ANALYTICAL EDITION
300
units (34,’35),the shape and size of the crystallites as well as the attraction forces between them, and the nature and the amount of the intercrystalline material will also have considerable influence upon the properties of the fiber. This will necessitate a consideration of the chemical constitution and microscopic structure of the fiber in connection with x-ray studies in order properly to interpret the x-ray results. Such studies are in progress and the modifications and limitations of the above general method when applied to specific fibers will be described in future publications concerning the application of this method to different types of fibers and to specific problems relating to these fibers. It is obvious that the method described in this paper is not limited to cellulose fibers but may be applied equally well to protein fibers, regenerated cellulose sheets, cold-worked metals, or any other material having a fiber structure. LITERATURE CITED Anderson, D. C., Ohio J . Sei., 28, 299 (1928). Bragg, Sir Wm., “Introduction to Crystal Analysis,” Van Nostrand, 1929. Chaumeton, P., and Yardsley, V. E., Brit. Plastics, 2,452 (1931). Clark. G. L.. “Auulied X-Raw.” McGraw-Hill, 1932. Clark; G. L., IND.~ENO.CKEM.,22, 474 (1930). Clark, G. L., Pickett, L. W., and Farr, W. K., Science, 71, 293 (1929). Eckling, K., and Kratky, O., A~aturwissenschaften,18, 461 (1930). Farr, W. K., and Clark, G. L., Contrib. Boyce Thompson Inst., 4, 273 (1932). Fiers-David, H. E., and Brunner, A,, Helv. Chim. Acta, 13, 47 (1930). Frey, A., Naturwissenschaften, 15, 760 (1927). Hall, A. J., Textile Colorist, 53, 520 (1931). Harrington, E. A., J . Optical Soc. Am., 16, 211 (1,928). Harrison, G. R., Ibid., 10, 157 (1925).
Vol. 5, No. 5
(14) Hartman, 2. Instrumentenk., 19, 97 (1899). (15) Hess, K., and Kate, J. R., “Chemie der Zellulose und ihrer Begleiter,” Akademische Verlagsgesellschaft, Leipsig, 1928. (16) Kelley, T. L., “Statistical Method,” Macmillan, 1923. (17) Koehler, A,, Trans. Am. SOC.Mech. Engrs., 53, 17 (1931). (18) Levin, E., and Rowe, F. M., Rayon Record, 4,1283 (1930). (19) Mark, H., J. Sac. Dyers Colourists, 48, 53 (1932). (20) Mark, H., Kunstseide, 12, 214 (1930). (21) Mark, H., Rayon Record, 7,165 (1933). (22) Mark, H., Trans. Faraday Soc., 29, 6 (1933). (23) Meyer, K. H., and Mark, H., “Aufbau der hochpolymeren organisohen Naturstoffe,” Akademisohe Verlagsgesellschaft, Leipzig, 1930. (24) Meyer, K., and Mark, H., Ber., 61B, 593 (1928); 2. physik. Chem., 2B, 115 (1929). (25) Morey, D. R., Textile Research, 3, 325 (1933). (26) Polanyi, M., 2. Physik, 7, 149 (1920) ; Naturwissenschafton, 9, 337 (1921). (27) Polanyi, M., and Weissenberg, K., 2. Physik, 9, 123 (1922); 10, 44 (1922). (28) Preston, J. M., Trans. Faraday Soc., 29, 65 (1933). (29) Riets, H. L., “Handbook of Mathematical Statistics,” Houghton Mifflin. 1917. (30) Ritter, G. J., Sisson, W. A., and Clark, G. L., IND.ENG.CHEM., 22, 495 (1930). (31) Schiamek, W., 2.physik. Chern., 13B, 462 (1931). (32) Schmidt, B., 2. Phzlsik., 71. 696 (1931). (33) Siegbahn, M., Phii. Mag., 48, 217 (1924). (34) Sponsler, 0. L., Protoplasma, 12, 241 (1931); Nature, 125, 634 (1930). (35) Sponsler, 0. L., and Dore, W. H., Fourth Colloid Symposium Monograph, Chemical Catalog, p. 174 (1926). (36) Vasil’ev, K. V., Trans. Inst. Econ. Mineral. Met. (Moscow), 34, 16 (1928). [C. A., 22, 4012 (1928)l. (37) Yule, G. U., “Introduction to the Theory of Statistics,” Griffin, London, 1922. RECEIVEDApril 15, 1933. Presented before the Division of Cellulose
Chemistry at the 85th Meeting of the American Chemical Society, Washington, D. C., March 26 t o 31, 1933.
