(phenylglycine), C6H5·NH·CH2·COOH, with caustic alkalis. The
yield was at first very unsatisfactory. It was subsequently found,
however, that by starting with phenylglycocoll-ortho-carboxylic
acid, the yield was sufficiently good to render the process a practical
success. The starting-point for the manufacture of synthetic
indigo is naphthalene, C10H8, which is oxidized, by heating with
concentrated sulphuric acid in the presence of a little mercury, to
phthalic anhydride, C6H4(CO)2O, which is then converted into
ortho-aminobenzoic acid, C6H4(NH2)(CO2H), by treatment with an
alkaline hypochlorite. This acid is then condensed with monochloracetic
acid to form phenylglycocoll-ortho-carboxylic acid,
C6H4(NH·CH2·CO2H)(CO2H), which on being melted with caustic
alkali yields indoxylic acid,
C6H4
C(OH)
NH
C·CO2H, and this readily
loses carbon dioxide and passes over into indoxyl,
C6H4C(OH)
NHCH.
By alkaline oxidation indoxyl is converted into indigotine.
The patent literature of processes for bringing about the conversion of the phenylglycine or its carboxylic acid into indoxylic acid, indoxyl and indigotine is enormous; a circumstance due to the fact that the efficiency of this operation controls the price of the synthetic dyestuff. Caustic soda has been practically given up, being replaced partly or wholly by caustic potash; in addition, alkaline earths, sodamide, nitrides, alkali carbides, &c., have been used. In 1906, Meister, Lucius and Brüning patented the addition of lead and sodium to a mixture of caustic potash and soda; the Basler Chemische Fabrik use a mixture of caustic potash and soda at 210°-260°; Léon Lilienfeld added slaked lime or magnesia to the fused alkali, with a subsequent heating in a current of ammonia at 150°-300°, and in 1908 patented a process wherein the melt is heated under greatly reduced pressure; this gave a yield of 80-90%.
Synthetic indigo comes into the market chiefly in the form of a 20% paste but is also sold in the solid state in the form of a powder.
Indigotine, C16H10N2O2, is a derivative of indol and its constitution is
It can be prepared in an almost pure state by extracting good qualities of Bengal or Java indigo or synthetic indigo with boiling nitrobenzene, from which it crystallizes on cooling in dark blue crystals having a metallic sheen. When heated in an open vessel it readily volatilizes, yielding a violet vapour which condenses on cooling in the form of crystals. Indigotine is also soluble in boiling aniline oil, quinoline, glacial acetic acid and chloroform, but is insoluble in water, dilute acids and alkalis and ordinary solvents like alcohol, ether, &c. By nitric acid and many other oxidizing agents it is readily converted into isatin, C8H5NO2. Heated with concentrated sulphuric acid it yields a disulphonic acid, C16H8N2O2(SO3H)2, the sodium salt of which finds application as an acid colour in wool dyeing under the name of Indigo carmine.[1] By the action of reducing agents, indigotine is converted into indigo white, C16H12N2O2, which is readily soluble in alkalis or milk of lime with a yellow colour. On exposing the alkaline solution to the air the indigo white is rapidly oxidized back to indigotine, and on these two reactions the application of indigo in dyeing and printing is based. (See Dyeing and Textile Printing.)
Various halogen (chlorine and bromine) substitutive derivatives of
indigotine have been introduced which, while not differing essentially
from ordinary indigo in their properties, produce for the most part
redder shades in dyeing. They are claimed to be faster and brighter
colours. It has been shown by Friedländer (Ber., 1909, 42, p. 765)
that the reddish violet colouring matter obtained from the colour-yielding
glands of the mollusc Murex brandaris, by means of which
the famous Tyrian purple of the ancients was dyed, is a dibromindigo,
C16H8Br2N2O2. A new departure in the synthetic dyestuffs belonging
to the indigo group was inaugurated by the discovery in 1906
by P. Friedländer of thioindigo red, a derivative of thionaphthen,
which is formed from phenylthioglycol-ortho-carboxylic acid,
C6H4CO2H
S⋅CH2CO2H.
This substance, on boiling with alkali and
then with dilute acid yields thioindoxyl,
C6H4CO
S
CH2, which
is converted by alkaline oxidation into thioindigotin, having the
constitution
C6H4CO
SC:CCO
SC6H4. The new dye-stuff is
therefore analogous to indigotine, from which it differs by having
the imino groups replaced by sulphur atoms. Thioindigo red can
be readily crystallized from boiling benzene, and forms reddish
brown crystals possessing a metallic reflex. Thioindigo scarlet,
C6H4CO
SC=CO
C6H4NH, is also obtained synthetically.
