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BOOK IX.

blow into the furnace in either a mild or a vigorous manner. For those oreswhich heat and fuse easily, a low hearth is necessary for the work of thesmelters, and the pipe must be placed at a gentle angle to produce a mildblast from the bellows. On the contrary, those ores that heat and fuseslowly must have a high hearth, and the pipe must be placed at a steep inclinein order to blow a strong blast of the bellows, and it is necessary, for thiskind of ore, to have a very hot furnace in which slags, or cakes melted frompyrites, or stones which melt easily in the fire 15 , are first melted, so that theore should not settle in the hearth of the furnace and obstruct and choke upthe tap-hole, as the minute metallic particles that have been washed fromthe ores are wont to do. Large bellows have wide nozzles, for if they werenarrow the copious and strong blast would be too much compressed and tooacutely blown into the furnace, and then the melted material would bechilled, and would form sows around the nozzle, and thus obstruct the openinginto the furnace, which would cause great damage to the proprietors’property. If the ores agglomerate and do not fuse, the smelter, mountingon the ladder placed against the side of the furnace, divides the charge witha pointed or hooked bar, which he also pushes down into the pipe in

16 “ Stones which easily melt in the fire.” Nowhere in De Re Metallica does the authorexplain these substances. However in the Interpretatio (p. 465) he gives three genera or orderswith their German equivalents, as follows:—“ Lapides qui igni liquescuni primi generis, —Schone flusse ; secundi,—fliisse zum schmeltzen flock quertze ; ter Hi,—quertze oder kiselstein.”We confess our inability to make certain of most of the substances comprised in the first andsecond orders. We consider they were in part fluor-spar, and in any event the third orderembraced varieties of quartz, flint, and silicious material generally. As the matter is ofimportance from a metallurgical point of view, we reproduce at some length Agricola’s ownstatements on the subject from Bermannus and De Natura Fossilium. In the latter (p. 268)he states : “ Finally there now remain those stones which I call ‘ stones which easily melt in“ the fire,’ because when thrown into hot furnaces they flow (fluunt). There are three orders“ ( genera ) of these. The first resembles the transparent gems ; the second is not similar,“ and is generally not translucent; it is translucent in some part, and in rare instances“ altogether translucent. The first is sparingly found in silver and other mines; the second“ abounds in veins of its own. The third genus is the material from which glass is made,“ although it can also be made out of the other two. The stones of the first order are not“ only transparent, but are also resplendent, and have the colours of gems, for some resemble“ crystal, others emerald, heliotrope, lapis lazuli, amethyst, sapphire, ruby, chrysolithus, morion“ (cairngorm ?), and other gems, but they differ from them in hardness. ... To the“ first genus belongs the lapis alabandicus (modern albandite ?), if indeed it was different“ from the alabandic carbuncle. It can be melted, according to Pliny, in the fire, and fused“ for the preparation of glass. It is black, but verging upon purple. It comes from“ Caria, near Alabanda, and from Miletus in the same province. The second order of stones“ does not show a great variety of colours, and seldom beautiful ones, for it is generally white," whitish, greyish, or yellowish. Because these (stones) very readily melt in the fire, they are“ added to the ores from which the metals are smelted. The small stones found in veins,“ veinlets, and the spaces between the veins, of the highest peaks of the Sudetic range ( Sudi-“ iorum montium), belong partly to this genus and partly to the first. They differ in size,“ being large and small; and in shape, some being round or angular or pointed ; in colour they“ are black or ash-grey, or yellow, or purple, or violet, or iron colour. All of these are lacking“ in metals. Neither do the little stones contain any metals which are usually found in the“ streams where gold dust is collected by washing. ... In the rivers where are collected“ the small stones from which tin is smelted, there are three genera of small stones to be found,“ all somewhat rounded and of very light weight, and devoid of all metals. The largest are“ black, both on the outside and inside, smooth and brilliant like a mirror ; the medium-sized“ are either bluish black or ash-grey ; the smallest are of a yellowish colour, somewhat like a“ silkworm. But because both the former and the latter stones are devoid of metals, and fly“ to pieces under the blows of the hammer, we classify them as sand or gravel. Glass is made“ from the stones of the third order, and particularly from sand. For when this is thrown“ into the heated furnace it is melted by the fire. . . . This kind of stone is either found