Plain collodion 8 ounces. Iodide of potassium (dissolved as per page 62) 24 grains. Bromide of ammonium 16 " This collodion should be allowed to stand and settle twenty-four hours before it is used: when wanted, it should be poured off into a collodion vial. The more free the collodion is from sediment and small particles of dust or undissolved cotton, the softer and more perfect will be the impression it makes. In case the above proportions of iodide of potassium should not produce a cream-colored coating, when it comes from the nitrate of silver bath, more may be added: for example, if the coating is of a bluish tint, I would dissolve 6 grains of iodide of potassium in water, as before, and then try it: shake well, and test it by putting a little on a slip of glass, and dipping it into the silvering solution; if it coats to a cream-color, it is right. It should be borne in mind, that after the addition of iodide of potassium here recommended, the collodion should be allowed to stand until settled, before undertaking to produce a picture, although the coating may be previously tested by means of a slip of glass. Solution of Bromide and Iodide of Potassium and Silver. Dissolve 130 grains of crystallized nitrate, of silver in 4 ounces of pure water, in a long 8-ounce vial. Then in a clean 1-ounce graduate, or some other convenient vessel containing half an ounce of water, dissolve 130 grains bromide of potassium. When this and the nitrate of silver are both dissolved, pour the solution of bromide of potassium into the vial containing the silver, and a thick yellow precipitate will fall. This is the bromide of potassium and silver. This should be washed by nearly filling the vial with water; shake it, and then let it settle, which it will readily do, and then pour on the water, leaving the yellow mass in the bottom of the vial; continue this operation of washing for at least ten changes of water; then, after draining off the water as close as possible, put into the vial four ounces of alcohol, shake it well and let it settle; then pour off as close as possible. By this means the water is nearly all taken out. Pour into the vial _three_ ounces of alcohol; then in a small mortar finely pulverize one ounce of iodide of potassium, and the solution, which was before clear, will be more or less of a yellow color, and the bulk of the yellow precipitate will be diminished. I have sometimes completely re-dissolved the yellow precipitate, but this does not often occur, except there be more water present than is advisable. It is better to have an excess of bromide of potassium in the solution. This can be seen by its being white, and remaining undissolved in the bottom of the vial. This solution should be prepared in the evening, or in a dark room, and only the light of a lamp or candle employed. Double Iodide of Potassium and Silver.