UOT’EMBER 15, 1938
ANhLYTIC-kL EDITION
Summary When a bead with a silver-platinum ratio of about 15 to 1 is parted with nitric acid, e\*en three successive treatments will not alwavs dissolve all the nlatinum. Bead.. containing only sih-er and palladium with the above silver ratio require only one parting with nitric acid t o dissolve the palladium completely. T h e presence of gold in the assay bead seems to assist the dissolving of platinum and palladium in the nitric acid
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Iridium, rhodium, and ruthenium definitelv interfered with the dissolving of platinum and palladium in the parting acid. in the bead decreased the action of The presence of the first parting acid on palladium.
Literature Cited D ~c J ~v, ~ B ~ L t r .Mines , Paper 270 (1921) (2) Smith, E. .I.,“The Sampling and Assay of the Precious Metals,” Charles Griffin and Co , Ltd , 1913. RECEIVED July i , 1938.
A Rapid Method for Gold in Cyanide Plating Solutions JOSEPH B. KUSHNER, 301 Echo Place, S e w York. N. Y.
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S DETERlIISII1-G the gold content of cyanide elec-
troplating solutions for control or evaluation purposes, most of the commonly known methods are too long drawn out or involved t o be of routine use t o the practical analytical chemist who must make many such determinations each day. The evaporation method ( 5 ) , the copper sulfate method ( d ) , the zinc-lead acetate method ( I ) , a n d the hydrochloric-ferrous sulfate method (,2) n-ere found by the author t o be unsuitable because of the excessive amount of time or the tedious operational procedure required. A method suggested by IF7eisberg (7) proved t o be sufficiently speedy (an analysis can be made in 2 hours) and simple but lacked accuracy, a s some of the gold precipitated in colloidal form and could not be retained on a filter paper or matting. However, further experimentation resulted in t h e improved method described in this paper.
Determination of Gold After thorough stirring, permitting WEISBERGPROCEDURE. any sediment to settle, pipet a 50-ml. sample into a 500-ml. Erlenmeyer flask. Place the flask under a good draft hood and cautiously add concentrated sulfuric acid until vigorous action ceases. Add 50 ml. more of acid and place the flask over heat, boiling for about 45 minutes until all the gold has precipitated in brown sponge form. Boil 5 to 10 minutes longer to coagulate the gold. Cool the flask and filter into a tared Gooch crucible, carefully washing all particles of gold onto the filter. Wash with hot dilute sulfuric and then with hot water until the washings are no longer acid. Dry and ignite in the Gooch until the brown sponge turns golden yellow in color. Cool to room temperature and weigh. Invariably a small but definite amount of gold precipitated in such a finely divided state a s t o pass through the asbestos filter m a t of the Gooch, even after continued matting with gold. This was evidenced b y t h e faint bluish brown color of the filtrate and the presence of the Tyndall effect on examination of the filtrate in a beam of light’. T h a t the gold came down in part in a colloidal state could only have been due t o the weak ionization of the concentrated sulfuric acid. This was proved by t h e fact that, if the sulfuric acid containing the gold in finely divided form was diluted with a large volume of water and further boiled, most of this colloidal gold precipitated. However, this change in method was hardly feasible because of the danger of explosion and spattering, the additional time required, and the fact t h a t the colloidal gold was not completely precipitated. T h e author found t h a t whenever silver was present in the electroplating solution (green gold), the gold almost always
came down perfectly and the supernatant sulfuric acid was crystal clear and showed no Tyndall effect. It was decided t h a t this perfect precipitation was brought about by a mutual suspensoid precipitation-i. e., t h e type t h a t occurs when a suspensoid solution of ferric hydroxide is mixed with a suspensoid solution of arsenic trisulfide-the assumption being t h a t t h e particles of silver formed in the early part of the process neutralize the charges on the finely divided gold particles and precipitate with them in a coagulated mass from which the silver dissolves on further boiling with sulfuric acid, leaving t’he gold in sponge form. If so, then adding a measured amount of a soluble silver salt t o a sample containing only gold, prior to the addition of the sulfuric acid, would bring about the same results. This was found t o be the case. Several experiments showed t h a t a wide latitude in the amount of silver salt was possible without ill effects, but in general the optimum amount of silver nitrate solution t h a t could be added mas just sufficient t o combine with the free cyanide present in the electrogilding solution. With this in view, the method of Weisberg was revised as follows:
