Modified Syringe for Extraction with Solvents of Low Density. A . I. Lledalia and ;R. IT. . Stoenner, Brookhaven National Laboratory, Upton, L. I., ?;. T.
the aqueous phase may hr forced out through the outlet tube and the !yringe rinsed by sucaking in water and air, shaking, and again forcing out the water. I t may be desirable to use the syringe for extractions with solvents denser than water-for example, different elements may be extracted surcessively from the same solution, such as ferric chloride with ether, then copper carbamate with carbon tetrachloride. For extrartion with dense solvents, the same procedure is used as with light solvents, but the outlet tube is turned in the opposite direction from that shown, and the whole syringe is inverted to permit the dense solvent to he famed out through the outlet tulle. The portion of the solution (in the dense solvent) left in the outlet tube below the stopcork is not lost, as v i t h conventional separatory funnels, but is drawn hack into the syringe when fresh solvent is sucked in. Experimental. As a test of the completeness of extraction with this apparatus, ferric chloride was extracted with isopropyl ether, as rrcommended by Dodson, Forney, and Swift (1).
extraction procedures of value in analytical M *SYthemistry use a solvent, such as ethyl or isopropyl ether, which is less dense than the aqueous medium from which the substall(.ach time with rinsing; or if only One separatory funnel is used, to reserve the aqueous phase in a separate colltainer and transfer it back to the funnel after ren10~7:il of the organic phase. During these operations the organic pllase generally becomes contaminated with aqueous emulsion \vvhic.h clings to the separatory funnel after drainage of the aqueous phase:. To avoid this cumbersome procedure, various assemblages of separatory funnels have been proposed (a), which, howcver, are both cumbersome and fragile. In Figure 1 is shown a simple apparatus b y m e a n s of which repeated extractions 1 1 ~ y be carried out without transfer of the denser phase out of the apparatus. The apparatus consists simply of a syringe with an eccentric, tip, to which are sealcd a stopcaock and an outlet tube. T h e spherical joint shown in the figure may be omitted for the sake of economy; however, its use gives greater flexibility, and permits extraction with solvents denser, than water. S y r i n g e 3 with eccentric tip are commercially available in various sizes, and are generally constructed of h o r osi I i r a t e g l a s s . Because there is some variation in manufacture, only the more closely Figure 1 fitting syringes should h e selected.
A solution of 0.0964 L I f ferric chloride in 7.87 Ar hydrochloric acid was analyzed by reduction with stannous chloride and mercuric chloride, f o l l o ~ e dby titration x i t h ceric sulfate. Aliquots of 25 ml. were placed in the syringe and extracted with three successive portions (20 to 25 ml.) of reagent grade isopropyl ether. Dilute hydrochloric acid was added to the combined extracts, the ether was boiled off, and the remaining eolution was analyzed as before. Taken, 134.8 mg. of iron; found, 134.9 mg. The aqueous phase, combined with three rinsings of the syringe with hydrochloric acid, was tested for ferric iron with thiocyanate. It vias found that less than 0.01 mg. of iron was present. To check the sharpness of separation of the two phases, a solution of 1.5 grams of cupric chloride dihydrate in 7.87 N hydrochloric acid was extracted once with isopropyl ether. Water was added to the extract, the ether was boiled off, and the copper vias determined with diethyldithiocarbamate. Found, 0.02 mg. of copper. LITERATURE CITED
( 1 ) Dodson, R. W., Forney, G. J., and Swift, E. H., J . A m . Chem. Soc., 58, 2573 (1936). (2)
Willard, H. H., and Diehl, H., “Advanced Quantitative Analysis,” p. 55, S e w l o r k , D. Van Xostrand Co., 1943.
REaEaRCH
carried o u t under the auspices of the Atomic Energy Coin-
mission.
Hydrocarbon Absorption by Stopcock Lubricants. Godfrey L. Cabot, Inc., Boston, hlass.
