( 665 ) 
There is not the least doubt that the two substances possess a 
quite analogous structure ; cleavability, optical orientation whilst the 
nature of the surface of the crystalplanes is quite in agreement. 
From mixed solutions of the two components are formed small 
ereenish-black mixed crystals with a vivid steel-blue reflexion. 
As generally happens in the case of most isomorphous mixtures, the 
crystallisation power is considerably smaller than with each of the 
components separately. Under the microscope such mixed crystals 
consist of thin olive-green little plates, which on their predominating 
plane show little or no pleochroism. In convergent light a splendid 
interfering image may be observed: slight inclination to the normal 
on the horizontal plane, elliptical rings, and small axial angle, larger 
however than in the two components. The double refraction is 
positive: the dispersion has a rhombic character and shows: Ome 
From the last motherliquors are deposited mixed crystals of a 
lighter shade representing silky needles as those above with less 
surface reflexion. Otherwise they are optical continuations of the 
above described mixed crystals. From mixtures of the two components 
in a melted condition these mixed crystals depose on the sides of 
the testtube in a fine steel-blue lustrous condition. 
The behaviour of the two isomorphous substances in the liquid 
condition is elucidated by ihe investigation of the melting curve of 
binary mixtures. On account of the dark colour of the fusion, the 
course of the solidification curve was traced by the graphical method; 
the determinations were made as usual in the van Eyk apparatus. 
It should be noticed that all these fusions solidify to solid phases, 
which also exhibit a splendid violet or blue reflexion. 
The nitroderivative has a greater latent heat of fusion than the 
nitrosoderivative ; in both cases the calorie effect was, however, very 
readily observable in the solidification. The lower solidifying line 
can by no means be determined so sharply as the upper one. 
It was found that: 
A mixture of 100"/, of p-Nitro and 0°/, p-Nitroso-derivative 
melted at 73°,6. 
A mixture of 85,14°/, p-Nitro- and 14,86 °/, p-Nitroso-derivative 
commences to solidify at 75°,2 and completely solidifies at 74°,9. 
A mixture of 72,5°/, of p-Nitro- and 27,5 °/, p-Nitroso-derivative 
commences to solidify at 76°,2 and completely solidifies at 75°,9. 
A mixture of 54,4 °/, of p-Nitro- and 45,6 °/, of p-Nitroso-derivative 
commences to solidify at 77°,6 and completely solidifies at 77°,3. 
A mixture of 38,64 "/, of p-Nitro- and 61,36 "/, p-Nitroso-derivative 
750% 
9. 
commences to solidify at 78°,2 and completely solidifies at 77 
