Moreover, it was frequently observed that the right-hand faces (110) and (̄110) of the primary prismform p were much more brilliant and truly plane than those on the left hand, (1̄10) and (̄1̄10), which were usually dull and often curved, as were also frequently the faces of the left-hand forms s and n. The right-hand distinguishing forms m and o, on the contrary, were generally most brilliant and gave admirable reflections of the goniometer signal-slit.
Fig. 65.—Crystal of Calcium Dextro-Glycerate.
Fig. 66.—Stereographic Projection of Calcium Dextro-Glycerate.
The following table represents the results of the angular measurements, twelve different well-formed individual crystals having been employed. The angles marked with an asterisk were the important angles the mean observed values of which were accepted as correct, being the best measured angles, and which were therefore used as the basis of the calculations.
| Table of Interfacial Angles of Calcium Glycerate. | ||||||
|---|---|---|---|---|---|---|
| Angle measured. | No. of measurements. | Limits. | Mean observed. | Calculated. | ||
| {ap = 100 : 110 | 42 | 52° 32′ | − | 54° 16′ | 53° 29′ | * |
| {pp = 110 : ̄110 | 20 | 72 7 | − | 73 33 | 73 4 | 73° 2′ |
| {ac = 100 : 001 | 13 | 68 22 | − | 69 42 | 69 3 | 69 6 |
| {cr′ = 001 : ̄201 | 13 | 52 4 | − | 52 31 | 52 13 | * |
| {r′a = ̄201 : ̄100 | 13 | 58 35 | − | 58 46 | 58 41 | * |
| cm = 001 : 011 | 10 | 31 47 | − | 32 19 | 32 3 | 32 2 |
| r′n = ̄201 : ̄2̄11 | 2 | 29 43 | − | 29 48 | 29 45 | 29 47 |
| {ao = 100 : 111 | 7 | 53 59 | − | 54 10 | 54 3 | 53 54 |
| {om = 111 : 011 | 7 | 18 20 | − | 18 35 | 18 26 | 18 29 |
| {ma = 011 : ̄100 | 13 | 107 22 | − | 108 24 | 107 41 | 107 37 |
| {an = ̄100 : ̄2̄11 | 11 | 62 32 | − | 63 44 | 63 6 | 63 10 |
| {ns = ̄2̄11 : ̄1̄11 | 1 | − | 21 35 | 21 27 | ||
| {sa = ̄1̄11 : 100 | 3 | 94 49 | − | 95 34 | 95 18 | 95 23 |
| {po = 110 : 111 | 9 | 43 51 | − | 44 44 | 44 35 | 44 38 |
| {oc = 111 : 001 | 9 | 32 56 | − | 33 15 | 33 7 | 33 7 |
| {cs = 001 : ̄1̄11 | 7 | 41 32 | − | 43 2 | 42 10 | 42 17 |
| {sp = ̄1̄11 : ̄1̄10 | 7 | 59 15 | − | 60 54 | 59 59 | 59 58 |
| {pc = ̄1̄10 : 00̄1 | 14 | 77 2 | − | 78 21 | 77 42 | 77 45 |
| {cp = 00̄1 : 110 | 16 | 101 39 | − | 103 36 | 102 16 | 102 15 |
| {pm = 110 : 011 | 9 | 52 15 | − | 53 25 | 52 42 | 52 41 |
| {mn = 011 : ̄2̄11 | 5 | 79 5 | − | 79 26 | 79 15 | 79 12 |
| {np = ̄2̄11 : ̄1̄10 | 5 | 47 41 | − | 48 23 | 48 4 | 48 7 |
| {pr′ = 110 : ̄201 | 14 | 106 35 | − | 108 42 | 108 5 | 108 1 |
| {r′p = ̄201 : ̄1̄10 | 26 | 70 54 | − | 73 32 | 71 55 | 71 59 |
| {ps = ̄1̄10 : 1̄1̄1 | 5 | 66 42 | − | 67 17 | 67 4 | 67 5 |
| {sr′ = 1̄1̄1 : 20̄1 | 6 | 40 36 | − | 41 29 | 41 5 | 40 56 |
| pm = ̄110 : 011 | 3 | 75 5 | − | 76 21 | 75 37 | 75 45 |
There is a moderately good cleavage parallel to the basal plane c = {001}.
The optical properties afford conclusive proof of the monoclinic nature of the symmetry. The plane of the optic axes is perpendicular to the possible symmetry plane, b = {010}, and the first median line makes an angle of 23° with the vertical axis c, emerging consequently nearly normal to the basal plane c = {001}, so that a section-plate parallel to the c-faces, or a tabular crystal or cleavage plate parallel to c, shows the optic axial rings and brushes well. The values of the apparent optic axial angle in air, 2E, and of the true optic axial angle within the crystal, 2Va, the latter measured with the aid of a pair of accurately ground section-plates perpendicular to the first and second median lines and immersed in oil, are given in the next table.
| 2E | 2Va | |||
|---|---|---|---|---|
| For | lithium | light | 51° 35′ | 34° 56′ |
| „ | sodium | „ | 52° 30′ | 35° 28′ |
| „ | thallium | „ | 53° 50′ | 36° 16′ |