The laboratory, or school of arts ... / Compiled from German, and other foreign authors. Illustrated with copper-plates. By G. Smith.

  • Smith, Godfrey, active 18th century
Date:
1755
Catalogue details

Licence: Public Domain Mark

Credit: The laboratory, or school of arts ... / Compiled from German, and other foreign authors. Illustrated with copper-plates. By G. Smith. Source: Wellcome Collection.

    18/410 (page 4)
    furnace, the lead and what elfe is mix’d with the filver is driven off by the blowing of two large bellows, and runs over in the form of Litharge; that, which firft comes is the white, and that which comes laft is the red Litharge. Of Ref i n i n g. REFINING or purifying of gold or filver, is an art by which the impurities that are mix’d with thefe metals are feparated, and this is done four ways, viz. by parting, the tejl *, cementation, and by mercury. Parting is done with aqua fort is; which the refiners make thus: They take of faltpetre 3]fc, dantzick vitriol 2}fc, and mix them in a mortar, and put the powder into a long-neck, or earthen veil'd, fo called from its figure: Six or eight of thofe long necks thus filled are placed in each fide of the furnace in a range built with iron bars, at about 9 inches diftance from each other, and clofed at the Tides with bricks, the up¬ per arches are left open to put in and take out the pots; Over the arches they lay large bars of iron, and then they cover all the top of the furnace with loam, the body of each long-neck lying expofed to the fire, and the neck without, to which the receivers of glafs are well luted j the lute is made of good loam, fome horfe dung, and a little colcothar. Tho’ the two former will do pretty well, in cafe the latter is not to be had ; The luting being well mix’d and applied, they make a gentle charcoal fire under the pots for 3 hours, and then they in- creafe it for 3 hours more, about the feventh hour they make a vehement hot fire for 4 hours, and fling in towards the end well dry’o billets of oak, of the length of the furnace, whofe fiame furrounds all the pots, and nnifhes the work : Next day * The tefi is a round iron ring, fome are made oval, about two, three, or more inches deep, according to their largenefs and the quantity of the filver to be refined. This ring is fill’d with wood- afhes well cleanfed, and prefs’d very clofe; at the top there is a cavity, commonly funk with an iron ball for to contain the filver: Before the afhes are quite dry, you put a cloth over it with fine afhes of trotter bones, which you fift upon, thro’ a fine hair fieve, then place it on a tile, in a wind furnace, cover it with a muffel, and make it red hot; when fo, then put in the filver to be refined. Vid. Plate II. fg. 1.