438 DR DUNCAN on Mudarine. 



The influence of temperature upon the power of solvents is 

 exceedingly curious and interesting. It has long been recog- 

 nized as a general law, that the proportion of solid principles 

 which are dissolved in fluids, is more or less increased by the as- 

 sistance of heat. Hence water, by decoction and digestion, com- 

 monly dissolves more speedily and more abundantly, than by cold 

 maceration, the soluble principles of compound bodies. . 



Various exceptions, however, to this general rule, have suc- 

 cessively been discovered. Sea-salt has long been known to be 

 equally soluble in cold and in boiling water. Afterwards, it was 

 found that lime and magnesia were actually more soluble in cold 

 than in boiling water ; and a still more remarkable relation be- 

 tween the solubility of certain saline substances and heat has 

 more recently been discovered. Sulphate of soda, and the nitrate 

 and muriate of barytes, by successive augmentations of tempera- 

 ture, have their solubility first slightly increased, then greatly 

 diminished, and again very rapidly increased. This phenomenon 

 is the less likely to be soon explained, that each salt follows in 

 this respect a different law, or that the curve of their solubilities 

 in relation to temperature in each is different. All the known 

 exceptions to the general law have been observed in the mineral 

 or inorganic kingdom, and from analogy we may conjecture that 

 many others exist in similar bodies, although not yet detected. 

 It is also necessary to remark, that when, in consequence of the 

 diminished power of the menstruum, whether by increase or di- 

 minution of temperature, the solvend is separated by precipi- 

 tation or crystallization, its nature is not altered, and it is equally 

 soluble in the menstruum as before, by diminishing or increasing 

 the temperature, or by adding an additional quantity of the sol- 

 vent. 



But, in regard to the organic kingdom, the law of increased 

 solubility, by increase of temperature, has been hitherto held to 

 be universal, except when the nature of the solvend is altogether 



