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different solubility relations compared with the normal phosphomolybdate, with respect to the usual washing solutions used in determining phosphorus. (3) Conditions are given for quantitatively precipitating vanadic acid when in solution alone, or accompanied b y a variety of other element;, b y means of ammonium phosphomolybdate. (4) In order t o determine quantitatively the vanadic acid so precipitated, ( a ) the possibility of freeing it from the accompanying molybdic acid was investigated. ( b ) Conditions for reducing i t without reducing the associated molybdic acid were developed. (c) A method for reducing it b y hydrogen, and other peroxides and titrating i t against permanganate was elaborated. ( 5 ) The method (c) was applied to a variety of steels, t o iron ores, manganese ores, and t o synthetic mixtures, in all-of which the vanadium was determined with great accuracy. BUREAU OF STANDARDS,
WASHINGTON. D. C.
A NEW METHOD FOR THE DETERMINATION OF VANADIUM; AN EXPLANATION. BY J. R. CAIN AND
D. J. DEMOREST.
Received January 25, 1912.
The discrepancy in results obtained b y us when using manganese dioxide, as mentioned in the paper on “ A New Method for the Determination of Vanadium,” page 249, 1 e d . u ~t o seek the cause. We exchanged samples of manganese dioxide and each found t h a t the other’s reagent behaved as stated in our respective papers. However, it was noted by Mr. Cain t h a t Mr. Demorest’s dioxide, which oxidized differentially, was much coarser than the manganese dioxide which the former had used, and which oxidized both the lower oxides of vanadium and iron. Upon grinding the coarse manganese dioxide very fine he found that it oxidized both iron and vanadium oxides as his own preparation had done. On the other hand, Mr. Demorest succeeded in separating a coarse portion from the manganese dioxide used b y Mr. Cain which oxidized differentially. Thus, the discrepancy is evidently due t o a difference, in the two cases, of the velocities of the reactions : (I) V,O, MnO, = MnO V,O, ( 2 ) FeO MnO, = Fe,O, MnO
+ +
+
+
Mr. Demorest’s reagent had a degree of fineness such t h a t in the brief period of treatment the velocity of reaction ( I ) was inappreciable and reaction ( 2 ) was completed; whereas with material of the fineness used b y Mr. Cain both reactions went to completion. The securing of such different results merely by changing the size of the grain of the reacting solid seems a matter worthy of further investigation.
April,
1912
THE RAPID DETERMINATION OF VANADIUM IN STEEL. Ry FRANK GARRATT. Received Dec. 20, 1911.
The writer has for some time used the following modification of Johnson’s method‘ for determining vanadium in steel. Johnson’s procedure is adhered t o in all respects, except that the oxidation of the chromium and vanadium in hot, dilute sulfuric acid with potassium permanganate is omitted. With this omission the method is extremely simple and, briefly, is as follows: Dissolve 2 grams of steel in about 5 0 ’cc. of dilute sulfuric acid; when solution is complete, oxidize the iron, and tungsten if present, b y adding about 5 cc, of concentrated nitric acid to the hot solution. Boil until nitrous fumes are expelled, or in the case of tungsten steels, until the separated tungstic acid is of a pure yellow color. Dilute the solution t o about 150 cc., filter if tungstic acid is present, and cool to room temperature. Dilute t o about 350 cc. in a suitable beaker, add a little ferrous sulfate solution, and obtain the old rose3hade with permanganate. Add the potassium ferricyanide indicator, and titrate a t once with standard ferrous ammonium sulfate solution for the vanadium value. As pointed out b y Johnson, blanks must be run on steels of similar composition, and consistent endpoints adhered to in the titrations. As outlined above, the determination, even in the case of tungsten steels, may be completed in 2 0 minutes. If tungsten is absent the filtration may, of course, be omitted, thus shortening the operation. If chromium is not t o be determined, there is no reason, of course, for its oxidation. As a matter of fact, without this oxidation the blanks seem t o be smaller and more uniform. Carbonaceous matter does not seem t o interfere in the subsequent titration. The writer thinks that Johnson’s scheme of adding the ferricyanide indicator t o the solution t o be titrated, gives the most practical method yet offered for the technical determination of vanadium in steel. Blair’s method,* with proper precautions, leaves nothing t o be desired in the way of accuracy, but it consumes too much time and care for a busy works laboratory. Cain’s methods is, of course, much shorter but i t does not offer the advantages in regard t o simplicity and rapidity that Johnson’s method possesses. Blair’s and Cain’s methods may well be considered desirable for standardizations and umpire determinations, but Johnson’s method seems to be the one for routine work. If the procedure described herewith is adopted, the determination of vanadium is much simplified, and takes its place with the rapid methods for determining carbon, phosphorus. manganese, etc. Certainly the laboratory doing routine work on vanadium steels need not worry about its determination. The following table gives some results obtained b y this rapid modification. Some of the steels contained no chromium, while others varied from 0.906.00 per cent. The presence of chromium offers 1
“Chemical Analysis of Special Steels, etc
J. A m . Chem. Soc , SO, 1229. 3 THIS JOURNAL, 3, 476. 2
,”
p. 8.
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1912
T H E J O C R N A L OF I L V D C S T R I A L AiYD EIVGI,VEERI-VG C H E M I S T R Y .
