V O L U M E 20, N O . 11, N O V E M B E R 1 9 4 8 The amyl alcohol, box-ever, reacted more rapidly and n-ithout formation of any insoluble precipitate. Therefore it was used exclusively for this purpose in subsequent determinations. I n four of the above standardizations, the reagent TTas heated in the presence of solvent for varying lengths of time before i t was decomposed with the amyl alcohol. Heating for as long as 15 minutes a t 98" C. did not result in evolution of hydrogen beyond that of the normal solvent blank. This eliminated the possibility that thermal decomposition of the hydride with evolution of hydrogen ( 2 ) might preclude its use at higher temperatures. I n Table I1 are summarized the experimental results obtained from the reaction of the fourteen compounds each n i t h 1 ml. of the hydride reagent. In each case 1 ml. of di-n-butyl ether (dried as above and stored over sodium wire) was used as solvent. In every case where active hydrogen was found, a correction of 0.15 ml. was subtracted for the observed solvent blank. The Roman numerals in the first column of Table I1 refer to the corresponding compounds listed in Table I, and the small letters to the reaction conditions indicated in Table I. In Table 111are summarized in the same way the experimental results derived from the reaction with methyl magnesium iodide of each of the compounds listed in Table I1 Tvith the exception of benzoin. I n the first two reactions, I1 and 111, 1 ml. of di-Ti-butyl ether was used as solvent with an observed correction of 0.04 ml. for the solvent blank. Also, 1 ml. of 0.396 M methyl magnesium iodide in diisoamyl ether was used in reactions I1 and 111. (On standardization, 1 ml. of reagent gave an average corrected volume of 8.86 ml. of methane.) HoLvever, in all reactions other than I1 and 111, 1 ml. of dry xylene served as the solvent together with 1 ml. of Grignard reagent of 0.412 M concentration in diisoamyl ether. (1 ml. of reagent + 9.23 ml. of methane.) The xylene, which had been dried over sodium for over 4 years, gave no detectable solvent blank. Preparation of Compounds. The following three compounds were prepared by methods reported in the literature: nitrile VI ( 4 ) ,ketone XI11 ( 6 ) , and methyl ester XI1 ( 1 ) . The preparation of the nitrile T' and the 8-lactone XIV nil1 be reported elsewhere. CU-PHESYL - a - CYCLOHEXYL - y - D I E T H Y L A h I I S O B U T Y R O ~ I T R I L E VIII. Sodium amide prepared from 5.2 grams of sodium in liquid ammonia nas suspended in 75 ml. of dry toluene. To this suspension held a t 50" to 60" C. \vas added over a period of 10
1029 minutes with stirring a solution of 44 grams (0.22 M) of a-phenyla-cyclohexaneacetonitrile VI1 in 75 ml. of dry toluene. The mixture was then stirred a t 80" to 90" C. for 1 hour more. To this suspension of sodium salt cooled to 25 C. were added with stirring over a period of 10 minutes 30 grams (0.22 M ) of 8diethylaminoethyl chloride. After stirring a t room temperature for 1 hour the mixture m s Tyarmed a t 50" to 60" C. for 30 minutes and then a t 80 to 90 O C. for another 30 minutes. The mixture n-as poured into 400 ml. of cold water. The organic layer was separated and extracted with excess 1 to 5 hydrochloric acid. Precipitation of the product with 20% sodium hydroxide yielded an oil which was taken up in ether, washed, and dried over anhydrous magnesium sulfate. Filtration and evaporation of t h e ether gave 54 grams (83%) of crude product which was distilled in vacuo. Yield, 47 grams (71%) of viscous pale yelloTv oil, boiling point 150-152Oat 0.3 mm., nZ
1.5 >
:3
1 .? 2
Total
163. 5
163,;
161.5
.\ iange of relative effective specimen size> of 1 to 12 (Table 11) was attained by the use of dumbbell cutting dies of four different widths and tensile test slabs of three different thicknesses. Thickness of the specimen was estimated to the nearest 0,0001 inch with a standard rubber thickness gage ( 1 ) . The length of each specimen xvas arbitrarily taken as the distance between the benchmarks; the nidth was measured by a method involving mass and specific gravity measurements ( 6 ) . Exact disposition of such factors as shape, breaks outside of benchmarks, and shoulder breaks was so complex that benchmarks commonly used with the given die were employed for convenience. The data in Tables I11 and IV were obtained in a similar manner except that the widths of the specimens were taken as the rated widths of the various dies, 0.125, 0.25, and 0.5 inch. In the case of the natural rubber stock, this procedure leads to an error for which correction must be made. I t will be noted that there is a definite downward trend in modulus values as the width of the cutting die was increased. Since there is no reason to believe that the moduli should vary over a range of specimen sizes, the observed trend must be due to errors introduced in accepting the midths of the specimens as exactly 0.125, 0.25, and 0.5 inch. The width of a die-cut tensile specimen is greater than the calipered width of the cutting die; the magnitude of the percentage error thus introduced is influenced, among other things, by the softness of the rubber and the width of the die. When soft stocks are used, the percentage difference between the width of the cut strip and the width of the die is greater with a narrow die than with a wide one. Unfortunately, data on the actual widths of the rubber specimens are not available; accordingly,
2600)
1
e
I
I
3
4
I
1
6
I
I
8
0
l
l
14
V/%, RELATIVE VOLUME
Figure 2.
