THE ANALYST. 129 INORGANIC ANALYSIS. Assay of Zinc Precipitates for Gold and Silver. C. Fulton and C. Craw- ford, (Eng. and bfkhzq Journ., 1901, Ixxii., 813 ; through Chern. Zed. Hep., 1902,13.) -Ordinary assay processes are useless here, much of the gold and silver being lost by volatilization and in the slag. The crucible test gives the highest average results for gold, but not for silver, and the loss in the slag varies even when the same condi- tions are maintained. The best proportions for the crucible test are : 1 to 10 assay- tons of zinc precipitate, 70 grammes of litharge, 5 grammes of sodium carbonate, 1 gramme of fluorspar, 5 grammes of quartz, and 2 grammes of borax. Of combined wet and dry methods, extraction with nitric acid is not satisfactory, owing to dissolu- tion of gold.The authors, therefore, recommend the following : 1 to 10 assay-tons of the sample are boiled for one hour with 20 G.C. of strong sulphuric a i d and 60 C.C. of water, cooled, and diluted to 100 C.C. ; 75 C.C. of a solution of rock-salt and 20 C.C. of one of lead acetate are added, and the precipitate, after settling for one hour, is collected and dried. This, with the filter ash, is cupelled with 30 or 40 grammea of lead. The results are good and very uniform : the gold is a little lower than that given by the crucible process, but the silver is higher. The loss in the slag is rela-130 THE ANALYST. tively small; but this slag and the cupel may be examined subsequently, and the necessary correction made. The sulphuric acid must be free from nitric acid.F. H. L. Volumetric Estimation of Bismuth in Ores. A. W. Warwick and T. D. Kyle. (Eng. and Nining Journ., April 13, 1901 ; through Chem. News, 1902, lxxxv., 3.)-One gramme of the finely-powdered ore is evaporated to dryness with 5 or 10 C.C. of strong nitric acid; another 5 C.C. of acid and 25 C.C. of water are added, and the whole is diluted to 100 C.C. Five grammes of ammonium oxalate or oxalic acid are introduced, boiled for five minutes, allowed to settle, and the supernatant liquid filtered off. The precipitate is boiled twice with 50 C.C. of water, and the washings are passed through the same paper. With an ordinary 10 per cent. ore this treatment should suffice to convert the bismuth oxalate into the basic salt; but if the filtrate is still acid, boiling must be repeated to neutrality.The precipitate on the paper is then dissolved in 2 to 5 C.C. of 1 : 1 hydrochloric acid, receiving the liquid in the beaker containing the bulk of the basic oxalate; this is warmed till entirely dissolved, and then diluted to 250 C.C. with hot water. The solution is neutralized with ammonia, and the resulting precipitate taken up in 1 : 4 sulphuric acid, adding a few C.C. in excess. Finally the liquid is titrated at between 70" and loo0 C. with permanganate. A permanganate solution in which 1 C.C. = 0.010 gramme Fe, will be equal to 0.0186 gramme bismuth; by diluting 100 C.C. of this with 86 C.C. of water a solution of permanganate will be obtained, of which 1 C.C. should equal 0.010 gramme of bismuth. A permanganate solution 1 C.C. = 0.010 gramme Fe ; found = 0.01868 gramme Bi.100 C.C. permanganate above + 86 C.C. of water ; 1 C.C. found = 0.01017 gramme Bi. Lead, iron, copper, zinc, arsenic, and tellurium do not interfere with the process. Care must be taken to avoid using too little or too much nitric acid. Hydrochloric acid must not be used to dissolve the ore. The results are accurate enough for all commercial work, and an analysis can be carried out in thirty or forty minutes. The figures quoted show maximum errors of - 0.0032 and + 0.001 gr@mme in determining 0-5 gramme of bismuth in presence of lead, copper, zinc, iron, and arsenic. F. H. L, Precipitation of Ferrous Sulphide by Means of Sulphuretted Hydrogen. A. Coppadoro. (Gaxz. Chim. Ital., 1901, xxxi. [2], 217; through Chem.Zeit. Rep., 1902, 40.)