Collodion, Or Coliodium (Gr. Kδλλa, glue, and είeδoς, form), an adhesive substance produced by dissolving gun cotton in ether and alcohol. The proportions recommended are, prepared cotton 8 parts by weight, rectified ether 125 parts, and rectified alcohol 8 parts. The presence of water in the alcohol and ether should be carefully avoided. The cotton is to be agitated in a bottle with the ether a few minutes, when the alcohol may be added, and the shaking continued. The product, a clear, colorless liquid, of the consistency of sirup, is next strained through a cloth, and the liquid kept in a tight bottle. It is very volatile, and on evaporating leaves a film which adheres with extraordinary tenacity to the surface of bodies. This property makes it a convenient application to cuts and wounds in the place of sticking plaster, either by brushing it alone over the edges of the incision, or by spreading it upon strips of linen. It was first applied to this use by Dr. J. Parker Maynard, of Boston, to whom the name was suggested in 1848 by Dr. A. A. Gould. Collodion is best prepared from gun cotton made by the process of Prof. Ellet. Gun cotton made by steeping the fibre in nitric acid does not always dissolve in ether and alcohol.

Prof. Ellet's, being always soluble, is preferred for this purpose, prepared as follows: 8 1/2 fluid oz. of sulphuric acid are added to 10 oz. of nitrate of potassa, mixed, and triturated in a mortar; 1/2 oz. of fine clean cotton is then thoroughly stirred into the mixture for about four minutes; the free acid is next removed by washing in water till all traces of it disappear. The gun cotton, being opened by picking and dried at a gentle heat, is dissolved in 2 1/2 pints of ether already mixed with a fluid ounce of alcohol. The solution is to be strained, and kept in closely stopped bottles previously well dried. A similar method is given by Lauras, and the cotton, which he calls xyloidin, produces by his process a quality of collodion possessing elasticity and suppleness, which adapt it for application to the skin, especially on the articulations where freedom of motion is an important object. To a mixture of 300 grms. of sulphuric acid of sp. gr. 1.847, and 200 grms. of dry nitrate of potassa, he adds 10 grms. of carded cotton. After being in contact 12 minutes the cotton is taken out and washed with cold water, rinsing it two or three times.

It is then immersed in a solution of 30 grms. of carbonate of potassa to 100 of water, again well washed with water, and dried at 77° to 86° F. Of this xyloidin 8 grms. are placed in a flask with 125 of ordinary ether, and 8 grms. of alcohol are added of sp. gr. .825. The mixture is well agitated and then combined with a preparation of Venice turpentine 2 grms., castor oil 2 grms., and white wax 2 grms., to which, after being heated, 6 grms. of ether should be added. - Collodion was first applied to photographic purposes in 1847, by Mr. Archer of England. It is used as a menstruum for affixing to a glass plate a film of some iodide, as of potassium, ammonia, or cadmium, a solution of which is mixed with it. - Collodion is used in medicine exclusively as an external application. Besides its use as an adhesive application to slight cuts and wounds, already referred to, it is often applied with decided advantage to sore and cracked nipples and to chapped hands, and used as a protection in some diseases of the skin, especially in chronic erythema, intertrigo, and herpes labi-alis. Whenever there is acute inflammation of any surface, the contractile action of collodion is apt to produce pain and irritation, and it should not then be used.

The annoying bleeding which sometimes follows the cut of a razor while shaving may be instantly stopped by an application of collodion. A mixture of 100 parts of collodion with 2 parts of glycerine makes a more agreeable application than collodion alone, and one equally efficacious. It forms with cantharides a convenient blistering agent. Collodion should be applied with a camel's hair pencil. It may be kept for a long time fit for use in a well stoppered bottle.