An X-ray diffractometer method similar to one used to determine the crystallinity of stretched rubber has been applied to partly devitrified glass. Percent crystallinity is equated to lOO(1, -I,)/ ( I , -ID). Ig, I,, and IB are respectively the noncrystalline scattering intensities measured at a single value of 28 for the parent glass (zero crystallinity), the partly devitrified glass, and a mechanical mixture of crystalline compounds chemically equivalent to the parent glass. The value of 26' is selected such that the noncrystalline scattering is high for the parent glass and at the same time is free of crystalline scattering in the case of the partly devitrified glass and of the mechanical mixture. The assumptions and approximations inherent in the method are discussed and their validity is tested. The method is rapid, virtually independent of the crystalline species present, and accurate to * 5 % or better.

lim 2( \ ) = lim 1( )~ exp(-x*/4T) (11") l-> CO J-> 03 Substitution of this into equation 5" and consideration of equation 3" leads to limy = ( )->/< J'J exp( -xs/4T)dx (12") This integral may be expressed in terms of the error function (see equation 25 in the text), and we have finally lim J = ( /2 /2 ) (13") Z-M" Thus ^lim ' ( , ) = ( VU y) (14") ^lim 2( ,<) = ( Vy) (15") where y = x/(2vT)

A technique is described for quantitatively examining the diffraction pattern of polydimethylsiloxane at and below room temperature with the x‐ray diffractometer. The crystalline fraction of the unstretched material is determined by the classical method developed for natural rubber. In the case of the stretched elastomer, a modified procedure is required which takes into account the extent of preferred orientation of the molecular chains. As the extension ratio is increased, the crystallization temperature rises and preferential orientation of the crystallites with respect to the extension axis increases. The crystallinity increases with decreasing temperature and appears to be independent of the extension ratio below −60°C. An over‐all crystalline fraction of 0.42 was measured for a silicone rubber specimen at −60°C. and an extension ratio of 6.3.

The 489' transformation in Na2C03 makes its first appearance at 67.5 mole yo. No level range is observed indicating that this transformation is not quite as spontaneous as its opposite member. The 361' transition in NaZC03 is not detectable until approximately 92.5 mole yo from which point its latent heat increases continuously. The X-ray data indicate that the upper and lower curves have approximately a 10 mole yo separation a t room temperature which explains the rapid decrease in the magnitude of the spontaneous latent heat. The consistency of the patterns in the 8-E two phase region indicates that the X-ray sample preparation resulted in a fairly good approach to equilibrium and this also lends support to the validity of the entire diagram as constructed.NOTE ADDED IN PRooF.-The author has hitherto been unable to offer any explanation for the heat effects a t ca. 620" reported in ref. 2. Subsequent to the compilation of this manuscript, a probable explanation for the "anomalous heat effects" was forthcoming in a private communication from Drs. which is abstracted herewith. I n the course of differential thermal analysis studies in the sodium carbonate-silica system we also have been unable to observe this peak (at ca. 600") when using analytical reagent sodium carbonate However, when using commercial sodium carbonate, which is known to contain up to 0.5% sodium chloride, a small peak a t about 620" is observed. D. T. A. curves of sodium carbonate-sodium chloride mixtures (both of analytical reagent quality) show a small peak a t about 620' which increases in area with increasing chloride content. Moreover Mellor' states that eutectic melting occurs between sodium carbonate-sodium chloride mixtures a t 636". Analytical reagent quality potassium carbonate shows no peak a t about 620", but a peak appears when analytical reagent quality potassium chloride is added as an impurity Mellor again gives the eutectic melting temperature of these two substances a t 636".

In general, extension of an elastomer results in a degree of preferred orientation of the molecular chains composing the amorphous phase. Therefore the amorphous fraction of a partially crystalline elastomer must be related to the integrated intensity of the amorphous diffraction halo rather than to the intensity at any one azimuth. A noteworthy exception is natural rubber, for which simple meridional measurements suffice. A Geiger-counter apparatus with beam monitor and temperature-controlling accessories is described for making accurate measurements of the x-ray intensities scattered at any azimuth and at small or moderate Bragg angles. Measurements of crystallinity in natural rubber are in essential agreement with the findings of previous workers. When polybutadiene is extended at room temperature, molecular orientation occurs, but little if any crystallization. Measurements at lowered temperatures show that the crystalline fraction becomes appreciable at about 0°C and that it increases with further reduction in temperature and with increasing extension ratio. Preferred orientation of the crystalline regions in extended polybutadiene has been measured quantitatively with the object of providing jointly with birefringence measurements a value of the birefringence of a single crystal of polybutadiene.