^ 8 Chemical and Physical Notes 



TABLE V. Giving the Tension of Saturated Steam in Milli- 

 metres and Inches, and the Corresponding Heights above 

 the Sea in Metres and Feet, for Temperatures in Celsius 

 degrees. 



the altitude, so that for the greatest altitude the thermometer 

 is the preferable instrument. 



Fixed Temperatures produced by Steam in contact with Salt 

 and Saline Solutions. At the same atmospheric pressure, the 

 tension of the vapour of water is reduced, not only by lowering 

 its temperature, but also, while the temperature is kept constant, 

 by dissolving any salt in it. The tension of the vapour of pure 

 water at 100 C. is 760 mm. If a small quantity of common 

 salt or chloride of sodium be dissolved in it, the tension of 

 its vapour is no longer 760 mm. at 100 C. ; it is necessary to 

 raise it to a higher temperature in order that its vapour may 

 attain this tension. In proportion as more salt is added to 

 the water, the higher is it necessary to raise the temperature 

 of the water, or rather the resulting saline solution, in order 

 to attain a tension of 760 mm. But there is a limit to the 

 amount of salt which water can dissolve when boiling under 



