FORMULA No. 2.
| Rectified Ether, sp. gr. ·750 | 6 | fluid drachms. |
| Alcohol, sp. gr. ·836 | 2 | fluid drachms. |
| Soluble Pyroxyline | 4 to 8 | grains. |
| Iodide of Potassium or Ammonium | 4 | grains. |
When the Collodion and Iodizing mixture are kept separate, the second formula will stand thus:—
| Rectified Ether ·750 | 3 | fluid ounces. |
| Alcohol of ·836 | 2 | fluid drachms. |
| Pyroxyline | 15 to 30 | grains. |
To each fluid ounce of this plain Collodion add 2 fluid drachms of the following Iodizing solution:—
| Alcohol, sp. gr. ·836 | 1 | fluid ounce. |
| Iodide of Potassium | 20 | grains. |
When the temperature of the Nitro-Sulphuric Acid used in making the Pyroxyline is high (140° to 155°), it often happens that the Collodion is too fluid with 4 grains of soluble paper to the ounce, and forms a blue transparent film of Iodide on dipping the plate in the Bath. In that case, increase the quantity of Pyroxyline from 4 grains to 6, or even to 8 grains to each ounce.
If the Collodion is glutinous, and produces a wavy surface, with less than 4 grains of Pyroxyline to the ounce, it is probable that the Alcohol is too weak, or that the soluble Cotton is badly made.
If flakes of Iodide of Silver are seen loose upon the surface of the film, and falling away into the Bath, the Collodion is over-iodized, and it will be impossible to obtain a good picture.
After the Collodion has been employed to coat a number of plates, the relative proportions of Alcohol and Ether contained in it become changed, from the superior volatility of the latter fluid: when it ceases to flow readily, and gives a more dense film than usual, thin it down by the addition of a little rectified Ether.