November 15,1934
I N D U STR I AL AN D E N G I N E E R I N G C H E M I ST R Y
female 0.75-inch (1.9-cm.) ground-glass joint, is fitted by means of a rubber sleeve, or, if preferred, joint and flask may be sealed together. The male joint is similarly treated with respect to the condenser, but in any case the system is 80 assembled that the end of the delivery tube is brought directly over one of the individual receivers SO that the droplets of distillate fall directly into the receiver without wetting the sides of the neck. TABLEI. FRACTIONAL DISTILLATION OF METHYLESTERSOF FATTYACID^^ FRLCTION BOILINQ POINT AT 3 MM.
WEIQHT c. Crams 1 165-166 2.8352 2 165-169 2,9516 3 169-172 3.1822 4 172-183 3.1690 1.4704 183t Taken 13.6370 Recovered 13.6984 Loes 0.0386 Percentage loss 0.30 Courtesy of Thelma Garvin.
477
This apparatus has given most satisfactory service in a 3-year trial in the hands of advanced students. It is rugged, requires the SerViceS Of no expert in its construction, is not costly to make, and takes up little space on the desk. Its dimensions and number of receivers can be varied to suit the needs of the operator. LITERATURE CITED (1) Bredt, J., Ann., 367, 354 (1909). (2) BriiN, J. W., Ber., 21, 3339 (1888). (3) Gautier, H., Bull. SOC. chim., [3] 2, 676 (1889). (4) Gorboff, A.,and Kessler, A., Ber., 18, 1363 (1885). (5) Thorne, L. T., Ibid., 16, 1327 (1883). (6) Wechmar, Houben-Weyl, “Die Methoden der organischen Chemie,” Vol. I, p. 568, Georg Thieme, Leipzig, 1921. RECEDIVBD September 10, 1934.
Ceric Sulfate for Estimating Tin in Bearing Metals L. G. BASSETT AND L. F. STUMPF, Rensselaer Polytechnic Institute, Troy, N. Y.
I
N THE usual method for estimating tin in bearing metals, the stannous tin is oxidized in hydrochloric solution with standard iodine solution which must be standardized against pure tin and checked frequently. H. H. Willard, N. H. Furman, and others in a series of papers in the Journal of the American Chemical Society from 1928 to 1934 have pointed out the advantages of ceric sulfate as a standard oxidizing agent., It may be used in hydrochloric acid solution and retains its original concentration over a long period of time. I n the present investigation the procedure as described by Hallett (2) was followed except that 0.1 N ceric sulfate was used as the oxidizing agent, using as indicator 5 ml. of a solution made by dissolving 1 gram of soluble starch and 10 grams of potassium iodide in 100 ml. of distilled water. It was also found that better results were obtained if 0.1 gram of antimony was dissolved with the sample. Runs were made on pure mossy tin with the results shown in Table I. TABLHI. ESTIMATION OF TIN TIN SAMPLE Gram 0.1032 0.1003 0.1080
TINFOUND Gram 0.1027 0.1001 0.1084
TINSAMPLI Gram 0.1082 0.1362 0.0996
TIN FOUND Gram 0.1080 0.1363 0.1003
In order to test the validity of the method on actual bearing metals containing possible interfering elements such as copper and arsenic, runs were made on Bureau of Standards bearing
metal samples, Nos. 53 and 54. No. 53 is a lead-base bearing metal containing 10.94 per cent of tin, and No. 54 is a tinbase bearing metal containing 88.24 per cent of tin. The results obtained are given in Table 11. TABLE11. ESTIMATION OF TININ BEARINQ METALS SAMPLE No.63 Weight of Tin sample found Gram % 1.0027 10.89 1.0010 10.87 1.0018 10.94
SAMPLB No. 64 Weight of Tin sample found Gram % 0.1904 88,23 0.1017 88.68 0.1927 88.06
From these results it appears that ceric sulfate may be used as the standard oxidizing agent in the analysis of tin in bearing metals with results precise to from one to four parts per thousand. The theoretical titer obtained by standardizing against anhydrous sodium oxalate (1) may be used. The solution does not have to be restandardized over a long period of time. In the authors’ work, extending over a period of 3 months, the solution did not change appreciably.
