GALVANIC AGENCY. 53 



geine, and very often ammonia escapes from turf 

 ■when treated with caustic alkali." 



Professor Schiibler says that pure earths, such 

 as sand, lime, magnesia, and gypsum, when dry, are 

 nonconductors of electricity, and that clays are also 

 imperfect conductors. When oblong pieces of all 

 the earths are scraped with a knife, they develop 

 negative electricity. Experiments show that when 

 solutions of humus are exposed to a current of gal- 

 vanic electricity decomposition immediately ensues ; 

 the geine collects about the positive pole, and the 

 earths around the negative. Dr. Dana supposed 

 that by means of this galvanic agency the rootlets 

 of plants were enabled to attract alkali even from 

 the particles of felspar and mica in the soil, while 

 it was yet in an insoluble condition. If this is true, 

 it would depend, says Dr. Hitchcock, to a consider- 

 able extent, on the subdivision of its particles. If 

 this be allowed, the presence of alkali in a soluble 

 condition in the soil is not important when the 

 rocks are present which contain it in an insolu- 

 ble state, as the rootlets will supply themselves 

 from this source. This may be another of the 

 wonderful provisions of Providence for the well- 

 being of the plant, because of the liability of the 

 soluble alkalies to be washed away by rains, while 

 in their original condition these little rootlets alone 

 contain the key to their treasures. 



Earths are composed of different substances, be- 



