A practical treatise on mechanical dentistry / by Joseph Richardson.

  • Richardson, Joseph, D.D.S.
Date:
1880
Catalogue details

Licence: Public Domain Mark

Credit: A practical treatise on mechanical dentistry / by Joseph Richardson. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

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    likely to render the gold brittle, the particular reagent which will most readily attack it may now be used. If, however, as is generally the case, the alloy is of uncertain composition, or contains various metals having distinct affinities, the process becomes, to some extent, experimental, and it may become necessary to use first one refining agent and then another, until sufficient separation is eiFected. Generally, it will be sufficient to use the nitrate of potassa alone, as most metals are oxidable. After roasting with nitre for half or three-fourtjjs of an hour, adding small portions at a time, the melted metals may be poured into ingot moulds previously warmed and oiled. If, after hammering, annealing, and rolling the ingot, it should still be found brittle, it must be re-melted, and chlo- ride of mercury used as the refining agent. This will remove any traces of tin which may be present. If the alloy, however, is greatly impoverished, it may be more advantageously treated with sulphuret of antimony; in which case the metal should be melted in a large crucible with about twice or three times their weight of the native sulphuret, which should be added in small quantities at a time. Tlie heat decomposes the sulphuret of antimony; the sulphur unit- ing with the base metals forming sulphurets, and the antimony uniting with the gold forming a leaden-colored alloy. The antimony may be parted from the gold alloy in the following manner: Place the mixture in a clean crucible, and when melted, force a current of air with a pair of bellows upon its surface; this oxidizes the antimony, which passes off in the form of vapor. The current should be mild at first, as too great a draught is apt to carry off portions of gold by a too hurried volatilization of the antimony. A current strong enough to produce visible fumes will be sufficient. When these cease, the crucil)le may be covered, and as the melting- point of the gold rises with the escape of antimony, the fire should be urged to a stronger heat, and before pouring, a for- cible current of air should again ])c thrown upon the surface of the melted metals to effectually dissipate any remaining por- tions of the antimony.
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