MAY 15, 1935
ANALYTICAL EDITION
Table IV summarizes the analyses of all the samples tested in the order of increasing total arsenic. The arsenic does not increase in direct proportion to iron, sulfur, or ash, although there seems to be a general trend in that direction. However, as shown in Table V, in general the arsenic content increases as the other inorganic constituents increase. TABLEv. Number of Samples Averaged 2 4 4 4
AVER.4GE
ANALYSESO F GROUPSTAKEN FROM TABLE IV
Total AsiOa
Iron
Sulfur
%
%
%
%
0.0003 0.0009 0.0014 0.0048
0.22 1.01 1.70 3.29
0.55 1.92 2.67 4.93
4.43 5.31 9.81 14.97
A8 h
165
However, most of the analyses check within 0.0003 per cent, indicating that the arsenic is probably diffused in extremely h e particles throughout the coaly substance and is not concentrated in particles of arsenopyrite of any appreciable size.
Acknowledgments The author wishes to acknowledge his indebtedness to A. C. Fieldner, who suggested and directed the course of this investigation; to Alden H. Emery, B. W. Gandrud, and E. P. Barrett for many helpful suggestions; and to H. H. Schrenk for check determinations and careful criticism of the manuscript.
Literature Cited (1) Archbutt L., and Jackson, P. B., J . SOC.Chem. Znd., 20, 448-50
Good checks in arsenic analyses were obtained with 1-gram samples of minus 100-mesh coal. For the high-arsenic Jefferson coal 0.1-gram samples were used satisfactorily. One cube of arsenopyrite which would just pass the opening in a 100-mesh screen would add 0.001 per cent of arsenous oxide t o a 1-gram sample.
(1901). (2) Scott, W. W , “Standard Methods of Chemical Analysis,” 4th ed., PP. 46-52, New York, D. Van Nostrand Co., 1925. R E C ~ I ~ November ED 10, 1934. Presented before the Division of Gas emistry at the 89th Meeting of the American Chemical Society, N. Y , April 22 to 26, 1935. Published by permission of the Director, U. S. Bureau of Mines (Notsubject to copyright.)
Volumetric Determinations of Halides Use of Dichlorofluorescein as an -Adsorption Indica KARL BAJIBACH a n d T. H. RIDER, The Wm. S. Rlerrell Co., C i n c i n n
A
DSORPTION indicators for the argentometric determination of halides were suggested by Fajans and his collaborators (3, 4) ; and Kolthoff, Lauer, and Sunde (5) chose dichlorofluorescein as the most suitable substance for the purpose. They gave the results obtained with dichlorofluorescein in the argentometric titration of chlorides, and indicated that equally satisfactory results could be expected in the titration of bromides and iodides. Their work is mentioned in a recent textbook ( 7 ) on quantitative analysis, which stresses the value of their method only in the determination of chloride. Osterberg (8) used dichlorofluorescein as an adsorption indicator for the estimation of chlorides in the blood, carrying out the titrations in an acetone-water solution. During the past two years dichlorofluorescein has been used in these laboratories in many routine titrations with complete satisfaction. This paper will describe the use of the indicator for the analysis of organic hydrochlorides in alcohol solutions, and will give analytical data concerning the argentometric titration of bromides and iodides. The chlorine analysis of Diothane (piperidinopropanediol dipheriylurethan hydrochloride, 1, 9), a new local anesthetic, is an important control test. It is desirable to carry out such analytical work on Diothane with the sample in alcohol solution, and it was found that dichlorofluorescein is as satisfactory an indicator in 75 per cent alcohol solutions as in aqueous solutions. Other organic hydrochlorides prepared in the Merrell research laboratories and some anesthetics on the market have also been analyzed in this way. Halogen determinations on many inorganic compounds have been carried out with dichlorofluorescein as the indicator; among them may be mentioned ammonium chloride, ammonium bromide, ammonium iodide, sodium chloride, sodium bromide, sodium iodide, calcium bromide, potassium
bromide, potassium iodide, mercuric chloride (after previous removal of the mercury), and hydriodic acid. The analyses of these inorganic salts were all carried out in aqueous solution.
