Pholas is a genus of burrowing bivalve molluscs, also known as piddocks in parts of England where they are used as bait. The species are found within such rocks as shale, chalk, limestone and the like. Like all burrowing bivalves, they have gaping shells, which in this genus are pure white in colour, and have accessory plates of lime attached. The animal is furnished with long siphons, having fringed extremities, and during life these siphons are protruded from the burrows, so that water, containing food and oxygen, may pass in. Research Pholas
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
Distillation is the volatilization and subsequent condensation of a liquid in an apparatus known as a still and heated by a fire or flame. The operation is performed by heating the crude liquid or mixture in a retort or vessel known as the body of the still. This is made of various shapes and materials, and is closed with the exception of a slender neck which opens into the condenser, a long tube through which the hot vapour from the still is passed. The tube is kept at a sufficiently low temperature to cause the vapour to condense, the common method of securing this being to surround the tube with a constantly renewed stream of cold water. In some cases ice or a freezing mixture may be required to effect condensation. On a large scale the condensing tube is coiled round and round in a tub or box, and is known as a worm. From the end of it the vapour condensed into a liquid drops into a receiver.
The simplest case of distillation is that of water containing solid matter in solution, the solid matter remaining behind in the still or retort while the water trickles pure into the receiver, through a worm made of block-tin, as most other metals are attacked by distilled water.
When the mixture to be distilled consists of two or more liquids of different boiling-points, such as alcohol and water, the more volatile comes off first, accompanied by a certain proportion of the vapour of the other, so that it is hardly possible completely to separate bodies by one distillation. This is effected by repeated successive distillations of the liquid with or without the addition of substances to retain the impurities. When the production of one of the ingredients only is aimed at by this process, it is called rectification, but when it is desired to separate and collect all the liquids present, or to divide a mixture into portions lying within certain ranges of temperature ascertained either by the thermometer or by the amount of liquor run off, or by the appearance of the distillate, etc, the process is called fractional distillation.
In the laboratory, distillation is employed for purifying water, for recovering alcohol and ether, for the preparation, purification, and separation of a great number of bodies. On the large scale distillation is employed in the preparation of potassium, sodium, zinc, mercury; of sulphuric acid, ether, chloroform, sulphide and chloride of carbon, essential oils and perfumes; purification of coal and wood tar, and the products obtained from them; and on an extensive scale in the manufacture of whisky, brandy, or other spirit.
The distillation of whisky has long been familiar in Britain, especially in Scotland and Ireland, and by the old pot-still is a simple operation indeed, and one that even yet is practised surreptitiously in out-of-the-way localities. On the large scale more elaborate apparatus are employed, and for alcohol of a cheap class Coffey's or other patent still is much used. Copper is the metal that suits best as the material for the stills used in distilling whisky. Sea-water is distilled in many cases for drinking or cooking purposes. This water is, of course, very pure, but its taste is rather mawkish.
Destructive distillation, or dry distillation, differs from the preceding in this respect, that the original substance is not merely separated into the bodies by the mixture of which it is formed, but is so acted on that it is completely decomposed, and bodies are produced which had no existence in the original matter. The term is restricted to the action of heat upon complex organic substances out of contact with the air. The products of destructive distillation are numerous and varied. On the manufacturing scale the process is conducted sometimes for one part, sometimes for another part of the products. Coal, for example, may be distilled primarily for the gas, but also for ammoniacal water, benzene, anthracene, as well as for the sake of the fixed carbon or coke, the volatile portions being too often neglected and practically wasted. But much more economical methods of making coke are now practised than formerly.
Wood is distilled partly for the sake of the pyroligneous acid and the tar, partly for the charcoal. Bones are distilled for the sake of the charcoal, though the oil is also collected. Shale is distilled both for the oil and for the paraffinwax, ammonia, etc, obtained. Research Distillation
Naptha is a volatile and highly inflammable solvent, colourless to white in colour and with a disagreeable odour. Naptha is prepared from coaltar, petroleum or shale oil. Research Naptha
Portland cement is the essential constituent in concrete, cementrendering and formerly in asbestos-cement sheeting. Portland cement is produced by burning limestone with clay or shale at a high temperature until it forms a clinkered mass, which is then cooled and ground into a fine powder. Research Portland Cement
Alum schist or alum slate is a variety of shale or clayslate, containing iron pyrites, the decomposition of which leads to the formation of alum, which often effloresces on the rock. It is named on account of much alum being prepared from it. It is greyish, bluish, or iron-black in colour; often possessed of a glossy or shining lustre; chiefly composed of clay (silicate of alumina), with variable proportions of sulphide of iron (iron pyrites), lime, bitumen, and magnesia. Research Alum Schist
In geology, the Carboniferous was the seventh geological period, 250,000,000 years ago. This era marked the formation of the coal beds. It is the great group of strata which lie between the Old Red Sandstone below and the Permian or Dyas formation above, and is named from the quantities of coal, shale, and other carbonaceous matter contained in them. They include the coal measures, millstone grit, and mountain limestone, the first being uppermost and containing the chief coal-fields that are worked. Iron-ore, limestone, clay, and building-stone are also yielded abundantly by the carboniferous strata which are found in many parts of the world often covering large areas. The thickness of the coal measures in South Wales has been estimated at 10,000 to 13,000 feet. As coal consists essentially of metamorphosed vegetable matter, fossil plants are very numerous in the carboniferous rocks, more than 1500 species of them having been named, a large proportion of which are ferns, tree, lycopods and large horse-tail like plants. The animals include insects, scorpions, amphibians, numerous corals, crinoids, molluscs, cephalopoda, sharks and other fishes. Research Carboniferous
Coal-measures are the upper division of the carboniferous system, consisting of beds of sandstone, shale, etc, between which are coal-seams. Research Coal-Measures
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Pholas
