1207
V O L U M E 2 2 , N O . 9, S E P T E M B E R 1 9 5 0 commercial latices of neoprene, natural rubber, and Geon polyblend. The method is rapid, reproducible, and easily applied, and produces films of excellent appearance, Figure 1 shows the molds and films of various polymeric materials prepared by this .technique. Despite the fact that the films appeared to be flaw-free, determination of the tensile values of a very large number of specimens gave inordinately low values in approximately 5% of the cases. The data tabulated in Table I show five specimens with low values of tensile strength and five reference specimens having higher values. All the samples tested were examined under a microscope using 20 to 1350 power magnification, and it was established that those samples which had low tensile values had broken through a bubble. These bubbles were visible only under the microscope, Figures 2 and 3 show a series of photomicrcgraphs of these ten specimcns taken a t 20X, which demonstrate this effect.
Table I. Tensile Strength of Polyethyl Acrylate Acrylonitrile 90-10 Copolymers Tensile Strength, UIti ma te Specimen No.
Lb./Sq. Inch
I
747
2 3
660 330,bubble present 800 227, bubble present 267, bubble present 302, bubble present 817 .~ 744 392, bubble presea
4
5 6 7 8
.10 9
Elongation, 7% 7.1n . -730 740 750 600 680 710 7x1 . .. 750 670
Despite the fact that the specimens with low tensile strength broke through a bubble, it is not axiomatic that a specimen containing a flaw will fail a t the flaw. I t has been shown that the stress concentration in the shoulder of the specimen is often sufficient to cause rupture a t that point in preference to another point of lower stress concentration that contains a flaw (1, 2, 4 ) . Examination of Figures 2 and 3 and Table I also shows that the presence of bubbles does not appear to affect the ultimate elongation materially.
DISCUSSION AND CONCLUSIONS
The knowledge of the tensile strength of a polymer is of importance to a polymer research laboratory in order to serve as a guide for further modification of polymer structure. The results obtained from flawed samples will frequently lead to unfruitful research. A product fabrication laboratory, however, is primarily interested in the strength of the polymer and the ability of the fabricator to make a flaw-free product. This situation. suggests the adoption of two techniques by the,testing laboratory. In testing for the polymer laboratory, each specimen is examined after testing under a microscope. Any specimen that breaks through a bubble or flaw visible when examined in this fashion is rejected. The results of five specimens that show no flaws a r e averaged and reported as the polymer tensile strength. For a product fabrication laboratory, any specimens that show visible flaws that would cause rejection of the finished product should be discarded and the balance tested. The average of five specimens that show no flaws under unaided visual inspection is reported 90 the average tensile strength of the article. SUMMARY
A method for casting and testing essentially flaw-free films from acidic type latices consists of casting against the interior cavity of a cylindrical gypsum mold. The method permits drying of the film from both surfaces and prevents the formation of an impervious surface film, which would later cause Imperfections. Films 0.060 to 0.090 inch thirk can be deposited in 1 to 2 hours using a latex containing 50% solids. Measurements of tensile strength and microscopic examination of saniples cut from the films cast according to this technique showed that those samplea which gave inordinately low values of tensile strength broke through a bubble visible only under the microscope. Suggestions are given for evaluating tensile test results. LITERATURE CITED
(1) Coker, E. G., and Filon, L. N. G., “Treatise on Photoelasticity,” p, 560,
London, Cambridge University Press, 1931.
(2) Division of Rubber Chemistry, Physical Testing Committee, Ind. Eng. Chem., 17, 535 (1925). (3) Maron, S. H., and Madow, B., ANAL.CREM.,20, 545 (1948). (4) “Proceedings of Second Rubber Technology Conference.” p. 442,
Cambridge, England, Heffner and Sons, 1949. RECEXYED January 27, 1950.
Effect of Temperature on Tributyl Phosphate as Extracting Agent for Organic Acids H. ARMIN PAGEL AND KENDALL D. SCHWAB University of Nebrasku,Lincoln, Neb. use of n-tributyl phosphate for extracting organic acids T z f m aqueous solution a t 25” * 2’ C. was reported earlier (I). Work recently completed shows the effect of temperature from 0 ” to 35’ C. for acetic, citric, tartaric, and glycolic acids.
Table I. Effect of Temperature on Distribution of Organio Acids in the Two-Phase System Water-n-Tributyl Phosnhate Acid Acetic
PROCEDURE
Fifty milliliters of ester (previously saturated with water to minimize volume change on mixing) and 50 ml. of the aqueous acid were pipetted into a 150-ml. glass-stoppered separator). funnel. The mixture was allowed to reach the bath temperature and then shaken vigorously for 30 seconds at about &minute intervals for at least 0.5 hour without being removed from the bath. Agitation for longer periods gave identical results. After phase separation had taken place, two 20-ml. pipetted portions from each phase were titrated with 0.1 or 0.5 N carbonate-free standard sodium hydroxide, using thymol blue indicator,
Acetio
Citric
Citric
Temp., Extracted’ 10.10 C. T, ( *o.u’ 0 66.3 15 64.4 25 63.3 35 62.3 0,0988 0 71.5 15 69.5 25 68.1 35 66.4 1.OOO 0 71.3 15 62.4 25 56.5 35 50.5 0.0992 0 80.1 15 70.9 25 63.9 35 56.6 (Cadinuad o n nazt page)
Concn.. N 1.125
c (Water) 1.97 1.81 1.73 1.65 2.51 2.28 2.14 1.98 2.48 1.66 1.30 1.02 4.03 2.44 1.77 1.30
ANALYTICAL CHEMISTRY
1208 ~
_-
--
In titrating the ester phase sample with aqueous base a twophase system is formed, wherein the indicator is almost completely extracted into the ester. Sharp end points were obtained, however, by injecting a small amount of indicator into the aqueous layer (lower) after each addition of base. In several instances the densities of t,he two phases were nearly identical, in which cases the rate of phase separation was very slow. A study of the effect of adding inorganic salts to increase the density of the aqueous phase to ha&en phase separation, and the effect of such salts on the distribution constant, is in progress.
