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Iron is used in the form of turnings, and melted with the copper and zinc under a layer of charcoal. But as zinc so readily volatilises it is advisable to employ zinc already containing iron, by which a more uniform alloy is obtained, with the minimum loss of zinc.

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§ 47. Fontainemoreau's Bronzes. - These bronzes are said to answer well for chill-casting, the metal being poured into iron moulds. By this means the alloys are rendered more homogeneous, because the rapid cooling prevents the separation of the constituents in accordance with their respective densities. The highly crystalline nature of the zinc is changed by the addition of copper, iron, or lead. The following are the proportions used:

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§ 48. These are copper-zinc alloys employed for joining the various parts of articles together by fusion. The solder must, therefore, have a lower melting point than the body to be soldered, but the fusing point of the solder should approach, as nearly as it conveniently can, to that of the article, as a more perfect and more tenacious junction may thus be effected. Brass solder belongs to the class known as hard solders, or brazing solders. It may be stated as a general rule that the melting point of copper-zinc alloys is higher in proportion to the amount of copper present, and therefore any quality of brass may be made into a suitable solder by adding zinc or copper as the case

may be. The alloy commonly used in soldering brass contains equal weights of copper and zinc. An easily fusible solder may be made with 34 copper and 66 zinc. In this case, however, it must be borne in mind that the joint would be much weaker than when the more difficultly fusible solder is employed, so that excess of zinc is to be avoided wherever possible. A readily fusible solder may be obtained by using 44 parts copper, 50 parts zinc, 4 parts tin, and 2 parts lead. Alloys containing lead are not to be recommended, since the lead tends to separate out and produce unsightly black spots, besides decreasing the strength of the joint. A good hard solder for the richer alloys of copper and zinc may be produced from 53 parts copper and 47 parts zinc. Brass solder is sometimes used for soldering iron and copper, and as these metals have a much higher melting point than brass, a much better quality of solder can be employed, and is indeed advisable in many cases, being much stronger. In these cases tin is often added as one of the ingredients, but it should be only sparingly used, as it increases the brittleness of the solder and thus becomes a source of weakness. The addition of tin to brass causes the yellow colour to pass into gray, or white, according to the content of tin employed, and mixtures may be obtained of a yellow, yellowish-white, and grayish-white colour. The following table indicates the different varieties :

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In making solder it is very important that the constituent metals should be of good quality, as impurities seriously interfere with the colour, malleability, and strength of the solder; great care should also be taken to insure a thorough mixture, so that the alloys may be uniform in composition. Solder is often made by melting brass with the requisite addition of zinc, thereby insuring a more perfect union and less loss of zinc than is the case when zinc is

added to molten copper. Solder is most commonly used in the granulated form, which is effected by pouring the molten alloy into water, or by pounding it in an iron mortar when strongly heated.

The most suitable mode of preparing brass solder is to melt the brass rapidly in a crucible, the metal being covered with a layer of the best powdered charcoal, and when thoroughly fused, to add the zinc, which has previously been heated to near its melting point. Stir vigorously for a few minutes to insure a thorough incorporation of the contents, skim the dross from the surface, and then pour, taking care that no dross or charcoal is carried over with the metal into the mould, or into the water, as the case may be.

One method of granulating is to take the ingot of metal from the mould immediately it has solidified and pound vigorously in a large iron mortar. Or to first raise the ingot of solder to the requisite temperature over a charcoal fire, and then crush to powder in an iron mortar.

Some manufacturers pour the molten metal into a ladle, and empty the contents of the latter from a considerable height into cold water, the metal in its descent passing through a wet broom, or similar contrivance, so as to divide it into fragments. The granulated metal is afterwards sifted through sieves of different sized meshes, so as to obtain the grains of uniform size.

Another plan is to pour the molten metal on to the surface of a large iron ball, placed in a shallow pan containing cold water, so that the top of the ball projects above the

surface of the water.

The metal is thus broken up into small fragments of fairly uniform size.

According to Krupp, the finest and most uniform product is obtained in the following manner :

"At some distance above the surface of the water, serving for the collection of the grains, a horizontal pipe is arranged which is connected either with a powerful forcing pump or a water reservoir. Before pouring the metal the cock on the pipe is opened, so that the jet of water issuing from the pipe is thrown in a horizontal direction over the vessel containing the water. Upon this jet of water the molten metal is poured. The greater the force with which the water is forced from the pipe, the greater also the force with which the stream of melted metal is divided, and by this means it is possible, within certain limits, to obtain grains of a determined size." As will be seen from the above description, the scattering of the stream of molten metal is based on the same principle as that employed in diffusing fragrant liquids in the air.

When solder is granulated by pouring into water, it is necessary to remove the grains from the vessel as soon as the operation is completed, and dry them quickly, so as to avoid unnecessary oxidation.

MANUFACTURE OF BRASS

§ 49. Allusion has previously been made to the two distinct modes of making brass, known respectively as the calamine and direct methods; the former being almost exclusively used until within the last fifty or sixty years, but is now practically obsolete, at any rate in this country. In the ancient or calamine method, metallic copper is mixed with oxide of zinc and charcoal, and the mixture strongly heated for twelve hours or more, when the zinc, reduced by the carbon and carbonic oxide present, alloys with the copper forming brass. Such brass has been claimed to be of superior quality to that made by the direct process, but as great improvement has taken place in the qualities of brass of late years, it is very doubtful, if the manufacture of calamine brass were to be resumed, whether the value of the metal for most purposes would be superior to what the market can at present command. The reputed high quality of brass made by the old method could only be maintained by exercising great care in the quality of the ore and copper employed, and selecting ores of uniform composition to produce a product of uniform and determined properties. The cost of production of calamine brass is less than that of brass made by the direct process, but the former method is much more tedious and troublesome, requiring a much longer time than is consistent with modern requirements, and for small founders is quite unsuitable.

CALAMINE BRASS

§ 50. For calamine brass the ores were submitted to a preliminary treatment in order to remove as far as possible other compounds, such as those of lead, antimony, and arsenic, which would injure the quality of the brass. Native calamine was calcined to remove carbonic acid, sulphur, or other volatile matter, and form zinc oxide. The calcined ore was then ground in a mill, any galena removed

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