Titration of Organic Hydrochlorides The 0.05 N silver nitrate solution used was standardized against dried pure sodium chloride (Mallinckrodt analytical reagent) with the following procedure: Approximately 0.12 gram of the sodium chloride was weighed and dissolved in 80 cc. of 75 per cent alcohol, 8 drops of dichlorofluorescein solution (0.1 per cent Eastman indicator, catalog No 373, in 70 per cent alcohol) were added, and the solution was titrated with the silver nitrate until the coagulated silver chloride precipitate acquired a distinct pink color. This pink color on the silver chloride was taken as the end point; the addition of a few more drops of the 0.05 N silver nitrate caused a pink color through the entire solution. TABLEI. TYPICAL TITRATIONS NaCl Grams 0.1171 0.1195 0.1187 0.1184
AgNOa Solution cc. 40.40 41.22 40.95 40.93
Normality of AgNOa Solution 0.04959 0.04958
0 04959
0 04950
In Diothane analyses a sample of about 0.85 gram was dissolved in 80 cc. of 75 per cent alcohol and the titration was carried out with the 0.05 N silver nitrate solution in the manner described above. Some results are: 8.17 per cent chlorine, 4 batches (Nos. 67751, 67977, 68131, 68593); 8.18 per cent chlorine, 2 bgtches (NOS,67369, 68362); 8.16 per cent chlorine, 1 batch (Yo. 67934); theoretical, 8.17 per cent chlorine.
INDUSTRIAL AND ENGINEERING CHEMISTRY
166
Other organic hydrochlorides analyzed are : a-Methylpiperidino ropanediol diphenylurethan hydrochloride, 8.01 per cent chfbrine; theoretical, 7.92 er cent chlorine. a-Piperidino-n-propylphenylcarbamate h dProchloride, 11 -82 per cent chlorine; theoretical, 11.87 per cent c&orine. Procaine hydrochloride, 13.07 per cent chlorine; theoretical, 13.05 per cent chlorine.
Titration of Bromides and Iodides Samples of ammonium bromide, sodium bromide, and potassium iodide were analyzed for halogen with silver nitrate solution and dichlorofluorescein and the results compared with those obtained on the same samples with the standard Volhard method. The 0.05 N silver nitrate solution was gravimetrically standardized, and the 0.03 N potassium thiocyanate solution used in the Volhard titrations was standardized against the 0.05 N silver nitrate solution, with ferric alum as the indicator. The procedure used in the Volhard titrations was essentially that described in the United States Pharmacopoeia (IO),except for the weights of sample and strengths of the standard solutions employed. The procedure used in the dichlorofluorescein titrations was the same as that described for the determination of chlorine in Diothane, except that the titrations were carried out in aqueous solution and that samples of about 0.2 gram of the bromides and 0.3 gram of the potassium iodide were used. These titrations were carried out in neutral or almost neutral solutions; strong light was avoided, as darkening of the silver halide precipitates made the end point more difficult to detect. TABLE11. TITRATION OF BROMIDE AND IODIDES Bromine Sodium Ammonium bromide bromide Dichlorofluoresceinmethod Volhard method Theoretical
Iodin? in Pqtssmum iodide
%
%
%
77.96 77.93 77.66
82.13 82.11 81.59
76.74 76.73 76.45
These salts were all of U. S. P. quality; their deviations from theoretical halide content were due to the fact that they were not of reagent purity.
Discussion
VOL. 7, NO, 3
necessary, a determination employing dichlorofluorescein as the indicator can be carried out in less time than one in which the Volhard method is followed. Possible errors due to selective adsorption of the excess silver nitrate on the silver chloride precipitate and the filter paper in the Volhard procedure are eliminated, and chances of manipulative error are lessened. The speed, accuracy, and broadnesfi of application of this procedure indicate that it may prove of value in determinations of un-ionized halogen in which the treatment of the sample during the analysis forms the corresponding sodium halide. Such an application may be seen in the modification of the Stepanow method proposed by Cook and Cook (g), in which the sample is digested with absolute alcohol and metallic sodium, resulting in the formation of sodium halide in the reaction mixture. The titration liquid would then contain the sodium halide, among other things, in an alcohol-water solution; and, as has been shown in this paper, dichlorofluorescein is a suitable indicator for such titrations. Other applications may lie in the sodium peroxide fusion method for organic halogen (6) or in the liquid ammonia-sodium process ( I I ) , in which the sample is dissolved in liquid ammonia, treated with sodium, and the sodium halide determined. I n the latter method Vaughn and Nieuwland used both the Fajans procedure, with eosin as an indicator, and the Volhard method for their titrations. Since the completion of this manuscript a new paper (6a) by Kolthoff has discussed the theory of adsorption indicators in some detail.
