cleaned by acid, so that on
clamping it vertically, dry spaces do not appear, it may be rinsed
with platinum distilled water and left to drain, the dust being, of
course, kept out by placing a bit of paper round the top. For
accurate work water thus prepared is to be preferred to anything else.
When the glass is very clean interference colours will be noticed as
the water dries away.

Carefully-purified alcohol may in some cases be employed where it is
desired to dry the tube or apparatus quickly. In this case an alcohol
wash bottle should be used, and a little alcohol squirted into the top
of the tube all round the circumference. The water film drags the
alcohol after it, and by waiting a few minutes and then adding a few
more drops of alcohol, the water may be practically entirely removed,
especially if a bit of filter paper be held against the lower end of
the tube. It is customary in some laboratories to use ether for a
final rinse, but unless the ether is freshly distilled and very pure,
it leaves a distinct organic residue.

When no more liquid can be caused to drain away, the tube may be dried
by heating it along its length, beginning at the top (to get the
advantage of the reduction of surface tension), and so on all down.
It will then be possible to mop up a little more of the rinsing
liquid. When the tube is nearly dry a loose plug of cotton wool may
be inserted at the bottom. The wool must be put in so that the fibres
lie on an even surface inside the tube, and the wool must be blown
free from dust. Ordinary cotton wool is useless, from being dusty and
the fibres short, and the same remark applies to wadding. Use nothing
but what is known as "medicated" cotton wool with a good long fibre.

The tube will usually soon dry of itself when the cover is lifted an
inch or so. If water has been used, the air-current may be assisted
by means of the water-pump, the air being sucked from the top, so that
the wool has an opportunity of acting as a dust filter; a very slow
stream of air only must be employed. For connecting the tube to the
pump, a bit of India-rubber tube about an inch in diameter, with a
bore of about one-eighth of an inch, may be employed. The end of the
rubber tube is merely pressed against the edge of the glass.

These remarks apply, with suitable modification, to all kinds of
finished apparatus having two openings. For flasks and so on, it is
convenient to employ a blowing apparatus,