Table I (Continued) 'Temp.,
Acid Tartaric
Concn.. S 1.001
*O.lo C. 0 15 25 35
Tartaric
0.0988
Glycolic
0.992
Glycolic
0.0983
0 15 25 35 0 15 25 35 0 15 25 35
0 Baaed on analyses of equal volumes of aqueoua and ester phases.
Extracted", 70( 10.1) C (Water) 41.8 0.72 34.6 0.53 30.5 0.44 28.7 0.36 49.5 0.98 39.3 0.65 33.5 0.50 28.7 0.40 34.9 0.54 31.8 0.47 29.9 0.43 28.3 0.40 39.1 0.64 35.0 0.54 32.6 0.48 30.5 0.44
LITERATURE CITED
(1) Psgel, H. A,, and McLafferty, F. W., ANAL. CHEM..20, 272 (1948).
-
.-
RECEIVED January 13, 1950.
Colorimetric Determination of Sodium Pentachlorophenate GUY R. WALLIN, H i g h Point, N. C.I ETHODS have been developed to meet the need for a sim-
M ple procedure for determining small amounts of sodium pentachlorophenate in solutions for mildewproofing, algae control, etc. 'The methylene blue procedure was developed first and at a time when the author was not aware that any other colorimetric procedure existed (at Cannon Mills, Kannapolis, N. C.). The copper method was developed much later. A good colorimetric procedure consists of oxidizing the compound to a quinone ( 4 ) . The oxygen bomb method and the Jme ignition method are also available (4). COPPER METHOD
480 520 560 WAVE LENGTH, Mp
600
640
Figure 1. Absorption of Colored Solution as outlined in the procedure. The amount of sodium pentachlorophenate can be determined by treating the foregoing colorless solution with potassium ferrocyanide, which is a very sensitive reagent for copper. The method has a range of 15 mg. and adheres to Beer's law over this range. The abridged spectrophotometric curve shown in Figure 1 was obtained with a Leita-Rouy photometer. Maximum absorption occurs a t 415 mp, and a filter covering this range should be used. 1 Present
x. c.
Amount Recovered,
Recovery,
g
Mg.
5 5 5 10
4.8 50 5 0 10.0
% 96 0 100 0 100 0 100 0 100 0 98 0 100 0 98 0 100 0
10
10 15 15 13
10.0
9 8 15 0 I4 7
15 0
PROCEI)URE
It wlts found that the copper salt formed by treating sodium pentachlorophenate with copper sulfate is sohble in 70% isopropyl alcohol with the production of an opalescent colloidal solution which clears with acidification. The desired acidity for the reaction of potassium ferrocyanide with copper is also obtained,
440
Table I. Recnveries Amount in Solution,
address, Chemical Laboratory, Burlingtoo Mills. Greensboro,
Reagents used are 1% copper sulfate, 70% isopropyl alcohol, 0.67 h' sulfuric acid, and 1% potassium ferrocyanide. The sample should contain approximately 10.0 mg. of active material. The sample is placed in a 125-ml. separatory funnel and 20 ml. of 1% copper Sulfate are added. The solution is filtered, the separatory funnel is rinsed with several portions of water, and the residue on filter pa er is Rashed thoroughly with distilled water Then 50 ml. of 709/0 isopropyl alcohol, acidified to the optimum point with 3 drops of 0.67 N sulfuric acid, are added to remove any residue present, and this alcohol is used to dissolve residue on filter paper into 100-ml. flask. The paper is washed with a little distilled water. Then 5 ml. of 1% potassium ferrocyanide are placed in the flask and the solution is mixed, diluted to 100 ml., and allowed to stand for 5 minutes. The colorimeter is set to its zero position with distilled water, and is read a t the end of a &minute period with a filter transmitting a t 415 mp. Sodium pentachlorophenate may be precipitated from water by copper sulfate, forming a purple salt which dissolves with a loss of color in acid alcohol. By treating the solution with potassium ferrocyanide the amount of copper involved in the reaction is determined. One mole of copper combines with 2 moles of sodium pentachlorophenate. Absolute or 70% ethyl alchol may be used; however, 70% isopropyl alcohol is cheaper and more available. This is an accurate method and a rapid one. The greatest error in recovery was 4%, which is within the range tolerated for colorimetric procedures. A determination may be completed in about 15 minutes. It is necessary to adhere to the time factors pointed out in the procedure, for the colored copper ferrocyanide is unstable, and its optical density changes rapidly with time. A large source of error will develop unless these points are kept in mind. Other phenols react in the same manner and will introduce a source of error. Commercial sodium pentachlorophenate contains some tetrachlorophenate plus a few related impurities commonly
