It is on this account that it
is well to weigh substances, which have been dried, between
close-fitting watch-glasses. The method of determining moisture is to
weigh out into the glasses 5 grams of ore, and dry in the water-oven
until there is no further loss of weight. On taking the glasses out of
the oven, they should be at once closed, the clip put on, and after
cooling in a desiccator weighed. If after a second trial the loss is the
same, or only increased by a milligram, the determination is finished.
Example:--
Weight of glasses + pyrites 31.0470 grms.
" " glasses 26.0470 "
-------
" " pyrites 5.0000 "
" " glasses + pyrites, dried 1 hour 30.8965 "
" " " " dried 1-1/2 " 30.8957 "
" " " " 31.0470 "
" " " " dried 30.8957 "
-------
" " moisture 0.1513 "
0.1513 ? 20 = 3.026 ~3.02%.~
[Illustration: FIG. 3.]
Sometimes it may be advisable to dry 10 grams, in which case multiplying
the loss by 10 will give the percentage.
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