Iodid eof Potassium...............................................................

166 grains.

Iodide of Cadmium...............................................................

183 "

Dissolve in as little water as possible, and evaporate by heat to dryness, stirring constantly. To each ounce of plain collodion add

Double Salts,...............................................................

6 grains.

Bromide of Cadmium,..........................................

2 1/2 "

In making up the plain collodion the quantity of alcohol per gallon should be about eight ounces short, and when the iodizing solution is weakened, as it is sensitive also for blue and green rays, while with purely iodized collodion this sensibility is wanting. - Shultz Sellack.

Intense Collodion. - As a means of obtaining density in negatives, it has been recommended to introduce into the collodion organic matter in the shape of sugar. Dissolve one grain of white sugar in a few drops of water, add this solution to the alcohol in making the collodion; one grain of sugar being sufficient for four ounces of collodion, and causing it to yield negatives of the utmost intensity. The introduction of too much sugar renders the film rotten, and in some cases it will be found desirable to reduce the amount here given. - J. L. Gihon.

134. It was in the year 1857, I believe, that I first made use of the iodides of potassium and cadmium in combination. I have, in connection with this double iodide, used the double bromides of cadmium and ammonium in the manner to be described, to prepare the double iodide and bromide, which is simple and easy to do, and leaves you with but two salts to weigh out when compounding your collodion. The potassium-cadmium iodide is prepared thus:

Potassium - Iodide,...............................................................

332 parts.

Cadmium - Iodide,...............................................................

336 "

Dissolve together in as small a quantity of distilled water as will dissolve them; evaporate by a gentle heat to dryness; stir at the last with a glass rod to granulate the salts. "When quite dry, bottle for use. Ammonium-cadmium bromide in the following proportions:

Ammonium - Bromide,...............................................................

196 parts.

Cadmium - Bromide,...............................................................

272 "

Dissolve and prepare same as the iodide. I now prepare two collodions, one iodized, the other bromized, enabling one to mix the collodions to suit any subject desired.

Iodized collodion, made with equal parts ether and alcohol, cotton to suit, and with six grains of iodide to the ounce.

added as below,the quantity will be correct. For one pound iodion take

Double Iodide,......................................................................................

96 grains.

Bromide of Cadmium,......................................................

40 "

Alcohol.................................................................................

1 ounce.

Careful watching is needed in evaporating the salts to complete crys-talli/.ation.

Both the quality and the quantity of cotton used in the mixture collodion are to be regarded. Our American manufactures run very uniform in quality as;a usual thing, and one you find out a sample that

Bromized collodion, made with five parts ether to three parts alcohol, cotton to suit, and ten grains bromide to the ounce.

Mixed in the following proportion, this collodion will be found to meet the wants of both landscape and portrait photography.

Two parts iodized to one part bromized; suitable for dry plates, and used wet, for interiors and dimly lighted subjects.

Three parts iodized to one part bromized; suited for children and quick exposures. Four parts iodized to one part bromized; a generally useful collodion.

Five parts iodized to one part bromized; suited for copying and subjects presenting little contrast

The nitrate bath should be sufficiently acid with nitric acid to immediately change blue litmus - paper, for the collodion has the property of neutralizing the bath. It is better not to use this collodion till it is one to three months old. Yet it can be brought into working condition in as many days by the addition of tincture of iodine; but I would recommend those who desire to try it, to bottle it up and lay it away in a cool place for a few months, for, like good wine, it improves with age. - John Carbutt.

There is no difficulty in preparing the double salts. To produce double ammonium - cad-miuin iodide, dissolve one hundred and forty-five parts iodide ammonium and one hundred and eighty-three parts iodide cadmium in water, and evaporate till it crystallizes. It crystallizes quite easily in slightly distorted cubes, and can be freed from the yellow mother lye by pressing. If you wish very clean salt, you will have to crystallize it again.

The single ammonium-cadmium bromide is prepared by dissolving three hundred and forty-four parts of crystallized bromide - cadmium and ninety - eight parts bromide ammonium in water, evaporating till crystallization; the latter may also be repeated. - Dr. H. "W. Vogel.

When we increase the quantity of cotton in a collodion, the sensitiveness of the preparation increase also. Dr.Zettnow recommends to use as much cotton as possible, but practically we soon reach a limit, as thick collodion does not flow readily; to this must be added, that if the proportion of collodion is increased beyond two and a quarter per cent, a decrease of sensitiveness takes place instead of an increase. The high-lights, of course, become more intense with a thick collodion, but the shadows are paler and the picture looks hard. The boundary-line to which we may go in increasing the thickness of collodion depends on the nature of the pyroxylin employed; of a short-fibred cotton a larger quantity may be taken than of a long - fibred variety. Dr. Zettnow maintains that the beauty of a pleases your fancy, you will have but little trouble to secure it again;

The action of the acids used in the manufacture of gun - cotton, with some samples of the raw cotton, produce such foreign bodies as gum, glucose, etc., but as a rule, they cause no injury. As to the quantity of gun-cotton to be used in collodion, there can be no real rule, but the formulae given are enough to guide one.