RESEARCH METHODS IN STUDY OF FOREST ENVIRONMENT. 125 



uring vessel, leaving- the very fine sand in the can, some silt and clay, 

 and a little water. This 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 

 decanted into the measuring vessel. More water is added to the 

 bottle and is thoroughly stirred. 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 clay, 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 clown 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 this 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 " Summary of Physical and Chemical Properties of Soil" 

 (p. 134). 



It will be noted in the following l<< : v that no grade coarser than 

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

 it is rustomary to pass the material through the 2 millimeter sieve 

 ampling and to base all calculation on the total weight of 

 this "fine earth"; that is, materia] not coarser than fine gravel. In 

 forest -<>il- coarser material is too commonly met with to be ignored, 

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



