EVAPORATION, BOILING TEMPERATURE, ETC. 21 



Pour the small portion of distillate first caught into a shallow tin 

 dish and see if it will burn. Pour some of the liquid remaining in the 

 flask into another dish and see if it will burn. 



DEFINITION. This process of changing a liquid into vapor 

 by means of heat and then of changing the vapor back into a liquid 

 by cooling it is called DISTILLATION. 



Because different liquids have different boiling points we are 

 often able to separate the liquids in a mixture as we have just 

 separated the alcohol from the water. It is not true, however, 

 that the alcohol has been entirely separated from the water by this 

 one distillation. The first portion of alcohol which passed over 

 and which we burned contained some water; the water which 

 remained in the flask at the close of the experiment likewise 

 contained some alcohol. To get the alcohol nearly free from 

 water it is necessary to re-distil several times. The factories 

 where alcohol is made in large quantities are called DISTIL- 

 LERIES because the alcohol when first made is mixed with 

 water and must be separated from it by means of distillation 

 (see Art. 447, page 394). We shall soon see that all the 

 kerosene and gasoline which we use have been separated from 

 petroleum by this same process of distillation. 



PROBLEMS 



NOTE. In solving the following problems always draw the three 

 horizontal lines to represent the three fixed temperatures and the two 

 vertical lines to represent the two scales as in Fig. 11. 



1. What reading on the centigrade scale corresponds to 100F.? 



Ans. 37%C. 



2. Lead melts at 326C. What is its melting point on the 

 Fahrenheit scale? 4ns. 618^F. 



3. Cast iron melts at 1200C. What is the melting point on 

 the Fahrenheit scale? 



1. If a certain sample of paraffin melts at 50C., what is its melt- 

 ing point on the Fahrenheit scale? 



5. If a liquid boils at 140F., what is its boiling point on the centi- 

 grade scale? 



6. Which is the higher temperature :- 10C. or 10F., and what 

 i> the difference (1) in Fahrenheit degrees, and (2) in centigrade 

 degrees? Ans. -10C.; (1) 4F.; (2) 2^C. 