Colorimetric Determination of Fluorine W. D. ARMSTRONG, Laboratory of Physiological Chemistry, University of Minnesota, Minneapolis, Minn. HE d e t e r m i n a t i o n of Fluorine in solution is determined by its these e x p e r i m e n t s were pubfluorine in silicon tetrafading action on the color of ferric acetylacetone. l i s h e d @), F o s t e r (4) has refrom ported a procedure developed fluoride The influence of the acidity of the solution and of on somewhat similar principles, a highly simplified apparatus (1) the presence of certain impurities 3 eliminakd using t h i o c y a n a t e as color required the development of a by determination of the fading caused by the reagent for iron. However, the method with which sulfatesand colored compounds formed by salts of volatile acids would not fluorine in a n aliquot of the solution, followed by a iron and its color reagents preinterfere. Soluble fluorides in measurement of the fading produced by an equal viously listed, with the exception Or slightly acid aliquot to which has been added a known quantity of acetylacetone, fade apprecireact with ferric iron to form a Of Jluorine. The fluorine content Of the aliquots ably in a short time. Furthercomplex which does not develop is calculated from the ratio of the fading of the more, the degree of fading caused s, color with the various reagents by a u n i t a m o u n t of fluorine for iron. The colorimetric titraunknown to that of the known, multiplied by the on all of the colored iron comtion r i ~ t J based ~ ~ d On this fact, quantity offluorine added in the second case. Dounds is markedlv altered bv as developed by Guyot (6) and ;light c h a n g e s i n - t h e acidity Greef (5); has undergone considerable modification, chiefly by Treadwell and Kohl @), and of the solution. It is very difficult to adjust the acidities by Fairchild (3). The procedure to be reported is an applica- of different solutions with sufficient exactness to permit tion of the same principle, but it allows the determination of reproducible results to he obtained with small amounts of microquantities of fluorine in the presence of substances which fluorine. A buffer with a pH slightly under 7 which did not itself affect the colored iron compound was not found. interfere with other methods. Attempts were made to adapt the principle directly to While the method already outlined and as reported by Foster colorimetric procedure. Solutions of ferric thiocyanate, can be applied with fairly accurate results when the necessary partially faded by various amounts of fluorine, were compared factors can be controlled, in the procedure here reported with similar solutions containing standard amounts of fluorine there is no necessity for observing these difficult precautions. or no fluorine a t all. Similar trials were made in which The color developed by ferric iron and acetylacetone has salicylic acid, 8-hydroxy quinoline, and acetylacetone were been made the basis of a colorimetric method for iron desubstituted for thiocyanate as color reagents for iron. Since termination by Pulsifer ( 7 ) . The stability of the compound
September 15,1933
I N DUSTR IAL A N D E NG I NEER I N G CH E MISTR Y
301
chloride and 1 cc. of the acetylacetone solutions. (It seems probable that a stock solution of ferric acetylacetone could be employed, but the writer has not tested such a procedure.) Add an aliquot of the unknown solution containing not over PRINCIPLE OF METHOD 0.25 mg. fluorine to one flask, and dilute both flasks to volume. It was found empirically when the conditions described Compare the solutions in the colorimeter with the solution containing no fluorine set at 20 mm. in the left cup. Take under Procedure were used that plotting the colorimeter twenty readings by increasing the depth of the solution in the readings of solutions of ferric acetylacetone faded by quanti- right cup and average the results. Repeat the procedure with ties of fluorine up t o 0.4 mg. against the fluorine content of the same size aliquot of the unknown solution, adding 1 cc. each solution gives a straight line (curve 1 in Figure 1). (0.1 mg. fluorine) of the standard solution of sodium fluoride to flask containing the unknown. Again take twenty readings, The slope of this line is altered b y changes in the acidity the as before, and determine the average. Calculate the results of the solutions and by certain other substances. It is there- according to the equation: fore necessary to prepare a standard having the same acidity (X - 20) DO.1 and concentration of impurities as the unknown by adding F = (Y - XI t o a n aliquot of the unknown solution a known quantity of fluorine. The reading of the unknown, subtracted from the where F represents the fluorine content of the total solution in reading of the unknown plus 0.1 mg. fluorine, gives the fading milligrams, X is the reading of the unknown, Y is the reading of the unknown plus 0.1 mg. fluorine, and D represents the ratio caused by the known quantity of fluorine. of the total volume af the solution to the volume of the aliquots. formed and its specificity in the presence of impurities makes acetylacetone a superior reagent for iron.
