1175
V O L U M E 21, NO. 10, O C T O B E R 1 9 4 9 field, there will be some overlapping where a particular element is selected by use of this code. For instance, when compounds of calcium are selected, in addition to all the cards having data on compounds containing calcium, other cards will fall. The deeply punched code number for calcium, however, assures that these additional cards will contain elements chemically related to calcium and will form only a small proportion of the cards sorted from the block. This difficulty could be overcome, in part, by extending the code to a larger number of groups (from 13 to 20 groups) or by using a three-number code for each element (one deep punch and two shallow). In its present form, it is felt that this difficulty would not for practical purposes be serious. Certain arbitrary rules could be set up to simplify this code-e.g., oxygen is coded in oxides only, carbon is coded in inorganic compounds only. If in a laboratory some elements were of particular interest and the overlapping mentioned above is undesirable, these elements could be given a direct code in the spare parts of the card. In the spare parts of the card organic compounds, metal-organic compounds, alloys, minerals, etc., could also be given a direct code. Other codes based on melting point, optical properties, innermost lines of the diffraction pattern, or other easily measured determinative property of a substance could be developed. CONCLUSION
The publication of powdcr diffraction data on punched cards of the type described would increase the cost of publication, but this
increase should be justified if the usefulness of the index were increased by making the data more available. The proposed code is only one of many that could be developed; the individual requirements of workers would necessitate variations of the method employed, and many of these variations would make use of the spare parts of the card. ACKNOWLEDGMENT
The writer wishes to thank A. F. Kirkpatrick of the American Cyanamid Research Laboratories for the suggestions made regarding the coding employed and J. W. Bryers of the McBee Company for his interest and help in the design of the card. LITERATURE CITED
(1) Am. SOC. Testing Materials, Philadelphia, Pa., “X-Ray Diffraction Data Index,” 1942. (2) Casey, R. S., Bailey, C. F., and Cox, G. J., J . Chem. Education, 23, 495 (1946). (3) Cox, G.H., Casey, R. S., and Bailey, C. F., I b i d . , 24, 65 (1947). (4) Frevel, L.K., IND. ENG.CHEM., ANAL.ED., 16,209 (1944). (5) Hanawalt, J. D., and Rinn, H. W., Ibid., 8,244 (1936). (6) Hull, A. W., J. Am. Chem. Soc., 41,1168 (1919). (7) Matthews, F. W., and McIntosh 4.O., Can. Chem. Process Inds.,31,63 (1947). RECEIVEDFebruary 3, 1949.
Determination of Pyridine and Its Homologs in Hydrocarbons by Ultraviolet Spectrophotometry H. D.
L E R O S E N AND
J. T. WILEY, T h e Texas C o m p a n y , Port Arthur, Tex.
Pyridine may be determined in samples of hydrocarbonsof the kerosene-naphtha range rapidly and by a relatively simple technique. The method may be extended to include quinoline and its homologs. I n its application to nitrogen bases, presumably pj-ridinehomologs, by measurement of ultraviolet absorption a t 270 mp, interference from phenol is serious.
T
HE characteristics of pyridine, quinoline, and their homologs in absorption of ultraviolet radiant energy are well known as evidenced by the many publications of their spectra. Some of their spectrograms have been issued by A.P.I. Research Project 44 (I). An examination of the ultraviolet ahsorption spectra of pyridine and quinoline (Figure 1) reveals their propitious nature for analytical spectrophotometry on two counts: The absorption maximum of each compound is steep and narrow, and each maximum occurs where the other shows a minimum or no absorption at all, That pyridine, in solutions of dilute inorganic acid, can be determined by spectrophotometric means appears reasonable; over the range of 1 to 25 p.p.m., the absorbances at 250 mp of standard pyridine solutions in dilute sulfuric acid bear a linear relationship to their concentrations. A search of Chemical Abstracts from 1907 to august 10, 1948, revealed only one analytical method for pyridine (and quinoline) based on ultraviolet spectrophotometry: the fairly recent method of Hofmann ( 3 ) . In this method quantities of pyridine as small as 0.01 mg. pw liter in air samples were absorbed in 1W sulfuric acid, following which the pyridine was determined by ultraviolet absorption a t 255 mF. The method reported herein bears a similarity to Hofmann’s; however, it was developed prior to any knowledge of the existence of Hofmann’s method.
