The tube should be warmed to ensure
complete dryness, and must be free from a misty appearance. Aspirate a
current of air through the apparatus, heat the mineral by means of a
Bunsen burner, cautiously at first, and afterwards to redness (if
necessary). The water is driven off and condenses in the calcium
chloride tube, which is afterwards cooled and weighed. The increase in
weight is due to the water. If the substance gives off acid products on
heating, it is previously mixed with some dry oxide of lead or pure
calcined magnesia.
EXAMINATION OF WATERS.
The assayer is occasionally called on to test water for the purpose of
ascertaining the nature and quantity of the salts contained in it, and
whether it is or is not fit for technical and drinking purposes.
In mineral districts the water is generally of exceptional character,
being more or less charged, not only with earthy salts, but also
frequently with those of the metals. Distilled water is only used by
assayers in certain exceptional cases, so that by many it would be
classed among the rarer oxides. Water of ordinary purity will do for
most purposes, but the nature and quantity of the impurities must be
known.
The following determinations are of chief importance:--
~Total Solids at 100° C.~--Where simply the amount is required, take 100
c.
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