Imatges de pàgina
PDF
EPUB

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 beft 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 inhabi tants of Hindoflan, 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 kins. In the fummer again, the reflection from the fides of the mountains, which are fteep and clofe 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 uie of them you please.

"Ifhall conclude with a few obfervations regarding the credibility of the relation: and, firft, that it is really brought from the Tibbet mountains is certain, as I have myfelf 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, if 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 CHEMIČAL OPERATIONS.

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

[ocr errors][merged small][merged small][merged small]

of the above coated retorts; after I have charged them with the fubftance, to be diftiled, I prepare a thin paste, made with common line feed oil and flaked lime well mixed, and perfectly plaftic, 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 brufh; the coating will be fufliciently 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 laft mentioned compofition every time it is charged with fresh materials: before I made ufe of this expedient, it was an even chance, in conducting operations in tone and earthen retorts, whether they did not crack every time; by which means great lofs has been fustained. "If at any time during the operation, the retorts fhould crack; spread fome of the oil composition thick on the part, and sprinkle fome

powder of flaked lime on it, and it immediately ftops the fiffure and prevents any of the diftilling 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 practife the fcience for commercial purpofes; it is my wifh it fhould be generally known; as many curious operations may be carried on with greater fafety, and at an eafier expence. I have communicated it to the duke de Chaulnes, who no doubt will make it known to the French chemits; and thall be happy to hear of its being of advantage to a fcience fo much cultivated in the prefent age."

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

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

[merged small][merged small][merged small][merged small][ocr errors]

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 modernifed, 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 fill, 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 cuftoms 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, thefe 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 neceffity 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 aufwered.

I then thought of contracting them below, but as the method of con. tracting them in front to the size of a final coal-fire grate has an unfightly appearance, as it makes a difagreeable blowing like a furnace, and as it is the occafion of confuming 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 admit of it, and alfo fhelving or floping in a conical kind of direction at the fides, as high as a man, standing 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 fimoking, and it had this good effect, of mak ing the rooms confiderably warmer; as this experiment fucceeded fo well, fince the only use of a chim ney is to convey away the fmoke, I determined to carry it ftill farther, in order to afcertain, with precision, how much space is abfolutely neceffary for that purpose, because all the rest that is fhut up must be fo much gained in warmth. Accordingly I laid a piece of flate acros the remaining aperture, removable

[ocr errors][merged small]

at pleasure, so 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 fmoke. I therefore enlarged it to half the space, 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 almoit 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, Inot 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 should 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 faft 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 cait iron plate, which I made ufe of inftead of flate, to diminish the face requifite for a chimney-weeper's boy to go up and down, the fuction or draught of air was fo great, that it was with difficulty I could fhut the door of the room, infomuch that I at first thought it was owing to a tightness 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 greateit cafe. 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 tightnefs 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 fioke 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 con. ftantly changed, that as fast as it is heated, it will be hurried away, with the fmoke, up the chimney, and of courfe your room will be constantly cold.

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

com

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 requilite. But in this new country, where crops of houfes may be expected to rife almost as quick as fields of corn, when the

principles upon which chimneys hould be erected ought to be thohoped, that not only this expence, roughly understood, it is to be 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 finall."

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

“T

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 thole hypothefcs; but fall only obferve, in general, that neither have their predictions answered, 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 refpect to the outward fhell or cruft; the fuppofition of there being four moveable magnetic poles within the earth; the hypothetis of a magnetic power, partly within and partly without the furf.ce 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 operations of nature. The late ingenious 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 creafed by cooling. was diminished by heating, and in

cious method of deriving the ex"Following Mr. Canton's judiplanation of natural appearances from properties actually proved by experiments, I think, that the inattraction, by heating and cooling creafe and diminution of magnetic of the magnet, as obferved by Mr. Canton, together with the refult of preceding chapter, feem fully fuththe experiments defcribed in the tion of the needle. ent to account for the general varia

of view all the caufes hitherto af"If we collect under one point certained, which can increafe or diminish the attraction between magnetic bodies, we fhall 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

and

« AnteriorContinua »