Summary Dichlorofluorescein has been used as an adsorption indicator in the argentometric titration of organic hydrochlorides dissolved in alcohol, and inorganic halides in alcohol or aqueous solutions. The analytical results have been within experimental error of the theoretical values on pure chemic& or of values obtained by the standard Volhard procedure on chemicals of ordinary commercial purity. Possible further applications of the method have been suggested.
Literature Cited (1) Am. Med. Assoc., J . Am. Med. Assoc., 103, 1777-8 (1934). (2) Cook, W. A., and Cook, Kathryn, IND. ENQ. CHBJM.,And. Ed., 5, 188 (1933). (3) Fajans and Hassel, 2. Elektrochem., 29,495 (1923). (4) Fajana and Wolff. 2. anora. allaem. Chem.. 137. 221 (1924). (5) Kohhoff, I. M., Lauer, W: M.,”and Sunde, C. J., J.‘Am. Chsrn. SOC.,51, 3273 (1929). (6a) Kolthoff, I. M., Chem. Rev., 16, 87 (1935). (6) Lemp, J. F., and Broderson, H. J., Ibid., 39, 2069 (1917). (7) Mitchell and Ward, “Modern Methods in QuantitativeChemical Analysis,” pp, 9, 67, New York, Longmans, Green and Co., 1932. (8) Osterberg, A. E., Proc. StuffMeetings Mayo Clin’nic,5, 300 (1930). (9) Rider, T. H., J. Am. Chem. SOC.,52, 2115 (1930). (10) U. S. Pharmacopoeia X, p. 439. (11) Vaughn, T. H.. and Nieuwland, J. A., IND. ENQ.CHEM,Anal. Ed., 3, 274 (1931).
Dichlorofluorescein is a satisfactory adsorption indicator for the argentometric titration of halides. Results of bromide and iodide titrations using this indicator compare favorably with those obtained with the standard Volhard method, but are usually slightly higher than those of the corresponding Volhard determinations; this can be expected from a considerat.ion of the principles involved in the two methods. I n one case, a slight excess of silver nitrate solution causes the dichlorofluorescein to be adsorbed on the silver halide particles and form its silver salt, which furnishes the end point; in the Volhard procedure, a slight excess of the thiocyanate solution produces the end point; since this excess of thiocyanate is subtracted from the quantity of silver nitrate solution added, the results should be slightly lower than in the titration in which dichlorofluorescein was used. Since only one standard solution need be used and no filtration is
RECHIIVED November 21, 1934. Presented before the Division of Medicinal Chemistry at the 88th Meeting of the American Chemical Society, Cleveland, Ohio, September 10 to 14,1934.
GOLDCOBALT ALLOYSNOT ENTIRELY SUITABLE FOR HIQHGRADERESISTANCE STANDARDS. Tests recently made at the National Bureau of Standards on alloys of gold and cobalt to determine their suitability for use in the construction of resistance standards show that, while some of these alloys are reasonably stable in resistance and have very small temperature coefficients of electrical resistance, their thermoelectric power against copper is very Iarge. For this reason the bureau believes that they are inferior to gold-chromium alloys of about the same proportions.
This conclusion is important since the unit of electrical resistance is maintained in the national standardizing laboratories by meang of wire-wound standards. The national laboratories are interested in improving the quality of these standards, either by improved methods of construction or by the development of better resistance alloys. J Besides stability, resistance alloys should have a low-temperature coefficient of resistance and a low thermo-electric power against copper.
