of Solutions of Soda and Potash. 367 



depended on the supposition that never more than two 

 hydrates coexisted in solution, whereas my results with the 

 freezing-points of soda solutions prove that at least four or 

 five hydrates may coexist (Chem. Soc. Trans. 1893, p. 897). 



Table IV. % gives the densities of soda solutions for every 

 round value of percentage strength, as constructed from the 

 readings of a figure similar to that in the diagram, the values 

 having been differentiated and the differences plotted out in 

 order to detect any errors which may have been made in 

 taking the readings. 



Results with Potash. 



The results with potash (Table V.) are much less interesting 

 than those with soda. They have been plotted out in a variety 

 of ways, and indicate the probable existence of four breaks ; 

 but none of these are by any means well marked, and they 

 would not repay the trouble of a more critical examination. 

 The probable positions of these breaks are : — 



43*2 per cent, corresponding to KOH + 4*05 H 2 0. 



35*4 „ „ „ KOH-J-5-68H 2 0. 



19-0 „ „ „ KOH + 13 H 2 0. 



8-0 „ „ „ KOH + 36 H 2 0. 



The first of these agrees with the recently isolated tetra- 

 hydrate (Chem. Soc. Trans. 1893, p. 298), and the second 

 occurs at the point where water ceases to crystallize from 

 the solution and the tetrahydrate begins to do so — a so-called 

 cryohydric point in fact. In many cases it has been found 

 that such a change of crystallization occurs at a point corre- 

 sponding to the composition of a hydrate existing, according 

 to independent evidence, in solution. 



It is noticeable that the densities in the case of potash 

 increase at an increasing rate with the strength, the reverse 

 being the case with soda. The sixth column in Table V. 

 gives the volume of unit weight of the potash in solution cal- 

 culated on the assumption that the water present occupies 

 the same volume as it would do if it were free. 



Table VI. contains the values for round percentage numbers. 



