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.

    59/334 (page 39)
    As these compounds dissolve in all proportions in the molten mass of metals, it is very difficult to satisfactorily- separate them for examination. Although metals may be mixed in the fused state, it by no means follows that they will remain in admix- ture if they are allowed to cool slowly, or sometimes even rapidly. If lead and zinc be thoroughly mixed in the molten state, and slowly cooled in a deep mould, the two metals separate almost completely; the zinc, being lighter, rises to the top, leaving the heavier metal at the bottom. With other metals there is sometimes a tendency, on solidification, for one of the constituents to become concentrated in the middle or at the surface of the mass, thus giving a casting which is not perfectly homogeneous. It is now well established that most of the possible associations of any two metals have more than one point of solidification, and do not freeze, as pure water does, at a single point. There is, however, in many series of alloys one particular association of the two metals which is more fusible than the rest of the alloys of the series. This alloy is called the eutedic alloy, and it possesses a single point of solidifica- tion, that is, when the eutectic alloy is cooled it sets sharply as a whole at a given temperature. Many associations of two metals contain an eutectic alloy and consequently have two points of solidification. As a molten mass of alloy cools down it begins to solidify at a certain point, but the eutectic alloy on account of its low solidifying-point remains fluid, and entangled in the portion which has set, until the tem- perature falls to the solidifying-])oint of the eutectic alloy, at which temperature solidification of the mass is completed. There is, therefore, in many cases abundant