Batches Of Crystals Research Articles

Standard of Purity for Cholesterol

Abstract Three recrystallization technics were used to fractionate five commercial cholesterol products and one artificial mixture. One technic involved the recrystallization of cholesterol from absolute ethyl alcohol, the second technic involved the recrystallization of cholesterol from glacial acetic acid, and the third technic used the dibromide derivative method. The molar absorptivities for the various crystal batches were in the range of 1610 to 1750 L. mole-1 cm.-1 at 620 mµ with a modified Liebermann-Burchard procedure. The molar absorptivities were in the range of 9,800 to 11,500 L. mole-1 cm.-1 at 560 mµ with a modified sulfuric acid-iron method. The original products and the ethyl alcohol recrystallized products showed molar absorptivities at the lower limits of the ranges, while the glacial acetic acid and dibromide derivative recrystallized cholesterol showed molar absorptivities at the higher limits of the ranges. Absorption peaks at 235 mµ for methyl alcohol solutions of the cholesterol preparations were used to estimate cholesterol impurities on the basis of 7-keto cholesterol acetate absorption values. The decrease of absorption in the ultraviolet spectral region established that impurities were removed from the cholesterol preparations studied.

A Notable Growth Spiral on Synthetic Diamond

IN previous communications1 it was reported that a few growth spirals of step height of some 100 Å. were observed on what were otherwise very smooth cubic faces of synthetic diamonds. These spirals were found only among one batch of crystals (1958) made by General Electric (U.S.A.). Of several thousand faces examined only two very clear-cut single-step spirals were found, together with another eight irregular, shallow, imperfect examples.

Photoelectromagnetic Effect in Insulating CdS

The short-circuit photoelectromagnetic current in insulating crystals of cadmium sulfide has been measured in a batch of electroluminescent crystals. The product ${(\mathrm{mobility})}^{3}$\ifmmode\times\else\texttimes\fi{}(lifetime) is found to be 1 ${\mathrm{cm}}^{6}$/${\mathrm{volt}}^{3}$ ${\mathrm{sec}}^{2}$. The sensitivity of the equipment is sufficient to detect the photoelectromagnetic effect for crystals whose product is as low as ${10}^{\ensuremath{-}5}$ ${\mathrm{cm}}^{6}$/${\mathrm{volt}}^{3}$ ${\mathrm{sec}}^{2}$.