ANALYTICAL CHEMISTRY
1168 Although it was possible to determine as little as 2 micrograms of copper (0.01% of the total sample) by means of the described microprocedure, the working range of the method should be limited to concentrations of 0.100 to 0.600 mg. of copper per milliliter of extract. The method was applied to a variety of samples (biological specimens, food samples, ores, slags, and ferrous and nonferrous alloys). Following the suggestion of Mehlig and Durst (8)concerning the application of colorimetric methods to determination of major constituents, samples of copper alloys (brass and bronze) were analyzed for copper in routine runs. Good and quick results were obtained with samples containing as much as 80% of copper. Generally the best results were obtained with samples containing 0.1 to 5y0 of copper by weight. The completeness of extraction of copper from the aqueous phase was tested in a twofold manner. First, a negative qualitative test was obtained on checking the aqueous phase after the copper was extracted. For this purpose several highly sensitive spot tests were applied. Then the chloroform phase was “reextracted” by shaking with 20 to 25 ml. of 1.5 to 3 M ammonium hydroxide. Under these conditions copper leaves the solvent medium and is found as copper-ammonia complex in the water phase. The excess of ammonia was then evaporated by boiling the solution and the copper content was rechecked by analyzing
the solution iodometrically or electrolytically. The average recovery of copper was 99.99 to 100%. Although some determinations were carried out successfully at p H as low as 2.2 and as high as 8.5, the optimum p H range for the described method lies between, p H 4.5 and 7.0. At this range the rate of extraction is greatly increased, whereas the extraction at lower or higher p H values requires a larger volume of solvent and more extracts. LITERATURE CITED
(1) Beilstein, F. K., “Handbuch der organischen Chemie,” 4th ed., Vol. 20, p. 192, Berlin, J. Springer, 1935. (2) Biasso, R., Ann. chim. applicata, 16, 96-8 (1926). (3) Elvehjem, C. 8 . ,and Lindow, W. C., J . Biol. Chem., 81, 435-43
(1929). (4) (5) (6) (7) (8) (9) (10)
Goethals, C. A., 2. anal. Chem., 104, 170-82 (1936). Kinsey, V. E., ANAL.CHEM.,22, 362-3 (1950). Ley. H., and Erler, O., 2.a n o ~ g Chem., . 56, 420-1 (1908). Lowry, 0. H., and Bessey. 0. A., J . Biol. Chem., 163, 633 (1946). Mehlig, J. P., and Durst, D., Chemist-Analyst, 37, 52-5 (1948). Spacu, G., Bul. soc. stiinte Cluj, 1, 282-91 (1922).
Welcher, F. J., “Organic Analytical Reagents,” Vol. 111, pp. 1-7, 40-1. New York, D. Van Nostrand Co., 1947.
RECEIVED December 27, 1949. Presented before the Division of Analytical Chemistry a t the 117th Meeting of the AMERICAS CHEMICAL SOCIETY, Houston, Tex.
Determination of Oli in Paraffin Waxes C. W. LAYTON Standard Oil Company of California, Richmond, Calif.
A rapid method for the determination of oil in petroleum waxes has been developed, in which the sample is chilled with dyed methyl ethyl ketone to -25 ’F., a portion of the solvent-oil mixture is filtered off, and an aliquot of the filtrate reacts with a sodium bisulfite solution i c a skim milk test bottle. The oil is separated from the mixtyre by centrifuging, and the volume is read. Results by this method check very closely with A.S.T.M. method D 721-47. This method is particularly suitable for samples of low oil content (under 5.0%) but with modifications has been used up to 75% successfully.