LITERATURE CITED (1) GFS Chemical Co., Cleveland, Ohio, BulIetin, “Ortho-Phenanthroline,” Method B, p. 22. (2) H d e t t , R. L.,J . Soc. Chem. In& 35,1087(1916). RECEIVBDJune 28,1934.
Cyclohexanol in Colorimetric Determination of Molybdenum LORENC. HURDAND FREDREYNOLDS, University of Wisconsin, Madison, Wis.
D
URING the course of a study of the variables involved in the colorimetric determination of rhenium it was found that the presence of small amounts of ether exerted an appreciable influence upon the development of the color. Ether is generally used to extract the thiocyanate-rhenium complex and it was thought that perhaps the erratic results often obtained might be due to an interaction of the ether and the rhenium thiocyanate or to an alteration accelerated by the ether. Accordingly a search was made for more inert extraction media. It was found that cyclohexanol exerted
practically no influence upon the reaction and that the colored complex was unusually soluble and stable in this solvent. Inasmuch as the conventional colorimetric method for molybdenum is identical with that for rhenium, it seemed probable that the same factors which contributed to the unreliability of the rhenium determination might account for some of the peculiarities often encountered with molybdenum. Cyclohexanol, like butyl acetate, is a better solvent for t h s thiocyanate than ether or ether mixtures. Consequently
ANALYTICAL EDITION Vol. 6, No. 6 smaller volumes of these menstrua are required for extracTABLEI. DETERMINATION OF MOLYBDEN UM No. tion and both have the decided advantage of lower volaOF tility. Cyclohexanol exhibits little tendency to decompose S A M P L E , U.9. Damn- MOLYBB U R ~ AOFU MINAD~NUM Av. DE- ERat room temperature and, unlike butyl acetate, its hydrolySTANDARDS TIONS Present Found VIATION R O R EXTRACTOR sis products do not promote color fading. It may be re% % % % 5 0.01 0.010 0.0002 0 covered from residues by neutralizing the free acid and dis- Cr-W-V No. 50 Cyolohexanol 3 0.01 0.009 0.0008 10 Ether tilling under reduced pressure. Cr-Mo-A1 No. 106 4 0.164 0.163 0.002 0.6 Cyolohexanol 2 0.164 0.162 0.002 1.2 Ether Solutions of stannous chloride and potassium thiocyanate 3 0.005 0.005 0.0000 0.0 Cyclohexanol were prepared in the manner described by James ( I ) . The Stainless No.73 3 0.005 0.005 0.0001 0.0 Ether 3 0.23 0.23 0.001 0 cyclohexanol was of the commercial grade marketed by E. I. Ferrotungsten No. 75 Cyclohexanol 0.24 0.007 4.3 Ether du Pont de Nemours & Co., Inc., and was used without further Ferrovanadium No. 61 23 0.23 0.72 0.68 0.002 5.5 Cyclohexanol purification. Prior to use it was allowed to stand in contact 2 0.72 0.67 0.021 6.9 Ether Spiegeleisen No. 66 3 0.005 0.005 0.0001 0.0 Cyclohexanol with a solution containing stannous chloride, potassium thio3 0.005 0.005 0.0001 0.0 Ether cyanate, and hydrochloric acid. The ether was treated as Manganese metal No. 67 3 0.015 0.015 0.0001 0.0 Cyolohexanol 3 0.015 0.014 0.0002 6.6 Ether described by Maag and McCollum (3). Analyses were made 0.009 0.009 0.0001 0.0 Cyolohexsnol according to James ( I ) , the exception being the substitution Ferromanganese No. 68 22 0.009 0.010 0.0003 9.9 Ether of cyclohexanol as an extractor. For purposes of compari- Chrom-molybdenum No. 72 2 0.149 0.151 0.001 1.3 Cyclohexanol son, samples of each material were analyzed by the ether 2 0.149 0.152 0.001 2.0 Ether extraction method (6). Table I gives a series of results obtained on a number of Bureau of Standards steels and moACKNOWLEDGMENT lybdenum-containing materials. Standards for comparison The authors are indebted to Arthur R. Stephens who aswere in all cases steels or materials of approximately the same sisted in checking the method. composition and molybdenum content. I n some cases where proper standards were unobtainable, known amounts LITERATURE CITED of molybdenum were added to solutions of the same type as (1) James, IND.ENG.CHmM., Anal. Ed., 4, 89 (1932). those being analyzed. Analysis of solutions of ammonium (2) King, IND.ENQ.CHBEM., 15, 350 (1923). molybdate and of synthetic mixtures yielded excellent re- (3) Maag and McCollum, Ibid., 17, 524 (1925). sults. R E C ~ I V EApril D 16, 1934. 478
Precipitation of Barium in the Copper-Tin Group of Qualitative Analysis WILLIAMT. HALLAND ROBERTB. WOODWARD, Massachusetts Institute of Technology, Cambridge, Mass.
