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mentions the head, tail, and feet parts of tanned skins; which, however, in the next page, under the head of the purification of the matters employed, prove to be untanned; having been merely steeped in lime, to take off the hair, and requiring therefore to be cleaned in running water, as there directed, to free them from the lime; and I am doubtful, whether those named in the fourth class, viz. the scrapings produced in dressing leather, can be employed without the aid of another process, not described, but which I shall mention in the sequel of this communication.

Page 180, line 8, electrical* I presume should be elastic and in line 28, the word gelatine* I also presume should be fut.

The process I alluded to, for preparing glue from tanned skins, is employed by the black or brown paper casemakers; and, as I have never seen it published, I apprehend it will prove acceptable to many of your readers : it consists in boiling scraps of such leather as the upper leathers of boots and shoes are made of, in stale urine, until they become soft and pliant, and capable of being stretched out considerably; when they must be well washed, to free them from the urine, and again boiled in a proper quantity of water, to form a glue of a fit consistence for use. This glue has a property which excellently adapts it to their purpose, namely, of becoming black, in consequence of the gallic acid contained in it, when the paper articles made with it are wiped over with a solution of sulphate of iron.

Besides the use of glue as size, employed by papermakers, as stated in page 179, it is also used as size by the paper-hanging-manufacturers, and they prepare a

*The translation of these words was correct.

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very delicately white one from the skin which covers the foreheads and ears of calves.

I cannot avoid the present opportunity of reprobating a practice, now becoming too common, of persons making use of the sanction of that valuable institution, The Society of Arts, as a sort of stalking-horse under which to usher their projects into public notice; when, in fact, they have not only not obtained that sanction, but, in the case of the communication, "On an Invention for reducing the Expense of Carriages on Railways," from Messrs. Tindal and Bottomly, of Scarborough, inserted in your last Repertory, they took especial care that it should not come under the consideration of the Society at all, until it had answered their purpose of prior communication to the public at large, as it is not dated until the 4th day of June, when the Society had adjourned its meetings!

4th August, 1814.

THOMAS GILL.

P.S. I observed in your last Repertory, an attempt to secure the monopoly, by patent, of making Scheele's green, or the arseniate of copper; the process for making which will be found in La Grange's Chemistry, and other chemical works; and differing very little, indeed, from the process attempted to be secured by patent.

Description

Description of an expanding Centre-Bit, by which circular Holes, of various Diameters, may be made.

By Mr. JAMES STONE, 30, Warwick-street, Golden-square. With Wood Engravings.

From the TRANSACTIONS of the SOCIETY for the Encouragement of ARts, ManufacturES, and COMMErce.

Five Guineas were voted to Mr. STONE for this Invention.

HAVING

AVING invented an expanding centre-bit for boring holes in wood, from about one inch to nine inches in diameter, and being advised by many persons who have seen it to lay it before the Society of Arts, &c. I submit it to their consideration, as it will in many cases accelerate the business of carpenters and other workmen.

REFERENCE TO THE ENGRAVINGS.

Figs. 1 and 2 explain two different methods of constructing these centre-bits; Fig. 1 being for forming very large holes, even as much as nine or ten inches in diameter; whilst Fig. 2 is for smaller sizes: but the principal convenience of either is, that it can be set to any reThe large tool, Fig. 1, con

quired size within its limits. sists of a straight bar of iron A A, with a shank B, projecting perpendicularly from it, and formed into a square at top, to be received into a stock or brace, in the manner of a common centre-bit; CD are two cutters sliding upon the bar A, and may be fixed by the screws E E, at any distance from the centre-pin F, to regulate the diameter of the hole intended to be cut out. The centre-pin Fis screwed into the underside of the bar, and its bare and sharp point projects some distance below the edges

of

of the two cutters CD; the cutter C is made rather longer than D, and is formed into two sharp cutting edges, and prevents the wood from splitting up, and making an uneven hole, by cutting two parallel lines round the circle, for the other cutter D, to follow in, and take out the wood between the lines.

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The form of these cutting edges is shewn on a larger scale in Figs. 3 and 4, the latter shewing the two sharp scribing edges to cut the sides of the circular groove; and the other, the sharp hooked edge, which cuts up the wood from between them, in the manner of a chissel.

Fig. 2 shews the construction recommended for smaller expanding centre-bits, the shank A is swelled out at its lower part into a square D, large enough to have a mortise throngh it for the reception of two arms, which are bent down at right angles at the ends, and form the two cutters B C; these arms lie beside each other in the mor tise, and can be removed from the centre both ways, to the size of the intended hole, both being bound fast in the mortise by the screw D; the centre-pin E, and the

two

two cutting edges, are like those shewn on a larger scale at Figs. 3 and 4; the one, Fig. 4, coming first into contact with the board to be perforated, makes two deep lines in it, parallel to each other, and of the same distance apart as the width of the opposite cutter, which is shewn at Fig. 3, and has a sharp edge formed on a surface rather prominent, so as to cut the wood out between the lines made by the first cutter.

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The middle point E is made pointed and sharp, in or der not to impede the action of the cutters when in use.

Description of Elevators or Machines by which Persons can be raised up to a great Height; and which Machines may be employed as Fire-Escapes, Observatories, or for Repairs of Buildings.

By Mr. THOMAS ROBERTS, of Wardour-street, Soho. With Two Plates.

From the TRANSACTIONS of the SOCIETY for the Encouragement of ARTS, MANUFACTURES, and COMMERCE. The Silver Medal and Twenty-five Guineas was voted to Mr. ROBERTS for this Invention. HEREWITH I send a model of an invention for the

consideration of the Society of Arts.

I constructed this model with the view of its being rendered serviceable in the event of a siege. I thought it might also be applied for the purpose of an escalade, VOL. XXV.-SECOND SERIES. Ee

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