S
EVERAL methods for determining oil in wax are in use in the petroleum industry. The standard procedure is A.S.T.M. D 721147 ( 1 ) or its semimicromodification ( 2 ) . A.S.T.M. D i2147 gives reliable results but requires too much elapsed time to be of value for plant control. The semimicroprocedure is a somewhat delicate operation because of the small quantities involved on sampling and testing, and considerntjle laboratory experience is required to obtain consintent, reliable results. The method described in this article was developed for testing deoiled wax in conjunction with plant operation where test results were needed as quickly as possible in the interest of plant efficiency. It was also desired to have a method which required no elaborate or delicate equipment, and which was as simple a3 possible, so that plant operators could obtain rcliable results. Another requirement was to avoid the evaporation of solvent in the interest of safety. The method described, which provides for the separation of oil from solvent by chemical means, meets the above conditions better than the previously mentioned methods
Cooling bath, an insulated bath which is divided by an insulated partition such that the temperature in one side can be maintainei at -50’ to -100” F., while the other side is maintained at -25 * 1 F. Dry ice and alcohol are suitable cooling media. Dimensions and design of the box may vary according to the volume of work to be done. Skim milk test bottle, &inch, with double neck, one neck graduated in 50 divisions; each division equals 0.002 ml. Thermometers. Two A.S.T.3I.cloud and pour, one A.S.T.M. low cloud and pour. Laboratory centrifuge, capable of turning approximately 1500 r.p.m. nith cups of dimensions suitable for holding the &inch skim milk test bottle. SOLVEYT AYD REAGENT
Dyed methyl ethyl ketone, commercial grade, refractive index a t 68” F. 1.378 f 0.002, and containing approximately 2 mg. per gallon of a red oil-soluble dye. Ten milliliters treated with a solution of sodium bisulfite as described in the method should not show more than 0.0005 ml. of oil. Sodium bisulfite, saturated solution, filtered just before using. PROCEDURE
APP4RiTUS
Beaker, 250-ml ; aluminum or copper. Allihn filter tube, length approxiniately 100 mm., capacity 30 ml.; fritted-glass filter disk of F o . I porosity and 20-mm. diamcter.
Precool a filter tube by inserting it in a beaker submerged in the - 2 5 ” F. bath. Weigh 36 * 0.5 grams of melted wax into a 250-ml. metal 1 grams of warm (120’ to 160” F.) dyed beaker, and add 82 methyl ethyl ketone. Place on .\.S.T.\I. cloud and pour therf
V O L U M E 2 2 , N O . 9, S E P T E M B E R 1 9 5 0
1169
For routine control work the above forinu1:r may he simplifimi without serious error as follows: Specific gravity of the separated oil may be assumed to be that Per Cent Oil Found of the sample--e.g., 125/130" F. American melting point = 0.900 Filtering -143/150°F . Micro Solid specific gravity. Temperature, 125/130° F. A M P AMP, Point on Grams of methyl ethyl ketone in the mixture at the tiine of F. Sample 1 Sample 2 sample 3 Oil. Av.. F, filtration may be assumed to be 80.5 and grams of sample 36.0. 0.54 0.76 25 - 12 0.43 The correction of the aliquot for thevolume of oil it eoot:iins 0.53 0.73 12 - 20 0.42 (0.002A) may be disregarded. 0.51 0.71 6 - 25 0 41 0.40 0.69 -8 - 30 0.38 The formula then simplifies to: - -~ ~- When C = 10. Oil, % by weight = 0.05.4 T h e n C = 5. Oil, % by weight = O.1OA Table 11. Oil C o n t e n t of Wax Samples Table I.
Filtering Temperatures us. Pour P o i n t
O
.I.S.T.M. D 721-47 AMP,
O
% oil
F.
