Volume 1
The universal dictionary of trade and commerce : with large additions and improvements, adapting the same to the present state of British affairs in America, since the last treaty of peace made in the year 1763. With great variety of new remarks and illustrations incorporated throughout the whole: together with everything essential that is contained in Savary's dictionary: also, all the material laws of trade and navigation relating to these kingdoms, and the customs and usages to which all traders are subject / By Malachy Postlethwayt, esq.
- Jacques Savary des Brûlons
- Date:
- 1766
Licence: Public Domain Mark
Credit: The universal dictionary of trade and commerce : with large additions and improvements, adapting the same to the present state of British affairs in America, since the last treaty of peace made in the year 1763. With great variety of new remarks and illustrations incorporated throughout the whole: together with everything essential that is contained in Savary's dictionary: also, all the material laws of trade and navigation relating to these kingdoms, and the customs and usages to which all traders are subject / By Malachy Postlethwayt, esq. Source: Wellcome Collection.
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![Hon, and fo loft all the filver that was mixed with the gold And, indeed, the before-mentioned method, by adding;ofib ver, which is called the method by quartation, is expenlive and laborious, fo as not to be very beneficially Pra<^ed the laro-e way of bufinefs; but for an affay it may do very well. ^Indeed, when the whole has been divided into fuch a number of hands as to make the feveral parts come cheap, it may be pra&ifed to fome advantage i as fome operators being wholly employed in the making aqua fortis ; others in purifying it, or bringing it to proof; others in laminating the iilver, an diffolving it; others in feparating and reducing the calx o the gold ; others in precipitating the filver with copper; an Others again in feparating the copper from the aqua tor is ; which, at prefent, turns to better account by being iold tor verd, as they call it, to the painters, or for more e icate p pofes, perhaps; large quantities thereof being continually ex¬ ported from England to France, for fome ufes not genera known. Hence the whole operation has been foun to an we the trouble, fo long as they can recover about a drachm o gold from a pound of filver. , There are certain workmen who have, of pretend to have, tne method of feparating gold from filver to much greater P™ 1 ’ without the ufe of aqua fortis or aqua regia, and bare y ya dexterous application of the fire; at leaft without any co y addition.-—This method is kept as a fecret; but may e no other, perhaps, than that of Homberg *; which confifts in fluxing the mixed mafs of gold and filver with equa Par_s ° rough nitre and decrepitated fait, placed at the ottom o t e melting-pot; the gold thus falling to the bottom, and leaving the filver fufpended, or detained, in the falts. Another way of effe fling this may depend upon a dexterous ufe of fulphur, which has the power of making filver melt away from a me¬ talline mixture, almoft as eafy as lead. * See the French Memoirs. Although the refining of gold by melting, and tefting it with antimony, or the glafs of antimony, as before obferved, is ge¬ nerally by the metallurgical chymifts thought a perfect way; yet M. Homberg f has {hewn, that even this criterion, as alfo quartation, cupelling with lead, fluxing with borax, &c. may fail, in cafe the gold be mixed with emery, of poffibly fome other things, f See the French Memoirs. When the gold is eager, as the workmen Call it, that is* brit¬ tle, they hold it a fecret to melt it with mercury fublimate. Bur, after all, no gold, perhaps, can be proved to be per¬ fectly pure, till it has gone through all the trials hitherto known, or even fome of a more curious nature, particularly melting with crude antimony and afterwards cupelling the re- gulus with lead; and, at laft, fufing it with borax: which procefs is recommended to thofe who require gold in abfolute purity for any ftandard, or curious operations. The methods of obtaining filver in purity are various, and differ according to the metal wherewith the filver is mixed, or allayed. If copper be the allay, the beft and cheapeft way to purify the filver is, to calcine it with half its weight of common fulphur; then melt the whole together, and throw into the pot, at feveral times, a due quantity of clean iron filings, which will immediately make the fulphur quit the fil¬ ver, and form a fcoria a-top, leaving the filver free from cop¬ per, iron, or fulphur, at the bottom. The method of aflaying the ores of the inferior metals, as lead, tin, copper, and iron. Accurate aflays upon thefe ores require proper furnaces, the due application of fire, and fuitable fluxes, adapted to the ref- peflive ores; and, indeed, ores of the fame kind frequently require different methods of affaying, as well as fmelting, in the large works. The moll general flux made ufe of upon thofe occafions is what the metallurgifls call the black flux, which is thus pre¬ pared, via. Take one part of nitre, and two parts of common tartar, and tC> Powder, and then mix them well together, and deflagrate the whole in a crucible, by lighting the mix¬ ture a-top, which will turn to a kind of alkaline coal: pul- je^e.tbe Pam.e> and keep it in a clofe glafs, to prevent its ouiolving, as it would do in a moift air. This flux is of general ufe; and, to have it ready at hand, ortens the bufinefs of making aflays, and renders the ope¬ ration more exadt than when crude tartar and nitre are em- p oyed, becaufe the deflagration might thus carry off fome SvtUr th-e °Je’ ar]d defraud the account- For that reafon the Zfiderll dlfc£!e<i to be