INDUSTRIAL AND ENGINEERING CHEMISTRY
652 TABLE Iv. Method Electrolytic (analyst 1) Spectrographic (analyst 1 ) Icdinetitration (analyst 2) Pyridine KCNS (analyst 3) Unknown' (analyst 4) Pyridine XCNS (analyst 5 Dithizone
-
ANALYSES OF STEEL
1
2
Sample 3 4
5
6
%
%
%
%
%
%
0.018 0.060 0.070 0.100 0.076 0.108 0.020 0.053 0.073 0.092 0.073 0.122 0.022 0.048 0.071 0.089 0.069 0.115 0.020 0.056 0.074 0.094 0.070 0.108 0.026 0.062 0.067 0.100 0,075 0.103
0.017 0.052 0.075 0.108 0,078 0.119 0.018 0.058 0.083 0.103 0.075 0.115 0.018 0.060 0.088 0.108 0.078 0.120
Vol. 15, No. 10
In Table IV data obtained by the dithizone method are to be found, together with data furnished by Weirton Steel Company on the results of the collaborative study. It is apparent that the dithizone method may be applied to steel without modification.
SOLDER.A 1.0-gram sample was dissolved in concentrated hydrochloric acid and bromine. After filtering off the lead chloride the solution was neutralized to a pH of 2 to 3. Co per was determined in a suitable ali uot by the regular procefw. The copper content of Bureau of h a n d a r d s Sample No. 127 was found to be 0.016 per cent as compared with 0.013 per cent determined spectrochemically and 0.014 per cent chemically by Ruehle and Jaycox (10).
Acknowledgment Samples of numerous foods were analyzed for copper. Recoveries of added copper were made from some sampks, and in a few cases results were checked by the Greenleaf method (7). Results of these analyses are given in Table 111. It is evident that the agreement between the dithizone method and the Greenleaf method is good and that copper recoveries from foods by the dithizone method are satisfactory. STEEL.Since samples of steel are analyzed occasionally for copper in this laboratory,the dithizone method was applied to a set of six steel samples which the Weirton Steel Company had distributed previously for a collaborative study of the determination of copper in tin plate base metal. The sample was prepared for analysis by dissolving 1 gram of steel filings in 100 ml. of hot 1 to 9 sulfuric acid. Redistilled nitric acid was added dropwise and heating continued until the solution was a clear yellow color. After cooling it was diluted to 250 ml. in a volumetric flask. A suitable aliquot was then analyzed for copper.
The authors wish to thank G. C. Jeniaon of the Weirton Steel Company for supplying steel samples and the results given in Table IV.
Literature Cited h a f , A. G., and Hollibaugh, W. C., IND.ENQ.CH~M., ANAL. ED., 12, 695 (1940). Biazzo, Ana. chim. applieata, 16, 2 (1926). Clifford, P. A., J. Assoo. 0iWa.l Agr. Chem., 21, 695 (1938). Coulson, E. J., Zbid., 19,219 (1936). Fischer, H., Angm. Chem., 47,685 (1934). Fisoher. H., and Leopoldi, G., Zbid., 47,90-2 (1934). Greenleaf, C. A., J. Assac. O W Agr. Chem., 25,385 (1942). Greenleaf, C. A., private communication. Liebhafsky, H. A., and Winslow. E. H., J. Am. Chem. Sm.,59. 1966 (1937).
Ruehle, A. E., and Jaycox, E. K., J . Optical Sac. Am., 33,
111
(1943).
Rusk, H. W., J. Assoo. Oflcial Agr. Chem.,25,980 (1942). Stearns, E. I., IND.ENG.CHEM.,ANAL.ED., 14, 568-9 (1942). Sylvester, N. D., and Larnpitt, L. H., Analyst, 60, 980 (1942).
Determination of Tungsten in Low-Grade Tungsten Ores F. S. GRIMALDI AND VICTOR NORTH
U. S. Department of the Interior, Geological Survey, Washington, D. C.
Two methods based on the Feigl-Krumholz test are described for rapid colorimetric determination of small amounts of tungsten in low-grade ores and tailings. Aliquot portions are adjusted to deal with quantities of tungsten ranging from 0.04 to 0.M mg. of W03. The maximum permissible concentrations of possible interfering ions have been determined and a graphical method of correcting for the usually slight interference of molybdenum is given.
T
H E time required for a tungsten analysis by gravimetric methods is a disadvantage in exploring for tungsten deposits or in control work on mill tailings. Some uncertainties are introduced in the determination of very small amounts of tungsten because of the possible interference of high concentrations of foreign ions introduced by the large sample necessary for the analysis. Procedures for the rapid determination of small amounts of tungsten have been reported by Russian chemists, but the literature is available to American laboratories only through abstracts. In view of the strategic importance of tungsten, the writers thought it desirable to report some new results on methods for its estimation based on the Feigl-Krumholz test.
