Experiments to determine the real and comparative expence of burning candles of different forts and fizes, as they are commonly made at Market-Harborough, in Leicestershire. Numb. of Weight of The time The time The expence in N: B. The time that one candle lafted was taken from an average of feveral trials in each fize. Ealy Bafy and safe method of restoring gold, when fullied, to its primitive luftre, without injuring the finest ground it may happen to lie upon; from the rev. Mr. Lewis's Philofophical Commerce of Arts. HE bright deep yellow co in regard to the veffels; thofe of fome metals being in certain circumftances corroded by them, fo as remarkably to difcolour the gold. A gilt fnuff-box, boiled with foap-boilers ley in a tin-pot, to clean it from fuch foulnefs as might adhere in the graved figures, and to prevent any deception which THE cly might hence arife in hydrostatic diftinguished by its name, is one of the most obvious characters of this metal. Its colour and beauty are of great durability, being in jured neither by air nor moisture, nor by any kind of exhalations, that ufually float in the atmosphere; as may be obferved in the gildings of fome public edifices, which have refifted the weather, and the vapours of London and other populous cities, for half a century or more. In this property confifts great part of the excellence of this metal for ornamental and fome mechanic ufes: there is no other malleable metallic body fo little fufceptible of tarnish or difcoloration, or fo little difpofed to communicate any ftain to the matters which it lies in contact with, As inftruments or ornaments of pure gold are liable to be fullied only from the fimple adhesion of extraneous fubftances; their beauty may be recovered, without any injury to the metal, however exquifitely figured, or without any abrafion of its furface, however thin and delicate, by means of certain liquids which diffolve the adhering foulness; a folution of foap, folution of fixt alkaline falts or alkaline ley, volatile alkaline fpirits, and rectified fpirit of wine. In the use of the alkaline liquors, fome caution is neceffary examination of it, became foon of an ill colour, and at length appeared all over white as if it had been tinned: fome pieces of ftandard gold, treated in the fame manner, underwent the fame change; and on trying volatile alkaline fpirits, prepared with quick lime, the fame effect was produced more fpeedily. On boiling the pieces thus whitened, with fome of the fame kind of alkaline liquors, in a copper veffel, the extraneous coat difappeared, and the gold recovered its proper colour. For laces, embroideries, and gold thread woven in filks, the alkaline liquors are in no fhape to be ufed; for, while they clean the gold, they corrode the filk, and change or discharge its colour. Soap alfo alters the shade, and even the fpecies of certain colours. But fpirit of wine may be used without any danger of its injuring either the colour or quality of the subject, and in many cafes proves as effectual for restoring the luftre of the gold, as the corrofive detergents. A rich brocade, flowered with a variety of colours, after being difagreeably tarnished, had the luftre of the gold perfectly reftored by washing it with a soft brush dipt in warm fpirit of wine; and fome of the colours of the filk, which were likewife foiled, became at the fame time remarkably M 3 bright bright and lively. Spirit of wine feems to be the only material adapted to this intention; and probably the boafted fecret of certain artifts is no other than this spirit difguifed among liquids, I do hot know of any other, that is of fufficient activity to difcharge the foul matter, without being hurtful to the filk; as to powders, however fine, and however cautiously ufed, they fcratch and wear the gold, which here is only fuperficial and of extreme tenuity. or fpecies of colour, they differ greatly in its durability; and their differences in other refpe&ts are still more ftrongly marked, and of more eafy difcovery. Defcription of an engine, in aulich the centrifugal force is happily applied to the raising of water; invented by Mr. Robert Erfkine; and from bis defigns executed by Mr. Cole, mathematical inftrument maker, near WAminfter bridge, Surry. HIS machine will be most eafily understood from an account of the principles on which it is founded. But though fpirit of wine is the most innocent material that can be employed for this purpose, it is not in all cafes proper. The golden covering may be in fome parts worn off, or the bafe metal, with Suppofe a tube, one part vertiwhich it had been iniquitously al-cal, and the other part horizontal, loyed, may be corroded by the air. fo as to leave the particles of the gold difunited; while the filver underneath, tarnished to a yellow hue, may continue a tolerable coJour to the whole in which cafes it is apparent, that the removal of the tarnish would be prejudicial to the colour, and make the lace or embroidery lefs like gold than it was before. A piece of old tarnished gold lace, cleaned by fpirit of wine, was deprived, with its tarnish, of the greatest part of its golden hue, and looked now almost like filver lace. Though no one of the other metallic bodies fingly has any degree of the beautiful yellow colour which glows in gold, the true gold yellow may nevertheless be pretty nearly imitated by certain combinations of other metals, particularly of copper with zinc. But how nearly foever thefe compofitions approach to gold in degree fufpended upon, and moveable round an axis; and the upper aperture less than the lower aperture; let this tube be filled with water, and immersed in water; the upper aperture being shut by a valve opening outwards; 'tis evident, the whole tube will remain full, though open at bottom, if the greateft height is not greater than that to which the air will fuftain a column of water. Again, fuppofe, the tube turned round its axis, the water in the horizontal part will require a centrifugal force, which, fufficiently increased, muft overcome the preffure of the air on the valve, and be thrown out; and, fince the air