printed at once, probably from a block consisting of as many separate pieces as there may be colours required, the invention consisting in the method of unlocking those with facility to perform the inking, and locking them again to take the impression; this has, we believe, often been attempted, but never hitherto with success. Illuminated printing of engravings is of course already well-known, as witness the splendid specimens produced of late years by Mr. George Baxter, the eminent woodengraver, especially in his beautiful "Pictorial Annual." Mr. Knight cannot be expected to compete with such finished productions as these, the only objection to which consisted in the expensiveness of the method by which they were produced. Economy is to be the grand feature of the new plan, but it will hardly succeed unless due attention be paid at the same time to excellence in an artistical point of view. is perfectly true, that by confining a solid cylinder of this material in a suitable cavity, and using a very accurately fitted piston or plunger, "lateral expansion" might be prevented; there are other difficulties, however, not so easily got over, among others, to wit, the decomposition by heat, of the caoutchouc, which would be the certain consequence of powerful concussion. This is a very inconvenient effect, and I fancy it would be no easy task to find a practical method of preventing its occurrence. It appears to me that nearly all the purposes to which the caoutchouc-rod spring would be applicable, are already fully met by the employment of spiral and other metallic springs, some very ingenious applications of which have recently been made in the buffers of railway-engines and carriages, and for some other purposes. For my own part, I cannot perceive what important advantages the application of caoutchouc in this form holds out, to compensate for the numerous inconveniences that would inevitably attend its employment. Under no circumstances would the result of this arrangement be “ a very fective spring," as J. R. would find should he take the trouble to experiment thereon. I am, Sir, yours respectfully, June 26, 1838. MILLS'S MERCURIAL PUMP-A FALLACY. ef Sir, I think it right to offer a few remarks on "Mills's Mercurial Pump," which you have "not considered unworthy of a notice in your excellent periodical;" vide No. 776, p. 189. I know nothing of Mr. Grier, (lecturer on natural philosophy in the Baronial Hall,) to whom the working model of Mr. Mills's pump was presented; but I cannot compliment him on his discrimi nation, that he did not at once detect and point out to Mr. Mills, the thorough fallacy of his contrivance. On the contrary, we are told, "its action was so satisfactory to the lecturer and his class," that a publication of the invention was solicited. In Mr. Mills's description, his pump is said to be "of the suction kind," but in the engraved illustration which accompanies it, is represented to be a lifting force-pump. Mr. Mills is somewhat explicit in giving a limit for the length of the feed-pipe, viz., 30 feet; but he gives no idea of the length required for the play of the mercury in the cylinder, a circumstance that would interfere most prodigiously with the efficiency of the pump, if the feed-pipe approached any way near the assigned limit. The close-topped intermediate moving cylinder, is directed to be so placed as to be capable of easy motion upwards and downwards, but without hinting at the manner in which this is to be effected, or by what means the parallelism is to be preserved, so as to secure the promised advantage of “little friction." If we suppose a pump constructed upon this principle, in the very best manner possible, with a clear perpendicular lift of 26 feet, the working cylinder would require to be nearly three feet high; for on raising it, the mercury would fall on the outside and rise within, in proportion to the extent of vacuum induced. Again, on depressing the handle, the mercury would, in the first instance, return to a state of equilibrium, and then, if the pressure of a column of water, air-vessel, &c., has to be encountered, the mercury would fall in the inner, and rise in the outer cylinder, until the height of the column was equal to the opposing pressure. It is this play or oscillation of the mercury that I have before alluded to, and which would, in practice, render almost nugatory more of the motive force, than the friction of any ordinary well-made pump. The second advantage claimed by Mr. Mills for his mercurial pump, is, "that for every inch stroke of the handle, the water will be raised one foot high!" Now, this effect depends entirely upon the relative sizes of the respective parts of the apparatus, without any reference to the fact of the pressure of one inch of mercury being about equal to one foot of water, a fact illustrative of the inconveniency to which I have adverted. There are other objections to this form of pump to which I need not now advert, but only observe in conclusion, that this is by no means a solitary instance, even in recent times, of clever men being imposed upon by the fallacious character of models. I remain, Sir, yours respectfully, London, June 28, 1838. FIRE-PROOF HOUSES.