A Manual Of Photography

THE COLLODION PROCESS. 261 To Prepare the Collodion.—Thirty grains of gun-cotton pre- pared as described should be taken and placed in 18 fluid ounces of ether, and then 2 ounces of alcohol should be added; making thus an imperial pint of the solution. The cotton, if properly made, will dissolve almost entirely ; any small fibres which may be floating about should be allowed to deposit, and the clear solution poured off previously to the process of iodizing it. To Iodize the Collodion —Mr. Archer’s method is as follows; and I believe no better course can be pursued. Prepare a saturated solution of iodide of potassium in alcohol, say 1oz., and add to it as mucli iodide of silver as it will take up. Or to 1 oz. of alcohol add an excess both of iodide of potassium and iodide of silver ; after a day or two, and with repeated shaking at intervals to facilitate the operation, a saturated solution of the two salts will be obtained, and if this is filtered off into another bottle it will always be found ready for use. The first bottle can be kept as a stock bottle, to obtain a still further supply by replenishing it with alcohol, and adding now and then small additional quantities of the two salts. The iodide of silver can be readily obtained by precipitation. For instance, take 1 oz. of solution of nitrate of silver used in the process, 30 grs. of nitrate of silver to 1 oz. of water, and add to it sufficient of a solution of iodide of potassium in water as will throw down the whole of the nitrate of silver as an iodide. When this precipitated iodide of silver has settled, which it very readily does, the liquid above must be poured off, and fresh water added, repeating this washing several times. The iodide of silver after this is dried, and then put into a bottle with a small quantity of alcohol, just sufficient to keep it moistened. The quantity of the solution of iodide of silver which can be added to 1 oz. of collodion must depend upon the quantity of alcohol in the collodion. . The collodion process now resolves itself into 1st. Cleaning the Class plate.—By far the most successful general manipulator in the ordinary forms of the collodion process is Mr. Horne; and that gentleman having most obligingly furnished me with the proof sheets intended for the Manual published by his firm, I have great pleasure in being enabled to give his most recent improvements. A variety of substances, such as tripoli, nitric acid, spirits of wine, &c., have been recommended for cleaning the glass: but all these Mr. Horne thinks are quite superfluous; the only articles actually necessary being a clean cloth or two, and a wash leather that has been well and thoroughly rinsed through several changes of clean water, to deprive it as much as possible of the dressing which a new