dust being avoided by
inserting a permanent plug of cotton wool in one of the leading tubes.
The efficiency of this method is greatly increased by using about one
foot of thin copper tube, bent into a helix, and heated by means of a
Bunsen burner; the hot air (previously filtered) is passed directly
into the flask, bottle, or whatever the apparatus may be. This has
proved so convenient that a copper coil is now permanently fastened to
the wall in one of the rooms of my laboratory.

The above instructions indicate greater refinement than is in general
necessary or proper for tubes that have to be afterwards worked by the
blow-pipe. In the majority of cases all that is necessary is to
remove the dust, and this is preferably done by a wad of cotton waste
(which does not leave shreds like cotton wool), followed by a bit of
bibulous filter paper. I would especially warn a beginner against
neglecting this precaution, for in the process of blowing, the dust
undergoes some change at the heated parts of the apparatus, and forms
a particularly obstinate kind of dirt.

In special cases the methods I have advocated for removing dirt and
drying without covering the damp surfaces with dust are inadequate,
but an experimenter who has got to that stage will have nothing to
learn from such a work as this.

Sec. 14. The Blow-pipe.

I suppose a small book might easily be written on this subject but
what I have to say--in accordance with the limitation imposed--will
be brief. For working lead glass I never use anything but an oxygas
blow-pipe, except for very large work, and should never dream of using
anything else. Of course, to a student who requires practice in order
to attain dexterity this plan would be a good deal too dear. My
advice to such a one is--procure good soda glass, and work it by
means of a modification of a gas blow-pipe, to be described directly.
The Fletcher's blow-pipes on long stems are generally very
inconvenient. The flame should not be more than 5 or 6 inches from
the working table at most, especially for a beginner, who needs to
rest his arms on the edge of the table to secure steadiness.

The kind of oxygas blow-pipe I find most convenient is indicated in
the sketch. (Fig. 2) I like to have two nozzles, which will slip on
and off, one with a jet of about 0.035 inch in diameter, the other of
about double this dimension. The oxygen is led into the main tube of
the blow-pipe by another tube of mu