Assaying is the estimation of the amount of pure metal, and especially of the precious metals, in an ore or alloy. In the case of silver the assay is either by the dry or by the wet process. The dry process is called eupellation from the use of a small and very porous cup, called a cupel, which is usually made of well-burned and finely-ground bone-ash or of magnesia. The cupel, being thoroughly dried, is placed in a fire-clay oven about the size of a drain-tile, with a flat sole and arched roof, and with slits at the sides to admit air. This oven, called a muffle, is set in a furnace, and when it is at a red heat the assay, consisting of a small weighed portion of the alloy wrapped in sheet-lead, is laid upon the cupel. The heat causes the lead to volatilize or combine with the other metals, and to sink with them into the cupel, leaving a bright globule of pure metallic silver, which gives the amount of silver in the alloy operated on. In the wet process the alloy is dissolved in nitric acid, and to the solution are added measured quantities of a solution of common salt of known strength, which precipitates chloride of silver. The operation is concluded when no further precipitate is obtained on the addition of the salt solution, and the quantity of silver is calculated from the amount of salt solution used.
An alloy of gold is first cupelled with lead as above, with the addition of three parts of silver for every one of gold. After the cupellation is finished the alloy of gold and silver is beaten and rolled out into a thin plate, which is curled up by the fingers into a little spiral or cornet. This is put into a flask with nitric acid, which dissolves away the silver and leaves the cornet dark and brittle. After washing with water the cornet is boiled with stronger nitric acid to remove the last traces of silver, well washed, and then allowed to drop into a small crucible, in which it is heated, and then it is weighed. The assay of gold, therefore, consists of two parts: cupellation, by which inferior metals (except silver) are removed; and quartation, by which the added silver and any silver originally present are got rid of. The quantity of silver added has to be regulated to about three times that of the gold. If it be more the cornet breaks up, if it be less the gold protects small quantities of the silver from the action of the acid. Where, as in some gold manufactured articles, these methods of assay cannot be applied, a streak is drawn With the article upon a touchstone consisting of coarse-grained Lydian quartz saturated with bituminous matter, or of black basalt. The practised assayer will detect approximately the richness of the gold from the colour of the streak, which may be further subjected to an acid test. The Goldsmith's Company of London is the statutory assay-master of all England. Research Assaying
A plateau or tableland generally denotes a large stretch of highland which is practically the same height above sea-level, and which descends on all sides to lower ground. Some plateaux, however, such as those of Tibet and Bolivia, that are fringed by high mountain ranges which tower above the plateau level, are known as intermont plateaux. Sometimes they are so completely enclosed as to have no outlet to the sea.
A plateau might be regarded as an elevated plain, but there is often a great difference between the surface of a plain and that of a plateau. As a plateau is high, rivers are swift and carve deep, narrow valleys instead of the broad, open valleys of the lower rivers of the plains. Such plateau areas as Wales and the Highlands of Scotland, are broken by deep, narrow valleys, and are termed dissected plateaux. On reaching the top of such an area one has a long view of a series of flat-topped mountain ridges. These ridges are all of approximately the same height, and if one imagines the clouds descending until they touched one ridge, then almost every other ridge would be similarly cloud-capped. Other good examples of plateaux are Tibet in Asia, the Ecuador and Bolivian plateaux in South America, and nearly the whole of the continent of Africa.
The Deccan of India is a plateau that has been tilted so that the western edge is much higher than the eastern edge, and all the main rivers drain eastwards. In many instances plateaux are formed by the denudation or wearing down of higher mountainous areas. Ultimately, such areas may become so low that they are nearly plains, i.e. peneplains, such as the land around HudsonBay. Millions of years ago lava was forced up through cracks in the earth's crust, and spread out over the land in great sheets which have since hardened to form plateaux of basalt.