If the solution to be tested is high in REVISEDPROCEDURE. gold content (0.5 to 20 grams per liter) take a 10-ml. sample; if low in gold content (0.5 gram or less per liter), take a proportionally greater sample. Transfer sample t o a 500-ml. Erlenmeyer flask, dilute with 50 ml. of pure water, and add sufficient 0.1 IV silver nitrate from a buret to combine completely with the free cyanide, using 5 ml. of a 2 per cent solution of potassium iodide as indicator (this is the equivalent of Liebig’s method for the determination of free cyanide, 6 ) . Place the flask under a good draft hood and cautiously add concentrated sulfuric acid until vigorous action ceases. Nom add 50 ml. more of sulfuric and heat the flask to boiling, adjusting the flame so that the ebullition does not become too violent. Discontinue heating the moment the precipitate of gold turns light brown in color and the sulfuric acid is absolutely clear. Decant the supernatant acid and treat the precipitate with 50 ml. more of concentrated sulfuric acid, heating to the boiling point to dissolve any silver sulfate that may be present. Decant this acid, leaving as little as possible in t h e flask. Carefully dilute the remaining acid with 200 ml. of distilled water and filter the contents onto a tared Gooch crucible lined with asbestos. Wash the precipitate with hot dilute sulfuric and then with hot wat’er until the washings are no longer acid. Dry and ignite at red heat until the brown sponge turns golden yellow. Cool to room temperature and weigh. T o compare the accuracy of this method with t h a t of t h e evaporation method, tests were made on standard samples prepared a s follows: c. P. gold weighed accurately to within 0.1 mg. was dissolved in a minimum amount of aqua regia and carefully evaporated
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INDUSTRIAL AND ENGIKEERING CHEMISTRY
to small volume three times t o drive off the excess nitric acid. This was diluted with water to about 250 ml. and sufficient c. P. potassium cyanide was dissolved in it to su ply the free cyanide content of the average gold plating bat’h Pabout 10 grams per liter, 3) upon dilution t o 1 liter. This solution was now carefully transferred to a I-liter volumetric flask and carefully diluted t o the mark with distilled water. T.4BLE I. ACCERACY O F blETHoDS Evaporation Sulfuric Sample Weight Method Difference Method G./1. G./1. MQ. G./1. 0.1048 -0.2 1 0,1050 0.1051 0.4999 -0 2 0.4998 2 0.5001 5.0044 -0.1 5.0044 3 5.0046 20.0099 -0.1 20.009s 4 20.0100
Av. -0.15
Difference Mg. f0.1 -0.3 -0.1 -0.2 A V . -0 13
Four samples prepared this may were analyzed by both
methods with the results given in Table I. This comparison shows that the sulfuric acid method is accurate for routine determinations of gold in cyanide plating solutions. I n actual laboratory practice the author has used this method with great success during the past year, his evaluation analyses closely checking with those of the chemists of submitting firms.
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The method will be found very convenient in control analyses, as from one sample the following determinations may be made: free cyanide, gold, silver if any (by precipitating silver in filtrate with hydrochloric acid and subtracting the known amount of silver added), and other base metals such as copper, nickel, and zinc, by analyzing the filtrate according t o standard methods.
Literature Cited (1) Bamford and Harris, “The Metallurgist’sManual,” p . 2 5 , London, Chapman and Hall, 1927. (2) Blum and Hogaboom, “Principles of Electroplating and Electroforming,” 2nd ed., p . 371, New York, McGraw-Hill Book Co., 1930. (3) Ibid., pp. 3656. ( 4 ) Fulton and Sharwood, “Manual of Fire Assaying,” 3rd ed., pp. 191-2, Kew York, McGraw-Hill Book Co., 1929. ( 5 ) Scott, TT. W., “Technical Methods of Metallurgical Analysis,” pp. 718-19, New York, D. Van Nostrand Co., 1933. (6) Treadwell and Hall, “Analytical Chemistry,” 5’01. 2, 7th ed., p. 606, New York, John Wiley & Sons Co., 1930. (7) Weisberg, L., private communication, 1934, RECEIVED August 6, 1938.
