V O L U M E 21, NO. 7, J U L Y 1 9 4 9
877
The C;ooch crucible twhriique is suitable for :ilniost any radioactive isotope which is capable of yielding a precipitatc i n such physical forni that it can be filtered off satisfactorily and forni a uniform layer of material on the surface of the disk. I n many caseq slight modifications of ytandard g r a v i m e t r i (kirocedure are necessary to obtain such uniform cliatribution of thti pribci pit ate. I11 ](,in
the particular pr(~1)for which the appa-
ratus was devised, phosphate containing P3*is prwipitated as aminoiiiurriphosphoniolybdat[,. The wsll-known tendFigure 2. Sectional View of (wcy of this prt4pitatc. .issemhl> for Solution of Preto crci'p has been overcipitate conie hy washing ,first \vith 5 C ; a m m o n i u m tritu(tt, t o ~'cinovethc nitric acid, arid t h v i i with a O.lC5 solution of .\c~rosol 11.1 in 5 5 ; ammonium nitrate. Occasioiially it is new+ sary t o use a rubher policeman to facilitate washing the last traccss of the precipitate down from the walls of the crucible onto t h t s disk. The aerosol and ammonium nitrate arc then washed out \\-itti tsthanol, and the crucible and contents arc1 dried in air. Othcr surface-active agents have bren tried, but none was as Fatisfactory as Aerosol Acetontl has liven used to wash nut t h c s salt and surface agent, but it tends to cause thc precipitatc to I)il(t up un,wi~nlyover the surface of tti(5 disk. Tho experiments in progress, \vhich coirsict i ~ f;I study of thc: ri~1:itivt~ turnover rates of thc :witl-.;oluhle phosphoi~uscompounds
of livr\r, itre such that it is niore satidiictory t o clrteriniiir~the radioactivity of the samples obtained before chemical determinations of their phosphorus content are made. The apparatus shown in Figure 2 has been devised to obtain quantitative solution of thrl phosphomolybdate precipitate.
The filter tube has been modified by making the terminal portion of tubing 4 mm. in outside diameter, to fit inside the neck of the 25-ml. volumetric flask used as receiver. The Lucite ring i i i which the flask sits serves to prevent, the flask from tipping ovt'r when tht. filter tube is removed. The suction flask consists of a 500-nil. Erlenmeyer flask with standard-taper ground joint neck. The bottom is cut off and thr edge ground flat to fit the grountlglass plate. A Pyres bottle with ground joint neck could be uscd instead of the Erlenmeyer flask. The phosphomolybdate prctcipitate is dissolved by adding 1 ml. of phosphate-free 1 S sodium hydroxide, filtering by suction, and washing with successive small portions of water. The contents of the flask are then rnade up to the mark and suitable aliquots taken for the colorimetric detixrmination of phosphorus. As a test of the completeness of the solution process, duplicati. aliquots of P32phosphate solution containing about 10,000 counts per minute were taken, carrier phosphate was added, and thv material was precipitat,ed in the usual manner. After countirrg, the precipitates were dissolved by the usual technique, and the. crucible was dried without any further washing and ag,tirr counted. One crucible now gave 6, the other, 4 counts per minuti: above background. The amounts of phosphorus encountered in the experimt,iit u i'ange from 50 to 1500 micrograms. Known amounts of pho phorus as phosphate, within this range, were precipitated as phi) phomolybdate and treated as descrihzd above. \Tith 100 to 200 micrograms, the recoreries were botween 98 and 10OC;. LITERATITRE CITED
(1) Arinstrong, \T, D.. and Schuljert, J . , .\s.AI.. CHEM.,20, BiO (1948). ( 2 ) Bernstein, W , , miti Ballentitic, 11.. Rrc. Sci'. Iustricments, 20, 347 (1949). (3) MacKeneie, A , J , , mid I ) r t i t i , L. .I.,. i s . ~ t('HLM., ., 20, ,559 (1948).
