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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    melting, owing to tlie fact tliat a small <]aantity of zinc oxide is dissolved by the metal. It also becomes con- taminated with iron from the ladle. If a small (juantity of charcoal is placed on the surface of the metal when meltino-, oxidation i« minimised. The zinc may be purified by placing a few lumps of ammonium chloride (sal-ammoniac) on the surface of the molten metal, then stirring well with a stick of wood and pouring. When melting zinc in an iron ladle care should be taken to avoid excessive heating, as zinc forms an alloy with iron under favourable conditions. A malleable iron ladle should be used, as cast iron is more readily attacked, the zinc in some cases penetrating the ladle and escap- ing. By coating the inside of the ladle with whiting or a wash of clay and heating carefully, accidents of this kind may be avoided. When zinc has become accidentally contaminated with lead it may be separated from the latter by melting and allowing it to solidify slowly. On account of its density the lead will fall to the bottom and may then be removed by means of a chisel. Compounds of Zinc.—The following compounds of zinc are those most frequently employed by dentists. Zinc Oxide (ZnO). Known also as Zinc White. This is the only known compound of oxygen and zitic, and is the chief ingredient in the plastic filling-materials known as oxy-chlorides and oxy-phosphates. It is prepared on a large scale by the combustion of metallic zinc in air, the fumes produced being led into a series of condensing chambers where the oxide is deposited. For pharmaceutical and dental jiurposes it is usually prepared by adding sodium carbonate to a solution of ziuc sulphate. The white precipitate of