Both products come into the market in the form of pastes and are
used in dyeing like indigo (see Dyeing). (E. K.)
INDIUM (symbol In, atomic weight 114.8), a metallic chemical
element, included in the sub-group of the periodic classification
of the elements containing aluminium, gallium and thallium. It
was first discovered in 1863 by F. Reich and Th. Richter (Journ.
für prak. Chem., 1863, 89, p. 444) by means of its spectrum.
It occurs naturally in very small quantities in zinc blende,
and is best obtained from metallic zinc (which contains a small
quantity of indium) by treating it with such an amount of
hydrochloric acid that a little of the zinc remains undissolved;
when on standing for some time the indium is precipitated on
the undissolved zinc. The crude product is freed from basic
zinc salts, dissolved in nitric acid and the nitric acid removed
by evaporation with sulphuric acid, after which it is precipitated
by addition of ammonia. The precipitated indium hydroxide
is converted into a basic sulphite by boiling with excess of sodium
bisulphite, and then into the normal sulphite by dissolving
in hot sulphurous acid. This salt on strong ignition leaves a
residue of the trioxide, which can be converted into the metal
by heating in a current of hydrogen, or by fusion with sodium
(C. Winkler, Journ. für prak. Chem., 1867, 102, p. 273). Indium
is a soft malleable metal, melting at 155° C. Its specific gravity
is 7.421 and its specific heat 0.05695 (R. Bunsen).
Indium oxide, In2O3, is a yellow powder which is formed on ignition of the hydroxide. It is readily reduced on heating with carbon or hydrogen, and does not pass into an insoluble form when ignited. The hydroxide, In(OH)3, is prepared, as a gelatinous precipitate, by adding ammonia to any soluble indium salt. It is readily soluble in caustic potash, but insoluble in ammonia.
Three chlorides of indium are known: the trichloride, InCl3, a deliquescent salt, formed by heating a mixture of the oxide and carbon in a current of chlorine; the dichloride, InCl2, obtained by heating the metal in hydrochloric acid gas; and the monochloride, InCl, which is prepared by distilling the vapour of the dichloride over metallic indium. The mono- and dichlorides are decomposed by water with the formation of the trichloride, and separation of metallic indium. Indium Sulphate, In2(SO4)3, is obtained as a white powder very soluble in water by evaporating the trioxide with sulphuric acid. Concentration of the aqueous solution in a desiccator gives a deposit of crystals of a very deliquescent salt, H2In2(SO4)4·8H2O. An indium ammonium alum, In2(SO4)3·(NH4)2SO4·24H2O is known.
The atomic weight of indium has been determined by C. Winkler and by R. Bunsen by converting the metal into its oxide. Thiel (Ber., 1904, 37, p. 1135) obtained the values 115.08 and 114.81 from analyses of the chloride and bromide, whilst F. C. Mathers (Abst. J.C.S., 1907, ii. 352) obtained 114.88 and 114.86. Indium salts can be recognized by the dark blue colour they give in the flame of the Bunsen burner; and by the white beads of metal and the yellow incrustation formed when heated on charcoal with sodium carbonate.
INDIVIDUALISM (from Lat. individualis, that which is not
divided, an individual), in political philosophy, the theory of
government according to which the good of the state consists
in the well-being and free initiative of the component members.
From this standpoint, as contrasted with that of the various
forms of socialism (q.v.) which subordinate the individual to
the community, the community as such is an artificial unity.
Individualism is, however, by no means identical with egoism,
though egoism is always individualistic. An individualist
may also be a conscientious altruist: he is by no means hostile
to or aloof from society (any more than the socialist is necessarily
hostile to the individual), but he is opposed to state interference
with individual freedom wherever, in his opinion, it can be
avoided. The practical distinction in modern society is necessarily
one of degree, and both “individualism” and “socialism”
are very vaguely used, and generally as terms of reproach by
opponents. Every practical politician of whatever party must
necessarily combine in his programme individualistic and socialist
principles. Extreme individualism is pure anarchy: on the
other hand Thomas Hobbes, a characteristic individualist,
vigorously supported absolute government as necessary to the
- ↑ Although bright shades of blue are produced with this derivative, they are not fast.
