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tlie isomorphous substitution of the halogens Cl, Br and ƒ in organic 

 molecules. The author first gives a short resume of the chief series 

 of inorganic compounds where CI-, Br- and /-compounds have been 

 compared in regard to their crystal-form. Even in c^ses where a 

 direct analogy in form does not occur an isof/«morphism may be 

 always proved to exist. 



The /-compounds differ in most cases from the others as regards 

 their behaviour. 



Only a few complete series of analogous halogen derivatives of 

 organic compounds have been investigated and in no case as to 

 their mutual behaviour in the liquid state. 



A complete crystallographical investigation was made of : pC/Joro-, 

 ji-Bromo- and p-fodoacetnnilide '), the melting points of which are 

 respectively, 179°, 1674° and 181°. The Bromo- and the /of/o-com- 

 pounds are both monoclinic, the C/t/oro-com pound differs and is 

 rhombic. The Br- and the /-compound present in symmetry and 

 parameters a distinct analogy with the rhombic 6V-compound ; the 

 plane of cleavage is, however, a totally different one ^). 



(7/-compound : Rhombo-pyramidal. 

 a:b:c = 1,3347 : 1 : 0,6857 ; ^ = 90°0'. Cleavable towards {100|. 



^/'-compound : monoclino-prismatic. ') 



a :i:c=:l, 3895:1:0,7221; i?=:90°19'. Cleavable towards {301). 



/-compound : monoclino-prismatic. ") 



a:b:c = 1,4185 : 1 : 0,7415 ; /J = 90°29'. Cleavable towards (301}. 



GossNER ') proved that the C7-compound is c/i'morphous and also 

 that it possesses a more labile monoclinic form. On the other hand, 

 the Br- and /-compounds are certainly also f/«morphous but here 

 the rhombic modification is the more labile. The more labile and 

 the more stable modifications possess very analogous parameters, 

 although their molecular structures are different. He thinks however 

 that the irregular 'positions of the melting points may be satisfac- 

 torily explained from all this. 



On the other hand, in the series Chlorobromo-, Dibromo- and 

 lodobromonitrophenol, all three derivatives are directly-isomorphous 

 with each other. (Structure : {OH) : (iVO,) : 5r = 1 : 2 : 4; CI, Br 

 and /on 6). 



1) B. GossNER, Z. f. Kryst. 38. 156—158. (1904). 

 3) Fels, Z. f. Kryst. 32. 386 (1900); Idem 32. 406. 



s) MüGGE, Z. f. Kryst. 4. 335; Fels, Z. f. Kryst. 37. (1903). 469; Wilson, Z. f. 

 Kryst. 36. 86. Abstract; Panebianco, Z. f. Kryst. 4. 393. 

 *) Sansoni, Z. f. Kryst. 18. 102. 

 6) GossNER, Z. f. Kryst. 38. 156-158. 



