The still finer sand is next separated with the sieve of 0.5 millimeter circular openings as indicated above. The sample may now be classified as follows: 1. Coarse pebbles, sticks, roots, etc., separated by hand. 2. Pebbles and coarse sand not passing a two millimeters sieve. 3. Sand not passing a one millimeter sieve. 4. Fine sand not passing a 0.5 millimeter sieve. 5. Fine earth passing a 0.5 millimeter sieve. =196. Classification of Orth.=[132]—As fine silt are reckoned those particles which range from 0.02 to 0.05 millimeter; as fine sand the groups from 0.05 to 0.2 millimeter; as medium sized sand those ranging from 0.2 to 0.5 millimeter and for large grained sand those particles ranging from 0.5 to 2 millimeters in diameter. Particles over two millimeters form the last classification. SEPARATION OF THE EARTH PARTICLES BY A LIQUID. =197. Methods of Silt Analysis.=—The further classification of the particles of a soil passing a fine sieve can best be effected by separation in water. The velocity with which the current moves or with which the particles subside will cause a separation of the particles into varying sizes. The slower the velocity the smaller the particles which are separated. There is, however, a large and important constituent of a soil which remains suspended in water, or in a state of seeming solution. This suspended matter would still be carried over by a current of water moving at a rate so slow as to make a subclassification of it impossible. This suspended matter passing off at a given velocity may be classed as clay, and it consists in fact chiefly of the hydrated silicate of alumina, or other particles of equal fineness. The laws which govern its deposit have already been discussed. The apparatus which have been used for silt analysis may be grouped into four classes. (1) Apparatus depending on the rate of descent of the particles of a soil through water at rest. The apparatus for decanting from a cylinder or a beaker belong to this class. (2) Apparatus which determine the rate of flow by passing the liquid through a vessel of conical shape. The system of Nöbel is a good illustration of this kind of apparatus. (3) Apparatus in which the elutriating vessel is cylindrical and the rate of flow determined by a stop-cock or pressure feed apparatus. The system of Schöne represents this type. (4) Apparatus in which the above system is combined with a device for mechanically separating the particles and bringing them in a free state into the elutriating current. The system of Hilgard is the type of this kind of apparatus.