Alum is a crystalline, astringent substance with a sweetish taste. It is a double sulphate of potassium and aluminium with water of crystallization. It crystallizes in colourless regular octahedra. Its solution reddens vegetable blues. When heated, its water of crystallization is driven off, and it becomes light and spongy with slightly corrosive properties, and is used as a caustic under the name of burnt alum.
Alum is prepared in Great Britain at Whitby from alum-slate, where it forms the cliffs for miles, and at Hurlet and Campsie, near Glasgow, from bituminous alum shale and slate-clay, obtained from old coal-pits. It is also prepared near Rome from alum stone. Common alum is strictly potash alum; other two varieties are soda alum and ammonia alum, both similar in properties. Iron alum (pale mauve) and chrome alum (deep purple) are compounds containing iron and chromium in place of aluminium.
Alum is employed to hardentallow, to remove grease from printers' cushions and blocks in calico manufactories; in dyeing as a mordant. It is also largely used in the composition of crayons, in tannery, and in medicine (as an astringent and styptic). Wood and paper are dipped in a solution of alum to render them less combustible. Research Alum
Borax or sodium tetraborate has long been obtained under the name of tincal, from India, the main source being not India but a series of lakes in Tibet. As imported it was in small pieces of a dirty yellowish colour, and was covered with a fatty or soapy matter. Tincal, which contains various impurities, was formerly the only source of borax; but besides Tuscany other sources of boric acid, more particularly in North and South America, and the salt mines at Stassfurt, etc, in Germany, were rendered available. North America yields large quantities, there being rich deposits of borax and boracic minerals on the Pacific slope. Pure borax forms large transparent six-sided prisms, which dissolve readily in water, effloresce in dry air, and when heated melt in their water of crystallization, swell up, and finally fuse to a transparentglass.
Borax has a variety of uses. In medicine it is employed in ulcerations and skin diseases, and its cleansing properties render it useful for various domestic purposes. It has valuable antiseptic and disinfecting properties, and is now much used for the preservation of meat, fish, and milk, especially meat. It is also employed in the soldering of metals, and in making fine glaze for porcelain, as it renders the materials more fusible. It is used as an ingredient of enamels, and in making beads, glass, and cement. It is also one of the mordants employed in calico-printing. Research Borax
Glauber's salt or Glauber salt is the crystalline decahydrate of sodium sulphate. It is so called because of the importance attached to its chemical and medicinal properties by Johann Glauber. It forms large colourless mono-clinic prisms, which effloresce on exposure to the air. It is soluble in water, and when heated melts in its water of crystallization. It is found in many localities, both dissolved in the water of mineral-springs and of saltlakes, round which it effloresces. Research Glauber's Salt
In chemistry, a hydrate is a compound that has discrete water molecules combined with it. The water is known as water of crystallization and the number of water molecules associated with one molecule of the compound is denoted in both its name and chemical formula. Research Hydrate
Gypsum is a common monoclinic mineral distributed in sedimentary rocks, often as thick beds. Gypsum is usually found under beds of rock salt as it's one of the first minerals to crystallize from evaporated saltwaters and is also produced in volcanic areas and in rock veins due to the action of sulphuric acid. Gypsum is used in the production of plaster of Paris. It is chemically a hydrated calcic sulphate and has the formulae CaSO4.2H2O and a relative hardness of 2.
Gypsum is found in a compact state as alabaster, or crystallized as selenite, or in the form of a soft chalky stone, which in a very moderate heat gives out its water of crystallization, and becomes a very fine white powder, extensively used under the name of plaster of Paris. This last is the most common, and is found in great masses near Paris, where it forms the hill of Montmartre, near Aix in Provence, and near Burgos in Spain.
Gypsum may be geologically of any age, but occurs abundantly in the more recent sedimentary formations, and is even now forming, either as a deposit from water holding it in solution, or from the decomposition of iron pyrites when the sulphuric acid combines with lime, or from the action of, sulphurous vapours in volcanic regions on calcareous rocks. When gypsum occurs without water it is called anhydrite, but in its most ordinary state it is combined with water. Research Gypsum
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Alum