-The author points out that when sulphuretted hydrogen is led through a ferric solution, the sulphur which is deposited carries down with it a small quantity of ferrous sulphide, as may be shown by extracting the precipitate with carbon bisulphide. A small amount of ferrous sulphide is also obtained when a solution containing sodium thiosulphate and ferric chloride is treated with an acid. The indispensable condition for the formation of the ferrous sulphide is the simultaneous separation of sulphur. F. H. L.THE ANALYST. 131 Action of Certain Reagents on Free Silicon. P. Lebeau. (Bull. Soc. Chim, 1902, xxvii., 42-44.)--A series of experiments are described in detail, which show that the reagents usually employed to dissolve steel, etc., are without action upon free silicon, even when in a fine state of division, and that that element will be left in the undissolved residue.C. A. 31. The Determination of Pemulphates. Charles A. Petere and Seth E. Moody, (Zeits. anorg. Chent., xxix., 326.)-The authors have been induced to make a comparison of the various methods for the estimation of persulphtes by the appearance of a paper by Namias (abstract, Chem. Centrbl., 1900, ii., 806), in which the method of Le Blanc and Eckardt (Zeitschr. Electrochem., v., 355) is stated to be inaccurate. I n this method the solution of the persulphate is treated with an excess of a standard solution of ammonium ferrous sulphate, either for ten minutes at temperature of GO’ to 80@, or for eleven hours at rooni temperature, and the excess of ferrous salt titrated with standard permanganate solution.Both rpodifications of the method gave accurate and concordant results, and experimentally it was found unnecessary to replace the air in the titrating vessel by carbon dioxide. I n Grutzner’s method (C‘hcnt. Centrbl., 1900, i., 835) the solution of the per sulphate is heated to boiling with a standard solution of arsenious acid, and potassium or sodium hydroxide, cooIed, acidulated with sulphuric acid, and made alkaline with potassium bicarbonate; the excess of arsenious acid is then determined with a standard iodine solution. This method also was found to give reliable results, provided that the small amount of arsenious acid oxidized by the reagents added was determined, and this correction applied in calculating the results.In Mondolfo’s method (Cltem. Zeit., xxiii., 699) the persulphate solution is heated with potassium iodide in a closed bottle in a water-bath to 60” to 80” for a short time, and the liberated iodine titrated with thiosulphate. There appeared to be a tendency towards low results with this method, but good results were obtained when the volume was kept small (25 c.c.) and the time of heating increased up to thirty minutes (for 0.12 gramme persulphate). The method described by Xamias (Zoc. cit.) differs from Mondolfo’s only in the fact that the mixture of persulphate and iodide is allowed to stand for eleven hours a t room temperature instead of being heated for a short time. This method also was found to give low results unless the volume of the solution is kept small.I n neither of the two last methods is the addition of sulphuric acid advantageous. Gooch and Smith’s method ( J O Z ~ L . Sci. [SZLZ.], 42, 220) for the estimation of chlorates was also used for persulphates as follows : To the solution of the persulphate an excess of a standard solution of potassium iodide and an excess of acid potassium arsenate are added, the whole made strongly acid with sulphuric acid, diluted, and boiled down to a third of its volume ; after cooling, the solution is made alkaline with potassium bicarbonate, and the residual arsenite titrated with iodine. The difference between the amount of iodine required and the amount contained in the potassium iodide added originally corresponds to the persulphate present. The results obtained were accurate, and agreed well with those obtained by the other methods.132 THE ANALYST. In conclusion, the method of Le Blano and Eckardt appear8 to be simple, rapid, and accurate, and furniehes results lying between those given by the other methods, Mondolfo's and Nctmiads, methods giving the lowest, tbnd Grutzner's and the arsenolte method the highest results, the extreme difference being about 1.5 rnilligrammes on 0.12 gramme. A. G. L.