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Updated: May 3, 2025
What is left is either iron oxide, "gossan," or the oxides of the other metals. Even lead can thus be oxidised, but requires more care as it melts nearly as readily as antimony and is much less volatile. The oxides in the thoroughly roasted ore will not amalgamate with mercury, and are not acted on by chlorine or cyanogen.
The lower parts of the country are everywhere covered by a bed, following the inequalities of the surface, of a honeycombed sandstone, abounding with oxides of iron. Beds of nearly similar composition are common, I believe, along the whole western coast of Australia, and on many of the East Indian islands.
The colours used by the Maypures are the oxides of iron and manganese, and particularly the yellow and red ochres that are found in the hollows of sandstone. Sometimes the fecula of the Bignonia chica is employed, after the pottery has been exposed to a feeble fire. This painting is covered with a varnish of algarobo, which is the transparent resin of the Hymenaea courbaril.
In the latter half of the sixteenth century, John Baptist Porta, who was the first to show how to reduce the metallic oxides and thus laid the foundation of several important industries, was summoned to Rome by Pope Paul II, and forbidden to continue his researches.
Innumerable springs issue out of this green, sloping meadow among the mountains, some of them icy cold, but over twenty of them hot, and seasoned with a great many disagreeable sulphates, carbonates, and oxides, and varying in temperature from ninety-five to one hundred and twenty-three degrees Fahrenheit.
Then of wood colours we have further: quercitron, Persian berries, fustic and the tannins or tannic acids, comprising extracts, barks, fruits, and gallnuts, with also leaves and twigs, as with sumac. All these colours dye only with mordants, mostly forming with certain metallic oxides or basic salts, brightly-coloured compounds on the tissues to which they are applied.
The third cause is, the corroding of zinc and lead used in pipes and reservoirs, producing oxides that are slow poisons. The only remedy is prevention, by having supply-pipes made of iron, like gas-pipe, instead of zinc and lead; or the lately invented lead pipe lined with tin, which metal is not corrosive.
The pigments used in painting on glass are principally matallic oxides and chlorides, and as, in most of these, the colour is not brought out until after the painting is submitted to heat, it is necessary to ascertain beforehand if the colours are properly mixed by painting on slips of glass, and exposing them to heat in a muffle.
Look at this: it is corroded by oxides, battered by ill-usage, stained with earth: it is not a group, not even a whole statue, it has neither head nor arms remaining; it is a mere broken fragment of antique sculpture, a naked body with a fold or two of drapery; it is not by Phidias nor by Praxiteles, it may not even be Greek; it may be some cheap copy, made for a garden or a bath, in the days of Hadrian.
The ores obtained from this copper mine had been chiefly red oxides, very rich blue and green carbonates, including malachite, and also native copper. The discovery of this mine, supporting, as it did at one time, a large population, marked a new era in the history of the colony.
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