SMOKE

visible vapor which rises from a burning substance; gaseous exhalations charged with minute particles of carbonaceous matter or soot. S. is the product of imperfect combustion of such substances as wood or coal. The s. nuisance in large manufacturing towns charges the atmosphere with soot and dirt particles which penetrate everywhere. Several methods of s. combustion have been invented. These chiefly deal with introducing oxygen to the particles of carbon so as to make them burn. In warm. weather the s. of towns gets away and is unnoticed in the atmosphere, but in winter or cold weather, when the atmosphere is charged with moisture, the s. is kept down and, mixing with the moist atmosphere, causes the black or brown fogs so common in our large towns. The s. of coal is black and of an oily and tarry nature, peat s. is azure blue, while burning wood gives off an almost invisible smoke, mainly composed of carbonic acid.