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. In dissolving the Pyroxyline, any fibrous or flocculent matter which resists the action of the Ether, must be allowed to subside, the clear portion being decanted for use. The Iodide of Potassium is to be finely powdered, and digested with the spirit until dissolved; it is better not to apply any heat. Both Iodide of Ammonium and Iodide of Cadmium dissolve almost immediately, if the salts are pure. The Collodion must be kept in a cool and dark place. When prepared with Iodide of Ammonium or Potassium it becomes at length high coloured and insensitive. The free Iodine may then be removed by a strip of pure zinc or silver-foil. When sensitiveness is not an object, many prefer working with an old, coloured Collodion, finding that it gives more intensity. It has been shown at page 97 that a peculiar change takes place in Collodion after iodizing, by which the intensity of the image is increased.