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copper, and fulphur. After being purified it fells in the market here for about fifteen rupees per maund; and I am affured, by many of the natives, that all the borax in India comes only from the place abovementioned.

"I am afraid you will think this at best but a very unfatisfactory and unphilofophical account of the matter; but what can be done, where the only mode of information is through fome of the wild and unfettled mountaineers? for the place is inacceffible even to the inhabitants of Hindoftan, and has never been vifited by any of them, except a few wandering Faquires, who have been fometimes led that way, either to do penance, or to vifit fome of the temples in the mountains. The cold in winter is defcribed to be fo intenfe that every thing is frozen up, and that life can only be preferved by loads of blankets and fkins. In the fummer again, the reflection from the fides of the mountains, which are fteep and close to each other (there being little or no plain ground betwixt

them), renders the heat infufferable.

"I have not loaded this account with any reflections or conjectures of my own. I have fimply given you the narrative of thofe from whom I had my information; and having put into your poffeffion all the data I have been able to collect upon the fubject, you may make what ufe of them you pleafe."


"Ifhall conclude with a few obfervations regarding the credibility of the relation: and, first, that it is really brought from the Tibbet mountains is certain, as I have felf often had occafion to fee large quantities of it brought down, and have purchafed from the Tartar mountaineers, who brought it to market; fecondly, I have never heard of its being either produced. or brought into this country from any other quarter; and, thirdly, it it was made on the Coromandel coaft, as fome books mention, I think there can be little doubt, but that the whole procefs would have been fully enquired into, and given to the public long before this time.".

WILLIS's Method of preventing STONE RETORTS from breaking during CHEMICAL OPERATIONS.

[From the Fifth Volume of the Tranfactions of the SOCIETY for the Encouragement of ARTS.]

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which when dry, are then ready for the proper preferving coating..

"The intention of this first coating is, that the fubftances thus fpread over, readily vitrifying in the fire, prevent any of the diftilling matters from pervading the retort, but does in no wife prevent it from cracking.

"Whenever I want to ufe any

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of the above coated retorts; after I have charged them with the fubftance, to be diftiled, I prepare a thin pale, made with common linfeed oil and flaked lime well mixed, and perfectly plaffic, that it may be eafly fpread with this let the retorts be covered all over except that part of the neck which is to be inferted into the receiver, this is readily done with a painter's brush; the coating will be fufficiently dry in a day or two, and they will then be fit for ufe.

"With this coating, I have for feveral years worked my ftone retorts, without any danger of their breaking, and have frequently ufed the fame retort four or five times; obferving particularly to coat it over with the last mentioned compofition every time it is charged with tref materials: before I made ufe of this expedient, it was an even chance, in conducting operations in fione and earthen retorts, whether they did not crack every time; by which means great lofs has been fuftained. "If at any time during the operation, the retorts fhould crack; fpread fome of the oil composition thick on the part, and fprinkle fome

powder of flaked lime on it, and it immediately flops the fiffure and prevents any of the distilling matter from pervading; even that fubtile penetrating fubftance the folid phofphorus will not penetrate through it. It may be applied without any danger, even when the retort is red hot; and when it is made a little ftiffer, is more proper for luting veffels than any other I ever have tried; becaufe if properly mixed, it will never crack; nor will it indurate fo as to endanger the breaking the necks of the veffels when taken off.

"As the above method of preferving retorts may be of fingular fervice to philofophical chemists, as well as thofe who practise the fcience for commercial purposes; it is my wifh it should be generally known; as many curious operations may be carried on with greater fafety, and at an cafier expence. I have communicated it to the duke de Chaulnes, who no doubt will make it known to the French chemifts; and fhall be happy to hear of its being of advantage to a science fo much cultivated in the prefent age."

Dr. RUSTON's Letter to Dr. FRANKLIN on the CURE of SMOKY


[From Dr. FRANKLIN's Philofophical and Miscellaneous Papers.]

"THE "They, of which I had the honour of converfing with you at your own houfe laft evening, is of fo much importance to every individual, as well as to every private family, that too much light cannot be thrown upon it.

