214 



MANURES. 



Sect. X. 6. 2. 



I 



cefs I fuppofe the carbon is rendered capable of being abforbed by the 



of its being expanded into a gas ; 



i' 



la£leal veflels of vegetable roots. 



The black liquor, which flows from dunghills, is probably a fluid 

 of this kind ; but I mean to fpeak hypothetically, as 1 have not veri- 

 fied it by experiment ; and the carbon may be (imply fupported in 

 the water by mucilage, like the coffee drank at our tea-tables ; or 

 may be converted into an hepar carbonis by its union with the fixed 



■ 



alkali of decaying vegetable matter, or by the volatile alkali, which 

 accompanies fome flages of putrefa£lion. See No. 10. 3. of this Sec- 



r 



tion. 



r . 



2. A fecond mode of its ferving the purpofes of vegetation I believe 

 to be by its union with carbonic acid, and rendering it thus foluble 

 in water in its fluid flate inflead 



F 



and that thus a great quantity of carbon may be drank up by vegeta- 

 ble abforbent vefl^els. 



In the pradlice newly introduced of watering lands by deriving 

 flreams over them for many weeks together, I am informed that wa- 

 ter from fprings is generally more efFe6lual in promoting vegetation 



than that from rivers ; which 



the azotic gas, or nitrogen, contained in fome fprings, as thofe of 



Buxton and of Bath, according to the. analyfis of Dr. Prieflley, and 

 of Dr. Pearfon ; yet I fuppofe it to be principally owing to the cal- 

 careous earth, which abounds in all fprings, which pafs over marly 

 foils, or through calcareous ftrata ; and which does not exifl in rivers, 

 as the falts wafhed into rivers from the foil all feera to decompofe 

 each other, except the marine fait, and fome magnefian fait, which 

 are carried down into the ocean. The calcareous earth like wife, 



though it 



may in part be owing to 



which is wafhed 



enters into new combinat 



as into 



t> 



ypfum, or perhaps into filiceous fand, and fubfides. Thefe folut 



of calcareous earth 



thofe waters, which are termed bard waters 



and which incrufl the fides of our tea-kettles, may pofTibly alfc 



tribute 



y- 



