CHAPTER III
QUANTITATIVE DETERMINATIONS
Comparative Usefulness of Different Methods.- In a general
way it may be stated that gravimetric methods permit great or
accuracy in determinations, while volumetric processes make
for rapidity in routine work with large numbers of samples. This
is due to the fact that one standardization of a solution forms the
basis for many determinations, provided that a sufficient quan-
tity of standard is made. Experience shows that, for a single!
determination, the time required to make and standardize a
solution, added to that required to make a determination by
means of this solution, often leaves the advantage in favor of the*
gravimetric method.
Whether the method used is gravimetric or volumetric, if
precipitation is an essential part of the process it must be remem-
bered that solubility is of the highest importance. No substance
has zero solubility arid, since the substance that is precipitating
leaves a solution that is saturated with itself, the part in solution
is necessarily not determined.
In the industrial laboratory methods are chosen, to a consid-
erable extent, upon the basis of time saving. However it sonus
times happens that for a given element or compound the known
convenient and, at the same time, accurate methods full in one
class only. As an example of this may be mentioned the* deter-
mination of the sulphate radical., which is almost universally
carried out by precipitating and weighing barium sulphate.
Scope of the Laboratory Work.™The time that is available
for the college laboratory course is, necessarily, inadequate
to the gaining of the skill that comes from extensive experience.
The entire field cannot be covered. The greater stress is there-
fore laid upon the learning of principles of correct nianitmlation
as well as of chemical processes. The laboratory exeranes that
are described in Part I of this book are selected largely with this