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. This mixed, in equal proportions with John Roach's quick, forms an excellent chemical combination. For this purpose, take one and a half ounce of each, to which add ten ounces water, for warm weather, or from six to seven for cold. Pour the whole into a large box, and it will work from two to four months. I am now using (1849) one charged as above which has been in constant use for three months, and works uniformly well. The above is right for half or full size boxes, but half of it would be sufficient for a quarter size box.

Coat to the first shade of rose over iodine, change to a deep rosy red over quick, and black about one tenth the first.

I would not now recommend the addition of "John Roach's quick," as I believe equally good results can be produced without it. This liquid is now used by many, and is very good for taking views.

Lime Water Quick.--This mixture is more used at present than all the other liquids ever introduced. It produced the most uniform results, giving the fine soft tone so characteristic in pictures produces from accelerators containing chlorine. To one quart of lime water (this can be had of any druggist) add one and a half ounce of pulverized alum. This should be shook at intervals for twenty--four hours; then add one ounce of chloride of iodine and three fourths ounce of bromine.

Lime Water.--This is easily prepared by putting lime into water, say a piece of quick-lime about the size of an egg into one quart of water. This should be shook occasionally for two or three days and allowed to settle, when the water can be poured off and used.

Use.--To one part of quick add six parts of water; coat to a light yellow over the iodine, to a rose color over the quick, and recoat about one tenth. The above coating may be increased or diminished, it matters not, so that there is not too much, and the proper proportions are preserved. Some add to the above a small quantity of magnesia, say about a teaspoonful to the quart of liquid.

Liquid Accelerator, No. 2.--The following was for a long time used by one of the first houses in the United States, and probably was one of the first liquids ever used. It produces a fine-toned picture, but is not considered as sure as the lime water quick:

Take rain water one quart, add pulverized alum until it is a little sour to the taste, and a small piece, say one half inch square, of magnesia. Filter through paper, and add chloride of iodine one half ounce, bromine sufficient to take it up, which is a little less than half an ounce.

Charge with one of quick to six of water; coat over iodine to a soft yellow, nearly, but not quite, bordering on a rose; over quick to a dark purple, or steel, and back one sixth to one tenth.