ANALYSIS OF DKAINAGE WATEKS. 99 



of phosphoric acid or ammonia could be detected ; 

 while four other drainage-waters were found to contain 

 not above 2 parts, and two others severally 4 and 6 

 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 rain falling in 

 the six summer months takes up from the surface soil 

 and carries down into the deeper layers. 



In lysimeters, or underground rain-gauges specially 

 constructed for the purpose, a collection was made of 

 the rain-water, which trickled through a layer of earth, 

 6 inches deep by 1 square foot in transverse section, 

 from the 6th April to the Yth October. The rain-gauge 

 kept at a neighbouring observatory indicated, up to the 

 1st October, a fall of rain amounting to 480*7 millime- 

 tres (18*75 inches).* 



Four lysimeters were filled with the same earth 

 taken from the subsoil of the stiff clay at Bogenhausen ; 

 in two of them (III. and IY.) the earth was manured 

 with 2 pounds of cow's dung ; the other two were left 

 unmanured. Nos. II. and IV. were sown with barley. 



Calculated upon a square metre (10*75 square feet) 

 of ground, the following were found to be the quanti- 

 ties of water that had passed through. Dr. Zoeller 

 determined the amount of soluble substances contained 

 in the water ; the quantities of phosphoric acid and 

 ammonia were too small to be appreciable : 



* The lysimeter consisted of a square box, open at the top, closed at 

 the bottom ; at a depth of six inches from the open top a sieve was in- 

 serted, from which, up to the rim, the box was filled with earth. The 

 rain falling upon a square foot of surface, and trickling through the six 

 inches of earth, was collected beneath the sieve, in the box. The box was 

 buried in an open field, up to the border, so that the earth in it was level 

 with the surface of the field. Two lysimeters were filled with lime soils 

 from the banks of the Isar ; but one of them broke, and the water could 

 not be collected : hence the results obtained from the other lost their im- 

 portance as a comparative experiment. 