Effect of Relative Volume on Tensile Strength
.I11 calculations that involved the special specimen were based on the thickness at the low point of the concavity. The thickness a t a point 0.05 inch distant from the center is less than 1% greater than the thickness a t the center. There is no, intention in this paper to imply that the design of the special test specimen is perfect. The suggestion is made simply as one atternpt to devise a specimen of small volume. RESULTS AND DISCUSSION
The results of varying the size of the test specimen on the observed tensile strength are shown in Tables 11, 111, and ISand in Figure 2.
ANALYTICAL CHEMISTRY
1032 A least squares treatment (3) enabled determination of constants a and b (Table V) in the equation
T
= a
+ b log VV" -
(8)
Table IV.
Effect of Specimen Size on Tensile Strength of Natural Rubber Stock
Modulus a t Observed Corrected 4 v . Sample Relative 500% Elongation, Tensile Strength, Tensile Strength, Dimensions, Inch Volume Lb./Sq. Inch" Lb./Sq. Incha Lb./Sq. Inchb 1 0 . 1 2 5 X 1 X 0.0765 383: 4255 4 140 2.018 3730 4025 4025 0 . 2 5 0 X 1 X 0.0772 0 . 2 5 0 X 2 X 0.0772 4.035 4085 3700 4050 0.500 X 2 X 0.0769 8.03 3915 3650 3830 , Average standard deviation, u , = 75 lb./sq. inch. Mean of sixteen tests. b Corrected to the average modulus value of 3730 lb./sq. inch. thus (3730) (4255)/(3835) = 4140. Observed variation in modulus is assumed t o be due t o a corresponding vadation ih width of specimen.
and location of the curves in Figure 2. Comparison of Equations 3 and 7 shows that k = 0.85 u and comparison of Equations 3 and 8 shows that To = a and k = -b/2.303. A t least as a first approximation, the theoretical relationship developed in Equation 3 appears to be verified. A tenfold increase in volume of the test specimen resulted in a decrease of 308 and 339 pounds per square inch in the average tensile strengths of X-243 and X-289 vulcanizates, respectively, and of 204 pounds per square inch for the natural rubber. Practical uniformity of all modulus values in each table is evidence of the fact that all specimens, regardless of size, were vulcanized to the same state of cure. The theoretical value of k given in Equation 6 is compared with the observed values in Table V. The agreement is satisfactory, considering the approximation used in deriving the equation and the possible error of the experimental work. I t can be shown mathematically (9) that the degree of skewness is directly related to k (or, equivalently, to u). I t was shoJvn previously (4) that the frequency distribution of tensile strength for GR-S was more skewed than that for natural rubber. This phenomenon is attributed to the higher u and k values associated with the tensile testing of GR-S. From the foregoing data and discussion, it is apparent that a testing procedure that employs specimens of different sizes can be adapted to evaluation of the homogeneity of cured rubber stocks. This observation is illustrated by the data of Table VI where for a normal stock and one that exhibited obvious defects, the increasc in tensile strength brought about by a decrease in the effective size of the test specimen is compared.
Table 11. Tensile Strength cs. Relative Volume of GR-S (X-243) Modulus a t 300% Tensile Strength, Relative Elongation, Lb./Sq. In." Lb./Sq. In.= Dimensions, Inch Volume 1350 1 1355 1.128 1345 1.507 2.025 1350 1400 2.240 1390 3.007 1355 4.025 1390 4.484 1375 6.025 1355 8.27 1385 9.07 1400 12.17 Over-all standard deviation, u, of tensile strengths 169 lb./sq. inch. 0 Mean of sixteen tests.
