Evaporator still-heads original form

Original Form of Evaporator Still-Head.—The general form of the apparatus, as originally designed, is shown in Fig. 37. Each section consists of three separate parts— 

The outer tube, a, of 22 to 24 mm. internal diameter, connected above and below with other sections, the length of each being about 10 or 10 5 cm.  

An inner thin-walled tube, b, of 7-5 to 8 mm. internal diameter and 60 mm. long, open at each end and widened below into the form of a funnel which rests on the constricted part of A and may be prevented from fitting it too accurately by fusing three or four minute beads of glass to the rim of the funnel. Two large holes, (b ), are blown on the sides of B near the top  

An intermediate tube, c, of about 14 mm. internal diameter and 50 mm. long, like a small inverted test 

When the vapour first reaches a section from below, a large amount of condensation takes place, and the narrow passage, 

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Choice of Still-Head.—A plain wide tube or one with spherical bulbs is the least satisfactory, but the pear still-head, owing to the diminished capacity of the bulbs and the increased efficiency, gives much better results. Of all forms, the evaporator is the best, because the capacity is very small relatively to the efficiency, and the amount of condensed liquid in it is smaller than in any other equally efficient still-head moreover, almost the whole of the condensed liquid returns to the still at the end of the distillation. With a liquid of low viscosity, like one of the lower paraffins, the quantity left in the still head is almost inappreciable, and in other cases it may bo reduced to a very small amount by disconnecting the apparatus, while hot, from the condenser, tilting the tubo from side to side to facilitate the flow of liquid back to the still and, if the original form of evaporator still-head is used, shaking out any liquid remaining in the funnels. 

Estimation of Loss by Evaporation. —The following may be taken as an example of the estimation of loss by evaporation. Mixtures of benzene and methyl alcohol, one with benzene, the other with methyl alcohol in excess (these liquids form a mixture of minimum boiling point), were distilled through an evaporator still-head of five sections of the original form, the distillation being stopped in each case when the middle point was reached. The following results were obtained ... 

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