INDUSTRIAL AND ENGINEERING CHEMISTRY
620
of culture chambers is highly important, especially in reducing sampling error variability. Metarrhizium sp. and Chaetomium globosum cause very rapid decomposition, are easily handled, and have other features that make them satisfactory test organisms. They are definitely superior to Chaetomium elatum, Alternaria sp. Hormodendrum sp., and Stachybotrys papyrogena. Ammonium nitrate was found to be a better source of nitrogen than sodium nitrate for the development of most of the fungi. The pH of the su6strate appears to have an important influence on the activity of cellulose-destroying fungi.
Acknowledgment Grateful acknowledgment is made to Ruth E. Rogers for suggestions in connection with the textile phase of the investigation, to L. M. Ames for identifying the species of Chaetomium, to Vera K. Charles for determining the identity of Stachybotrys papyrogena, to Charles Thom for the tentative identification of Metarrhizium sp., and to Katharina Bollenbacher and Helen G. Wheeler for valuable laboratory assistance
Vol. 14, No. 8
with the transfer of cultures and breaking strength measurements.
Literature Cited (1) -4m.SOC. Testing Materials, Standards on Textile Materials
(1941). (2) Armstrong, Chemistry & Industry, 60, 668-74 (1941). (3) Bur. Agr. Chem. Eng., U. S. Dept. Bgr., personal communication (1942). (4) Furry, Robinson, and Humfeld, ISD. ENG.CHEM.,33, 538-45 (1941j , ( 5 ) Levine andveitch, Ibid., 12, 139-41 (1920). (6) Prindle, Tertile Research, 4, 413-28, 463-78 (1934). (7) Ibid., 5, 11-31 (1934). (8) Rigler and Greathouse, Science, 92, 363-4 (1940). (9) Rogers, Wheeler, and Humfeld, U. S. Dept. Bgr., Tech.Bull. 726 (1940). (10) Searle, J . TeztileInst., 20, T162-74 (1929). (11) Thayson, Bunker, Butlin, and Williams, Ann. A p p l i e d Biol., 26, 760-81 (1939). (12) Thom, Humfeld, and Holman, Am. Dyestuf Reptr., 23, 581-6 (1934). (13) Veitch and Levine, Science, 49, 618 (1919). PRESENTED before the Division of Cellulose Chemistry a t the 103rd Meeting of the AMERICAN CHEMICAL SOCIETY, Memphis, Tenn.
Rapid Volumetric Method for Determination of Sulfate Ion MERLE RANDALL AND HENRY 0. STEVENSON, University of California, Berkeley, Calif.
B
ALAKHOVSKI and Ginsburg ( I ) suggested in 1931, but did not investigate, a volumetric method for the determination of sulfate ion, which consisted of adding a known amount of barium chloride to the solution containing sulfate and titrating the excess with sodium pyrophosphate. The following reactions occur:
+ +
Ba++ SO4-- = BaSOn(s) 2Ba++ PZO,---- = BalP,O,(s)
(1) (2)
,4n excess of pyrophosphate ion hydrolyzes and the end point is determined by using some such indicator as phenolphthalein. The barium sulfate is found by difference. Barium pyrophosphate is soluble to the extent of only 0.01 part in 100 parts of water a t 20" C. (Hodgman and Lange, b), and by using a water and alcohol medium, it was believed this solubility could be further decreased. The sodium salt of the pyrophosphate ion was chosen, since barium pyrophosphate is soluble in ammonium salts. Since the reaction of barium toward the sulfate ion is known and understood, the problem concerned the reaction of barium ion with pyrophosphate ion. Actually, the method was found to be experimentally unsatisfactory because (1) the alkalinity of the pyrophosphate ion depends upon its hydrolysis in water, and this hydrolysis is too slow t o give a satisfactory and reproducible end point. (2) At low alcohol content, the solubility of barium pyrophosphate is great enough to allow some hydrolysis of the pyrophosphate, thus giving a premature end point. The amount of sodium pyrophosphate needed to react with a given amount of barium a t various proportions of alcohol is shown in Figure 1. The results are erratic. As the alcohol content increases, the amount of pyrophosphate ion required to titrate the barium increases rapidly. Since no constant value of barium could be ascertained, the method was abandoned.
