Laboratory Glass-Working for Scientists - Sciencemadness Dot Org

GLASS KNIVES AND DIAMONDS
so that the distance between the rollers can be varied according to the
size of the tubing to be cut.
Clamps
Good clamps for holding glass apparatus in position are essential to
the scientist. Also, in many of the operations described in this book
the glass-working scientist will need to hold the glass tubes in
position with clamps.
The best form of clamp has both arms of the claw independently
movable with a screw to tighten up each (FIGURE 8,J). Many standard
forms have only one tightening screw, and one movable arm is
/ n
FIGURE 8. Two types of clamp
drawn towards the other whose position remains fixed (FIGURE 8, IT).
These are less convenient. Two prongs in each arm of the claw are
desirable and lead to more stability than a two-and-one prong
arrangement. A claw lining of asbestos or cork is preferable to
rubber, and a machined boss makes for ease of manipulation and
uniformity of pressure.
Abrasives
Class may be ground to shape by using one of five abrasives. These
are (/) grinding sand, (2) emery, (5) carborundum, (4) pure alumina
or corundum, and (5) diamond powder. Each abrasive has its own
particular property. Grinding sand is used for very rough grinding.
It is mixed with water and the glass is ground to shape against a
suitable surface. Grinding sand is very coarse and unsuitable for
refined work, for which emery, carborundum or corundum are used.
Emery is graded from coarsest to finest as 1, 0, 00, (XX), 0000. The
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