DISTILLATION 



115 



placed, and put it on a sand-bath, as shown in Fig. 86. Let the neck of 

 the retort pass into the neck of a flask suitably supported over a basin of 

 water. By means of a Bunsen burner boil the water in the retort, and 

 keep the flask cool by continually pouring water on to it. Notice that the 

 steam which passes over into the flask is condensed again into water, which 

 is quite clear and tasteless. 



iii. The distillation of alcohol. Fit up the apparatus as shown in Fig. 

 88. Note that the lower tube of the condenser is to be attached to the 

 water tap, and the upper to run into the sink. Place a mixture of alcohol 

 and water in the flask. Heat gently, and collect as much liquid as possible 

 that distils at the boiling point of alcohol, 78 C. Examine the resulting 

 liquid. Will it burn ? 



Condensation. By heating a liquid the liquid is changed into vapour. 

 This change may take place slowly and gently, as in evaporation ; or 

 quickly and vigorously, as in boiling. But by -whichever process 

 vapour is obtained, it can, by the 

 reverse plan of cooling it, be recon- 

 verted into liquid. This change, 

 from the state of vapour back 

 again to the condition oi liquid, is 

 called condensation, and the vapour 

 is said to have been condensed to a 

 liquid. Water- vapour is invisible, 

 but when it is cooled sufficiently, 

 visible particles of water are formed 

 from it. This can easily be seen 

 by boiling water in a flask fitted as 

 in Fig. 87. Water- vapour is pro- 

 duced inside the flask, but it cannot 

 be seen. When, however, the hot 

 vapour issues from the tube into 

 the colder air outside it is con- 

 densed, and particles of water 

 become visible as steam. A cold 

 plate held close to the spout of a 

 kettle from which steam is coming 

 will cool the steam, converting it 

 into water, which will be seen 

 trickling down the plate. 



Common instances of condensation. Most boys and girls have 

 noticed the condensation of vapour taking place at some time or other 

 on a cold day. For instance, if the doors and windows of a room are 

 kept tightly closed, and there is a good fire burning, the inside of the 

 window panes soon becomes covered with moisture, which, forming 



FIG. 87. The invisible water vapour is 

 condensed into visible steam when it comes 

 in contact with the cooler air. 