Av. Sample
-
Table 111. Effect of Specimen Size on Tensile Strength of GR-S (X-289) Av. Sample Dimensions, Inch 0 . 1 2 5 X 1 X 0.0782 0.250 X 1 X 0.0795 0 , 2 5 0 X 2 X 0.0783 0 . 5 0 0 X 2 X 0.0788 Average standard deviation, a Mean of sixteen tests.
Modulus Tensi1e a t 300% Elongation Strength, Relative Lb./Sq. In.(" Lb./Sq. In.Q Volume 2770 3115 1 3010 2.034 2775 2755 2960 4.005 2770 2790 8.065 u , of tensile strengths = 119 lb./sq. inch.
Table V.
Comparison of Experimental and Theoretical Values of k Av. Dev. in k
GR-S (X-243) GR-S (X-289) Natural rubber Average a
Tensile Strength, Lb./Sq. Inch 169 119= 75
a
-b
3480 3123 4134
308 339 204
4 n unusually low value for X-289.
Exptl., -b/2.303 134 147 88 123
Theoretical. 0.85 u 144 101 64 103
S o r m a l value is about 150.
Table YI. Application of Homogeneity Test to Two Mixes of GR-S (X-289) Observed Tensile Strength, Lb./Sq. I n c h Defective stocka Normal stock Standard size specimen 2720 3480 Special low-volume specimen 3585 3970 490 Difference 865 a Cured stocks of this mix evhibited pits and cones on broken surfaces.
Table YII.
Standard specimen Special specimen
Tensile Test of Pure Gum Tensile Strength, Lb./Sq. Inch Natural rubber Seoprene GK 2430 4020 3960 5600
The degree of homogeneity of cured rubber stocks can be evaluated by varying the specimen size or by determining the standard deviation for a given size. The former method requires fener tests, is the more rapid, and would be practicable if fairly large ratios of specimen sizes could be obtained, a condition that is rather difficult to realize with the present standard testing equipment. Specimens of 4 X 0.5 and 0.125 X 0.5 inch would give an ample range; however, no stock with even a moderate elongation can be tested on the standard equipment with a strip long enough to accommodate 4 inches between bench marks. An interesting by-product of this investigation is the application of the special specimen to the tensile testing of gum stocks of natural rubber and of neoprene. Usually gum stocks of natural rubber and neoprene break in the shoulder of the specimen a t the point of minimum radius. The recorded values of the tensile strength of these specimens are based on the cross-sectional area of the specimen a t the constricted portion. However, because of the shape of the standard specimen, the stress a t the edge of the shoulder is greater than the stress a t the straight, constricted portion. It has been observed that the recorded tensile strengths of neoprene gum stocks are markedly affected by the number of nicks a t the shoulder of the die. It appears then, that the rupture of gum stocks breaking a t the shoulder is , in the nature of a tear which starts from the surface where the stress is greatest. Carbon black stocks, though likewise suffering the greatest stress a t the shoulder during the stretching operation, ordinarily break from some nuclear point of heterogeneity inside the specimen. For this reason the recorded tensile strengths of specimens that break in the shoulder are low because the stress at the breaking position is greater than the stress recorded a t that instant by the tensile machine.
V O L U M E 20, N O . 11, N O V E M B E R 1 9 4 8 However, when the new form of specimen is used, the sample is forced to break near the center-the thinnest portion of the strip-because of the deliberate localization of stress a t that point. This localization of stress is different from that oocurring a t the shoulder in one important respect-the stress a t the center is easily measured, but the stress a t the shoulder cannot be accurately determined. The validity of the contention is supported by the large increase in tensile strength resulting from the use of the special specimen as shown in Table VII. The differences do not, of course, involve the property of heterogeneity, but merely reflect the differences in the mechanism of rupture. I t is therefore suggested that for any composition that exhibits breaks a t the shoulders of standard specimens, higher and more representative tensile strength results may be obtained by using $he special type of specimen. LITERATURE CITED
(1) A.S.T.M. Standards on Rubber Products, D412-41. 251 (1946). (2) Davies, 0. L., and Horrobin, S., Rubber Chem. TechnoZ., 10 (1) 180 (1937); Trans. Inst. Rubber Ind., 12, 85-92 (1936).
