36 
SOLUBILITY OF SALTS IN WATER AT HIGH TEMPERATURES. 
Concerning these ten salts the following remark may be made. If we write them 
down in the order of their melting points, beginning with the most fusible, we do not 
indeed find that the figures expressing their solubilities follow the same order. 
Though it is true that one example of this may be seen in the iodide, bromide, und 
chloride of potassium, such a relation could hardly be expected to be general amongst 
the rest, differing as they do in composition and in other properties. But if their 
solubilities are compared at temperatures of 100° and above, we find that the rate 
of increase of solubility follows the order of the melting points. In other words the 
ratio of the solubility at, say, 180°, to the solubility at 100°, is greatest in the most 
easily fusible, whilst the rest follow in regular succession. This is shown in the 
following table. 
Formula 
of salt. 
Melting 
point. 
Parts of salt* dissolved by 100 parts of 
water at 
Ratio of 
VI. to IV. 
Ratio of 
VI. to V. 
Ratio of 
V. to IV. 
0° 
100° 
130° 
180° 
1. 
n. 
III. 
IV. 
V. 
VI. 
VII. 
VIII. 
IX. 
AgNOg 
217 
121-9 
830 
1825 
? 
2-20 
KNOg 
339 
13-3 
265 
565 
? 
2-13 
KClOg 
359 
. 3-3 
56-5 
88-5 
190 
3-36 
2U 
1-56 
K 2 Cr 0 0 7 
400 
- 4-9 
102 
156 
285 
2-79 
1-82 
1-52 
KI ' 
634 
130 
204 
243 
327 
1-60 
1-34 
1-19 
KBr 
699 
53-4 
102 
118 
143 
1-40 
1-21 
1T5 
KC1. 
734 
29-2 
56’5 
66 
78 
1-38 
1-18 
1.16 
NaCl 
772 
35-5 
36-6 
40-3 
44-9 
1-23 
111 
1-10 
Na^SCfi 
860 
hydrates 
hydrates 
42-0 
44-2 
1-05 
K.SO, f 
? 
8-3 
25 
28 
34 
1-36 
1-21 
112 
The only salt which does not fall strictly into order is potassium sulphate; but 
concerning this we are in doubt as to the melting point, and since it gave a good 
deal of trouble the determinations of solubility at the higher temperatures may not 
be quite exact. It is difficult to believe that the relation we have indicated is merely 
accidental. 
* The solubility, when not the result of a direct experiment, is taken from the curve by 
interpolation. 
t The melting point of potassium sulphate is doubtful. It is probably higher than that of sodium 
sulphate. According to Carnelley ( loc. cit .) the potassium salts generally melt at temperatures above 
the melting points of the corresponding sodium salts. Thus : 
NaNOg, m.p. 316°, KNO s , m.p. 339°. 
On the other hand- 
NaClOg, m.p. 302°, 
Nal, m.p. 628°, 
Na 3 C0 3 , m.p. 814°, 
KC1, m.p. 734°, 
KC10 3 , m.p. 359°. 
KI, m.p. 634°. 
K 0 CO 3 , m.p. 834°. 
NaCl, m.p. 772°. 
