536 On the Distillation of Binary Mixtures. 



was unlikely that a distillate could be obtained stronger than 

 about 90 per cent. As regards apparatus, the retort and 

 still-head are replaced by a long length (12 metres) of copper 

 tubing, 15 mm. in diameter. This is divided into two parts, 

 arranged in spirals, like the worms of common condensers, 

 and mounted in separate iron pails. The lower and longer 

 spiral was surrounded with water which was kept boiling. 

 The water surrounding the upper spiral was maintained at a 

 suitable temperature, usually 77° C. The copper tubes 

 forming the two spirals were connected by a straight length 

 of glass, or brass, tubing of somewhat greater bore, and pro- 

 vided with a lateral junction through which the material 

 could be supplied. The connecting piece and the spirals 

 were so arranged that the entire length was on a slight and 

 nearly uniform gradient, rising from near the bottom of the 

 lower pail to the top of the upper pail. On leaving the 

 latter the tube turned downwards and was connected with an 

 ordinary Liebig's condenser capable of condensing the whole 

 of the vapour which entered it. At the lower end of the 

 system of tubing the watery constituent is collected. In 

 strictness the receiver should be connected air-tight and be 

 maintained at 100°. In distilling the stronger mixtures (60 

 or 75 per cent, alcohol) this precaution was found advisable 

 or necessary ; but in the case of the weaker ones the water 

 could be allowed to discharge itself through a short length 

 of pipe whose end was either exposed to the atmosphere or 

 slightly sealed by the liquid in the receiver. 



The feed of the mixture was arranged as a visible and 

 rather rapid succession of drops, and was maintained at a 

 uniform rate. In the case of the stronger mixtures the 

 evaporating power of the lower coil was hardly sufficient, 

 and was assisted by applying heat to the feed, so that a good 

 proportion was evaporated before reaching the main tube. 

 The weaker mixtures on the other hand could be fed in with- 

 out any preliminary heating. The uniform regime should be 

 maintained long enough to ensure that the liquids collected 

 at the two ends shall be fairly representative and not com- 

 plicated by anything special that may happen before the 

 uniform regime is established. 



During the operation every part of the tube (not too near 

 the ends) is occupied by a double stream — an ascending 

 stream of vapour and a descending stream of liquid. Be- 

 tween these streams an exchange of material is constantly 

 taking place, the liquid, as it descends, becoming more 

 aqueous and the vapour, as it rises, becoming more alcoholic. 

 In view of the slowness of the feed and the length of the 



