ON ISOMORPHOUS DERIVATIVES OF BENZENE. 



169 



an inspection of series 2 ; in this case tlie ratio cjb is more nearly constant 

 throughout the series than in the case in series 1. In series 3, obtained by 

 displacing the acidic hydrogen atom in parabromoformanilide by either 

 Me or Et, the ratio a 'h again shows approximate constancy. No simple 

 relationship is observable between parabromacetanilide and its methyl or 

 ethyl derivative. Parabrom- and paraiod-acetanilide are isomorphous ; 

 the corresponding chloro-derivative is not isomorphous with them, although 

 it bears a marked morphotropic relationship to them.^ Group 6 forms a 

 well-marked isomorphous series. 



Otten - has observed that butyranilide is dimorphous, but has not 

 examined the substance in great detail ; a study of this compound has 

 shown that the dimorphism is of a very remarkable character. At 

 ordinary temperatures the anilide sepai-ates from alcoholic solutions in 

 large transpai-ent crystals of pyramidal habit, which are distinctly 

 orthorhombic, showing a characteristically orthorhombic interference 

 figure of small optic axial angle. The axial ratios of such crystals are 

 a : b : c=0-6920 : 1 : 0-6792. On preserving crystals which had been 

 measured at a constant temperature of 8° to 11° they have been found to 

 change gradually, and in the course of three months completely, into 

 tetragonal crystals, without at the .same time losing their brilliancy and 

 transparency. The axial ratio a ; c=0-6652 : 1 in these crystals ; they 

 exhibit the characteristic uniaxial interference figure. On preserving the 

 definitely tetragonal material at OO" for eighty days the reverse change 

 occurs, the crystals becoming orthorhombic and biaxial, although the 

 axial ratios never revert to quite their original values. The density of 

 the orthorhombic form is 1-130, whilst that of the tetragonal form is 1-139. 



The molecular volumes of several of the anilides have been determined, 

 ■with the object of examining the relations between the topic axial ratios 

 of Muthmann ; ^ the ordinary axial ratios seem, however, in most cases to 

 express the morphotropic relationships just as clearly as the topic ratios. 



Iso- and Poly-vior^yhous substituted Benzene-sulphonic Chlorides and Bromides. 



It has already been stated •* that the sulphonic chlorides and bromides 

 derived fi-om the 1:3:4 dihalogen-benzene-sulphonic acids together 

 form an isotrimorphous series. Dr. Jee's further study of this group has 

 led to important results. The series includes anorthic, orthorhombic, and 

 monosymmetric terms, in the manner shown in the following table :— 



Compare Fels, Dissert., Leipzig, liiOO. 

 Zcits.f. Kryd.. 1894, xxii 407. 



/eits. f. Kryxt. xvii. :!'.)!. 

 JJ A.'lhjixu-t, lyltii, p. 6Si<. 



