RESEARCH .METHODS IN STUDY OF FOREST ENVIRONMENT. 125 
uring vessel, lea vino- 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 1-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 Avater, 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 this fine material when the general humidit} r 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. 
G. 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 Phvsical 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 