1033 (3) Davis, D. S., “Empirical Equations and Nomography,” p. 32, Xew York, McGraw-Hill Book Co., 1943. (4) Higuchi, T., and Leeper, H. M.,unpublished report to Subcommittee on Test Methods of the Committee on Specifications for Synthetic Rubber, Office of Rubber Reserve. ( 5 ) Juve, A. E., B. F. Goodrich Co., private communication. (6) Leeper, H. M., unpublished report to Subcommittee on Test Methods of the Committee on Specifications for Synthetic Rubber, Office of Rubber Reserve. (7) Office of Rubber Reserve, “Specifications for Government Synthetic Rubbers,” Jan. 1, 1947. ( 8 ) Ott, Emil, “Celluloje and Cellulose Derivatives,” p. 1035, New York, Interscience Publishers, 1943. (9) Peirce, F. T., J . Test& Inst., 17, T355 (1926); 18, T475 (1927). (10) Reece, W.H., Trans. Inst. Rubber Ind.. 11, 312 (19353. (11) Wiegand, \V.B., and Braendle, H. A., IXD. ENG.CHEnr., A s . 4 ~ . ED., 1, 113 (1929). RECEIVED April 28, 1048. Presented before the Division of Rubber Chemist r y a t the 113th Meeting of the AMERICAS CHEMICAL SOCIETY, Chicago, Ill. Investigation carried o u t under t h e sponsorship of the Reconstruction Finance Corporation, Office of Rubber Reserve, in connection with t h e Synthetic Rubber Program of the United States Government.
Determination of Small Amounts of Oxygen in Gases L. J. BRADY, Air Reduction Sales C o m p a n y , New York, N. Y . A rapid procedure has been developed for determining the oxygen content of such gases as nitrogen, argon, acetylene, and mixtures of carbon monoxide, carbon dioxide, and nitrogen. The oxygen concentrations conveniently evaluated by this method lie within the range of 0.1 to less than 0.001%. The analysis is not affected by hydrocarbons, phosphine, or sulfur compounds in small quantities.
B
ECAUSE an increasingly large number of industries require
gases virtually free from oxygen, analytical procedures for determining the oxygen content of such gases are important. Numerous analytical devices for evaluating the oxygen content of gases, utilizing the heat of formation of ivater in the presence of a suitable catalyst, have been described. Recently a commercial instrument employing this principle was discussed by Cohn (3) The use of ferrous salts for the determination of oxygen was originated by Rlohr (7) and developed further by Shaw (9), who determined the ferrio ion colorimetrically with thiocyanate in acid solution. Unfortunately, this method cannot readily be extended to gases having an oxygen content less than 0.001%. Winkler (11), in a classic investigation, developed the use of manganous hydroxide and an iodide to determine the oxygen dissolved in nater. In this method the oxidized manganous hydroxide liberates upon acidification an amount of iodine equivalent to the dissolved oxygen initially present. Various investigators (6, 8,12) have adapted this scheme to the determination of oxygen in gases. The time per analysis and the general complexity of the apparatus leave these methods open t o serious objections. Binder and Weinland (1, 2 ) first described the use of pyrocatechol in the presence of ferrous salts to determine the oxygen content of gases. Their method depends upon the fact that pyrocatechol forms a compound with ferrous iron nhich is stable against oxidation in acid solution but in alkaline solution is rapidly oxidized to an intensely red ferric compound by oxygen even when the oxygen is present in trace amounts. White (IO) described a colorimetric method based on the oxidation of alkaline photographic developers such as pyrogallol and amidol by oxygen t o form quinones. An oxygen absorbent comprising sodium anthraquinone-psulfonate in the presence of sodium dithionite was studied in considerable detail by Fieser (j), who reported that the sodium 9
anthraquinone-p-sulfonate acted only as a catalyst, although his experimental results indicated othern-ise. He stated that the reduced sodium anthraquinone-0-sulfonate adsorbed oxygen as follou~s: COH
c0H CO
and that the dithionite then reacted as follows:
+ H20 +
the net result being Sa2S20c
l/202
+2NaHSOS (3)
He stated that although some oxygen was probably absorbed directly according to Equation 3, the first reaction appears to be much the faster of the two. It is logical to assume, therefore, that any reducing agent capable of reducing the sodium anthraquinone-p-sulfonate could replace the dithionite. Experience has shown that amalgamated zinc can be used for this purpose (4). The present procedure for the determination of the oxygen content of gases is based on the observation that an alkaline
