The crystals were colourless well-formed prisms which proved to be of monoclinic symmetry, the best individuals being formed by very slow evaporation of the aqueous solution. They were terminated at both ends by pyramid and dome faces, and sometimes grew to the length of a centimetre. The actual crystal elements found after a full series of measurements were as under:—
CALCIUM DEXTRO-GLYCERATE.
Crystal system: monoclinic.
Class of Monoclinic System: sphenoidal or monoclinic-hemimorphic.
Habit: prismatic.
Monoclinic axial angle: β=69° 6′.
Ratio of axes: a : b : c = 1.4469 : 1 : 0.6694.
Forms observed:
| a = {100}, | c = {001}, | r′ = {̄201}, | p = {110}, |
| m = {011}, | o = {111} | s = {̄1̄11}, | n = {̄2̄11}. |
It will thus be seen that the system and the class are precisely those of the two active tartaric acids, which renders the case the more interesting. The usual appearance of the crystals is shown in Fig. 65, and the stereographic projection is given in Fig. 66, which will elucidate the symmetry more clearly, the plane of projection being the plane of symmetry The latter, however, in this class is inoperative, the two ends of the digonal symmetry axis, which runs perpendicularly to the plane of the paper, being differently terminated, as in the tartaric acids. The faces of the forms o = {111} and m = {011} were never found developed on the left side of the symmetry plane, that is, on the left side of the crystal as drawn in Fig. 65, the symmetry plane running perpendicularly to the paper vertically from front to back; they were only present on the right. Conversely, the faces of s = {̄1̄11} and n = {̄2̄11} were never found developed on the right, but only on the left of the plane of possible symmetry.