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Purification
of Water for Scientific Purposes
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Purification
of Water for Scientific Purposes The
water supply of a town is watched to ensure its fitness for drinking ; but it
is still far from being “chemically pure,” and so for many scientific
purposes it is unsuitable. Two grades of water are ordinarily distinguished
for laboratory work: i.
Distilled
water. ii.
Conductivity
water. Distilled
water can be made by means of an apparatus comprising a distilling flask and
Liebig condenser, but partly on account of the slight solvent action of water
on the glass, and partly because of the considerable quantities required in
the average laboratory, some form of water-still designed for the purpose is
usually employed. One form out of the many, which have been devised for such
work, is illustrated. Such a still is usually made of copper plated with tin,
and the principle involved in its use is identical with that of the simple
distillation apparatus using a Liebig’s condenser and distillation flask. Distilled
water prepared in this way is pure enough for most chemical work, but for the
investigation of matters such as the conductivity of solutions, it is still
not pure enough. The yet purer water required for these purposes are known as
conductivity water, and its preparation has already been described. Source: Mellor’s Modern Inorganic Chemistry, Revised and Edited by G.
D. Parkes, M. A., D. Phil., Fellow of Keble College, Oxford. In collaboration
with J. W. Mellor, D. Sc. With diagrams and illustrations. Longmans, Green
and Co. London – New York – Toronto. Vapo(u)r
Pressure – Distillation Distillation
consists of boiling a liquid and condensing the vapo(u)r produced. It is used
for separating a liquid from the solid matter dissolved in it, for example,
in obtaining fresh from sea water, and also for separating the more volatile
constituents of a mixture from the less volatile. The apparatus used for the
purpose is called a still ; if the condenser were sloped the other way, so
that the condensed liquid ran down to the left into a vessel placed to
collect it there, and not back into the boiler, then the arrangement would
form a still. Fresh
water is obtained on board ship by distilling sea water. When sea water is
evaporated, the salt remains behind and the vapo(u)r given off condenses as
pure water. If it is to be used for drinking, it is made to absorb air, and
some mineral salts added to improve the taste. It is advisable not to carry
the process of distillation too far in this case, but to throw away the
liquid remaining behind when diminished to about a quarter of its original
volume, because otherwise there is a risk of some of the solid matter being
carried over with the vapo(u)r. Source: Intermediate Physics by R. A. Houstoun, M.A., D.Sc. Lecture on
Natural Philosophy in the University of Glasgow. Formerly Examiner in Physics
in the University of Edinburgh and St. Andrews. Longmann, Green and Co.
London – New York – Toronto. Other
pages for distillation: Yield
(extract) essential oil by steam distillation in atmospheric pressure. Purification of Water
for Scientific Purposes. Application
of the Kinetic Theory to Liquids, Equilibrium and Vapo(u)r Pressure of Liquid. Email: postmaster@arasi.freeservers.com Last Update February 11th,
2003. |
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