. The American encyclopædia of commerce, manufactures, commercial law, and finance. sul>-stance from others of ditterent degrees of volatil-ity with which it may be mixed. The theory andsuccessful execution of the process assume theirgreatest simplicity when the substances to be sep-arated differ so greatly in their volatility that,without appreciable error, one can be assunieil tobe nonvolatile at the boiling point of the good illustration of this special case is affordedby the customary process used for the purificationof water. A natural sweet water may in generalbe assumed to co
. The American encyclopædia of commerce, manufactures, commercial law, and finance. sul>-stance from others of ditterent degrees of volatil-ity with which it may be mixed. The theory andsuccessful execution of the process assume theirgreatest simplicity when the substances to be sep-arated differ so greatly in their volatility that,without appreciable error, one can be assunieil tobe nonvolatile at the boiling point of the good illustration of this special case is affordedby the customary process used for the purificationof water. A natural sweet water may in generalbe assumed to consist of three parts: 1st, waterproper, which always forms somelliing like HH percent or more of the whole ; 2d, non-volatile salts ;3d, gases. To obtain pure water from such ma-terial, we need only boil it in a distillation appara-tus, so as to raise from it dry steam, which steamwhen condensed yields water contaminated onlywith the gases. To expel these, all that is neces-sary is to again boil it for a short time; the off with the first portions of steam, so that the. lis 133 — CoMMOS DisTiLiiNO Apparatus residue, when allowed to cool in absence of air,constitutes inire water. In the IJ. of two substan-ces of api)roximately equal molecular weight andlatent heats of vaporization, supjiosing neither topredtuninate overwhelmingly over the other, theone with the lower boiling point will predominatein the early, and the other will gradually accumu-late in the later, fractions of the distillate. Andsimilarly with mixtures of three or more further the respective boiling points are re-moved from one another the more complete a sep-aration can be effected; but in no case is theseparation perfect. It is, however, easily seenthat the analytic effect of a O. can he increased bycausing the vapor, before it reaches the condenser,to unilcrgo inirlml condensation, when naturallythe less volatile parts chiefly will run back. Thisartifice is largely employed by chemists,
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