83 
Angular values : Observed: Calculated : 
650, = (O01) (TOO i="). Go oe — 
Gd Oil). (sb. LE a 
n:m = (110): (110) =* 110 64 — 
1 
c:r =(001):(201)= 58 304 58° 234 
o:r —=(211):(201) = 33 574 33 51 
m:q = (110):(011) = 47 18 ATi 221 
o:m=(211):(110) = 44 7 43 54 
ee nt == (OOle: (11 Oy 76 4 76 104 
m:q = (110):(011)=: 73 3 Tay 2k 
& 
Perfect cleavable parallel to {001}. . 
An apparently second modification was, on more detailed inves- 
tigation, really identical with the one described. However, yet 
another, truly polymorphic modification was observed *), crystallizing 
in extremely thin, unmeasurable, small plates with normal extinc- 
tion; they are first deposited from solutions, but are rapidly changed 
into the crystals described in the above. 
The needles here investigated, have oblique extinction: on m 
at an angle of 224° with the direction of the c-axis. 
The specific weight of the crystals at 17° C. was: 1,165; the 
equivalent-volume is thus: 181,11. 
Topical parameters: 7%: wy: w = 8,4931 : 5.3942 : 4.3494. 
We are occupied with tentatives to obtain condensation -products 
of other aldehydes and amines of the aromatic series, with the 
purpose to find other cases of polymorphism or isomerism with 
bases of this kind. Perhaps we shall be able to return to this 
question within a not too remote future. 
Laboratory for Inorganic and Physical 
Groningen, May 1920. Chemistry of the University. — 
') H. Orr, Monatshefte f. Chemie, 26, 340 (1905). 
