V O L U M E 2 5 , NO. 11, N O V E M B E R 1 9 5 3 color solution times 4 equals per cent tetrachlorohydroquinone in the leather when the sample weight and dilution recommended are used. Analytical Results, Accuracy, and Precision. Table IV shows the recovery of known amounts of tetrachlorohydroquinone added to 12 different types and tannages of leathers. The leather samples were placed in the extraction thimbles and measured amounts of a standard solution of tetrachlorohydroquinone in ethyl acetate were added, so that the leather absorbed all of the solution. The thimbles and contents were then placed near a hot plate for evaporation of the solvent, and allowed to stand for several days to ensure any fixation of the fungicide in the leather that might occur. Extraction and determination of the fungicide were then made according to the procedure given. The results given in Table I V may be used to evaluate the accuracy and precision of the method ( 5 ) . Theoretically, the amounts of ktrachlorohydroquinone found plotted against the amounts added should yield a straight line passing through the origin and having a slope of unity if no bias exists, The actual line obtained, fitted by the method of least squares to the analytical results, had an intercept not significantly different from zero and a slope not significantlv different from unity. There is therefore no evidence of bias in the method. The standard deviation of a single measurement calculated from the data is 0.7 mg. This is equivalent to a standard deviation of 0.03% based on the dry leather weight, using the prescribed sample x-eight (2.5 grams). DISCUSSION
The color development in solutions containing leather extract? is somewhat slower than with the standards, but the m a i n i u m is reached by all solutions when the time intervals given in the procedure are adhered to. Small amounts of water in the sample or in the solvent do not seem t o interfere, because practically the Bame calibration curves have heen obtained with 80 to 90% ethyl
1727
acetate as with the anhydrous solvent. The color is somewhat sensitive to sunlight. As the benzoyl peroxide solution become8 yellow on standing and may then give erratic results, it should he prepared the same day that it is used. Under the conditions of the test, quinone and hydroquinoiie give a faint purple-blue color which is slow in developing, so that these compounds will interfere only if present in considerable amounts. The method does not distinguish between tetrachlorohyclroquinone and chloranil, but for the purpose for M-hich this method was developed this is not important. Both compounds are fungicidal and are probably easily converted from one to the other, depending on the oxidative conditions in the leather. Phenols and chlorinated phenols do not interfere, nor does ally tanning agent or other leather component that has been encountered. ACKNOWLEDGMENT
This FT0i-k was support'ed by funds supplied by the Office of the Quartermaster General, and the author thanks Ray Treichler of the Research and Development Division of that office for his interest and suggestions. The absorption spect,ra u-ere determined by E. G. Person, Chemistry Division, Xational Bureau of Stanrlards, and his aseistance is gratefully acknotTledged. LITERATURE CITED
(1) Am. SOC. Testing Materials, Committee D-11, Designation D 297-50 T (1950). (2) Rurchfield, H. P., and AlcXew, G. L., PhgtoprcthoZogl/, 38, 299 (1948).
(3) Sisido, Keiiti, and Tagi, Hirosi, .ISAL. C"FX., 20, 677 (1948). (4) Sivadjian, Joseph, B1d1.SOC. chini. [5], 2, 623 (1935). ( 5 ) Touden, W, J., "Statistical Methods for Chemists," Chap. 5 , S e w Tork, John Wiley Pr Sons, 1951. (6) Zimniernian, E. W., and Panghorn. E. F., J . A m . Leather Chenlisis Bssoc., 46, 342 (1951).
RECEIVED for review June
19, 1953. Accepted August 26, 10.53.
Hydrogen Fluoride Solvent System Apparatus for Polarographic Studies.
Rotating Electrode
JOHN W. SARGENT, ALAN F. CLIFFORD', AND W-ARREN R. LEMMOX Central Research Department, Minnesota Mining Manufacturing Go., S t . Paul, Minn. The extreme acidity of hydrogen fluoride makes i t difficult to construct satisfactory apparatus for precision measurements. Suitable design principles for an apparatus to study liquid hydrogen fluoride solutions conveniently without fear of corrosion or contamination have been attained. The equipment should be fabricated from Kel-F (polytrifluorochlornethylene), thus permitting visual observation and allowing solutions acidic toward hydrogen fluoride to be studied. As an example, a polarographic cell with a rotating microelectrode has been found to operate satisfactorily. A n apparatus so designed is versatile and adaptable and should facilitate future studies in the hydrogen Bunride system.
