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[From the IVth Volume of the TRANs actions of the Society for the Encouragement of Arts, Manufactures, and Commerce.]

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method alluded to above, of obviating the objections hitherto made

to thcm. “To the celebrated John Joachim Becher we owe the invention of portable furnaces, contrived for performing the different kinds of chemical processes, of which he has given us a full history and explanation, with many plates, in his work entitled, Scyphus Becherianus. In the introduction to that work, the author says, That having observed some workmen melt iron in a small furnace, it occurred to him that something might be contrived by which the several chemical processes might be conveniently performed; and that having completed his ideas on this head, some of the first furnaces made were purchased by Dr. Dicken'on, physician to the king, prince Rupert, and the honourable Mr. Boyle. “He directs the furnace to be made of plate-iron, having rivets fastened at different places, with heads projecting sufficiently within the infide of the furnace : As the furnace was to be (to the thickness of an inch and half) lined with a lute composed of clay and sand; these rivets were intended to prevent its cracking, and falling from

the sides. “The use of such a contrivance as this appeared so commodious to

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when dry, but before a fire is lighted, with fresh lute, which will, if artfully managed, adhere pretty well to the first layer: but there still remains an insuperable obstacle, which is, the iron rivets that pass through the fides of the furnace, into lute, expanding in great heats, and contracting with cold, in a degree very different from that of the mixture of clay and sand that surrounds them, they are continually cracking the lute, and serve rather to separate and throw it off from the iron plate, than to retain and fix it. “The chief objećtion to the black lead furnaces of Dr. Lewis, is the thinness of the crucibles of which they are formed ; this not only permits a large proportion of heat to escape, but when the furnace grows red-hot, tends very much to incommode the operator, and heat the room wherein any experiments are making. “It is with a view to remedy these inconveniencies, rather thani to propose any new form of a furnace, that this paper is submitted to the consideration of the society; and this end is obtained by uniting, in some degree, the three above mentioned contrivances, by adopting the iron of the furnace of Becher, the bricks of Vigani, and the size of Dr. Lewis, which seems best adapted to experimental enquiries. “To form the body of the furnace, which is the only part intended to be here described, (as any person conversant with these machines, will readily fashion the dome and other parts as may best suit their intention; ) procure a cylinder, about eleven inches in diameter, and twelve or fourteen in length, made of strong plate iron, rivetted together; or, as the thick- ness

ness of the lining, will prevent its ever becoming hot enough to melt hard solder, it will be much neater, if the joint be brazed : at one end, which is to be confidered as the bottom of the cylinder, a piece must be cut out about four inches square, which is to be the opening to the ash-hole, to this an iron door is to be fitted; just above this opening, three iron pins, projećing half an inch or more withinside the cylinder, must be well rivitted on, at equal distances from each other; four or five inches above these pins let another hole be cut in the iron cylinder, and a door fitted to it, this serves for putting in the fuel, when the furnace is used for distilling, and such operations as require only a gentle heat. “ On the pins before mentioned, lay an iron grate, and let the whole of the cylinder, above this grate, be lined with fire-bricks, the joints well fitted, and laid in loam ; by this means the objection to the lute of Becher and Shaw, is obviated ; and as the bricks may be left an inch and half or more in thickness, the heat will be better retained than in the black lead furnaces of Dr. Lewis. To secure the iron door, whenever the furnace is to be used as a wind hole, or any strong fire raised therein, a piece of fire-brick is to be fitted to the opening, and the door shut, which will effectually preserve the iron from injury. * It has been customary to make portable furnaces in the form of a truncated cone, the finaller end being the lower part, that different sized grates, may fit at different heights; if this shape is still thought

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by leaving those bricks that are next the grate, thicker than those towards the upper part, and the diminution may either be regular, or projections left at the heights required, on which the different grates may rest. “Fire-bricks, fit for this purpose, are easily obtained in every part of this kingdom, and in London they are constantly to be met with, at a low price, being sent hither of two kinds, under the names of Windfor bricks, and Nonsuch bricks; the first so called from being brought from the town of that name, and the other from their being made at Nonsuch Park, near Epsom, Sur

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of fire well, and are of so soft a texture, as readily to admit of cutting and grinding into any form requited, so as to be easily adapted to the figure of the furnace ; and as the loam or earth of which they are made, is also brought to town for setting them, that also may be readily obtained; and thus small portable furnaces, more durable, and better adapted to the making chemical experiments than any I have hitherto met with, are e fily and at little expence constructed. “The very respectable authors I have already quoted, have given such precise and accurate descriptions of the forms best adapted to the uses intended, that no additions need be made to their works on that head; and the well known furnace of Dr. Black of Edinburgh, when lined with bricks, as now recommended, will be found greatly to exceed in utility, those which having been hitherto lined with lute, have becrl liable to the ubjections stated above.”

NATURAL.

NATURAL HISTORY of the GIANT’s CAUSEWAY.

I From LETTERs concerning the Northern Coast of the County of

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By the Rev. WILLIAM HAMILto N. )

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