86 



REPORT — 1903. 



being strictly isomorphous,' in the case of the meta- derivatives, the 1:3:4 

 series formed an isotrimorphous group, the 1:3:5 series an isotetra- 

 morphous group. 



During the past year Mr. Harding has determined the constants of five 

 of the eight members of the 1:2:4 ortho-series, viz., the chlorides derived 

 from the acids Nos. 1, II, and IV and the bromide of acid No. II : — 



Br 



II 



III 



IV 



Of the chlorides, I and II are practically identical crystallographically ; 

 the chloride of IV was obtained in quite a distinct form, belonging, how- 

 ever, to the same crystallographic system. The bromide of II was obtained 

 in both these forms, so that it establishes a connecting link between the 

 two isomorphous series which evidently exist. 



Great diificulty was experienced in making the measurements owing 

 to the low melting-points of the sulphon-halides and the extraordinary 

 way in which they crystallise (from a mixture of benzene and petroleum) 

 in very thin micaceous plates ; it was discovered, however, that by using 

 petroleum of higher boiling-point more massive crystals could be obtained ; 

 forms fit for measurement were eventually secured by this artifice. 



It would seem that the character of the solvent has a definite influence 

 on crystalline form, especially in the case of substances which manifest 

 polymorphism. When opportunity ofTers it will undoubtedly be desirable 

 to study this question experimentally. 



The anilides, which have higher melting-points than the halides. 

 crystallise with much greater facility ; the opportunity has been taken to 

 study several of these. Mr. Harding finds that the orthodichloranilide 

 exists in two forms, one orthorhombic the other monosymmetric ; and 

 that whilst the dibromo- and bromochloranilides crystallise in a form 

 isomorphous with the monosymmetric form of the dichloranilide, the 

 fourth anilide crystallises in a second monosymmetric form. 



Mr. Harding has also measured the 1 : 3 dibromo- 2 sulphochloride 

 and has thus made a beginning with the 1:2:3 metaseries. 



Although the material is available, it has been impossible hitherto to 

 obtain two of the para-compounds and three 1:2:4 derivatives in. 

 forms suitable for measurement ; it is hoped that the difficulty will be 

 overcome and that the experience which has been gained will make it 

 possible to extend the investigation to the remaining terms of the meta- 

 and ortho-series at no distant date. It is very desirable, for this purpose, 

 to have large quantities of material at disposal and that special apparatus 

 should be devised which will make it possible to effect the crystallisation 

 under constant conditions. 



' Mr. Harding has recently been able to obtain a sixth member of this series — 

 the 1 01 : 4 Br : >3 sulpbobromide — in measurable form, and finds that it is isomorphous 

 with five which Mr. Gidden measured. Mr. Gidden did not succeed in preparing this 

 compound. 



