64 



Chemical and Physical Notes 



of the writer's observations in Switzerland at nine different 

 altitudes, varying from 400 to 2773 metres. It appears that 

 the alteration in the solubility of NaCl between the tempera- 

 tures 91 C. and 1 00 C. is so slight that the relative depression 

 of vapour tension is not sensibly affected. 



The practical value of these results is that, if a thermo- 

 meter be exposed to the action of pure saturated steam, and 

 to a boiling mixture of steam and NaCl, and the temperature 

 noted in each case, the difference of these temperatures, com- 

 pared with the tabular value of t T for the existing barometric 

 pressure, furnishes a direct and easily applied control of the 

 graduation of the thermometer over the observed range. 



TABLE VIII. Giving the Barometric Pressure at which a 

 Boiling Mixture of Steam and Chloride of Sodium has a 

 certain Temperature; the Limits of Temperature 

 109 and 99 C. 



For information about other salts in this respect, the 



reader is referred to the writer's paper on ' Steam and Brines.' 



Before passing from this subject attention may be directed 



