542 ME J. Y. BUCHANAN ON 



be able to use directly the values observed at the existing pressure, and our table affords 

 the meaus of doing .so, assuming that the readings of our thermometers as corrected are 

 exaot. 



In Table III. are given the saturation values for the simple salts. They are arranged 

 in order of the temperature of the boiling mixture (t ), and this temperature indicates 

 quite clearly the locality where the observation was made. The second column contains 

 the values of f„ — T, from which, with the first column, the values of T are at once 



obtained. The third column contains the relative reduction of vapour tension (±-^ 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 observations with KC1 show a 



p — P 

 diminution of the value of — — :1 with a fall of barometric pressure, and consequeut 



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 KC10 3 , for which the mean values are — 



Locality : — 

 t-T, 



Ih 



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

 promptitude so soon as the temperature 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 suffi- 

 cient importance for the present research to justify their being printed. The salt which 



p — P 



appears from the value of ° to vary least in solubility at its boiling point is 



Po 



(NH 4 ) 2 S0 4 , and in this respect it closely resembles NaCl. Nitrate of sodium was 

 observed only at Pontresina and Schafberg. It could not be observed near sea level with 

 either of the thermometers used in the investigation. Nitrate of potassium was 

 excluded altogether from boiling mixtures both because of the great elevation of boiling 

 point, and on account of the readiness with which it solidifies to a crystalline mass the 

 moment the temperature begins to fall. 



The chief part of the research is contained in Table IV. Three columns are devoted 

 to each experiment ; namely, (t — T) the elevation of the boiling temperature of the 

 mixture or brine above that of pure water at the same time and place ; W the weight of 

 steam condensed in the time from the beginning of the experiment until the value of 

 t — T has become as tabulated ; and W(f — T) the product of the corresponding pair* of 



Edinburgh. 



Pontresina. 



Schafberg 



3-80° C. 



3-30° C. 



3-06° C. 



0-1250 



01138 



01078 



