addition to the chemicals employed by the practical Daguerreotypist.
This acid is formed by acting upon common salt (which is chloride
of sodium) by concentrated sulphuric acid. The water of the acid
is decomposed, and its hydrogen combines with the chloride of the salt
to form muriatic acid, and this unites with the sulphuric acid
to form sulphate of soda; 60 parts of common salt and 49 parts
of concentrated sulphuric acid, afford, by this mutual action,
37 parts of 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.