Disodium Hydrogen Phosphate Method Although the sodium pyrophosphate method was unsatisfactory, the authors felt that some other salt might be substituted, and disodium hydrogen phosphate was found satis factory. The extreme alkalinity of monohydrogen phosphate, HP04--, is well known. The presence of alcohol should have little or no effect upon its hydrolysis, and a t the same time alcohol serves to cut down the solubility of barium hydrogen phosphate, BaHP04. The reaction is: Ba++ HPO,-- = BaHPOp(s) (3) rlmmonium compounds must not be present, because of the solubility of barium hydrogen phosphate in the presence of ammonium ions.
+
Percent alcohol FIGURE1. STO-D.4RD SODIUM PYROPHOSPHATE SOLUTION REQUIRED TO CHANGE POINT OF METHYLRED IN ALCOHOL-WATER MEDIA
August 15, 1942
ANALYTICAL EDITION
A known amount of barium chloride was added with mechanical stirring, to the acidic solution containing the soluble sulfate. Alcohol was then added to the solution, and the whole was brought to neutrality against methyl red (0.1 per cent in 95 per cent alcohol). The solution with the barium sulfate in suspension was made very slightly acidic by the addition of one drop of hydrochloric acid of concentration equivalent to that of the disodium hydrogen phosphate solution. This latter solution was standardized by the same method against known barium chloride. TABLE I. EFFECTOF ALCOHOLCONCENTRATION ox BARIUM HYDROGEN PHOSPH.4TE ENDP O I N T Trials
M1. 1
0 .0 ...
2 3 4 5 6 7
0.5 1.0 2 .o 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 10.0 10.0 10.0 15.0 15.0 15.0 20.0 30.0
8
9 10 11 12 13 14 15 16 17 18 19 20
Alcohol by Volume
NslHPO, MI. 0.25 12.80 13.90 14.12 14.35 14.58 14.75 15.35 15.51 15.75 16.05 16.30 16.30 16.31 16.30 16.27 16.30 16.33 16.34 16 35
CaHsOH
70 0.0
2.1 4.0 7.7 11.0 14.0 16.8 19.1 21.1 23.7 25.7 27.5 27.5 27.5 27.5 36.3 37.5 45.0 52.1 62.0
621
standardized 0.1 .%f hydrochloric acid is added. Sufficient alcohol is now added to ensure a final solution containing more than 27.5 per cent by volume. The excess of barium chloride is titrated with approximately 0.05 LM disodium hydrogen phos hate to the permanent yellow end point of the methyl red, the xsodium hydrogen phosphate is standardized against the barium chloride solution without addition of any sulfate, and the sulfate is then computed by difference. EXPERIMENTAL RESULTS. Potassium sulfate was used. For standardizing the phosphate solution, 0.00530 gram of barium chloride required 1 ml. of disodium hydrogen phosphate solution. The original addition of barium chloride was 0.14014 gram, being an excess in each case. The results are given in Table 111. SULFURIN PETROLEUM. The method was checked in one of the Tide Water Associated Oil Company’s control laboratories and agreed closely with the gravimetric barium sulfate method. ilpproximately 0.8-gram samples of petroleum oil containing about 2 per cent of sulfur were weighed, and fired in an oxygen bomb, the resulting acids mere washed from the bomb and oxidized completely to sulfate ion, and the method was used as outlined above. The entire procedure required but 35 minutes and agreed with the standard gravimetric method within 1 to 1.5 per cent, being lower in each case. TABLE111. BARIUM HYDROGEN PHOSPHATE METHOD FOR S u b FATE
The titration may be done rapidly. It will appear to have gone to the end point when the yellow color is first observed. However, upon standing momentarily, the yellow color fades, probably owing to desorption of barium ion. The true end point will be given when the pink no longer reappears. EFFECTOF ALCOHOL CONCENTRATIOX. Constant results for barium content mere obtained when the alcohol content was 27.5 per cent or more of the final volume. Ordinarily 20 ml. of unknown mas taken for the titration. A white porcelain evaporating dish was found to be ideal for watching the color change of the end point. The effect of the alcohol concentration is given in Table I. An average value of 16.32 ml. of disodium hydrogen phosphate was taken as having titrated 0.08650 gram of barium chloride. Thus. using methyl red as an indicator, 1 gram of disodium phosphate equals 1.4239 grams of barium chloride. TABLE 11. EFFECTOF ADDEDSODIUM AND POTASSIUM CHLORIDES O S B.4RIUhf HYDROGES PHOSPHATE JJETHOD Salt
Added Gram
Gram
NaCl
0.05516 0.11032 0.16547 0.22063 0.06088 0.12176 0,24353
0.08650 0.08650 0.08650 0.08650 0,08650 0.08650 0.08650
KCl
BaCh
ClHrOH MI 10 10 10 10 10 10 1.5
SagHPO,
Alcohol by Volume
.M1.