Feigl and Krumhok (1) showed that a weakly alkaline tungstate solution would slowly develop a yellow color upon the addition of thiocyanate and an acid stannous chloride solution. The color reached a maximum after 30 minutes and it was found that Beer's law was valid from 0.01 to 0.1 mg. of tungsten trioxide. FernjanEiE (8) substituted titanous chloride for stannous chloride and developed the same color instantaneously. Other investigations along similar lines have been carried out by Russian chemists (9, 5 , 6, 8,9). In applying the test to ores the authors preferred to retain stannous chloride as the reducing agent because it is colorless and less care is necessary to obtain satisfactory results. Stannous chloride is preferable when much iron is to be reduced and necessary in the presence of phosphate, as certain combinations of titanium and phosphorus also produce a yellow color.
Reagents and Apparatus Potassium thiocyanate solution. Dissolve 25 grams of reagent grade potassium thiocyanate in 100 ml. of water. Stannous chloride solution. Dissolve 20 grams of the dihydrate in 100 ml. of concentrated hydrochloric acid and 100 ml. of water. Sodium hydroxide solution 1 (approximately 40 per cent). Dissolve 40 grams of sodium hydroxide in 60 ml. of water. Solution 2 (approximately 20 per cent). Dissolve 20 grams of sodium hydroxide in 80 ml. of water.
ANALYTICAL EDITION
October 15, 1943
Mg. of
MOO3
in' Final A l i q u o t
FIGURE 1. INTERFERENCE OF MOLYBDENUM Standard tungstate solution. Solution 1. 1 ml. = 0.002 gram of WOa. Dissolve about 0.71 gram of molybdenum-free sodium tungstate dihydrate in water and dilute to 200 ml. in a volumetric flask. Check the tungstic oxide content by gravimetrically determining WOa. Solution 2. 1 ml. = O.ooOo4 gram of WOs. Dilute a suitable volume of solution 1. Colorimeter. A Klett colorimeter was used in this work.
Experimental For convenience, the Fei 1 Krumholz procedure was modified by using a larger volume final comparison. A lower concentration of stannous chloride than originally recommended was found to give satisfactory results. The final volume of the test solution used by the writers was 26.5 ml. One milliliter of potassium thiocyanate reagent was added to 10.5 ml. of the experimental tungstate solution containing about 0.12 gram of free sodium hydroxide. This corresponds to an alkalinity of about 0.3 N and was used for all subsequent tests. Next, 5 ml. of stannous chloride solution and 10 ml. of concentrated hydrochloric acid were added. The color was compared in a colorimeter with a similarly treated standard.
fi
Under these conditions Beer's law was valid up to 0.5 mg. of tungsten trioxide. Iron, antimony, calcium, magnesium, aluminum, phosphate, sulfate, combinations of iron and phosphate, iron and sulfate, ammonium, and sodium salts do not interfere. Soluble silica does not interfere but may occasionally precipitate out. Iron accelerates the development of the tungsten color. Among the colored metal ions tested, those listed in Table I do not interfere if the final aliquot contains less than the quantities indicated. A few of these elements interfere still less if the tungsten color is concentrated by means of an organic solvent, such as amyl acetate. There is no interference when phosphates are present with smaller quantities of vanadium than indicated in Table I. Chromates have not been encountered in tungsten ores. Copper
TABLE I. LIMITOF INTERFERENCE OF CERTAIN ELEMENTS Element Xi
co
Cr V
Maximum Amount Permissible in Aqueous Solution
M Q.
3. 1.
