Hydrochloric Acid (Muriatic Acid).—This acid forms a valuable 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. 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.
The common 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.