125/130 125/130 125/130 143/150 143/150 143/150
0.26,0.22
0.21,0.17 0.48.0.58 0.29,0.22
0.63,0.70 0.45,0.49
Deviation 10.02 t0.02 tO.05
t0.04 t0.04 t0.02
Bisulfite Method DeviaYooil tion 0.30,0.30 0 0.20,0.20 0 0.55.0.58 *0.02
0.30,0.30 0.73.0.73 0.53,0.55
0 0
*o.oi
~
B from A.S.T.M. f0.06 +0.01 +0.04 +o 0.1 +0.06
+o.n7
.4verage deviation between methods +O 03 ~-
__
___~ -
mometer iii the beaker, and, if the sample is not completely di+ solved, heat on a steam hot plate (or equivalent), while stirring, until it just dissolves. Transfer the beaker to the -50" to - 100' F. bath, and stir with the thermometer, scraping off the wax coat Ivhich is formed on the sides and bottom as completely and rapidly as possible. Continue stirring until the mixture has a slushy consistency, after which stirring may be intermittent. When the temperature drops to -20" F., stir continuously until i t drops to -25' F. Transfer the beaker to the -25" F. bath, place the precooled filter tube in the mixture nearly to the bottom of the beaker, and attach a vacuum line t o the filter tube. Turn the vacuum on slightly, and when an estimated 15 ml. of filtrate are in the filter tube, detach the vacuum line, remove the filter tube from the beaker, and transfer the filtrate to a test tube or other suitable container. Pipet 5 ml. of the filtrate, if it is estimated the oil content is over 2.57&,or 10 ml. if under 2.5%, into a skim milk test bottle. Add 5 nil. of distilled water and 20 ml. of a saturated solution of sodium bisulfite to the skim milk test bottle. Press the end of a rubber t u t x attached to the vacuum lin:. against the open end of the capillary neck, and adjust the vacuum so that maximum agitation occuri without loss of liquid from the bottle. Continue the agitation for 3 minut>es,then detach the vacuum line. Add water to the bottle until the surface is in the upper one third of the calibrated portion of the capillary neck. Centrifuge the bottle at approximately 1500 r.p.m. for 5 minut'es and read the number of divisions of separated oil t o the nearest half-division (smallest division = 0.002 ml.). Calculat,e the oil content by means of the following formula:
~
~
~ EXPERIMENTAL ~ ~ DATA ~
e
For the purpose of this investigation, oil is considered as "zero pour point oil," determined by filtering three samples of various melting point wax a t four different temperatures, with the results shown in Table I. A wire is constructed with about a 0.5-inch (1.25 cm.) length at right angles t o a small loop. Microsolid point is determined by placing a small amount of oil on the end of a thermometer bulb and embedding the small loop of wire in the oil. By chilling the embedded wire in the vertical position and allowing it to warm slowly in the horizontal position, the temperature a t which the wire starts to fall from t,he horizontal position is recorded as the micro solid point, and is correlated with the pour point of the oil. With the wire used zero pour oil has a micro solid point of 6' F. Each wire must be standardized against zero pour oil before use.
It was concluded from the data in Table I that a filtering temperature of -25" F. would give zero pour point oil. In order to obtain data on the accuracy of the outlined method, a number of samples were run in duplicate by A.S.T.M. D 721-47 and this method. The duplicate results in Table TI were determined by different operators. The average deviation between methods is better than the repeatability of the A.S.T.M. method. No experimental work was done with microcrystalline or high melting point waxes. coYcLusloYs
The oil content of paraffin wax, as determined by this method, agrees closely with results obtained by A.S.T.M. D 721-47 on commercial waxes of the usual low oil content. The advantages of the method are simplicity, reliability, and speed. Approximately 0.5 hour is requited for completing the test. Another advantage is that it avoids evaporation of solvent, and thus includes light oils if present in the determination. LITERATURE CITED
Testing Materials, A.S.T.M. Committee D-2, "Standards on Petroleum Products and Lubricants," Method D 72147, Philadelphia, Pa. (2) Wiberley. J. S., and Rather. .J. B., J r . , ANAL. CHEY..20, 972 (1) -hn.Soc.
where A = number of 0.002-ml. divisions of separated oil, B = specific gravity of separated oil, C = ml. of aliquot treated with sodium bisulfite solution, D = grams of methyl ethyl ketone added to the sample, and W = weight of sample. (0.805 is the specific gravity of methyl ethyl ketone at 20" C.)
(1948). R E C E I V EJanuary D 27, 1QA0.
Improved Potentiostat for Controlled Potential Electrolysis JAMES J . LIKGANE A Y D ST.4NLEY L. JONES, Harcard University, Cambridge 38, M a s s .
P
OTESTIOSTATS, which automatically perform the function of maintaining the potential of an electrode constant during an electrolysis, have not yet become commercially available, so that those who wish to exploit the planifold analytical applications ( 4 ) of the controlled potential electrolysis technique must construct for themselves the necessary apparatus. In recent years a number of different types of potentiostat have been described (1-5), whose relative merits are best assessed by reference to the original papers.
The inst.rument desvribed herein, whose operating principle is indicated schematically in Figure 1, is an improved version of an instrument previously described ( 4 ) . The chief improvement is the use of a rectifier and filter circuit to enable operation from an ordinary 110-volt alternating current line and the concomitant employment of Variac autotransformers to control the alternating current input and hence the output direct current voltage applied to the elec.trol,vsiq rrll.
