( 17^' ) 



Departm. of Agriculture, Farmers' Bulletin N". 17, Washington 1894) 

 are, according to the description, undoubtedly caused by a conta- 

 gium fluid um, but it is still dubious whether the infection is only 

 transferred by grafting and budding, or, — ■ which is more pro- 

 bable, — also by a virus existing outside of the plant. 



Chemistry. — „0« congealing- and jneUing-pJienomcna in substances 

 sJioiring tautomerism". By Prof. H. W. Bakhuis Roozeboom. 



The latest discoveries on tautomerism, which have shown, that 

 tautomeric substances in the liquid state must be considered as 

 mixtures of two kinds of molecules of different structure, have raised 

 the problem how to explain the complicate congealing- and melting- 

 phenomena of such substances, in case both forms or one of them 

 can appear in the solid state. 



Some remarkable investigations on this subject have of late been 

 made by Bancroft and his disciples, wdiich were a continuation 

 of a theory of Duhkm. 



At an attempt to unravel the investigations of Claisen on this 

 subject, the reader had come to the same conclusions, which may 

 be united to a perfectly clear graphic sketch. 



Bancroft having already published this, there would be no reason 

 to revert to the subject, if not all examples chosen by him, referred 

 to cases in which all the melting- and congealing-points were found 

 in the region of temperatures in which equilibrium is still obtained 

 between the two forms in the liquid state. 



In such a case we generally have the disadvantage of there being 

 no certainty about the mixing-proportion of the two substances at 

 the moment of melting or congealing. Consequently it is impossible 

 to give quantitative representations. 



To arrive at a good understanding of the phenomena, it is there- 

 fore desirable to begin with a deduction of the conduct of tautomeric 

 substances, the congealing temperatures of which are below the 

 temperature-limit where in the liquid state transformation between 

 two forms is still possible. 



If we call the two forms « and /?, we may build up a sketch 

 in which the mixing-proportion of « and /:? is measured on the 

 horizontal axis of — 100 and the temperature on the vertical axis. 



According to the supposition made above, the congealing appears 

 in the ordinary and simplest form of the congealing of mixtures 

 of two sub&tances i. e. starting from the melting points A and B 

 of the two modifications, we have two melting-lines AC' and BC 



