A photo-electric device for the evaluation of structure factors
H. Lipson, C. A. Taylor · Acta Crystallographica · 1949
e from exposure to the atmosphere, as even brief contact with water vapor caused immediate deterioration.Protection was effected by coating the crystals with a very thin layer of cellulose nitrate obtained by dipping the crystal in a 4 % neutral a~nyl acetate solution before mounting.'Ih this way it was possible to preserve the crystals for several days.Weissenberg photographs were taken of the equator and first and second layer lines with the crystal rotated about the c axis, which was parallel to the long dimension of the crystal.These photographs were obtained through facilities made available by Prof. B. E. Warren of the Massachusetts Institute of Tectmology.In this laboratory, additional rotation photographs were taken of the crystal SHORT COMMUNICATIONSrotated about the a and b axes.It was observed that the a and b axes lie in directions approximately 45 ° to the crystal faces.The unit cell was found to be orthorhombic with the following dimensions: a=11.64,b=9.05, c=5.18A.The following systematic absences wore observed: h00 with h odd, 0k0 with k odd and 00l with l odd.These indicate that the space group is P21212 ~.The density of the proline crystals, as determined by flotation in a mixture of p-bromotoluene and n-butyl bromide, was 1-35 g.cm.-a.The number of molecules per unit cell was calculated to be 3-9.This indicates that the unit celI conrains four molecules.