70
16.25 16.30 16.30 16.32 16.28 16.31 16.31
34.2 33.0 31.9 30.9 35.4 35.4 30.1
EFFECTOF S-ALTS ox BARIUM-IOK DETERMINATIONS. The effect of the following ions was tested: Fe+++, Fer+, Mn++, Cu++, Cd-+, K+, and Na+. The heavy metals whose ions form insoluble hydrogen phosphate salts-all the above ions with the exception of sodium and potassium-were found to interfere. This is not of serious consequence, however, since the interfering metal ion is easily removed. The solutions containing added sodium and potassium chloride were calculated to have required 16.31 ml. of disodium hydrogen phosphate for the amount of barium chloride added. See Table 11.
Sulfate Determinations An excess of approximately 0.05 M known barium chloride solution is added with mechanical stirring to an acidified solution of the unknown sulfate at approximately 0.05 M . The solution,
without filtering, is made neutral to methyl red and one drop of
so4 Calcu-
CzHsOH by lated NazHPO4 Volume so4 Found Error Gram 70 MI. Gram % 0.03874 10.55 38.10 0,03884 0.28 0.04334 8.65 35.21 0,04347 0.30 0.04334 8.77 36.20 0,04318 -0.38 0.02504 16.50 29.66 0.02476 -1.11 0.04643 7.51 36.50 0.04627 -0.34 0.04643 7.53 36.48 0.04621 -0.47 0.05030 5.95 35.19 0,05007 -0.47 0.05030 5.92 43.70 0,05016 -0.29 0.06060 1.78 46.30 0,06028 -0.53 The last five trials were mixtures of sulfuric and nitric acids in varying proportions. The last three had approximately 0 1 gram of added sodium chloride. T I h r E . For soluble sulfates, each trial requires about 10 minutes for completion. At no time is filtering necessary. The end point may be approached most rapidly and with the greatest safety when titration is done in a white porcelain casserole. To save time and material, and when the final volume is suspected of being 100 ml. or more, an aliquot should be used. Summary The method suggested by Balakhovski and Ginsburg was proved unsatisfactory. Using disodium hydrogen phosphate as the titrating agent, a satisfactory and rapid method for sulfate and barium ions was found. Barium chloride is added in excess to a sulfate-containing solution, and the excess is titrated to the methyl red end point with standard disodium hydrogen phosphate in an alcohol and mater medium. With ordinary precision, and in the hands of a competent analyst, the method may be expected to give results within 0.5 per cent and require 10 to 15 minutes. The method is applicable in.contro1work, especially for rapidly determining the sulfur content of oils, and for rapid barium determinations.
Acknowledgment The authors wish to express their gratitude to E. T. Lange of the Tide Water Associated Oil Company for his courteous assistance and cooperation in making it possible to test the applicability of this method in the petroleum industry. -v
Literature Cited (1) Balakhovski and Ginsburg, 2.anal. Chem., 86,344 (1931). (2) Hodgman and Lange, “Handbook of Chemistry and Physics”, Sandusky, Ohio, Handbook Publishers, 1942.
