mon sulphuric acid is made by burning sulphur, which forms
sulphurous acid. To convert this into sulphuric acid and gain more
oxygen, nitric acid, which is rich in that body, is added. It forms a
limpid, colorless fluid, of a specific gravity of 1.8. It boils at 620
deg.; it freezes at 15 deg. It is acrid and caustic, and intensely
acid in all its characters, even when largely diluted.

Its attraction for basis is such that it separates or expels all other
acids, more or less perfectly, from their combinations. Its affinity
for water is such that it rapidly absorbs it from the atmosphere, and
when mixed with water much heat is evolved. It acts energetically upon
animal and vegetable substances, and is a poisonous, dangerous
substance to get on the skin. It is a powerful oxidizing agent; hence
its use in the galvanic battery, for which purpose it is mostly used by
the Daguerreotypist. The fumes of this being so much more offensive
than nitric acid, the latter is sometimes used. It is also employed in
some of the more sensitive accelerators.

ACCELERATING SUBSTANCES.

Remarks on the Accelerating substances Used in the Daguerreotype.--I
have now arrived at a point in this work, where the eye of the
Daguerreotype public will intently search for something new. This
search will prove in vain, at least so far as regards those who have
enjoyed and embraced the opportunities for studying the principles of
our art. Every experienced operator has in a degree become familiar
with the mechanical uses of all the agents employed, while I fear but
few understand the properties, and laws governing those properties,
which are so indispensable to produce an image impressed upon the
silver surface.

There are three substances which form the bases for producing a
Daguerreotype; silver, iodine and bromine. Each forms a separate body
which is indispensable to the operators success as the art is now
practiced in America. With these three, compounds of great variety are
formed.

The silver surface is first thoroughly cleaned and freed from all
organic matter, then exposed to vapor of iodine, producing an iodide of
silver. The plate upon which is this salt, is again exposed to the
vapor of bromine, forming a bromo-iodide of silver, a salt also.

As most of the various accelerators are compounds of bromine, with
either chlorine or fluorine combination, they partake somewhat of the
nature of these latter, giving results which