There are several issues to consider when deciding
whether to make a physical composite of separate samples
collected to represent different parts of the same lot (or
consignment) See Note 2. When the analytical parameters of
interest are additive (for example, proximate and ultimate
analyses) the preferred method is to test the individual samples
and perform a ton-weighted mathematical average to determine
the result for the lot (or consignment). See Note 3. On the other
hand, when the sought-after parameters are non-additive (for
example, ash fusibility and Hardgrove grindability), analysis of
a composite sample is the only way to achieve a meaningful
test result. Another consideration is that since there are no
provisions in this standard for dividing samples of top size
larger than 250 μm (No. 60) by means other than riffling or
mechanically subsampling, the exact weights needed for preparation
of composite samples containing larger particles are not
attainable. Taking these and other issues into account leads to
the requirement that preparation of composites be performed
with strict adherence to the procedures which are described
below and are summarized in Table 2. The details pertaining to
the preparation of composite samples must be agreed to by all
concerned parties.