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A treatment is given of the effect of network flaws due to the finite chain length of the primary elastomer molecules on the elastic properties of rubber vulcanizates. In this treatment full allowance is made for the elastically inactive material which exists either as sol or as loose ends of the network. The cases of linear primary molecules with either a random distribution of lengths or with uniform lengths are considered, and the results are compared with those of earlier theoretical treatments.

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An experimental and theoretical study of the introduction of crosslinks into stretched peroxide-vulcanized rubber by heating it with di-cumyl peroxide in vacuo is described. The observed permanent set and swelling behaviour is in fair agreement with theoretical predictions.An important property of vulcanized rubber is an increase in the unstrained length after stretching, the so-called permanent set. When stretching is for short duration at ordinary temperatures the set is in fact not permanent but decreases with time and largely disappears after swelling. This reversible set has been attributed to secondary forces of the rubber network.l.2 In contrast, stretching at higher temperatures in oxygen produces an irreversible set, which can be attributed very plausibly to the formation of chemical cross-links.3Cross-link formation in stretched networks has been considered as a factor in oxidative ageing, during which a second factor, network degradation, is also operative. Neither process has been investigated separately, and consequently quantitative tests of any theory could not be readily applied.Andrews, Tobolsky, and Hanson 3 have visualized a process of rupture of the GO were made on each strip in this series and the decane removed in wacuo at 60" C over

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A general procedure for the determination of oxirane oxygen is described. The method, originaIly proposed by Nicolet and Poulter, is based upon the quantitative opening of the oxirane ring by means of a 0.2 N solution of anhydrous hydrogen chloride in absolute ethyl ether. The method is specific for the determination of oxirane oxygen, it may be employed N STUDYIXG the mechanism of the air oxidation of unsatu-I rated fatty materials, it is essential to determine the quantity of each of several types of oxygen-containing groups in the product. It is customary to analyze for hydroxyl, carboxyl, carbonyl, and ester oxygen, but no work has been reported on the determination of oxirane oxygen (-C-C-) in such materials, even I I \/ 0 though it is well known that oxirane compounds are formed during the air or oxygen oxidation of unsaturated compounds (3, 4).Recently, Hilton (6) has suggested a method for determining oxirane oxygen in oxidized rubber, the basis for which is the reaction of diethylamine with the oxirane group under pressure in a sealed tube, followed by analysis of the reaction product for nitrogen. This method is time-consuming and inconvenient, and it is not suitable for control work. The method of Nicolet and Poulter (r), however, appears to be admirably suited for the analysis of air-oxidation reaction mixtures for oxirane oxygen. This method which is based upon the quantitative opening of the oxirane ring by means of a solution of anhydrous hydrogen chloride in absolute ethyl ether (Equation 1) :(1)was applied by them only to the analysis of the 9,lO-epoxystearic acids, derivable for oleic and elaidic acids. But whether the method is specific for oxirane oxygen and whether it is applicable to a variety of oxirane compounds in which the oxirane group is a t different positions in the molecule had to be determined before it could be employed for the analysis of air-oxidation mixtures. REAGENTS in the analysis and determination of the purity of a wide variety of oxirane compounds, and it is suitable for the determination of oxirane oxygen in air-oxidation reaction mixtures. The reaction of anhydrous hydrogen chloride with oxirane compounds in absolute ethyl ether solution is suggested as a general method for preparing chlorohydrins. heavier solid stopper.) Liquids are weighed by difference from dropping bottles; solids are weighed into tared flasks. The maximum weight of sample should be taken only when it is known that the oxirane oxygen content lies near the minimum value of the range given. Adherence to these values will ensure a proper (at least 100%) excess of hydrochloric acid-ether solution. Wash down the sides of the flask with 5 ml. of absolute ethyl ether and add exactly 25 ml. of the hydrochloric acidether solution. Stopper the flask and swirl gently to dissolve the sample. Allow the solution to stand for 3 hours at room temperature. .4dd 50 ml. of 95% ethyl alcohol and 1 ml. of the phenolphthalein indicator solution, and titrate the excess acid with 0.1 S sodium hydroxide solution. Conduc...