In order to find the percentage of organic matter in soil from several different locations,
a student collected the samples, weighed them
immediately, roasted them for several minutes
in a flame to burn off organic matter, and
weighed them again. The student concluded
that the difference between the first and second
weights represented the weight of the organic
matter in the soil. The most serious mistake that
the student made in this experiment was in
(1) taking large samples
(2) weighing the samples before roasting them
(3) failing to dry the samples before first
weighing them
(4) assuming that roasting could remove the
organic matter