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Magenta, however, permanently dyes the woollen as it did not the cotton. Alizarin only stains the untreated woollen, whilst the piece treated with alumina is dyed red, and that with iron, purple. If, however, the pieces treated with iron and alumina had been dyed in the Magenta solution, only one colour would have been the result, and that a Magenta-red in each case.
When all the angular fragments are of volcanic rocks the mass is usually termed a volcanic breccia. Laterite is a red or brick-like rock composed of silicate of alumina and oxide of iron. The red layers called "ochre beds," dividing the lavas of the Giant's Causeway, are laterites. These were found by Delesse to be trap impregnated with the red oxide of iron, and in part reduced to kaolin.
The excess of hydrochloric acid accomplishes this liberation. By disintegrating the fused mass with a considerable volume of dilute acid the silicic acid is at first held in solution to a large extent. Immediate treatment of the fused mass with strong acid is likely to cause a semi-gelatinous silicic acid to separate at once and to inclose alkali salts or alumina.
The first table contains a very attractive collection of minerals, including the varieties of jasper; all kinds of opals the sun opal, the semi-opal, wood opal, and wood partially opalised. The second table is covered with varieties of Silicates of Lime, magnesia, and alumina; also soapstone, keffekil, or the meerschaum, highly esteemed by smokers, serpentine, chrysolite, &c.
The rocks above 5000 feet were gneiss; below this, cliffs of very micaceous schist were met with, having a north-west strike, and being often vertical; the boulders again were always of gneiss. The streams seemed rather to occupy faults, than to have eroded courses for themselves; their beds were invariably rocky or pebbly, and the waters white and muddy from the quantity of alumina.
Oxide of load was added in some cases, not as a coloring matter, but as a flux, to facilitate the fusion of the glaze. In other cases the pigment used was covered with a vitreous coat of an alkaline silicate of alumina. The pigments were not applied to an entirely flat surface.
"In another, he found the lead obtained from it to yield silver in the proportion of 72 ounces 5 dwts. to the ton or 2000 pounds. "The copper specimen was the red oxide, and yielded as follows: Copper,............ 71.80 Iron,.............. 7.84 Oxygen,............ 12.34 Silicia, Alumina,.. 8.02 100 parts.
Dumfriesshire; Sweden. A still lower part of the Llandeilo rocks consists of a black carbonaceous slate of great thickness, frequently containing sulphate of alumina, and sometimes, as in Dumfriesshire, beds of anthracite.
Calcite. In places the limestone is perfectly crystallized, and of a pure white or other color, when it forms an attractive mineral, and often worth removing. The limestone of the main quarry, carefully averaged, was found to have the following chemical composition. Lime. 11.09 Magnesia. 37.94 Carbonic acid. 30.61 Silica. 10.22 Water and loss. 4.90 Iron and alumina. 5.24 100.00
It is a variety of hornblende, composed of silica, lime, and magnesia, with a little alumina. It probably occurs in places in the vicinity of this block, and in finer specimens, as these are frequently, when near the surface, much weathered and worn. This is a characteristic granular limestone mineral, and a very interesting one. We will again meet it when examining the New York city localities.
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