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The details of this method of precipitation of zinc are fully discussed in an article by Dakin, !Ztschr. Anal. Of the natural silicates, or artificial silicates such as slags and some of the cements, a comparatively few can be completely decomposed by treatment with acids, but by far the larger number require fusion with an alkaline flux to effect decomposition and solution for analysis.
The whole story of this lava bed is so clearly told in its blackened and extinct remains, that it needs no stretch of the imagination to recreate the scene. It is again, a heaving, palpitating sheet of fire; the dead slags are aglow, and the burned-out furnaces cast up their molten, blazing contents, as of old.
The greater number consisted merely of a ring of red scoriae or slags, cemented together: and their height above the plain of lava was not more than from fifty to a hundred feet; none had been very lately active.
It was also remarked that in the crystalline slags of furnaces augitic forms were frequent, the hornblendic entirely absent; hence it was conjectured that hornblende might be the result of slow, and augite of rapid cooling. This view was confirmed by the fact that Mitscherlich and Berthier were able to make augite artificially, but could never succeed in forming hornblende.
SCORIAE and PUMICE may next be mentioned, as porous rocks produced by the action of gases on materials melted by volcanic heat. SCORIAE are usually of a reddish- brown and black colour, and are the cinders and slags of basaltic or augitic lavas.
Carie with you for that purpose all sorts of garden seeds, as wel of sweete strawing herbs, and of flowers, as also of pot herbes and all sorts for roots, &c. Lead of the first melting. Lead of the second melting of the slags. To make triall of the vent of Lead of all kinds. English iron, and wier of iron and copper. To try the sale of the same. Brimstone.
Lavas present a general resemblance to the slags and clinkers which are formed in our furnaces and brick-kilns, and consist, like them, of various stony substances which have been more or less perfectly fused.
In this way he discovered that light substances were attracted by alum, mica, arsenic, sealing-wax, lac sulphur, slags, beryl, amethyst, rock-crystal, sapphire, jet, carbuncle, diamond, opal, Bristol stone, glass, glass of antimony, gum-mastic, hard resin, rock-salt, and, of course, amber.
On his return he reported that at two cable lengths from the shore he had no soundings with a 160 fathoms of line; that when he landed he found no fresh water, but rain water lying in holes in the rocks, and that brackish with the spray of the sea, and that the surface of the country was wholly composed of large slags and ashes, here and there partly covered with plants.
Refining. We quote Mr Vivian: 'The pigs from the roasters are filled into the furnace through a large door in the side: the heat is at first moderate, so as to complete the roasting or oxidising process; after the charge is run down, and there is a good heat on the furnace, the front door is taken down, and the slags skimmed off.
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