Laboratory Glass-Working for Scientists - Sciencemadness Dot Org

THE USES OF ASBESTOS
there is a likelihood of the flame being played on to other parts of the
apparatus, it is advisable to screen these parts with sheets of asbestos
board or by binding them with asbestos cord or paper. The bench is
also liable to suffer from the effects of hot glass and hot tools being
laid down unless it is protected by a sheet of asbestos board or similar
material. Hard asbestos board is better for this purpose than the soft
type as the latter has a tendency to contaminate the tools with loose
fibres which may be transferred to the glass being worked.
Asbestos gloves protect the hands both from glassware which
would otherwise be too hot to hold and from the effects of radiant
energy. But they suffer from the disadvantage that, owing to the
nature of the material, they tend to be clumsy and do not allow small
objects to be picked up easily. Unless large sizes of tubing are to be
worked there seems to be little advantage in the use of these gloves.
But with operations with a hand torch on large Pyrex tubing,
asbestos gloves are often essential—after a time the torch becomes
too hot to hold, because it is heated by radiation and convection from
the hot glass. The gauntlet type of asbestos glove is desirable for
these operations.
When new asbestos paper and tape is used on apparatus, it may be
desirable first to heat it in a gas-air flame to remove the binder.
Glass-Blowing Spectacles
It may be found that in operations in which it is necessary to observe
the glass deforming or flowing whilst it is in the flame, vision is
obscured by the sodium glare from the glass. Special glasses are
made to filter off this yellow light and also much of the infra-red
radiation. Spectacles or goggles made from such glasses are available
commercially. The glass itself resembles the cobalt glass used in
qualitative analysis flame tests, and may also contain rare earth
oxides. Didymium goggles contain neodymium and praseodymium,
and selectively absorb light in the sodium D region. The effect of the
radiant heat from the glass is tiring to the eyes and may be reduced
considerably by wearing ordinary sun glasses made with Crookes
glass. These glasses reduce the light and heat intensity but do not
significantly cut out the sodium glare. If ordinary sun glasses are
used, care must be taken to see that the frames are not easily inflammable
in view of the possibility of accidents.
Glass Knives and Diamonds
Glass knives are of two main kinds. The inexpensive ones are made
of hardened carbon steel, and the more expensive ones are made of a
very hard alloy. The latter kind keep their edge for a long time, but
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