CHAPTER V. 



CHEMICAL HISTORY OF LAKE LAHONTAN. 



Section 1.— GENERAL CHEMISTRY OF NATURAL WATERS. 



The investigation of the chemical history of a lake properly begins 

 with the study of the meteoric waters that supply its hydrographic basin. 

 Lakes are filled to some extent by direct j^recipitation from the atmosphere, 

 but mainly by tributary streams and springs ; it is evident, therefore, that 

 we should look to these channels for the sources of the dissolved mineral 

 matter which all lakes contain. It is true that lakes are sometimes formed 

 by the isolation of portions of sea water, or may occur over beds of salt or 

 other easily soluble rocks; but such cases are exceptional and their abnor- 

 mal character easily accounted for. 



RIVER WATER. 



Even rain water and freshly fallen snow are not absolutely pure, but 

 usually contain some organic and saline matter, together with carbonic 

 acid, nitrogen, ammonia, chlorine, etc., which have been dissolved during 

 their passage through the atmosphere. In an arid region, like the Great 

 Basin, where the soil is commonly alkaline, and its surface frequently coated 

 over large areas with saline efflorescences, the dust that is carried high in 

 the air by the winds is richly charged with soluble salts which are dis- 

 solved by the falling rain, thus rendering it less pure than the meteoric 

 waters of more humid regions. Rain water on reaching the earth dissolves 

 the more soluble minerals with which it comes in contact, and becoming 

 charged with carbon dioxide (carbonic acid), together with Inimic and 

 crenic acids, and other organic products, it forms such an energetic solvei'' 



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