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ON THE X-RAY DIFFRACTION EFFECTS FROM SOLID FATTY ACIDS

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Science  12 Jun 1925:
Vol. 61, Issue 1589, pp. 613-614
DOI: 10.1126/science.61.1589.613

Abstract

Powder reflections, as well as single face reflections of large spacing, have been obtained from palmitic and other fatty acids. Single specimens with all the optical properties of a crystal and giving the same large spacing X-ray reflections as solidified films on glass have been grown from solution of palmitic acid in acetone. This acid, at least, therefore appears to be truly crystalline under these conditions and not in a "smectic" or other sub-crystalline state. Since the X-ray data from this acid are strictly analogous to those from other typical "smectic" substances, it seems necessary further to conclude that no definite X-ray evidence yet exists for this "smectic" state.

The symmetry of palmitic acid is either monoclinic or triclinic and the long carbon chains are not normal to the face producing the large spacing reflections. Such spacings are therefore not direct measures of the lengths of these chains.

By growing single plates of the acid from solution more intense reflections from the long spacings have been obtained than from films made by solidifying the acid on glass or mica. Such single crystals may prove especially useful as gratings in long wave length X-ray spectrography.