an impurity, although this is far less common than it was some years
ago.

=Chromic Acid, Chromate, Bichromate of Potassium.=--These act as
corrosives when solid or in concentrated liquid forms. In dilute
solutions they act as irritants. Used as dyes; have proved fatal more
than once. Those engaged in their manufacture suffer from unhealthy
ulcers on the nasal septum and hands. The former may to some extent be
prevented by taking snuff. Lead chromate (chrome yellow) is a powerful
irritant poison. Two drachms of the bichromate caused death in four
hours.

_Tests._--Yellow precipitate with salts of lead, deep red with those of
silver.

_Treatment._--Emetics, magnesia, and diluents. Washing out of the
stomach with weak solution of nitrate of silver.

XXVII.--GASEOUS POISONS

=Carbon Dioxide.=--Carbon dioxide is a product of combustion and
respiration, and is generated in many ways during fermentation. It is a
constituent of _choke damp_ due to explosions in coal-mines, and is
given off from lime-kilns, brick-kilns, and cement-works. It is often
met with in dangerous quantities in wells and in brewers' vats. From 10
to 15 per cent. in the atmosphere would prove fatal, but even 2 per
cent. inhaled for long would produce serious symptoms. The proportion
usually present in air is 0.04 per cent.

_Symptoms._--Inhalation of the _pure_ gas causes spasm of the glottis,
insensibility, and death from asphyxia, at once; _diluted_, causes sense
of weight in forehead and back of head, giddiness, vomiting, somnolence,
loss of muscular power. Insensibility, stertorous breathing, lividity of
face and body, and death from asphyxia. Convulsions occasionally.

_Post-Mortem Appearances._--Face swollen and livid, or calm and pale;
lividity is most marked in eyelids, lips, ears, etc.; limbs usually
flaccid, abdomen distended; right side of heart, lungs, and large veins,
gorged with dark-coloured blood. Brain and membranes congested.

_Treatment._--Pure air, cold affusion, stimulants, artificial
respiration, galvanism, inhalation of oxygen, venesection, transfusion.

=Carbonic Oxide.=--This is one of the most poisonous of gases. It is
evolved in the process of burning charcoal and coke in stoves or
furnaces. Water-gas, obtained by passing steam over heated coke,
contains 40 per cent. of the substance, the remainder being chiefly
hydrogen. It forms the chief part of the deadly 'choke damp' after an
explosion in a mine. Two per