CHEMISTRY OF NATURAL WATERS. 173 



that but few substances can entirely resist its action. By the time the sur- 

 face waters have united to form rills, they contain sufficient mineral and 

 organic matter to have a complex chemical composition. On through their 

 historj', as they form brooks, creeks, and rivers, and finally merge with the 

 ocean or some inland sea, they are constantly increasing their sum total of 

 dissolved mineral matter, and are at the same time concentrated by evapo- 

 ration. The waters of a river when filtered from all suspended matter and 

 evaporated to dryness leave a solid residue which is the principal portion 

 (the more volatile substances escaping) of the foreign matter held in solu- 

 tion. These waters are fresh in the every-day use of the term, but in fact 

 owe their pleasant taste and, to a great extent, their health-giving qualities, 

 to the mhieral substances held in solution. In the following table the an- 

 alyses of the waters of a number of American rivers are given, for the pur- 

 pose of indicating what salts are contributed to lakes in greatest abundance 

 by their tributaries. The principal impurities in nearly every instance are 

 calcium and carbonic acid, probably combined in the waters as calcium 

 bicarbonate; sometimes, however, calcium sulphate is in excess of any 

 other salt, as in the case of the Jordan River, Utah. Surface waters derive 

 their chemical impurities mainly from the rocks over which they flow, and 

 consequently vary in composition with the geological character of their 

 hydrographic basins. When draining a granitic or volcanic area they are 

 usually rich in potash and soda; when flowing over limestone they are fre- 

 quently saturated with calcium carbonate. This is illustrated in the Far 

 West by the streams entering the Bonneville and Lahontan basins In the 

 former they have their sources in the Wasatch Mountains where limestones 

 occur, and are usualh' rich in calcium carbonate; potash is commonly ab- 

 sent, and soda, if present, is comparatively small in amount. In the Lahon- 

 tan basin volcanic rocks predominate and the streams contain a higher 

 percentage of potash and soda than is usual in a region underlain by sedi- 

 mentarj' rocks. 



By inspecting the table it will be seen, as stated above, that the most 

 abundant of all the various substances carried in solution by the streams of 

 this country is calcium carbonate. On averaging the amounts given in the 

 tables we have 0.15044 part per thousand as the average of total solids. 



