206 ACID CHLORIDES.
entirely free from phosphorus compounds; it is, however, admir-
ably suited for use as a chlorinating agent in organic chemistry.
Its odor is suffocating and offensive.
A few drops of thionyl chloride added to a little water react
slowly, — more rapidly on warming, — yielding hydrochloric and
sulphurous acids.
To test for the presence of phosphorus, add some nitric acid to
the solution just obtained, evaporate to dryness on the water-
bath, dissolve the residue in a little water, and test with ammonium
molybdate.
Dependent preparation: Symmetrical Ethyl Sulphite, No. 155.- Nitrosylsulphuric Acid, HOSO 2 .NO 2.
Although it contains no chlorine, nitrosylsulphuric acid can be regarded
as in the same class with the acid chlorides, because its characteristic atom
grouping, — SO 2. NO 2 , is entirely analogous to that which is present in sul-
phurylchloride, or in sulphuric acid monochloride. It is, like the two latter
compounds, converted by hydrolysis directly into sulphuric acid.
Nitrosylsulphuric acid can be formed by the interaction of sulphur dioxide
and nitric acid:
SO 2 + HN0 3 = HOSO 2 .NO 2
or of sulphuric acid and nitrous acid:
2H2SO, + N 2 O 3 = H 2 O + 2HOSO 2 .NO 2
Because of its formation in the lead chambers of sulphuric acid plants
when insufficient water is supplied, this compound has long been known by
the name of "chamber crystals " (cf. No. 86).
Place 100 g. of anhydrous nitric acid (cf. No. 34) and 25 g. of
anhydrous acetic acid in an Erlenmeyer flask and surround the
flask with a freezing mixture. For introducing sulphur dioxide,
insert a tube 1 cm. in diameter through the cork. The top of this
tube is closed with another cork and just below this stopper a
side arm is provided through which the gas is to enter. Whenever
the lower end of the tube becomes clogged with crystals, the
stopper may be removed for a moment and the obstruction dis-
lodged with a stirring rod (cf. No. 46). Generate the sulphur
dioxide from 200 g. of copper turnings and 400 g. of concentrated
sulphuric acid (or from bisulphite solution), and pass it through a
sulphuric acid wash bottle.
Pass the gas rapidly into the reaction flask, shake the mix-
ture from time to time, and take particular care that it is kept