A S A liquid with a high dielectric constant and a very low viscosity, hydrogen fluoride should provide an excellent ionizing solvent. Although the polarographic technique can supply valuable information about reactions in this interesting solvent
1 Present address. Department of Chemistry, The University. Cambridge, England.
equipment to handle and study liquid hydrogen fluoride solutions was undertaken. DESCRIPTION OF EQUIPMENT
when solutions acidic toward hydrogel] fluoride ( 1 ) are used. Fabrication of the equipment from Kel-F, polytrifluorochloro-
ANALYTICAL CHEMISTRY
1728 ethylene, permits observation and satisfies the need for corroeionresistant materials to allow handling of solutions acidic toward hydrogen fluoride. In addition the nonwettable character of the Kel-F makes the apparatus easy to clean. The hydrogen fluoride comes in contact with no metal other than the electrodes. For versatility the apparatus is designed in units which are connected by Kel-F lines, as the following flow chart illustrates.
HF Cylinder (Gen. Chem.) I
1 1
Needle Valve 3.8-inch Kel-F Line
The mixing cylinder is equipped with a reflux condenser, a gas inlet (with needle valve) for stirring, and a needle valve at the bottom. 9 1 1 needle valves are similar in principle to the one shown in Figure 1, and are modeled after a standard hoke needle valve. From the mixing cylinder a 1/4-inchline leads to the polarographic cell. The body of the cell, with a capacity of 25 ml., is milled from solid 1.5-inch Kel-F rod for immersion in a cooling bath. The cell is fitted with a threaded cap with four openings: hydrogen fluoride inlet, reflux outlet, rotating electrode, and electrical connection to the quiet electrode. The aluminum metal rim on the cap retains the mercury which covers the top of the cell during operation. A mercury pool may be used as the quiet electrode, electrical contact being made through the mercury well shown in Figure 3, or a metal plate with an area many times that of the microelectrode may be inserted.
Drying Cell Seedle Valve '/(-inch Kel-F Line
Reservoir I
I 1
Details of the mixing cylinder, also constructed from 1-inch Kel-F tubing, are shown in Figure 1.
Details of the polarographic cell are shown in Figure 2.
.L Condenser
I
condenser. The reservoir is jacketed with glass for coolant circulation. From the reservoir a l/rinch line leads to the mixing cylinder.
Needle Valve '/(-inch Kel-F Line
Details of the rotating electrode are shown in Figure 3.
Mixing Cylinder
The metal microelectrode consists of a wire which is pressfitted into the Kel-F shaft through a hole drilled about 0.002 inch smaller than the wire diameter. The wire penetrates into the hollow center of the Kel-F shaft, which is filled with mercury. The mercury in the shaft makes contact with a Nichrome wire which circles the upper rim of the electrode. The entire top of the cell is covered with mercury during operation, the mercury acting as a vapor seal and providing electrical contact with the rotating electrode through the Nichrome wire. The electrode is rotated by a two-phase induction motor, speed variation being obtained by varying the voltage across one phase and keeping the voltage across the other phase constant.
Needle Valve '/(-inch Kel-F Line
Polarographic Cell
r""'"1 22 T P I -HF
INLEl
The rotating electrode as shown in Figure 3 is the final design, which was evolved through several stages. The first electrode
,
c.28 N.F T A P H F INLET
FOR -/
O PENI NO FOR RO TATI NG ELLCTROOE G A S INLET-
NEEDLE
1
L
2
, TPI e8 M.F. T A P FOR REFLUX OUTLET
VALVE IO-32N F 84-24 N F P AC KI NG
Figure 1. iMixing Cylinder .ALUYINUY
The condenser is a glass-jacketed length of 3/einch Kel-F tubing, connected through a reduction flare fitting of Kel-F to the '/(-inch inlet line of the drying cell. B s the industrially produced hydrogen fluoride contains small amounts of water and other impurities, it is dried by electrolysis and distilled before use (3). The efficiency of the drying operation is attested by the drop in conductivity of the hydrogen fluoride from an initial conductivity of 500 ma. a t approximately 7.0 volts to 8 ma. a t 12.0 volts (19' C,). .The drying cell has a capacity of 50 ml. of liquid hydrogen fluoride. The body of the drying cell was milled from solid 1.5-inch Kel-F rod and equipped with a screw cap. The cap contains five openings: hydrogen fluoride inlet, reflux condenser, leads to the two nickel electrodes, and a vapor outlet. The vapor outlet line ('/(-inch Kel-F tubing) leads through a needle valve to the hydrogen fluoride reservoir. The reservoir has a capacity of 30 ml. of liquid hydrogen fluoride and is constructed from a length of 1-inch Kel-F tubing with a needle valve at the bottom. The top is closed by a plug with two openings: hydrogen fluoride vapor inlet, and reflux
L
T
E
f
L
O
N SLEEVE
I t T. P. I.
i
l
$O I A . 4
Figure 2. Polarographic Cell
V O L U M E 2 5 , NO. 1 1 , N O V E M B E R 1 9 5 3
1729
was somewhat smaller and the hole in the cap of the polarographic cell was only slightly larger than the shaft of the electrode. This electrode required precise centering and would not operate for an>-length of time without binding. The hole through the cell cap was then enlarged somewhat, and a Teflon (polytetrafluoroethylene) sleeve inserted. .4 similar rotating electrode constructed of Teflon operated fairly satisfactorily. Because Teflon is self-lubricating, any contact of the electrode shaft with the Teflon sleeve did not result in binding. However, Teflon does not have the rigidity of Kel-F and the electrode shaft tended to warp and snap off. Therefore, the electrode was again made of Kel-F and the hole through the cell cap was enlarged to its present size, eliminating the need for precise centering.
