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metal itself. This implies always the condition that the metal should be fusible at the same degree of heat, or nearly, at which the slag is fusible; also that it should not evaporate by that heat.

Sublimation. Metals which are very volatile cannot be advantageously smelted; they are distilled, and in some cases sublimation is resorted to. There is not the slightest difficulty in smelting zinc, under a cover of carbonate of soda and potash, with carbon. But such a flux is expensive; and when not closely attended to while fluid, the loss is greater than the value of the metal obtained. It is for these reasons found to be cheaper to mix the oxide or carbonate of zinc with carbon, and distil it; or to mix the zinc blende with iron and perform the same operation. The heat applied in these processes is by far higher than it is in smelting, and may cause the use of ten times as much fuel; still it is asserted that distillation is cheaper than smelting. Mercury is fre quently produced by a simple sublimation, without the addition of flux or coal; so also is arsenic. But in most instances, carbon and such substances as decompose the ore are added to it.

Refining.Refining gold and silver is done in large or small reverberatory furnaces, of which the bottom forms a cupel. Copper or lead is refined in reverberatories by melting, and the addition of fluxes. Tin is purified in reverberatory furnaces, and also in iron pots, being stirred by wood so as to oxidize its impurities. Zinc is refined in the same manner and by the same means. Iron is refined in charcoal forges, in run-out fires, in reverberatories, and in puddling and reheating furnaces.

Liquefaction. This is a delicate operation, but it is of great utility. Bismuth is obtained by liquefac

tion. If the ore of this metal is heated with proper fluxes and in a proper apparatus, to a degree of heat which will melt the bismuth only, it will flow out from the ore, and form metal without the rocky and foreign matter being converted into a fusible slag. Antimony may be obtained by the same means, and in fact every kind of metal, provided the remains of the ore do not melt partially, so as to enclose grains of metal in a refractory, pasty cinder. As a mode of refining, it is chiefly used in separating silver from copper. When 11 parts of lead are melted with 3 parts of argentiferous copper, and this alloy is cooled slowly, the lead and silver may be made to flow out from the copper and lead; and the fluid lead thus obtained contains all the silver. The mode of operation in this case is generally to melt lead and copper perfectly, then cool it slowly. The copper and lead alloy, being the most refractory of the compound, will crystallize first, and the silver and lead last. When this combination of lead and silver, and the combination of lead and copper, is heated in a proper apparatus, the first will flow out at a certain heat and leave the other, which remains as a skeleton of the form of the whole body of alloy. Impure tin is refined on the same principle: when a pig of tin is laid on the highest part of the sloping hearth of a reverberatory furnace, and gently heated, the pure tin flows out first, and leaves behind a skeleton of iron, copper, and other metals, which do not melt at a low heat, and which are removed. This principle may be applied for the separation of metals by filtration: when, for instance, alloy is brought upon a body of sand, bone-ashes, lime, or similar matter, and melted, the moist fluid of the metals in the alloy will flow out first, pass through

the sand, and a skeleton of the refractory metals will remain.

Crystallization. Most of the metals crystallize readily; all of them crystallize by proper treatment. Antimony and iron are particularly distinguished for their power of crystallization. The alloys of metals are not so much inclined to form regular bodies, at least not at the same degree of heat: for these reasons alloys may be separated from the pure metal. The fluid metals act here on the same principle as a salt dissolved in water. This property of metals and alloys has led to a valuable refining process for silver. When argentiferous lead is melted and then slowly cooled, the pure lead will sooner crystallize than the alloy of silver and lead, and a

part of the pure lead may be gradually removed by a skimmer, or drainer. No perfect separation ensues here, for the coagulated lead still contains silver, and the richer the alloy, the more silver is contained in the crystallized lead. Still, metal which contains but 10 ounces of silver in a ton of lead be concentrated with little expense, to lead of 30 ounces of silver per ton. When these principles are intelligently applied, much may be expected of them in the way of refining metals.

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Table of Squares, Cubes, and Fourth Power of Numbers.

Root. Square. Cube. 4th Power. Root. Square.

Cube.

4th Power.

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It is by the second kind of lever that the greatest effect is obtained from any given amount of power; hence the propriety of the application of this principle to the working of force-pumps, and shearing of iron, as by the lever of a punching-press, &c.

Rule, second kind.-Divide the whole length of lever, or distance from power to fulcrum, by the distance from fulcrum to weight, and the quotient is the proportion of effect that the power is to the weight or resistance to be overcome.

Ex. Required the amount of effect or force produced by a power of 50lbs. on the ram of a Bramah's pump, the length of the lever being 3 feet, and distance from ram to fulcrum 4 inches.

36

3 feet 36 inches, and 4-5=8, or the power and resistance are to each other as 8 to 1; hence 50 x 8=400 lbs. force upon the ram.

The lever on the safety-valve of a steam boiler is of the third kind, the action of the steam being the power, and the weight or spring-balance attached the resistance; but in such application the action of the lever's weight must also be taken into account, and may be simply ascertained by such means as represented in fig 2, plate D, where a is a Salter's balance attached to the lever by a light line, immediately at the point of pressure on the valve, and which, raised by hand or otherwise, will indicate the lever's action at that point.

This is perhaps the most frequent application of the third kind of lever to mechanical advantage, and that in which great nicety is required in estimation of effect: hence observe, as in other levers, there are three distinct points that require to be particularly attended to; namely, the weight, fulcrum, and re

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