eight hours, in closed cylinders, with caustic soda and potassium chlorate, at a temperature of 180° C, the sodium salts of alizarin and sim- ilar compounds, called purpurins, are obtained; (4) the sodium salts of alizarin and purpurin are then dissolved in water, and. by addition of liydrochloric acid, alizarin itself and the pur- piirins are set free and precipitated in crystal- line form. The precipitate is collected in filter- ])resses, thoroughly washed with water, and brought into the market in the form of a rather thin paste usually containing either 10 or 20 per cent, of alizarin. Pure alizarin can be read- ily obtained from this paste by sublimation. Alizarin was first made on an industrial scale by Perkin in 1809.
Alizarin is to some extent soluble in hot water. In the dyeing processes, fabrics are first soaked in a solution of the retjuired mordant, and after the latter has been decomposed by steam or with alkali, leaving an insoluble metallic hj-droxide in the fibre, alizarin solution is applied to produce the desired "lake." Chemically, alizarin is a dioxy-anthraqui- none, having the structural formula Kitro-alizarin (commercial alizarin orange), which is itself a coloring matter, yields, when heated with glycerin and sulphuric acid, an- other color, alizarin blue, usea in calico printing. Alizarin, carmine is another important alizarin color: it is much used as a substitute for cochineal.
The artificial production of alizarin on a large industrial scale has naturally brought about im- portant changes in the agriculture of the coun- tries where madder used to be extensively cul- tivated. Consult Gnehm, Die Anthracen- farhsloffe (Brunswick, 1897).
AL'KAHEST, or ALCAHEST (a word arbitrarily formed by Paracelsus after Arabic fashion). The universal solvent of the alchemists. See Alchemy.
AL'KALIES. See Antidotes.
ALKALIES (Fr. alkali, ultimately from Ar.
al. the H- kcily, ashes of saltwort). A term ap-
plied to the compounds of hydrogen and oxygen
with the metals lithium, sodium, potassium,
rubidium, cesium, and the radical ammonium.
The alkalies are all soluble in water, and have the
property of neutralizing acids as well as of turn-
ing solutions of blue litnuis red. The word al-
kal, which is derived from the Arabic, and
means ash, was orginally given to the ashes of
sea-plants, and was applied first to potash, called
the vegetable alkali, and then to soda, which
was derived from rock salt, and called mineral
alkali. These two became known as the fixed
alkdlicfs. in distinction from ammonia, which was
called the rolntile alkali. The alkalies are ex-
ceedingly caustic, and act as powerful corrosive
poisons. They show great avidity for acids, and
combine with them, forming salts, in which the
special properties of both acid and alkali are
generally destroyed; hence, they are said to neu-
tralize one another. (See AciDS.) The alkalies
find extensive use in the arts, as in the manu-
facture of soap and of baking powders, and in
dyeing. The alkaline eartlis, lime, magnesia,
Ijaryta, and strontia, form a group of substances
closely allied to the alkalies, but differing from
the latter in being less soluble and by the fact
that their carbonates are insoluble in water.
Consult: G. Lunge, A Theoretical and Practical
Treatise on the Manufacture of tiulphiiric Acid
and Alkali (London, 1891); and The Alkali-
Makcr:s' Handbook (London, 1891).
AL'KALI FLAT. See Plata.
AL'KALIM'ETER (alkali + Gk. fieT,)ov, met ran. measure). An instrument used for the determination of the amount of alkali contained in commercial alkalies. It is usually a glass tube graduated into parts of 100, and called a burette. To make a determination, a given
weight of alkali is dissolved in water and an
acid of known strength is poured from the al-
kalimeter into the solution until the latter is
just neutralized. The exact point of neutraliza-
tion is determined by means of a substance
called an indicator, which changes its color when
a slight excess of the acid is added. The amount
of acid used determines the percentage of alkali. Consult: Hart, A Handbook of Volumetric Analysis (New York, 1878); Sutton, A Systematic Handbook of Volumetric Analysis (London, 1890).
AL'KALI SOILS. A term applied to soils occurring in regions of deficient or irregular rainfall, which contain unusually large amounts of soluble salts concentrated in or near the surface. Under certain conditions of moisture these salts appear on the surface of the soil in the form
of a crust or powder known as relt in India, sabach in Egypt, and alkali in America. The main constituents of this saline ettlorescence are sodium sulphate, sodium carbonate, and sodium chloride, mixed in varying proportions. There are present besides, according to Hilgard, salts of calcium and magnesium and smaller amounts of potassium sulphate, sodium pliosphate, and
sodium nitrate, these salts furnishing the most
important elements of plant food. Two main
classes of alkali are distinguished: "black" al-
kali, in which sodium carbonate predominates,
and which is on this account highly corrosive
and injurious to vegetation; and "white" alkali,
the predominant constituent of which is sodium
sulpliate, and which is nnich less harmful to
plant growth than is the black form. A saline
form in which sodium chloride predominates is
also frequently met with. Black alkali derives
its name from the dark-colored spots and water-
puddles observed where it abounds, which owe
their color to the organic matter dissolved from
the soil by the sodium carbonate.
Practically the same soluble (alkali) salts oc- cur in all soils, but in humid regions the abun- dant rainfall prevents their accumulation on or near the surface, carrying away in the drainage those salts for which the soil has not a strong absorptive power. In regions of deficient rain- fall, on the other hand, the scanty moisture which reaches the soil merely serves to dissolve the salts and carry them down a short distance into the ground, whence they are rapidly drawn up bj' the capillary rise of the water. The mois- ture, evaporating at the surface, leaves the salts accumulated there. Such accumulations of alkali are also found in regions which have a rainy and a dry season (as in parts of India), and where the rains occur commonly in sudden and violent downpours, which quickly pass without wetting the soil to any considerable depth.
