ANALYSIS OF DRAINAGE WATIHIS. 91 



tlian the external atmosphere ; hence the air coming up 

 from tlie drain-pipes may contribute to keep the tempera- 

 ture of tlie arable siirfoce higher than it would be without 

 this current of aii\ The air in the drains is generally 

 richer in carbonic acid than is the case with atmospheric 

 air. 



The effect which drainage produces upon the fertility 

 of land may in itself be deemed a proof that plants 

 cannot derive their food from the water moving about in 

 the soil. This view is strongly supported by the analysis 

 of well, di-ain, and spring water. (See Appendix D.) 



The di\ainage-waters contain all the substances which 

 the rain-water, percolating the surface soil, is capable of 

 dissolving : they contain various salts in trifling propor- 

 tions, and among these mere traces of potash ; ammonia 

 and phosphoric acid are generally absent. In analyses 

 specially made for this purpose, Thomas Way found that 

 in four (drainage) waters no appreciable quantity of potash 

 could be detected in 10 pounds of water; three other 

 waters were found to contain from 2 to 5 pounds of 

 potash in 7,000,000 pounds of water. In three waters 

 no appreciable quantities of phosphoric acid could be 

 discovered : four other waters were found to contain 6 to 

 12 pounds of phosphoric acid, and 0-6 to 1-8 pounds of am- 

 monia in 7,000,000 pounds of water. In a similar series 

 of analyses, Krocke]- found that ni six drainage-waters 

 no appreciable traces of phosphoric acid or ammonia 

 coidd be detected ; while four other drainage-Avaters 

 were found to contain not above 2 parts, and two others 

 severally 4 and G parts of potash, in 1,000,000 parts 

 of water. 



The facts now stated are corroborated by a series of 

 direct and most instructive experiments made by Dr. Fraas, 

 to ascertain what substances the raiii faUin^ in the six 



