[Illustration: FIG. 6.--Sectional diagram of tar-still with arched bottom. The fireplace is at _i_; the hot gases pass over the bridge _k_ and through _g_ into the flues _h_, _h_. The pipe at _c_ is to supply the still with tar; _a_ is the exit pipe connected with the condenser, and _b_ a man-hole for cleaning out the still. The condenser and bottom pipe for drawing off pitch have been omitted to avoid complication.] It is customary at the present time to collect four distinct fractions from the period when the tar begins to boil quietly, _i.e._ from the point when the small quantity of watery liquor which is unavoidably entangled with the tar has distilled over, by which time the temperature in the still is about 110 deg. C. The small fraction that comes over up to this temperature constitutes what the tar-distiller calls "first runnings." From 110 deg. C. to 210 deg. C. there comes over a limpid inflammable liquid known as "light oil," and this is succeeded by a fraction which shows a tendency to solidify on cooling, owing to the separation of a solid crystalline hydrocarbon known as naphthalene. This last fraction, boiling between 210 deg. C. and 240 deg. C., is known as "carbolic oil," because it contains, in addition to the naphthalene, the chief portion of the carbolic acid present in the tar. From 240 deg. C. to 270 deg. C. there comes over another fraction which shows but little tendency to solidify in the condensing coil, and which is known as "heavy oil," or "creosote oil." From 270 deg. C. up to the end of the distillation there distils a fraction which is viscid in consistency, and has a tendency to solidify on cooling owing to the separation of another crystalline hydrocarbon known as anthracene, and which gives the name of "anthracene oil" to this last fraction. When the latter has been collected there remains in the still the black viscid substance known as pitch, which is obtained of any desired consistency by leaving more or less of the anthracene oil mixed with it, or by afterwards mixing it with the heavy oil from previous distillations. The process carried out in the tar-still thus separates the tar into--(1) First runnings, up to 110 deg. C. (2) Light oil, from 110 deg. to 210 deg. C. (3) Carbolic oil, from 210 deg. to 240 deg. C. (4) Creosote oil, from 240 deg. to 270 deg. C. (5) Anthracene oil, from 270 deg. to pitch. (6) Pitch, left in still.