June 15, 1942
ANALYTICAL EDITION
soon became apparent that neither precipitate was well suited for the quantitative estimation of palladium because of solubility.
DETERMINATION OF PALLADIUM IN PRESENCE OF XITRATE SULFATE. It was essential to determine whether
AKD
sulfate and nitrate would interfere in the determination of palladium as the chloride complex. Using the procedure already described and adding varying amounts of sulfate and nitrate, the first ten results given in Table V were obtained. The last six were obtained in a somewhat different manner. Table V shows that even in the presence of large amounts of nitrate and sulfate the procedure gives accurate results, and that even though the nitrate and sulfate complexes are first formed they are rapidly transformed into the chloride compound upon the addition of chloride ion, indicating that the latter is the least soluble.
Summary A method for the gravimetric determination of palladium involves the precipitation of the compound Pd(C4H30CHNOH)&12 with beta-furfuraldoxime. It is shown to give accurate results for amounts of palladium ranging from 2 to 30 mg. By this method palladium may be directly determined in the presence of platinum, ruthenium, rhodium, iridium, iron, cobalt, nickel, copper, manganese, mercury, zinc, aluminum, antimony, bismuth, tin, cadmium, calcium, strontium, barium, magnesium, sodium, potassium, chromium, thorium,
493
titanium, zirconium, molybdate, vanadate, tungstate, phosphate, arsenate, borate, selenite, sulfate, and nitrate ions. The determination of palladium in the presence of gold, silver, mercurous, lead, and ceric ions is impossible. The method is believed to have three advantages over the familiar dimethylglyoxime procedure: The precipitate has a higher molecular weight, and hence lower palladium content; as the reagent, beta-furfuraldoxime, is water-soluble, there is no danger of the reagent precipitating out; and furfuraldoxime precipitate is much easier to handle in filtration.
Literature Cited (1) Diehl, H., “Applications of Dioximes t o Analytical Chemistry”, p. 15, G. Frederick Smith Chemical Co., 1940. (2) Feigl, F., Krumholz, P., and Rajmann, E., Mikrochemie, 3, 165 (1931). (3) Hanus, J., Jilek, A., and Lukas, J., Chem. News, 131,401 (1925); 132,l ( 1 9 3 6 ) . (4) Hillebrand, W.F., and Lundell, G. E. F., ”Applied Inorganic Analysis”, p. 636, New York. John Wiley & Sons, 1929. (5) Holser, H., 2. anal. Chem., 95, 392 (1933). (6) Meulen, H. ter. and Hesslinga, J., “Neue Methoden der organ-
isch-chemischen Analyse”, Leipzig, Akademische Verlagsgesellschaft. 1927. (7) Renoll, M. TV., Midgley, T., and Henne, A. L., IND. ENG.CHEM., ANAL.ED.,9, 566 (1937). (8) Schmidt, W., 2. anorg. allgem. Chem., 80,355 (1913). (9) Scott, W. W., “Standard Methods of Chemical Analysis”. 5th ed., p. 266, New York, D. Van Nojtrand Co., 1939 (10) [bid., p. 724. (11) Tschugaeff, L., 2. anorg. Chem., 46, 144 (1905). (12) Yoe, J. H., and Overholser, L. G., J . A m . Chem. Soc., 61,2058 (1939).
Semiautomatic Fractionation A Rapid Analytical Method BASSETT FERGUSON, JR., Ugite Sales Corp., Chester, Penna.
