Stereotype consists of plates of metal taken, by casting, from a forme of type set up for the purpose: an impression was formerly carried on by plaster-of-Paris moulds, but lately what is termed the papier-maché process is adopted. The paper used is now made in England, and the prepared sheet is placed upon the type and beaten upon it. Paste is then filled in where there are blanks, and another and thicker sheet of the prepared paper is placed over all, dried, and pressed. When this is properly done the paper is hardened, and preserves an impression of the type set up. The paper mould is then put into an iron box, and molten metal run in. In a very short time a “stereotype” plate is prepared from the paper, which can be used again if necessary. The metal plate is put on the machine.
There are several compounds of antimony, which, though valuable to chemists, would not be very interesting to the majority of readers. We will therefore at once pass to the Noble Metals.
The Noble Metals.
There are nine metals which rank under the above denomination:—Mercury, Silver, Gold, Platinum, Palladium, Rhodium, Ruthenium, Osmium, Iridium. We will confine ourselves chiefly to the first four on the list.
Mercury, or Quicksilver, is the first of the metals which remain unaltered by exposure to atmospheric air, and thus are supposed to earn their title of nobility. Mercury is familiar to us in our barometers, etc., and is fluid in ordinary temperatures, though one of the heaviest metals we possess. It is principally obtained from native cinnabar, or sulphide of mercury (vermilion), and the process of extraction is very easy. Mercury was known to the ancients, and is sometimes found native. In the mines the evil effects of the contact with mercury are apparent.
This metal forms two oxides,—the black (mercurous) oxide, or suboxide (Hg2O), and the red (mercuric) oxide, or red precipitate. The chlorides are two,—the subchloride, or calomel, and the perchloride, or corrosive sublimate. The sulphides correspond with the oxides; the mercuric sulphide has been mentioned. Its crimson colour is apparent in nature, but the Chinese prepare it in a particularly beautiful form. Many amalgams are made with mercury, which is useful in various ways that will at once occur to the reader.
Silver is the whitest and most beautiful of metals, and its use for our plate and ornaments is general. It is malleable and ductile, and the best conductor of electricity and heat that we have. It is not unfrequently met with in its native state, but more generally it is found in combination with gold and mercury, or in lead, copper, and antimony ores. The mines of Peru and Mexico, with other Western States of America, are celebrated—Nevada, Colorado, and Utah in particular. The story of the silver mine would be as interesting as any narrative ever printed. The slavery and the death-roll would equal in horror and in its length the terrible records of war or pestilence. We have no opportunity here to follow it, or its kindred metals with which it unites, on the sentimental side; but were the story of silver production written in full, it would be most instructive.
Fig. 417.—Native silver.
Silver is found with lead (galena), which is then smelted. The lead is volatilized, and the silver remains. It is also extracted by the following process, wherein the silver and golden ore is crushed and washed, and quicksilver, salt, and sulphate of copper added, while heat is applied to the mass. From tank to tank the slime flows, and deposits the metals, which are put into retorts and heated. The mercury flies off; the silver and gold remain in bars.