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
Guignet's Green is a green pigment prepared by heating in a reverberatory furnace a mixture of three parts of boracic acid and one of potasium bichromate, made into a thick paste with water. This colour is quite fixed - it does not alter by light or reagents, and it is quite harmless, so that it forms an excellent substitute for the greens which contain arsenic and copper. Research Guignet's Green
The Queen's Tobacco-pipe (also called the Queen's Pipe) was a popular name for the oven, later replaced in 1892 by a furnace, situated in the north-east corner of the tobacco warehouses of the London Docks. It was so called because it was used for burning all sorts of contraband but especially tobacco and cigars. Research Queen's Tobacco-pipe
Edward Goodrich Acheson was an American chemist and inventor. He was born in 1856 at Washington, Pennsylvania, and died in 1931. From 1880 to 1881 he did research on electric lamps as an assistant to Thomas Edison. After 1884 he worked independently to develop the electric furnace for the conversion of carbon into diamonds, without success. In 1891 he invented carborundum (silicon carbide) and artificially prepared graphite. Research Edward Acheson
During the Second World War, Special Operations Executives and resistance fighters in occupied Europe filled dead rats with explosive and left them in railway train coal stores in the hope that they would be thrown into the furnace along with the coal and explode, causing disruption to the occupying forces railway communications. Research Exploding Rats
Acetylene is a highly inflammable gas of the hydrocarbon family used for welding and cutting metals. It was discovered by Berthelot. In 1862 Friedrich Wohler discovered that carbide of calcium treated with water produced lime and acetylene. In 1895 acetylene was cheaply produced on a commercial scale and subsequently was used for general lighting.
Acetylene is colourless, and has a rather pleasant ethereal smell when pure, but as ordinarily prepared it is not quite pure, containing small quantities of sulphuretted and phosphuretted hydrogen, and having a strong and disagreeable odour. It can be liquefied by cold and pressure, and may even be obtained in the solid form as a snow-like mass. It is one of the constituents of ordinary coal-gas, but is present in very small quantities. It burns readily, being ignited at a temperature below that at which coal-gas is ignited. If there is not a sufficient supply of air the flame is dull and very smoky, but when a proper burner is used acetylene gives a very white and brilliant flame, its illuminating power being far higher than that of coal-gas. It possesses properties that may render it dangerous in certain circumstances, and these have to be guarded against. The gas itself may be made to explode by (a) high temperature and great pressure, and (b) a detonation some little distance away, and in the liquid form the risk of explosion is so great that in Britain and elsewhere liquid acetylene is forbidden to be stored and used. When mixed with chlorine it explodes spontaneously. Like other combustible gases it forms an explosive mixture with air.
Acetylene has been known for a considerable time, and may be produced in various ways, but only in the late 19th century did it come into extensive use as an illuminant, and only since a cheap method of producing carbide of lime (calcium carbide) was discovered, the gas being readily prepared by bringing this substance into contact with water. Calcium carbide was manufactured by subjecting a mixture of coke and lime to the heat of an electric furnace, and when it is brought into contact with water the carbide is decomposed, and acetylene and lime or hydrate of lime are produced. To provide a supply of acetylene gas for lighting purposes various forms of generator were in use, and in these the carbide was either brought slowly into contact with the water, or the water was brought gradually into contact with the carbide, or the two was brought together at intervals and again separated. The gas had to be evolved at a low temperature, and under a low pressure, and in the absence of air. Before being used it had to be purified by passing it through suitable substances. A dry process of production was introduced in the late 19th century. Several kinds of burners and lamps were used, and portable lamps were quite common by 1900. Country mansions and such detached residences were often lighted by acetylene gas. A license was required to enable a person to keep more than 28 lbs. of calcium carbide stored in any building. Research Acetylene
An aludel was a vessel of earthenware or glass formerly used for condensation by the alchemists and early chemists. The aludel was shaped like an Indian club and was used for condensing on the inside the metallic fumes produced in the process of distilling the more volatile metals out of their ores. Aludels were connected in series, typically between 500 and 600 connected to a single furnace. Research Aludel
Annealing is a process to which many articles of metal and glass are subjected after making, in order to render them more tenacious, and which consists in heating them and allowing them to cool slowly. When the metals are worked by the hammer, or rolled into plates, or drawn into wire, they acquire a certain amount of brittleness, which destroys their usefulness, and has to be remedied by annealing. The tempering of steel is one kind of annealing. Annealing is particularly employed in glass-houses, and consists in putting the glass vessels, as soon as they are formed and while they are yet hot, into a furnace or oven, in which they are suffered to cool gradually. The toughness is greatly increased by cooling the articles in oil. Research Annealing
In smelting, bloom is the name given to a lump of puddled iron, which leaves the furnace in a rough state, to be subsequently rolled into the bars or other material into which it may be desired to convert the metal. The name is also applied to a lump of iron made directly from the ore by a furnace called a 'bloomery.' Research Bloom
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