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tmd as fmall an cxpence, if not left, and thefe, upon trial, were found to fucceed equally well.
Having obferved that the iron leaves, or plates, are covered with a fmall layer of a fort of raft which they contract in the fire, and which the acid liquor took very little hold of; he judged it might be better to expofe the plates to ruff, in order to the cleanfing them eafily of it ; as ruft is always accompanied with a fort of fermentation, and the particles of ruft, found on the furface of the iron, would be fure to raife up every thing in their way. To this pur- pofe he fteeped the plates of iron in waters, in which were feparately diflolved alum, common fait, and fal armoniac. Some other plates he did not fteep in thefe liquors, but only juft dipped them in, and then expofed them to the air to ruft. All thefe liquors, thus ufed, caufcd the iron to ruft very freely, but the fal armoniac beft of all. After two days, during which every plate had been dipped into this menftruum only twice or thrice, he ordered both thefe, and thol'e which had been left fteeping during the fame fpace of time, to be fcowered ; and on comparing them together, it was found, that thofe which had been dipped, and expofed to the air, became much cleaner than thofe which had been all the time fteeped. The ruft covered all the furface in the latter, without raifing the fcale ; whereas, in the former, the furface was raifed into blifters of ruft, which carried it wholly off with them. Thefe difl'olvents, though very weak, are obferved to produce the defired effect, a? well as ftronger, which muft be much dearer ; but among the latter he prefers vinegar in France, which fucceeds very well, and being plentiful there, is very cheap. This operates fo quick on the iron, that the plate need only be once dipped into it, and immediately taken out again, and fet in a moift place, where it will ruft in eight and forty hours. If the dipping is repeated three or four times, the rufting will be Mill more expeditious, and efpecially if a fmall quantity of fal armoniac be diflolved in the vinegar, about a pound to the puncheon. This will make a very efficacious men- ftruum, the vinegar diffolving iron very well, and the fal armoniac rufting it fooner than any other fait. This, how- ever, muft be ufed very moderately, and the plate muft be fteeped in cold water afterwards, to take oft' any particle that might yet remain upon it, otherwife it would be mbieS to ruft after it was tinned.
There are fevera] other ways of making iron ruft, as keep- ing it m a moift cellar, expofing it to the dew, fprinkling it with fimple water, or, which is ftill better, with water| in which fal armoniac has been diflolved, feveral times a day; and in thofe countries where the pyrites is common, the vitriolic waters, which partake of it, will do it very well. This water may be prepared at little or no expence, only by heaping up large quantities of the pyrites, and Iet- ing it moulder in the air, then putting it into common wa- ter, and making a lixivium of it.
The leaves of tin, when they are finifhed, are always found to be more bright and glofly on one fide than on the other, which is owing to the plates of iron having always feveral roughnefles on one fide, where it has been molt expofed to the hammer. Thefe roughnefles are what are principally to be eaten down by the menftruums; for which reafon Mr. Reaumur greatly prefers fprinkling, or wetting them, to fteeping ; becaufe in fteeping, as both fides are°equally expofed to the force of the menftruum, the fmooth fide muft be confequently eaten away too far, while the other is but eaten barely enough ; this occafions a lofs of the iron, which the author propofes to fave by fprinkling, or fimply wetting, as then the bad fide only might be fubjefled to the action of the menftruum.
There are two other cautions, very neceffary to be obferved in this part of the work. The firft is in the management of the plates, before they come to be prepared ; which is, in the beating of them, to turn them continually about, fo that all parts of every plate may he equally extended. And the other is, to plunge them into fome foft clay, or fullers earth, before they are heated, that they may not folder them- felves together.
Which ever method of rufting the plates be ufed, it is al- ways ncceflary to fcowcr them with fand as foon as it is done; and when they are thus cleaned, they muft be im- mediately plunged into water, to prevent their rufting aaain, and they are to be lett in this water till the inftant in which they are to be tinned, or, in the language of the workmen, blanched. The people employed in this part of the opera- tion, are called Handlers, and the others who, aflift at the cleaning the plates, the feakrs. The blancher makes as great a fecrct of his art, as the fealer does of his, and it was with great difficulty that Mr. Reaumur obtained it. The manner of doing it is this.
