muriatic acid and 72 parts
of sulphate of soda. The muriatic acid of commerce has usually a
yellowish tinge, but when chemically pure it is colorless. The former
is commonly contaminated with sulphurous acid, sulphuric acid,
chlorine, iron, and sometimes with arsenic.

Muriatic acid, from the fact of the presence of the chlorine, is used
in the Daguerreotype process for dissolving gold, and in combination
with various accelerators. Its presence can be detected by ammonia. A
strip of paper dipped in this and waved to and fro will emit a thick
white smoke if the acid vapor be in the atmosphere. The ammonia
neutralizes the acid fumes. By reversing the experiment we can
determine whether vapor of ammonia be in the air, and also deprive
these suffocating and dangerous gases of their injurious properties,
and remove them from the air. Every Daguerreotype operator should be
furnished with, at least, a six ounce bottle of aqua ammonia. Its
operation is very nearly the same on bromine and iodine vapor.

Hydrofluoric Acid (Fluorohydric Acid).--This acid is used to form some
of the most volatile and sensitive compounds employed in the
Daguerreotype. It is one of the most dangerous bodies to experiment
with: it is volatile and corrosive, giving off dense white fumes in the
air. It combines with water with great heat. At 32 deg. it condenses
into a colorless fluid, with a density 1.069. It is obtained from
decomposition of fluorspar by strong sulphuric acid. It readily
dissolves the silica in glass, and consequently cannot be kept in a
vessel of that material. It is prepared and kept in lead. It is
employed in accelerators on account of its fluorine.

One small drop on the tongue of a dog causes death. The operator who
wishes to use it should pour some of the liquid for which he intends it
into a graduate, or other vessel, and then add the desired quantity of
acid. If by accident any of the spray should fall upon the skin, it
should at once be copiously drenched with water.

Sulphuric Acid.--There are two sorts of this acid: one is an oily,
fuming liquid; this is made in Nordhausen, in Saxony, and is commonly
called "Nordhausen sulphuric acid," or oil of vitriol. The other which
is the kind used in connection with the Daguerreotype, is common
sulphuric acid. It is somewhat thinner, and when undiluted is not
fuming. This acid may be obtained in a solid and dry state, called
anhydrous sulphuric acid.

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