~The Explosives derived from Benzene.~--There is a large class of explosives made from the nitrated hydro-carbons--benzene, C_{6}H_{6}; toluene, C_{7}H_{8}; naphthalene, C_{10}H_{8}; and also from phenol (or carbolic acid), C_{6}H_{5}OH. The benzene hydro-carbons are generally colourless liquids, insoluble in water, but soluble in alcohol and ether. They generally distil without decomposition. They burn with a smoky flame, and have an ethereal odour. They are easily nitrated and sulphurated; mono, di, and tri derivatives are readily prepared, according to the strength of the acids used. It is only the H-atoms of the benzene nucleus which enter into reaction. 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 deg. to 85 deg. 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 deg. C.; specific gravity at 0 deg. 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 deg. C., and is still liquid at 28 deg. 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":--