The aqueous solution is introduced Ijy placing the solution in a container with a pointed bottom, and then suckin it into the syringe; rinsings of the container are then introducefin the same manner. The aqueous solution may also be pipetted directly into the open syringe barrel, clamped in a nearly horizontal position, with care tQavoid introduction of this solution into the capillary tip during insertion of the plunger. (If the open syringe barrel were held vertically, a portion of the solution would enter the capillary tip and be lost when the plunger was inserted, as this can be done only with the stopcock open.) The organic solvent is next sucked in through the outlet tube by drawing out the plunger. Some air is also drawn in, the stopcock is closed, and then the syringe is shaken. The plunger will not dro out during shaking; if pressure is generated by volatilization o f t h e organic solvent, the plunger is forced out a short distance until, according t o the gas law, the volume of the gas space is increased by a factor of 1 P, where P is the vapor pressure of the solvent in atmospheres. The syringe is then held as shown in Figure 1, and after separation of the phases, the lighter phase is forced out through the outlet tube. The eccentric tip is kept a t the top, so that none of the organic phase is trapped. The amount of liquid delivered can be closelv controlled; and the organic solvent is expelled free from water. More organic solvent is then sucked in through the delivery tip, thus rinsing the contents of the tip back into the syringe, and further extraction. are performed as before. Finally,
If. H. Polley,
measurement of calorimetric heats of adsorption of hyIthe drocarbons on carbon black a t 100” C. ( 5 ) ,mercury cutoffs in adsorption apparatus, which were used successfully a t room N THE
temperature ( 1 , 6 ) ,were rejected because of the appreciable vapor pressure of mercury a t the higher temperature. The use of glass stopcocks in such a system requires a lubricant of low vapor pressure, insoluble in hydrocarbon vapor and of good consistency a t both room temperature and 100” C. After considerable investigation of lubricants recommended for use with hydrocarbon vapors ( 2 , 4 ) ,a cellulose acetate grease made by a slight variation of the method of Pearlson (5)was found to possess excellent working characteristics in the presence of hydrocarbons a t elevated temperatures.
+
Preparation of Cellulose Acetate Lubricant. To 45 grams of 200 molecular weight polyethylene glycol 6.0 grams of commercial cellulose acetate were added and the mixture TVW heated on an oil bath a t 140” C. about 25 minutes. Then 0.6 gram of cellulose acetate was added and heating was continued until the preparation was homogeneous. About 29 grams of citric acid, heated on
545
ANALYTICAL CHEMISTRY
546 a n oil bath to 190" C., were added and the mixture iTa8 heated a t 190" C. for another hour, with frequent stirring. The grease was cooled and dehydrated in a vacuum desiccator. At room temperature i t became extremely viscous and tacky. EXPERIMENTAL PROCEDURE AND RESULTS
In conjunction with the search for'a suitable stopcock lubricant, a separate testing procedure was adopted to determine the extent of hydrocarbon absorption by the lubricant. The apparatus employed for this Rtudy was similar to that developed for the measurement of heat8 of adsorption a t 0 " C. ( I ) , using mercury cutoffs.
0 0 (3
APIEZON L OOW-CORNING SILICONE FLUOROGREASE F.CD.-441
4.0
vapor pressure, good consistency a t high temperature, and negligible hydrocarbon absorption. It was found, however, t h a t at the end of a 14-hour calorimetric run there was a slight breakdown of the grease, necessitating the cleaning and regreasing of the stopcocks. LITERITURE CITED
R..I.,Polley. A f . H., Smith, TY. R., and Wendell, C. B . , Jr.. J . A m . C h e m . jCoc., 69,2294 (1947). ( 2 ) Davis, P. T., Grossman. J . , and Harris, B. L., ASAL. CHEZI.,21, (1) Beehe,
194 (1949). (3) Pearlson, W.H.. I s n . Esti. ('HEM., .ISAL. ED., 16, 415 (1944). 14) )Sanderson, R. T., "Vacuum Manipulation of Volatile Compounds," pp. 10-11, Sew Tork, John Wiley & Sons, 1948. (5) Schaeffer, W.D., Polley, hf. H., and Smith, W. R., J . Phyn. h Colloid C h e m . , 54, 227 (1950). (6) pea end ell. C'. B., Jr., I s n . ENG.('HEX., .ISAL. ED., 18, 454 (1946).
