698
THE JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Vol. 13, No. 8
A Simple Method for the Determination of Vanadium in Ores and Metallurgical Products By R. B. Schaal FIRTH-STERLING STEEL C O . ,
So many methods have been proposed for the determination of vanadium, that some excuse seems required for the publication of further material on this subject. This excuse is more than supplied by results returned to us on the analysis of a standard sample of high speed steel, which was submitted to three commercial and five works laboratories. The true vanadium content of the steel was 1.53 per cent. Results obtained by these laboratories varied between 0.86 and 1.74 per cent. Previous to this time a modification of Johnson's method had been used at this works for the determination, but during the investigation of the standard sample we became convinced that our results were uniformly low, as much as 0.10 per cent on a 1.50 per cent sample. The present method is believed to meet all the requirements of accuracy, speed, ease of execution, and economy so necessary for routine and general use. THEORETICAL AND PRACTICAL CONSIDERATIONS The method depends upon the reduction of vanadic acid, by prolonged boiling with strong hydrochloric acid, to the tetravalent condition, and subsequent reoxidation with a suitable solution of potassium permanganate to the pentavalent state. The reactions involved are well known, and may be stated as follows: ViOs 2 HCl = V2Or HzO Clz (1) The reaction is completely displaced to the right by the removal of one of the reaction products, the free chlorine, by boiling.
+
5Vs04
+
+
+ 2KMn04 + 6HCl = 5v206 + 2KC1 + 2MnC1~
-t 3Hz0 (2) This reaction is found to run to completion with a sharp end-point, in a nearly neutral solution containing a suitable excess of ammonium phosphate, and admits of the presence of large amounts of iron, chromium, molybdenum, cobalt, nickel, uranium, titanium or zirconium, besides the amounta of manganese usually present in all samples. The color of ferric chloride is destroyed by the ammonium phosphate. Chromium, because of its deep green color, tends to obscure the end-Doint. This fact offers no difficulty to the chemist familiar with the determination of chromium by the ferrous sulfate-permanganate method, the end-point appearing as faint old rose reflections through the green. The use of an ordinary Mazda lamp behind a white screen clarifies the end-point to a remarkable degree, and the use of this device is recommended for all samples containing 3 per cent or more of chromium. Molybdenum has been present in tests to the extent of 10 per cent, and apparently interferes in no appreciable manner. As the reduction of the vanadium by hydrochloric acid is selective with respect to molybdenum, this element remains in the oxidized state and is not affected by permanganate under the conditions obtaining in the titration. Cobalt and nickel have been added in amounts up to 5 per cent of each, the only effect being the production of a slight green color. Elements whose phosphates are insoluble, or partly so, under the given conditions, notably uranium, titanium, .and zirconium, cloud the solution, but do not otherwise interfere. If present in appreciable amounts the precipitates may be removed by filtration. 1 Received
March 18, 1921.
