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at all. Larger and thicker difks of lead are fometimes found I fonorous, but never fo much fo, as the figures firft defcribed. There are alfo two circumftances, in which the mafs from the ladle itfelf is not fonorous ; the one is, when it is co- vered with a coarfe fpungy cruft, and the other, when its edges are extremely thin for any confiderable fpace. The fcum is prevented, by carefully taking it off while the metal is in fufion ; and when the edges are as thin as paper, as is frequently the cafe, there is nothing farther neceflarv, than to pare them carefully off. The found is always found to become more and more clear, as they are cutaway. This is eafily tried, and it is readily determined how far tliefe edges are to be pared down, by placing the mafs in equi- librio, on the top of a finger, and ftriking it with a key, or any other hard body, nay even with another piece of lead.
It is very evident then, that it is the being caff in a certain form that renders lead fonorous, notwithftanding the natural foftnefs of its parts ; and that in fuch circumftances, in fpite of this obftacle, it makes very quick vibrations. It is not the form, however, which does this alone, fince pieces of the fame figure, made by hammering and cutting, have no more found than lead in any other fhape ; the fufion there- fore, and the cafting or cooling from fufion in this fhape, is an effential point. The external figure is neceflary, but there is alfo requifite an internal configuration of the parts of the metal, which bare hammering or cutting can never give ; nay, fo far from giving the reality of founding to lead, ham- mering is able to take it from it; for all thefe naturally fono- rous cafts of lead become greatly more dead and dull on being hammered, or ftruck upon by any hard body. The author of thefe obfervations has, in another place, given an account of the arrangement, which the particles of all metals take in their cooling from a ftate of fufion; and has ohferved, that in had the particles arrange themfclves into a fort of fibres in this action. It was eafy to conclude from hence, that this arrangement of the particles of the lead might be that which rendered a ca'ft of fuch a figure fono- rous ; this was eafily tried, fince, if it was fo, the difturbing thefe fibres in their arrangement muff impair, or deftroy the founding ; but experiment {hews fuch a conclufion to be too hafty, and that the lead, though it be fhook about in the ladle during the time of its cooling, or injured in the ar- rangement of its parts by any other means, yet does not lofe any thing of its fonorous quality. Though the arrange- ment of the parts of this metal into fibres be not, however, the occafion of its becoming fonorous, yet it is eafy to ob- ferve, that thefe fibres are compofed of fevcral arrangements of granules ; and thefe may be ftill continued, in their na- tural ftate, during the cooling, though they are prevented by the motion from running into their natural arrangements. Thus the fhaking the matter while cooling may, by preventing the concretions of thefe fibres, do no injury to the found, while the blows of a hammer, which muff evi- dently deftroy the figure of thefe granules, may naturally be fuppofed wholly to take it off; fince this quality plainly depends upon the vibrations of the particles of the metal on being ftruck ; and thefe granules, while in their own natu- ral figure, and difpofcd in a mafs of a determinate fhape, may eafily be conceived to be capable of a vibration, which they can no longer exert, when they are beaten flat, inter- mingled with one another, and that the figure of the mafs they form is altered.
Thefe fpeculations are not without their ufe. It is not to be fuppofed indeed, that any form, into which lead can be caft, can make it capable of anfwering the purpofe of the more fonorous metals in bells, C3V. but it is very probable, that the cafting. metals, naturally fonorous, into a fhape, or figure, which alone can render a metal, naturally mute, highly founding, would make their founds greatly mere per- fect, more loud and clear. Experiment alone can determine this, and diftinguifh what is only probable, and what is true. It fhould (cem that the prefent form of bells, which doubtlefs had their origin from the obferving that pots, and other veffels, made for more immediately neceflary ufes, gave a great found ; and thence, when bells were to be made, they call: them, as nearly as conveniently might be, of that figure. Had they had equal opportunities of obferving the fonorous quality of metals caft into the fhape of fer- ments of fpheres, it is very probable that all the bells m the world had now been of that form. The figure of bells ufed at prefent, is indeed very convenient for the fufpend- ing them in churches; hut there is great reafon to fuppofe that a proper metal, caft into the form above-mentioned, would be more fit than in any other for houfe clocks, where a great found is required. As the artift is limited to fize in this, and in many other things of a like kind, there is great reafon to believe this fonorous quality of lead, in a certain form, may give very ufeful hints for the curious artificer to improve the common practices upon. It appears from the whole, that bells may be made of lead, which would be fufficienrly fonorous, but they would not he lafting. Their figure muft nccefi'arily be that of a fegment of a fphere, thickeft in the middle, and becoming gradually thinner towards the edges ;
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and the tmc proportion of this decreafe of thiefchefs might be eafily found by experiments, and when found, would pro- bably prove this metal to be more fonorous than it is yet found to be. It appears alfo from the whole, that lead is a metal naturally fonorous, though that was never fuppofed before; that there is one peculiar form, in which it is mol fo; and that we deftroy this property by hammering it, which deflroys thofe granules on which its vibrations depend. Mem. Acad. Par. 1726.
