โ Scribed by George K. Burgess; P.D. Sale
No coin nor oath required. For personal study only.
TI~IERE has been devised a simple, thermo-electric method suitable for the determination of the purity of platinum ware. This method does not mar the article tested, and gives data for the classification of platinum in terms of its equivalent iridium (or rhodium) content.
There were examined by the thermo-electric method 164 pieces of platinum ware, of which 26 per cent. contained less than 0. 5 per cent. iridium and 67 per cent. less than 2 per cent. of iridium. Of 84 crucibles, 36 per cent. contained less than 0. 5 per cent. iridium and 87 per cent. less than 2 per cent. iridium.
A method has been developed for determination of the exact loss on heating of platinum crucibles by means of a suitable electric furnace containing no heated metal parts.
Fourteen crucibles of various makes and grades were examined for loss in weight on heating and after acid treatment following each heating. Their magnetic susceptibilities were also determined. The susceptibility of pure platinum is" zero, and the range of susceptibility of seven crucibles is I to 125.
The heating losses per ioo cm. 2 of practically iron-free crucible surface at I2oo ยฐ C. ranged from o.71 mg. to 2.69 rag. per hour, the lesser losses being for crucibles containing rhodium and the greater losses being associated with iridium.
Iron appears to lessen somewhat the loss of weight on heating, but its presence is objectionable on account of the soluble oxide formed on the crucible surface. The chemical analysis and magnetic measurements place the crucibles in only approximately the same order as to iron content; the magnetic susceptibility is not, however, proportional to the iron content.
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