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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 bismuth, 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 precipitate. 



This was closely examined. It might be expected, a priori, that 

 a certain amount of salt would have the same absorbent effect on a 

 given quantity of light, whether it were dissolved in much or little 

 water, and that as the absorbent power of water is practically nil, it 

 would appear to the eye of precisely the same depth and character 

 of colour in the two cases. And this actually holds good in the 

 majority of instances ; but to prove it a special contrivance was 

 necessary, in order to make the same quantity of light impinge upon 

 the solution before and after dilution. This was effected by means 

 of colourless cylindrical glasses of uniform diameter and the same 

 size, closed at one end with a flat plate of glass, so that when placed 

 upright they could hold liquids : they stood in a case so contrived 

 that all the light which passed through the strong or diluted solu- 

 tion, as looked through from above, had to enter by the flat plate 



