A manual on dental metallurgy / by Ernest A. Smith.

  • Smith, Ernest A. (Ernest Alfred)
Date:
1903
Catalogue details

Licence: In copyright

Credit: A manual on dental metallurgy / by Ernest A. Smith. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    which, after thorough mixing, the brass is added in small pieces nntil the necessary composition has been obtained. Owing to the high temperature required for the fusion of the nickel and the low melting-point and oxidisabie nature of zinc, the preparation of this alloy is attended with a considerable loss of zinc ; special care is accordingly required in its production. When re-melting the alloy it is necessary to add a portion of zinc to compensate for the loss, and it is advisable to add this zinc after the' fusion of the alloy has been effected. On account of this oxidation the relative amounts of the constituents are altered: it is therefore difficult to obtain an alloy of definite composition. In all cases a layer of charcoal should be placed on the surface to prevent oxidation as far as possible. Properties.—^German silver is greyer in colour and harder than silver, and is capable of receiving a high polish. It is also tough, tenacious, malleable, and ductile, and works well under the hammer or between the rolls. It is crystalline after casting and requires careful annealing before rolling or hammering, but after the crystalline character has been thus overcome the alloy may be rolled and hammered into a variety of shapes. Sound castings are secured by the use of borax, glass, or other good flux. When exposed to the atmosphere German silver acquires a yellow tint due to the presence of sulphuretted hydrogen, and in acid solutions, such as vinegar, with access of air, it becomes gradually coated with a layer of green verdigiis. It is superficially oxidised when heated in air, and at a bright red heat the alloy fuses, a pro])ortion of the zinc burning away. The alloy is readily soluble in nitric acid. Impression