- DE WITTE'S FIRE-PREVENTIVE COMPOSITION. Sir, From the extreme interest I have ever taken in the best methods of preventing the occurrence of calamitous fires, and for arresting their progress— with the share I have had in the discussion of these topics in your pages—you may very well suppose I have not been inattentive to the recent proceedings of Mr. G. J. De Witte, with his Patent Firepreventive Composition. In a prospectus issued a short time since for the formation of a "Fire-preventive Company," the patentee very justly observes, that "the prevention of so dreadful a calamity as fire will always be considered of the first importance to society, and the discovery of a composition which effectually renders timber and other materials indestructible by that element, will form a new era in the building of houses, shipping, and every erection in which wood is employed." He then goes on to state, that " the experiments which have been already submitted to the public, have convinced the scientific world of the extensive utility of this invention, and of the impossibility of burning timber when covered with this preparation. By a cheap and easy process, walls, ceilings, partitions, staircases, &c., can be covered with this fire-proof material. It is alike applicable to houses under repair as well as when building,-a slight coating being sufficient to secure the woodwork from burning." Having been informed that the patentees were preparing a house in Dorsetstreet, Clapham-road, for an experimental illustration of the perfect efficacy of their plan, I took an opportunity of inspecting their progress. The house, which was a small one, in connection with another adjoining, had been built in the usual way, with the intention of being fitted up in the ordinary style; it had a very liberal allowance of timber in its construction, but was a mere shell when taken up by Mr. De Witte and his colleagues, who proceeded to protect the boards and other timbers, the floors, ceilings, stairs, and wood-work generally, with their patent fire-proof composition, without in any way disturbing the original foundation or superstructure. Their composition in appearance very closely resembles grey or slate-colored mortar; it is exceedingly pleasant to work, dries extremely hard, is free from expansion or contraction under all variations of temperature, and preserves its cohesive properties to the last. When dry it is susceptible of as fine a polish as marble, and forms a better ground for the reception of paint than any other substance I am acquainted with; it can be stuccoed with ornamental devices in the usual manner, in accordance with the taste of the architect or builder. The preventive process having been completed, Wednesday, the 6th of June, was appointed for the experiment, which was to put to a conclusive test the efficacy of the preparation. A great crowd collected near the spot, which was favourable for the accommodation of a large assemblage, on account of the open space afforded by the fields in the vicinity. An inclosure was made behind the premises for those persons who had been invited by the Directors. The company assembled, consisted of men of science, practical builders, several directors of insurance companies, and persons of importance and property, all of whom appeared to take a deep interest in the result of the experiment. The upper floor was covered with shavings in great abundance, to which a number of deal planks were subsequently added. The first floor front room was fitted up as a chamber, with bed and furniture, chairs, tables, &c., as nearly as possible in the usual style of furniture, although, perhaps, less valuable, certainly not less combustible; on the contrary, this floor was likewise embedded with, at least, eighteen inches deep of dry shavings, with a plentiful supply of planks, &c. In consequence of the suggestion of some of the visitors, (who, on going over the premises had objected to the composition being exposed on the surface of the floor as offensive to the eye,) the floor, which had been prepared with the non-conducting composition, was covered over with a veneering of thin deal, which caused the flooring to present the usual appearance. Soon after two o'clock the scientific incendiary perpetrated an act which would have brought certain destruction upon any ordinary building; the shavings, wood, &c., on the upper floor were first fired, and burned with great rapidity, but laying low upon the floor, the appearances to those persons on the outside of the build ing was not such as to prove altogether satisfactory. On igniting the combustible, in the first floor furnished room, however, a different effect was produced; the shavings, as a matter of course, were soon in a blaze, the bed and other furniture rapidly took the infection, and the windows being without sashes, a strong wind blew through the house, which caused the flames to rage with a degree of fury one might have supposed to be altogether beyond the ordinary means of relief. The immense volume of fire that poured from the window, produced a semblance of what might, in common parlance, be designated "a dreadful fire." At this moment the interest of the spectators was raised to the highest pitch: the furniture, &c., was entirely