of certain Mine Waters. 



167 



The water issuing from the back of the crosscut at Dolcoath 

 deposits in considerable quantities a soft reddish-grey precipi- 

 tate which frequently assumes stalactitic forms. Similar incrus- 

 tations, although generally less abundant, are found in nearly all 

 deep mines wherever water issues from the vicinity of a vein 

 and flows over the surface of the adjacent rock. 



Three analyses made of air-dried specimens of this substance 

 afforded the following: results : — 





I. 



II. 



III. 





36-30 

 trace 

 32-47 

 trace 

 2-65 

 12-77 

 15-90 



36-29 

 trace 

 32-52 

 trace 

 2-51 

 1252 

 15-98 



37-75 

 trace 

 32-55 

 •68 

 2-52 

 11-45 

 15-20 







Arsenious acid 







WateH ~ umumcu . 



[ hygroscopic 





10009 



99-82 



100-15 



Nos. I. and IT. are duplicate analyses of the same specimen, 

 made in my laboratory ; No. III. is an analysis of another spe- 

 cimen, made, at my request, by my friend Mr. Dugald Campbell. 



It may appear somewhat remarkable that a plentiful de- 

 posit of arsenate of iron should be formed from water in which 

 only traces of arsenic could be detected, and in which the amount 

 of iron present is so inconsiderable. On examining, however, 

 the jars in which the water had been collected for analysis, a 

 small amount of a flocculent brownish deposit was found at the 

 bottom of each; this, on being thrown on a filter and subse- 

 quently analyzed, was found to contain 31*52 per cent, of arsenic 

 anhydride and 25*27 per cent, of ferric oxide. The ferric 

 arsenate, together with a little clay, had been deposited before 

 the clear water was siphoned off for analysis; this accounts 

 for the small amounts of iron and arsenic retained in solution. 



These waters differ materially from those of the lithium spring 

 at Huel Seton, which contain above a thousand grains of solid 

 matter per gallon, while those from the Phoenix Mines and from 

 Dolcoath contain respectively but 14*91 and 46*97 grains per 

 gallon. The Huel Seton water is believed to be derived from 

 the sea by percolation through a fault; the waters, of which 

 analyses are now given, are probably the result of the infiltra- 

 tion of surface-water through the workings of the mines, and 

 through fissures in the respective veins. 



