182 



CHEMICAL AFFINITY. 



SOLUBILITY OF SALTS IN 100 PARTS OF WATER* 



32 50" 68 86 104 122" 140" 158 176 194" 212 230" 



It will be observed that the perpendicular lines advance by 

 9 degrees, the first being 32% and the last 230. The solubility 

 of nitrate of potash increases from 13 parts in ICO water at 

 32, to 80 parts at 118, or very rapidly with the temperature. 

 Sulphate of soda is seen by the form of its curve to increase in 

 solubility from 5 parts at 32 to 52 parts at 92% but then to 

 diminish in solubility with farther elevation of temperature. 

 In this salt, sulphate of magnesia and chloride of barium the 

 solubility is expressed in parts of the anhydrous, and not the 

 hydrated salt. The lines of chloride of barium and chloride of 

 potassium are parallel, shewing a remarkable relation between 

 the solubilities of these two salts, which does not appear in any 

 others. The line of chloride of sodium is observed to cut all 

 the lines of temperature at the same height, 1 00 parts of water 

 dissolving 37 parts of that salt at all temperatures. 



Chemical affinity acts only at insensible distances, and has 

 no effect in causing bodies to approach each other, which are 

 not in contact, differing in this respect from the attraction of 

 gravitation which acts at all distances, however great, although 

 with a diminishing force. Hence, the closest approximation of 

 unlike particles is necessary to develope their affinities, and 

 produce combination. Sulphur and copper in mass have no 

 effect upon each other, but if both be in a state of great divi- 

 sion, and rubbed together in a mortar, a powerful affinity is 

 brought into play ; the bodies themselves disappear, and sul- 



