第26章

A solution of sufficient strength can be made by moistening or just covering the iodine with water.

Chloride of Iodine as an Accelerator.--This is probably one of the best accelerators that can be used for coating the plate for taking views;it works too slow, however, to meet the wants of the operating room, yet its use was formerly, for a long time, adhered to by some of our best professors. In producing views with this, we are successful in obtaining well-developed impressions, with a depth of tone and richness of appearance not to be met with in the productions of any other substances.

I give its use as furnished me by an old and experienced operator, and published in Humphrey's Journal, vol. i. p. 180:

"As the process of using chloride of iodine may be of interest to some of our subscribers, I take pleasure in giving the following manipulation.

To one ounce of chloride of iodine add two ounces of water;place this mixture in a coating-box, the same as quick stuff;coat the plate with dry iodine to a light yellow, or lemon color;then bring the coating to a deep pink over the chloride.

The plate must be recoated over the dry iodine."This combination has been very successfully used in one of our most extensive establishments in this city, and the superiority of the pictures produced by it was considered as an equivalent for the additional time required to bring out the impressions.

Chlorine as an Accelerator.--I shall here refer to but a single experiment in which I employed chlorine gas for coating the plate.

I was provided with a retort, the neck of which was fitted to the jar of my coating-box, through a hole drilled for its reception.

This was fitted perfectly tight in my coating-box. I placed some pure undiluted bromine water and the agents necessary for producing chlorine gas (in small quantity) in the retort.

The result was that my first experiment produced an impression completely solarized in all its parts by an exposure of four seconds of time, which would have required an exposure of twenty seconds to produce a perfectly developed impression by the usual process.

Another trial immediately produced one of the finest toned impressions I ever saw, perfectly developed in one second of time.

My next two or three experiments proved total failures.

I was unable to produce even a sign of an impression.

By accident my retort was broken, and not being in a locality convenient to obtain another, my experiments were necessarily suspended.

My attention was not called to this subject again for several years, when I noticed an account of some similar experiments by F. A. P. Barnard and Dr. W. H. Harrington, the latter of whom is now of the firm of Dobyns & Harrington, of New Orleans.

From reading this article, I found my own difficulties explained.

Too much of the chlorine gas was present in my coating jar.

I would like to see some of our enterprising operators investigate this combination.

It is a singular fact, that the vapors of bromine and chlorine combining upon the iodide of silver, produce a more sensitive coating than when the two are combined in solution, as in chloride of bromine solution.

Those having Humphrey's Journal at hand, can refer to vol. i. p. 142.

To use Bromine Water or other Accelerators in Hot Weather.--An excellent plan for using bromine water is as follows:

Fill a two-ounce bottle quarter full of it, and then fill the bottle with fine sand, which serves to preserve a low temperature;then place the bottle in a porous cup, same as used in the battery;fill this also with sand, and close the end with plaster of Paris.

Place this in a coating-box, and it will be found to act with great uniformity and be quite permanent.

Bromide of Lime, another accelerator, can be used in the same manner, except it is, only necessary, when a solid sensitive is used, to mix it with the sand without placing it in a bottle.

This method is employed with great success by a few, who have regarded it as a secret worth keeping.

A Combination, requiring the Use of only One Coating-box.--It is often wondered by beginners, why some solution requiring only one coating cannot be employed. This can be done, but the results are not so satisfactory as when two or more are employed.

Such an accelerator may be produced by adding alcoholic solution of iodine to a solution of chlorate of potash, until the latter will take up no more of the former, and to each ounce, by measure of this solution, ten drops of a saturated solution of bromide in water are added.

The solution of chlorate of potash is made by diluting, one part of a saturated solution of the salt with ten parts of water.

The use of the chlorate is simply as a solvent of iodine.

Fats as Accelerators.--The use of fats, oils, or greasy substances, has been one of the most emphatic prohibitions about the Daguerreotype plate. Yet it has been proved that its presence in a small quantity upon the silver surface has the effect of reducing the time of exposure in the camera from two-thirds to three-fourths. An application may be made as follows:

Pour sweet oil, or rub beef or mutton fat, on a common buff, which is free from all polishing powders. With this, buff a well-cleaned plate, and it will leave a scum, which should be mostly removed by using another buff, which should be clean.

Coat the plate in the usual manner, and the result will be a great reduction in the time of exposure in the camera.

The impression produced upon a plate so prepared presents, when coming from the vapor of mercury, a grey, scummy appearance, which, on the application of heat in gilding, does not improve;hence its use is not generally adopted.

We have instituted some investigations upon this subject, and in the present volume, we shall not refer to it further.

Those wishing to learn more fully the effect of light upon organic substances will find Robert Hunt's "Researches on Light"an invaluable work.

LIGHT AND OPTICS.