HE fubject of fmoky chim

"A fmoky house and a fcolding wife, Are (faid to be) two of the greatest

ills in life."

"And however difficult it may be to remedy one of thofe ills, yet any advances we may be able to make towards removing the incon veniences arifing from the other,


cannot fail to be favourably received by the public. As they are fhortly to be favoured with your fentiments on that fubject, poffibly the following obfervations, which were in fact occafioned by neceffity, and are the refult of my own experience, may not be altogether undeferving of notice.

When I left London and went to live in Devonshire, in the latter end of the year 1777, it happened to be my lot to dwell in an old manfion which had been recently modernised, and had undergone a thorough repair. But as in moft of the old houfes in England, the chimneys, which were perhaps originally built for the purpofe of burning wood, though they had been contracted in front, fince coal fires came into general ufe, to the modern fize, yet they were ftill, above, out of fight, extravagantly large. This method of building chimneys may perhaps have anfwered well enough while it was the custom to fit with the doors and windows open; but when the customs and manners of the people began to be more polifhed and refined, when buildings and architecture were improved, and they began to conceive the idea of making their chambers clofe, warm, and comfortable, these chimneys were found to fmoke abominably, for want of a fufficient fupply of air. This was exactly the cafe with the houfe in which I first lived, near Exeter, and I was under the neceflity of trying every expedient I could think of to make it habitable.

The first thing I tried, was that method of contracting the chimneys by means of earthen pots, much in ufe in England, which are made on purpofe, and which are put upon the tops of them; but this method by no means anfwered.

I then thought of contracting them below, but as the method of contracting them in front to the fize of a fmall coal-fire grate has an unfightly appearance, as it makes a difagreeable blowing like a furnace, and as it is the occafion of confum. ing a great deal of unneceffary fuel, the heat of which is immediately hurried up the chimney, I rejected this method, and determined to contract them above, a little out of fight. For this purpose I threw an arch acrofs, and alfo drew them in at the fides. This had fome effect, but as this contraction was made rather fuddenly, and the fmoke, by ftriking against the corners that were thereby occafioned, was apt to recoil, by which means fome part of it was thrown out into the room; I determined to make the contraction more gradually, and therefore run it up at the back, where the depth of the chimney would admiț of it, and alfo fhelving or floping in a conical kind of direction at the fides, as high as a man, itanding upright, could conveniently reach, and by this means brought the cavity within the fpace of about twelve by fourteen or fixteen inches, which I found fufficiently large to admit a. boy to go up and down to fweep the chimneys. This method I found to fucceed perfectly well, as to curing the chimneys of fmoking, and it had this good effect, of making the rooms confiderably warmer; as this experiment fucceeded fo well, fince the only ufe of a chim, ney is to convey away the finoke, I determined to carry it ftill farther, in order to afcertain, with preciñion, how much fpace is abfolutely necellary for that purpose, because all the reft that is fhut up must be fo much gained in warmth. Accordingly I laid a piece of late acros the remaining aperture, removable

at pleasure, fo as to contract the fpace above two thirds, leaving about three inches by twelve remaining open; but this space, except when the fire burnt remarkably clear, was fcarcely fufficient to carry away the finoke. I therefore enJarged it to half the fpace, that is, to about fix by feven or eight inches, which I found fully fufficient to carry away the fmoke from the largest fires.

When I removed into the Bedford Circus in Exeter, though the houfe was modern, and almost perfectly new, yet the chimneys were large; in confequence of which almost every room of it fmoked. My predeceffor, who was the first inhabitant, had been at great expence in patent ftoves, &c. but without effect; but by adopting the method I have just now defcribed, I not only cured every chimney of fmoking, but my houfe was remarked for being one of the warmest and most comfortable to live in of any in that large and opulent city.

