Abstract
During the course of this study we have found short-path distillation to be an especially useful procedure for separating volatile substances from macromolecular weight materials. For this reason and because the still which we have used most frequently has some rather novel features, it seems appropriate to devote the third paper of the series to a general description of our technique. Figure 1 is a schematic drawing of the still. Tube A is the heater tube, to the outside of which the samples in sheeted out form are attached by means of copper wire. The heater tube contains about 30 cc. of a liquid whose boiling point is the temperature at which the distillation is to be conducted. The liquid is boiled by an internal heating element regulated by means of a variable transformer. The leads H to the heating element enter through a rubber stopper in the upper end of the heater tube which is open to the atmosphere through flask G. For low-boiling heater liquids such as methanol, a condenser must be attached to the upper end of the heater tube. For the work described in the present series of papers, Cellosolve, b.p. 133° C, was used as the heater liquid. Tube B of Figure 1 is the condenser tube. Ordinarily, air cooling is sufficient to condense such materials as the usual rubber antioxidants, softeners, accelerators, fat acids, sulfur, etc. For special purposes, tube B is cooled by wrapping it with rubber tubing through which tap water was circulated or it is cooled with dry ice. The gap of this still, i.e., the distance from the heater tube to the condenser tube, is about 2 cm. The U-tube C, made of 1.25-inch glass tubing, constitutes a trap. It usually has been cooled with dry ice and acetone in I. That U-tube is connected to a booster pump D through a second dry-Ice trap. The pressure usually used has been less than 0.01 mm. and has been measured by a McCleod gage attached to E below the dry ice trap F. Where higher pressures have been used, the vacuum source has usually not included the booster pump.
Fractionation of Milk Fat by Short-Path Distillation
