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The melting temperatures of five emulsion polymerized polybutadienes containing varying amounts of trans‐1,4 units were determined. Since slow heating rates were used subsequent to the initial crystallization, melting temperatures were observed that were appreciably higher than previously indicated. The data were analyzed according to the theory of the melting point depression of copolymers, and a lower limit for the heat of fusion per 1,4‐trans unit of 18.5 cal./g. was obtained. This value is larger than that for natural rubber and explains why calorimetric measurements of the heat of fusion apparently give abnormally high values. The index of refraction and densities of the amorphous polymers were determined at 25°C. and the specific refractivities found to be constant and independent of polymer constitution in the composition range studied.

;\ rap id m ethod for t he estimation of natural r ubber in vulcani zates of GR-S a nd nat ura l rubber by m eans of infra red spectrosco py is reported . Sampl es were carefully prepared to co ntal!1 known amou nts of .natural and GR-S rubber; the samples \I'ere v ulcan ized, extracted wL t h acetone, and dn ed III a vac u um oven. Specim ens from eac h sam ple were pyr olyzed in a combu st ion furn ace at 550 0 C. and the liquid pyrolyzates were a nalyzed by mfra red absorptLOn spectroscop y . An e mpLL"lcal relationship was de veloped in which thc band in te nsit ies at 11.02 a nd 11.25 mi crons were r elated to natural rubber content . Th e exp erimental error of .the m ethod is characterized by a stand ard deviation of a s ingle d etermln atLO n of 0 .023, \I'hlCh represe nts a pprox imately 3-percent nat ural rubber.

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The role of ultraviolet radiant energy and effect of presence of monomer on degradation of polystyrene were st udied by means of ultaviolet absorption techniques. It was found that ~xposure of pure pol,Ystyrene to ultravio~e t .radiant energy resulted in increased absorption III th~ ultravIOlet regIOn of 280 to 400 millimicrons, whICh advanced progressively as exposure t une lllcreased. The presence of monomer increased the rate of d egradation without altering the general type of abso~·p.tion. A post-radiation effe~t was noted in both the pUlified polymer and polymer contallllllg monomer styrene. Agam, t he presence of monomer increased the ra~e of progress of the post-radiation effect. Possible mechanisms are postulated for t he ultravIOlet degradatIOn, and the concept of e ntrapped free radicals is considered as a possible explanation for the post-radiation effect observed.

in relative humidity . This switching mechanism also is adaptable for giving rapid and discrete changes in temperature.It is designed to operate at test-chamber temperatures above 0 0 C, but may readily be used at temperatures as low as -40 0 C. The low temperatures are achieved, however, at some sacrifice of the maximum attainable relative humidity. For most of the test-chamber temperature range, practically any desired relative humidity may be produced by the apparatus.Independent checks on the performance of the apJournal of Research of the National Bureau of Standards paratus by means of the gravimetric method of moisture determination and the psychrometric method show an aver age agreement in relative humidity of 1.2 percent as measured and as given by the apparatus, eq 2.The author gratefully acknowledges the assistance of R. A. Baum of the Shop Division in the construction of t he apparatus and of E. T. Woolard in the experimental work.WASHINGTON, August 14, 1950. Vol. 45, No.5, November 1950 Research Paper 2146 An Improved Apparatus for Determining Moisture in Rubber by Distillation with Toluene By Max TryonAn improved apparatus has been developed for the determination of water in rubber by distillation with toluene. The volume of the water collected is measured in a graduated capillary tube, which allows more precise m easurement than the tapered tube formerly used . The interior of the trap and condenser is coated with a water-repellent silicon e polymer to prevent water droplets from adhering to the walls and to improve t he accuracy. This paper describes the construction of the apparatus and a procedure for coating its interior with the silicone pol ymer. A method for calibration of the trap is included in a general procedure for use of the equipment.

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