76 
in detail. The yellow (metastable) modification, melting at 70° C., 
is rhombie-bipyramidal, with the parameters: a:b:c=0,3732:1: 
:0,4228, and the forms: {010}; {011}; {101}; {102}. Its bire- 
fringency is of positive character; the optical axial plane is parallel 
to {100}. The crystals show a cleavability parallel to {100} and 
{010}; their specifie gravity at 17° C. is: dso = 1,248, from which 
the equivalent-volume is calculated at: 169,75, and the topical para- 
meters at: 7: pw: w = 3,8269: 10,2471 : 4,3322. 
The red modification, which melts at 74° C., and to which the 
yellow form changes at 34° C., is monoclinic-prismatic. The para- 
meters published by the author do not agree with those calculated 
from his angular values: they are really : 
a:b6:c = 0,2362 : 1 : 0,6579; 
B= 7498, 
if the same angles be used as by the author mentioned. The occur- 
ring forms have the symbols: {010}, {001}, {110}, and {O11}. The 
optical axial plane of these strongly pleochroitic, negatively bire- 
fringent erystals is perpendicular to {010}; the cleavage occurs 
parallel to {001} and {010}. The specific weight of the erystals is: 
1,263 at 17° C.; the equivalent-volume is therefore: 167,06, and 
the topical parameters are calculated at: x: y: w = 2,4511 : 10,3770: 
:6,8271. The transition of the yellow into the red crystals occurs 
in such a way, that the two modifications are rigorously orientated 
with respect to each other in two different ways, the faces of {010} 
of the two forms remaining always parallel to each other; — a fact 
clearly demonstrating the intimate relation of their internal structures. 
It is worth remarking here, that the dimensions in the direction 
of the b-axes in both modifications appear to be almost the same 
(namely: 10,3, as topical parameter), while the intergrowth of the 
a- and g-erystals parallel to {010} occurs in such a way that either 
the c-axis of the one modification coincides with the c-axis of the 
other, or the a- and c-axes of the crystals appear to be interchanged, 
although in these directions the topical parameters do not show a 
direct relation to each other. 
§ 3. II. o-Methoxy-m-methyl-benzylidene-aniline. 
This substance, which has the composition : 
CH; 
CH=N—C,H; 
OCH, 