65 701 60 u)
w 55
a W
50 4
g
45
0
P 40
3s IZ W a
30
5
2s
0
:
20
@ L,-J
I5
:
In
2.0
3.0
4.0
5.0
E-VOLTS
Figure 4.
Typical Current-Voltage Curve 1. 2.
Decreasing potential Increasing potential
pendent, but, if the same time interval is used, they are reproducible. Figure 3.
Mercury Well ( L e f t ) and Rotating Electrode ( R i g h t )
LITERATURE CITED
(1) Clifford, A . F., Ph.D. thesis, University of Delaware, 1949. (2) Clifford, -4.F., and Balog, G., Nuclear Sci. Abs., 5, (17), 694 (1951).
All condensers and the hydrogen fluoride reservoir are cooled by circulating refrigerated ethyl alcohol (-35” (3.). The polarographic cell is cooled by a circulating bath of tetrachloroethylene, kept a t 0” f 0.4’ C. The Kel-F lines are joined by flare fittings or threaded joints. The Kel-F tubing can be flared with a standard flaring tool by immersing the tubing and the tool in boiling water to soften the Kel-F. If the tubing is allowed to cool to room temperature before the flaring tool is removed, a permanent flare is obtained. The male fittings are machined from Kel-F (Figure l ) , but standard brass flare nuts are used. All fittings and threads are greased with Fluorolube (Hooker). All openings to the atmosphere are protected by indicating Drierite mixed with sodium fluoride pellets. OPERATION
The apparatus is purged with dry nitrogen, and hydrogen fluoride vapor from the cylinder is condensed into the drying cell. Voltage (12.0 volts) is then applied across the two nickel electrodes and the hydrogen fluoride is electrolyzed until dry. Electrolysis is continued until the conductivity is very low (8 ma. at 12.0 volts). -4fter drying, the hydrogen fluoride is distilled over into the reservoir. The desired amount of liquid hydrogen fluoride is then bled through a needle valve into the mixing cylinder, in which has been placed a weighed amount of organic or other material to be dissolved in the hydrogen fluoride. This solution is stirred thoroughly bv bubbling dry nitrogen through the cylinder. After thorough mixing, the solution is let into the polarographic cell through another needle valve. To ensure temperature equilibrium of the hydrogen fluoride solution with the cooling bath, the electrode rotation is started some time before measurements are taken. The apparatus has been used to study anodic reactions in liquid hydrogen fluoride. The typical current-voltage curve shown in Figure 4 was obtained with a microelectrode of nickel (anode) rotating a t 800 r.p.m. The cathode was a nickel plate with an area many times that of the microelectrode. The solution was 0.12144 barium fluoride in hydrogen fluoride, plus possible trace amounts of water. The potentials measured were applied potentials. The current-voltage curves obtained are time-de-
(3)
Simons, J. H., Znd. Eng. Chem., 32,
178 (1940).
RECEIVED for review February 14, 1953. Accepted August 3, 1953. Contribution 65, Central Research Department. Minnesota Mining & Manufacturing Co.
Identification of Thiophene and Benzene Homologs, Mass Spectral Correlations-Correction In the article “Identification of Thiophene and Benzene Homologs, Mass Spectral Correlations” [Kenney, I. W., Jr., and Cook, G. L., - 4 ~ 4CHEJI., ~ . 24, 1391 (1952)], the two paragraphs in the second column on page 1392, beginning “One compound shown. . ” and “Rearrangements at the moment. . . . . . .,” should be omitted. In Table I11 the pattern shown for tert-amylbenzene is erroneous. The material used to obtain the pattern for tert-amylbenzene was a commercial sample redistilled at the Petroleum and OilShale laboratory of the U. s. Bureau of Mines at Laramie, TYyoming. A center cut from this distillation wa8 used to obtain the pattern. It has since become evident that the purchased material was not tertamylbenzene. As a consequence, the special correlations developed for this compound are not necessary, as the corrected pattern fits the general correlations. Since, publication of the article tert-amylbenzene has become available through API Project 6. A corrected pattern for tertamylbenzene based on SPI standard sample 1014 is shown below: Parent peak Parent less 1 Parent less 15 Parent less 29 Parent less 31 Parent less 43 Parent less 57
%
13.8
...
2.7 100.0
4.3 3.8 54.7
m / e 79 m / e 78 m / e 77 m / e 43 m / e 41
%
7.5 4.5 9.8
1.2
15.3
G. L. COOK
