V O L U M E 2 1 , NO. 12, D E C E M B E R 1 9 4 9
1539
mingham for the loan of vaiious electrical measuring apparatus, the Anglo-Iranian Oil Co., Ltd., for the loan of the spark equipment, and the Institute of Petroleum for supplying the majority of hydrocarbons used in this work. LITEHATCHE C I T E D
(1) Broersma, S.,Watmernian, H. I., Westerdijk, J. B., and Wiei,sina. E. C., Physica, 10, 96 (1943). (2) Bruhat, G., and Guinier, A., C o m p t . rend., 197, 1028 (1933), (3) Foehr, E. G., and Fmske, 31. It., Ind. Eng. Chem., 41, l Y X
(1949). Gabiano, M. P., A ~ Lp h.y s . , 20, 68 (1933). (6) MacFarlane, W., and Wright, R., J. Chem. SOC.,136, 114 (1933) (6) Miescher, E., Nelv. Phys. Acta, 4, 398 (1931). (4)
17) Perkin, W. H., J . Chenr. Soc .61,309 (1892) ; 69,1058 (1896) 1882-1907. (’) (9) Roberts, R. W., Wallare, L. .1.,and Pierce, I. T., Phil. Mag., 17, 946 (1934). (10) Rodger, J. W., and Watson, W., Phil.Trans. Roy. SOC.(London), 186(A),621 (1895). (11) Scherer, M.,Pub. sci. et tech. miniut8ie air ( F r a n c e ) , S o . 50, 1 (1934). (12) Schutz, it..,“Magneto-Optik,” ”Handbuch der experimentelle Physik,” Vol. XVI, 1,p. 17, Akadamie Verlag, Leipzig, 1936. (13) Spiers, H. M.,“Technical Dat,a on Fuel,” 4th ed., British National Committee. World Power Conference, London, p. 58, 1937. (141 Waring, C. E., Hyinan, H . , aiid Steingiser. S.. J . A m . Chem. Soc.. 62, 2028 (1940). RECEIVED Septeiiiber 1 , 1948.
Analysis of Thallium Halide Crystals H. B. KNOWLES .Vational Bureau of Standards, Wushington, I ) . C
I
N T H E preparation mil investigation of the properties
of
thallium iodide-thallium bromide crystals (2, 3 ) for use in experimental studies in loiig n.avr-length spectrometry a relatively simple analytical procedui,e that permits a determination of the romposition of the crystal6 is desirable. Little published information is available concerning either the details of the v:iriour methods used in the preparation of the cryst,als or suitabk methods by which a reliable chemical analysis can be effected. 1f it is assumed t,hat the pure materials used in the preparation of the crystal undergo 110 decomposition or change-that the final produrt is composed only of thallium iodide and thallium bromide--a determination of any of the three components prrmitq the coniposition of the crystal t o the computed. A determination of either the iodide or the bromide appears most att’ractive. If subsequent investigation indicates the presence of iodine and hromine in forms other tlitiii iodide and bromide, the foregoing msumption fails and the prohleni becomes more complex. A preliminary study at the Sational Bureau of Standards indicated that, when a sample of the c r y t a l is treated with dilute acid and zinc, satisfactory decomposition results in the precipit,ation of metallic thallium ( 1 ) and the liberation of hydriodic and hydrobromic acids. Decompositiori of the sample is best effected whm the sample is in a fine state of subdivision. Following filtration and washing of the insoluble metallic residue, a potentiometric titration of the halides with silver nitrate gave satisfact>oryresults for t,he iodide. On continued titration under the prevailing cc111ciitions, less satisfactory results for the bromide were ohi ainrd hecause of a weak and uncertain end point. Experiments in which known mixtures of potassium iodide and potassium bromide were titrated potentiometrically with silver nitrate indicate that when the solution contains approxiniately 2y0 by volume of sulfuric acid, a positive error that averages froiii I to 2 parts per thousand results. At 1oFTer concentrations of arid unsatisfactory results were obtained because of an eucessiw COII.rumpt,ionof silver nitrat,e. A procedure has been developed, based on decomposit’ioii of the sample aa described, followed by tit’ration of the iodide with .dver nitrate and an indirect determination of the bromide. Accurately weigh a 1-gram sample of the crystal, obtained by filing the material with a No. 2 file (rejecting any chips or coarse material), in a 500-ni1. gl -stoppered wash bottle. Add 20 grams of granulated zinc (30-mesh) and 100 ml. of sulfuric acid 13 97) and digest the mixture a t room temperature, with occafiiorial agitation, until there is no evidence of unattacked materinl Add 5 grams of granulated zinc and 5 ml. of diluted w l -
+
+
turic acid (1 1) to the wa5h bottle and digest for 30 to 45 minutes with occasional agitation. Filter the solution through a -mall filter containing a little zinc, and wash both flask and filter ~5 ith small portions of diluted sulfuric acid (1 99). Reserve the filter and residue of zinc and thallium. Titrate the iodide potentiometrically, using silver iodide and calomel electrodes, with itandard 0 1 S silver nitrate added dropwise m hile the solution is Ltirred vigorously by mechanical means. The titration should be performed without delay to minimize oxidation of the iodide by Air Transfer the reserved residue of zinc and thallium with filter to the wash bottle and treat with 100 ml. of sulfuric acid ( 2 98) Digest for a few minutes, filter, and titrate potentiometricallj with standard 0.01 ,!-silver nitrate. The recovery, approximating 0 04 to 0.06 ml of 0.1 S silver nitrate, is added t o the amount already found and the Ieiult is calculated as thallium iodide
+
+
C onhrrnatory evidence of composition is afforded by a deteriiiinalion of the thallium bromide.
L)tAcunipose a n-eighed sample of approximately 0.5 gram in the manner just described, precipitate the iodide and bromide with -11ver nitrate, and filter, wash, dry, and weigh in the conventional riianner. Deduct from the weight of the combined silver halides rhr. silver iodide equivalent of the thallous iodide already found. (’alculate the thallous bromide equivalent of the remaining silver brrtmidP 1 fen experiments on two samples of thallous iodide-thalloue by the foregoing procedures g a v e
1 ~r (iniiile crystals
Sariiplr A
I’halloiis iodide -4\-.
‘Thallous broriiidr AV,
Sample H
%
%
57.82 57.90 57.80 57 84 42.18 42.20
61.16 61.10
I
42.19
...
61.13
38.74 38.76 38.75
The method in practice presents but few difficulties aside from he end point that denotes complete precipitation of the silver iodide. This end point must be approached slowly, and adequate lime afforded for the establishment of equilibrium. 1
LITERATURE CITED
William, “Select Methods of Chemical Analysis,” 3rd ed., New York, Longmans, Green and Co., 1894. Satl. Bur. Standards. Tech. .\‘~zL.s BidL, 32, 96 (1948). 3) Plyler, E. K., J . Rcar.(~rch.V(!fl. H i r r . Stnndnrds, 41, 125 (1948).
( 1’r Crookes, i2,:
K E ~ E I V E DAl,ril 1 2 . 1W!i
