Benzene was discovered by Faraday in 1825, and detected in coal-tar by
Hofmann in 1845. It can be obtained from that portion of coal-tar which
boils at 80° to 85° by fractionating or freezing.[A] The ordinary benzene
of commerce contains thiophene (C_{4}H_{4}S), from which it may be freed
by shaking with sulphuric acid. Its boiling point is 79° C.; specific
gravity at 0° equals 0.9. It burns with a luminous smoky flame, and is a
good solvent for fats, resins, sulphur, phosphorus, &c. Toluene was
discovered in 1837, and is prepared from coal-tar. It boils at 110° C.,
and is still liquid at 28° C.

[Footnote A: It may be prepared chemically pure by distilling a mixture of
benzoic acid and lime.]

The mono-, chloro-, bromo-, and iodo-benzenes are colourless liquids of
peculiar odour. Di-chloro-, di-bromo-benzenes, tri- and hexa-chloro- and
bromo-benzenes, are also known; and mono-chloro-, C_{6}H_{4}Cl(CH_{3}),
and bromo-toluenes, together with di derivatives in the ortho, meta, and
para modifications. The nitro-benzenes and toluenes are used as
explosives. The following summary is taken from Dr A. Bernthsen's "Organic
Chemistry":--

SUMMARY.
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| C_{6}H_{5}(N0_{2}) Nitro-benzene. Liq. B.Pt. 206° C. |
| |
| C_{6}H_{4}(NO_{2})_{2} Ortho-, meta-, and para- di-nitro-benzenes. |
| Solid. M.P. 118°, 90°, and 172° C. |
| |