Lead, in medicine. This metal is celebrated by fome chemical writers for its great medical virtues; but after all, it feems to be a metal which ought to be given internally with the greateft caution, and to be rather calculated for outward application. Its ore is lb poifonous, that the fleam, arifmg from the fur- naces where it is worked, infects the grafs of all the neighbour- ing places, and kills the animals which feed on it. Its beft preparation is faccharum faturni ; which, though able to do great good in hemorrhages, and fome other cafes, is apt, however, to bring on colics of fo violent a kind, that the remedy often proves worfe than the difeafe. The preparations of lead, mod in ufe, are, 1. Minium, or red lead. 2. Litharge. 3. Plumbum uftum, burnt lead. 4. Cerufs. And 5. Saccharum faturni, fugar of lead. See Minium, Litharge, &c. Cyel. and Suppl.
Bal/am of Lead, an external medicine, greatly famed for its effects in old and fharp ulcers. It is made by mixing one ounce of fugar of lead with two of oil of turpentine, and fitting this mixture in a fand-heat till the fait is difl'olved. By this means the oil acquires a red colour, and is called balfam of lead.
Black Lead, in mineralogy. See Black lead.
Burnt Lead, plumbum uftum, is only intended for external ufe. It has the fame virtues afcribed to it, in ointments and plafters, as litharge or minium. Mixed into an un- guent with lard alone, it makes a good ointment for the piles.
Calcined Lead. See Glass of lead.
Cohefun o/Lead. When one mafs of lead is applied to an- other, with both furfaces fmooth, its cohefion is very extraor- dinary. Dr. Defaguliers tried it with two balls of lead, the one weighing two pounds, and the other one pound ; from each of which having cut a fmall fegment of only the diameter of a quarter of an inch, he prelfed them together with his hands, giving them a twift, to make the furfaces touch as clofely as could be. Thefe fupported one another, and the weight of fixteen pounds ; but a little more feparated them. When examined, after they were feparated, the touching furfaces were found not to exceed a tenth of an inch in dia- meter. But it is to be obferved, that on repeating the ex- periment, the weight required to feparate the balls was never twice exactly the fame ; as indeed it never is in any of the experiments of this kind, and that from very obvious rea- fons.
Glafi of Lead. See Glass of lead.
Mock Lead, a name given to a glittering fubflance found in lead mines. See Galena inanis and Blende.
Native Lead. See Plumbum nativum.
Red Lead. See Minium.
Lead ore. Mr. Boyle obferves there is great difference, dif- cernible by the eye, between different lead ores. Some is fo like fteel, that the workers call it fleet ore. And this being of more difficult fufion than ordinary, they mix it with other ore, by them called firm ore, when they commit it to the furnace. He fays, he likewife took notice of an ore, which, for its aptnefs to vitrify, and ferve potters to glaze their veffels, the miners call pattern ore, and fell it dearer than other ore. Lead ore often yields filver, but not always. Mr. Boyle mentions fome lead ore, he tried, fo rich, as to yield feventy per cent of lead; yet did not, though tried by one of the moft expert artifts, give one grain of filver. Boyle's Works Abr. Vol. 1. p. 156.
The poifonous quality of this ore is fuch, that the people who live in the countries where it is dug, and near the places where it is waflied, can keep neither dog nor cat, nor any kind of fowl, but all die in a fhort time ; and it has been known that a little houfe, in which lead ore had been kept for fome time, though afterwards made very clean, and bedded with fern, yet calves being then put into it, all have died in a very fhort time; and" it is a too common melancholy obfervation, that children are often known to die ftrangely and fuddenly about thefe places. If any fort of cattle are known to eat of the grafs on which the fleam, that arifes from the melting of lead, falls, they are always obferved to die a while after. Philofophical Collections, N 3 2. p. 6.
Si/gar of Lead. See Saccharum faturni.
Lead, among bowlers. See Bowling.
Lead, in the manege, is a term ufed to exprefs the part that begins any motion firft. A horfe going in a ftreight line, always leads, or cuts the way with his right foot. This is called in French entamer le chemiir. See EntameR.
Lead walling, in the fait works, on the fall fprings in fome
parts of England, is the term ufed for that quantity of brine
that is. neceflary for twenty four hours boiling in one houfe.
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