p-Hpdroxvphenylarsonic Acid as a Reagent for Titanium and Zirconium J
C. T. SI1IIPSOR’’ ASD G. C. CHANDLEE, The Pennsylvania State College, State College, Pa.
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EVERAL investigators have reported the value of certain arsonic acids as reagents for the gravimetric determination of zirconium (2, 4, 6 ) , thorium (4, tin (S), and iron (1). The need for a reagent that would give a convenient and satisfactory separation of titanium from the common elements, and particularly from iron, led to a further investigation of this field. p-Hydroxyphenylarsonic acid was found to be a very favorable reagent for titanium. I n the presence of dilute mineral acid it gives a n effective separation of titanium from iron and most other commonly occurring elements in one precipitation. It is also a n excellent reagent for zirconium. I n mineral acid solutions not stronger than 0.5 K it also gives a quantitative precipitation of tin, but the possibility of using it as a reagent for this element has not been investigated in detail.
tate filtering. After cooling to room temperature filter off the precipitate. Kith a good paper (No. 42 Whatman) and a filter cone one may employ suction advantageously. Wash the precipitate about five or six times with a wash liquor of dilute (0.25 A‘) hydrochloric or sulfuric acid containing about 0.5 gram of reagent per 100 cc. Rhen iron is present 1 or 2 grams of ammonium thiocyanate should also be added to each 100 cc. of this liquor. Finally wmh the precipitate two or three times with a dilute (2 per cent) aqueous solution of ammonium nitrate, and then ignite it in a porcelain crucible (with propped lid) at low temperature until all the carbon is burned off, then at the full heat of a Bunsen or Fisher burner until constant weight is attained, leaving a residue of titanium dioxide. The ignition must be carried out in an efficient fume hood.
An average deviation of 0 . i part per thousand was found in analyzing pure standard solutions of titanium by this method. Separation of Titanium from Mixtures
Determination of Titanium MATERIALS.The p-hydroxyphenylarsonic acid used in this
investigation was supplied by the Mallinckrodt Chemical Works and was suitable for use without further purification. A 4 er cent aqueous solution was found to be convenient for use. ure standard solutions of titanium sulfate were prepared and standardized by qccepted methods. All other reagents were of c. P. or equivalent grade. Dissolve the sample (containing not more than PROCEDURE. about 0.06 gram of titanium dioxide) in hydrochloric or sulfuric acid solution and remove interfering elements by appropriate means. The amount of acid present should be such that the solution will be approximately but not more than 0.60 N in hydrochloric or 1.80 N in sulfuric acid after the reagents have been added and the precipitation is complete. After adjusting the volume to about 200 cc., heat the solution to boiling and (after the addition of 2 to 3 grams of ammonium thiocyanate when iron is present) add 100 cc. of a 4 per cent aqueous solution of phydroxyphenylarsonic acid. Continue boiling gently for at least 15 minutes to coagulate the precipitate and thus facili-
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Present address, Rahm a n d H a a s Company, Bristol, Pa.
IKON A K D PHOSPHATE. A synthetic sample (containing 0.0636 gram of TiOz, 0.1392 gram of FezO3, and 0.071 gram of P z O ~~v-as ) analyzed by the above procedure for titanium, with a recovery of 0.0636 gram of titanium dioxide. Another sample, containing the same amount of titanium and iron but no phosphate, gave the same result. ALUMINUM, ZISC, COBaLT, KICKEL, BERYLLIUAf, AND BASIC CHRonirunr AKD MASGANESE. From a composite sample (containing 0.0521 gram Ti02,0.051 gram of A120310.063 gram of CrZO3, 0.079 gram of MnO. 0.081 gram of ZnO, 0.075 gram of COO,0.075 gram of K O , and 0.030 gram of BeO) 0.0521 gram of titanium dioxide was easilyseparated. From another such mixture containing 0.0636 gram of titanium dioxide this procedure returned 0.0636 gram. C a L c I u h i AND >1.4GNESI~>l. TKO samples containing, respectively, 0.0521 and 0.0636 gram of titanium dioxide with a mixture of 0.056 gram of calcium oxide and 0.040 gram of magnesium oxide were analyzed. The results were 0.0521 and 0.0636 gram of titanium dioxide. DICHROMATE, PERUANGANATE, L-RANYL, AKD V A N A D Y L IONS.
A composite sample (containing 0.0636 gram of TiOa,0.052 gram of Cr20,, 0.071 gram of MnO, 0.180 gram of V ~ O Sand , 0.286
