第23章

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.

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 can be detected by the experienced operator.

Thus muriatic acid is added for its chlorine, which can generally be detected by the impression produced, being of a light, soft, mellow tone, and in most cases presenting a brilliant black to that colored drapery.

Those who wish to experiment with agents for accelerating substances, should first study to well understand their peculiar nature and properties;as well, also, to endeavor to find out what will be the probable changes they undergo in combination as an accelerator. This should be done before making the experiments. From the foregoing it will be seen that numerous compounds are formed from the same basis, and, consequently, it would be a waste of time and a useless appropriation to devote more of our space than is necessary to give the principal and most reliable combination.

In America, the words "Quick" and "Quick Stuff," are more generally used for and instead of the more proper names, "Sensitives," or "Accelerators," etc.

As it has by use become common, I frequently use it in this work.

Liquid Accelerator, No. 1.--This mixture was used by me in 1849, and is given as it appeared in my "System of Photography,"published at the above date:

Take pure rain or distilled water, one quart, filter through paper into a ground stopper bottle, and add, for warm weather, one and a half ounce chloride of iodine; or for cold, one ounce; then add one ounce bromine, and shake well.

Now with care not to allow the vapor to escape, add drop by drop, thirty drops of aqua ammonia, shaking well at each drop. Care must be taken not to add more at a time, as it evokes too much heat.