M C K E E S P O R T , PBNNSYLVANIA
By far the most important effect of the ammonium phosphate is that of converting any excess hydrochloric acid present, above the amount actually needed for the completion of the reaction, into the less highly ionized phosphoric acid, and thus minimizing the danger of action between the excess acid and the potassium permanganate. It is absolutely necessary that the directions for the final acidification of the solution be rigidly adhered to, if uniform results are to be expected. It should also be pointed out that excessive cold slows the reaction unnecessarily. If conducted a t 20" C., however, the reaction proceeds with a rapidity which leaves nothing to be desired. The end-point does not disappear, as is the case in titrating cold sulfuric acid solutions, so slowly as to leave doubt as to the precise end of the reaction, but becomes permanent a t once. SOLUTION OF THE SAMPLE STEEL-weigh 2 g. of drillings or millings into a 500-cc. Erlenmeyer flask, cover with 60 cc. 1 : 1 hydrochloric acid, and heat until all action ceases. Rkmove from the hot plate. add 5 cc. strong nitric acid, and boil down to 10 cc. ORES-weigh 1 to 5 g., depending upon the vanadium content, into a 600-cc. beaker, digest with 60 cc. strong hydrochloric acid until the soluble portion is dissolved, add 5 CC. strong nitric acid and 2 cc. hydrofluoric acid, and e v a p orate to dryness. FERROVANADIUM-weigh Out 0.5 6. Of the 100-mesh powder into a 600-cc. beaker, cover with a watch glass, and add carefully 5 to 10 cc. strong nitric acid. Add 2 cc. of hydrofluoric acid, and heat. When violent action has ceased, add 40 cc. strong hydrochloric acid, and evaporate to dryness. REDUCTION OF THE VANADIUM To the sample prepared as in the foregoing paragraph, add 40 cc. strong hydrochloric acid, and evaporate to 10 cc. The nitric acid is thus completely expelled, and the vanadium partly reduced. Add 40 cc. more of the strong hydrochloric acid, and again evaporate to 10 cc. The vanadium is completely reduced, and the acidity greatly lessened. Add 60 cc. distilled water, and filter, using suction, through a 0.5411. crushed, ashless, paper plug. Wash five times, using 15 cc. of cold distilled water for each washing. Any tungsten or tantalum which the sample contained is now removed. Transfer the clear filtrate to the original container, and add 60 cc. of a 15 per cent solution of ammonium phosphate. Add ammonia drop by drop until a bulky precipitate of ferricphosphate appears. Add, a few drops a t a time, 1 :1 hydrochloric acid until the precipitate just clears; then add 2 cc.inexcess. In the case of ferrovanadium, where the color of large amounts of vanadium in the nearly neutral solution appears as a very deep orange color, reduce the color by adding 10 cc. 1 : 1 sulfuric acid. If the color still appears deep enough to obscure the end-point, add 10 cc. more of the ammonium phosphate and 10 cc. more 1 : 1 sulfuric acid. Prepare a beaker (600-cc.) by etching a line at the 300-cc. .mark. Just prior to titration transfer the solution to this vessel, and dilute to the mark. TITRATION Run in the standard potassium permanganate until two drops produce the first permanent pink. Blanks, made up to nnnroximate as nearlv as nossible the material under ._ ~--Lr--
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T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Aug., 1921
699
should be exactly 50 cc. If necessary, adjust the solution and re-standardize. One cc. of this solution is equal to exactly 0.002 g. of vanadium. The author has little confidence in the so-called “practical test” method of standardization, except as i t is used in conjunction with theoretical values. If results and theory do not agree, something, i t would seem, is decidedly wrong STANDARD PERMANGANATE SOLUTION-T~~ &andard Potas- with either the process or the standard used. We believe sium permanganate solution is 0.0392156 N and is n ~ &UP the standardization with sodium oxalate establishes with as follows: certainty the vanadium value of the permanganate. We are, however, careful to run, parallel with each series of Potassium permanganate.. ......................... 2.5 g. Sodlum or potassium hydroxide. ..................... 5.0 g. tests, a standard sample, as a check upon the work. 2000 CC. Distilled water to m a k e . . .......................... It may be said in conclusion, that a rigid comparison of To standardize this solution, weigh 0.1314 g. of Bureau the new method with that of Blair, as modified by the Amerof Standards sodium oxalate into a 400-cc. beaker, and cover ican Vanadium C O . ,with ~ Cain’s phosphomolybdate method,. with 200 cc. distilled water at 80” C. Add 10 cc. 1 : 1 SUI- and with the method of the Bureau of Standards, bringp furic acid, and titrate slowly with the permanganate solution out an excellent agreement. I n the particular case of t h e until the further addition of a single drop produces a faint high-speed steel mentioned in the introduction the new method permanent pink. Match this color in another beaker con- gives 1.53 to 1.55 per cent vanadium, and for the Governtaining the same amounts of water and acid. Deduct the ment No. 50 Standard (0.756 per cent), 0.75 to 0.77 even, amount of permanganate needed to produce the end-point with ordinary care. The blank, in these instances, was, from that used in the titration of the oxalate. The result found to be quite high, from 1.9 to 2.0 cc.
examination, are to be carried through parallel with each series of tests, and the amount of permanganate required by the blank is to be deducted from the amount required to titrate each sample. Blanks on some materials, especially those containing chromium, will be quite large, but they are accurate, and may be deducted with confidence.
