Young — Vapour- Pressu7-es, Sfc, of TJdrty Pure Siibstances. 385 



devised ; and after a series of systematic reorystallizatious had beeu carried 

 out, a product melting almost constantly at 4*7° was obtained. There was 

 still, however, a slight fall of temperature before solidification was complete ; 

 but the quantity of material was too small to allow of further purification, 

 and it was thought that the amount of impurity must be very small indeed. 

 I have been recently informed by Dr. Timmermans that a specimen of 

 hexamethylene has been prepared by direct combination of benzene witli 

 hydrogen in presence of heated nickel, obtained by reduction of nickel oxide 

 (method of Sabatier and Sanderan), and that the melting-point of this 

 specimen is 6-5°. If this higher melting-point is correct, it is evident 

 that the hexamethylene separated from Galician petroleum was not quite so 

 pure as was hoped; but since the boiling-point of the admixed iieptane is 

 so close to that of hexamethylene, it is probable that the errors in the observed 

 physical constants are only slight. 



Specific gravity at 074°, .... 079675 

 Boiling-point under normal pressure, . 80'85° 



9. Benzene} — A large quantity of commercial benzene was distilled, and 

 was then twice frozen. It was repeatedly shaken with strong sulpliuric acid 

 to remove thiophene, and was finally purified by fractional distillation. The 

 melting-point was 5*58°. 



Specific gravity at 074°, .... 0-90006 

 Boiling-point under normal pressure, . 80'2° 



10. Fluorobenzene} — This compound was prepared as described by 

 Wallach^ and Wallach and Heusler'* by the action of concentrated hydro- 

 fluoric acid on benzene diazopiperidide, CsHs • N : N • NO5H10. By 

 fractional distillation a product of perfectly constant boiling-point was 

 obtained. 



Specific gravity at 0°/4°, .... 1-04653 

 Boiling-point under normal pressure, . 85-2° 



11-13. Chlorobenzene, Bromobenzene. loclobenzene.^ — These substances were 

 obtained from Kahlbaum, and were purified by fractional distillation. 



Specific gravity Boiling-point under 



at 0°/4°. normal pressure. 



Chlorobenzene, . . . 1-12786 132-0° 



New specimen and new tube, . 1-12805 



Bromobenzene, . . . 1-52182 156-0° 



New specimen and new tube, . 1-52178 



lodobenzeue, .... 1-86059 188'45° 



'Trans. Chem. Soc, Iv., p. 486, 1S89. » Anualen, ccxliii., p. 219, 18 



2 Annalen, ccxxxv., p. 255, 1886. ''Trans. Chem. Soc, loc. cit. 



