1346
ANALYTICAL CHEMISTRY
been to move the controlled valve into a eeparate small vessel which is connected by a short wide tube to the sulfuric acid manostat. An automatic switch shuts off all power to the still if the pot pressure deviates appreciably from a chosen value. There is no real danger of loss of distillate through simultaneous turning of the funnel and discharge of the siphon. As the movement of the funnel is very rapid compared with the discharge of the liquid, only a small portion of any fraction can be lost, the rest being distributed between two tubes. However, if the off period is made long enough, it will exceed the limited period after the on period, during which siphoning can occur. This critical period depends on the on period, the boil-up rate, and the flow properties of the distillate, but in the authors' experience an off period of 5 minutes has proved more than sufficient for complete drainage of Cla alcohols. If siphoning does not occur within about 3 minutes after an on period, it will not occur until after the next on period. Therefore, if the on period is made sufficiently long, no loas of distillate need be feared.
provide high solvency and freedom from fire hazard. Tetrachloroethylene is somewhat preferable for laboratory use in that accumulation of water and resultant loss of solvent are minimized by its high boiIing point and Iow solubility for water, and a greater amount of solvent is condensable by an article of given thermal capacity. Precautions and Operating Rules. The unit should be covered at all times when not in use and should be placed in a hood or well-ventilated area to avoid the accumulation of toxic concentrations of vapors. Chlorinated hydrocarbon solvents are cumulative liver poisons; great care should be taken to avoid-inhalation of vapors. Flammable solvenh should not be used.
VAPOR ZONE
TO WATER T U tOOClNG MILS
