IX.] CHEMISTKY OF NATURAL WATERS. 99 



found in fissures of the chalk in England. On the absence 

 of free hydrated alumina from soils, see Miiller, cited as above 

 (2), XXXV. 292. 



10. The organic matter dissolved by the surface-waters 

 serves to reduce to the condition of sulphurets the various sol- 

 uble sulphates which it takes up at the same time or meets 

 with in its course. These sulphurets, decomposed by carbonic 

 acid, which is in part derived from the atmosphere, and in part 

 from the oxidation of the carbon of the organic matter, give 

 rise to alkaline and earthy carbonates on the one hand, and to 

 sulphuretted hydrogen on the other. In this way, under the 

 influence of a somewhat elevated temperature, are generated 

 sulphurous waters, whether of subterranean springs, or of trop- 

 ical sea-marshes and lagoons. The reaction between the sul- 

 phurets thus formed and the salts or oxides of iron, copper, and 

 similar metals which may be present, gives rise to metallic 

 sulphurets. The decomposition of sulphuretted hydrogen by 

 the oxygen of the air produces native sulphur ; with which are 

 generally found associated sulphates of lime and strontia. By 

 virtue of these reactions, soluble sulphates of lime and magnesia 

 may be completely eliminated from waters, the bases as insol- 

 uble carbonates, and the sulphur as sulphuretted hydrogen, free 

 sulphur, or a metallic sulphuret. Moreover, as Forchharnmer 

 has pointed out in the paper already cited, sulphuret of potas- 

 sium in the presence of ferruginous clays is also completely 

 separated from solution, the sulphur as sulphuret of iron, and 

 the alkali as a double aluminous silicate. 



11. We have thus far considered the composition of sur- 

 face-waters as modified by the decay of vegetation, or by the 

 reactions between the matters derived from this source and the 

 permeated sediments. Not less important however than the 

 elements thus removed by substitution from sedimentary strata 

 are those which are liberated by the slow decomposition of the 

 minerals composing these sediments. 



It has long been known that in the transformation of a feld- 

 spar into kaolin, the double silicate of alumina and alkali takes 

 up a portion of water, and is resolved into a hydrous silicate of 



