832 LOWERING OF TEMPERATURE BY EVAPORATION. 



to remove the vapour as fast as it is formed, the 

 evaporation proceeds at a much increased rate, and the 

 temperature of the liquid may fall to 15. 



A pair of bellows are best for the experiment. If none are at 

 hand, the current of air may be blown by the rnoutb through the 

 liquid, provided the warm air is first passed through cold water. 

 Fig. 401 shows a suitable arrangement for this purpose. A capacious 

 bottle is about half filled with water and closed by a cork, twice 

 perforated for the reception of two glass tubes, which have a width 

 of about 5 or 6 mm . One of the tubes which dips into the water 



FIG. 401 ( real size}. 



and goes nearly to the bottom of the flask has a piece of india-rubber 

 tubing attached to the end through which the air is blown in by the 

 mouth. The other tube is bent twice at right angles ; one end passes 

 just through the cork, and the other dips into a large test-tube which 

 may be clamped in the retort-stand and is one third filled with 

 ether. When air is strongly blown through the apparatus the 

 test tube becomes covered with a coating of ice, and a thermometer 

 dipped in the liquid falls to 15. 



The india-rubber tube should be pretty long, so that the experi- 

 menter need not be too near the test tube containing the ether. The 

 great quantity of ether vapour produced is apt to cause headache. 

 On account of the inflammability of the vapour, the experiment 

 should not be performed by gas or candle light. The india-rubber 