R I . . c E I ~ ~SeptrinhPr ;u 13. l!j48, lti~i,.archrarricd o i i f nt Hrookhnven National Laboratory under tlie au-pi
15.00 11.5R 11.41
13
8
4
4
pleted iii approxiiliarely 50 minutes. Samples smaller thaii those somptimes used for macroanalysis have been satisfactory-i.e., in the range of 0.10 gram or less. There is no apparent reason why the apparatus could not be adapted to the semimicro m ~ l successe fully. The results shoirri in Table I indicate that thr niethotl is capable of sufficient accuracy. These data were obtained by students with no previous experience i n the use of the Dumas apparatus. I11 each case only two determination? were inntie. LITERATURE CITED
with :L Chroniel-Aluinel thermocouple placed iii the center of the spiral showed a saving of from 6 to 8 minutes in the cooling period. The removal of the tube from the furiiace also shortens the heating period, for all sections of the furnace may be kept at full heat while the boats are being changed. I n this n a y the new sample mny be inserted, the tube returned t o the furnace, and the nest ruii started within 15 minutes of the time that the sneeping is coniplrted for the previous run. The reduced copper spiral lasts for wveral runs without any attention, and the copper oxide is sufficient for three or four runs before reosidation is necessary. Vsing the apparatus as described, :tnd with the combustion tube previously pwpared, four consecutive runs can be made in 4 hours or less. In some c:tses orie deterniinatiori hn.s been coni-
(1) l..islier, H . L., “Laboratory Manual of Organic C~lieinistry,”4 t h ed., pp. 341-70, ?Jell- York, John Wiley & Sons, 1938. (2) Gattermann, L., and Wieland. H., “Laboratory Methods of Organic Cheinistiy,” 24th ed., pp. 68-7, Kew York, Macmillan Co., 1938. 13) Hein, F., 2 . anyeta. Chern., 40,864 (1927). (4) Kirst,en, R’., -&SAL. CHEY.,19, 925 (1947). (5) Niederl, J. B., and Niederl, V., “Organir Quantitative Micro,” 2nd ed., p p . 79-82, Sew York. John Wiles. & Sons, 1942. ( G ) Ibid., p. 96. (7) Trautz, 0. It., and Siederl, J . B., Isu.ENG.C H & . \ f . ,A S L I . .1.1).. 3 , 151 (1931). HECEIYE:U Alarch 2 2 , 1948. Presented hefore the Division of Inalgtical and Slicro Chemistry a t the 113th Sleeting of the A M E R I C A CH6\iIc.iir S SOCIETY, Chirago, Ill.
Microdetermination of Total Carbon in Carbonates, Cyanides, and Alkali or Alkaline-Earth Organic Salts and Mixtures J.K. LAFOKCE, D. F. KETCHURI, ~ D A E.. BALLAIHD Kodak Research Laboratories, Rochester, X. Y . Y T H E course of work on the iiiicrodetermination of carbon * i n alkali cyanides and carbonates containing CI4, it was found tlcsirable to recover the carbon as barium carbonate for subsequent isotopic analysis in the niaw spectrometer. It appeared that the use of the organic microcombustion apparatus and the mllect,ing procedure of Dauben and co-workers ( 1 ) might offer a shsfactory method, provided that the cyanide or carbonate c:irbou could be liberated quantitatively and collected. The use of sodium bisulfate to cover the sample in the platinum niicrocombustiori boat proved to be a satisfactory solution to this problem, and some extensions of this procedure were made xhich showed that i t is equally applicable to the estimation of carbon in organic salts of alkalies and for the estimation of total carbon in mixtures of organic and alkali or alkaline-earth carbonates and cyanides. . l a the procedure i b in effect :t hisulfate fusion in an oxygen :ctmosphere, it should prove v:iluahle with difficultly combustible orwriic substances.
Apparatus. Ll Hallett niicrocointiu~tionapparatus ( 3 )and tube filling with an autoniatically propelled pyrolysis furnacc ( 2 ) a t 750” * 25” C. was used. Procedure. A 5- to 20-my. sample, or enough to give from 3 to 20 mg. of carbon dioxide, was weighed accurately into a platinum microcombustion boat and covered with approximately 60 nip. of powdered sodium bisulfate. The combustion was carried out in the normal manner, and the liberated carbon dioxide was absorbed in Ascarite. The Drierite tube must, be placed between the combustion tube and the APcarite absorption tube t o absorb the water formed.
Discussion. The accuracy and precision of the method, as shown in Table I, were about as high as could be expected for the determination of organic carhun i n t h i q apparatus ( 4 ) .
Table I. Compound KzC03
CaCOa BaC03 K C N , 98.0%
NasCOa Potassium acid phthalate
Benzyl isothiourea hydrochloride Potassium carbonate J
Determination of Carbon
Sample Taken
COS Found
MQ.
MQ.
13.30 12.76 15.73 14.34 13.24 15.80 12.52 15.20 15.78 14.01 16.07 14.03 13.40 14.16 16.20 16.22 9.04 7.95 7.59 6.71 8.42 5.29 12.80
0.20 3.96 5.07 4.51 5.89 6.98 5.53 0.380 3.60 2.60 10.77 9.41 8.95 9.54
0.10 ‘.87 18.10 12.56 13.16 11.59 14.61 13.24
Carbon Found
70
