Headden — SiliciG Acid in Mountain Streams. 171 



the water carried H'S grains of mineral matter in each imperial 

 gallon, 1 per cent of which was siHcic acid ; at Bonn it carried 

 11'9 grains, 5 per cent of which was silicic acid ; at Arnheim, 

 ll'l grains, of which 6 per cent was silicic acid. The Rhone, 

 sample taken near Geneva, yielded 13 grains total solids to the 

 imperial gallon, of which 8*2 per cent was silicic acid ; this, 

 8'2 per cent, is, with the exception of the 21 per cent for the 

 sample of Rhine water taken at Strassburg, the maximum 

 shown by the forty-five European rivers. 



Spring waters as a rule carry still smaller amounts of silicic 

 acid than the river waters. Thirty-two analyses given in Watts 

 Chem. Diet., Art. Water, show IT and 22 as maximum per- 

 centages, the total solids being 7"3 and 4"3 grains respectively. 

 Analyses of twenty-nine artesian waters show 3 per cent as the 

 maximum quantity of silicic acid present in their mineral 

 matter, which in this sample equalled 36*7 grains per gallon. 



Mineral springs sometimes show larger percentages of silicic 

 acid in their mineral constituents, but even these, the springs 

 of the- Yellowstone i^ational Park and one or two others, gey- 

 sers, excepted, show maxima of 18 and 23 for the percentages 

 of silicic acid in their total solids. This statement is based on 

 the analyses of 179 American and QQ foreign mineral springs. 



I deem these data sufficient to justify the assertion that sil- 

 icic acid usually constitutes a comparatively small percentage 

 of the total solids contained in the waters of fresh and mineral 

 springs as well as of those contained in river waters. 



The lake and oceanic waters, particularly the latter, have 

 suffered such varied and deep changes in regard to the compo- 

 sition of their mineral content that the silicic acid has either 

 been entirely removed or its quantity has been reduced to a 

 mere trace ; the maximum that I can find given is 0*05 per 

 cent of the total solids present. It is usually absent. 



The water of the springs of the Yellowstone National Park, 

 and of a few others, contains silicic acid in very notable quanti- 

 ties. Such springs frequently, if not always, have an elevated 

 temperature. This, however, is not the case with the springs and 

 wells referred to; and the rivers, as is well known, have a low 

 temperature, their waters being cooled by the melting of snow 

 accumulated within the areas of their drainage. The presence 

 of silicic acid in the waters of the former class of springs is 

 attributed to' the action of heated water aided by pressure and 

 the presence of alkalies. The heat in these cases is of volcanic 

 origin, a residual volcanic effect, while the alkalies are supposed 

 to be obtained from the alteration of the various kinds of fel- 

 spars, one or more of which is present in most kinds of rocks, 

 especially in volcanic rocks. Such theories are in no manner 



Am. Jour. Sci.— Fourth Series, Vol. XYI, No. 92.— August, 1903. 

 12 



