SULPHUR TRIOXIDE. 59
molecular, whereas the liquid sulphur trioxide proves to be monomolecular
when studied in the same way. It seems probable, therefore, that the solid
form is a polymer of the liquid.
Make a slight bend in a 40 cm. long combustion tube at a
point about 6 cm. from one end, and insert the bent end in one
opening of a two-necked globular receiver (Fig. 16); to the other
neck connect a glass tube leading to the ventilating flue of the
hood under -which the apparatus is constructed. Make the
joints tight by means of asbestos cord. Close the front end of
the combustion tube with a cork through which one arm of a
T-tube is inserted in order that sulphur dioxide and oxygen may
be introduced at the same time. Fill a section of the combustion
tube, 12 to 15 cm. long, with loosely-packed, platinized asbestos
which is prepared by moistening the required amount of asbestos
with 5 c.c. of 10% chloroplatinic acid solution, drying and igniting
the mass. After the experiment the platinized asbestos can be
purified by washing and again igniting, and it is then ready for
use again. The whole apparatus must be perfectly dry; even
the asbestos cord with which the joints are made tight must be
previously ignited.
Place the combustion tube in an asbestos chamber (cf. Fig. 4),
whose edges measure 15, 4.5, and 4.5 cm. respectively. There
should be a wide slit in the bottom for the entrance of the flame,
and an opening in the cover to carry away the combustion products.
Place a wide burner at some distance below the combustion
tube, and regulate the flame to maintain the temperature of the
platinized asbestos at about 400°. This temperature may be
read with a mercury thermometer which has been filled under
pressure,- or it may be estimated quite closely with a 360° ther-
mometer if the latter, upon being placed inside the asbestos
chamber, shows but a slow rise of its thread above the 350° mark.
Pass oxygen from a steel cylinder or a gasometer through a
wash bottle containing concentrated sulphuric acid, which serves
to dry the gas and at the same time to show the speed with which
it is being drawn. Admit the oxygen through one arm of the
T-tube into the combustion tube, and through the other branch
of the T-tube introduce sulphur dioxide which is generated by
the action of 400 g. concentrated sulphuric acid upon 100 g.
copper. This gas must likewise be passed through sulphuric acid,