SOLUTION. 1 S I 



last portions slowly and with difficulty, and at last when sa- 

 turated is incapable of overcoming the cohesion of more salt 

 that may be added to it. The solubility in water of another 

 body in the liquid state is not restrained by cohesion, and is 

 in general unlimited. Thus alcohol, and also soluble salts 

 above the temperature at which they liquefy in their water of 

 crystallization, dissolve in water in any proportion. Generally 

 speaking also those salts dissolve in largest quantity which are 

 most fusible, or of which the cohesion is most easily overcome 

 by heat, as the hydrated salts, and among anhydrous salts, 

 the nitrates, chlorates, chlorides and iodides which are all re- 

 markable for their fusibility. In this species of combination, 

 bodies are not materially altered in properties, indeed are little 

 affected except in their cohesion. 



The union also between a body and its solvent differs in a 

 marked manner from proper chemical combination in the re- 

 lation of the bodies to each other which exhibit it. Bodies 

 combine chemically with so much the more force as their 

 properties are more opposed, but they dissolve the more 

 readily in each other, the more similar their properties. Thus 

 metals combine with non-metallic bodies, acids with alka- 

 lies; but to dissolve a metal, another metal must be used, 

 such as mercury ; oxidated bodies dissolve in oxidated solvents 

 as the salts and acids in water ; while liquids which contain 

 much hydrogen are the best solvents of hydrogenated bodies, 

 an oil, for instance, of a fat or a resin, alcohol and ether dis- 

 solving the essential oils and most organic principles, but 

 few salts of oxygen acids. The force which produces so- 

 lution differs, therefore, essentially from chemical affinity in 

 being exerted between analogous particles, in preference to 

 particles which are very unlike, and resembles more, in this 

 respect, the attraction of cohesion. 



A more accurate idea of the varying solubility of a salt at 

 different temperatures may be conveyed by a curve constructed to 

 represent it, than by any other means. The perpendicular lines in 

 the following diagram, indicate the degrees of temperature which 

 are marked below them, and the horizontal lines, quantities of 

 salt dissolved by 100 parts of water. The proportion of any 

 salt dissolved at a particular temperature may be learned by 

 carrying the eye along the perpendicular line, expressing that 

 temperature, till it cuts the curve of the salt, and then hori- 

 zontally to the column of parts dissolved. 



