A Manual of Practical Assaying

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

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Стр. 132 - ... cooled, it will be left at the point of greatest elongation. What is now required is the measurement of the distance which the index has been thrust forward from its first position; and this, though in any case but small, may be effected with great precision by means of the scale.
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. 626 - The saline mass to ormed is dissolved in the smallest possible quantity of water, and the solution is poured off with all due precaution. The acid distilled over into the receiver is poured upon the undissolved portion of the ore in the retort, and again distilled. The second distillation generally effects the complete solution of the platiniferous matter. If the distilled liquor be not colourless it must be returned into the retort and redistilled.
Стр. 133 - ... from its first position; and this, though in any case but small, may be effected with great precision by means of the scale. 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 be brought down upon the shoulder of the register, formed by the notch cut away for the reception...
Стр. 112 - ... 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 versa.
Стр. 133 - A similar observation must be made after the register -has been exposed to the increased temperature which it is designed to measure, and again cooled, and it will be found that the nonius has been moved forward a certain number of degrees or minutes. The scale of this pyrometer is readily connected with that of the thermometer by immersing the register in boiling mercury, whose temperature is as constant as that of boiling water, and has been accurately determined by the thermometer. The amount...
Стр. 607 - Gold and Copper, proportion of Lead. — The alloys of gold and copper are cupelled like the alloys of gold and silver ; but as copper has a very great affinity for gold, it is necessary to use a larger proportion of lead to ensure its oxidation when combined with gold than when united with silver. This proportion varies according to the standard and the temperature. It is admitted that for the same standard there must, under similar circumstances, be twice as much lead used in the cupellation of...
Стр. 399 - ... solution. When the precipitation approaches its end, or when the precipitate commences readily to subside, some drops of a neutral solution of nitrate of silver are deposited on a porcelain plate, and the...
Стр. 50 - ... 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 made indiscriminately, the result being the same in either case. CORRECTION FOR MOISTURE. — This correction must be made after the two previous. As...
Стр. 76 - German silver, &c., can be melted with great ease, and that all the metallurgical and chemical processes that are commonly effected in platinum and porcelain crucibles can be promptly accomplished in the smallest cylinder of this furnace ; and in the case of platinum vessels, with this special advantage, that the oil-gas is free from those sulphurous compounds the presence of which in coal-gas frequently causes damage to the crucibles. REQUISITE BLOWIHQ POWEB.

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