Headden — Silicic Acid in Mountain Streams. 183 



I stated above that it was a mistake not to have filtered off 

 the felspar before precipitating the iron oxid, for had I done so 

 I could have determined how much silica, if any, was carried 

 down with the oxid, but as it is we have an imitation of what 

 takes place in all river and spring waters where ferrous salts 

 occur, i. e. oxidation and precipitation of the ferric hydrate. 

 The analysis is too low when we subtract the whole of the car- 

 bonic acid and oxygen equivalent to the chlorin found. There 

 is no doubt but that the most if not all of the CO2 was expelled 

 upon ignition. I have found it to be almost completely expelled 

 even when there was not enough silicic acid to account for it, 

 and there is no means of judging how much was left in this 

 residue, if any, so I have subtracted the whole of it. If the 

 analysis were really badly made and the missing 3-3 per cent 

 were all sodic oxid, which is by no means the case, there would 

 still be a very considerable excess of acids. 



The general resemblance of these results except in the relative 

 quantities of potassic and sodic oxids is striking, the more so as 

 they agree with one another and are unlike ordinary river waters. 



the experiments with the felspar and the character of the 

 mine water show that they are such as are normally produced 

 by the action of water and carbonic acid upon this mineral 

 without the aid of higher temperatures or pressures. 



These experiments further indicate the course and character 

 of the action of water upon felspar— ^i. e. it attacks those mole- 

 cules containing calcium and sodium, possibly existing as mole- 

 cules of labradorite and albite, more readily than those contain- 

 ing potassium — further that the silicic acid is dissolved as such 

 by a process of hydration and exists in the solution as free silicic 

 acid or as a very complex or condensed acid : the former seems 

 much more probable. 



These facts, if they be accepted as such, account for the 

 character of the Rio Grande water, it being just such a water 

 as the local conditions would account for. The. spring and well 

 waters are simply the same water — i. e. water running into the 

 valley from the mountain streams and sinking into the lower 

 strata, which are composed of sands derived from the breaking 

 down of the rocks composing the adjacent mountains contain- 

 ing an abundance of felspar, and are not mixed with other 

 water or subjected to conditions which cause radical changes 

 in their dissolved mineral matter. 



These facts easily account for the silicification of vein matter 

 and the deposition of chalcedonic quartz, etc. in veins and else- 

 where. The possible influence of organic acids, especially at 

 the surface, has been suggested because it is so often mentioned. 

 I had an aqueous solution of humic acids and some pre- 

 cipitated and washed humus; a quantity of felspar was treated 



