430 



So (i i^ appreciably greater for u-nltroanisoJ, than for anisol \ for 

 o-nitrotoluene iniicli greater than for tolaene; for nitrobenzene much 

 greater than for benzene; for aniline and o-toluidine, much greater 

 than for benzene or toluene. Just so for pyridine appreciably greater 

 than for l^enzene; etc. 



3. The .siib.stitation of aromatic liydrocarbon-radicals instead of 

 H-atonis makes the values of the molecular surface-energy also con- 

 siderably firenter. 



So tlie values for salol are much greater than for the other 

 salicylates; of benzylbenzoate it is nuich greater than of hoth the 

 other benzoates; oi' acetophenone much greater than oï diinctJiylcetone 

 or methylpropy ketone; of (liethyl-benzyethylinalonate much greater than 

 of diethylmalonate itself; etc. 



Only continued investigations in this direction «.an however, as 

 has already been said, prove with more certainty, if these rules may 

 be considered as general ones. Researches of this kind will be 

 started in this laboratory within a short time. 



Laboratory for Inorganic Chemistry 

 of the University. 

 Groningen, June 1914. 



Minaralogy. — " On the real Symmetry of Cordierile and Apophyllite" . 

 By Prof. H. Haga and Prof. F. M. Jaeg^:r. 



§ 1. In continuation of our investigations^) on the symmetry of 

 crystals, which can be discerned as mimetic or pseudosymmetrical, 

 we will give in the following a review of the results obtained in 

 our experiments relating to the cordieritè {iolite; dichroite) and to the 

 apophyllite {albine; ichtJtyophtalm). Of both kinds of silicates specimens 

 of diferent localities were at our disposal, — a fact, which hardly 

 can be over-estimated in the study of RöiNTGEN-patterns, as will be 

 proved below. We will describe in the following pages successively 

 our observations with: a) Cordierite; b) Apophyllite. 



§ 2. a. Investigations on the true symmetry of Cordierite. 



Cordierite, asilicate of the chemical composition: H^{Mg,Fe)^Al^Si^fi^.., 

 belongs to those minerals, which like the arragonite, imitate the 

 habitus of hexagonal crystals by means of particular polysynthetical 

 twinformations. In literature it is only mentioned, that it is "rhombic" 



b H. Haga and F. M. Jaeger, these Proceedings, XVI. p. 792. (1914). 



