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.