Collect a representative sample of the material. In general more than
one sample should be taken from a spot and a large number of samples
should be collected rather than a few large samples. If the surface
layer is darker and a lower layer consists of pure clay sample only the
surface layer. Samples may be analyzed either separately or as
composites of careful mixtures. After the sample has settled a few
minutes roughly drain or siphon the excess water. Allow sewage sludge to
stand for one hour before draining it free from excess water unless it
is essential to determine the moisture content of the sample originally
collected. If sludge cannot be analyzed within twenty-four hours it is
better not to use air-tight bottles and to add small quantities of
chloroform and keep in the ice box to retard decomposition. At the time
of collection carefully examine mud from the bottom of surface water for
evidence of sewage pollution and macroscopic and microscopic animal and
plant organisms. Record the predominant species. Note the physical
appearance of the material, particularly its color, odor, and
consistency. Express all analytical results in percentage on a dry
basis.