denum and precipitates all the copper and eliminates the arsenic. Filter through asbestos. Prepare the Jones reductor as shown on page 39, except that the tip of the reductor should be lengthened so as to reach to the bottom of the flask, put in 2 c.c. of the ferric sulfate-phosphate solution for each 0.01 gram of molybdenum supposed to be present and sufficient water to cover the end of the reductor tube.

The reductor should be filled with 2 per cent H2SO4 before it is used to reduce the molybdenum.

Again add 2 grams of zinc to the sulfuric acid solution of the molybdenum, heat for five minutes, then pour the solution into the reductor, using sufficient suction to allow 20 c.c. to pass through the reductor per minute. When all the molybdenum solution has been poured into the reductor, wash the beaker with hot water and, finally, pass through the reductor 200 c.c. of warm 2 per cent H2SO4. At no time must the reductor be allowed to become empty so that air can suck into the flask.

The reduced molybdenum ((Mo2(SO4)3) is a clear green in color, but as soon as it comes into contact with the ferric solution it changes to red, owing to oxidation by ferric iron with corresponding reduction of the iron. Titrate immediately with a standard permanganate solution until a faint pink is obtained.

If a decinormal solution is used, each cubic centimeter will titrate 0.0032 gram of molybdenum; if the iron value of the permanganate is known, each cubic centimeter will titrate molybdenum equal to the iron value multiplied by 0.5748.

Ferric Sulfate-phosphate Solution.-Dissolve 100 grams ferric sulfate, 150 c.c. phosphoric acid (1.75 sp. gr.) and 20 c.c. sulfuric acid (1:1) in 830 c.c. water.

Notes on the Process.-The residue left after molybdenum sulfide is dissolved may contain some molybdenum. Test it as follows: Digest the paper and residue with 20 c.c. HNO3, 10 c.c. H2SO4, and 5 grams of sodium chlorate. Heat until the solution is clear, boil to dense fumes of SO3, and cool. Add 20 c.c. of 1:5 HCl and 10 c.c. of 1:1 H2SO4, 5 c.c. of 5 per cent KCNS and 10 c.c. of 25 per cent SnCl2 solution. If molybdenum is present, the solution will become red, the depth of red color depending upon the amount of molybdenum present. The amount of molybdenum can be determined by comparison against standard. solution, and correction made.

The zinc used in the volumetric process always contains some iron which titrates as molybdenum. Hence a blank determination must always be made. The permanganate should be standardized against. iron as directed on page 37, and also against a sample containing a known amount of molybdenum. The volumetric method depends upon reducing the molybdenum by zinc under carefully controlled conditions. The analyst should run several tests to find just how rapidly the solution may be run through the reductor and complete reduction be attained. The amalgamated zinc should be of 20-mesh size, amalgamated with 1⁄2 gram of mercury to 150 grams of zinc and should contain less than 0.01 per cent iron. After having been used for forty or fifty determinations, the zinc should be renewed. The reduced molybdenum is oxidized by contact with air, hence no air should be drawn through the reductor and the reduced solution must be titrated immediately.

When blanks are properly made and care is used in the volumetric determination, results should be accurate to 0.03 per cent.

The use of the ferric phosphate solution in the reductor flask makes the end point sharper and reduces the danger of oxidation of the solution upon exposure to the air, since the ferric iron oxidizes molybdenum, producing ferrous iron which is less easily oxidized by air. The titration by permanganate really consists, then, in titrating divalent iron which has been quantitatively produced by reduction with trivalent molybdenum. The reactions are: 3Fe2(SO4)3 + MO2(SO4)3 + 8H2O= 6FeSO4+2H2M0O4 + 6H2SO4. The reduced iron is oxidized by permanganate by the well-known reaction.

The gravimetric determination of molybdenum as lead molybdate is a very accurate and reliable method. It is not interfered with by large amounts of salts. The molybdate can be precipitated in faintly acid solutions free from impurities in the presence of copper, cobalt, nickel, zinc, manganese, magnesium and mercury, barium, strontium, uranium, arsenic, cadmium and aluminium. Cobalt, vanadium and tungsten interfere but are separated from the molybdenum by hydrogen sulfide.

