New procedure for the analysis of dental gold alloys

Abstract

From a study of cond itions under which certain base metals known to be associated with native grain platinum could be collectively separated from the plat inUIT\ metals and gold, a new procedure has been developed for analyzing dental gold 1o,,!10YS which differs cssentially from that published by W. H. Swa nger in 1926.The procedure as a pplied to dental gold alloys provides for the separ ation and gravimetric determination of silver, ~ridium, tin, gold, indium, copper, zinc, nickel, palladium, rhodium, and platinu m. Briefly it is as follows : Silver chloride and metallic iridium are precipitated when the alloy is decomposed by aqua regia. Tin is next separated by a new t echn ic of controlled h ydrolysis. Gold is then precipitated by sodium nitrite, and next, by adjusting thc alkalinity with sodium hydroxide to the end point of thymolphthalein, indium, copper, zinc, and nickel are coll ectively separated from rhodium and platinum. At this alkalinity a small proportion of palladium precipitates with the base metals but is recovered from them with dimethylglyoxime. Palladium, rhodium, and platinum are separated from one anoth r by the usual methods of this laboratory. The four base metals are separated, in order, by precipitating indium with ammonium hydroxide, copper, and subsequently zinc, with ,hydrogen sulfide, and nickel with dimethylglYoxime.It was found that manganese, iron, cobalt, and chromium are also quantitatively precipitated in a solution containing nitrite at the end point of thymolphthalein, and that it is possible to separate lead from palladium and platinum at the end point of xylenol blue, if the lead is precipitated as carbonate.Suggestions ate made for using the procedure as a refining method for crude material containing gold and the platinum m etals.

X-ray spectrometric analysis of noble metal dental alloys

“…Each disk so cast weighed about 35 g. The surfaces of the disks were then precision machined for the X-ray measurements. The compositions of the castings were determined by wet chemical analysis according to the method of Gilchrist [3], and the results of the analysis are shown in table 1.…”

“…The analysis of noble metal alloys by traditional methods of solution chemistry [3]2 is one of the more complex and time-consuming tasks confronting the analytical chemist. Three to four man-weeks are usually required for the analysis of three samples in duplicate.…”

Circular of the Bureau of Standards no. 433:

“…-Analytical methods. The publication by the National Bureau of Standards of the compositions of dental gold alloys of many types, together with the methods used in analyzing them [8,80], created a wholesome atmosphere, which had far-reaching influence.…”

Analysis of gold and platinum group alloys by x-ray emission:

“…The optimum conditions for the x-ray emission intensity measurements were determined experimentally and are given in Table 1. 2.2 Materials. The chemical compositions of five gold alloy standards were determined by wet chemical analysis [1] and the results are shown in Table 2. The batch compositions, determined from careful weight measurement before alloying by The J. M. Ney Company, for three commercial alloys are listed in Table 3.…”