. Plastics and plastic filling; as pertaining to the filling of all cavities of decay in teeth below medium in structure, and to difficult and inaccessible cavities in teeth of all grades of structure. being done, another work is doing — the work which isin progress on the part of the ingredients; that work whicheventuates in the proper hardening of the amalgam mass whenit is properly incorporated. The overheating by combining with too much mercury meltsout certain of the ingredients in unknown quantities. If thealloy is a two-metal alloy, combined without regard to test re-sults, of course co
. Plastics and plastic filling; as pertaining to the filling of all cavities of decay in teeth below medium in structure, and to difficult and inaccessible cavities in teeth of all grades of structure. being done, another work is doing — the work which isin progress on the part of the ingredients; that work whicheventuates in the proper hardening of the amalgam mass whenit is properly incorporated. The overheating by combining with too much mercury meltsout certain of the ingredients in unknown quantities. If thealloy is a two-metal alloy, combined without regard to test re-sults, of course comparatively little injury will ensue; the ma-terial, not being good, cannot be made very much less good;but in a fine alloy, compounded with great care and in suchproportions as give excellent test results, the withdrawal ofany proportion of any of its ingredients is, presumptively, det-rimental, and the withdrawal of indefinite quantities of all itsingredients is, as I have said, injurious in degree just in pro-portion to its original excellence. The overcooling by addition of too much filings has just theopposite effect; it chills the mercury in such wise as to prevent*See Appendix, Sec. THE MAKING OF AMALGAM. 89 a given amount from doing its proper work of fusion. Thisis distinctly shown in the prompt manner in which an insuf-ficiently plastic mass of amalgam will take up alloy, long filed, will take up by this unscientific mode ofmixing as much mercury as new alloy, freshly filed, which isabout one-fifth more than is required to make a good plasticamalgam. This at once transforms an excellent amalgam intoa comparatively poor one. Therefore, it is directed to prepare amalgam BY weight insuch proportions as have been found upon trial to make themass just right for working in any given case. This does notdirect that the weighing shall be hy iveights^ but by proportions;and it will be noticed, in the weighing of different alloys, thatdifferent proportions of m
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