cannot enter against a ftream of water, which has already overcome its preffure, the weight of the atmosphere on the water in the well muft neceffarily force it up, to fupply the place of what is ejected. Hence, Hence, in this machine, the water thrown out acts the part of a pifton on the column of water to be lifted. The horizontal part is called the ejected tube, or radius, and - the mouth of it the aperture of ejection. In conftructing this machine, there may be two or more ejecting tubes, provided the fum of the apertures of ejection be less than that of the bore of the tube through which the water afcends; and the higher the water is raifed, the larger must be the bore of the tube, in proportion to the apertures at which the water is difcarged, be caufe the velocity with which the atmosphere forces up the water through any tube, diminishes in a certain proportion the higher it is lifted. In fhips, the ejecting tubes may be immediately under the deck, moveable by a wheel and pinion, the frame-work to reft on the deck. In the largest machines, it will take up the space of about three feet fquare only. The fpace occupied by the ejecting tubes, fuppofing the cafe, which prevents the water from difperfing all round, to be upon the deck, need not exceed five feet diameter, and a foot deep, though the machine be made large enough to throw out three tous per minute; because it has been found by experiment, that an ejecting radius of only two feet is fufficient for a machine thirty feet high, being lately proved by a machine of that height, which threw out at the rate of a ton a minute, with fix ordinary hands not accustomed to work at a winch. a flider, pulled up and pushed down by an iron rod which reaches the deck; the ufe of this is to ftop the bottom of the machine, when it is filled with water, by an aperture at the extremity of one of the ejecting tubes. At the bottom is likewife a valve, which aufwers the fame purpofe with the flider in machines, where the required centrifugal force can immediately be given to the ejecting tubes. The valves on the apertures of ejection fhut of themselves by fprings, and open only when the centrifugal force overcomes the preffure of the air; the machine, once filled, remains full, while worked, as long as there remains any water at the bottom to be raifed. The joint by which the ejecting tubes have liberty to move, while the conveying tube is at reft, is contained in a cylindrical cup, immediately under the head, and the whole weight of the moveable part is fuftained at the extremity of the axis, which axis ends in a conical point, and terminates at the top of the fixed tube, refting in a focket, upon a screw; which fcrew and focket are supported by three radii at the upper part of the conveying tube: the air is excluded by a collar of leather which lies upon a flank of polished brass; the leather is immoveable, being faftened to the cylindrical cup by a ring of brafs with fcrews paffing through both. Another bras ring preffes with its weight (which is fometimes augmented by fprings) upon the inner circle of the leather, to keep it flat on the brafs flank, which, along with the head of the At the bottom of the machine is machine, moves below it. The under M4 under fide of the flank touches nothing; the only friction of this joint then is that of polished brass, moving under oiled leather, which, from the fmoothness of the furfaces, and their proximity to the centre, muft neceffarily be very fmall. That the air cannot enter the machine by this joint, is evident, because the fuction being in General thoughts on roads and wheelcarriages; being the frait of a gentleman's amufements in va rious avocations from family bu finefs. Introductory Definition. HAT we be wards, and water or oil in the cup T food, in what we write on above the leather, the air preffing to get in excludes itself, the joint being in fact a circular valve. This machine has many advantages over other pumps, befides its throwing out a greater quantity of water than any hitherto invented; particularly its not being liable to accident, there being no part of it which by working can be fuppofed to give way; the axis being of iron, about two inches fquare, and only two feet and a half long. It cannot choke with fand, ballaft, or any thing which prevents the operation of other pumps; and an accident from a cannon-ball can as easily be repaired in this as any pump whatever, by replacing the part thot away; for the whole machine takes to pieces at different joints fcrewed together; and an entire machine may be fitted up in a quarter of an hour. The inventor has a patent for Great Britain and the plantations, notwithstanding which he propofes to oblige thofe who have occafion for fuch machines on the moft moderate terms; one of them will last 40 years, and for a common mer. chant-fhip will not coft 30l. the fubject, we hope the candid will allow us the following leading principles, or maxims, withing, a perfect ftyle or elegance of out fearching for, or even expect. expreflion. 1. That all carriages go eafier down hill than on level ground, eafier on level ground than up bill, and harder up hill, as the fine of the angle of afcent, (or nearly fo), till the angle becomes about 20°; or till the perpendicular afcent may be about one third of the base line, at which time no power can be faid to draw a load up the same fmooth hard plane that itself may ftand upon*. fort of fine gravel as may be confi II. That fandy roads (and fuch dered as next akin to fand) are, generally Speaking, the most pleasant and beft roads we though in general they may be so, bave. But, univerfal; for it feldom happens yet that meaning is far from being that the roads under the general idea of fandy roads will bear much work in long, continued, gentle rains; therefore fuch roads must have breadth, in proportion to the work they are expected to bear, which muft ever be at the difcre By fmooth and hard is meant, fuch a condition as a mafon may be suppofed to leave the face of a stone in from his axe or chiffel, or when the Common roads are in their hardeft or smootheft condition. |