COLOUR OF WATER. 263 



consideration as a chemical element. The 

 purest water with which we are acquainted, 

 is undoubtedly that which falls from the 

 atmosphere. Having touched air alone, it 

 can contain nothing but what it gains from 

 the atmosphere, and it is distilled without 

 the chance of those impurities which may 

 exist in the vessels used in an artificial ope- 

 ration. We cannot well examine the water 

 precipitated from the atmosphere as rain 

 without collecting it in vessels, and all artifi- 

 cial contact gives more or less of contamina- 

 tion; but in snow, melted by the sun beams, 

 that has fallen on glaciers, themselves formed 

 from frozen snow, water may be regarded as 

 in its state of greatest purity. Congelation 

 expels both salts and air from water, whether 

 existing below, or formed in the atmosphere ; 

 and in the high and uninhabited regions of 

 glaciers, there can scarcely be any substances 

 to contaminate removed from animal and 

 vegetable life, they are even above the mine- 

 ral kingdom ; and though there are instances 

 in which the rudest kind of vegetation (forms 

 of the fungus or mucor kind) is even found 



