d, but I find that the glass tube
(Verbrennungsroehr) made by Schott & Co. of Jena, which can be obtained
through any firm of dealers in apparatus, is far better than the
ordinary tube.

By following these instructions, any one who has learned how to work
with lead or soda glass will find it easy to manipulate hard glass.

CHAPTER III.

_CUTTING AND BENDING GLASS--FORMING GLASS APPARATUS BEFORE THE
BLOW-PIPE--MAKING AND GRINDING STOPPERS TO APPARATUS, ETC._

In the later pages of this Chapter it will be assumed that the
operations first described have been mastered. The beginner should
therefore practise each operation until he finds himself able to perform
it with some degree of certainty. Generally speaking, however, after the
failure of two or three attempts to perform any operation, it is best to
give up for a few hours, and proceed to the work next described,
returning to that upon which you have failed subsequently. If,
unfortunately, it should happen that the work next in order involves the
performance of the operation in which the failure has occurred, it is
best to pass on to some later work which does not demand this particular
accomplishment, or to rest a while, and re-attack the difficulty when
refreshed.

=Cutting Glass Tubes.=--The simplest method of cutting a glass tube is
to make a sharp scratch with a file across the glass at the point where
it is desired to cut it, and on pulling apart the two ends, it will
break clean off. It is important that the file be sharp. In pulling
apart the ends the scratch should be held upwards, and the pull should
have a downward direction, which will tend to open out the scratch. In
the case of a large tube, a scratch will not ensure its breaking clean
across. The tube must be filed to some depth, half-way, or even all
round it. A good way of breaking a tube is to place the file in the
table after scratching the glass, to hold the glass tube above its edge
with one hand on each side of the scratch, and to strike the under side
of the tube a sharp blow upon the edge of the file, directly beneath the
scratch. In this way very even fractures of large and moderately thin
tubes may be made. It answers particularly well for removing short ends
of tube, not long enough to hold; the tube is held firmly upon the file,
and a sharp blow given to the short end with a piece of large tube or a
key.

A file whose faces have been ground till they are nearly smooth, so as