Page 82 - Demo

Apparatus and Supplies
Dewar Flasks for Liquid Nitrogen
Dewar Flask, Small
A safe means of transporting, storing, handling and dispensing liquid nitrogen. Wide mouth opening allows for easy filling and dispensing. Manufactured from borosilicate glass, these flasks are very heavily insulated, and wrapped with an exterior aluminum metal housing that extends nearly to the top rim of the flask adding extra safety protection. All flasks have a special vented, polypropylene stopper to minimize evaporation. Smaller flask may be used with a vacuum trap apparatus for cooling purposes. See page 486 for vacuum trap apparatus.
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Dewar Flask, Large
These lightweight Dewar flasks are recommended when required storage time exceeds 24 hours. Aluminum construction allows storage of liquid nitrogen for several weeks! Handles make dispensing a simple task.
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Dishes
Crystallizing Dishes
Borosillicate glass dishes used for heating and cooling baths, crys- tallization, disposal by evaporation and sand baths for microscale experiments. Available in two sizes.
Petri Dish, Borosilicate Glass
These dishes will remain clear after repeated wet or dry sterilization. Tops and bottoms are marked with different colored enamels for quick identification.
DISHES continued on next page.
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Dewar Flask, Large AP8560
Catalog No.
Description
Outside Diameter
Inside Diameter
Inside Depth
Capacity
Price/Each
AP1490
Dewar Flask, Small
33⁄8"
23⁄4"
117⁄8"
1000 mL
$177.95
AP1491
57⁄8"
41⁄4"
71⁄2"
1900 mL
415.35
Dewar Flask, Small AP1490, etc.
Catalog No.
Description
Expiration Rate
Outside Diameter
Overall Height
Capacity
Price/Each
AP8560
Dewar Flask, Large
0.40 L/day
75⁄8"
165⁄8"
4L
$ 940.30
AP8562
0.22 L/day
113⁄8"
21"
10 L
1017.30
Dewar Flask, Large AP8562
Catalog No.
Description
Size
Price/Each
GP9171
Crystallizing Dishes
80 x 40 mm
$16.30
GP9172
150 x 75 mm
55.55
Petri Dish, Borosilicate Glass GP3019, etc.
Crystallizing Dishes GP9171, etc.
Catalog No.
Description
Price/Pkg.
GP3019
Petri Dish, Borosilicate Glass, 100 x 15 mm
$47.25/6
GP3020
84.55/12
Questions Most Commonly Asked About Liquid Nitrogen
How is liquid nitrogen made? Liquid nitrogen is made by cooling and compressing air until it liquifies. The liquid air is allowed to warm up, and the nitrogen boils off first and is collected, leaving the oxygen and argon as liquids. The collected nitrogen gas is then compressed and cooled back into a liquid. It is quite easy to produce and relatively inexpensive.
How long can liquid nitrogen be stored in a Dewar flask? Our best esti- mate is that a good 1000-mL Dewar flask will lose approximately 500 mL for every 24-hour period stored. The larger the Dewar flask, the slower the loss rate.
Where can I purchase liquid nitrogen? We have had our best success purchasing liquid nitrogen from local welding supply firms. Also look in the Yellow Pages under “Gas.”
How much does liquid nitrogen cost? Cost varies widely. Most outlets charge a minimum fee of $10.00. You may pay as little as $1.00 per liter to more than $3.00 per liter.
How can you safely transport liquid nitrogen in your car? Place the specially vented polypropylene stopper into the flask to minimize evapora- tion. Find a good-size cardboard carton that will be stable in your car. Place the Dewar flask in the center of the carton, and stuff crumpled newspaper into the carton to tightly hold your flask. Place the carton with your flask in the car and transport it directly to your school. Do not store your Dewar flask in your car for an extended period of time. Transport the Dewar flask as far
from driver and passengers as possible to avoid any exposure from accidental spillage. Drive with the windows slightly vented, not tightly sealed.
Can I use a regular Thermos® bottle to hold liquid nitrogen? No, do not use a regular Thermos bottle! Why? Every Thermos-type vessel differs. The one you might select to use could have a plastic exterior that would crack and break from the temperature of the N2(l). An unsafe situation will result. You might be tempted to use such a container and unknowingly the screw cap would be placed on the Thermos. As the N2(l) warms, gas pressure will develop in the bottle and an explosion will result. Choose the safer option of using a dedicated and safer laboratory Dewar flask.
Is liquid nitrogen safe? Liquid nitrogen should never be stored or trans- ported in a tightly sealed container. The expanded gas may cause the container to explode. Liquid nitrogen can cause frostbite on contact with skin. Wear protective clothing! If you accidentally spill liquid nitrogen on clothing, do not let the soaked clothing remain in contact with the skin. Always use liquid nitrogen in a well-ventilated area. Protective eyewear should be worn by the demonstrator and the demonstration participants.
How can I dispose of excess liquid nitrogen? As N2(l) warms in an open container, it simply returns to its natural gaseous state. The simple method of disposal is exposure to air at room temperature. Avoid doing this in a poorly ventilated area.