A N A L Y T I C A L CHEMISTRY
600 rhodium is obtained. The acetone solution is stable, no perceptible change in color intensity being noted in 4 days. REACTION OF 2-MERCAFTOBENZOXAZOLE WIT11 OT€IEH PLATINUM METALS
Table I. t
I inai \ oliime 100 ml
Under the same conditions of precipitation as with rhodium, P t + + + + , Pd++, I r + + + + , and A u + + + give precipitates with 2mercaptobenzoxazole. The reactions shown below were obtitiricvl using 5 mg. of the platinum metal in 25 ml. of solution. Platinum. Immediate chocolate-brown precipitate changing to brownish yellow on heating; partially soluble in acetone. Palladium. Immediate red precipitate changing to orange yellow on heating; partially soluble in acetone. Iridium. Slight brownish red precipitate on heating, partially soluble in acetone. Rhodium. Red precipitate on heating; readily soluble iii acetone. Gold. Purple-brown precipitate changing to light bronii oti heating; insoluble in acetone. INTERFERENCE O F PLATIVUM METALS
The platinum metals interfering most strongly are platinum and palladium. Iridium in low concentrations does not interfere. Large quantities of gold cause no interference, because the gold precipitate is insoluble in acetone. Table I shows typical results in the colorimetric determination of rhodium with Zmercaptobenzoxazole. The noninterference of iridium in a t least equivalent amounts is particularly noteworthy, for rhodium is usually left with this element in the systematic analysis of the platinum group metals ( 2 ) . Solvents. Hexane, benzenr, ethyl ether, methanol, ethanol, and carbon tetrachloride do not dissolve the mercaptobenzouazolate. Methyl ethyl ketone and dioxane, although readily dissolving the rhodium precipitate, show no advantages over acetone. Water in Acetone. Measurements of the extinction ( a t 420 mp) of solutions varying from 1 to 30% in water were the same R P V O I Ithis ~ limit difficulty is encountered due to complex pie-
Determination of Rhodium with 2-llercaptobenznxazole
Extinction measured using blue filter w i t h L u m e t r o n Model 400.4) R h Present Y Rh Found, 'I 12 11 25 26 60 58 120 120 94 1207 Pt 116 94 1407 Pd 150 94 0.5 mg. A u 94 94 1.0mg. Au 96 94 507 Ir 92 94 1007 Ir 89 94 2007 Ir 94 940 f 1.5 mg. Ir 937
++ + +++ +
cipitating out of solution; precipitates appear if more than 35% water is present. Reagent Solution. The rcagent is stable for a t least 2 weeks. If reagent solution is allowed to stand, t,herhodium precipitate obtained proves difficultly soluble in acetone. Complete transmittancy is obtained beyond 360 mp for 10 mg. of the reagent in 100 ml. of acetone and excess reagent causes no interference. Excess Acid. Variations in the acetic acid concentration from 1 to 30y0,in the precipitation of the complex, showed no change i n the extinct,ion obtained. LITERATURE CITED
Currah, J. E., McBryde, W. -4.E., Cruikshank. .%, .J., a n d Beamish, F. E.. IND.ENG.CHESI.,AXAL.ED.,18, 120 (1946). (2) Gilchrist, Raleigh, 2nd Kit-hers, Edward, J . .4m.Chern. SOP.,57, (1)
2565 (1935). (3) Haines, R. L., nnrl lly:in, D. E.. C a n . .I. Rrsenrch, B27, 72
(1949).
Kienitz, H., and Romhock. L., 2 . rrnnl. CAem., 117, 241 (1939). (5) Ubaldini, I., and Sel)bin. I,.. d ? l n . rhiui. apph'cotfi, 38, 241
(4)
(1948).
Fractional Sublimation on a Removable Transparent Fihn ALEXANDER 0. GETTLER, CHARLES J. URIBERGER,
A N D LEO C,C)l,DR41:\1 Chief Medirnl Exominrr's O f i r e , Vew York, V. Y.
An apparatus is described for separating the components of il mixture of organic compounds hy sublimation at reduced pressure. The sublimate is deposited on a removable transparent plastic film. Microscopic examination of the sublimate as well as chemical tests thereon may he performed withniit removing the sublimate frnm the film.
S
UBLIMATION procedures have long been recognized as a --- separated by a single sublimation, a subsequent dissolution promeans for separating and purifying those organic compounds cedure will obviously defeat the original purpose of the suhwhich may, upon heating, undergo direct transition from the liniation. To overcome this difficulty, a procedure was devised whereby solid to the gaseous phase without decomposition. The number of sublimable compounds has been greatly increased by the use of the sublimed crystals, without further manipulation, may be examined directly on the collecting surface. ,4sublimation tube reduced pressure. The advantages of sublimation over other consisting of two cylindrical sections connected by a ground-glass methods of purification have been adequately discussed by joint was designed and constructed as shown in Figure 1. The Hubacher (2). Many sublimation apparatus and techniques have been demale ground-glass joint is of constant diameter throughout its scribed ( 2 ) , in which the sublimate is usually collected on the entire length and has exactly the same diameter as the rest of the tubing to which it is connected. This feature eliminates the surface of a glass receiver. I n order to perform subsequent chemical or microscopical tests, the crystalline sublimate must dead space a t the joint usually found in the standard type of ground-glass joints. The use of this straight-walled sublimabe removed either by a scraping process or by dissolution in a tion tube permits the insertion of a transparent cellophane film suitable solvent. If a scraping procedure is employed, the more or less well formed crystals are likely to be damaged. If (which serves as a condensing surface for the sublimate) without the presence of any dead space hetween the film and inner wall two or more components of a mixture have been fractionally
V O L U M E 22, NO. 4, A P R I L 1 9 5 0
601
The parts consist of a oylindried aluminum block, A , 6 inches (15 em.) hi h and 4.5 inches (11.25cm.) iudiameter, ohtainab?efromtbe Aluminum Company of America; Cenco meohanieal latch electrical reset relay, No. 98330, B; Cenco deKhotinsky single-pole double-lock bimetdic thermoregulator, No. 90025, C; fourGeneralEleotric 120-watt 115-valt, 3 X 0.5 inch cartridge heaters, D; ten voltmeter-type binding posts, E; and a 300" C. thermometer, F. The auxiliary equipment includes a vacuum pump, vtmnnn gage, freezing trap, aud Dewar Bask. The aluminum block and assembly are mounted on a 0.5inch Transite board with three 1-inch legs. The electricsl connections for the thermoregulator and relay accompany the apparatus supplied by the manufacturer. The leads for each of the four cartridge heaters connect to a psir of binding posts and a 110-volt direct current supply, and the lines from the regulator and relay are connected t o the two remaining binding posts. In this wav. any combination of heaters with series or oarallel ~
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w h i n a temperature diff&o&l
