Geology 



there are also other bodies, such as oxides, sulphides, 

 titanates, and phosphates, present in smaller quantities. 

 It has been proved that a molten igneous magma is in 

 reality a solution, and that it obeys the laws of ordinary 

 solutions. Now it is a well-known fact that common 

 substances as salt, sugar, saltpetre, and washing soda 

 are much more soluble in hot than in cold water. If a 

 hot saturated solution of one of them be made and 

 allowed to cool, the solid will separate out as crystals, 

 until only the quantity appropriate to the lower tempera- 

 ture will remain in solution. Finally, if the cooling be 

 continued, the water itself will crystallize out as ice, and 

 the whole mass will be solid. In cases of this kind it is 

 customary to speak of the water as the solvent, and of 

 the crystals as the dissolved substances, but there is 

 really no difference in their condition when in complete 

 solution, both are then in the liquid form, and their 

 relationship is mutual. 



Solutions of one liquid in another are also known, 

 and in some instances there is no limit to their mutual 

 solubility. For example, alcohol and water can be 

 mixed in any proportion, and can only be separated by 

 distillation. 



Other liquids only dissolve in definite proportions, 

 while others again are mutually insoluble. A very in- 

 teresting example is to be found in the case of phenol 

 (carbolic acid) and water. At temperatures of 68 

 Fahrenheit and over, these liquids can be mixed in all 

 proportions, and if a mixture, say, half-and-half, be made 

 at that temperature, and then allowed to cool, it will 

 separate into two layers, one of which will consist of 

 water with a little phenol, and the other of phenol with 



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