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A Textbook of Assaying: For the Use of Those Connected with Mines. by John Jacob Beringer;Cornelius Beringer
page 67 of 691 (09%)
readings is taken, and gives the quantity of metal added. It equals the
quantity of metal in the portion of the assay. If this portion was
one-half of the whole, multiply by two; if one-third, multiply by three,
and so on. When the quantity of metal in very dilute solutions is to be
determined, it is sometimes necessary to concentrate the solutions by
boiling them down before applying the re-agent which produces the
coloured compound. Such concentration does not affect the calculations.

~Gasometric Assays.~--Gasometric methods are not much used by assayers,
and, therefore, those students who wish to study them more fully than
the limits of this work will permit, are recommended to consult Winkler
and Lunge's text-book on the subject. The methods are without doubt
capable of a more extended application. In measuring liquids, ordinary
variations of temperature have but little effect, and variations of
atmospheric pressure have none at all, whereas with gases it is
different. Thus, 100 c.c. of an ordinary aqueous solution would, if
heated from 10∞ C. to 20∞ C., expand to about 100.15 c.c. 100 c.c. of a
gas similarly warmed would expand to about 103.5 c.c., and a fall of one
inch in the barometer would have a very similar effect. And in
measuring gases we have not only to take into account variations in
volume due to changes in temperature and atmospheric pressure, but also
that which is observed when a gas is measured wet and dry. Water gives
off vapour at all temperatures, but the amount of vapour is larger as
the temperature increases.

By ignoring these considerations, errors of 3 or 4 per cent. are easily
made; but, fortunately, the corrections are simple, and it is easy to
construct a piece of apparatus by means of which they may be reduced to
a simple calculation by the rule of three.

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