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The fusion of metals and the mode of mixing them in the crucible to form alloys require much care, because alloys are very difficult to make, especially when the metals, of which they are composed are of such a character as have a kind of antipathy for each othersuch, for instance, as copper and lead. The method to pursue in mixing them is as follows :First, melt the least fusible of the metals (that requiring the highest temperature) of which the alloy is to be composed, and after it is fused, keep up the heat until the metal acquires such a temperature as will bear the introduction of the other metals without instantaneous and sensible cooling. After this, introduce the other metals in the order of their inf usibilitythe most difficult to melt first. Whatever may be the proportions of the metals, it is indispensable to melt the most refractory first, and especially when it is to be the principal base, such as copper in all bl8sses. The liquidity of this metal gives, indeed, the measure of the temperature necessary to complete the alloy All the metals to be added, after the most refractofY is first added, should be heated in the flame of the furnace, in order to elevate their temperature, so that there should be as little difference as possible between the heat of the molten metal in the crncible, and that to be added to it. This is especially necessary when a volatile metal, like zinc, is to be added to copper, because when it is melted very suddenly, it is liable to crack the crucible. The contents of the crucible must be stirred well after the introduction and fusion of each of the component parts of the alloy. When all are added, the crucible is covered, and an increased heat given to the fireintense according to the difficulty with which the metals enter into fusion. In alloys containing a large proportion of zinc, the surface of the metal in the crucible should be covered with a thin layer of charcoal powder. This precaution is not necessary, unless the alloy contains a metal requiring a high temperature for its fusion, as, for instance, copper or iron. In alloys oontaining tin, however, a laler of charcoal placed in the crucible is liable to convert part of the metal into dross, therefore ground clean sand should be used in place of it. All alloys should be vigorously stirred when run into molds. The crucibles employed should be thoroughly cleaned after each operation. Such are the general conditions which should be followed in making alloys. Copper melts at Fah. ; zinc at 700 Fah. ; lead at 590 Fah. ; tin at 450 Fah. ; cast-iron at Fah. A dull red heat is estimated at Fah. ; a bright red heat at Fah., and a white heat at Fah. In practice it is generally found that a minute q11antity of old, introduced into a new alloy imparts to the composition greater homogenety. Alloys should be first cast into ingots, then re-melted to be cast into boxes, or any article for which they are required. Why this should be done is simply a matter of practical experience, it having been found that castings of bronze and brass give, at the second melting (when the proportions of the metal are correct), a cast of a superior grain and a greater soundness. An alloy composed of zinc, tin, lead and copper, should be made by forming the three first metals into an alloy and casting them into ingots, then melting the copper, and adding this alloy to it. By this mode of making the copper alloy, a very superior casting is obtained. In England where the manufacture of brass is carried on very extensively, the furnaces employed for smelting have movable covers of a dome shape. The crucibles employed are of Stourbridge clay, one foot deep and eight inches in diameter, each furnace holding nine crucibles. The duration of a charge is twelve hours ; the fuel used is coal and coke, and 64 pounds of copper and 88 pounds of ground calamine (zinc ore) are thc proportions of each charge. When a heat of twelve hours is completed, the crucibles are taken out with tongs, the brass is skimmed to remove the slag, and the molten alloy then run into ingot molds. Muntz metal, so well known, is composed of 60 parts copper and 40 parts of zinc. Muntz obtained a patent in England for the application of brass sheathing for ships, and when he died a few years since, he left a fortune of 600,000about three millions of dollarsall made by his patent. He was an able business man, and knew how to work his patent to the best advantage, hence his great success. A brass composed of 4.69 copper and 31 zinc is very suitable for hammering. A brass of 5.64 copper and 36 zinc is usefulfor brazing iron ; 6.75 copper and 25 zinc ; 7.5It copper, and 27t zinc. In general, common brass may be calculated to contain 2 parts of copper and 1 of zinc. Dutch metal is composed of 84.5 copper and 15.5 of zinc. It is of a pale yellow color, and so malleable as to be capable of beating out into leaves, and so thin as to be employed for cheap gilding. Chinese brass is composed of 56.9 copper, 38.27 zinc, 3.30 lead, 1.08 tin, and 1,48 iron. It is very strong and durable. A little lead improves bradS for turning purposes, and it is usual to put it in just before pouring out, and about three ounces of lead to ten pounds of brass is the amount used. Fine brass wire is woven into fabrics liKe those of cotton yarn for sieves, bolting cloths, &c. Tin wire is made into a warp for the loom, the weft wound on a spool, and placed in a shuttle which is thrown by the weavers by hand, from side to side, in the same manner that old-fashioned hand loom cloth weaving was executed. Two men are necessary to work one loom, each throwing the shuttle -alternately. Brass wire has s?me peculiar properties. When annealed it is very soft, easily bent, and woven in the loom, but it must be rendered elastic for common use. The elasticity or spring is imparted to it by stretching and heating in a frame ; in other words, "the spring is licked into it." When kept fa- a considerable length of time in a state of hikh tension, brass wire is liable to snap suddeaty. It should therefore never be employed, as it oftentimes is, for suspending chandeliers and such like objects. ------------- . ,--------- Nitre Beds.At Bahie, in the Brazils, near Sao Francisco river, 180 leagues from the city of Bahia, a great natural deposit of nitrate of soda has been discovered, extending sixty miles along the valley.
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