1072 



As a rule, however, in order to attain tliis solution, a withdrawal 

 or addition of water will be necessary in addition to a withdrawal 

 of KNO3. The general equation thus becomes: 



0,59 KNO3 I i 0,235 KNO3 ) 



0,41 NaCl = .V H,() 4- // KKO3 -h - 0,765 NaCl 

 2,83 H,0 ) ( 6,40 H,0 ^ 



If from this we calculate the values .x, y, and z, we find 



.i- = — 0,600 y = 0,464 ' c = 0,536. 

 x is negative, that is to say that to the liquid h must be added 

 water so as to prevent the point c to be surpassed. If this is not 

 done NaCl will deposit as well as KNO^ and the salpetre obtained 

 will be impure. 



In a continuous process the liquid obtained, c, will be again 

 converted into the solution b by addition of fresh NaNO, and KCl 

 in which case separation of NaCl takes place. 



The transformations of h to c at 5° and from c to b at 100° now 

 take place according to the subjoined equations: 

 ^ 0,59 KNO, I I 0,235 KNO, 



0,41 NaCl + 0,600 H,0 = 0,464 KNO, + 0,536 0,765 NaCl 

 2,83 H,0 I I 6,40 H,0 



and 



. 0,235 KNO, 1 i 0,59 KNO, 1 



0,536 0,765 NaCl + 0,464 KCl + 0,464 NaNO, =- 0,41 NaCl + 

 I 6,40 H.,0 \ \ 2,83 H,0 ) 



+ 0,464 NaCl + 0,600 H,0. 

 Hence, we have reverted to the initial condition, namely 1 gr. 

 mol. solution b of 100°, being 134,5 grams and during the circulation 

 process we have converted 0,464 grm. mols of NaNOj or 0,345 grm. 

 mols. per 100 grams of solution. On cooling, 0,6 mols. = 10,8 grams 

 of water had to be added to this solution which on raising the 

 temperature to 100° had again to be evaporated. 



II. If we start again from a solution in which equivalent quantities 

 of NaNOg and KCl are dissolved and allow the evaporation again to 

 take place at 100°, but the crystallisation of KNO3 at 25°, the final 

 solution becomes c' (coinciding incidentally with P., at 25°) 0,64 

 NaCl, 0,36 KNO3, 5,01 H,0. 



The reaction taking place when the liquid h is cooled, is then: 

 ,0,59KNOJ iO,64NaCl 



^ !o,41 NaCl + 0,321 H,0 = 0,305 KNO, + 0,504 0,36 KNO, 

 ^i2,83H,0 ) (5,01 H,0 



