July 15, 1941
ANALYTICAL EDITION
TABLEV.
TABLEVI.
mined by making six double passes a t 515' or ahove. Analysis of a cylinder of nitrous oxide for anesthesia showed 99.7 per cent purity.
HYDROGENATION OF ETHYLENE
(Gas mixture: CzH, 16.5,Hz 83.5 per cent) Analysis 1 2 3 4 5 375 318 318 286 286 Temperature, C. So. of passes 4 4 8 4 7 40 40 40 40 40 Rate, ml. per min. C2Hd b y hydrogenation, 70 16.5 16.0 16.5 15,s 16.3
6 286 10 40 16.5
REDUCTION OF KITROUS OXIDE
(Gas mixture: hydrogen, nitrous oxide b y explosion 33 7, 33 8 % ) Analysis 1 2 3 4 5 6 491 460 518 515 491 Temperature, C. 518 S o . of passes 6 12 6 4 8 4 40 40 40 40 40 R a t e , mi. per min. 40 33.6 30 8 33 8 33 2 33 7 S?O, 5 33.7
below 310". I n hydrogenating ethylene, the reaction proceeds so rapidly a t first that the remaining ethylene does not poison the catalyst, so that hydrogenation can be effected a s low as 234', although the reaction becomes extremely slow.
Nitrous Oxide
+
+
459
The reaction N20 Hz + Ifz H20 can be carried out by explosion technique. Kitrous oxide was mixed with hydrogen and analyzed by explosion. The gas mixture was passed through the catalyst tube and the oxidation temperature determined (Table VI). Nitrous oxide may be deter-
Summary A platinized silica gel catalyst containing 0.125 per cent of platinum lowers the oxidation temperature of methane and carbon monoxide by approximately 100' C. from that obtained with a 0.075 per cent catalyst. Temperatures are given for the complete oxidation of carbon monoxide, methane, ethylene, and acetylene and for the start of oxidation for ethane and propane. Nitrous oxide may be reduced over the catalyst by a limited excess of hydrogen a t 515" C. The catalyst tube can replace the copper oxide tube and explosion (or slow-combustion) pipet in any commercial gas analysis apparatus. Large samples may be used rithout danger of explosion.
Literature Cited (1) Branham and Shepherd, J . Reseaych Natl. Bur. Stardards, 13, 377-89 (1934). (2) Kobe and Arveson, IND.ENG.C m h f . , Anal. Ed., 5 , 110-12 (1933). (3) Kobe and Barnet, Ibid., 10, 139-40 (1938). (4) Kobe.and Brookba:!, I b i d . , 6, 35-7 (1934).
(5) U. S. Steel Corp., Methods for the Sampling and Analysis of Gases", p. 14, Pittsburgh, Carnegie Steel Co., 19%:. PRESENTED before the Division of Gas and Fuel C h e m k t r y at the 100th Meeting of the American Chemical Society, Detroit, N c h .
Detection of Certain Metals in Minerals and Ores An Ammonium Hypophosphite Fusion Method IT. B.
TALKENBURGH AND T. C. CRAWFORD, Uni\ersity of Colorado, Boulder, Colo.
VAN
HEN fused with ammonium hypophosphite many minerals and ores are decomposed, the resulting melt often being highly colored. The color of t'he melt directly, or after being treated with water or hydrogen peroxide, is the basis of the tests described here for chromium, cobalt, columbium, manganese, molybdenum, tellurium, titanium, uranium, vanadium, and tungsten. Hypophosphites are powerful reducing agents. They decompose upon being heated, giving off hydrogen and phosphine, which ignite. Ammonium hypophosphite decomposes as follows ( I ) : 7NH,H,P02 +2HPOS H4Pz0~ 7KH3 3PH3 2H2 H20
+
+
+ +
+
The clear melt that is obtained serves as an excellent medium for shoviing any color imparted bo it by the reduced mineral. The fused mass has a low melting point, about 60" C., and is readilysoluble in water. Sodium and potassium liypophosphites are not suit'able for this fusion because upon decomposition they form salts with relatively high melting points, instead of the low melting acids that are obtained from the ammonium salt.
Method About 0.1 gram of the finely powdered mineral is strongly heated in a small evaporating dish n-ith 2 grams of ammonium hypophosphite. The hypophosphite soon begins to decompose nnd the gases evolved ignite, forming n-ater and oxides of phosphorus. -4fter 2 minutes a quiet fusion mixture is obtained n-hich is uied for t h e individual tests.
Detection of Metals COBALT, TITASIUX, ASD TUSGSTEK..These three metals give blue melts, but t'he cobalt melt turns pink upon cooling. For the detection of tungsten, enough water is added dropwise to the warm melt to keep the surface moist. .Is the wat'er penetrates the melt, t,he blue color changes to a striking violet. The violet, color appears immediately when appreciable amounts of tungsten are present, but 10 to 30 minutes may be required when only very small amounts are present. If the blue color of the melt is due t o titanium, the water above the melt becomes a delicat'e ant1 almost imperceptible rose color. The addition of hydrogen peroxide gives an intense orange-red color. Ammonia cause3 the rose color to change t o blue, but this change is not, 30 sensitive as the color change with hydrogen peroxide. Vanadium also gives a reddish color witli hydrogen peroxide, but the \-anadium melt is red when hot and green vhen cool: hence it is easy to dist'inguish between titanium and vanadium. Since cobalt, titanium, and tungsten are usually not associated together in minerals, these tests are specific for theqe three metals. T - ~ N A D I u I I , C H R ~ M I T X , 4 S D ~ R A K I U I I . The>e t h e e metals impart a green color t o t'he melt. T-anadium gires a reddish color t o the melt n-hen hot, which gradually changes t o yellow and finally to green on cooling. The addition of wat'er gives a pale green solution n-hich turns pink when ligdrogen peroxide is added. The addit'ion of ammonium carbonate soluhion to the green melt until the solution is dis-
INDUSTRIAL AND ENGINEERING CHEMISTRY
460
TABLEI. SENSITIVITY OF TESTS Material Tested
Metal Detected
Mg.
