the Physical Properties of Compounds. 125 



NH 



XXV. 



DiamidostiTbene. 



-CH=CH- 



m.p. = 170*. 



NH, 



* This, though nearly, is not quite so symmetrical as (1.4 ; 1.4) azotoluene. 

 Azotoluene (1.4; 1.4). 



CH, 



-N=N- 



CH, 



m.p. 



144. 



Azotoluene (1.2; 1.2). 

 OH3 CH 3 



-TS=TS- 



m.p. = 137. 



Ethenyldiphenylamidine. 

 C 6 H 6 — NH— CH 2 — CH=N.C 6 H 5 



m.p. = 132. 

 Ethenylisodiphenylamidine 



Phenylac etoph eny 1 

 amidine. 



CH 3 . C. 



X *(C 6 H 5 ) 3 



m.p. = 63. 



C 6 H 6 .CH 2 .C, 



CH, 



Benzenyltolylaniimide. 



.C 6 H 5 ^N.C 6 H 4 .CH, 



C 6 H 5 .C 

 \NH 2 \nh 2 



m.p. = 128. m.p. =99. 



Azotoluene (1.3; 1.3). 



CH, 



-TS=TS- 



m.p. = 54. 



The influence of symmetry on the melting-point is still 

 further shown by the following table, which contains the 

 melting-points of the most symmetrical modification of a few 

 of the mono-, di-, tri-, tetra-, penta-, and hexa-derivatives of 

 benzene; from which it will be seen that the melting-points 

 of the mono- aDd penta-derivatives are comparatively always 

 very low, whilst those of the other derivatives are high ; the 

 reason being that benzene cannot form symmetrical mono- 

 and penta-derivatives, whereas a symmetrical form of a di-, 

 tri-, tetra-, and hexa-derivative is always possible. 



Phil. Mag. S. 5. Vol. 13. No. 79. Feb. 1882. L 



