REFERENCES ON DETERMINATION OF VANADIUM:

DEMOREST, J. Ind. Eng. Chem., 4 (Apr., 1912).

JOHNSON, "Chemical Analysis of Special Steels, Steel Making Alloys and Graphites."

CRITES, J. Ind. Eng. Chem., 3, 574.

CAIN and HOSTETTER, J. Am. Chem. Soc., 4, 250.

U. S. Bureau of Standards, Reprint 161.

GOOCH and GILBERT, Z. anorg. Chem., 32, 175 (gravimetric).

WARD, Chem. Met. Eng., 23(1920), 28.

SCHALL, J. Ind. Eng. Chem., 13, 698-699 (vanadium in ores).

KELLEY, and others, J. Ind. Eng. Chem., 13, 939-4 (electrometric).
U. S. Steel Corporation, "Methods for Analysis of Ferro-alloys."

CHAPTER XI

DETERMINATION OF CHROMIUM IN STEELS AND ALLOYS

Chromium is present in steels largely as carbide of chromium unless the chromium is in large amount. Usually the chromium is not much over 1 per cent of the steel, although in special steels, such as high-speed steel, it may go up to 5 per cent or more. Other alloys containing large amounts of chromium are the resistance alloys, such as nichrome.

The determination of chromium is almost always accomplished volumetrically. Chromium exists in solutions as the trivalent and hexavalent compounds. The measurement of the amount of chromium in solution is very accurately and easily accomplished by determining the amount of a standard reducing solution, usually ferrous sulfate, which is required to reduce the chromium from hexa- to trivalent condition.

Process for Chrome Steels.-Dissolve 2 grams of the drillings in 60 c.c. of a solution containing 35 c.c. of water, 8 c.c. of H2SO4 and 2 c.c. of phosphoric acid, heat until effervescence nearly ceases, add 5 c.c. of HNO3 and boil until solution is complete and fumes of oxides of nitrogen are expelled. If any residue of WO3 appears, filter it and wash thoroughly with dilute nitric acid. Add silver nitrate solution containing 0.2 gram of silver nitrate for each per cent of chromium present, dilute to 300 c.c., heat to boiling and add 8 c.c. of a 15 per cent ammonium persulfate solution. When the permanganate color is well developed add 2 c.c. of 1:1 HCl and boil until the pink color disappears and the persulfate is decomposed, usually about 10 minutes. (Instead of oxidizing with persulfate in the presence of silver nitrate, it is satisfactory to add a 4 per cent KMnO, solution to the boiling solution until the permanganate color persists on boiling five minutes and MnO2 precipitates. Then add 2 c.c. of 1:1 HCI and boil until the precipitate is dissolved and all chlorine expelled.) Cool, dilute to 400 c.c. and titrate the chromium as follows: Add decinormal ferrous sulfate solution until all the yellow tints

disappear, indicating complete reduction of chromic and vanadic acids. Add 10 c.c. more of ferrous sulfate and then titrate with decinormal permanganate until a faint pink is obtained which persists for one minute with continued stirring. If vanadium is present, the end point comes slowly, owing to the slow reoxidation of vanadium. In this case it is best to add the permanganate until a strong pink color is obtained, then nearly to discharge the pink by carefully adding decinormal sodium arsenite.

After the end of the titration of chromium the vanadium may be determined by the addition of ferrous sulfate and proceeding as under vanadium. A blank determination should be run to determine the amount of permanganate required to give a visible end point in the solution. If the electrometric end point is used, the end of the titration is sharper. (See page 252.)

The Analysis of Ferrochrome.-Ferrochromium is insoluble in acid, hence must be fused. Proceed as follows: Fuse 0.50 gram of the powdered sample with 7 grams of sodium peroxide in a nickel crucible, maintaining the fusion liquid for several minutes. Cool and disintegrate in a beaker with 300 c.c. of hot water until no hard lumps remain. Acidify with 50 c.c. of 1:1 H2SO4, add 2 c.c. of 1:1 HCl and boil until all permanganic acid is destroyed and the liberated chlorine expelled, cool and add decinormal ferrous sulfate until the yellow color of chromic acid is completely discharged and 10 c.c. in excess. Titrate the excess of ferrous sulfate with decinormal permanganate until a pink color is obtained which persists for one minute with stirring.

