Number 163       Zrtburl.E ittle,3nc. CHEMISTS, ENGINEERS             7(ovember 1940

COLD SPECTRA
A NEW laboratory investigational tool has ap-
peared that offers great possibilities for rapid
and accurate analysis of a wide variety of kinds of
chemicals, especially for routine or repetitive work.
So far-reaching is its activity and so small is the
quantity of material required for analysis that the
new device has been nicknamed the " cold spectro-
graph." As is often the case when nicknames are
used, the dignified name for regular use is some-
what undecided, varying from the original one of
dropping mercury electrode through polarograph
to amperograph and electro-chemograph, accord-
ing to the various workers and the makers of the
apparatus. Commercially available equipment is
either manually operated or semi-automatic, de-
livering a chart with a wavy line.
This apparatus, as most of the names imply,
operates through electrical properties of matter,
in solution form, and analyzes a wide variety of
kinds of substances, inorganic and organic. It is
highly discriminating for many of the elements or
radicals and makes findings of great definiteness,
although blind to some elements or groups. The
number of blind spots, however, decreases with the
skill of the operator, and one having a mastery of
the instrument can take advantage of " tricks " to
do rather amazing things with it. The device can
be used for quantitative measurement through
calibration against standards. In general, in the
recording-type instrument, stepwise curves, or
" waves," are obtained on the record-sheet, with
the height of the step indicating the particular
element or radical present, and the width of the
" tread " of the step the quantity present. A single
chart can give the record of a large group of com-
ponents. Then, by a shift of conditions, as of
acidity, a new chart can be taken which serves as
a check on some of the components, but may reveal
others or separate pairs that were previously too
close together for complete determination.
The sensitive part of the apparatus consists of
a glass tube drawn out to a fine point, containing
mercury, which is allowed to fall at a standardized
slow rate through the solution being analyzed, to
collect on the bottom of the dish. Electrical con-
nections are made to the dropping electrode and
to the pool of mercury at the bottom. Before
measurements are made, any oxygen dissolved in
the water of the solution must be swept out of the

instrument by a stream of inert gas, such as nitro-
gen. The operation of the recording instrument
depends entirely on the amount of current that
flows for each particular degree of electrical po-
tential applied to the two electrodes. In general, a
negligibly small amount of current flows until the
potential reaches a critical value, when the current
becomes quite appreciable, depending on the quan-
tity of the " found " component, after which the
current does not further increase until another com-
ponent in the solution produces the next step, and
so on across the chart. Reversal of the electrodes
then allows survey of another part of the field.
Current flow is impeded by the electrical " polar-
ization" or plugging of the circuit in the vicinity
of the dropping electrode, which stoppage exists
until the characteristic and critical breaking volt-
age is reached, allowing relatively free flow of
current. The electrical potential at the step de-
pends upon the so-called electro-positiveness or
electro-negativeness of the chemical element. So-
dium and potassium, for example, are strongly
electro-positive, zinc and iron are intermediate,
and copper is low. The acid elements and group-
ings are negative, to characteristic degrees.
Since the polarograph must be carefully cali-
brated by an experienced operator and alternative
procedures investigated before application to a
new analytical problem, the method seems best
adapted to high-speed, routine analysis. Recent
investigations have pointed toward use of the
polarograph in the clinical laboratory, where speed
and accuracy are always sought. Many determina-
tions of biological materials are time-consuming;
bio-assays of vitamins and hormones require days
or weeks to perform and sometimes have a pos-
sible error up to oo per cent. With the polaro-
graph, measurements may conveniently be made
of the components or impurities of drinking water,
the juices of plants, animal fluids, and a great
variety of hormones and vitamins.
While the polarograph is by no means a simple
tool and each new use must be investigated to de-
termine the applicability of the method, the tech-
nique has progressed so far that complete sets of
apparatus are commercially available. During the
18 years since the first application of the polaro-
graph principle a literature based on its use has
appeared and, as this body of knowledge grows,
more and more research and control laboratories
are finding it a useful tool.

PJO     MANUFACTURER who hopes to continue serving the American public
can aford to coast along on his present processes.
HARVEY S. FIRESTONE, JR.