consumed, but the flames did not communicate to the adjoining apartment npon the saine floor, nor to those above or below it. Fully proving what it was the object of these experiments to establish, viz., that fire can be confined to the apartment in which it originates by means of this composition, which effectually prevents contagion. The only sign of injury to any portion of the building was exhibited by a lintel over one of the windows, the wood-work of which being charred by the intense heat directed upon it, a small quantity of gas escaped through a minute fissure in the composition and burned for a few seconds only. The other apartments of the house were then subjected, in succession, to tests equally severe, by heaping shavings on the floor, which were fired, and more fuel added, until each of them might have been compared to the atmosphere of so many ovens; the result, in every case, proving equally successful. Some iron hooping had been introduced into the ceiling of the first floor room, the expansion of which, by the excessive heat it was subjected to, caused the displacement of a considerable portion of the plastering; but the composition remained entire, and duly performed its office as was proved by several parcels of gunpowder which had been deposited between the ceiling and the floor above remaining untouched. This effect of iron hooping, is exactly that which has been anticipated by Mr. Cade, in his letter at page 184 of your last No., and, I think, Mr. C. will be disposed to give the preference to the patent composition, as being, in all respects, much superior to tiles for giving the protection required. After the combustible matters had fairly exhausted themselves, several gentlemen minutely examined the premises, and reported that they found the fabric perfectly sound. Indeed, every person who witnessed the experiment, must have been satisfied of the great value and import ance of this discovery; of its efficacy there is no doubt, and the additional expense of the composition will not, it is said, exceed 207. in a ten-roomed house, so that the public have the opportunity whenever they choose, to put an end to those disastrous conflagrations which every now and then spread dismay and ruin among the inhabitants of populous towns and cities. Several of the fire-brigade were in attendance in Dorset-street, to watch the progress of the experiment; among them was a fireman of thirty-five years standing, who came primed with natural prejudice, having witnessed several unsuccessful attempts of a similar class, and even he pronounced the " arrangements to be very good; the best he had ever seen." Mr. Sylvester, who accompanied Dr. Farraday, acknowledged, that "he had come to see the experiment, prejudiced against it, but the result had changed his mind, and he was satisfied that the inventors had satisfactorily established their principle." Mr. Shepperd, Architect, (Royal Exchange,) expressed himself in similar terms. I may, hereafter, resume this subject, but for the present, I remain, Sir, yours respectfully, London, June 21, 1838. ON THE TANNING PROPERTIES OF ELM BARK. Sir,-No tree grows in more profusion in this country than the elm; it forms a feature of embellishment to every diversified aspect of rural domain; it is one of the most hardy of the vegetable tribes, and grows to a size of great beauty and luxuriance, and, although not a favourite tree of the poets, it is frequently seen towering above their much-vaunted and venerated" monarch," the oak, which in many soils bears but a stinted and mediocre appearance. However, the purport of this paper is to inquire of any of your correspondents, (who may have turned their attention to the subject,) what degree of utility and importance the elm tree may be said to possess as regards the tanning properties of its bark. The late Sir Humphrey Davy has given us a comparative analysis of its astringent properties, as compared with the staple commodity of oak bark; but Sir H.D. was a philosophical experimentalist, and tanners (many of whom I have conversed with upon the subject) seem to be wholly unaware of elm bark possessing any serviceable qualities as a basis for their business. Oak bark has become a plentiful article since the opening of the continental trade to us, say, from 1814 to the present time, but prior to that period, having no other than our home growth to supply the tanner's wants, it had not only reached a most exorbitant price, but had become so exceedingly scarce, (especially in some parts of the north of England and Scotland,) that many tanners were seriously impeded in their business, owing to an inadequate and precarious supply. When I visited Morpeth, in Northumberland, in 1813, Messrs. Benjamin Woodman and Robert Hall, tanners of that place, informed me that their supply of bark was so inadequate to their wants, that they could not work more than three-fourths of their yards in consequence. When I travelled in the foreign hide and skin line in 1811, 1812, and 1813, (a time when English oak bark was exceeding scarce and dear, I think 387. the load,) I made inquiries of several tanners, as to whether they had ever made any experiments, successful or otherwise, elucidatory of any tanning development evinced