A still head with a constant take-off rate has been developed for a laboratory column. Using the packed column described, an analysis by fractionation may be accomplished in approximately one hour, with sufficient accuracy for most plant control purposes. The analytical still is semiautomatic in operation, one man being able to operate as many as five stills simultaneously.
a
T
H E requirements of analytical methods used in routine control of a continuous chemical process are distinct from those of methods used in research and development work. It is important that any routine analysis selected give necessary and sufficient data for routine plant control. In addition, the test should consume as little time as possible, so that rapid results may be obtained. The simplest technique is usually best for the control laboratory and least likely t o involve serious errors by the operators. I n a petroleum refinery, still performance can usually be determined by simple physical tests on the still products: specific gravity, viscosity, color, and boiling range. These properties sufficiently define the relatively wide-boiling bands of similar hydrocarbons found in a finished petroleum product. In a chemical plant making careful separation of close-boiling
and often homologous hydrocarbons, however, these tests are unsatisfactory for still control. Only occasionally can Satisfactory still performance be defined in terms of product density, refractive index, or by simple chemical test, and the common “boiling range” gives only a vague idea of the percentage composition of a mixture. I n the absence of simple analytical controls it is most reasonable to rely on analytical fractionation by distillation, thereby using the same method for analysis that is used for separation in the plant process. But an analytical fractionation is customarily time-consuming and requires more or less constant attention while running. Thus, when routine analysis by distillation was deemed necessary for chemical plant control, it became imperative to develop a method for analytical fractionation sufficiently accurate and rapid for the needs of still control, and requiring a minimum of man power for operation. (By continuous distillation cuts are made which vary in composition from C3 hydrocarbons, through C4 and CSolefins and diolefins, benzene, toluene, and xylene, to aromatic mixtures boiling as high as 300‘ C.) For this purpose the analytical still shown in Figure 1 vas constructed, incorporating the novel features of a constant product take-off rate and automatic temperature recording.
.lipparatus b
T h e refluxing distillate drains from t h e bulb condenser into cell K , first filling K (capacity 2 t o 3 ml.) and then overflowing
494
.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 14, No. 6
back to the fractionating column. At lated box which is cooled either by packing 30-second intervals the 50-ohm solenoid the top with solid carbon dioxide or by memagnet, A , is activated by an electric chanical refrigeration to prevent supertimer. This attracts the iron core in the heatin of vapors and toluene is circulated lass tube extending down through the througf >he condenser, after being cooled Eulb condenser and connected with a glass by passing through a coil immersed in dumbbell in K . The dumbbell is thus toluene and solid carbon dioxide. A box raised long enough to drain the contents temperature of -25' C. and condenser of K into the product take-off line, while inlet temperature of -65" C. may be obthe upper portion of the dumbbell seals tained, and are found satisfactory for the the top of K and prevents additional liquid propane-butane separation. An electric from entering. The dumbbell then drops heater is used to supply heat to the still into its former position, sealing the prodpot. For samples boiling above room temuct take-off line, while the reflux fills K and perature, water is used in the condenser overflows as before. and no insulating box is used to enclose the still. A Bunsen burner is normally used The period when the magnet is actifor heating. vated may be lengthened to permit more Since the required accuracy of temperaviscous distillate to drain from K , withture reading could not be approached by out altering the reflux ratio or take-off thermocouples unless individually calibrarate. The product taken off each cycle ted, a six-point TAG recording potentiomis constant to vc-ithin 0.05 ml., and as this eter together with resistance thermometers error shows no definite trend through the was obtained from the C. J. Tagliabue Co., distillation, it is well within the limits of Brooklyn, N. Y., to serve a battery of six accuracy of the method. analytical stills. A special scale of -20' Funnel E, supported by glass prongs, to t-150" C. supplied the range required, acts as a reservoir, keeping the column and a chart speed of 45 cm. (18 inches) packing wet during the take-off period. F per hour gives an optimum curve dimension. Resistance thermometer B is connected With this column 200 ml. of sample may to a