COLLODION (from the Gr. &M a' ,

See also:

• GLUE (from the O. Fr. glu, bird-lime, from the Late Lat. gluten, glus, glue)

glue)  , a colourless, viscid fluid, made by dissolving gun-cotton and the other varieties of pyroxylin in a mixture of alcohol and ether . It was discovered in 1846 by Louis Nicolas Menard in Paris, and independently in 1848 by Dr J . Parkers Maynard in Boston . The quality of collodion differs according to the proportions of alcohol and ether and the nature of the pyroxylin it contains . Collodion in which there is a great excess of ether gives by its evaporation a very tough film; the film left by collodion containing a large quantity of alcohol is soft and easily torn; but in hot climates the presence of an excess of alcohol is an advantage, as it prevents the rapid evaporation of the ether . Under the microscope, the film produced by collodion of good quality appears translucent and colourless . To preserve collodion it should be kept cool and out of the action of the light; iodized collodion that has been discoloured by the development of free iodine may be purified by the immersion in it of a strip of silver foil . For the iodizing of collodion, ammonium bromide and iodide, and the iodides of calcium and cadmium are the agents employed (see PHOTOGRAPHY) . Collodion is used in surgery since, when painted on the skin, it rapidly dries and covers the skin with a thin film which contracts as it dries and therefore affords both pressure and protection . Flexible collodion, containing Canada balsam and castor oil, does not crack, but, on the other hand, does not contract . It is therefore of less value . Collodion is applied to small aseptic wounds, to small-pox pustules, and occasionally to the end of the urethra in boys in order to prevent nocturnal incontinence .

Collodion and crystals of carbolic

acid, taken in equal parts, are useful in relieving toothache due to the presence of a carious cavity . Vesicating or Blistering Collodion contains cantharidin as one of its constituents . The styptic colloid of Richardson is a strong solution of tannin in gun-cotton collodion . Similarly collodion may be impregnated with salicylic acid, carbolic acid, iodine and other substances . Small balloons are manufactured from collodion by coating the interior of glass globes with the liquid; the film when dry is removed from the glass by applying suction to the mouth of the vessel . M . E . Gripon found (Conipt. rend., 1875) that collodion membranes, like glass, reflect light and polarize it both by refraction and reflection; they also transmit a very much larger proportion of radiant heat, for the study of which they are preferable to mica .