+
CbrOs TazOs mixture Columbite (40% CbzOa) Columbite WOa Ferberite (6.26% Was) Ferberite (26.8% Was) XazW04 Scheelite Wolframite Hiibnerite Ti09 Brookite Perovskite Ilmenite CO (Koa)2 Smaltite VtOs NH4V03 Carnotite (1.28% VzOa) Roscoelite (5.04% VZOK) Uranyl acetate Carnotite (O.ZS% UaOs) Cr (NO!) s Chromite
Moos
Weight of Sample
Molybdenite (4.07% Mo) Wulfenite MnSO4 Pyrolusite TeOa Sylvanite
50 1.50 100
25 100 30 3 (WOd 120 100 100 10 100 120 100 2 100 10 2 200 50 4 200 18 100 4 150 100 0.05 (Mn) 50 10
100
Cb Cb Cb
w
W W W W W
w
Ti Ti Ti Ti co co V
v
V V U U
Cr Cr
M O M O
110 Mn Mn Te Te
tinctly basic, followed by the addition of hydrogen peroxide, gives a yellow-orange colored solution if uranium is present. It is better to filter off any solid matter in order to observe the color of the filtrate. Neither vanadium nor chromium gives a yellow-orange color in basic solution. If the green color of the melt is due to chromium, no change in color takes place when hydrogen peroxide is added. MOLYBDEKUM. All molybdenum minerals give a reddishbrown melt, except molybdenite, which is not completely decomposed by the fusion. Therefore, in testing for molybdenum, the melt is treated with concentrated nitric acid, the acid is boiled off, and the mixture is heated t o fusion again. The resulting melt is green or blue-green, which changes to yellow upon addition of water. MANGANESE.Manganese minerals give a clear melt. When concentrated nitric acid is added and the excess acid
Vol. 13, No. 7
boiled off, the melt takes on the well-known color of permanganate. Nitric acid does not usually oxidize manganese to permanganate, but in the presence of the melt it does this readily. Sone of the metals in the usual scheme of analysis interferes with this test for manganese. TELLURIUM. Tellurium minerals are reduced to metallic tellurium by the fusion and small globules of the metal may be seen floating on the surface of the melt. Strong heating for 2 or 3 minutes causes a deep wine color to appear around each globule of molten tellurium. Addition of water to the warm melt causes the wine color to turn black. COLUMBIUM. Columbium minerals impart no color to the melt but fine black particles are observed throughout the melt. When concentrated hydrochloric acid is added, the mixture heated to boiling, and a small piece of mossy tin added, an intense blue color develops in a few seconds if columbium is present. Since columbium and tantalum are nearly always associated together in minerals, this test can be used for the detection of both metals.
Sensitivity of Tests Table I shows that these tests are applicable to different minerals containing the elements for which the tests have been devised, and are sufficiently sensitive t o detect appreciable quantities of the metals in question. It is not claimed that by this method any one of these metals can be detected in the presence of any or all of the others, but it is possible to detect any one metal in any of the naturally occurring minerals thus far tested. Tungsten, for example, can be detected in any one of the tungsten minerals which the authors have been able to obtain. Manganese was detected in a mixture containing 0.5 mg. each of silver, lead, mercury, bismuth, copper, cadmium, arsenic, antimony, tin, cobalt, nickel, chromium, aluminum, zinc, and manganese. During the fusion iron and copper are reduced to colorless compounds which in no way interfere with the tests. If a mineral gives no color, all the metals included in these tests are absent, except columbium and manganese.
Literature Cited (1) Rammelsberg, C.,J. Chem. SOC.,26, 1, 13 (1873).
Use of Bromate in Volumetric Analysis Determination of Arsenic and Antimony Using Internal Indicators at Ordinary Temperatures G. FREDERICK SMITH AND R. L. MAY University of Illinois, Urbana, Ill.
G
YORY'S method (1) for the determination of arsenic and of antimony by titration of strong hydrochloric acid solutions of the trivalent elements, using potassium bro~matewith methyl orange or indigo sulfonate as internal indicators, requires that the reaction be carried out a t 80" to 90" C. The same determination can be carried out at lower hydrochloric acid concentration and a t room temperature if the reaction is followed potentiometrically, as shown by Zintl and Wattenberg (6). More recently benaopurpurin B was proposed by RaIkhinshteIn (2) for the determination of antimony using bromate, and Utzel (4) sug-
gested a colloidal suspension of alpha-naphtholflavone as a reversible indicator for bromate titrations. Since the determination of arsenic and antimony using the Gyory (1) method is still preferred by industrial analytical laboratories and has not been discarded in favor of the Zintl and Wattenberg (5) or other procedures, suitable modification of the Gyory methods, by means of which the reaction is carried out a t ordinary temperatures, has been suggested to the authors. This article describes the use of three internal oxidation indicators of the irreversible type in the Gyory procedure, by means of which the oxidation of arsenic and of
