BOOK IX.
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down some of the powdered charcoal into it from the wall, so that the slagsmay be separated from the hot metal, and so that it may be covered, lestany part of it, being very hot, should fly away with the fumes. If afterthe slag has been skimmed off, the powder does not cover up the whole of thetin, the smelter draws a little more charcoal off the wall with a scraper. Afterhe has opened the tap-hole of the forehearth with a tapping-bar, in orderthat the tin can flow into the tapping-pot, likewise smeared with lute, heagain closes the tap-hole with pure lute or lute mixed with powdered charcoal.The smelter, if he be diligent and experienced, has brooms at hand with whichhe sweeps down the walls above the furnace ; to these walls and to thedust chamber minute tin-stones sometimes adhere with part of the fumes.If he be not sufficiently experienced in these matters and has melted at thesame time all of the tin-stone,—which is commonly of three sizes, large,medium, and very small,—not a little waste of the proprietor’s tin results ;because, before the large or the medium sizes have melted, the small have eitherbeen burnt up in the furnace, or else, flying up from it, they not only adhere tothe walls but also fall in the dust chamber. The owner of the works hasthe sweepings by right from the owner of the ore. For the above reasonsthe most experienced smelter melts them down separately ; indeed, hemelts the very small size in a wider furnace, the medium in a medium-sizedfurnace, and the largest size in the narrowest furnace. When he melts downthe small size he uses a gentle blast from the bellows, with the medium-sizeda moderate one, with the large size a violent blast; and when he smeltsthe first size he needs a slow fire, for the second a medium one, and for thethird a fierce one ; yet he uses a much less fierce fire than when he smeltsthe ores of gold, silver, or copper. When the workmen have spent threeconsecutive days and nights in this work, as is usual, they have finishedtheir labours ; in this time they are able to melt out a large weight of small
" the dried beds of torrents. The miners wash these sands, and that which settles they heat“ in the furnace. It is also found in gold mines, which are called alutiae. A stream of water“ passing through detaches small black pebbles variegated with white spots, the weight of“ which is the same as gold. Hence it is that they remain in the baskets of the gold collectors“ with the gold ; afterward, they are separated in a camillum and when melted become white
“ lead -” ’ . . . .
There is practically no reference to the methods of Cornish tin-working over the whole
period of 2,000 years that mining operations were carried on there prior to the Normanoccupation. From then until Agricola’s time, a period of some four centuries, there areoccasional references in Stannary Court proceedings, Charters, and such-like official documentswhich give little metallurgical insight. From a letter of fVilliam de Wrotham,. Lord Wardenof the Stannaries, in 1198, setting out the regulations for the impost on tin, it is evident thatthe black tin was smelted once at the mines and that a second smelting or refining was carriedout in specified towns under the observation of the Crown Officials. In many other officialdocuments there are repeated references to the right to dig turfs and cut wood for smeltingthe tin. Under note 8, p. 282, we give some further information on tin concentration, andthe relation of Cornish and German tin miners. Biringuccio (1540) gives very little informa-tion on tin metallurgy, and we are brought to De Re Metallica for the first clear exposition.
As to the description on these pages it must be remembered that the tin-stone has beenalready roasted, thus removing some volatile impurities and oxidizing others, as describedon page 348. The furnaces and the methods of working the tin, here described, are almostidentical with those in use in Saxony to-day. In general, since Agricola’s time tin has not seenthe mechanical and metallurgical development of the other metals. The comparativelysmall quantities to be dealt with ; the necessity of maintaining a strong reducing atmosphere,and consequently a mild cold blast; and the comparatively low temperature demanded,gave little impetus to other than crude appliances until very modern times.
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