In-crus-ta′tion.
1. (Masonry.) A facing or covering to a wall of a different material from that of which it is mainly built, such as marble or stone. 2. A thin sheet of wood applied upon a wooden surface. See veneering.
3. (Steam-engine.) The deposit from the water adhering to the inside of a boiler. As nothing but pure water enters into the composition of steam, it has long been a problem in steamengineering to get rid of impurities in water which it is found necessary to use in steam-boilers. Among these impurities may be mentioned the salt in seawater, lime in the water of limestone regions, and minerals in many forms, which are often found in water supposed to be pure until thus tested. The accumulation of salt in a marine boiler would soon fill it, if there were no way for its removal. In practice it is generally “blown off,” when the salinometer indicates a certain point of saturation. Lime in some forms incrusts a boiler very rapidly, having been known to form a scale several inches in thickness in a few days. This scale is a poor conductor of heat, and a large proportion of the products of combustion are lost by its interposition. It also weakens the boiler, and has been the cause of many explosions. Condensers are used to supply pure water to boilers. See condenser. Feed-water heaters have a purpose, besides utilizing waste heat, to compel the deposition of impurities before the feed-water reaches the boiler. Mechanical agitators, beaters, scrapers, etc., are often employed to remove crust from a boiler. Chemical treatment of feed-water, or of water in the boiler, is a matter which has received much attention from engineers and scientists. Sawdust acts both chemically and mechanically to prevent incrustation, the tannic acid it contains uniting with the lime to form tannate of lime, which deposits itself as a slimy body. Clay has sometimes given good results, but sand is almost always present in some quantity, though small, and, if it passes over in priming, is very detrimental to the valve-faces, the cylinder, and the piston. Starch and sugary substances have the effect to clarify some waters, the viscid character of the glucose preventing agglomeration of the foreign matters, and forming scum instead of crust. Fatty bodies, tar, and graphite tend to prevent adhesion. The nature of the water to be treated determines the substance which shall be used. Scott's English patent, 1828, describes a mode of catching the deposit which forms the incrustation by placing pans or trays in the boiler; these intercept the falling deposit. Taylor's English patent, 1830, has a sedimenttrough the length of the boiler, and forming a narrow chamber below the same, out of contact with the fire. The contents of this chamber are occasionally blown out, carrying the sediment. To avoid the expenditure of space in stating at length the various materials which have been placed in steam-boilers to retain the mineral particles in suspension, or to prevent their adherence to the boiler, it may be stated that they consist of —
| Acids, — | Lime-paint. |
| Acetic. | Linseed-cake. |
| Hydrochloric. | Linseed-oil. |
| Muriatic. | Logwood. |
| Nitric. | Malt. |
| Oxalic. | Meal. |
| Alkalies. | Metal in strips or scraps. |
| Ammoniacal salts. | Molasses. |
| Animal fats, — | Moss. |
| Marrow, etc. | Mucilage. |
| Arsenical salts. | Muriates in variety. |
| Ashes. | Nutgalls. |
| Barks in great variety Ground | Oak-bark and sawdust. |
| Baryta. | Ochre. |
| Black-lead. | Oils in variety. |
| Bones. Ground | Oxalates in variety. |
| Borax. | Oxides in variety. |
| Bran. | Paints in variety. |
| Broom-corn. | Peat. |
| Burgundy-pitch. | Petroleum. |
| Camphor. | Phosphates in variety. |
| Carbonates in variety. | Pitch. |
| Caustic alkalies. | Plants of various kinds. |
| Charcoal. | Plumbago. |
| Chlorides in variety. | Potash. |
| Clay. | Potatoes. |
| Coal-tar. | Resins. |
| Copper. Salts of | Sal-ammoniac. |
| Copper scraps. | Sand. |
| Cream of tartar. | Saponaria. |
| Creosote. | Sawdust of various woods. |
| Cutch. | Shells. Ground |
| Decoctions of bark. | Soap. |
| Dextrine. | Soda. |
| Electric devices. | Soda-ash. |
| Fatty oils. | Soot. |
| Felt. | Sponge. |
| Fibrous materials. | Starch. |
| Flaxseed. | Stones. |
| Galvanizing devices. | Sugar. |
| Gambier. | Sulphates in variety. |
| Gas-tar. | Sulphur. |
| Glass. Broken | Sumac. |
| Glue. | Tallow. |
| Graphite. | Tan-bark. |
| Gravel. | Tannin. |
| Gums in variety. | Tar. |
| Hay | Terra-japonica. |
| Horns. Internal portions of | Tin. Salts of |
| Hydrocarbons. | Tobacco. |
| Iron. Salts of | Turf. |
| Iron scraps. | Turmeric. |
| Isinglass. | Urine. |
| Kerosene. | Valonia. |
| Lampblack. | Vegetable dyes. |
| Lead. Salts of | Voltaic devices. |
| Leather scraps. | White-lead. |
| Leaves in variety. | Wood-fiber. |
| Lime. |