fired at the toP i otherwife a Cw°0 e?le Part m,ght be loft in the deflagration, which ter thVe muc^ m0re tumuftuous and violent, if the mat¬ ter was thrown into a red-hot crucible. powder 'and°miytake foUr ovmces> atld reduce it to of pure* iron and W‘tb °ne ounce °f clean filings them al,ogetherta“f, “ £ “ “«* «“ : -«'« na»; and you will find the lead dearly fepamXin “him^ ASS at the bottom of the crucible, which will {hew you what qtiaiis tity of pure lead fuch ore will yield, and confequently will enable you to judge of the true value of fuch ore. Aftays upon tin ore may be made in much the fame manner, after due calcination, but without the iron filings, and only intermixing with the blaclf flux a quantity of common char- coal-duft, by way of precipitator of the pure metal. Copper ore is aflayed in this manner, viz. firft calcine or roaft it well, then take two ounces thereof, and reduce it to a pretty fine powder, and mix it in a mortar with twice its quantity of the black flux, intermixed with charcoal-duft j after which, fufe it brifkly in a wind-furnace, that it may flow thin for about half an hour or more, and the quantity of pure copper will be precipitated at the bottom of the cru¬ cible. The caufe of the effefl depends upon a reparation of the ter- reftrial, fulphureous, or other heterogeneous parts of the ore, which are either here vitrified, or otherwife detained by the flux, at the fame time that it does not alter the metal; whence, by its fuperior gravity, it finks pure to the bottom of the cruci¬ ble, as being fet free, by thin fufion, from its terreftrial and fulphureous parts. The procefs for the aflaying of iron ore is far more difficult and tedious than for any of the other. 1. Roaft, burn, or calcine the ore with charcoal in the open air, in order to diffipate, by that means, as much of the ful¬ phureous and arfenic quality as you can, and to render the ftony and terreftrial matters, incorporated therewith, the more eafily vitrifiable. When grown cold, pulverize it pretty fine, and roaft it a fecond time in contafl with charcoal fuel, but in a much ftronger fire than you did the firft time, till it no longer emits any fulphureous fmell. 2. Compofe a flux of three parts of the black flux, with one part of fufible pulverized glafs, or of the like fterile anfulphu- reous fcoria’s; and add glafs-gall and coal-duft, of each one half-part. Add to this flux three times the quantity of your calcined ore, and mix the whole well together. Then chufe a very good crucible, well luted within with winds or loam finely prepared for adhefion, to prevent the melting of the crucible; put into it your ore mixed with the flux ; cover it over with common fait, and {hut it clofe with a tile that will ftand the fire, and with good luting applied to the joints. 3. Elevate your pot upon a proper ftand, four or five inches above the bars of your wind-furnace, to prevent a cold bot¬ tom. Surround the whole with ftrong charcoal, not very large and light them at top. Bring up your fire gradually, keeping; it well fupplied with fuel, that the vefTel may never be naked at top. Having thus continued your fire to its full ftrength * for about three quarters of an hour, or an hour, then take ouE your veflel and ftrike feveral times the pavement, upon which it is fet, that the final] grains of iron which happen to be dif- perfed, may be cohered into a regulus, which you will find after having broken the veflel. * * Your wind-furnace muft be well built, have an high chim¬ ney, and a large cave, to increafe the blaft of air to fuch a degree if needful, that the flame {hall come out of the top of a chimney three ftories high. The beft form of a wind- furnace, for this purpofe, is that refembling the form of a jar, to cover with a tile. 4k When the regulus is weighed, try its degree of malleability ; to which end make it red-hot, and, when fo, ftrike it with a hammer; if it bears the ftrokes of the hammer, both when cold and when red-hot, and extends a little, you may pro¬ nounce your iron very good : but if, when either cold or hot, or in both Itates, it proves brittle; you may judge it not to be quite pure, but ftill in a femi-mineral condition. The worfe the charadleriftics of your iron are, the greater the furrows will be found in it, when broken, which is called by the workmen, coarfe-gramed, or coarfe-fibred. By this procefs however, you may judge nearly of the quantity and quality of the iron, which fuch ore will produce. 1 ?r\X°flIeft°rftT1Jrability ]° iron’ the bodies which render I 11 h ^ feparated’ and the particles more juxtapo- fited, that all heterogeneous matter concealed, in its interftices, SiW f6 ?'' 3hrS may be convenientiy d°ne on a hearth, like that of a fmtth s forge, having a bed made with charcoal duft, put into this bed the coals and the iron to be melt¬ ed, heaped up in good quantity in ftrata ; then with the bel¬ lows blow the fire pretty ftrongly, and the iron may be brought to a fufion. and, if it does not melt foon of itfelf, and emit riTs3’ Durm!IerChe ary t0 hdp °n the meltinS with fufible fco- . During this operation, a great many fiery fparkles will be thrown out from the iron, which diminiffi, as the bon approximates more and more to purity. Then let the burning fire Sthr re^OVed» and,the Nona's be conveyed out of the fire through a channel made for that purpofe- but when the iron grows folid, let it be taken red-U out’ofthe fire and tried, by finking it with a hammer, fuitable to its bulk- ult pr°,Vei ,Crude lt,l!> ,et the operation be repeated - ,id when a. laft fufficieatly purified, ]et it be hamme^ en ed feveral ways, by making it red-hot feveral times over- this done, it will no longer be brittle, even when cold. Of](https://iiif.wellcomecollection.org/image/b30459436_0001_0200.jp2/full/800%2C/0/default.jpg)