The results of some analyses of sodium fluoride solutions are given in Table I. The fading caused by a unit amount of fluorine varies slightly because of the pH of the solutions and, in some cases, due to the fact that different solutions of ferric chloride were used in the separate analyses. TABLEI. ANALYSISOF SODIUMFLUORIDE SOLUTIONS F FOUND F PRESENT* I N TOTAL IN TOTAL UNKNOWN SOLUTION SOLUTION Mm. Mm. Mg. Mg. 24.45 28.88 0.500 0.500 24.45 28.90 0.500 24.30 0.485 28.71 24.44 28.90 0.495 22.16 25.55 0.245 0:iio 22.14 26.45 0.245 20.84 0.100 o:iio 25.01 20.74 24.44 0.100 0:oiJo 20.40 24.41 0.045 #.The aliquots in all cases represented one-fifth of the total volume of the READINQ O F
READINQ OF UNKNOWN
+ 0.1 MG. F
... ...
solution.
FIGURE 1. FADING OF FERRIC A C E T Y L A C E T O N BY E DIFFERENT AMOUNTS OF FLUORINE
Theory would demand that the data from such a n experiment as that indicated in curve 1, Figure 1, should give a hyperbola when plotted if the solutions obeyed Beer's law and the colored element suffered no change on dilution. Evidently there are equilibrium conditions in solutions of ferric acetylacetone and fluorine such that the fluorine and acetylacetone compete for the iron and each added increment of fluorine meets with a more severe competition. APPARATUSAND PROCEDURE COLORIMETER. A light filter such as the blue Bausch and Lomb 3610 must be used in the eyepiece of the Duboscq colorimeter, since the colors of solutions containing different concentrations of ferric acetylacetone vary from red to yellow and cannot be matched directly. FERRICCHLORIDE.Prepare a solution of ferric chIoride containing 0.3 mg. iron per cc. Protect it from light during use and discard after 2 to 3 hours. ACETYLACETONE. Prepare a 0.5 per cent aqueous solution from the freshly distilled product. STANDARD FLUORINE SOLUTION.Prepare a solution containing 0.1 mg. fluorine per cc. from sodium fluoride of known purity. If the solution contains carbonates, add a few drops of phenolphthalein and introduce 0.1 N hydrochloric or nitric acid dropwise to the boiling solution until it no longer turns pink on further boiling. Immediately make the solution slightly alkaline with 0.1 N sodium hydroxide and allow it to cool in a stoppered flask. Make this, or a solution not containing carbonates, Just acid to phenolphthalein and add a drop of dilute acid (1 to 100). To each of two 25-cc. volumetric flasks transfer 1 CC. of the ferric
LIMITATIONS OB METHOD The effect of salts of volatile acids and other substances likely t o be present in silicon tetrafluoride distillates and other fluoride solutions has been investigated. One-tenth gram sodium chloride and 0.2 gram sodium sulfate alter the color of ferric acetylacetone, but 0.05 gram of the first salt and 0.1 gram of the second, either alone or together, are without influence on the colored compound. Therefore, the aliquots of the unknown solution should not contain more than the latter amounts of these two salts. Sodium nitrate up to 0.4 gram and saturated silicic acid up to saturation are without effect on the color of ferric acetylacetone. The solution must be neutral or slightly acid and must contain no ion which forms a precipitate or undissociated salt with ferric iron or with fluorine. OF SODIUM FLUORIDE SOLUTIONS CONTABLE11. ANALYSES TAINING IMPURITIES
+
READINQ O F
UNKNOWN READING OF UNKNOWN 0.1 MG. F Mm. Mm. 21.11 22.24 21.26 22.53 21.84 20.61 20.58 21.74 21.75 20.58
F FOUND IN
TOTAL
SOLUTION Mg.
F PRESENT"
TOTAL SOLUTION IN
Mg .
0.490 0.600 0.495 0.245 0:iio 0.250 0.250 0:i60 4 The aliquot8 in all case8 represented one-fifth of the total volume of the solution. Each contained.0.1 gram NalSOd, 0.1 gram NaNOs, 0.04 gram NaCI, and 5 cc. saturated silicic acid.
Of the substances mentioned above only sodium sulfate reduces or alters in any other way the fading action of fluorine on the color of ferric acetylacetone. Curve 2, Figure 1, shows the results of two experiments similar to the one whose results are recorded as curve 1, except that the aliquots of
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ANALYTICAL EDITION
302
the fluoride solutions in one case contained 0.1 gram sodium sulfate, and in the other, 0.1 gram of the same salt and also 0.1 gram sodium nitrate, 0.04 gram sodium chloride, and 5 cc. saturated silicic acid. The colorimeter readings in the two experiments agreed within experimental limits and are therefore plotted as one curve. Curve 1 shows the results when the aliquots contained no impurities and when they contained 0.1 gram sodium nitrate, 0.04 gram sodium chloride, and 5 cc. saturated silicic acid. Although the effect of sodium sulfate is to reduce the degree of fading of ferric acetylacetone caused by fluorine, and to render the procedure less sensitive, the accuracy of the results is not materially affected, as is evident from Table 11. Later experiments have shown that the sulfate collected ia the receiver of a
simplified silicon tetrafluoride evolution apparatus (1) is not sufficient to alter appreciably the fading action of fluorine on the colored substance.
