407] F. S. Holmes 209 



clay loam, and the third was a mixture, of equal parts, by 

 volume, of the other two. Pots of each kind of soil were 

 equipped with auto-irrigators having respectively one, three 

 and five porous cups, thus giving nine combinations. The 

 containers were tinned sheet-metal cylinders approximately 

 15 cm. in diameter and 17 cm. in height. The porous cups 

 were evenly distributed within the soil mass, when but one 

 was used it occupied the center. A mercury tube was so ar- 

 ranged that all water entered the soil against a pressure of 

 from 5 to 6 cm. of a mercury column. Evaporation was pre- 

 vented by sealing covers on the containers with plastiline. 

 The cylinders were filled to a uniform depth of 16 cm., an at- 

 tempt being made to secure as uniform packing as possible 

 throughout the entire series. 



Weighings of the containers were made at intervals of two 

 or three days, for the first twenty days, and thereafter at 

 weekly intervals, to determine the rates at which water was 

 being absorbed and to approximate the moisture content of 

 the soil. Approximately three-fourths of the water taken 

 up by the loam and by the sand-loam mixture occurred dur- 

 ing the first ten days, but the sand took up only about one- 

 half of its total amount in the same period. Approximate 

 equilibrium of the soil moisture content was reached in about 

 seventy-five days, in the case of the loam; in about eighty 

 days in the case of the mixture ; and in about ninety days in 

 the case of the sand. The number of porous clay cups em- 

 ployed seemed to have no influence upon the length of time 

 required for the attainment of equilibrium by either the loam 

 or the loam-sand mixture. With the sand, however, the 

 number of cups appeared to influence the length of this time 

 period. With three cups equilibrium was reached sooner than 

 with one, and with five sooner than with three. 



When the weighings of the cylinders and observations on 

 the water reservoirs showed that the soil had ceased to absorb 

 water, the cylinders were opened and samples were taken for 

 soil-moisture determinations. Two 1-cm., full-depth cores 

 were taken from each container, one core from as near a cup 



14 