Ni
co
0 . 3 Cr 0.2 V
Maximum Amount Permissible with Extraction Mg. No interference 20 c o 0.4
Cr
1.3 V
653
precipitates out as cuprous thiocyanate. If sufficient thiocyanate solution is present, however, the supernatant liquid will @ve the characteristic test for tungsten. By experiment, 0.1 gram of copper required 2 ml. of potassium thiocyanate solution for satisfactory development of the tungsten color. Lead precipitates out as the chloride when over 60 mg. of lead are present, but no interference with the development of the color was noticed. Citric acid, in amounts in excess of 0.5 gram, interfered with the maximum development of the color. Of course nitrates and other oxidizing agents interfere with the reducing action of stannow chloride. More than 1 gram of sodium chloride or 2 grams of ammonium chloride will precipitate from the final acid solution but do not alter the tungsten color. Arsenic should be absent; it precipitates out slowly as metallic arsenic. The interference ranges from a brownish opalescence to a black precipitate according to the amount of arsenic present. This behavior of arsenic is very characteristic and easily recognized. Titanium in quantities under 10 mg. does not interfere appreciably. Larger quantities produce a yellow color in the solution which is intensified in the presence of phosphate. Molybdenum produces a weak yellow color similar to the yellow of tungsten. The interference of molybdenum is illustrated in Figure 1. The data for the curve in Figure 1were obtained by applying the general method to various mixtures of tungstate and molybdate. The interference of molybdenum is negligible when present in the final aliquot in quantities below 0.6 mg. of molybdenum trioxide. For rapid work the curve may be used to apply corrections. Molybdenum itself may be quickly determined colorimetrically in a separate aliquot of the same solution used for tungsten (4).
Procedures for Tungsten Ores 1. GENERALMETHOD. Fuse 1.0 gram of sample with 5 grams of sodium peroxide in an iron crucible. Digest the cooled melt with hot water containing a little alcohol to assist in reducing manganate. After the peroxide is destroyed filter into a 250-ml. volumetric flask, washing the residue well with warm 0.5 per cent sodium hydroxide solution. To a 10-ml. aliquot in a 50-ml. beaker add by pipet 0.5 ml. of water, 1 ml. of potassium thiocyanate solution, 5 ml. of stannous chloride solution, and 10 ml. of concentrated hydrochloric acid in the order mentioned. -A standard containing 0.20 mg. of WOc should be pre ared at the same time. For this purpose pipet into a 50-ml. feaker 5 ml. of standard tungstate solution, 5 ml. of water, and 0.5 ml. of sodium hydroxide, Solution 2. Follow with the reagents mentioned above. After 1.25 hours match the standard against the sample in a colorimeter. Best resulta are Gbtained when the standard and the sample have about the same tungsten concentration. 2. PREFERRED METHODWHEN MOLYBDENITE OR ARSENIC Is PRESENT. During the solution of the sample in this method, and in the absence of oxidizing agents, molybdenite is not att#acked and arsenic, volatilizing as arsenic trichloride IS effectively removed. This method is adapted to the determination of small quantities of tungsten because alkali salts are kept to a minimum and no collection methods need be used for concentrating the tungsten. When acid-soluble titanium minerals are resent in excess of 1 per cent titanium dioxide, this method ten& to give low results because of some tungsten retention by titanium phosphate. The writers' experience with tungsten ores from many localities indicates that soluble titania generally does not exceed 0.2 per cent titanium dioxide, a quantity which does not interfere. To 0.5 to 2 grams of finely grqund sample in a 100-ml. beaker add 1 ml. of 1 to 3 phosphoric acid and 40 ml. of concentrated hydrochloric acid. Cover the beaker and allow the solution to digest on the steam bath for about 20 minutes. Remove the cover and evaporate the contents to dryness. Add 10 ml. of 1 to 4 hydrochloric acid and digest for a t least 10 minutes. Dilute to 50 ml. with water and warm. Add paper pulp, and filter into a 100-ml. volumetric flask. Wash the residue with water. To a 10-ml. aliquot add 0.5 ml. of sodium hydroxide, Solution 1, and 1 ml. of potassium thiocyanate solution. Now add the stannous chloride and hydrochloric acid as in procedure 1. Allow the mixture to stand 1.5 hours and compare with a standard made at the same time in the manner indicated in procedure 1.
654
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Acknowledgment
TABLE 11. COLORIMETRIC ESTIMATION OF TUNQSTEN No. 1 2 3 4 5 7.
Mineral Scheelite Scheelite Scheelite Scheelite Scheelite Scheelite Psilomelane
Location Alaska California Alaska Alaska Alaska Alaska Arisona
8 9 10 11 12 13
Scheelite Scheelite Scheelite Coronadite Scheelite Psilomelane
Alaska Alaska Alaska New Mexico Alaska New Mexico
14
Molybdenite
Idaho
6
~~~
Per Cent of W OProcedure 1 Procedure 2 colorimetrii colorimetri; Gravimetrio
...
0.08 0.15 0.11 0.18 0.31 0.48 0.55
0.04 0.10 0.11 0.19 0.26 0.48 0.52
0.60 0.71 0.73 2.0 1.1 1.2
0.83
... ... ... ...
0.60 0.88 0.75 11 .. 81 52 1.29
...
