Fahr., is had by a mixture of 3 parts lead, 1 part bismuth, and not over 1/100 part tin. It is wonderful how small a quantity of tin serves to improve the alloys of lead and bismuth, giving them a white, clear lustre, preventing oxidation, promoting fusibility - in short, producing almost a new metal.

3438. Cadmium Alloys for Dentists' Moulds

3438.     Cadmium Alloys for Dentists' Moulds. By the use of cadmium we may produce still harder alloys than any of the preceding, possessing in an equal degree every other desirable quality. Thus, 10 parts of tin, 1 part of antimony, 1 of copper, and 1 of cadmium, produce a compound which has about the hardness of zinc; it casts perfectly, and is nearly all that could be desired, except that, like the copper die metals, it is rather brittle for certain castings. (See No. 3437.) Substituted for copper in these connections, cadmium appears to confer greater hardness and toughness, and, up to a certain point, promotes fusibility. 9 parts of tin, 1 part of antimony, and 1 part cadmium, furnish a very hard and tough metal of a compact, homogeneous structure, which casts without shrinkage, forming a perfect die with a smooth, bright face. It melts at about the melting point of tin. In the employment of cadmium, care must be taken not to subject it to a heat high enough to volatilize it. To avoid this danger, it is best to unite the other metals first, and then add the cadmium at a heat barely sufficient to melt it. The great objection to this metal is its expensiveness.

3439. Alloy of Nickel and Copper

3439.    Alloy of Nickel and Copper. A mixture of 1 part nickel and 2 parts copper produces a grayish-white metal, tenacious, ductile, and moderately fusible.

3440. Alloys of Platinum and Copper

3440.    Alloys of Platinum and Copper. A compound of 1 part platinum and 4 parts copper is of a yellow-pink color, hard, ductile, and susceptible of a fine polish.

An alloy of 3 parts platinum and 2 parts copper is nearly white, very hard, and brittle.

3441. French Bell Metal

3441.    French Bell Metal. The metal used in France for hand-bells, clock bells etc., is made of 55 to GO parts copper, 30 to 40 parts tin, and 10 to 15 parts zinc.

3442. Red Tombac

3442.    Red Tombac. Put into a crucible 51/2 pounds copper; when fused add 1/2 pound zinc; these metals will combine, forming an alloy of a reddish color, but possessing more lustre than copper, and also greater durability.

3443. White Tombac

3443.    White Tombac. When copper is combined with arsenic, by melting them together in a close crucible, and covering the surface with common salt, to prevent oxidation, a white brittle alloy is formed.

3444. Speculum Metal for Telescopes

3444. Speculum Metal for Telescopes. Melt 7 pounds of copper, and when fused add 3 pounds zinc and 4 pounds tin. These metals will combine to form a beautiful alloy of great lustre, and of a light yellow color, fitted to be made into specula for telescopes. Mr. Mudge used only copper and grain tin, in the proportion of 2 pounds of the former to 141/2 ounces of the latter.