by the elm bark, and their uniform reply (with one exception) was, that they knew nothing at all about it, and had never tried it. Now, the person I gained some information from, was the late Mr. Cousins, tanner, of Five Head, near Curry Rivell, in Somersetshire. He informed me he was then trying elm bark, upon a small scale, upon some dressing hides, but that he found it did not answer; for although, he said, he was satisfied it possessed sufficient astringency and power to penetrate into the animal pores, and to transform the substance into leather, still, he said, he perceived so many discolourations and stains arising on the surface of these hides during the process of manufacture, that he expected when he had brought them into a state of thorough tannage, to be a considerable loser by his experiment. I forgot, at the moment, to point out to Mr. C. what I am well satisfied was the sole cause of the discolouration and stains he complained of. They must have been owing entirely to his having used the said elm bark in its rough or unprepared state, (i. e. without its first being made clean by shaving; and sure enough, if it had been the finest Sussex oak bark that was ever put into a tan-pit, and so used, the article it assimilated with would have been sure to be proportionally deteriorated. When we consider how many years, centuries, that most useful tanning stimulant, larch bark, remained unknown, and was brought to light by a mere rustic depradator, in the county of Durham, it is extremely probable that many other vegetable acids may, ere long, be discovered, suitable to act as an efficient substitute, or, at least, as a valuable assistant to oak bark, as a tanning stimulant; for although the banners of peace are at the present moment pleasingly flaunting between us and the continental nations, the time may come when war will again supersede our friendly intercourse and barterings. Independent of this, we know it to be one of the wisest principles of national economy, never to purchase an article at a foreign market, when we can procure it upon cheaper terms, and better in quality at home.† I remain, Sir, Your most obedient servant, ENORT SMITH. Marlborough Terrace, Albany Road. This is a literal fact, although a person in highly superior circumstances got the credit of it. It is an incontrovertible fact, that our English oak bark is of a much superior quality to that imported from Holland and other parts of the continent. The tanning business, although "as old as Joppa," still appears to be in its infancy, for if we may believe the statement of Messrs. Herapath & Cox, heavy butt hides, such as used to require six to eight months to perfect, through the kindly assimilation of the animal and vegetable juices, will now be ready for the shoemaker's lapstone in three weeks! Surely some more expeditious mode of wearing out shoes ought to be discovered, to keep pace with this leathern wonder of modern times. GREAT WESTERN RAILWAY. Sir,-From the various reports and opinions that are in circulation on the above undertaking, it is perfectly clear to me that the subject is not generally understood by the public, and that very erroneous conclusions have been drawn from unwarrantable data, probably arising from the absence of correct informa tion. Your valuable journal being a source of substantial facts, the following remarks may probably not be uninter esting at the present moment. A writer in the Railway Times says, that this railway and carriages, being nearly double the width of ordinary lines, the expenditure in the formation must be twice as great. It is evident this writer either does not understand the subject, or if he does, that he wishes to continue a system of misrepresentation, and which a very few words will be sufficient to prove. The distance of the rail being 7 feet instead of 4 feet 8 inches, the extra width of the two lines will also be 4 feet 8 inches; and as I presume that the middle and side ground will be about the same as on other roads, the above extra width will be the total extra expense in the earth work. To show by figures what this would amount to, I will instance a piece of cutting for an ordinary railway in ground requiring the slopes to be what is called "two to one," (that is, that every foot in depth requires 2 feet for its horizontal base,) the depth of cutting being 20 feet and the width of road 30 feet. The width of this cut at the top would be 110 feet, and the sectional area 155 yards. The cost of a mile of such cutting, at 1s per cube yard, would be 13,640. Now, let the width of this road be increased to 34 feet 8 inches, the sectional area will be 166 yards, and the cost of a mile 14,6087., making a difference of 9687., which is, certainly, far from being double. This remark on comparative expense applies to excavations, embankments, and tunnels. With regard to the extra width of the rails which is said to be such a disadvantage in working, it is easy to show that the reverse is the case. In the first place, as the centre of gravity need not be higher in these than in other carri ages, it is almost, if not altogether impossible, that such carriages can be overturned by any thing being inadvertently left or maliciously placed on the rails. |