( 472 ) 



ation etc. which are greater than is allowed in strictly isomorpliOiis 

 substances, so that it is bettor to speak of isoniorphotropism instead 

 of isomorphism. 



Now according to (jtarelli and Calzolari, Dihenzifl and Benzyl 

 aniline form mixed crystals ; also Azobenzene and Benzylaniline ^). 

 This in connection with the resnlts previously oiitained by Muthmann^) 

 according to which the Terepht/talic-wethyl-efher is isomorphotropous 

 with Ai,4 — , and Ai.s — J)iJiy<h'Oterep]ithaUc-flimethyl-ether and the 

 ^, g — and Ai^5 — Dihyclroferephthalic-cUethyl-ethers are isomorpho- 

 tropons with the Aj — Tetrahydroterephthalic-diethyl-ether, whilst, in 

 addition tlie p-Dio.vyterep/ithalir-eihers behave in an analogous manner 

 to the p-Dioxydihydroterephtlialic-etlier.^ and arc capable of forming 

 with these mixed phases in the solid state, the Italian investigators 

 believe they are justified in coming to the conclusion that if two 

 aromatic mhstances can form mixed crystals, their liydro-products 

 can do the same. 



The universal application of this rule is at once upset by Hydrazo- 

 henzene and DihenzyJ, which, cryoscopically, behave quite normally 

 but differ in their crystalline form as shown above. 



It was, therefore, to be expected that Azobenzene and Hydrazo- 

 benzene would form no mixed crystals. Experiments taught me 

 indeed that from tlieir mixed solution in ether Hydra zobenzene is 

 deposited first in colourless, perfectly pure crystals. Afterwards these 

 are accompanied by pure red crystals of Azobenzene; they were 

 Aerified by the melting point. 



I have also determined the melting point line of mixtures of the 

 two substances. This line has two branches and an ordinary eutec- 

 ticum situated at 59°, 25 and corresponding with a concentration in 

 ^rc-eompound of 76.2 mol "/„. 



Here are a few data: 



Azobenzene nielts at 67°.8 C. 



4- 9.6 "/„ Hydrazobenzene „ „ 63°.4 C. 



+ 17.7 7„ „ „ „ 60M C. 



+ 23.8 7, „ „ „ 59^250. 



+ 47.0°,; „ „ „ 84° C. 



+ 70.5 7„ „ „ „ 102°.5 C. 



Hydrazobenzene „ ,, 125°.2 C. 



1) Bruni, Ueber feste Lösimgen. Samml. cbem. techn. Vorlrage. Bd. VI. (1901). 

 p. 48. 



9) MuTHMANN, Z. f. kryst, 15. 60; 17. 460: 19. 357. 



