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

in the air, and can, like the other alloys of palladium, be used for dental purposes.

      II.—Palladium 6 parts, gold 18, silver 11, and copper 13, gives a reddish-brown, hard, and very fine-grained alloy, suitable for the bearings of pivots in clock works.

      The alloys of most of the other platinum metals, so called, are little used on account of their rarity and costliness. Iridium and rhodium give great hardness to steel, but the commercial rhodium and iridium steel, so called, frequently contains not a trace of either. The alloy of iridium with osmium has great hardness and resistance and is recommended for pivots, fine instruments, and points of ship compasses.

      Palladium Silver.

      —This alloy, composed of 9 parts of palladium and 1 of silver, is used almost exclusively for dental purposes, and is well suited to the manufacture of artificial teeth, as it does not oxidize. An alloy even more frequently used than this consists of platinum 10 parts, palladium 8, and gold 6.

      Palladium Bearing Metal.

      —This alloy is extremely hard, and is used instead of jewel bearings in watches. It is composed of palladium 24 parts, gold 72, silver 44, copper 92.

      Platinum Alloys.

      Platinum has usually been alloyed with silver in goldsmith’s work, 2 parts silver to 1 of platinum being taken to form the favorite “platinum silver.” The object has been to produce an alloy having a white appearance, which can be polished, and at the same time has a low melting point. In addition to this platinum alloy the following are well known:

      I.—A mixture of 7 parts platinum with 3 parts iridium. This gives to platinum the hardness of steel, which can be still further increased by taking 4 parts of iridium.

      II.—An alloy of 9 parts platinum and 1 part iridium is used by the French in the manufacture of measuring instruments of great resisting power.

      Compounds of copper, nickel, cadmium, and tungsten are also used in the construction of parts of watches; the latter acquire considerable hardness without becoming magnetic or rusting like steel.

      III.—For this purpose a compound of {74} 62.75 parts platinum, 18 parts copper, 1.25 parts cadmium, and 18 parts nickel is much recommended.

      IV.—Very ductile platinum-copper alloys have also been made, e.g., the so-called Cooper gold, consisting of 3 parts platinum and 13 parts copper, which is almost equal to 18-carat gold in regard to color, finish, and ductility. If 4 per cent of platinum is taken, these latter alloys acquire a rose-red color, while a golden-yellow color can be produced by further adding from 1 to 2 per cent (in all 5 to 6 per cent) of platinum. The last-named alloy is extensively used for ornaments, likewise alloy V.

      V.—Ten parts platinum, 60 parts nickel, and 220 parts brass, or 2 parts platinum, 1 part nickel and silver respectively, 2 parts brass, and 5 parts copper; this also gives a golden-yellow color.

      VI.—For table utensils a favorite alloy is composed of 1 part platinum, 100 parts nickel, and 10 parts tin. Articles made of the latter alloy are impervious to atmospheric action and keep their polish for a long time. Pure white platinum alloys have for some time been used in dental work, and they have also proved serviceable for jewelry.

      VII.—A mixture of 30 parts platinum, 10 parts gold, and 3 parts silver, or 7 parts platinum, 2 parts gold, and 3 parts silver.

      VIII.—For enameled articles: Platinum, 35 parts; silver, 65 parts. First fuse the silver, then add the platinum in the spongy form. A good solder for this is platinum 80 parts, copper 20 parts.

      IX.—For pens: Platinum, 4 parts; silver, 3 parts; copper, 1 part.

      Platinum Gold.

      —Small quantities of platinum change the characteristics of gold in many respects. With a small percentage the color is noticeably lighter than that of pure gold, and the alloys are extremely elastic; alloys containing more than 20 per cent of platinum, however, almost entirely lose their elasticity. The melting point of the platinum-gold alloy is high, and alloys containing 70 per cent of platinum can be fused only in the flame of oxyhydrogen gas, like platinum itself. Alloys with a smaller percentage of platinum can be prepared in furnaces, but require the strongest white heat. In order to avoid the chance of an imperfect alloy from too low a temperature, it is always safer to fuse them with the oxyhydrogen flame. The alloys of platinum and gold have a somewhat limited application. Those which contain from 5 to 10 per cent of platinum are used for sheet and wire in the manufacture of artificial teeth.

      Platinum-gold Alloys For Dental Purposes.—

	I	II	III
Platinum	6	14	10
Gold	2	4	6
Silver	1	6	—
Palladium	—	—	8

      Platinum Silver.

      —An addition of platinum to silver makes it harder, but also more brittle, and changes the white color to gray. An alloy which contains only a very small percentage of platinum is noticeably darker in color than pure silver. Such alloys are prepared under the name of platine au titre, containing between 17 and 35 per cent of platinum. They are almost exclusively used for dental purposes.

      Imitation Platinum.

      —I.—Brass, 100 parts; zinc, 65 parts.

      II.—Brass, 120 parts; zinc, 75 parts.

      III.—Copper, 5 parts; nickel, 4 parts; zinc, 1 ¹/₂ parts; antimony, 1 part; lead, 1 part; iron, 1 part; tin, 1 part.

      Cooper’s Pen Metal.

      —This alloy is especially well adapted to the manufacture of pens, on account of its great hardness, elasticity, and power of resistance to atmospheric influences, and would certainly have superseded steel if it were possible to produce it more cheaply than is the case. The compositions most frequently used for pen metal are copper 1 part, platinum 4, and silver 3; or, copper 21, platinum 50, and silver 36.

      Pens have been manufactured, consisting of several sections, each of a different alloy, suited to the special purpose of the part. Thus, for instance, the sides of the pen are made of the elastic composition just described; the upper part is of an alloy of silver and platinum; and the point is made either of minute cut rubies or of an extremely hard alloy of osmium and iridium, joined to the body of the pen by melting in the flame of the oxyhydrogen blowpipe. The price of such pens, made of expensive materials and at the cost of great labor, is of course exceedingly high, but their excellent qualities repay the extra expense. They are not in the least affected by any kind of ink, are most durable, and can be used constantly for years without showing any signs of wear.

      The great hardness and resistance to the atmosphere of Cooper’s alloys make them very suitable for manufacturing {75} mathematical instruments where great precision is required. It can scarcely be calculated how long a chronometer, for instance, whose wheels are constructed of this alloy, will run before showing any irregularities due to wear. In the construction of such instruments, the price of the material is not to be taken into