1071 



eutecticum forms the terminus of the line indicating the change of 

 the point G with the temperature, the sohition G, at temperatures 

 somewhat below the eutecticum will contain less water than the 

 solutions of pure NaNOj or KNO3 saturated at the same temperature. 

 Uyeda's idea that the increased solubility of NaNO, by addition 

 of KNO3 would point to the formation of a double salt in solution 

 is, therefore, not confirmed. 



Application to the conversion process. 



Let us now see how from the figures obtained may be deduced 

 the most appropriate process for the preparation of potash salpetre 

 and let ns calculate the yield of the conversion in the following 

 methods of working. 



I. KCl and NaNOg are mixed in equimolecular quantities (say, 

 half a gram. mol. of each), dissolved in water and the liquid 

 evaporated at 100° isotherm. When the water content of the liquid 

 has sunk to in = 3,5 (point a in tig. 2) solid NaCl begins to deposit. 

 The composition of the liquid now changes in the direction ah. At 

 h (point of intersection with the line FP^) the solution is also 

 saturated with KCl. A further evaporation would then cause KCl to 

 deposit as wel as NaCl so that the liquid would change its composition 

 in the direction /^P, (100°). As we only wish to separate NaCl, the 

 water content may, therefore, not fall below that of solution h. The 

 solution h has the composition : 



0,59 K , 0,41 Na , 0,59 NO, , 0,41 CI , 2,83 H,() . 



The change of liquid a (0,5 NaNO,, 0,5 KCl, 3,50 HO,) to liquid 

 b and solid NaCl has then taken place according to the following 

 equation : 



0,5 Na 0,5 K 1 / 0,59 KNO., i 



0,5 CI 0,5 NO3 = 0,153 NaCl + 1,10 H,0 + - 0,41 NaCl 

 3,50 H,0 ) ^^ ( 2,83 H,0 ) 



{a) {h) 



Let us now imagine the solution h separated from the solid sodium 

 chloride and cooled to 5°. 



This solution lies in the diagram for h° in the region of KNO3 . 

 It is strongly supersaturated with KNO3 '<^^^ will allow this to 

 crystallise. Its composition then changes in the direction hac. The 

 most extreme solution attainable without depositing solid NaCl is 

 the solution c, the composition of which is 0,235 KNO3, 0>''^65 NaCl, 

 6,40 H,0. 



70 



Proceedings Royal Acad. Amsterdam. Vol. XVI 



