ill. J PERCOLATION OF WATER 89 



capacity for water, or pore space, may not vary very 

 greatly for different soils, there is a much wider and 

 more important divergence between the amounts of 

 water they will retain by surface tension alone, this 

 latter being the important factor in judging of the power 

 of the soil to retain a reserve of moisture for crops. 



It will, however, be found that this determination, 

 like that of the maximum water capacity of the soil 

 (p. 73) will vary somewhat with the same soil according 

 to the condition in which it is left after sampling and 

 preparation for analysis. It is practically impossible 

 to reproduce in the laboratory the state in which the 

 soil existed in situ or to bring into the laboratory an 

 unchanged sample of the soil in the field. In con- 

 sequence the conclusions that can be drawn from 

 determinations of maximum and minimum water capacity 

 of the soil are limited and of little service in practice. 

 Of more value is a determination of the optimum 

 working condition of a soil, a conception introduced 

 by F. K. Cameron. It represents that condition of the 

 soil in which it is neither too dry nor too wet to be 

 worked, when under the operations of cultivation it can 

 be readily broken down into fine aggregates without 

 becoming puddled. It is the condition that must be 

 attained on a strong soil before it can be made into 

 a good seed bed. 



Several pounds of the dry soil are placed in a large 

 basin and slowly wetted with a fine spray of distilled 

 water, care being taken with a clay soil not to over wet 

 any portion. The soil is carefully worked about with 

 the hands to equalise the wetting, and it will be found 

 that a point is eventually reached when the soil is 

 distinctly moist, but yet can be broken down to a crumb 

 without getting into a pasty condition. With a heavy 

 soil time must be given as this condition is neared, the 



