498
ANALYTICAL CHEMISTRY
paper. The paper and residue were partially dried under a heat lamp and tightly folded. This was wrapped in a 5.5cm. paper and tamped into a Coors 00000 porcelain crucible. This crucible was placed inside a larger crucible, ignited over a Meker burner a t full heat without first allowing the paper to char, as is the usual practice. The contents of the crucible were reduced in hydrogen over a Meker burner, flushed with nitrogen, and allowed to cool in a stream of nitrogen. The crucible and contents were then placed in a 125-ml. conical beaker and 50 ml. of aqua regia were added. When the palladium was dissolved the crucible was removed with platinum-tipped tongs and rinsed well with water. The solution was evaporated to dryness, fresh aqua regia was added, and the evaporation was repeated twice. After three evaporations with hydrochloric acid, the residue was dissolved in 8 ml. of hot 1 to 32 hydrochloric acid. This was diluted with 25 ml. of water and filtered while hot. The filtrate and washings were diluted to 100 ml., the palladium n a i reprecipitated and coagulated, and the mixture was cooled in the same way as the first precipitation. The precipitate was caught on a Royal Berlin porcelain filter crucible of A-2 porosity, dried for 3 hours a t 115” C., and weighed. The results of several assays using a basic slag are shown i n Table I, Nos. 4, 5, and 6. Only the palladium contained in the first button was determined by the gravimetric procedure. The colorimetric method was used for the second and third button..
require the colorimetric procedure; in this case one must use for the standard curve blank buttons (or lead nitrate solutions) of composition comparable to those obtained from the assay. The gravimetric procedure is recommended only for buttons obtained from materials rich in palladium. In the double precipitation of palladium with salicylaldoxime filtrate losses were shown to be negligible. The amount of lead contaminating the second precipitate was shown to be insignificant Both methods were applied successfully to regular assay buttons from synthetic ores, although only results from a basic ore are given in this paper. A critical examination of the distribution of palladium with the baqic and other slags is being made.
DISCUSSION
(1) Ayies, G. H., and Tuffly, B. L., AXAL.CHEW,24, 949 (1952). (2) Flagg, J. F., and Furman, N. H., IND.EXG.CHEW,AN
