ON THE SOLUBILITY OF SALTS. 301 



would afford us data to lay the foundation of a rational theory. The scheme 

 embraces so much that I am in no danger of being suspected of the design 

 of executing it all. It may be asked, why then sketch a plan which I could 

 not execute ? Because, in the first place, as I have already endeavoured to 

 show, the determination of the true law of solubility of even a single salt, 

 involves the whole of the questions which this scheme of experiments is pro- 

 posed to investigate; and consequently, in any attempt to determine such a 

 law, the whole of them must of necessity be more or less studied. And in 

 the second place, because I believe that in the investigation of details we 

 are apt to forget the generalities to which they are subordinate, an error 

 which is avoided by following a plan in which every result, however trivial, 

 finds its place and immediate use. Science will gain more in this way than 

 by desultory experiments, which, in consequence of their isolation, remain for 

 a long time barren. 



1. I have found that many hydrated silicates, sulphate of lime, &c, when 

 immersed in water and exposed to a high temperature, lost part or all their 

 hydrated water. This suggests an important question— Do all hydrated salts 

 lose their water, if heated in that liquid to a very high temperature? And 

 if so, do any of them offer a similar phenomenon to that which certain 

 hydrated salts present when heated in the air, namely, of losing their water 

 in successive portions as the temperature rises? Thus, for example, the salt 

 2KO, PO, + 3HO loses one equivalent of HO at 100°, a second at 180°, and 

 the third only perfectly at a red heat. The question suggested here applies 

 to all salts that contain constitutional water. In such a salt as that above 

 mentioned, is each molecule held by a different amount of force? and does it 

 therefore enter with a different atomic volume into the compound ? or is each 

 equivalent held with the same force at the commencement of the operation, 

 the change of constitution being the result of a modification of equilibrium 

 produced by the heat? It appears to me that the study of the action of 

 saturated solutions of salts upon the crystals of the hydrated salt at different 

 temperatures would throw much light upon these questions, as well as upon 

 the very important one of whether hydrated salts retain their water in solu- 

 tion. I hope very shortly to be in a position to report upon this branch of 

 the subject. 



2. The second series of experiments is to be devoted to the investigation 

 of the influence which different proportions of an acid exert at different tem- 

 peratures upon the maximum solubility of the different salts which it forms 

 with such bases as do not yield any known higher acid salts than those ex- 

 perimented upon. Some singular anomalies are presented by salts in this 

 respect, as, for example, the well-known ones, KO, N0 5 being more soluble in 

 dilute nitric acid than in pure water, while BaO, N0 5 is precipitated from a 

 strong solution by nitric acid. A similar series must be made for the influ- 

 ence of bases upon the solubility of such salts as they form, with those acids 

 with which they do not yield recognizable basic salts. 



3. The next series will be devoted to the study of the influence which 

 different proportions of soluble acids exert, at different temperatures, upon 

 the maximum solubility of soluble salts containing a different acid soluble in 

 water, and with the base of which the intervening acid does not form an in- 

 soluble compound. In the cases contemplated here, there would be, accord- 

 ing to Berthollet, decomposition in proportion to the mass of the intervening, 

 acid. We have direct evidence of this when HC1 acts upon a solution of 

 CuO, N0 5 ; but hitherto we have had no means of proving it where the solu- 

 tions were colourless. Besides the obvious importance of such experiments 

 in connexion with the subject of affinity generally, I think they will afford 



