( 017 ) 



some of tlie cliief data observed in hotli oompounds are placed here 

 in juxtaposition : 



p-Iodobenzoic Ester : p-Bromobenzoic Ester -. 



Rhombo-bipyraniidal Rhombo-bipyramidal 



a:b:c=l ,4144 : 1 : 0,8187 a:b:C = 1,3967 : 1 : 0,8402 



Forms : Forms : 



jlOOj, jOlOj, |011!, J2J0J, 1112}, il22i. llOOj, {OlOj, i011|,{210j, !112|, {122! 

 On {100| delicate stripes On jlOOj delicate stripes 



parallel c-axis. parallel c-axis. 



Cleavable along b. Imperfectly cleavable along b. 



Axial plane is jOOlj ; 1^' Diag. is b. Axial plane is |010| ; l^t Diag. is b. 

 Angles: Angles: 



a:p = d5°16' a : 2) = U°5G' 



b:v = 51°49' b:v = 51°10' 



0:0 = 42°55 etc. o -. o = 43°50' etc. 



The dispersion in the /-derivative is of an opposite character to 

 that in the i??'-compound ; the apparent axial angles are almost e(pial 

 if that of the /-derivative is measured in «-Broraonaplithalene and 

 that of the /^/--derivative in oil of Cassia. 



It seems remarkable, that in our case the Bromo- and lodo-com- 

 pounds behave in an analogous manner and that it is the Chloro- 

 compound which exhibits here a deviating character. 



In order to show the further relation of the three compounds the 

 binary melting point lines were determined and represented in fig. 9. 



Tiie melting point line 7i/'-/-compound does not deviate markedly 

 from the straight line, the ditference is really negligeable. The lowering 

 of the melting point of the /-derivate is, therefore, practically directly 

 proportional to the number of added molecules of the 5r-compound. 



The melting point lines Cl-I- and C/-5r-compound take an analogous 

 course, that is to say, all the melting points lie between the lowest 

 and the highest melting point. Both melting point lines belong to 

 the rising type of Roozeboom, which may occur in isodimorphous 

 substances. The lower branch and the mixing limits could not be 

 found by thermometrical methods. The existence of these two branches 

 may indeed be proved, and they are even situated at some considerable 

 distance from the top branches — at least at the side of the com- 

 pounds having the highest melting points — as was found by Dr. 

 B. R. DE Bruyn. It is, however, not possible to determine this line 

 witli suflicient accuracy. The progressive change of the cooling-curve 

 is of such a nature that a discontinuity is observed from which we 



