DISTILLATION. 795 



one end of a siphon which is set up at a suitable height above 

 the apparatus for distilling ; or it may be connected with the water- 

 pipes in the house if they are available for the purpose, and the flow 

 may be regulated by means of the water-tap. If a siphon is used 

 the flow must be regulated by a pinch cock, which is placed upon 

 the india-rubber tube. In regulating the flow it is only requisite 

 that the lower portion of c c shall always contain cold water ; it does 

 not much matter if the water which flows off at e is pretty warm. 

 The liquid to be distilled is contained in a retort or flask for boiling, 

 and a glass-tube, bent once or twice at right angles and passing 

 through a cork in the neck of the flask, serves for conveying the 

 vapour into the tube a b. As the bore of a b should be rather 

 narrow, the perforated cork would have rather thin sides ; it is 

 therefore best to fix the tube which leads into a b by means of a 

 short piece of india-rubber tubing. If a retort with a narrow neck 

 is used, a clean wide india-rubber tube maybe simply slipped at one 

 end over the mouth of the retort and at the other over the opening 

 at a, thus establishing direct communication between the retort and 

 the condenser. The end b must sit loosely in the mouth of the 

 vessel in which the distilled liquid is received, so as to allow the 

 escape of the air from it, which is swept into it by the steam from 

 the retort or flask in which the liquid is boiled, and also to permit 

 any steam to escape which may not have been condensed in its 

 passage through the tube a b. 



The boiling should not be too strong, or drops of the impure 

 liquid might be carried over as a fine spray by the rapidly evolved 

 steam. 



That solid bodies remain behind in the distillation of a liquid 

 may be shown by adding to the water to be distilled a trace of 

 mao-enta and a little salt. The distilled water has no taste and is 



o 



colourless. The magenta is generally deposited upon the sides of 

 the boiling vessel, and may be removed by adding a few drops of 

 hydrochloric acid, and shaking the flask or retort. 



When about half of the liquid has passed over, the operation 

 should be stopped, as the flask or retort is apt to crack when the 

 quantity of liquid is considerably reduced. 



Like every other gaseous substance, steam has a 

 certain expansive force, in virtue of which it exerts 

 pressure on the sides of the vessel in which it is con- 

 tained. At the temperature of boiling water the pres- 

 sure, or tension, of the generated steam is exactly equal 



