COLLODION (Gr. x021144c, °like glue), a solution, in mixed alcohol and ether, of soluble pyroxylene (or ugun-cotton”. It is colorless and highly inflammable. The gun-cot ton that is used in its manufacture is commonly prepared by the action of a mixture of nitnc and sulphuric acids upon cotton-wool that has been first boiled in a solution of sodium car bonate (to remove all greasy and resinous mat ters) and afterward thoroughly washed and dried. The following procedure is followed in the subsequent operations: Three fluid ounces of strong nitric acid are poured slowly into two fluid ounces of water, and nine fluid ounces of strong sulphuric acid are added, stirring con stantly. When the mixture has cooled to about 140° F., 100 grains of the prepared cotton-wool are added in tufts weighing about 10 grains each. At the end of 8 or 10 minutes the acid is poured off and the cotton is subjected to gentle pressure to expel the greater part of the fluid that its fibres have retained. The cotton is next thoroughly washed with water and a weak solution of sodium carbonate until the acid has been entirely eliminated, after which it is allowed to dry. The product is 4soluble gun-cotton.° It does not differ materially, in appearance, from the original cotton; but if the operations to which it has been subjected have been correctly carried out, it will be found that the cotton has become soluble in a mixture of equal parts of alcohol and ether. Commer cial collodion contains 100 to 120 grains of gun cotton to 10 ounces of ether and 5 ounces of alcohol, a further 5 ounces of alcohol being added after the salts have been dissolved. Be fore the advent of the dry-plate process, col lodion was greatly used in photography for the preparation of sensitive plates; and at the pres ent day it is used to some extent in this way, especially in certain branches of photo-engrav ing. In the preparation of these plates the col
lodion is first iodized and brominized by the addition of the iodide and bromide of cadmium or of ammonium, or a mixture of both, and the addition of a few drops of nitric acid, and is then poured over a carefully cleansed glass plate. The volatile solvent evaporates rapidly, leaving a film of iodized gun-cotton upon the glass. Immediately before the exposure ts made the coated plate is immersed in a solution of nitrate of silver, with the result that a deposit of iodide and bromide of silver, sensitive to light, is formed in the guncotton layer. The prate is next exposed in the camera, and after ward developed by a ferrous sulphate solution in water. Collodion is used in the place of adhesive plaster, in the case of trivial injuries, to afford protection from the air, and from pyogenic and other objectionable germs. Whe.n applied to the injured spot it quicicly dries, leaving a tough, elastic coating which is im pervious to moisture. It wa.s first employed in surgery by Dr. J. Parker Maynard, of Boston, Mass., in 1847. In this application it is often znedicated in various ways,. one of the best known examples being blistering collodion, which contains cantharides, and is applied to the skin for the purpose of producing a blister. Medicated collodion is also largely used in chiropody.