In order to develop a rapid method for the analysis of pyridine and quinoline compounds, knoirn to be present in California naphthas, ultraviolet spectrophotometry was tried. Pyridine and some of its methyl-substituted compounds showed absorption peaks in the region from 250 to 270 m u (I). Spectrophotometric analyses for such constituents could not be applied directly to refinery samples of gasoline, naphtha, and kerosene, inasmuch ar they may contain varying amounts of aromatic hydrocarbons which show strong absorption in the region extending approximately from 240 to 280 mw. OUTLINE OF METHOD
Pyridine, a weakly basic substance, is readily extracted with dilute phosphoric acid from hydrocarbons such as naphtha, gasoline, and kerosene. The absorbance (optical density) of that extract, or a suitable dilution, is measured a t 258 mp. The value obtained is converted to concentration of pyridine by reference to a standard graph. From that concentration its content in the original sample is readily calculated. EXPERIMENTAL
Apparatus and Reagents. Beckman quartz spectrophotoiiieter, Model DU (or equivalent instrument), fully equipped.
Separatory funnels, 125 mi. Volurn+c flasks, glass-stoppered, of various sizes. Volumetric pipets of various sizes. Phosphoric acid (H?POd, 10% by weight in aqueous solut,ion. Calibration of Instrument. A master solution of pyridine (colorless, for Karl Fischer reagent, 214-H, Eastnian Kodak Company) was prepared by dissolving 0.1320 gram in enough 1Oc7, by weight phosphoric acid to makr 1 liter of solution. Dilutions ranging from 0.0013 to 0.0264 gram of pyridiiie p ~ rliter of solution were prepared from that master mlution, using distilled water as the clilnt~nt. The determination of the absoiptioii characteristics on the dilution i.orriiisting of 0.0132 gram of pyridine per 1itc.i. revealed an absorption maximum at 263 mp, Accordingly, absorbance measurements were made on the several tiilut ions at 255 mp, using distilled water
i t possessed negligible ultraviolet ahsorp-
tion.
After applying absorption cell
$%>
2.40 /
2.00
I
-
FIGURE I ULTRAVIOLET ABSORPTION CURVES
FOR PYRIDINE 8. QUINOLINE IN 0.1% H 2 S 0 4
W
0 z
$ 5: 2
1.60-
1.20 -
-
? oao0.40-
0.00 xx)
25-
-Q-
Pyridine (49ppm) Quinoline (26ppml
\
! \
220
240
260
280
I
x)o
320
340
360
I
380
I
400
1177
V O L U M E 21, NO. 10, O C T O B E R 1 9 4 9 Transfer a portion of the final dilution to a 10-mm. silica absorption cell. Measure its absorbance, after setting the reference cell filled with distilled water t o read 100% transmittance, a t a wave length of 255 mp and a slit width of 0.40 mm. (The exact values of the wrave length and the slit width vary slightly among spectrophotometers.) Correct the absorbance observed, if necessary, for the absorption cell correction and the absorbance of the tilank. Using the standard graph (Figure 21, prepared in the calibration of the instrument, convert the corrected absorbance to its equivalent concentration of pyridine. R-ith that information, the pyiidine content may be calculated from these formulas: Pyridine content, mg. per 100 nil. Pyridine content, [VI.