They flux the tin in a large iron crucible, which has the figure of an oblong pyramid with four faces, of which two oppofite ones are lefs than the two others. The crucible is heated only from below, its upper part being luted with the furnace all round. The crucible is always deeper than the plates, which are to be tinned, are long; they always put them in downright, and the tin ought to fwim over them, auria. Vol. I,
LAV
To this purpofc artificers of different trades prepare plates of different fhapes, but Mr. Reaumur thinks them all exceptionable. But the Germans ufe no fort of preparation of the iron, to make it receive the tin, more than the keep- ing it always fteeped in water till the time ; only when the tin is melted in the crucible, they cover it with a layer of a fort of fuet, which is ufually two inches thick, and the plate muft pafs through this before it can come to the melted tin. _ The firft ufe of this covering is to keep the tin from burning; as if any part fhould take fire, the fuet would foon moiften it, and reduce it to its primitive ftate again. 1 he blanchers fay, this fuet is a compounded matter. It is indeed of a black colour, but Mr. Reaumur fuppofed that to be only an artifice to make it a fecret, and that it is only coloured with foot, or the fmoke of a chimney ; but he found it true fo far, that the common unprepared fuet was not fufficient ; for after feveral attempts, there was always fomething wanting, to render the fuccefs of the operation certain. The whole fecret of blanching, therefore, was found to lie in the preparation of this fuet ; and this he at length difcovered to confift only in the firft frying, and burn- ing it. This fimple operation not only gives it the colour, but puts it into a condition to give the iron a difpofition to be tinned, which it does furprifingly. The melted tin muft alfo have a certain degree of heat, for if it is not hot enough, it will not flick to the iron ; and if it is too hot, it will cover it with too thin a coat, and the plates will have feveral colours, as red, blue, and purple, and upon the whole will have a caft of yellow. To pre- vent this, by knowing when the fire has a proper degree of heat, they might try with fmall pieces of iron; but, in general, ufe teaches them to know the degree, and they put in the iron when the tin is at a different ftandard of heat, according as they would give it a thicker or a thinner coat. Sometimes alfo they give the plates a double layer, as they would have them very thickly covered. This they do by dipping them into the tin, when very hot, the firft time, and when lefs hot, the fecond. The tin, which is to give the fecond coat, muft be frefh covered with fuet, and that with the common fuet, not the prepared. Philof. Tranf. N°4o6._ p . 634.
LATUS, in zoology, the name of a fifh of the coracinus, or umbra kind, caught in the Nile, and in the Adriatic and Mediterranean feas. It much refembles the common cora- cinus, but is larger, and has not the beard which hangs from the chin in that fpecies, and its body is fomewhat rounder. It is efteemed a very delicate fifh. Randelet. de Ptfc. p. 130.
Latus, (CyeL) in anatomy, a name given by many authors to one of the mufcles of the anus, now generally called the levator am.
Latus mufculm, in anatomy, is alfo a name given by Riolanus, and others, to a mufcle called by Albinus latijjirmi! alii, and by others platyfma myodes, and quadratus genes. Part of this mufcle arifing from the cheek, is called by Santorini the mufeulus riforius novus. See Quadratus.
Latu %-pulfus, a tread pulfe, a term ufed to exprefs that fort of pulfe, in which the artery is very fenfibly dilated at every ftroke.
LAVACRUM, in botany, a name given by fome authors to the common wild teafel, or dlpfacus fohijlrh major. Ger. Emac. Ind. 2.
LAVARETUS, in zoology, the name of a fmall fifh called by fome the gang-fijh, and the rUngau, and by Marggrave the cunmata. It feems of a middle nature, between the trout and herring kind, and is caught in vatt quantities in the months of March and April, in feveral of the lakes in Germany, and is pickled, and fent to different parts of the world. It feldom grows to more than four inches long, and the figure of its body is like that of the herring, flatted, broad, and oblong. Its back is black, and its belly white. It has two fins upon the back; the one near the head, and of the common kind ; the other near the tail, and of the nature of the generical fin of the truttaceous fillies, free from rays or nerves, and fat. Its tail is forked, and it has a pair of fins under its gills, and another pair on the belly. Its head is bright, and in a manner pellucid, and is marked with black fpots. IVillugUy, Hift. Pifc. p. 183.
LAUDICOENI, among the Romans, applauders, or perfons who, for a reward, attended the rehearfal of plays and ora- tions, in order to raife, or join in the acclamation. See Acclamation and Applause.
LAVENDULA, lavender, in bot.uy, the name of a genus of plants ; the charafters of which are thefe. The flower confifts of one leaf, and is of the labiated kind. The upper lip is erect, roundifh, and ufually bifid ; the lower is divided into three fegments. The piftil arifes from the cup, and is fixed, in the manner of a nail, to the hinder part of the flower. This is furrounded by four embryo's, which after- wards become fo many feeds, ripening in the cup of the flower. To thefe marks it may alfo be added, that all the fpecies of lavender bear their flowers in compaft fpikes at the tops of their branches.
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