[155] Preferably considerably below. If the distillate be not rich in benzol, a temperature so low as 8 or 10°, or even 4-5°, Fahr. may be necessary or, at all events, advantageous.
[156] Filtration under pressure is thought by some chemists to be preferable. For this purpose a ‘Beart’s Coffee-pot’ (or a similarly constructed apparatus), was often employed by Mansfield, and is recommended by Prof. Muspratt.
2. Commercial:—By submitting light coal-tar naphtha to distillation, either at once, or after it has been agitated with a little oil of vitriol, and decanted, care being taken that the temperature does not exceed 200° Fahr.
A drawing and description of the apparatus invented by Mansfield for the preparation of benzol from coal-tar naphtha is given below.
A is the still placed on a furnace R; C is filled with cold water. As soon as the oil in the still boils, the vapours are condensed in B, and flow back into A; this continues until the water in C has been heated to a certain temperature, when the vapours are condensed in the cooler D, the liquid flowing at n into the carboy S. As soon as the water in C begins to boil, all the substances contained in the coal-tar naphtha and volatile at 212° Fahr. are condensed and collected in S. A very pure benzol is obtained by this apparatus. By opening the tap m, the hydrocarbons which boil over 212° Fahr. can be rectified. The stopcock i is used for opening the still.
In the benzol works the apparatus shown below is employed.
A is the still, B the condenser, C a water-tank. At the commencement of the operation the water in C is heated by means of the steam-pipe D which communicates with the steam boiler. The tube G is attached to the still; i is a contrivance for filling, b for emptying it. The condensed water is carried off by means of H. By freezing benzol and pressing the solid substance obtained, it may be rendered quite pure.
Prop. Pure benzol is a clear, colourless, very mobile liquid, having a strong, characteristic, and rather agreeable ethereal odour. It is neutral to test-paper; exceedingly volatile at all temperatures; insoluble in water; miscible with alcohol and with ether; highly inflammable; burns with a brilliant flame, emitting clouds of smoke, which rapidly condense and fall as a shower of fine sooty, carbonaceous matter; boils at 176° Fahr.;[157] solidifies, at 32°, to