recorder which plots vapor temperabe distilled a t 40-mm. pressure, at 5 to 1 ture. Pressure is read on a closed-end reflux ratio, in 40 minutes after reflux has manometer connected a t C. Tie rod D been established. A 200-ml. sample is strengthens the still head and reduces used as standard, although a larger charge breakage. The vacuum-jacketed fractionis employed in certain analyses to permit ating column has glass bellows F to allow increased accuracy. thermal expansion. A screen resting on glass prongs at H supports carding teeth Procedure column packing. Three-way stopcock G permits ienting receiver t o air and also Using a sample which is a mixture of connects to a 19-liter (&gallon) surge benzene, toluene, and xylene, 200 ml. are bottle, vacuum control, and pump. measured into the still pot at a given temThe bulb condenser design, consisting perature, normally room temperature. of bulbs of decreasing size, is particuSufficient heat is a plied to the pot to larly efficient. Most of the vapor is constart the sample reluxing in the column, densed in the larger bulbs, where the and then to attain maximum throughput in FIGURE1. ANALYTICAL STILL large openin s prevent choking, while the column, which occurs just below the the upper an! smaller bulbs condense the flood point. Incipient flooding in the last traces of vapor and prevent carry-over. column may be taken as an indication that The still, using a conventional packed maximum efficiency is being obtained. column, is o erated a t ap roximately maximum throughput. After reflux hapbeen establighed (thjs repuires 10 to 15 minutes) The take-off &vice takes a &finite amount of product at regular the vapor temperature-recording device is allowed to come to a time intervals. The overhead temperature is recorded on a chart constant (minimum) temperature (requiring an additional 5 to 10 moving at a uniform rate, so that a curve of temperature against minutes) and the switch is then thrown, allowing the electric distillation time is plotted. Since the rate of production is contimer to activate the product take-off device at regular intervals. stant, the same curve represents overhead temperature us. per The distillation is continued until an overhead temperature of cent distilled. With this method of operation the reflux ratio 135" C. is reached, when the distillation is stopped. The volume varies with the throughput, which is kept so high that the ratio is of the distillate is observed and written directly on the distillation curve, together with the distillate temperature if it varies from always at least 5 to 1. the temperature of the charge. All volumes may then be corrected to a common temperature if necessary, before calculaWith this apparatus, the automatically recorded curve permits consistent and reasonably accurate analysis of the ~ a ~ ~ ~ ~advantageous f o u n dto record also the volume dishydrocarbon mixture into its component parts. The still tilled at the several significant temperatures 0: "cut points" column selected must be efficient enough for the most difselected for aalculation purposes, in this case 81 , log', 111.5', and 135" C. ficult separation encountered in the given system of analysis, and must be of sufficient capacity and throughput rate to Figure 2 shows the distillation curve plotted by the vapor process the required amount of sample within a given time, temperature recorder. This curve shows directly per cent which for the author's purpose is one hour or less. distilled us. vapor temperature. The calculation is made as A vacuum-jacketed, silvered glass column was chosen having fo~lo~vs: the following dimensions and characteristics: 1. All the material between 79' and 81" C. is considered benzene. teeth 2. All the material between 109' and 111.5" C. is considered toluene. 3. All the material above 136" C. is considered xylene. 4. The area under the intermediate portions of the curves (81' to 109" and.lll.5" to 135" C.) is integrated graphically and (This column, as well as the still head, is supplied to the Ugite the average boiling point of the intermediate fraction is thus determined. Reference to a prepared table will give the percentSales Corporation specification by Ace Glass, Inc., Vineland, N. J., which also supplies glass still pots with interchan eable age composition corresponding to any average boiling point. ball and socket joints, lass vacuum control apparatus t o k g i t e This table (or curve) may be taken from the literature or calcu-lated from the McCabe-Thiele diagram for the alpha of the two Sales specifications, etcf For fractionation of materials boiling between propane components under consideration, and should be available to the(-44.5' C.) and benzene (79-81' C.), the still is placed in an insuanalyst making routine calculations.
June 15, 1942
Test Mixture No.
TABLEI. C4
2 3 4
5
6
7 S
9 10
.. .. .. .. .. .... 9i:o
0.5
Ci
%
%
3.8
..
91.3 0.7
4.9 99.3
,.
i:s
9i:o
26:6 99.0 0.5 2.0 99.5
7614 1.0 99.5
_.
..
%
0.8
.. ..
.
%
..
..
3:3
96:7
1.2
99.2
.. .. .. .. ..
.. .. .. .. .. ..
__
%
.. .. ..
