170 On Steam and Brines 



boiling mixture (/), and this temperature indicates quite 

 clearly the locality where the observation was made. The 

 second column contains the values of tT y from which, with 

 the first column, the values of T are at once obtained. The 

 third column contains the relative reduction of vapour tension 



f p P\ 

 J produced by saturating the water with the salt at 



its boiling temperature. 



The means of the observations at the same heights above 

 the sea are inserted between lines. 



The case of NaCl has been already discussed. The ob- 



, p 



servations with KC1 show a diminution of the value of 



P 



with a fall of barometric pressure, and consequent fall of 

 boiling temperature. This is observed in all the other salts 

 experimented with, and depends chiefly, if not wholly, on the 

 diminished solubility of the salt at the lower temperature. 

 Although, in kind, the effect is the same in all the salts, it 

 varies much in amount. It is most pronounced in the case of 

 KC1O 3 , for which the mean values are : 



Locality : . . . Edinburgh Pontresina Schaf berg 



t-T 3-8oC. 3'3oC. 3'o6 C. 



~7 0-I2SO 0-II38 0-I078 



It is also well marked in the case of NH 4 C1. This salt 

 also crystallises with great promptitude so soon as the tem- 

 perature falls at all. As is well known, salts differ much in 

 this respect. A large number of cooling observations were 

 made with NH 4 C1, and with some of the other salts, and 

 eutectic points were observed, but they are not of sufficient 

 importance for the present research to justify their being 



printed. The salt which appears from the value of ^ 



to vary least in solubility at its boiling-point is (NH 4 ) 2 SO 4 , 

 and in this respect it closely resembles NaCl. Nitrate of 

 sodium was observed only at Pontresina and Schaf berg. It 

 could not be observed near sea-level with either of the ther- 

 mometers used in the investigation. Nitrate of potassium 

 was excluded altogether from boiling mixtures both because 



