SOLUTION. 157 



12. SOLUTION. 



As stated under Water, the term solution is applied to any homo- 

 geneous liquid mixture that results when solids, liquids, or gases 

 an; brought in contact with a liquid and disappear in the liquid. 

 (There are a few instances of solution of a gas in a solid, and of a 

 solid in a solid.) Solutions are transparent, and the dissolved mate- 

 rial is so thoroughly disseminated that its particles cannot be dis- 

 tinguished by the eye from those of the solvent. Moreover, there is 

 perfect distribution of the dissolved matter and no tendency for it to 

 settle. An opalescent or opaque appearance of a liquid is evidence 

 that there is matter held in suspension, and this matter will settle in 

 time, or may be filtered out. Dissolved substances cannot be re- 

 moved by filtration, as they pass through the pores of the paper as 

 readily as the liquid does. 



For the majority of substances there is a limit to the amount that 

 can be dissolved in a given amount of liquid. This limit ranges 

 from an almost infinitesimal amount in some cases to a fairly large 

 quantity in others. Thus, at ordinary temperature, the amount of 

 ferric oxide that is dissolved by 100 c.c. of pure water is extremely 

 small, while about 90 grammes of crystallized magnesium sulphate are 

 dissolved. No substance is absolutely insoluble, but many are so 

 sparingly soluble that for practical purposes they are considered in- 

 soluble. In some cases two substances may be mixed in any pro- 

 portions, for example, water and alcohol. But usually the solubility 

 of one liquid in another is limited, and when two such liquids are 

 shaken together they separate after a time into two layers, the liquid 

 in each layer being saturated with the other liquid. Thus, when ether 

 and water are shaken together at ordinary temperature they separate 

 on standing with the lighter (ether) layer on top, and 100 grammes 

 of water dissolve 2.1 grammes of ether, while 100 grammes of ether 

 dissolve 11 grammes of water. Pairs of liquids which are only slightly 

 soluble in each other are known as immiscible solvents, and are often 

 employed in certain kinds of chemical work for transferring a sub- 

 stance from one liquid to another. This operation is known as ex- 

 traction, and depends for its success upon a great difference of solu- 

 bility of the given substance in the two solvents. The division of a 

 substance between two immiscible solvents, after thorough shaking 

 and separation of the liquids, is proportional to its solubility in each 

 solvent. If a substance is 100 times more soluble in chloroform 

 than in water, and its aqueous solution is shaken thoroughly with 

 chloroform, the concentration of the substance in the chloroform 



