PRACTICE XXVII 



A STUDY OF THE CAPILLARY POWER OF SOILS 



A class exercise to be arranged by the instructor. 



The capillary power of soils is influenced by several factors, 

 the most important being their physical composition, texture, and 

 compactness. In field soils all of these are changed by continu- 

 ous cropping, and capillary action is therefore altered. Of these 

 factors physical composition is most important. 



Prepare the tubes as in the preceding Practice. 



Tubes li to 2 inches in diameter are better for this and the 

 succeeding Practice than smaller tubes. 



Fill tube No. 1 with the stock sand or sandy loam. 



Fill tube No. 2 with brown silt loam. 



Fill tube No. 3 with clay or clay loam. 



Fill tube No. 4 with loess. 



Fill tube No. 5 with sand 50 per cent and loess 50 per cent. 



Fill tube No. 6 with sand 50 per cent and clay 50 per cent. 



Fill tube No. 7 with sand 90 per cent and peat 10 per cent. 



Fill tube No. 8 with loess 50 per cent and clay 50 per cent. 



Fill tube No. 9 with loess 90 per cent and peat 10 per cent. 



Fill tube No. 10 with clay 90 per cent and peat 10 per cent, 

 all finely pulverized and air-dry. 



Great care must be exercised in filling these tubes not to 

 separate the coarse particles and granules from the finer mate- 

 rial, especially in the mixtures. The mixtures may be made in a 

 large pan or by running through a grinder. Uniform filling may 

 best be accomplished by holding the tube perpendicularly while 

 pouring the soil in through a funnel. The tubes may be com- 

 pacted and supported as in the preceding Practice. Uniformity 

 in compaction is very important. 



Readings may be made by students in groups as in the preced- 

 ing Practice and recorded on a sheet posted for the purpose, 

 recording the total height to which water has risen at the end 

 of 1 hour, 2 hours, 3 hours, 6 hours, 9 hours, 12 hours, 24 hours, 

 and each day following for at least 14 days. 



Plot curves, using the data obtained at the end of 24 hours 

 and up to and including that secured on the fourteenth day. 



Why does loess show a more rapid rise than clay ? 



At the end of 1 hour which shows the greater rise, clay or the 

 20- to 40-mesh sand ? Which at the end of a week ? Why ? 



REFERENCES. The same as given under Practice XXVI. 



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