| Glacial acetic acid | 25 | drops |
are added.
| (B.) Silver nitrate | 10 | g. |
| Distilled water | 100 | ccm. |
Immediately before use 100 parts of solution A are mixed with 5 parts of solution B, and the intensification continued till the desired density is obtained. Negatives can be reduced by placing them whilst damp in a solution of—
| Potassium permanganate | 1 | part |
| Distilled water | 300 | parts |
When this has acted sufficiently, the plate is well washed, {43} flowed over with a five per cent. solution of potassium cyanide, and then well washed. When the dyed emulsion is used this must be done, after developing, in red light.
A very excellent method of preparing an orthochromatic collodion emulsion has been described by Hübl,[2] which can be used either wet or dry. Repeated trials made in the Imperial Military Geographical Institute, in our establishment, and in the Photographic Institute in Vienna have proved the advantageous use of this method for orthochromatic work. The raw emulsion, according to Hübl, is prepared as follows:—40 g. of silver nitrate are dissolved in 50 ccm. of warm distilled water, and as much ammonia added as will give a clear solution; then 100 ccm. of alcohol are added and the whole allowed to cool. 30 g. of ammonium bromide are dissolved in 35 ccm. of water and 70 ccm. of absolute alcohol with gentle heat.
[2] “Encyclopædie der Photographie,” Heft 3, and Eder’s “Jahrbuch,” 1892, p. 387.
To make the emulsion 450 ccm. of four per cent. raw collodion are placed in a strong glass flask which will hold a litre, and to this in the dark room the silver solution added. Some of the wool separates out, but by vigorous shaking this can again be dissolved. A part of the silver salt also remains suspended in the liquid in the form of fine crystals. The ammonium bromide is added in three or four parts whilst warm. After shaking thoroughly for several minutes the emulsion is precipitated by distilled water, which is repeatedly added till the separation is complete. The emulsion, which is now powdery, is placed on a linen filter, washed several times with distilled water, squeezed to press out the last of the water, damped two or three times with alcohol, and then pressed. Whilst still damp with alcohol the emulsion is dissolved in from 800 to 1,000 ccm. of alcohol and ether, mixed with 0·5 grs. of codeine, and allowed to rest for some days, when it will be ready for use.
The preparation of the eoside of silver solution is effected as follows:—10 g. of yellow-shade eosine are dissolved in 250 ccm. of boiling water and 5 grs. of silver nitrate in 50 ccm. of water added hot. The solution is allowed to settle, then filtered, and then washed first with boiling water and then with alcohol on the filter, and then dried in a dimly-lighted room.