Add to a beaker containing 300 c.c. of water and 50 c.c. of 1:1 H2SO4 the same amount of ferrous sulfate as used in the preceding titration, and titrate. The difference between the permanganate used in the two titrations is the permanganate equivalent to the chromium present.

If the permanganate used is exactly decinormal, the chromium equivalent to 1 c.c. of permanganate is 0.001733. If the iron value of the permanganate has been obtained by standardization against iron, as directed on page 37, the chromium value of the permanganate per cubic centimeter is obtained by multiplying the iron value by 0.310.

The addition of ferrous sulfate reduces both vanadic and chromic acids, but when the reduced solution is titrated with per

manganate the end point comes after the vanadium has been reoxidized to its pentavalent form, hence, in effect, the vanadium has no influence on the amount of ferrous sulfate and permanganate required for the titration.

Notes on the Process.-The phosphoric acid is used to hold tungsten in solution; it also decreases the depth of the color in the solution. If chromium is present in the sample in very small amounts, at least 5 grams of sample should be used and the ether method of separating chromium, vanadium, etc. from iron used, as directed on page 129. The same conditions of solution are then produced as directed above and the chromium titrated as usual.

Instead of using ammonium persulfate or potassium permanganate for oxidizing chromium to chromic acid, sodium bismuthate may be used in place of the permanganate and the process carried on exactly the same. REFERENCES:

KELLEY and WILEY, J. Ind. Eng. Chem., 13, 1503-1504 (electrometric).

BARBA, The Iron Age, 52, 153.

Proc. Am. Soc. Test. Mat., 20, I, 647-654 (method for ores).

TOWNSEND, "Forging and Heat Treating 8," no. 7 (bibliography).
ARNOLD and IBBOTSON, "Steel Works Analysis," p. 161.

MCFARLANE, "Laboratory Notes on Iron and Steel Analysis," p. 211.
JOHNSON, "Chemical Analysis of Special Steels, Steel-making Alloys,
Etc.," p. 59.

BLAIR, "The Chemical Analysis of Iron," p. 217.

MCKENNA, Proc. Eng. Soc. Western Pa., 16, 119.

WALTER, Chem. Ztg., 34, 2.

ZINBERG, Stahl u. Eisen, 28, 1819.

BARTONEC, Chem. Zentr. (1909), 2017 (gravimetric and volumetric).

CHAPTER XII

THE DETERMINATION OF TUNGSTEN AND SILICON IN STEEL

Tungsten may be found in steel in amounts up to 25 per cent and is generally accompanied by chromium up to as high as 6 per cent.

When a steel containing tungsten is dissolved in a mixture of nitric and hydrochloric acids and the solution is evaporated to dryness and the residue treated with hydrochloric acid, the tungsten is left insoluble as WO3 with the SiO2. In order to render the WO, entirely insoluble, more than one evaporation to dryness is necessary. When the residue is treated with sulfuric and hydrofluoric acids the silica is driven off while the tungstic anhydride is left behind. The tungstic anhydride is always contaminated with ferric oxide and must be purified for perfect results. The chromium in the filtrate is oxidized to chromic acid and titrated with ferrous sulfate.

The tungsten is usually and best determined gravimetrically by weighing as WO3, but, since the WO, is an acid anhydride, it may be determined volumetrically by titrating with a standard alkali solution.

Tungsten steels are very hard and difficult to drill. If they are annealed at 750°C. for a couple of hours, they will become soft enough to drill.

Process of Analysis.-Place 2 grams of the drillings in a 200c.c. casserole and add 40 c.c. of hydrochloric acid (sp. gr. 1.19) and heat nearly to boiling. When action ceases, add from time to time a few drops of nitric acid until the steel is entirely decomposed. In this way the sample is dissolved without the separation of WO3. When decomposition is complete add 5 c.c. HNO3, evaporate to dryness, dissolve the residue with 60 c.c. of 1:1 HCl, heating until all iron is dissolved, add 50 c.c. of water and heat for a few minutes longer, then filter through an 11-cm. filter paper. Again evaporate to dryness, dissolve and filter. Wash thoroughly with 1:10 HCl until the precipitate is free from iron. Chromium and vanadium may be determined in the filtrate.