V O L U M E 26, NO. 3, M A R C H 1 9 5 4
593
carboilate or sodium carbonate plus sodium tetraborate or sodium bisulfate followed by solution of the melt in hydrochloric acid, will not necessarily ensure clean crucibles. Recommended procedure for cleaning platinum crucibles: Fuse with sodium carbonate alone or with mixtures of sodium carbonate and sodium tetraborate and dissolve the melt in dilute hydrochloric acid; then heat a t 1200' C. for 1 hour in a muffle furnace and remove a n y stain in boiling concentrated hydrochloric acid. If the stain is appreciable, repeat the heating and finally burnish with fine sand. I n all procedures for analysis of silicates and rocks, the same crucible used for the sodium carbonate fusion should be used for ignition of silica; furthermore, the procedure itself should be
so explicit t,hat the above difficulties will Loth be knoir~i and
avoided. LITERATURE CITED
(1) Dittler, E., "Gasteinsanalytisches Praktikum," p. ( 5 . h r l i n ,
Walter de Gruyter & Co., 1933. ( 2 ) Duparc, Louis, Bull. S O C . franp. niin., 42, 1.56 (1919). (3) Hillebrand, W. F., Lundell, G. E. F., Bright, 1%..i.,a n d Hoffman, J. I., "Applied Inorganic Analysis," 2nd ed.. p. 845, New
York, John Wiley & Sons, 1953. (4) Jacob, J.. "=inleitung zur Chemischen G ~ s t e i i ~ s a r ~ a l ~p. s e .6, " 1928. (.5) Shell, 11. I?., .LN \I.. CNEM.,22, 326 (1'350). RECEIVED fur rcvivw .Tunc 16, 19.53. .iccepteil D i ~ : c ~ n b o16, r 19:;j
Polarographic Analysis for Arsenic and Antimony G.P. HAIGHT, 1 R . l Naval Research Laboratory, Washington,
r "is
D. C.
laborntory lias had occ:wion to try v:irious trace met IiotlP
1 of detei~miningarsenic and antimony. All methods, iiicludirig the one ulider discussion, involve concentration b y dissolving
arsenic and antimony compounds in GAVsulfuric acid and reducing to arsenic and stibine by the action of arsenic-free zinc. Colorimetric mothods have heretofore been applied with only fair agreement lwiiig olitnincd for different methods. 3Iolybdenuni blue for arsenic ( 5 )arid rhodemiiie-I3 for :intiniony ( ? ) have been used after trapping the hydride concentrates in niercwrica chloiide solution. A modified rolorinictric sulfidc ( 6 ) determination has also been atteniptotl after absorption of the hydrides on silica gel impregnated \vith silver nitrate. This latter method of absorption yields tiipositive antimony and arsenic, both of which yield n-cll-defined aiid clearly sqxirated polarographic waves in a solution 1M iii Iiydi~oc~liloi~ic acid and 1.11 in tartaric actid, a solution suggested l)y the results of Ranibach ( 1 ) and Lingane (3). suitable for esti~:ic~tiiig both arsenite and antimor:i grl. A rapid po1arogr:iphic method for the detection :ind detei~iniii;itionof arsenic and :iiitinioiiy ha,s thus h e n easily achieved. T h e nicJthod caould be applied directly to :in:ilyai: t o solutions pis of g:i.ws c~ontaiiiingarsine axid stibine as ~rc~ll coiit:iiiiing :trsciiic*: i i i t l :intimony cwnipountl~. 41'1'4RATL-S
AND .\I.iTERI.iLS
A S:irgent l l o d e l SS recording polarograph i r a s used for :ill nieasurcnienti:. For careful measurements of potentinl the niachine \vas opc,rnted manually with a potentiometer attached to the dropping mcrrury and reference electrodes for precise e.m.f. determination. Either a conventioiial mercury pool cell, or an H-cell according to Liiiganc :tnd Laitinen ( 4 ) was employed, depeiiding on thc typc of data sought. All nieasurements werr made at 30" f 0.5" C. Reagent grade chemic-als were employed throughout. Silica gc.1 in granular form \ r a p impregnated with silver nitrate simply by evaporating silver nitrate solution to dryness while in contact with the silica gel. CIIARACTERISTICS OF . ~ w r I ~ r o n - ( m TO ) AVTIMONY(O) POLAROGRAPHIC WAVE
The half-wave potential is -0.138 volts os. the standard calomel electrode and is independent of the conccntration of tripor;itive antimony. The slope of the plot of E us. log i/(& - 1') i.+ 0.020, the theoretical slope for L: revcrsiblc 3-electron change ( 2 ) . The diffusion current constant i d / C n ~ 2 / 3 t ' / 6is, 3.66 where i d is the diffusion current in microamperes, C is the mil'. iiolar conccntration of tripositive antimony, 7 n is the number of milligrams of mercury flowing per second, and t, the time for each drop in seconds. Above a concentration of 2 x 10-4.11of tripositive ariti1 Present addre-s, Cliciiiistry I h l i a r t m c n t , I-nircr.=ity of I