LITERATURE CITED (1) (2) (3) (4) (5) (6) (7) (8)
Armstrong, W. D., IND.ENQ.CHEM.,Anal. Ed., 5, 315 (1933). Armstrong, W. D., Proc. SOC.Ezptl. Biol. Med., 29,414-15 (1932). Fairchild, J. G., J. Wash. Acad. Sci., 20, 141-6 (1930). Foster, M. D., J.Am. Chem. Soc., 54,4464-65 (1932). Greef, A., Ber., 46, 2511-13 (1913). Guyot, M. P., Compt. Rend., 71, 274-5 (1870); 73, 273-4 (1871). Pulsifer, H. B., J. Am. Chem. SOC.,26, 967-75 (1904). Treadwell, W. D., and Kohl, A., Helv. Chim. Acta., 8, 500-7 (1925); 9,470-85 (1925).
RECEIVBD May 29, 1933.
Determination of Pyridine Bases in the Presence of Ammonia F. H. RHODESAND K. R. YOUNGER, Cornel1 University, Ithaca, N. Y.
T
HEPrude gas from by-product coke ovens contains considerable quantities of the vapors of pyridine, quinoline, isoquinoline, and their homologs. The “tar bases” of higher boiling points are, for the most part, condensed with the tar, but considerable quantities of the vapors of the more volatile bases are carried forward into the ammonia saturator and are there absorbed as their sulfates. The concentration of the sulfates of the organic bases in the saturator bath liquor finally attains a concentration a t which the rate of removal of the tar bases as impurities on the crude ammonium sulfate becomes equal t o the rate of introduction into the bath. The accurate determination of the tar bases in saturator bath liquor and in crude ammonium sulfate is rendered difficult by the presence of ammonium sulfate in large excess and by the wide variation in the basicities of the individual bases. Some of these compounds are so very weakly basic
0
/O
20
30
40
Cc. o f NaOH added. FIGURE 1. TITRATION OF HYDROCHLORIDES OF PYRIDINE BASES 1 2: 3.
Pyridine h drochloride a-Picoline Xydrochlorjde ,?-Picoline hydrochlorlde
that their salts are largely hydrolyzed in neutral solution; others are almost as strongly basic as is ammonia and can be liberated only by making the solution so strongly alkaline that most of the ammonia is set free. One method that has been used to determine pyridine bases in saturator bath liquor is to treat a measured volume of the solution with an excess of sodium hydroxide, distill the ammonia and tar bases into a dilute acid solution, render this solution alkaline, and add
an excess of a solution of sodium hypobromite to oxidize the ammonia, distill the tar bases into standard acid, and titrate the excess of acid with standard alkali, using methyl orange or some other indicator sensitive to weak bases. This method is not very satisfactory. A large amount of the hypobromite solution must be added to oxidize the large excess of ammonia, the recovery of the bases is often incomplete, and the end point in the final titration is not a sharp one. Various expedients for minimizing these disadvantages have been suggested (I,$) but no really satisfactory method has been described for determining tar bases in the presence of large amounts of ammonium salts. The authors have found that the various tar bases can be determined by electrometric titration and that this procedure eliminates some of the disadvantages inherent in the older methods.
PRELIMINARY EXPERIMENTS One hundred cubic centimeters of an approximately 0.25 N solution of pyridine in dilute hydrochloric acid were titrated with approximately normal standard solution of sodium hydroxide. After each addition of the standard alkali the pH of the solution was measured, using a quinhydrone electrode and balancing against a saturated calomel electrode. Preliminary experiments had shown that the standard hydrogen electrode is rapidly poisoned by pyridine and other organic bases and by some of the impurities that are normally present in saturator bath liquor. For this reason the quinhydrone electrode was used, despite its liability to error in strongly alkaline solutions. Within the range of pH encountered in the authors’ work the quinhydrone electrode gave results that were entirely satisfactory for the accurate determination of the tar bases, although in a few cases the absolute values of the pH a t the extreme alkaline end may be in error. The results obtained in the potentiometric titration of pyridine by sodium hydroxide are shown by curve 1 on Figure 1. Free pyridine begins to be liberated when the pH of the solution reaches 2.8; the liberation of pyridine is complete a t a pH of about 8.5. The break that indicates the beginning of the liberation is not extremely sharp. Pyridine is such a weak base that its hydrochloride is hydrolyzed to a very considerable extent. The difficulty of determining pyridine ac-