Drying Spectrographic Electrodes Directly on Arc Stand. A. J. Mitteldorf, Armour Research Foundation of Illinois Institutc of Technology, Chicago 16, Ill.
a conventional 1.5-meter A.R.L. spectrograph is used to determine the silicon content of specially distillcd w t t r r . .Is the c.oncentration of silicon involved is very snuill (less than 0.0005(;;), contamination, especially from dust in the air, presents a large problem. In order to redwe this rontamination a scheme for drying t k t r o d e s directly by an arc on t'he arc stand has been devised, which reduces to a minimum handling of the graphite electrodes and also the amount of timcs that the electrodes are exposed. CCASIOS*I.T.Y
After each rlcrtxode is p r e h r n e d , a measured quant i t y (0.1 ml.) of w a t e r s a m p l r is placed in its cup, using a micropipet, while the electrode remains in its KNURLED c l a m p . -4 s e l f ignited direct current arc is then directed to the side of t h e e l e c t r o d e about 2 cm. below the top of the cup. Applied a t 12 amCLAMP peres for ahout 1 s e c o n d , the heat from the arc is conducted to the water in t h e c u p a n d causes it to evaportite raoidlv. If this arc is aoulicd for too long a time. the water may sputter out of the cup. The universal arc-spark stand (h.R.L. Model 2061) is well suited for drying electrodes by this technique. The electrical connection normally used for the Petrey stand serves to support a sr5iveling clamp, 1% hich in turn holds a length of pointed, high puritv graphite rod 0.25 inch in diameter. To dry the water out of the cupped electrode, the upper electrode is raised about 2 cm (to prevent arcing to i t ) and the side electrode is pivoted into the position shown in the diagram. Because the gap between the side and main electrodes (about 2 mm.) is shorter than t h a t between the upper and main electrodes, the arc is struck between the former two bv the Llultisource. After the arc from the side electrode has drieb. the main electrode, the side electrode is swung away and the upper electrode is brought back into position for arcing the material and expoying the spectrogram.
l
P R E S S U R E , MM.
Figure 1. n-Hexane Absorbed on Stopcock Lubricants at 100" C.
ripproximately 0.10 gram of grease was placed in a n adsorption cell and outgassed a t 100" C. to free the sample of occluded air and moisture. Because of xidely different temperature-viscosity relationships, the extent of surface and thickness of the sample varied slightly. The dead space was determined with helium and the sample evacuated once more. The n-hexane, olitained from Humphrey-Wilkinson, Inc., S e w Haven, Conn., and stated to be of a t least 95 mole yopurity, was further purified by several bulb-to-bulb distillations. During the experiment the adsorption cell u a s immersed in a boiling water bath. Four highvacuum greases were investigated in this manner, including Apiezon L, Dow-Corning silicone, a perfluoro grease ( 2 ) supplied by the Organic Chemicals Division of the Du Pont Co , and the cellulose acetate lubricant. The results of the absorption study are shown in Figure 1, in which the isotherms a t 100" C. are plotted for n-hexane vapor on the four stopcock lubricants. As the sorption process is very slow, these values only approximate the true equilibrium readings. Each point was obtained after at least 20 minutes' exposure. After this period, the rate of pressure drop had decreased to less than 0.1% per minute. It may be seen from these isotherms t h a t Apiezon L and Dow-Corning silicone lubricants slowly absorb large quantities of hydrocarbon vapor. The perfluorocarbon fraction was fairly satisfactory in this respect, but in use the stopcock film became striated within a short time at 100 C. The cellulose acetate preparation, on the other hand, has a low
__
~
Using this scheme for drjing electrodes, calcium and magnesium as well as silicon contamination has been reduced to such a n extent t h a t the limiting source of contamination is now the electrodes themselves. Even in commercial graphite electrodes of the highest purity, these elements frequently occur as troublesome impurities.
