Use a large quantity of the sample. Obtain the combined chlorides of
sodium, potassium, and lithium (see pp. 58–59). Transfer the combined
chlorides to a small Erlenmeyer flask (50 or 100 cc. capacity) and
evaporate the solution nearly, but not quite, to dryness. Add about 30
cc. of redistilled amyl alcohol. Connect the flask, the stopper of which
carries a thermometer, with a condenser[E] and boil until the
temperature rises approximately to the boiling point of amyl alcohol
(130° C.), showing that all the water has been driven off. Cool slightly
and add a drop of hydrochloric acid to convert small amounts of lithium
hydroxide to lithium chloride. Connect with the condenser and continue
the boiling to drive off again all water and until the temperature
reaches the boiling point of amyl alcohol. The content of the flask at
this time is usually 15 to 20 cc. Filter through a small paper or a
Gooch crucible into a graduated cylinder and note exact quantity of
filtrate, which determines the subsequent correction. Wash the
precipitate with small quantities of dehydrated amyl alcohol. Evaporate
the filtrate and washings in a platinum dish to dryness on the steam
bath, dissolve the residue in water, and add a few drops of sulfuric
acid. Evaporate on a steam bath and expel the excess of sulfuric acid by
gentle heat over a flame. Repeat until carbonaceous matter is completely
burned off. Cool and weigh the dish and contents. Dissolve in a small
quantity of hot water, filter through a small filter, wash, and return
filter to dish, ignite, and weigh. The difference between the original
weight of dish and contents and the weight of the dish and small amount
of residue equals the weight of impure lithium sulfate. The purity of
the lithium sulfate should be tested by adding small amounts of ammonium
phosphate and ammonium hydroxide, which will precipitate any magnesium
present with the lithium sulfate. Any precipitate appearing after
standing over night should be collected on a small filter and weighed as
magnesium pyrophosphate, calculated to sulfate, and subtracted from the
weight of impure lithium sulfate. From this weight subtract 0.00113 gram
for every 10 cc. of amyl alcohol filtrate exclusive of the amyl alcohol
used in washing residue because of the slight solubility of solid mixed
chlorides in amyl alcohol. Calculate lithium from the corrected weight
of lithium sulfate. Dissolve the mixed chlorides from flask and filter
with hot water, evaporate to dryness, ignite gently to remove amyl
alcohol, filter and thoroughly wash; concentrate the filtrates and
washings to 25 to 50 cc.
Footnote E:
The amyl alcohol may be boiled off without the use of a condenser, but
the vapors are very disagreeable.
To the weight of potassium chloride add 0.00051 gram for every 10 cc. of
amyl alcohol used in the extraction of the lithium chloride, which
corrects for the solubility of the potassium chloride in amyl alcohol.
Calculate to potassium.
The weight of sodium chloride is found by subtracting the combined
weights of lithium chloride and potassium chloride (corrected) from the
total weight of the three chlorides. Calculate sodium chloride to
sodium.