Iaggrtl l ~ f ~ h i nthe t l bath, until a t the final nicltiiig point the bath temperature was 1' to 2' higher t'han the recorder. Once thc *ample was all melted, thc recortlcr teniperature rose rapidly and caught up n.ith the bath. This is furth(,r (+tlcnce that this system give's :L fairly wliable record of the sample tempc~r:xtiiri~ during fusion. llcasurcment of the piston t r a w l a t the sewr:iI points indicates that. roughly, 1 0 5 travel corresponds to the "wetting" point and 2;Yc travel t'o the nirniscus point. This may not be true for snniples such as =1 I-. which eshihi t odc I-sliaped curves. Thc~ t,eniperature accuracy of the nicthotl is cssentially that of t l i p recorder (=0.5'). The shape of tlic curve tlrnwn is iiiflueiicetl to sonic' CI-
tent by the packing of the sample, but the results with different operators agree very well, Principal variation nil1 be in the interpolated netting and meniscus points, more with impure than pure samples. The melting point is not so influenced. For a single operator, the results are identical within the limitations of the recorder itself. Because the instrument measures only volume changes, subtle changes such as polymorphic transformations, desolvation, etc., without appreciable volume change nil1 not he recorded. Hon-ever, shrinkages, often unnoticed in a capillary, show up well. The instrument has proved very useful in providing objective data on the melting bchavior of man:- samples,
particularly from repeated preparations of a compound. LITERATURE CITED
(1) Dubosc, -4.,Mat. grasses 6 , 3308-9 (1913); Reo. prod. chim. 28, 115 (1928). (2) Furst, A., Shapiro, J. J., ANAL.CHEM. 26, 1082-5 (1954). (3) MacAIullin, R. B., J . Am. Chem. SOC. 48, 439-43 (1926). (4) Monand, P., Bitll. soc. chini. France 1955. 1601-2. ( 5 ) Paimer, H. F., Kallace, G. H., J . A m . Chem. Soc. 48, 2230-2 (1926). (6) Stock, J. T., Fill, AI. A., Anal. Chim. Acta 2, 282 (1918). ( 7 ) SttIll, D. R., ISD. EXG.CHEX.. ANAL. ED. 18, 234-42 (1946). (8) Ueberreitrr, K , Orthmann. H. J., Kitnststofe 48, 525 (1958). RECEILEDfor review >Iay 2.3, 1960. Accepted A h g u s t 22, 1960. Division of Analytical Chemistry, 138th Meeting, .4CS, S e i r Tork, S . T., September 1960.
Quantitative Determination of Low Atomic Number Elements Using Intensity Ratio of Coherent to Incoherent Scattering of X-Rays Determination of Hydrogen and Carbon C. W. DWIGGINS, Jr. Petroleum Research Center, Bureau o f Mines, U . S. Department o f the Interior, Bartlesville, Okla.
b A new method based on the intensify ratio of coherent to incoherent scattering of x-rays has been developed for the determination of low atomic number elements. The method has been used to determine hydrogen and carbon in hydrocarbons, particularly petroleum, and in a matrix containing additional elements. Corrections for the sulfur and nitrogen content have been developed. Carbon and hydrogen may be determined in quadruplicate in 20 minutes or less. Conventional x-ray spectrographic equipment may be used without modification. The precision and accuracy of the method appear to equal or surpass those of conventional microcombustion methods for many types of samples.
A
h t h cohiwnt (Raylcigh or uiimotiifitd) arid incoherent (C'oin~iton or niotiificd) scattering of x-rays 11:1~(, been long known. fenrI
