air but can again become effective when you heat a wet sample. Organic soils are undesirable as foundation or base  course  material.  They  are  usually  removed  from the  construction  site  and  wasted. BITE OR GRIT TEST The bite or grit test is a quick and useful method that is used to identify sand silt, or clay. In this test, a small pinch of solid material is ground lightly between the teeth. The soils are identified as follows: .  SANDY  SOILS.  The  sharp,  hard  particles  of sand grate harshly between your teeth and are highly objectionable. This is true even of the fine sand. l  SILTY  SOILS.  The  silt  grains  are  so  much smaller than sand grains that they do not feel nearly so harsh between your teeth. They are not particularly gritty  although  their  presence  is  still  easily  detected. l CLAYEY SOILS. The clay grains are not at all gritty, but feel smooth and powdery like flour between the teeth. Dry lumps of clayey soils stick when lightly touched with your tongue. SLAKING  TEST The slaking test is used to assist in determining the quality of certain soil shales and other soft rocklike materials. To perform this test, place the soil in the sun or in an oven to dry. Then allow it to soak in water for at least 24 hours. After this, examine the strength of the soil. Certain types of shale disintegrate completely and lose all strength. ACID TEST The  acid  test  is  used  to  determine  the  presence  of calcium carbonate. It is performed by placing a few drops of hydrochloric acid on a piece of soil. A fizzing reaction  (effervescence)  to  this  test  indicates  the presence  of  calcium  carbonate.  The  degree  of  reaction gives  an  indication  of  the  concentration.  Calcium carbonate normally is desirable in a soil because of the cementing action it adds to the stability. (Some very dry noncalcareous  soils  appear  to  effervesce  after  they absorb the acid. This effect can be eliminated in all dry soils  by  moistening  the  soil  before  applying  the  acid.) This  cementing  action  normally  develops  only  after  a long  curing  period  and  cannot  be  counted  upon  for strength in most military construction. The primary use for this test is to give abetter value of fine-grained soils that you have tested in place. SHINE TEST The shine test is another means of measuring the plasticity characteristics of clays. A slightly moist or dry piece of highly plastic clay has a definite shine when rubbed with a fingernail, a pocketknife blade, or any smooth metal surface. On the other hand, a piece of lean clay does not display any shine, but remains dull. FEEL  TEST The feel test is a general-purpose test that requires experience  and  practice  before  reliable  results  can  be obtained.  Two  characteristics  you  can  determine  by  the feel test are consistency and texture. The natural moisture content of a soil is of value as an indicator of the drainage characteristics, nearness to the water table, or other factors that may affect this property.  A  piece  of  undisturbed  soil  is  tested  by squeezing  it  between  the  thumb  and  forefinger  to determine its consistency. The consistency is described by such terms as hard, stiff, brittle, friable, sticky, plastic, or soft. Remold the soil by working it in your hands. Observe changes, if any. You can use the feel test to estimate the natural water content relative to the liquid or plastic limit of the soil. Clays that turn almost liquid on remolding are probably near or above the liquid limit. If  the  clay  remains  stiff  and  crumbles  upon  being remolded, the natural water content is below the plastic limit. The term texture, as applied to the fine-grained portion of a soil, refers to the degree of fineness and uniformity. The texture is described by such expressions as floury, smooth, gritty, or sharp, depending upon the sensation produced by rubbing the soil between the fingers. Sensitivity to this sensation may be increased by rubbing some of the material on a tender skin area such as the wrist. Fine sand feels gritty. Typical dry silts will dust readily and feel relatively soft and silky to the touch. Clay soils are powdered only with difficulty but become smooth and gritless like flour. QUESTIONS Q1.  The  purpose  of  a  geological  survey  is  to  take which  of  the  following  actions? 1.  Locate  rock  formations  in  the  field  and determine  their  physical  characteristics 2. Determine rock age and distribution 3.  Determine  types  of  rock  and  their  mineral content 4.  All  of  the  above 16-20