The houfe I now live in in Philadelphia, I am told, has always had the character of being both cold and fmoky; and I was convinced, as foon as I faw the rooms and examined the chimneys, that it deferved that character; for though the rooms were clofe, the chimneys were large: and we fhall ever find, that if our chimneys are large, our rooms will be cold, even though they fhould be tolerably clofe and tight; because the conftant rufhing in of the cold air at the cracks and crevices, and alfo at every opening of the door, will be fufficient to chill the air, as fast as it is heated, or to force the heated air up the chimney; but by contracting the chimneys I have cured it of both thefe defects. There was one remarkable circumftance

attending the contraction of the chimney in the front parlour, which deferves to be attended to; which was, that before I applied the caft iron plate, which I made ufe of inftead of flate, to diminish the space requifite for a chimney-fweeper's boy to go up and down, the fuction or draught of air was fo great, that it was with difficulty I could fut the door of the boom, infomuch that I at first thought it was owing to a tightnefs of the hinges, which I imagined must be remedied; but upon applying the iron plate, by which the pace was diminished one half, the door fhut to with the greatest eafe. This extraordinary preffure of the air upon the door of the room, or fuction of the chimney, I take to be owing in fome measure to the unufual height of the house.

"Upon the whole, therefore, this fact feems clearly afcertained, viz. That the flue or fize of the chimney ought always to be proportioned to the tightness and clofe nefs of the room; fome air is undoubtedly neceflary to be admitted into the room in order to carry up the fmoke, otherwife, as you juftly obferved, we might as well expect fmoke to arife out of an exhausted receiver; but if the flue is very large, either the room is tight, and the fmoke will not afcend, or it is pretty open, and the confequence will be, that the air of your room will be fo frequently and fo conftantly changed, that as fast as it is heated, it will be hurried away, with the fioke, up the chimney, and of courfe your room will be constantly cold.

"One great advantage attending this method of curing fmoky chimneys is, that, in the first place, it makes no awkward or unfightly ap pearance, nothing being to be feen but what is ufual to chimneys in


common; and, in the fecond place, that it is attended with very little expence, a few bricks and mortar, with a plate or covering to the aperture, and a little labour, being all that is requisite. But in this new country, where crops of houfes may be expected to rife almoft as quick as fields of corn, when the

principles upon which chimneys should be erected ought to be tho roughly understood, it is to be hoped, that not only this expence, fmall as it, but that all the other inconveniences we have been speaking of, will be avoided, by conftructing the flues of the chimneys fufficiently small."

THOUGHTS on the CAUSE of the VARIATION of the NEEDLE. [From CAVALLO's Treatife on Magnetifm.]


HIS wonderful phenomenon has, fince it was firft difcovered, employed the thoughts of very able philofophers; many hypothefes having been offered, not only for its explanation, but even to foretel the future variations in various parts of the world. I need not detain my reader with a particular history of thote hypothefes; but fall only obferve, in general, that neither have their predictions anfwered, nor were any of them founded upon evident principles. The fuppofition of a large magnet being inclofed within the body of the earth, and of its relatively moving with respect to the outward fhell or cruft; the fuppofition of there being four moveable magnetic poles within the earth; the hypothefis of a magnetic power, partly within and partly without the furface of the earth; together with feveral other hypothefes on the fame fubject, are not only unwarranted by actual experiments, but do neither feem analogous to the other opera tions of nature. The late ingeni ous Mr. Canton, F. R. S. was the first, who endeavoured to account for the daily variation of the magnetic needle by the heating and

cooling of the magnetic bodies in different parts of the earth's furface; which was in confequence of his having firft obferved, that the action of the magnet on the needle was diminished by heating, and increafed by cooling.

"Following Mr. Canton's judicious method of deriving the explanation of natural appearances from properties actually proved by experiments, I think, that the increafe and diminution of magnetic attraction, by heating and cooling of the magnet, as obferved by Mr. Canton, together with the refult of the experiments defcribed in the preceding chapter, feem fully fuftient to account for the general variation of the needle.

"If we collect under one point of view all the caufes hitherto af certained, which can increase or diminish the attraction between magnetic bodies, we shall find, that the attraction between the magnet and iron, or between magnet and magnet, is increafed by cooling, by a regeneration of iron, or phlogif tication of its calx, and, within certain limitations, by the action of acids upon the iron; that this attraction is diminished by heating, I 4


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