. in vsicvio and in Gases, nic^il / }/i 273 



artificial atmospheres, the thermometers being immersed in the 

 vapour, necessarily gives accurate results for homogeneous liquids 

 when the actual pressure is exactly determined ; for it is by this 

 method that the boiling-point of thermometers is fixed. But 

 vv^hen solutions of fixed substances in volatile fluids, or mixtures 

 of several unequally volatile matters are in question, the tension 

 of the vapour may be very difi'erent according as it is determined 

 in the static condition, if I may use the expression, — the vapour 

 and the volatile liquid being both immersed in a medium of 

 invariable temperature, — or in a dynamic state^ under the influ- 

 ence of a current of heat which traverses the apparatus, the 

 liquid receiving the heat which produces the vaporization, whilst 

 the vapour is subjected to refrigerating agencies which produce 

 its partial condensation. The limits which I am compelled to 

 observe in this note prevent me from giving further development 

 to these considerations. 



Part II. — On the Boiling-points of Saline solutions. 



Everyone knows that saline solutions require a higher tempera- 

 ture to boil them than pure water under the same pressure. For a 

 given salt the excess of temperature increases in proportion to 

 the quantity of matter dissolved. All soluble substances do not 

 possess in the same degree the faculty of retarding the boiling- 

 point of the water in which equal weights of them are dissolved. 

 This faculty does not depend only upon their solubility; it appears 

 to result principally from a special affinity of the substance for 

 water. 



Rudberg has made the very curious observation, that when 

 concentrated saline solutions are kept boiling at temperatures 

 much above 100° C. under the ordinary pressure of the atmo- 

 sphere, the vapours which they emit nevertheless only possess 

 the temperature which they would present if they were disen- 

 gaged from pure water in ebullition under the same pressure. 

 Rudberg has made a great number of experiments on the most 

 various solutions, and with very exact instruments. The con- 

 clusion which he has drawn from them is as follows : — Whatever 

 temperature a solution must attain before boiling, the vapour never 

 presents a higher temperature than that which it would have had if 

 it had been disengaged from pure water ; in other words, it presents 

 the temperature at which the tension of this vapour, at saturation 

 in vacuo, is in equilibrium tvith the pressure under which the ebul- 

 lition takes place. This conclusion must of course refer, not only 

 to the saline solutions experimented upon by Rudberg, but also 

 to all solutions in a volatile liquid of substances which are fixed 

 at the temperature of its ebullition. 



It is not difficult to account for this circumstance, that a saline 

 PML Mag. S. 4. Vol. 8. No. 52. Oct. 1854. T 



