118 EXPERBIEXT STATION. [Jan. 



one of which at least is perfectly flat, having an inside hreadth 

 of .8 centimeter and a width 1 to 1.5 millimeters. This 

 tube is about 10 centimeters long. The lengths of A and B may 

 be varied, however, but it has been found that tubes of these 

 dimensions work well in the ordinary laboratory centrifuge. 

 The method of procedure is as follows : the tube is filled to within 

 about 4 centimeters of the top with distilled water and the gram 

 of soil added. A rubber stopper is then placed in the tube and 

 the soil thoroughly incorporated with the w^ater by shaking for 

 a few minutes. The tube is then placed in the centrifuge and 

 run for a period of five minutes at a speed of about 1,200 revolu- 

 tions per minute. The tube is then rem.oved and clamped to an 

 upright stand sho\vii in Fig. 2, and a millimeter scale is attached 

 so that with a horizontal microscope the size of the soil particles 

 as shown by the eyepiece micrometer and the reading on the 

 scale may be had at the same time or by swinging the micro- 

 scope in a horizontal plane. millimeter on the scale cor- 

 responds with the bottom of the soil column in the tube. The 

 microscope is then focussed on the soil particles and raised until 

 a majority of the particles are less than the minimum size of 

 those of fine sand, i.e., less than .05 millimeter; the scale read- 

 ing is then taken and noted. The microscope is then raised 

 until the particles are less than those of the minimum size for 

 silts, viz., .0005 millimeter; the scale reading is again noted 

 and the scale reading at the top of the soil column also noted. 

 We have the readings as follows: — 



Millimeters. 



Very fine sand, 3.0 



Very fine snnd and sills, ........ 4.5 



Very fine sand and silts and claj^, ...... 7.0 



The column is divided, therefore, into volume per cents, as 

 follows : — 



Per Cent. 



Very fine sand, 42.85 



Silts, 21.43 



Clays, 35.72 



If there were 2.34 grams of soil left after the last sifting we 

 should have weights of very fine sand, silts and clays as follows, 



