Henley's Twentieth Century Formulas, Recipes and Processes. Various

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СКАЧАТЬ 2.5 parts Zinc 0.5 part

      This alloy has a fine white color, and can be readily rolled into thin sheets. For that reason it is well adapted for lining tea chests and for the production of tobacco and chocolate wrappers. The copper and zinc are used in the form of fine shavings. The alloy should be immediately cast into thin plates, which can then be passed through rolls.

      Magnetic Alloys.

      Alloys which can be magnetized most strongly are composed of copper, manganese, and aluminum, the quantities of manganese and aluminum being proportional to their atomic weights (55.0 to 27.1, or about 2 to 1). The maximum magnetization increases rapidly with increase of manganese, but alloys containing much manganese are exceedingly brittle and cannot be wrought. The highest practicable proportion of manganese at present is 24 per cent.

      These magnetic alloys were studied by Hensler, Haupt, and Starck, and Gumlich has recently examined them at the Physikalisch—technische Reichsanstalt, with very remarkable and interesting results.

      The two alloys examined were composed as follows:

      Alloy I.—Copper, 61.5 per cent; manganese, 23.5 per cent; aluminum, 15 per cent; lead, 0.1 per cent, with traces of iron and silicon.

      Alloy II.—Copper, 67.7 per cent; manganese, 20.5 per cent; aluminum, 10.7 per cent; lead, 1.2 per cent, with traces of iron and silicon.

      Alloy II could be worked without difficulty, but alloy I was so brittle that it broke under the hammer. A bar 7 inches long and ¹/₄ inch thick was obtained by grinding. This broke in two during the measurements, but, fortunately, without invalidating them. Such a material is evidently unsuited to practical uses.

      The behavior of magnetic alloys at high temperatures is very peculiar. Alloy I is indifferent to temperature changes, which scarcely affect its magnetic properties, but the behavior of alloy II is very different. Prolonged heating to 230° F. produces a great increase in its capability of magnetization, which, after 544 hours’ heating, rises from 1.9 to 3.2 kilogauss, {72} approaching the strength of alloy I. But when alloy II is heated to 329° F., its capability of magnetization fails again and the material suffers permanent injury, which can be partly, but not wholly, cured by prolonged heating.

      Another singular phenomenon was exhibited by both of these alloys. When a bar of iron is magnetized by an electric current, it acquires its full magnetic strength almost instantaneously on the closure of the circuit. The magnetic alloys, on the contrary, do not attain their full magnetization for several minutes. In some of the experiments a gradual increase was observed even after the current had been flowing five minutes.

      In magnetic strength alloy I proved far superior to alloy II, which contained smaller proportions of manganese and aluminum. Alloy I showed magnetic strengths up to 4.5 kilogauss, while the highest magnetization obtained with alloy II was only 1.9 kilogauss. But even alloy II may be called strongly magnetic, for its maximum magnetization is about one-tenth that of good wrought iron (18 to 20 kilogauss), or one-sixth that of cast iron (10 to 12 kilogauss). Alloy I is nearly equal in magnetic properties to nickel, which can be magnetized up to about 5 kilogauss.

      Manganese Alloys:

      Manganese Bronze

      is a bronze deprived of its oxide by an admixture of manganese. The manganese is used as copper manganese containing 10 to 30 per cent manganese and added to the bronze to the amount of 0.5 to 2 per cent.

      Manganese Copper.

      —The alloys of copper with manganese have a beautiful silvery color, considerable ductility, great hardness and tenacity, and are more readily fusible than ordinary bronze. A special characteristic is that they exactly fill out the molds, without the formation of blowholes, and present no difficulties in casting.

      Cupromanganese is suitable for many purposes for which nothing else but bronze can advantageously be used, and the cost of its production is no greater than that of genuine bronze. In preparing the alloy, the copper is used in the form of fine grains, obtained by pouring melted copper into cold water. These copper grains are mixed with the dry oxide of manganese, and the mixture put into a crucible holding about 66 pounds. Enough space must be left in the crucible to allow a thick cover of charcoal, as the manganese oxidizes easily. The crucible is placed in a well-drawing wind furnace and subjected to a strong white heat. The oxide of manganese is completely reduced to manganese, which at once combines with the copper to form an alloy. In order to prevent, as far as possible, the access of air to the fusing mass, it is advisable to cover the crucible with a lid which has an aperture in the center for the escape of the carbonic oxide formed during the reduction.

      When the reduction is complete and the metals fused, the lid is removed and the contents of the crucible stirred with an iron rod, in order to make the alloy as homogeneous as possible. By repeated remelting of the cupromanganese a considerable quantity of the manganese is reconverted into oxide; it is, therefore, advisable to make the casts directly from the crucible. When poured out, the alloy rapidly solidifies, and resembles in appearance good German silver. Another reason for avoiding remelting is that the crucible is strongly attacked by the cupromanganese, and can be used but a few times.

      The best kinds of cupromanganese contain between 10 and 30 per cent of manganese. They have a beautiful white color, are hard, tougher than copper, and can be worked under the hammer or with rolls. Some varieties of cupromanganese which are especially valuable for technical purposes are given below:

	I	II	III	IV
Copper	75	60	65	60
Manganese	25	25	20	20
Zinc	—	15	5	—
Tin	—	—	—	10
Nickel	—	—	10	10

      Manganin.

      —This is an alloy of copper, nickel, and manganese for electric resistances.

      Mirror Alloys:

      Amalgams For Mirrors.

      —I.—Tin, 70 parts; mercury, 30 parts.

      II.—For curved mirrors. Tin, 1 part; lead, 1 part; bismuth, 1 part; mercury, 9 parts.

      III.—For glass balls. Tin, СКАЧАТЬ