.. .. .. ..
Ca
c,
%
%
%
3.1
91.5
..
0.7
5.4 99.3
i:6
9616
..
.. 2i:O 98.5 0.6
si:5
2.5
0.4
99.6
78:O 1.5 99.4
.. ..
AVCRAGL a? IZZTOLUENE ,46114-b.4 XYLLWE .54,14. 7.6
Suuu*Rr
BENZENE - 32.4 T o ~ u r ~ .r 30.0 XrLeNr
%
.. ._ .. ..
lined above gill &ow some toluene to be present. Therefore, sufficient c. P.
Test Analysis
Ca
Ci
Ca
495
:MIXTURES
ANA1
Actual Composition
% 1
ANALYTICAL EDITION
37.6
0.8
.. .. ..
..
4.5 1.8 98.2
..
subtracting the added toluene from &e
95 6
final result.
..
..
..
If, instead of single compounds, it is required to distinguish between g o u p s .. .. of compounds in succeeding boiling ranges, a somewhat more empirical method must be employed. A cut point is selected such that the amount of distillate coming over below the cut Doint will be ecluivalent to the total amount of the-lower boiling group present. The cut points and method of calculation for any type of sample can best be determined by experiment, either with synthetic mixtures of pure compounds, or with typical samples, accurately analyzed by independent means. This is a method for the oft-repeated routine analysis, where the geueral nature of the sample to be analyzed is known, and where rapid results are important. There are three cases where a larger amount of sample than the standard 200-m1:charge may be used to advantage:
.. ..
.. ..
..
..
1. Where the sample containing a small quantity of low-boiling material is being analyzed for the sole purpose of determining the quantity of the low boiler, a !age charge may be distilled up to the point where all the low boiler has come off m less time than it takes to distill a charge of standard size t o completion. Hence, 8 400-ml.. charge is customarily used and greater accuracy is ther eby obtained. 2. Where a special test reqnirin more than routine accuracy is ti1 be run or a large number of Fractions is to he determined
5. The several portions of each component axe added, deductions we made for any flux oils added, and the finished result is obtained. The two or more components may be present in nearly equal or in very different proportions. The operating hold-up of the still selected is 60 t o 75 ml. This means that if the highest boiling component comprises less than 30 per cent of the total sample, it will be insufficient in quantity t o force all the lower boiling material overhead. Therefore, the use of a varietv of flux oils according to the needs of the individual analysk is incorporated as an integral part of this method. For example, a benzene stream containing 0 to 10 per cent of toluene has 125 ml. of c. P. toluene flux added to the standard 200-ml. sample, and the distillation is carried to the initial boiling point of c. P. toluene, 109" C. An overall material balance is unneoessary if normal precautions are maintained to avoid distillate losses; the total material boiling below toluene subtracted from the 200-ml. total sample gives the toluene content of the sample. A flux oil is also reqii r e d in the case of a midl quantity of component of intermeiliate boiling range. And y s i s of miu-2.J .-.1 . . uapeuub u-u AuLilrA _ pesence of any tures of pure compouuua intermediat'e component in sufficient quantity to establish a well-defined distillation "flat" in the boiling range of the pure component.
~~
~~~~~
~
&tionation cannot he obtained, for, in the extreme
RE
3. FRACTIONATION APPARATUS
INDUSTRIAL AND ENGINEERING CHEMISTRY
496
in a cut of wide boiling range, an increase in the charge size is desirable to sharpen the analytical tool. Samples of 300 to 2000 ml. have been used for this type of work, depending on the time interval available and the complexity of the separation. 3. Where it is desired t o separate two close-boiling groups and consistent results cannot be obtained using the standard charge, a larger charge may be required to decrease the effect of column hold-up, even though speed must be sacrificed.
Test Results Table I gives the results of analysis of several synthetic mixtures, using the still and analytical methods described herein. The degree of accuracy shown in this table has proved to be dependable, in the main, under routine control laboratory conditions during a period of more than a year. The accuracy of this method cannot be compared to that of
Vol. 14, No. 6
inorganic quantitative analysis, but where approximations of the order shown are sufficient, it has proved of value in getting results in a quick and relatively simple way.
