Molecular distillation presents a method of separation for substances of high molecular weights which would suffer thermal decomposition at the higher temperatures that would be required for conventional distillation. In general, the separatory power of molecular stills is poor and in order to obtain relatively pure substances from mixtures, a series of redistillations may have to be performed. The distillation of individual substances under molecular distillation conditions is best characterized by an elimination curve which is a plot of the yield of the substance against the temperature of distillation. Composite curves, similarly, describe the elimination of a mixture of substances. It was the purpose of this investigation to study the distillation characteristics of several anthraquinone dyes by the determination of single and composite elimination curves, and to attempt to separate binary mixtures of dyes by various redistillation techniques. The glass centrifugal molecular still with a five-inch rotor and a ball-jar condensing surface available at the beginning of the investigation was almost completely reconstructed as an all-metal unit employing copper and brass as the materials of construction. Final design included a vacuum-enclosed drive for the rotor. Other modifications included a copper, magnetically-operated feed pump; copper tubing flow lines with silver-soldered connections; copper feed, residue, and distillate reservoir tanks; spark plug leads for heater and motor lead attachments within the vacuum system; feed and residue thermocouples employing copper tubing as part of the copper lead of the copper-constantan hot junction; a silicone gasket for seal of the bell jar to the base plate; a copper feed tube and nozzle; and a vacuum pumping system consisting of two vertical diffusion pumps connected in series and exhausted to two megavac pumps and a hyvac pump to evacuate the distillate tank. Initial tests were made to obtain a constant-yield oil and to standardize an operating technique. A mixture of light and heavy mineral oils was found to be a satisfactory constant-yield oil. Several tests were made using a continuous temperature rise technique in which the distillate fractions were collected as the temperature rose slowly over the collection increment. 1,4-Diethyl-diamineanthraquinone, 1,4-diisopropyldiaminoanthraquinone, and 1,4-dibutyldiaminoanthraquinone dyes were distilled using this method. A discontinuous temperature rise technique replaced the continuous technique when it became evident that this initial technique could not be satisfactorily standardized. Instead of a continuous temperature increase as distillation progressed, the temperature was held constant while fractions were collected for a predetermined time interval required for five nominal passes of the feed across the rotor. A standardized technique was then developed end used for all subsequent tests, The conditions of operation under the technique were as follows: pressure, 6 ± 1 microns of mercury, absolute; rotor speed, 2000 ± 50 revolutions per minute; feed rate, 65 ± 2 milliliters per minute; nominal number of passes of the feed across the rotor for each fraction, 2; and difference between the feed and residue temperatures, 10 degrees Centigrade. The oil solvent, constant-yield oil, was a mixture of 300 milliliters of light mineral oil to 350 milliliters of heavy mineral oil for each test. Three anthraquinone dyes, celanthrene red 3B, 1,4-diethyldiaminoanthraquinone, and 2,6-dimethyldiaminoanthraquinone, were distilled individually using the standardized technique. The elimination curves were plotted and the maxima found to be 121, 152, end 159 degrees Centigrade, respectively. Equal weight binary mixtures of celanthrene red 3B and 1,4-diethyldiaminoanthraquinone, celanthrene red 3B and 2,6-dimethyldiaminoanthraquinone, and 1,4-diethyldiaminoanthraquinone and 2,6-dimethyldiaminoanthraquinone were distilled to study the effect of difference in the temperature interval between elimination maxima on the composite curve. The effect of varying the weight ratio was studied by the distillation of binary mixtures of 2:1, 1:1, and 1:2-1/2 weight ratio of celanthrene red 3B to 1,4-diethyldiaminoanthraquinone. A tertiary mixture of equal weights of the three dyes used in binary mixtures was distilled to note the added complexity of the composite curve. Attempts to separate binary mixtures were made by extractive redistillation in which additional mineral oil was mixed with the cumulative fractions from the original distillation before redistillation and repeated redistillation in which the cumulative fractions were merely redistilled without addition of any more oil. It was concluded from the investigation that each dye in a mixture distills independently of the other dyes preset. The introduction of each two GHZ groups in the 1,4 position of the anthraquinone series was found to increase the elimination maximum by approximately 10 degrees Centigrade. From a study of the composite curves for the various binary mixtures, it was decided that identification of two substances in an unknown mixture was possible if the second substance was in quantity at least 1/6 that of the first substance and had an elimination maximum at least 20 degrees Centigrade different from the first substance. A comparison of the weight per cent of 1,4-diethyldiaminoanthraquinone removed from the mixture with celanthrene red 3B by the two redistillative techniques indicated that extractive redistillation provided better separation than repeated redistillation with 75.5 weight per cent removed from the cumulative fractions up to 140 degrees Centigrade compared to 68.7 and 52.8 weight per cents removed by the first and second redistillations, respectively. / Master of Science