October 16th, 1906.] PROCEEDINGS. xi 



It is clear that in passing from chondrodite to humite by 

 addition of the increment Mg._,Si0 4 , the latter is introduced into 

 the assemblage as a layer parallel to the axial directions a and b, 

 and perpendicular to the axis c, and that this process is repeated 

 in passing from humite to clinohumite. The dimensions of this 

 increment layer agree closely with those of the mineral forsterite, 

 and a similar close agreement is found between the calculated 

 and observed dimensions of the layer which may be regarded 

 as the foundation of the series and has the composition of 

 prolectite. 



The method of treatment here adopted is applicable to 

 double salts and to substances containing solvent of crystallisa- 

 tion in general, and shows that such molecular complexes are to 

 be regarded as close-packed assemblages of the two or more 

 component molecular complexes. 



Fig. 1. Fig. 2. 



The problem involved in determining the configuration ot 

 the benzene molecule becomes practically determinate when the 

 above methods are applied to the crystalline form and chemical 

 properties of the hydrocarbon. The configuration of benzene 

 which is thus arrived at is depicted in Figs. 1 and 2, which 

 represent the plan and elevation respectively of the molecule. 

 The dimensions of the close-packed homogeneous assemblage 

 built up of units such as these are in harmony with the equiva- 

 lence parameters deduced from the crystalline hydrocarbon and 

 its per-halogen derivatives, namely : — 



CeH'e, x :y : z = i>'ioi : 3*480 12780; /3 = 90°. 



C 6 C1 6 , „ =3-0169 : 3-5894 : 27714; i3 = Sf 50'. 



C 6 Br 6 , ,, =3-0181 : 3-6097 : 2-7587; /3 = 87° 18'. 



