THORIUM COMPOUNDS FROM MONAZITE. 237
abundant source was sought.^1 This was found in the mineral monazite, a
phosphate of the rare earths and of thorium, which contains 4 to 7% of thorium
oxide and 50 to 60% of the rare earths, about one-half of the latter being
cerium oxide. This mineral occurs frequently, although only in small
amounts, in primary rocks; but it is found in some places concentrated in
secondary deposits.Add 100 g. of finely powdered monazite sand, a little at a time,
to 150 g. of concentrated sulphuric acid which is heated to 200°
in an evaporating dish upon a Babo funnel. Keep the mass at
this temperature for half an hour after all of the mineral is added;
then allow it to cool completely, and pour it very slowly with
constant stirring into 300 c.c. of water, whereby the temperature
must not be allowed to rise above 25° at any time. Filter off the
residue.
Separation of Thorium. To the filtrate add in small portions
a solution of 50 g. of oxalic acid in 500 c.c. of water until no further
precipitate forms. Filter off the precipitate, and wash it first with
water containing small amounts of oxalic and sulphuric acids, and
finally with a little pure water. Yield, about 75 g.
Filter off the precipitate, and wash it first with water containing
small amounts of oxalic and sulphuric acids, and finally with a
little pure water. Yield, about 75 g.
Make the filtrate approximately neutral with sodium carbon-
ate and again add oxalic acid to throw out thorium. This second
precipitate is of one-third to one-fourth the quantity of the first,
and is not entirely free from phosphates. It is well to set it
aside and to work it up together with the fresh mineral when
making the next preparation.
Boil up the moist oxalates with a solution of 230 g. of anhy-
drous sodium carbonate in one liter of water; the thorium dis-
solves as sodium thorium carbonate, while the rare earths remain
behind as carbonates. Filter the warm liquid immediately, and
acidify the filtrate with hydrochloric acid; 3 to 4 g. of thorium
oxalate are precipitated.
In order to recover the remainder of the thorium from the
mixture of insoluble carbonates, dissolve the latter in just the
necessary amount of nitric acid, evaporate the solution to dry-(^1) It is interesting to note that although one kilo of thorium nitrate was
worth about S500 in 1894, the price had fallen to $4 in 1912. It is however
$7.50 in 1928. (Price of potassium iodide about $7.)