ed to a cold solution. Another mode of separating the two
acids is to convert them into calcium salts, which are then treated with
a perfectly neutral solution of cupric chloride, soluble cupric citrate
and calcium chloride being formed, while cupric tartrate remains
undissolved. Citric acid is also distinguished from tartaric acid by the
fact that an ammonia solution of silver tartrate produces a brilliant
silver mirror when boiled, whereas silver citrate is reduced only after
prolonged ebullition.

Citric acid is used in calico printing, also in the preparation of
effervescing draughts, as a refrigerant and sialogogue, and occasionally
as an antiscorbutic, instead of fresh lemon juice. In the form of lime
juice it has long been known as an antidote for scurvy. Several of the
citrates are much employed as medicines, the most important being the
scale preparations of iron. Of these iron and ammonium citrate is much
used as a haematinic, and as it has hardly any tendency to cause gastric
irritation or constipation it can be taken when the ordinary forms of
iron are inadmissible. Iron and quinine citrate is used as a bitter
stomachic and tonic. In the blood citrates are oxidized into carbonates;
they therefore act as _remote alkalis_, increasing the alkalinity of the
blood and thereby the general rate of chemical change within the body
(see ACETIC ACID).

CITRON, a species of _Citrus_ (_C. medica_), belonging to the tribe
_Aurantieae_, of the botanical natural order Rutaceae; the same genus
furnishes also the orange, lime and shaddock. The citron is a small
evergreen tree or shrub growing to a height of about 10 ft.; it has
irregular straggling spiny branches, large pale-green broadly oblong,
slightly serrate leaves and generally unisexual flowers purplish without
and white within. The large fruit is ovate or oblong, protuberant at the
tip, and from 5 to 6 in. long, with a rough, furrowed, adherent rind,
the inner portion of which is thick, white and fleshy, the outer, thin,
greenish-yellow and very fragrant. The pulp is sub-acid and edible, and
the seeds are bitter. There are many varieties of the fruit, some of
them of great weight and size. The Madras citron has the form of an
oblate sphere; and in the "fingered citron" of China the lobes are
separated into finger-like divisions formed by separation of the
constituent carpels, as occurs sometimes in the orange.

The citron-tree thrives in the open air in China,