Two well-known examples of such plateaux are in Antrim (Ireland), and on the Deccan of India to the east of Bombay. Many of the most extensive areas of plateaux in the world are composed of very hard old rock. The GuianaHighlands, most of Africa, Arabia, the Deccan of India, and the West Australian plateaux are all composed of rocks of similar age. The ancient plateau lands are principally valuable for their minerals, such as the gold of Western Australia; the iron and manganese of the Brazilian Highlands; the gold, copper, and diamonds of the African plateau; and the gold of the Lena plateau in Siberia. Where plateaux are found in tropical areas they are important because, being cooler than the neighbouring lowlands, they offer greater possibilities for successful European settlement and development. The highlands of Brazil, Kenya, and Tanganyika are illustrations of this. Much of the tropical plateau area is covered by savannah grasslands. Most of these areas are not yet developed, but offer possibilities for the production of a large variety of both animal and vegetable products when communications have been developed and further settlement has taken place. Research Plateau
Originally, a sarcophagus was a stone coffin manufactured from stone quarried at Assos in the Troad. It was popularly believed that the coffin would consume the body placed within it within forty days. Later the term came to be applied to any stone coffin. In ancient Egypt many stone coffins were made from limestone, basalt, marble or granite. Granite chiefly being used for the bodies of royalty and priests. Research Sarcophagus
Friedrich Heinrich Alexander Humboldt (Baron von Humboldt) was a German traveller and naturalist. He was was born in 1769 at Berlin and died in 1859. His father held the post of royal chamberlain at Berlin. He studied at the Universities of Frankfort-on-the-Oder, Berlin, and Gottingen, and also at the commercial academy in Hamburg.
His first work was Observations on the Basalt of the Rhine published in 1790. In 1791 he studied mining and botany at the mining school in Freiberg, and subsequently became overseer of the mines in Franconia. In 1797 he resolved to make a scientific journey in the tropical zones along with a friend, Aime Bonpland. They landed at Cumana, in South America, in July, 1799, and spent five years in exploring scientifically the, region of the Orinoco and the upper part of the Rio Negro, the district between Quito and Lima, the city of Mexico and the surrounding country, and the island of Cuba. In 1804 they arrived at Bordeaux, bringing with them an immense mass of fresh knowledge in geography, geology, climatology, meteorology, botany, zoology, and every branch of natural science, as well as in ethnology and political statistics.
Humboldt selected Paris as his residence, no other city offering so many aids to scientific study, and remained there arranging his collections and manuscripts until March, 1805, after which he visited Rome and Naples in company with Gay-Lussac, but eventually returned to Paris in 1807, when the first volume of his great work, Voyage aux Regions equinoxiales du Nouveau Continent, appeared; the thirtieth and last was published in 1827.
In 1827 Humboldt, who had been offered several high posts by the government of Prussia, and had accompanied the king on several journeys as part of his suite, was persuaded to give up his residence at Paris and settle at Berlin, where he combined the study of science with a certain amount of diplomatic work. In 1829, under the patronage of the CzarNicholas, he made an expedition to Siberia and Central Asia, which resulted in some valuable discoveries, published in his Asie Centrale.
In 1835 he published at Paris his Examen Critique de la Geographic du Nouveau Continent. In 1845 appeared the first volume of the Cosmos, his chief work, a vast and comprehensive survey of natural phenomena, in which the idea of the unity of the forces which move below the variety of nature is thoroughly grasped. Research Friedrich Humboldt
Basalt is an igneous rock, consisting of augite and triclinicfeldspar, with grains of magnetic or titanic iron, and also bottle-green particles of olivine frequently disseminated. It is usually of a greenish black colour, or of some dull brown shade, or black. It constitutes immense beds in some regions, and also occurs in veins or dikes cutting through other rocks. It has often a prismatic structure as at the Giant's Causeway, in Ireland, where the columns are as regular as if the work of art. It is a very tough and heavy rock, and is one of the best materials for macadamising roads. Research Basalt
Datolite is a mineral of secondary origin found usually in cavities in basalt lavas and similar rocks. It has the formulae CaBSiO4(OH) and a relative hardness of 6. Research Datolite
In geology, a dike or dyke is a term applied to intrusions of igneous rock, such as basalt, greenstone, etc, which fill up veins and fissures in the stratified systems, and sometimes project on the surface like walls. Research Dike
Abbreviations
Research Assaying