The Gold Number of Commercial gel at ins'^"'^ By Felix A. Elliott and S. E. Sheppard EASTMAN KODAKCo., ROCHSSTER, N. Y .
As piirt of an inquiry into the physical and chemical properties of gelatins i t was of interest to determine the extent to which gelatins could be clmsified by the variation of their gold numbers. Zsigmondy4 has defined the gold number of colloids as the number of milligrams of colloid necessary just to prevent the precipitation of 10 cc. of standard gold solution by 1 cc. of 10 per cent sodium chloride solution. L
PREPARATION OF GOLDHYDROSOL A well-prepared gold solution should not appear turbid in reflected or transmitted light and should appear deep red in a thickness of 6 to 7 cm. It will withstand heating to boiling without precipitation. A turbidity noticed in direct reflected light is caused by particles larger than the average and indicates an inhomogeneity of the solution. Under Ibe ultramicroscope a well-prepared solution exhibits a lively Brownian movement. The presence of an unresolvable hazy background indicates a considerable number of amicroscopic particles generally tolerated, but large yellow flashes in any great number across the field condemn the solution, as these are caused by the larger, undesirable gold particles. Many methods are to be found in the literature on the preparation of gold solutions, but Zsigmondy’s is very simple and satisfactory for this work. Very pure water is obtained by distilling water twice in a block tin stdl with a block tin Coil condenser. MTater with a conductivity of 1.2 X was easily obtained and was satisfactory when used. The next precaution is to make all glassware to be used in the preparation chemically as well as physically clean. Zsigmondy insists on Jena resistance glass, but four Of the leading American makes were used when properly cleaned, with excellent results. Three solutions are necessary: (1) 6 g. AuCL.HC1.Received April 8, 1921. Published as Communication No. 118 from the Research Laboratory of the Eastman Kodak Company. 8 This work was done in October 1917 and discontinued on account of the wux. 4 Ann., a01 (1898),29. 1
3H20 dissolved and made up to one liter with conductivity water; (2) one liter of 0.18 N K2C03 solution; and (3) a 0 . 3 per cent solution of formaldehyde. According to Zsigmondy, 120 cc. of water prepared as above is heated and 2.5 cc. of gold chloride solution are added, then 3.5 cc. KzCO3 solution. This is stirred to insure uniformity and heated to 100” C. It is removed from the heater and 3 to 5 cc. of the formaldehyde solution are added with lively stirring. A much smaller amount of formaldehyde solution was found sufficient. This had been observed by L. W. Eberlin in this laboratory in 1914, but it was not known whether this variation was due to uncertainty as to the strength of the formaldehyde. The more recent work has shown that the amount necessary is a function of the rate of addition (roughly inversely proportional). If the formaldehyde is added (0.5 per cent solution) a drop a t a time and well stirred after each addition, this procedure followed untiI the solution begins to show a faint red tinge, and the additions now made only after a further color change is no longer produced by the previous drop, a deep red and extremely clear solution will be obtained. This solution was made up in lots of 2 liters to insure maximum uniformity throughout many tests, and about 2 CC. of 0.3 per cent formaldehyde were used. PREPARATION OF GELATIN SOLUTIONS So-called hard, medium, and softgelatins were tested. ’rhe solutions were all made up with conductivity water a t 500 c., each being heated 4 hrs. to complete equilibrium. After slow cooling to 200 these so~utionswere diluted to 0.001 per cent. A series in four steps was formed and the gold hydrosol added, followedbythe sodium chlorge solution. I n Table 1 are shown representative data obtained with seventeen different commercial gelatins of the three classes on the market, soft, medium, and hard. The data for the five samplesquoted aFe representative of the different classes. The two color changes under each concentration are, first, the immediate color and, second, that observed after 24 hrs.. 1
See Scott,
“
Standard Methods of Chemical Analysis,” p . 273.
