1. Let the name be written on a piece of paper, and, while the ink is still wet, sprinkle over it some finely-powdered gum Arabic, then make a rim round it, and pour on it some fusible alloy in a liquid state. Impressions may be taken from the plates formed in this way, by means of printing ink and the copper-plate press.
2. By the use of transfer ink and lithography.
SILBER LIGHT. This light is thus described in ‘Dingler’s Polytechnic Journal,’[161]—This mode of illumination is recommended where gas cannot be had.
[161] ccix, 79 (‘Journ. Chem. Society,’ vol. xi, new series, 1273).
The material used is oil, which is converted into gas before combustion takes place, whereby the combustion of the wick is greatly lessened (one wick may last a year); the accumulation of impurity is obviated, and the prevention of smell completely effected. The light is regular and uniform, and of a white colour. The light, with a burner 11⁄4 inch wide, is equal to that of 28 sperm candles, each consuming 120 gr. per hour, and with one 13⁄4 inch wide a light is obtained equal to 50 such candles.
The burning apparatus consists of a row of concentrically enclosed double cylinders, perpendicularly arranged at definite intervals. The innermost cylinder contains the wick between its two walls, the hollow space in the interior serving to convey fresh air to the interior of the flame. The second cylinder conveys air to the outer side of the wick, and the third contains oil, and is in direct communication with both wick and reservoir. The mouths of all these chambers have a dome-shaped head, and form a suitable opening in this; the gas streams forth in such a manner that it comes in contact with a current of air, and thus a complete combustion is attained.
According to the nature of the oil burnt the construction is somewhat varied in its minor details. Rape oil or light hydrocarbon oils are mentioned.
SIL′ICA. SiO2. Syn. Silicic anhydride, Silicic acid, Silex, Siliceous earth†, Earth of flints†. This exists in quartz and rock crystal in a nearly pure state. The sands of rivers and the sea-shore, flint, and almost all the scintillating stones, chiefly consist of it.
Silica occurs under two conditions—the crystalline and the amorphous. The former variety has a sp. gr. of 2·642; the amorphous of 2·2-2·3. Some of our well-known native gems and precious stones consist almost wholly of one of the above forms of silica. In agate and calcedony the two varieties are combined. Amethyst is silica, coloured purple by ferric oxide. Onyx is formed of calcedony arranged in layers of different colours. Cornelian is a red or brown variety of silica coloured with
ferric oxide, whilst opal is amorphous silica combined with varying quantities of water. Silica is present in the stems of certain plants, such as wheat, many grasses, to which the shining appearance of the stems is due, &c. The Italians polish marble with the ashes of burnt straw, the usefulness of which for such a purpose depends upon the silica contained in the straw; for similar reasons the Dutch rush is thus employed. Silica also occurs in solution in many natural waters. In the geysers, or boiling springs of Iceland, it exists in large quantity.