None
None
0.14
... ... 0.31
0.45 0.54
0.74
c
Results on Tungsten Ores The tungsten or- were first analyzed gravimetrically, using 4gram portions easentially by the procedure outlined by Scott (7). Colorimetric estimations using procedures 1 and 2 are given in these are seen to be good in the I1 for range up to 1 per cent tungsten trioxide.
Vol. 15, No. 10
Notes
... ~ontainkb:AS Contained As
...
Total M n 4 8 % BaO 14% ’ ”
The authors wish to thank M. Fleischer for the analyses of samples 7 and 13 and C. Milton for No. 3; also William Schlecht and R. C. Wells for kindly reviewing the manuscript.
Literature Cited
(1) Feigl, F., and Krumholz, P., 2.angew. ... Chem., 45, 674 (1932). (2) FernjanEiE, S., Z. anal. Chem., 97, 332 Pb30%”‘ (1934). Total Mn 50% (3) FernjanEiE, S., Zapodakuya Lab., 6, 289 BaO SrO 15% (1937). MoSzand 1.86% (4) Grimaldi, F. S., and Wells, R. C., IND. ENO.CHEY.,ANAL.ED.,15,315 (1943). (5) Poluektov, N. S., Zavodakaua Lab., 10, 92 (1941). (6) Popov, K. M., and Dorokhova, M. N., ZM., 9,1315 (1940). (7l . , Scott. W. W.. “Standard Methods of Chemical Analvsis”. 5th ed.; Vol. 1, p. 1005,New York, D.Van Nostrand Cia, 1939. (8) Shakov, A. s., Zaoodskuya Lab., 470 (lggl). (9) Voznesenskii, A. T.,ZM., 9, 25 (1940).
...
PaleemNTEn before the Division of Analytical and Micro Chemistry at the 108th Meeting of the AMERICAN CEEMICAL SOCIETY. Pittsburgh, Penna. Published by permiasion of the Director, U. 8. ~eOlOgiC81Survey
Microbiological Determination of Pantothenic Acid Further Studies A. L. NEAL AND F. M. STRONG, College of Agriculture, Udveroity of Wisconsin, Madison, Wis.
The procedure for microbiologiixtl determination of pantothenic acid has been modified by additions to the balal medium and improvements in the method of growing inoculum. The modified method is capable of measuring smaller amounts of pantothenic acid and gives concordant results at increasing levels of sample.
The present paper is concerned (a) with a study of methods for liberating “bound” pantothenic acid in the sample, (b) with procedures designed to remove interfering fat-soluble substances from the test solution, and (c) with efforts to modify the b a d medium in such a way as to avoid the effect of water-soluble, stimulating factors and to prevent “drift”. Except for the modifications detailed below, the general procedure previously described (19) has been followed in the present work for setting up assays and calculating results.
Cultures and Inoculum
A
LTHOUGH published methods for the micrpbiological assay of pantothenic acid (8, 13) have been widely Used
and have been made the basis for various conclusions regarding the physiological and nutritional functions of this vitamin, certain discrepancies raise serious questions as to the reliability of the results. Among these difficulties may be listed lack of agreement with animal tests, the large “drift” frequently observed, and the fact that minor variations in the method of preparing the sample may cause wide fluctuations in the final assay values. Furthermore ( l a ) ,anomalous results were obtained in attempting t o carry out recovery experiments on hydrolyzed samples of fresh liver and kidney. Some of the reasoas underlying these troubles have recently come to light. The effect of fatty acids on the growth of Lactcrbacillwr casei has been discovered (d, I d ) , and methods for avoiding their interference in the riboflavin assay have been worked out ( I , 1.2). It has also become apparent that certain watcrsoluble substances of an unknown nature, and apparently prcsent mainly in brans, are capable of stimulating the bacterial response (5, 7 , 1 5 ) .
Evidence has accumulated in carrying out a large number of assays that the best rcsponse is obtained when the inoculum is not carried through several transfers in the liquid medium as formerly recomrnendcd, but is grown directly from a stab culture. It also appears advisable to transfer the stab cultures weekly instead of monthly. To grow inoculum, cells from a suitable stab are transfcrred into a tube containing 10 cc. of the basal medium (see below) plus 1 microgram of calcium pantothenate. After 24 hourdincubation at 37’ ( * 1”) C. the cells are centrifuged out and resuspended in 10 cc. of saline, and the resulting cell suspension is used as inoculum. Thus there is no “subculture” made between the stock stab culture and the inoculum and the cell suspension is not so extensively diluted with saline as before (IS). One should return to a stab each time inoculum is to be grown. One stab culture may bc used several times if proper precautions are taken to avoid bacterial contamination.
Basal Medium The previous basal medium haa been modified by adding glutamio acid and a supplement prepared from Vitab, by increasing
