62 



Chemical and Physical Notes 



by the salt at the bottom of CB. The tube is then weighed. 

 It is then connected with the steam generator and steam 



blown through, which in a 

 few minutes produces a mag- 

 ma of boiling brine mixed 

 with salt, while the thermo- 

 meter takes the maximum 

 temperature, and retains it 

 until the solid salt approaches 

 complete solution. 



The graduation of the 

 thermometer thus receives a 

 useful check at this part of 

 the scale. If it is wished to 

 verify the thermometer at 

 any temperature intermediate 



between 100 C. and io8'4 C, steam can be passed through 

 until the temperature of the boiling solution has fallen to the 

 degree wished, and by weighing the apparatus, or determining 

 the chlorine, the amount of steam condensed is found ; and, 

 as that of the salt is known, the strength of the solution, 

 which boils at this particular temperature, under the observed 

 barometric pressure, is obtained, and that temperature can 

 always be again recovered independently of the thermometer 

 with which the original observation was made. 



The elevation of the boiling-point of a saturated solution 

 of a salt above that of pure water is affected by the barometric 

 pressure. For chloride of sodium the rise may amount to as 

 much as 8'45 C. at the sea-level ; and in the course of 

 experiments made in Switzerland it has been found to fall 

 to 8-o C. at a height of 2770 metres above the sea. If, 

 however, we represent by t the boiling temperature of the 

 saturated solution, and T the boiling-point of pure water at 

 P, the barometric pressure at the moment : then, if / be the 

 barometric pressure under which pure water would boil at 

 temperature /, the ratio / : P appears to be constant, and 

 equal to i'345. 



In Table VII we find the barometric pressure (P), given 



