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A Manual of the Chemistry of the Carbon Compounds

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THE CARBON COMPOUNDS, 339<br />

solutions. It forms large colourless crystals, resembling alum; it<br />

melts at 64°, and boils at 236°,<br />

DibromopJmd C6H4-| Q^ is produced by <strong>the</strong> fur<strong>the</strong>r action <strong>of</strong><br />

bromine, and forms glistening, white crystals, melting at 40°, and subliming<br />

even at <strong>the</strong> common temperature.<br />

Tribromophenol C6Ha -J Q& is obtained as a crystalline precipitate<br />

by adding bromine water to an' aqueous solution <strong>of</strong> phenol. It is<br />

quite insoluble in water, and this reaction may be used for <strong>the</strong> quantitative<br />

determination <strong>of</strong> phenol, as well as for detecting small<br />

quantities <strong>of</strong> it—for example, in urine, or in drinking water from<br />

wells situated near gas-works, &c. Aniline and some o<strong>the</strong>r bodies<br />

give similar precipitates with bromine water; but that produced<br />

by phenol differs from <strong>the</strong>se by beingeaaily reduced to phenol, which<br />

can be recognized by its characteristic smell This reduction is<br />

readily effected by treating tribromophenol with dilute sulphurio acid<br />

and sodium amalgam,<br />

Telm- and Paticibromojihenol are also known; both are crystalline<br />

solids.<br />

Moniodoplwnol CaH4-| «„ exists in three isomeric modifications.<br />

The two <strong>of</strong> <strong>the</strong>se are formed toge<strong>the</strong>r by acting with iodine and iodic<br />

acid on an alkaline solution <strong>of</strong> phenol:—<br />

5CflH6.OH + 2I2 + HIO3 = 5C6H4I.OH + 3H2O<br />

(Ww-wdop/ienoJ is also obtained pure by boiling diazo-iodobenzene<br />

sulphate with water. It forms flat, glistening needles, possessing<br />

a faint but disagreeable smell; nitric acid decomposes it with <strong>the</strong><br />

separation <strong>of</strong> iodine.<br />

Metadodophcnol is an oily liquid, but has not yet been obtained<br />

perfectly pure.<br />

Paraiodophenol has been prepared from <strong>the</strong> dlazo-iodobenzeiw<br />

sulphate obtained from para-iodaniline. It crystallizes in needles,<br />

aud yields, with fuming nitric acid, substitution-products, without<br />

iodiue being liberated. The same compound is also formed, toge<strong>the</strong>r<br />

with a small quantity <strong>of</strong> its isonusrides, by acting with iodine on<br />

phenol in <strong>the</strong> presence <strong>of</strong> mercuric oxide:—<br />

2CaHt.OH + 2I? + HgO - 2C0H4I.OH + HgI2+ H2O<br />

DIOXYBENZEKE8.<br />

The three isomeric dioxybenzenes have been prepared by fusing <strong>the</strong><br />

iodophenols with caustic potash :—<br />

7, 2

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