Asphaltc is a limestone saturated with naphtha, found in a natural state on the Continent at places enumerated below. It can also be made artificially by a combination of bitumen (in the form of pitch) with other solid matter. The natural asphalte is generally ground and run . into moulds, with sand and a little pitch (when it is called mastic), and sold in small blocks containing a little more than a cubic foot. It is made fit for use by being melted in a furnace and applied on the walls while hot; and as it has the qualities of being frost-proof, damp-proof, and fire-proof (up to a certain degree), it can be used for damp courses, for protecting damp walls, covering roofs, and for baths, skirtings, and street paving. It should be laid by experienced workmen, in layers from | to i inch thick, and rubbed to a smooth surface, on a suitable bed of concrete, also floated to a smooth level top, as a foundation for the work.
Of the various kinds of asphalte in the market the following are the chief: -
Limmer, found near Hanover in a natural state, and used for general purposes in the usual way.
Seyssel, or Claridge's asphalte, as it is called, is found in the Jura mountains, near Pyrmont-Seyssel, on the eastern frontier of France, in a rocky state, containing about 90 per cent of carbonate of lime and 10 per cent, of bitumen. There are three qualities of it - the fine, fine-gritted, and coarse-gritted - used for the different kinds of work previously enumerated.
Val-dc-Travers asphalte is found near Neufchatel, in Switzerland, in a rock containing from 12 to 20 per cent, of bitumen, which renders it a first-class asphalte, and suitable for the best work.
Asphalte damp courses are often made by mixtures containing coal-tar pitch and real pitch, in the original natural form of bitumen, the material which makes the limestone rock asphaltic, and which is found in its pure state in Palestine, near the Dead Sea, and also in the island of Trinidad.
Granite is an igneous rock, containing quartz, feldspar, and mica, usually in the proportions of about 5, 4, and 1 respectively. Found in Scotland at Peterhead and Aberdeen, in Aberdeenshire, and in Kirkcudbrightshire; while in England it is found at Mount Sorrel, in Leicestershire, and several places in Devon and Cornwall.
The quality of the granite depends on the quartz, both for hardness and durability, while the feldspar gives it its colour, and has a great effect on its weathering properties, bad feldspar causing the disintegration of the mass. The mica, though in small quantity, is a source of weakness, and must not be taken into account, except when there is too much of it.
Granite is quarried by blasting and wedging; it is dressed in the quarry, because it is so hard when it loses its sap, and it is capable of taking a high degree of polish. It is used chiefly for ornamental purposes in the building trade, principally for shafts or columns and bases to large buildings. The Leicestershire granite is of a pink colour; the Devon and Cornwall varieties are chiefly grey; and the Scotch kinds either red or grey; while Syenite, or Syenitic granite (found in Egypt, and containing hornblende instead of mica in the first instance, and, in addition to the quartz, feldspar and mica), is darker in colour owing to the hornblende, and tougher than the British varieties.