re is a convenient book on this subject, by Dr.
Shenstone (Rivingtons), so that what I have to say will be as brief as
possible, consistent with sufficiency for everyday work. As a matter
of fact there is not very much to say, for if ever there was an art in
which manual dexterity is of the first and last importance, that art
is glass-working.

I do not think that a man can become an accomplished glass-blower from
book instructions merely--at all events, not without much unnecessary
labour,--but he can learn to do a number of simple things which will
make an enormous difference to him both as regards the progress of his
work and the state of his pocket.

Sec. 3. The first thing is to select the glass. In general, it will
suffice to purchase tubes and rods; in the case where large pieces
(such as the bulbs of Geissler pumps) have to be specially prepared by
pot-blowing, the student will have to observe precautions to be
mentioned later on. There are three kinds of glass most generally
employed in laboratories.

Sec. 4. Soft Soda Glass, obtained for the most part from factories in
Thuringia, and generally used in assembling chemical apparatus.--This
glass is cheap, and easily obtainable from any large firm of apparatus
dealers or chemists. It should on no account be purchased from small
druggists, for the following reasons:-

(a) It is usually absurdly dear when obtained in this way.

(b) It is generally made up of selections of different age and
different composition, and pieces of different composition, even if
the difference is slight, will not fuse together and remain together
unless joined in a special manner.

(c) It is generally old, and this kind of glass often devitrifies with
age, and is then useless for blowpipe work, though it may be bent
sufficiently for assembling chemical apparatus. Devitrified glass
looks frosty, or, in the earlier stages, appears to be covered by
cobwebs, and is easily picked out and rejected.

Sec. 5. It might be imagined that the devitrification would disappear
when the glass is heated to the fusing point; and so it does to a
great extent, but for many operations one only requires to soften the
glass, and the devitrification often persists up to this temperature.
My experience is that denitrified glass is also more likely to crack
in the flame than good new glass, though the difference in this
respect is not very strongly marked with narrow tubes.

Sec. 6. Flint Glas