TO IODIZE:
| Alcohol | 5 oz. |
| Iodide Ammonium | 60 grs. |
| Iodide Cadmium | 30 |
| Bromide Cadmium | 20 |
Dissolve the iodides in the 5 oz. alcohol or in the whole 10 oz., if desired, then put in the 100 grains cotton, shake well, then add the 10 oz. ether and shake till the cotton is all dissolved; it will be ready for use in a few hours, and will improve with age.
THE NEGATIVE BATH.
The silver solution for a negative bath is prepared in substantially the same manner as for a positive.
Two thirds of the amount of silver nitrate intended to be used, should be dissolved in the quantity of water required to make the bath, and a grain or two of iodide of potassium added and placed in the sunlight until the solution has changed color, become turbid, and again clear and colorless. This change is caused by a minute portion of the silver combining with the organic matter and with other impurities in the water, if there are any; a molecular change then takes p30 places, oxygen is evolved and the infinitesimal portion of silver changes to a metallic state and sinks to the bottom, carrying with it the impurities, which induced the chemical action or change.
The solution may now be filtered, the remaining portion of the silver nitrate added, and with a few drops of pure nitric acid, the solution will be ready for use. But if on trial it is ascertained that it will not give satisfactory results, it will be found that it has not been sufficiently excited, or an acid reaction has not been induced.
If the first supposition is true, more iodide of potassium must be used, as a silver solution must receive as much or nearly as much of the iodide as it will hold in solution, before it will work harmoniously with the collodion; the grain or two put in the solution with the first portion of nitrate of silver have not been sufficient.
A very little more may be added, which will combine with the silver, forming a white curdy precipitate, which, on shaking the bottle, will in a short time redissolve. If any remains, it should be filtered out, as no more can be held in solution.
An other plan is rather more convenient, but requires more time. It is to coat with collodion as large a plate as the bath will receive; immerse it in the bath, leaving it there some hours, usually all night.