184 Headden — Silicic Acid in Mountain Streams. 



with distilled water just as in the experiments described with 

 the addition of a liberal quantity of these ; the results agreed 

 well with those obtained with water and COj alone after 

 deducting the fixed residue contained in the humus; the dura- 

 tion of this experiment was twenty-two days. I am not pre- 

 pared to state that such acids play no part in the decomposition 

 of rocks, but the result of this experiment indicates that they 

 play a less important part than the statements frequently met 

 with would indicate, and which, furthermore, the composition 

 of the ash obtained by incinerating them would also suggest. 



A remarkable feature in the result of these experiments is 

 the fact that while the felspar contains only a small percentage 

 of lime, less than two-tenths of one per cent, the residue 

 obtained on evaporating the water to dryness shows a large 

 percentage of it, 10 to 23 per cent. The strontia was detected 

 only when as much as live grams of felspar were used ; the 

 lithia, however, was detected in one gram, but both were easily 

 detected in the residue. This accounts for a characteristic of 

 our waters, i. e. the presence of strontia and lithia, and I inter- 

 pret this as strong corroborative proof that, however changed 

 the waters may be, they originally obtain the greater part of 

 their mineral constituents from the decomposition of the fel- 

 spars. The uniform presence of strontia and lithia in our 

 waters puzzled me greatly until the results of these experi- 

 ments revealed the source from which they might be derived, 

 as I knew of no lithia or strontia-bearing mineral in the 

 mountains which would account for their presence. Apropos 

 to the occurrence of these elements in felspar 1 may add that 

 of 2T1 analyses of felspars of all varieties which I have found 

 given, only three show lithia even in traces, and only two show 

 strontia. But being present in our case they serve to confirm 

 the view that the felspars principally furnish the mineral con- 

 stituents of the waters. The amounts of sulphates and chlorids 

 have their own particular interest, but the same importance 

 does not attach to them as to the silicic acid already more fully 

 discussed. 



State Agricultural College, Fort Collins, Colo. 