‘c =
=
c x F’ x v
c x E’ x
100
100
looo
wherr) C = concentration (mg. per 100 nil.) of pyridine read from standard graph (Figure 2) F = dilution factor or ratio 1- = volume of sample t,aken in millilit,ers 11- = weight of sample taken in grams OTHER APPLICATIONS
The suitability of pyridine for determination by ultraviolet spectrophotometry suggested that its homologs, as well as quinoline. and its homologs, might likewise be so determined. The method actually was. used to determine basic nitrogenous compounds (nitrogen bases) in California naphtha. S o at’tempt was made t o establish their chemical nature. The fact that they ahsorbed maximally at 270 mp and showed no absorption a t 310 mp (where quinoline absorbs) indicated the possibility of their heing pyridine homologs. Work done by the Union Oil Company on the ultraviolet absorption of methylpyridines, as shown in several spectrograms issued by A.P.I. Research Project 14 (I)! indicated a shift in maxima toivard longer wave lengths as thc result of methyl substitution on the pyridine ring. Inasmuch as the chemical identity of t,henitrogen bases was not established, and they probably consisted of mixtures, somewhat empirical means were necessary in preparing a standard graph for :tnalytical purposes. Exhaustive acid extractions of several large samples of California naphtha were made and the combined estracts served as the master solution of nitrogen bases. I t s concentration was determined by isolating and weighing the nitrogen Iiases contained in an aliquot portion. A standard graph like that for pyridine was then made. Even though the procedure for nitrogen bases gave relative rather than absolute values, useful results were obtained. It was realized, however, that nonnitrogenous acid-extractable compounds might be included as nitrogen bases. S n analysis for
nitrogen was not made on the nitrogen bases isolated, partly because a t that time it was thought. that no satisfactory method existed. For naphthas ot,h13r than the stock studied; i t would be necessary to prepare a separate standard graph, for the absorption characteristics of the nitrogen ba.ses may vary from st,ock to stock. INTERFERENCES
Logically, any substance extractable from hydrocarbon solutions by dilute phosphoric acid and possessing an absorption foi, ultraviolet energy at 253 mp will interfere in the determination of pyridine by the described method. An investigation of substances possessing those requisites was not made. In the application of the procedure t o t,he analysis of nitrogen bases contained in California napht.ha, however, the serious interference of phenol Kas discovered. It was found that phenol was extractable from its solution in spectroscopic solvent with lOT0 by weight phosphoric acid: Seidell ( 3 ) gave the solubility of phenol as 4% in 25vo by weight phosphoric acid (HIPOd), increasing wit’h dccreasing strength of the acid. Occasionally, in determining riitrogc.11 bases in Ca1iforni:i naphtha, :t solid substance formed at the interface of the iiaphth;~ and arid layers. Its nature \\-as n o t known: however, an alcoholic solution of that solid exhibited a spectrogram similar t o that for the nitrogen basei;. Becn,use of the strong likelihood that such solids \ ~ c r eor contained nitrogen bases, means to reduce or prevent their occurrence should be used. A considerable reduction in the size of sample taken proved very helpful in the one inst an ce tried , ACKNOWLEDG.MENT
Permission of the management of The Texas Company to release the information enibodietl herein is gratefully acknowledged. An expression of thanks is also due IT. S. Palmer, L. V. Kike, G. H. Aliller, T. C. Roddy, J r , jand S . IV. Denton for their valuable suggestions offered in the course of the investigation. The kind assistance of Elken Gibson in preparing both graphs is gratefully acknon-ledgeti. LITERATURE CITED ( 1 ) .\mericaii Petroleum I n s t i t u t e Research Project 44, Ultral-iolet Spectral Data, Serial 3-0s. 34-37, 108, 111, 213-214. ( 2 ) Hofmann, Edwai.d, A r c h . H u g . 26. Bakt., 128, 169-78 (1942). (3) Seidell, d.,“Solubilities of Organic Compounds,” 3rd e d . . Vol. 11, p. 3 7 7 , New York, I). V a n Nostrand G O . , 1941.
RECEIVED .January 17, 1949. Presented at t h e Fourth Annual Southwest CHEWCAL SOCIETY, Shreveport, La.,December Regional Meeting. .I\~F:RIc.%s 10 and 11. 1918.
SURFACE TENSION MEASUREMENT MAYNARD R. EUVERARD AND D.-INIEL R. HURLEY Finishes Division, Interchemical Corporation, Newark 1 , aY.J .
I
S THE latter part of 1946, subsequent t o the development of
the Interchemical inclined tube viscometer (a),i t was observed that the conversion factor developed to convert time in seconds for the bubble to flow over a given distance in a tube, to kinematic viscosity was not exactly the same for all materials measured. Upon investigation of this phenomenon, it was postulated that the variation was probably due to surface tension. Barr ( 1 ) has s h o r n that surface tension is a definite factor influencing the rate at which an air bubble will move through a tube held in a vertical position. There is no reason to believe, therefore, that surface teiision would not also be a factor when the tube is held in a position slightly inclined from the horizontal.
The difference in the horizontal bubble lengths (when thr volume of the bubble is held constant) of materials having a considerable range of surface tension indicated that the measurement of this bubble length might very well afford a very simple means ot determining surface ttwsion. Prtaliminary investigations were initiated to determint. thr ratio of the height of the air space above the liquid in a tuhe, which is the controlling factrr for the volume of the air hubble in a tube of given dixmrter. and the lrngth of the static bubblc when the rubr is plawd in a horizontal position. Earlier data indicated that this ratio was approuimatelv constant over a sizabl(3rarigr of bubble volume. H o w v r r , a more accuratc and detailed btudy recentlv conducted has shown that this ratio