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to determine that i t really is platinum, and to reveal the presence of other members of the platinum group. In t,he regular course of assaying for the precious metals, gold is parted from silver by dissolving the Per cent. V. silver in nitric acid. If platinum be present in small Per cent. V Difference amounts only, it will readily go into solution in the by rapid B y Blair's Added as by No. method. NHIVOB. rapid method method. nitric acid. If now a limited amount of hydrogen 1 0.14 .... 0.15 +0.01 sulphide be added to the solution from parting, any 2 0.25 ,... none 0.25 platinum present will be precipitated as sulphide, 3 0.47 ,... 50.02 0.45 along with some silver sulphide. On filtering off 4 0.64 ,... +0.01 0.65 5 0.89 ,... -0.01 0.88 the precipitate (which generally is sufficiently washed 6 1.13 .... none 1.13 by the operations necessary to transfer i t from the 7 1.27 .... +0.02 1.29 8 1.31 .... 1.31 none precipitating dish t o the filter), the moist filter is 9 1.37 .... 1.37 nonc transferred to a small porcelain crucible, dried a t a 10 4.67 .... 4.68 +0.01 low heat, and burned off b y gentle ignition. This 11 . . 0.15 0.16 +0.01 12 .... 0.50 0.50 none transforms the sulphide precipitate into a metallic 13 .... 1 .oo -0.01 0.99 sponge, which is wrapped in a small piece of thin lead 14 .... 1 .oo 0.98 -0.02 foil and cupelled. The resulting bead is then parted I:IRTH STERLIXG STEEL COMPANY. in strong sulphuric acid, when the platinum will be MCKEEWORT,P A . left as a dark residue, generally.collected in spongy form, even when minute in quantity. This sponge, after reboiling in fresh acid, if necessary, is suitably washed by decantation, annealed, and weighed. THE DIRECT DETERMINATION OF SMALL AMOUNTS O F PLATINUM I N ORES AND BULLION.' Generally, the final metal speaks for itself as being platinum, but, if there should be any doubt, it may By FREDERIC P. DEWEY. By the old method of determining platinum in ores be dissolved in a drop or two of aqua regia and gently and bullion, the silver-alloy first obtained in the regu- evaporated. The solution obtained may be tested lar course of assay is parted in strong sulphuric acid with potassium iodide, or a few small crystals of and the residual metal weighed. This is realloyed ammonium chloride may be added, when the charwith silver b y a second cupellation and parted in acteristic precipitate will show itself. As a further nitric acid, the residual metal being again weighed. test this may be filtered off and gently ignited to Any difference shown between the two weighings is produce spongy platinum. ,If the amount of the assumed t o be, and is called, platinum. Sometimes final metal be considerable, the platinum may be i t is so, and if any considerable amount of platinum determined by the double-chloride method. Any be present, there will be a decided difference between decided difference shown would indicate the presence the two weighings; but a slight difference is no real of other members of the platinum group, for which evidence whatever of the presence of platinum. On direct test could then be made. For precipitating the platinum and the necessary the other hand, the second weight may equal or possilve'r from the parting-solution, a very dilute solution sibly exceed the first, even when traces of platinum are present. Again, other members of the platinum of hydrogen sulphide should be used. One part of group may go into solution in nitric acid more or a strong solution should be diluted t o from 10-20 less. If present, these would be called platinum parts with water. If the solution of silver nitrate be and escape detection. The method does not provide strongly acid, it should be largely diluted, or i t may any direct tests whatever as to the presence or ab- first be evaporated and then diluted. The very sence of platinum. I t is often indecisive and some- dilute hydrogen sulphide solution should be added times gives erroneous .results. I t is, therefore, quite. very slowly to the silver nitrate solution with constknt stirring. The solution is, of course, a t once unsatisfactory. darkened, but there should be no immediate separaBeing called upon many- times to determine platinum, tion of a visible precipitate The solution should be in a wide variety of materials, particularly when present stirred occasionally, and in about 2 hrs. flocks of in very small amounts, I have realized the disadvanprecipitate should appear. I t may be filtered in tages and defects of this old method. from 3-4 hrs., but i t is a good plan t o let i t stand In an article on the solubility of gold in nitric acid,z over night if possible. I have briefly outlined a method of gathering a little The amount of hydrogen sulphide required depends, gold out of a solution containing much silver, which of course, upon the amount of platinum present. If furnishes the basis of an excellent method for the this should be roughly known or suspected, the amount direct and absolute determination of small amounts used should generally be enough to precipitate the of platinum and har che added advantage that the platinum and from three t o five times as .much silver. metal weighed may be subjected to suitable tests, On an entirely unknown ore. I should a t first use I Presented a t the Sew York meeting of the American Institute of cc. of strong hydrogen sulphide solution diluted to Mining Engineers, February, 1912. and puhlished in the Bulletin of the 1 5 cc., and reserve the filtrate from the sulphides for American Institute of Mining Engineers, April, 1912,Serial X o . 64. retreatment. if necessary. On an unknown bullion J . Am. Chew. SOC., 31, 323 (1910).
no complications, however, simply increasing the blank t o be deducted from the ferrous ammonium sulfate used in the final titration.
* _
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