Laboratory Methods of Inorganic Chemistry, 2nd English Ed. 1928

TJNSYMMETRICAL DIETHYL SULPHITE. 211

few drops of alcohol, drive off the latter by boiling a short time,

cool, and acidify the solution with dilute sulphuric acid. Sul-

phur dioxide escapes and can be recognized by its odor.

Saponify a second portion in like manner by adding barium

hydroxide together with a few drops of alcohol; boil off the

alcohol and acidify the cooled solution with nitric acid. At first

no change is noticed, but on boiling a cloudiness appears which

is caused by the precipitation of barium sulphate.

156. Unsymmetrical Diethyl Sulphite, C 2 H 5 .SO 2 .OC 2 H 5.

To prepare silver sulphite, which is to serve as the starting

material for this preparation, pass a stream of sulphur dioxide

into a solution of 150 g. silver nitrate in 500 c.c. of water. Keep

the mixture cooled with water, and continue the process until a
small filtered portion of the solution no longer gives a precipitate
with hydrochloric acid. Drain the precipitated silver sulphite
immediately and wash it successively with water, alcohol, and
ether; then dry it over sulphuric acid in a vacuum desiccator.
The next day place the silver sulphite and 1.1 times its weight
of ethyl iodide in a flask, provided with a return condenser, and
allow the mixture to stand overnight. The top of the condenser
should be closed with a calcium chloride tube to exclude moisture;
the outer jacket should be filled with water, but a constant flow
need not be maintained. After 24 hours, add 150 to 200 c.c. of
thoroughly dry ether (which has stood for several days in con-
tact with sodium wire), and boil the mixture six hours on the
water-bath with return condensation, still protecting from atmos-
pheric moisture with the calcium chloride tube. Filter the liquid
from the silver iodide
1
and wash the latter with ether; distil the
ether from the filtrate, using a tower containing glass beads. Then
fractionate the liquid in a smaller flask, using a tower with a column
of glass beads 13 cm. high and 1.5 cm. wide (cf. No. 151). Reject
the first runnings up to 100°; collect two fractions, first from 100°
to 200°, and second at above 200°, and ref ractionate these portions

repeatedly according to the process described in No. 151. The

(^1) Recover the silver from the silver iodide residue by reducing it with a
warm solution of sodium hydroxide and dextrose, and then melting the silver
powder obtained with twice its weight of sodium carbonate.