A Manual of Practical Assaying

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Longmans, Green, and Company, 1868 - Всего страниц: 697
 

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Стр. 675 - Fahr., and then note its weight ; it will be found to have lost a certain amount, which will correspond to the weight of the bulk of water it has displaced. Divide its weight in air by the loss of weight in water, and the quotient will be the required specific gravity. This will be more readily understood by an example. Suppose we find the mineral to weigh 80 grs.
Стр. 85 - The size of the crucible, and the height of the perforated cylinder, are to be so adjusted that the bottom of the crucible shall be struck by the hottest part of the gas flame ; that is to say, the space left between the face of the gas-burner and the bottom of the crucible must not exceed 2^ inches. The crucible is provided with a closelyfitting cover, and pebbles are then filled in between the crucible jacket and the furnace cylinder e, and are covered over the crucible until both the pieces of...
Стр. 87 - Choice of Crucibles. — The experiments above referred to were made •with coal gas at the ordinary pressure, and with a blast of cold atmospheric air. Greater effects can be produced by the use of oxygen gas, or of heated atmospheric air. But a difficulty stands in the way of the use of these greater degrees of heat in the want of crucibles capable of enduring their action. With cold atmospheric air, pure nickel and pure iron dissolve every kind...
Стр. 97 - only in size, c represents a thin brass cap, which fits the air-box a, but moves easily round it. d is a flat, castiron box, with many holes round the margin, and a few small ones on the top. This box fits loosely on the upper part of the tube b, and when it is placed upon it, and the gas is lighted, the flame produced consists of a series of radiating jets, forming a horizontal circular flame of about 7 inches in diameter.
Стр. 96 - ... above are clearly reflected. The clay ring may be withdrawn by lifting the plate B. A less perfect exclusion of air may be obtained by employing a narrow crucible placed rather low down in its support. A small iron dish should be placed beneath the tube L, to receive any melted substance that may fall. The chief conditions of success in the use of this furnace are sufficient gas, a suitable degree of draught, and proper regulation of gas to air. The advantage which Mr. Gore's gas furnace possesses...
Стр. 495 - Manufactures. but by the weight or volume of the standard solution of common salt necessary to exactly precipitate the silver previously dissolved in nitric acid. The term of complete . precipitation of the silver can be readily recognised by the cessation of all cloudiness when the salt solution is gradually poured into that of the nitrate of silver. One milligramme of that metal is readily detected in 150 grammes of liquid ; and even a half or a quarter of a milligramme may be detected, if the...
Стр. 193 - GLASS OF LEAD (Silicate of Lead). — The silicates of lead are preferable to litharge in the treatment of substances containing no silica, or which contain earths or oxides not capable of forming a compound with oxide of lead, excepting by the aid of silica. It may be made by fusing 1 part of sand with 4 parts of litharge : if required more fusible, a larger proportion of litharge must be added. 19. BORATE OF LEAD. — The borates of lead are better fluxes than the silicates when the substance...
Стр. 132 - This is independent of the register, and consists of two rules of brass, accurately joined together at a right angle by their edges, and fitting square upon two sides of the blacklead bar. At one end of this double rule a small plate of brass projects at a right angle, which may...
Стр. 112 - ... adding the latter to effect the mixture, at first by stirring up the mass lightly with a pointed stick or fork ; it will then be found easy, by a little management, to obtain a good mixture without making it very moist. The luting ought to be made as dry as possible, consistent with facility in working it. The wetter it is, the more liable to crack in drying, and vice versd.
Стр. 50 - ... inversely proportionate to the weight, and directly proportionate to the pressure ; so that if we had 100 cubic inches of air when the barometer was 29 inches it would be as : — 30 : 29 :: 100 : 96'6 or if the barometer stood at 31 inches when the 100 cubic inches were measured, it would be as : — 30 : 31 :: 100 : 103-33 so that the rule is : — as the mean pressure is to the observed pressure, so is the observed volume to the true volume. The correction for temperature or pressure may be...

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