118 ELEMENTS OF LABORATORY WORK 



collected, and the rest rejected. The last portion also is 

 freshly distilled, and the vapour coming off below 99 C. is re- 

 jected. If necessary, this process of fractional distillation is 

 repeated until liquids of constant boiling-point are obtained. 

 The boiling-points are those characteristic of alcohol and 

 water respectively. A determination of their density will 

 also indicate that they are different kinds of matter. 



A liquid which gave no indication of its complex constitu- 

 tion has now been resolved into two different kinds of matter, 

 which cannot themselves be further resolved by this process. 



THERMOMETER 



COLD WATER. U JO WASTE 



Fig. 40. 



The temperature of the vapour coming from the surface of 

 each during ebullition does not -vary, except so far as the 

 pressure of the atmosphere may vary. Each liquid is, with 

 regard to this operation, the same in all its parts. Each 

 liquid possesses a specific boiling-point and a specific density. 

 So far they are distinct and individual. 



77. Changes observed when Silver Nitrate is maintained 

 at a High Temperature. Weigh a clean dry crucible. Intro- 

 duce a small quantity of pure dry silver nitrate, and weigh again. 

 The known quantity of silver nitrate is then gently heated by 



