256 Analysis of Mineral Constituents in Biological Materials
METHOD
A sufficient volume of the acid extract (prepared for CaO estimations),
which would give at least 0.2000 gram of mixed chlorides, was taken in 100 c. c.
beakers and evaporated to dryness on water bath. The dry residue is moisten-
ed with a drop of HC1 and a little water. Clear baryta water is next added
until the mixture just turns blue to litmus paper. It is then boiled for a few
seconds and filtered hot (the precipitate is not allowed to settle) and washed
with hot water without allowing the precipitate to clot on the filter paper.
Four to five washings with hot water are quite enough to make it chloride-free.
The filtrate which is received in beaker is then evaporated just to dryness.
When cold, alcoholic (NH 4 ) 2 CO 3 prepared according to the indication given in
the Rowett bulletin is then added, well stirred and the emulsified liquid is
transferred quantitatively to 100 c.c. graduated flasks and made up to the
mark with the same reagent. The mixture is shaken vigorously a number of
times and then allowed to stand overnight. On the next day it is filtered
through a dry funnel and filter paper into a dry beaker. 50 c.c. of the filtrate
which should give 0.1000 gram of mixed chloride are pipetted into a weighed
vitreosil basin and completely evaporated to dryness on a water bath. The
alcoholic mixture is found to evaporate very rapidly. It is necessary to attend
the evaporation at this stage to avoid the danger of spurting. A small amount
of distilled water and 5 c.c. of strong HCl are now added and the solution is
evaporated to complete dryness on the water bath. The perfectly dried residue
of the mixed chloride is then subjected to careful heating over the Bunsen
burner until thick white fumes of NH 4 salts no longer appear. The heating is
very cautiously continued by holding the basin with pair of tongs and gently
rotating over the flame till the residue left on the basin is absolutely white.
In no case should the residue be allowed to melt. It is then cooled and weighed
as NaCl + KCl. From this mixed chloride, potassium is subsequently
estimated by the perchloric acid method.
By subtracting the estimated potassium as chloride from the original NaCl
+ KCl, the amount of sodium present in the unknown solution can be
calculated.
ESTIMATION OF POTASSIUM
For the routine estimation of potassium, we have found that the British
official method (as described by Wright 1938) by the perchloric acid method is
very suitable. The shortness of the procedure and the low cost of pure per-
chloric acid are points in favour of the adoption of the method for routine
analysis.
METHOD
The pure NaCl + KCl after being weighed is dissolved in a small quantity
of hot water and completely transferred into a glass basin. 5 c.c. of HClO 4
is then added and the basin is placed on the water bath, kept inside a fume
cupboard. As the content in the basin gets heated up, copious fumes of
HClO 4 start to evolve and the liquid gradually assumes a syrupy consistency.
The basin is removed from the bath, allowed to cool, 10 c.c. of 95 per cent by
weight of alcohol are added, and the content is well stirred with a thin rod.
The rod is washed inside the basin with a small amount of alcohol and the
contents of the basin are allowed to settle for sometime. The supernatant