457 



as the transition point lies too far cabove the boiling point, so that 

 th'e i?-crystals cannot be obtained inetastable fiom these solutions 

 eitiier. I have, therefore, tried to make the transition suitable 

 foi- demonstration by crystallisation from another solvent. The ex- 

 periments of § 6 led me to surmise that glycerine would be suitable 

 for this. If on an object glass we evaporise a solution saturated at 

 the ordiiiar} tempei'ature to initial crystallisation, and if then we 

 place the oltject glass under the microscope, we can clearly observe 

 the cubi deposited in the heat. After some lime a transformation 

 then takes place, which propagates through the solid mass, and at 

 the same time we see crystal siveletons of the known shape appear 

 from the cubi. 1 have been able to demonstrate this transition by 

 means of microscopic projection at the latest Physical and Medical 

 Congress. The demonstralioii is stdl easier to cany out with ammonium 

 bromide, as the point of ti'ansition lies at still lower temperature 

 here, which I shall show in a following paper. The phenomena 

 are entirely the same for animoniuni chloride and bromide. 



9. Alloii'opii or isoinei-y. The phenomena which are explained by 

 the assumption of more kinds of molecules, are expresseil b}- a great 

 number of names in the literature. Among these phenomena the 

 occurrence of a substance in several solid phases will also oflen, if 

 nol always, have to be reckoned. In organic chemistry we have, 

 namely, many examples of substances which can occur in two or 

 more solid states, to which different molecular structure is assigned 

 (tautomery, desmotropy). In § 1 I discussed an indication for the 

 occurrence of two kinds of molecules also for ammonium chloride. 



A rational collective name for the occurrence of more than one 

 kind of molecules and more than one solid phase has however not 

 yet been adopted, and yet this seems very desirable. The advantage 

 lies in this that general tliermodynamical relations (for homogeneous 

 and heterogeneous equilibria) hold for both phenomena, which equations 

 are therefore independent of the more subtle differences in structure 

 of the molecules. Thermodynamically desmotropy, tautomery, isomery, 

 raetaniery, allelotropy, pseudomery etc. etc. are namely perfectly equi- 

 valent, at least for so far as they refer resp. to homogeneous or 

 heterogeneous states. If we consider which of the available denomi- 

 nations is suitable as a collective name, oidy allotropy and isomery 

 present themselves for consideration in my opinion. The word isomery, 

 however, is pretty generally current for the occurrence of molecules 

 of equal molecular, weight, which differ only in way of binding. 

 There is no objection in my opinion to the use of allotropy as a 



