ought too
near the nozzle of the burner. I have found the patent burner of Mr.
Jackson (Brin's Oxygen Company, Manchester) most satisfactory, and it
offers the advantage that several jets can be combined in a group easily
and inexpensively for work on large apparatus. The large roaring flames
such as are used, I understand, for welding steel are very expensive,
and not very efficient for the work here described.

=The method of making Silica Tubes.=--Before commencing to make a tube a
supply of vitreous silica in rods about one or two millimetres in
diameter must be prepared. To make one of these, hold a fragment of the
non-splintering silica described above in the oxy-gas flame by means of
forceps tipped with platinum so as to melt one of its corners, press a
small fragment of the same material against the melted part till the two
adhere and heat it from below upwards,[26] till it becomes clear and
vitreous, add a third fragment in a similar manner, then a fourth, and
so on till an irregular rod has been formed. Finally re-heat this rod in
sections and draw it out whilst plastic into rods or coarse threads of
the desired dimensions. If one works carefully the forceps do not suffer
much. I have had one pair in almost constant use for several years; they
have been used in the training of five beginners and are still
practically uninjured.

[26] This is to avoid bubbles in the finished glass.

The beginner should work with a gauge and regulator on the bottle of
oxygen, and should watch the consumption of oxygen closely. A large
expenditure of oxygen does not by any means necessarily imply a
corresponding output of silica, even by one who has mastered the initial
difficulties.

When a supply of the small rods of vitreous silica has been provided,
bind a few of them round a rod of platinum (diameter say, 1 mm.) by
means of platinum wires at the two ends and heat the silica gradually,
beginning at one end after slightly withdrawing the platinum core from
that end, till a rough tube about four or five centimetres in length has
been formed. Close one end of this, expand it, by blowing, into a small
bulb, attach a silica rod to the remote end of the bulb, re-heat the
bulb and draw it out into a fine tube. Blow a fresh bulb on one end of
this and again draw it out, proceeding in this way till you have a tube
about six or eight centimetres in length. All larger tubes and vessels
are produced by developing this fine tube sui