( 151 ) 



easily be made in sulfates of univalent and bivalent metals, without 

 altering their crystallization. In double arseniate of ammonium and 

 calcium phosphoric and vanadic acid cannot fill the place of arse- 

 nicic acid, while in lead-apatite the thi'ce acids can be exchanged 

 Avithout any visible change in the form and structure of the crystals. 

 Here isomorphism is restricted to small groups of compounds, whose 

 limits are narrow and sharply defined ; in other cases the limits of 

 isomorphous groups are very wide, wider than generally admitted. 

 Take for example the double arsenate of ummonium and calcium, 

 (NH4,)3 Ca As O4 + 6 H3 0. In this compound Ca can be exchanged 

 for Ba, Sr, Pb, Mg, Mn, Fe, Co, Ni, Zn, Cd and Cu. Nearly 'the 

 same extension of change is found in triple acetates of the type: 

 Na Mg (U03)3 (C2 H3 02)9 + 9 II2 0. They form rhombohedral 

 crystals, imitating the regular (tetrahcdric) crystals of the compound 

 Na (UO2) (C2 H3 02)3. Speculation on a possible connexion between 

 the wide range of isomorphism in complicated double and triple 

 compounds with their constitution leaves the impression, that their 

 form is ruled and fixed by constantly recurring nuclei of great 

 volume, or, with other words: that isomorphism and morphotropisra 

 have a cause in common. The nucleus of the triple acetates is the 

 compound Na (UO2) (C2 H3 02)3. Morphotropism plays here a pro- 

 minent part, accompanying isomorphism and producing a striking 

 imitation of regular forms in rhombohedral crystals. Obviously a 

 connexion exists between these phenomena and tl)e combination of 

 isomorphism and morphotropism, found in some families of minerals, 

 e. g. the pyroxenes, where exchange of Mg for Ca, of Ca for Zn 

 or Mn does change the system of crystallization, while the general 

 shape or habitus of the crystals remains unchanged. 



Chemistry. — „On the action of mdhjlk alcohol on the unides 

 of hibitsic ackls'\ By Prof. S. Hoogewerff also in the name 

 of Dr. W. A. VAN Dorp. 



In April of this year we have placed in the Recueil des Tiavaux 

 ('himiques des Pays-Bas et de la Belgique a short account, which 

 shows that, by heating the imides of bibasic acids with methylic 

 alcohol containing muriatic acid, the methylic ethers of the amido- 

 acids, corresponding to the imides, are formed in some cases. 



At least this was observed with the phenylimides of succinic acid 

 and maleic acid, also with those, substituted in the radical of the 

 acid. For example the pheuylimide of maleic acid with methylic alco- 



11* 



