AN APPARATUS FOR MAXIMUM OR MINIMUM BOILING-POINT STUDY
The experiment involving the study of maximum or minimum boilingpoint mixtures is generally carried out as follows: The apparatus is arranged for ordinary distillation. Successive samples of the mixtures are slowly distilled and samples of distillate and residue collected corresponding to the various boiling points. The samples withdrawn are then analyzed and the mole fractions plotted against the boiling points. The object of the sampling is to'obtain a small amount of the vapor and the liquid phases which are a t equilibrium with each other a t a known boiling point. The distillate coming over a t that particular moment should have as nearly as possible the same composition as the vapor phase. For this purpose i t is desirable to make the stillhead and condenser rather short to avoid as far as possible any time lag in the condensation of the distillate sample. In the arrangement of apparatus described above, which is that described in a t least two widely used laboratory manuals of physical chemistry,* the error due to differences in composition of the vapor phase in different parts of the system is not eliminated. The following is a description of an apparatus (see illustration) which permits the collection of samples of distillate in equilibrium with the residue a t any temperature within the range of boiling points of the liquids used. The condenser consists of a tube (A), the opening a t one end (B) being at the side rather than a t right angles to the axis of the tube. The condenser is arranged so as to reflux the liquid with the opening (B! down. The distilling flask (C) consists of a 500-cc. round-bottomed flask to which is sealed a side tube (D). To remove samples of residue and distillate, the source of heat is removed and the condenser ( A ) rotated 180° on its axis. The vapor in the r d u x condenser (in equilibrium with the liquid) condenses and collects in the cup formed when the opening (R) of the tube (A) is up.
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* MACKAND FRANCE, "A Laboratory Manual of Elementary Physical Chemistry," 1st edition, D. \'an Nmtmrd Co., New York City. 1928, pp. %SO. I)ANIELS. MATIIRWS. AS" \\IILLLIMS. " I < x ~ ~ r i ~ n e n Physicill tsl Chemistry." 1 ~ rdition, t hIcCraw-Hill Rook Co.. New York City, 1929, p. 59. 1114
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The thermometer is then removed and samples of both distillate and residue can be taken with a pipet through opening D. The author has made use of this apparatus in his laboratory sections in physical chemistry for two years and finds that i t is easier to set-up and manipulate than the apparatus ordinarily described for the same purpose. The boiling point becomes constant for each mixture and the temperaturecomposition curves have thus far been better than those obtained with the ordinary distillation method.