Acknowledgment The author wishes to acknowledge the helpful information and suggestions furnished by Edward H. Smoker, the work of Mark D. Snyder, Louis T. Lazzarini, and others of the Ugite Sales Corporation laboratory, and the cooperation of Floyd Hughes and others of Ace Glass, Inc., in fabrication of the apparatus. The photograph of the apparatus (Figure 3) by Theodore Shmanda, and the drawing of Figure 2, by Robert Kauffman, both of the Ugite Sales Corporation, are acknowledged with thanks.
The Film Balance As an Analytical Tool for Biological and Food Research GEORGE E. BOYD AND WILLI.i>I D. HARKINS University of Chicago and Universal Oil Products Company, Chicago, Ill. Surface films may be used to detect minute amounts of certain insoluble organic substances, and to identify unknown compounds when some knowledge of the homogeneity of the material is available. Data obtained from film pressurearea measurements are often of decisiFe value in the proof of the structure of complex organic molecules. Recent refinements in the technique appear to afford a method for determining the molecular weight of large molecules such as proteins, polymers, etc. The most widely used tool in the study of insoluble films is the combination of the surface trough and balance. The vertical and horizontal balance types of film balances are in use in this laboratory and a detailed description and theoretical discussion of the former are given, with a discussion of the technique of their use and the limitations and precautions involved. Accessory tools, such as the dark-field ultramicroscope with a cardiod condenser and apparatus for the determination of surface potential and surface viscosity, are described. Measurements of the permeability of films may he made. Temperature control is of great importance. To illustrate the nature of the data obtained, application of the method of surface films to a number of recent diverse scientific problems is described.
A
N OIL may be spread on water or mercury as a monomolecular or polymolecular film, but all films of the
latter type, commonly designated as duplex, are unstable and change spontaneously into a monolayer and a lens (6). Since films and membranes play a predominant role in biology, and are of fundamental importance in many lines of industry, it is essential to know not only what types of apparatus may be used to reveal their characteristics, but also what techniques are best suited. One of the most remarkable features of the film balance is that it is possible by its
use to determine the length, breadth, and approximate molecular weight of certain types of large molecules by only an hour’s work. The volume of any pure oil which covers 1 sq. cm. of the surface of water is given by the thickness of the film. If the thickest monolayer of a pure organic gubstance which can be obtained by compression is about 4.5 A,, the molecules lie flat on the surface. With thicker films the interpretation should be based upon various types of data. Often the position of a polar group in molecules of compounds such as vitamin D (calciferol), or in other sterols, can be shown by the film balance either to disagree or t o agree with that given by organic chemists who have studied their structure. I n cases of disagreement it has been necessary to change the earlier structural formulas.
The Film Balance The most valuable of all the types of apparatus for the study of oil films is known as the film balance, or filmometer, and this is used to determine the film pressure, s,a t any given molecular area, u. The pressure of any film is, by definition, the difference between the surface tension of the clean surface of the subphase, yo, and that of the subphase when covered by the film, y,, or .rr = YO
- Y/
(1)
The justification for the designation of the difference between two tensions as a pressure lies in the fact that two-. dimensional T U and TUTdiagrams (Figure 1) resemble very closely three-dimensional P-V and P-V-T diagrams, respectively. Thus, in the two-dimensional gas law, T U = nkT, the value of k is that of the Boltzman constant of a threeerg deg.-’) which plays dimensional gas ( k = 1.371 X a n important part in the theory of two-dimensional systems. Thus, from Equation 1, any apparatus, by means of which both of these surface tensions may be determined, could be. considered as a film balance. The first of these was used in 1891 by Pockels ( 1 2 ) . The apparatus consisted of a long rectangular trough, filled with water to the brim. The surface of the water was made clean by “sweeping” or “scraping” the surface by the use of a barriw which consisted of a