P
RIOR to 1920 it was the usual practice in qualitative
analysis to precipitate the copper-tin group by introducing hydrogen sulfide into a hot solution containing a little free hydrochloric acid. Students were warned not to pass hydrogen sulfide into a solution containing nitric acid or aqua regia. In the 1920 edition of Noyes’ excellent text ( I ) , nitric, rather than hydrochloric, acid is recommended for dissolving solid substances, making the solution 0.3 N in nitric acid before precipitating with hydrogen sulfide. Except when arsenic is present, the precipitation takes place in the cold. Arsenic forms very insoluble sulfides. Although arsenic sulfide cannot be dissolved appreciably by hot hydrochloric acid, it is precipitated very slowly from cold, dilute acid solutions of an arsenate, Noyes recommends, therefore, filtering off the precipitates that form on passing hydrogen sulfide into the cold solution, heating the filtrate to about 90” C., and introducing more hydrogen sulfide. If a yellow precipitate forms slowly from the hot solution, strong hydrochloric acid is added, the solution is evaporated to dryness and, after adding more hydrochloric acid, is saturated with hydrogen sulfide first in the cold and later a t 70” to 90” C. This procedure has been copied into other textbooks (2). In working with solutions containing 40 mg. of arsenic as potassium arsenate and 40 mg. of barium as chloride, several students in qualitative analysis recently failed to find any barium. After testing all the precipitates obtained in the analysis, it was eventually found that the barium had been precipitated as barium sulfate during the precipitation with hydrogen sulfide. If a solution containing arsenate in 0.3 N hydrochloric acid is treated with hydrogen sulfide at 90” C . , a precipitate of
arsenic sulfide soon forms and no appreciable dissolving of the precipitate takes place when the solution is evaporated to dryness after adding some concentrated hydrochloric acid. If the experiment is repeated with a solution which is 0.3 N in nitric acid at the start, the precipitate of arsenic sulfide sometimes disappears completely during the evaporation. If the solution contains barium ions, these are precipitated as barium sulfate, while the arsenic sulfide is dissolving. A series of experiments was carried out with varying quantities of arsenic and of barium, following as closely as possible the procedure recommended by Noyes for precipitating the copper-tin group. I n the absence of a precipitate of arsenic sulfide there was no precipitation of barium. During the evaporation with hydrochloric acid, the excess hydrogen sulfide is boiled off before the nitric acid or aqua regia becomes strong enough to oxidize sulfide to sulfate. When this oxidizing acid becomes concentrated sufficiently to dissolve arsenic sulfide, it is also strong enough to oxidize sulfide to sulfate. The danger of forming barium sulfate during precipitation with hydrogen sulfide can be avoided by using hydrochloric instead of nitric acid to make the solution 0.3 N in mineral acid before treating with hydrogen sulfide or by filtering off any arsenic sulfide precipitate before removing nitric acid by evaporation with hydrochloric acid. LITERATURE CITED (1) Noyes, A. A., “Qualitative Chemical Analysis,” Rumford Press, Concord, N. H., 1920. (2) Treadwell, F. P., and Hall, W. T., “Analytical Chemistry. Vol. I Qualitative Analysis,” p. 289, John Wiley & Sons, N. Y.,1932. R ~ C B I VSeptember ~D 1, 1934.
