BENZOLE. 125 



of collodion remains unbroken, and by thus protecting the 

 sore obviates the necessity of dressing it with ointment. It is 

 a much more active, cleanly, and convenient vesicant than 

 the unguent, cantharid. (Lond. Pharm. Journ. 1850.) 



Benzole. — This liquid carbohydrogen, so valuable as an 

 economical solvent of caoutchouc, gutta-percha, resins, and 

 other difficultly soluble substances, is readily prepared by 

 Mansfield's process (Journ. of Chem. Soc. i., and Chem. Gaz. 

 vii.) from coal-tar. 



The light coal-naphtha, obtained in the early stage of the 

 distillation of coal-tar, is distilled in a metal retort having its 

 head surmounted with a chamber containing cold water, so 

 that the liquids less volatile than water may be condensed and 

 fall back into the retort or into a separate receiver, while those 

 more ethereal pass on in vapor to a condensing vessel kept 

 cool with water or ice. The liquid ceases to pass as soon as 

 the water in the chamber commences to boil, because all vapor 

 volatile below 212° has then been driven over into the con- 

 denser. The distillate is rectified by a second distillation as 

 above, taking care, this time, that the temperature of the 

 water surrounding the head of the still shall not quite reach 

 176° F., that being the boiling point of Benzole. The dis- 

 tillate obtained before the temperature within the retort has 

 risen to 194° F., is a yellowish volatile oil, which at 4° F. 

 drops one-half of its bulk in crystals. 



This liquor, by agitation with one-tenth its volume of strong 

 nitric acid for the removal of the oxidable substances, and, 

 subsequently, after separation from the acid, with one-fourth 

 its volume of oil of vitriol, to separate neutral oils, basic, and 

 coloring matters, is prepared for the last distillation. All the 

 distillate obtained below 194° is to be reserved and washed 

 with water, and finally with an alkaline solution. The purifi- 

 cation is completed by congealing it at 4° F. and pressing out 

 the solid portion, filtering, and drying by means of chloride 

 of calcium. 



The volatility of benzole imparts great value to it as the 

 solvent of resins for forming varnishes, or artificial cuticles in 

 l2 



