Sand. The sand to be employed should be as nearly like that 

 used by McCall as is possible. (A sample may be obtained from 

 Dr. A. G. McCall, Maryland Agric. Exp. Sta., College Park, Md.) 

 This sand shows about 98 per cent, of SiO^ The grains are not 

 much rounded (artificially crushed quartz should not be used 

 in the present cooperation nor should thoroughly rounded sand 

 be used) . The mechanical analysis (by sieves) shows the follow- 

 ing proportions as to diameters of particles: 1.0 to 0.5 mm., 

 1.4 per cent.; 0.5 to 0.25 mm., 86.4 per cent.; 0.25 to 0.10 mm., 

 11.5 per cent.; 0.10 to 0.05 mm., 0.7 per cent. It has a water- 

 holding capacity of 31 per cent., on the dry-weight basis (Hilgard 

 method, with a column one cm. high. (See Hilgard, Soils, page 

 209). It should be remembered that the washing process re- 

 moves much of the most finely-divided material, so that the data 

 just given are applicable to the sand after washing. A sand that 

 does not satisfy these requirements may be corrected by addition 

 or removal of proper amounts of certain groups of particles 

 (using sieves). The water-holding capacity should agree with 

 that stated above, within a range of plus or minus one per cent. ; 

 that is, it may have any value between thirty and thirty-two per 

 cent, (dry-weight basis). 



Before using, the sand is to be thoroughly washed, with tap or' 

 well water and then with distilled water. Washing is to be accom- 

 plished as follows: Fill a large glazed crock (about five-gallon 

 capacity) about two thirds full of water and pour sand into this, 

 stirring vigorously until crock is about two-thirds full of sand. 

 Then direct a stream of water into the sand (as by inserting end 

 of garden-hose nearly to bottom of crock), allowing water to 

 overflow at top of crock; continue this washing (with violent 

 agitation of the sand) until the overflow is free from sediment. 

 Decant, refill crock with distilled water, stir sand vigorously, and 

 decant again. Refill with distilled water, stir and decant once 

 more. After second decanting of distilled water, spread sand 

 on clean paper and allow it to become air-dry, avoiding dust or 

 other foreign matter. 



Prepai^ation of Crocks. For culture pots, cylindrical half- 

 gallon stoneware crocks (glazed within and without, but not 

 dark-colored externally) about 14 cm. high and 14 cm. in diam- 

 eter, are to be used. For definite reference, they should be 

 serially numbered with paint, and solution designations may be 

 marked on them with wax pencil. 



Twenty-five hundred grams of air-dry washed sand is to be 

 used for each crock, which should fill it to within about two centi- 



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