( 81 ) 



at ürst sight, the use of c = |001|, r = \201\ and </ = |211|, in man,y 

 respects more obvious. 



Measured: 

 m = (100) : (110) = 49° 2673' 

 m = (201) : (110) = 68 257, 

 q =(011) -.(Oil) = 58 477., 

 r = (201) : (001) = 52 32V, 

 a =(201): (100) = 55 427, 

 a = (001) : (100) = 71 44 

 q =(201): (Oil) = 58 97, 

 r = (Oil) : (001) = 29 24 

 b = (110) : (010) = 40 49 

 ??i=(110):(ïl0) = 81 7 

 m=(011):(IlO) = 53 34 



Calculated. 



-q 

 c 

 c : a ^= 



9. 



1)1 



111 



A distinct cleavabilitj was not found; perhaps 5^ is a plane of 

 cleavage. The symmetrical extinction on the planes of |110| amounts 

 to about 3"^ with regard to the vertical axis ; a further optical 

 investigation was excluded. 



The density of the crystals is apiwoximately^) 1,145; by putting 

 in the above formula 7 and A =: 90^ we obtain for the proportion 

 of the topical axes: 



X : if^ : to = 8.2234 : 6.6840 : 3.9650. 



If we compare the crystal parameters of the two heteromorphous 

 modifications of benzylphthalimide with the parameters of henzylpJttal- 

 iso-iniide we at once notice an interesting relation between the 

 crystalline forms of these substances. 



Compound : 

 u-Benzylphtalimide. 

 ^•Benzylphtalimide. 

 Benzylphtal-iso-imide. 



Symmetry : 

 Tiiclino-pinacoidal. 

 Monoclino-prismatic. 

 Monoclino-prismatic. 



Crystal-parameters : 

 a : b : c=0,8443 : 1 : l,3600.(a,(3,y; s.a.) 

 a : b : c=0,8476 : 1 : 0,5092. ^=70°42' 

 a:b:c=l,23032):l:0,5932. (3=71°46' 



1) Approximately, because the opaque crystals did not give a sufficient guarantee 

 of homogeneity and because the substance is attacked on the surface by contact 

 with Thoulet's solution. 



-) It may be observed that the proportion a : b would become for m } 230 

 0,8202: 1. 



6 

 Proceedings Royal Acad. Amsterdam. Vol. VII. 



