The Students' Guide in Quantitative Analysis - Free Ebooks Library

VOLUMETRIC ANALYSIS. 4I
solutions of known strength, the amount of the reacting
substance being calculated from the volume of the liquid
used." The first principles and method of procedure have
been foreshadowed in Analysis No. 3, III., Determination
of Iron by Marguerite's method, For explanation of gen-
eral volumetric methods, see P'rcs. § 54, and consult Stit-
ion's Handbook of Volumetric Auulysis, also Mohr's Lchr-
bncli iter c/iauisch-aHalytischen 'fitririuelhodi:
Principles, When volumetric analysis first came into
use, the standard solutions were so prepared as to give
results in percentages ; thus in Alkalimetry, osio standard
solution of acid was used for potash, another for soda, etc.
The modern system is based on the fact that acids and
alkalies (as well as other reagents) neutralize cacli other in
the proportion of their molecular weights, or of simple
multiples of the same ;
consequently standard solutions are
so prepared that one litre contains one-half or the whole
of the molecular weight of the reagent weighed in grms.
For example, the molecular weight of HCl being 36.5 and
that of KHO 56.1, 36.5 grms. of HCl exactly neutralize
56.1 grms. of KHO, and if these respective amounts be
dissolved in one litre of water, the whole of one solution
will not only neutralize the whole of the other, but any
aliciuot part of one will exactly neutralize a similar aliquot
part of the other. And by using graduated vessels, (bu-
iettes,)the amount of reagent used is determined by the
volume of the siluuon. (Before employing burettes,
pipettes, and graduated flasks, care should be taken to test
the accuracy of the graduation.)
Standard Solutions. Solutions containing the molecu-
lar weight of the reagent expressed in grms. per litre are
called normal solutions ; in the case of di-basic acids
(H.SO^, HoCA etc.) and of " di-acid " alkalies (NajCOj)