Process for Ferromolybdenum.-Dissolve 12 gram of the finely crushed sample with 10 c.c. of 1:3 HNO3, 10 c.c. of 1:1 H2SO4 and a few drops of HF. When solution is complete, evaporate to fumes of SO3. Cool, add 50 c.c. of water, heat until solution is complete, cool and nearly neutralize with ammonia, but not until the solution takes on a red tint. Heat nearly to boiling and pour very slowly and with vigorous stirring into 75 c.c. of hot ammonium hydroxide. Wash the beaker in which

the solution was made with dilute ammonia, transferring the washings to the main solution. Add paper pulp obtained by macerating two 9-cm. papers, stir well and filter on an 11-cm. filter paper. Wash thoroughly with hot water, wash the precipitate back into the beaker, dissolve in a slight excess of H2SO4, nearly neutralize with ammonia and again pour slowly and carefully into 75 c.c. of 15 per cent ammonia nearly boiling. Filter and wash as before, combine the two filtrates in a 500-c.c. beaker, add 3 grams of tartaric acid and pass a rapid stream of H2S through the warm solution. The solution becomes a deep red, owing to the formation of thiomolybdate. The small amount of sulfides which form is filtered and washed thoroughly with H2S water.

Warm the solution and add 1:1 H2SO4 until the solution becomes slightly acid. This point is marked by the cessation of effervescence and the disappearance of the red color. Allow the molybdenum sulfide to settle, filter and wash with hydrogen sulfide water until all salts are removed. The water should be slightly acid with H2SO4.

The filtrate from the MoS, contains some molybdenum. Add 15 c.c. of HNO3 and 5 c.c. of H2SO4, evaporate until dense fumes of SO3 are obtained, cool, add 10 c.c. more HNO3 and again. evaporate to fumes and the removal of most of the H2SO4. This destroys all organic matter. Cool, dissolve in 50 c.c. of water, add 2 grams of tartaric acid and ammonia until alkaline and 10 c.c. in excess, warm and saturate it with H2S. Filter any precipitate which is formed, acidify the filtrate with 1:1 H2SO4 and filter the molybdenum sulfide as above.

Finish the analysis by either volumetric or gravimetric method as described above, except that more sodium chlorate will be needed to oxidize the molybdenum sulfide.

Process for Ores.-Proceed exactly as directed for ferromolybdenum. If vanadium and tungsten are absent, the process may be greatly shortened by omitting the hydrogen sulfide precipitation, but it is always safest to assume that they are present.

Note. The tartaric acid is used to prevent vanadium and tungsten from precipitating as sulfide with the molybdenum.

REFERENCES:

BONARDI and BARRETT, Tech. Paper 230, U. S. Bureau of Mines.
PETTY, The Chemist-Analyst, no. 30 (1920).

CAMP and MARDEN, J. Ind. Eng. Chem., 12, 998.

U. S. Steel Corporation, "Methods for the Analysis of Alloy Steels."
RANDALL, Am. J. Sci., 24 (1907), 313.

CHAPTER XIV

THE DETERMINATION OF TITANIUM

Titanium may be present in steels up to a few tenths per cent. It is generally present in pig iron in small amounts. In ferrotitanium there may be as high as 75 per cent present. Ores contain from nearly zero up to a good many per cent of titanium.

In steels the titanium is present as solid solution in iron and as crystals of titanium nitride and titanium cyanamide. The titanium present in solid solution is soluble in acids, the rest is insoluble. Ores contain titanium chiefly as the minerals rutile (TiO2), ilmenite (FeTiO3), titanite (CaTiSiO5) and other less important minerals.

Titanium may be determined gravimetrically by weighing as TiO2, or volumetrically by reduction with zine to trivalent condition followed by titration with permanganate. When present in amounts below 0.5 per cent, it is best determined colorimetrically. This is done by adding hydrogen peroxide to the 5 per cent sulfuric acid solution and producing a yellow color which is compared with a standard solution treated in the same way. The peroxide oxidizes the titanium to the hexavalent

form.

Titanium may be separated from iron when the iron is divalent by boiling the dilute, slightly acid solution, when the titanium precipitates out as titanic acid. Or the titanium may be separated from the iron when to the acid solution containing the iron in the ferrous condition is added an excess of ammonia containing enough alkali cyanide to form ferrocyanide with the iron. The ferrocyanide stays in solution, while the titanium precipitates as Ti(OH)4. This precipitate, whether made from acid or alkaline solution, if formed from a solution containing large amount of iron, is always impure. If the precipitate is then fused with sodium carbonate and the fusion is extracted with water, the titanium remains insoluble as sodium titanate, while phosphorus, silica, chromium, aluminium and vanadium go into solution. The titanate is dissolved in acid, the Ti(OH), is again precipitated and weighed as TiO2. Titanium is more easily precipitated from an acid solution when phenylhydrazine (C6H5.NH.NH2) is used.

Ti(OH), cannot be precipitated from solutions containing tartaric acid, from which solutions iron may be precipitated as sulfide.