66 Royal Society : — 



December 10. — The Lord Wrottesley, President, in the Chair. 



The following communication was read : — 



" On the Chemical Action of Water on Soluble Salts." By Dr. 

 J. II. Gladstone, F.R.S. 



Before extending my researches on chemical affinity among sub- 

 stances in solution, it seemed desirable to ascertain, if possible, what 

 specific chemical action water exerts on a salt. This inquiry is beset 

 with unusual difficulties, and unfortunately my experiments have not 

 led to any conclusive result. Yet some of the observations made 

 during the course of the inquiry have a value independent of theory, 

 and a brief notice of them may not perhaps be deemed unworthy of 

 a place in the Proceedings of the Royal Society. 



It is well known that many anhydrous salts will absorb water, and 

 still remain solid bodies, either amorphous or crystallized. In such 

 a case the water combined is always in simple atomic relation with 

 the salt itself ; great heat is often evolved, and a change of colour 

 frequently ensues. These "hydrated" salts (as they are usually 

 considered) are generally soluble in water ; and it is the condition 

 of such a body when dissolved that opens a wide field for speculation. 

 The water may act merely as a solvent ; or it may unite without de- 

 composition with the dissolved salt, becoming an integral part of the 

 compound in solution ; or reciprocal decomposition may ensue, each 

 electro-positive element combining with each electro-negative one in 

 certain proportions ; or the ultimate result may be due to two or more 

 of these modes of action in conjunction. 



When a "hydrated" salt is dissolved in a minimum of water, 

 nothing is usually observed beyond the new physical properties 

 resulting from the change in its state of aggregation and the absorp- 

 tion of heat. No change of colour, as far as I can find, ever ensues, 

 though a change in the amount of fluorescence may occur. When 

 an anhydrous salt, which will not combine with water to form a 

 solid compound, dissolves, a change of colour does sometimes ensue. 

 Sometimes, however, an evident decomposition takes place, the hy- 

 drogen and oxygen of the water combining each with one of the 

 elements of the other binary compound, and the products of this 

 action remaining uncombined. Chloride of bismuth and citrate of 

 ammonia are instances. But in the vast majority of instances, the 

 salt MR and the water HO do not suffer reciprocal decomposition, 

 unless indeed, as has been contended, the resulting MO, HR remain 

 combined together in solution. 



If a reciprocal decomposition of this character actually occurs, it 

 may be anticipated by analogy, that by increasing the amount of HO, 

 more MR will be decomposed. Now, if additional water be added 

 to saturated aqueous solutions of pentachloride of antimony, ferric 

 sulphate, ammoniacal nitrate of copper, or nitrate of bisnmth, decom- 

 position results, and a precipitate forms proportional within certain 

 limits to the amount of water added ; but not one of these is a salt 

 of the simplest constitution. Sometimes, however, a change is ren- 

 dered apparent in simple salts by a change of colour without the 

 formation of a precij)itate. 



