RESEARCH METHODS IN STUDY OF FOREST ENVIRONMENT. 125 



leaving the very fine sand in the can, some silt and clay, and a little 

 water. The material is also transferred to the washing bottle. 

 As the first measure of liquid in the bottle will be very rich in silt 

 and clay at least one minute should be allowed for the very fine 

 sand to settle. After this time the silt and clay are partially de- 

 canted into the measuring vessel. More water is added to the bottle 

 and is thoroughly btirred. With each successive washing the time 

 is reduced, so that as the water becomes nearly clear the sand is 

 allowed just 30 seconds to settle through a 4-inch column of water. 

 It will be noted that the settling is somewhat slower if the water is 

 extremely cold. 



5. All the very fine sand is now in the wash bottle, in which it may 

 be dried and weighed, and all of the silt and clav, with a considerable 

 volume of water, in the measuring vessel. It will be economical to 

 obtain the weights of the silt and clay by merely sampling this large 

 volume after thorough stirring. Perhaps 100 cubic centimeters may 

 be drawn off for centrifuging from a total volume of 2 liters. The 

 amount and fineness of the material thrown down in the centrifuge 

 will depend on the time of centrifuging and the speed of the machine. 

 These should be adjusted after repeated trial and examinations of 

 the suspended particles under the microscope. (See Briggs, Martin, 

 and Pearce (117).) However, as the standards for "clay, ,: "silt/ 

 etc., are purely arbitrary any investigator may, for his particular pur- 

 poses, adopt his own, as by deciding on a period of centrifuging 

 which will in every case clear the water of particles of visible size. 



The centrifuging completed, the clay water is decanted off into 

 one evaporating dish, and the silt in each tube is washed out with a 

 fine jet of water into another. These are dried in the oven. Care 

 should be used to avoid weighing either the clean dishes or dishes 

 containing tins fine material when the general humidity is very 

 high. The amount of silt and clay in the evaporators having been 

 determined, the total amount for the whole sample is readily cal- 

 culated. 



6. The quantities have now been determined in nine grades, and 

 the percentage of the whole which each grade represents may be 

 readily computed. The several percentages may be entered on the 

 form for u Summary of Physical and Chemical Properties of Soil" 

 (p. 134). 



It will be noted in the following key that no grade coarser than 

 coarse sand is mentioned. In analyses made by the Bureau of Soils 

 it is customary to pass the material through the 2-millimeter sieve 

 before sampling and to base all calculation on the total weight of 

 this ''fine earth"; that is, material not coarser than fine gravel. In 

 forest soils coarser material is too commonly met with to be ignored, 

 and its importance from certain points of view may be as great as 



