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be carried too far and the pulp will become worthless for rapid filtration. A practically ash-free pulp can be made out of unwashed Swedish filter paper by use of a little hydrofluoric acid with the hydrochloric acid. When the mixture is used, however, it is necessary, of course, to use a ceresin, paraffincoated, or Bakelite vessel.
Vol. 17, No. 3
The advantages of this method of filtration are: (1)Effective retention of fine precipitates such as barium sulfate. (2) Rapid filtration. (3) Negligibleash whenbothacidsareusedinmakingthepulp. (4) More thorough washing of precipitates, with less wash water.
A New Method of Determining Palladium' By Herbert E. Zschiegner ROESSLER & HASLACHER C H E M I C A L CO.,PERTH AMBOY,N.J.
T IS usual in analytic practice to precipitate palladium, either as palladium cyanide, palladious iodide, or ammonium palladichloride, subsequent to the removal of platinum. Palladium may also be precipitated from the hydrochloric acid solution with dimethylglyoxime,* and in some instances is separated by selective solution (nitric acid), though the latter method is not applicable in the presence of platinum. Where these methods with the exception of the glyoxime precipitation are applied directly, without &st removing the platinum, some of the latter will be carried down, necessitating a second and even a third precipitation. On the other hand, if platinum, which may constitute 99 per cent or more of the whole, is first removed it will be likely to contain some of the palladium and will also require re-working. The separation of the platinum metals is a t best a long and tedious process, attended as it is by such disturbing factors as hydrolysis, catalysis, incomplete and reversible reactions, etc. The method here described provides for the rapid and accurate estimation of palladium directly from a solution in which platinum and other platinum metals predominate. It is especially useful where it is necessary to determine impurities in samples of technical and so-called C. P. platinum, the estimation of gold, silver, and base metal impurities being accomplished a t the same time.
I
Procedure
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Two grams of the sample are dissolved in aqua regia and the solution is evaporated to dryness, care being taken that no metal is reduced as such. Reduction to lower chlorides may be ignored even though these are latterly more difficultly soluble in water. Neither is it necessary to eliminate nitric acid by repeated evaporation with hydrochloric acid. The residue is taken u p with 100 cc. of water and heated nearly to boiling, then removed from the heat and treated with 5 grams of sodium nitrite, stirring until the chlorides of the platinum metals are completely dissolved. The solution dears in a very few minutes, except for the precipitation of gold, which should not be confused with undissolved chlorides or products of hydrolysis. Water is then added until the volume reaches 250 cc. when another 5 grams of sodium nitrite is dissolved in the solution with stirring. The complete conversion of the chlorides to nitrites is then effected by heating gently for one hour a t a temperature not to exceed 80' C. After cooling, the solution is neutralized with normal sodium carbonate and made alkaline with a 1 2
Received October 4, 1924. Wunder and Thuringer, Z. anal. Chem , 51, 101 (1913); A n n . chim.
a m l . , 17, 201.
further addition of 0.2 CC. Alcoholic phenolphthalein is used as indicator. Gold, silver, and the base metals are precipitated. After 30 minutes these are filtered off, washed, ignited, and re-dissolved for the estimation of contained impurities. Palladium is then precipitated from the filtrate with a cold 1 per cent of dimethylglyoxime in alcohol. (Nickel, the only interfering element for the alkaline glyoxime precipitation, has been removed by the preceding operation.) Stirring hastens the precipitation of the palladium, which is then allowed to settle and coagulate for 3 hours. If less than 0.05 per cent of palladium is present, the precipitate is allowed to collect for 12 hours. The precipitate is filtered off on a weighed Gooch, washed, first with cold water, and finally with hot water, and dried a t 90" C . The precipitate is weighed as (CBHIIN40& Pd, containing 31.68 per cent palladium. It is essential that the solution be kept cool following the conversion to nitrites, else the alcohol of the phenolphthalein or of the dimethylglyoxime may cause reduction of platinum metals from the alkaline solution. Tests of Method
I n the trial tests of this method, the palladium glyoxime after weighing was ignited, reduced in hydrogen, and weighed as the metal. The composition of the (CpHI4N40&was further verified by applying the method to a sample of palladium analyzing 99 per cent pure. The sample weighed 0.0130 gram, equal to 0.01287 gram palladium. The precipitate weighed 0.0406 gram. Applying the factor 0.3168, the palladium recovery is 0.01286 gram. The accompanying table comprises the results of six tests made on a sample containing 2 grams of platinum and 0.0080 gram palladium. The platinum used contained very small quantities of iron, copper, nickel, iridium, rhodium, and ruthenium. Palladium added Gram 1 0.0080 2 n nnxn 3 0.0080 4 0.0080 5 0.0080 6 0.0080 Weighed as (CsH1bN4Ol)aPd.
No.
a
Palladium recovered'' Gram 0,0079
n nom 0.0080 0.0080
0.0081
0.0079
After weighing, the precipitates were ignited, reduced, and weighed as the metal, which was then dissolved and precipitated from hydrochloric acid solution with potassium iodide. The palladium iodide was also ignited, reduced, and weighed. I n each case the results coincided with the original figures obtained by calculating from the glyoxime.
