744 



JOHN JOHNSTON 



pressure of water which must be maintained in order to secure the 

 appropriate concentration. This vapor pressure becomes equal to 

 I atm. at about 120° (the ordinary boiHng-point of a saturated 

 aqueous solution of KNO3) ; increases, as we ascend the curve, to a 

 maximum, which in this case is only 2 or 3 atm., and finally de- 

 creases to zero at the point K. In systems such as this — namely, 

 in which the liquid may have (under the appropriate conditions) 



30Cf 



200 



30Cf 



ZO<S- 



FiG. 2. — To show the similarity between the equilibrium diagrams of the system 

 LiNO^-KNOa, H^O-KNO^, H^O-CrOj. 



any composition ranging from one pure component to the other — 

 the magnitude of the maximum equilibrium pressure depends 

 mainly on the melting-point of the salt; where the melting-point 

 is low, as for KOH, the maximum pressure is less than i atm.; 

 where it is high, as for potassium silicate, the maximum is some 

 hundreds of atmospheres. Nevertheless, as is evident from the 

 diagram, the lowering of melting-point produced by a comparatively 



