PerkinElmer aanalyst 200 User Manual page 62

Preparing Your Lab
Cylinder information
The nitrous oxide supply should be at least 99% pure. Cylinders of nitrous oxide are available
from local suppliers.
Nitrous oxide is supplied in the liquid state, initially at a pressure of about 5000 kPa (725 psig). A
size 1A cylinder of nitrous oxide contains about 14800 liters (523 cubic feet) and will typically
last for 10–12 hours of burning time.
Heated regulator
Since the nitrous oxide is in liquid form, the pressure gauge does not give a true indication of how
much nitrous oxide remains in the cylinder until the pressure starts to fall rapidly as the residual
gas is drawn off. When nitrous oxide is rapidly removed from the cylinder, the expanding gas
causes cooling of the cylinder pressure regulator and the regulator diaphragm can freeze. This can
cause erratic flame conditions or, in the most extreme case, a flashback.
It is therefore advisable to use a double-stage or heated regulator for nitrous oxide to prevent
freezing of the diaphragm and a loss of pressure regulation. A suitable nitrous oxide pressure
regulator is available from PerkinElmer.
Acetylene supply requirements
Warning: Acetylene – Explosion Hazard
Acetylene can decompose explosively at pressures higher than 103 kPa/
1.03 bar/15 psig.
•
Always make sure that the acetylene outlet gauge pressure is below these
WARNING
values.
Acetylene can react with copper to form a readily explosive compound.
•
Never use copper tubing or fittings for acetylene gas lines.
Grade
Suitable acetylene (ethyne), such as 'atomic absorption grade' or welding grade, typically has a
minimum purity specification of 99.6% with the actual assay being about 99.8%. Acetylene is
supplied dissolved in acetone (propan-2-one) to prevent explosive decomposition. You should not
use acetylene that is dissolved in any other solvent. Experience indicates that solvents can be
carried through the regulator with the acetylene and can weaken, to the point of rupture, the walls
of the tubing carrying the acetylene to the burner, causing a potential hazard.
Cylinder information
A size 1A acetylene cylinder contains about 8500 liters (300 cubic feet) of acetylene and usually
lasts about 30 hours of burning time with an air-acetylene flame. With a nitrous oxide-acetylene
flame, the same size cylinder will last about 10 hours.
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