CO2 cylinder (syphon type)
Dry ice has many uses. As well as simply watching it sublimate, you could also use it for cloud chambers, dry ice pucks, cooling thermistors and metal wire resistors in resistance experiments, and experiments related to the gas laws. Don't be tempted to get a small cylinder - it will run out too quickly.
What type of cylinder, where do I get CO2 and what will it cost?
A CO2 gas cylinder should be fitted with a dip tube (this is also called a ‘syphon type’ cylinder). This enables you to extract from the cylinder bottom so that you get CO2 in its liquid form, not the vapour.
NOTE: A plain black finish to the cylinder indicates that it will supply vapour from above the liquid. A cylinder with two white stripes, diametrically opposite, indicates it has a syphon tube and is suitable for making dry ice.
A cylinder from British Oxygen will cost about £80 per year for cylinder hire and about £40 each time you need to get it filled up. (The refill charge can be reduced by having your chemistry department cylinders filled up at the same time.)
If the school has its own CO2 cylinder there will be no hire charge, but you will need to have it checked from time to time (along with fire extinguisher checks). Your local fire station or their suppliers may prove a good source for refills.
CLEAPSS leaflet PS45 Refilling CO2 cylinders provides a list of suppliers of CO2.
A dry ice attachment for the cylinder
Dry ice can be made using an attachment that fits directly onto a carbon dioxide cylinder with a syphon tube. Section 13.3.1 of the CLEAPSS Laboratory Handbook explains the use of this attachment (sometimes called Snowpacks or Jetfreezers).
You can buy a Snowpack dry ice maker from Scientific and Chemical. The product number is GFT 070 010
VWR International sells Snowpacks through its UK distributor. The version that makes 30 g pellets of dry ice is catalogue number 3285042/02.
Philip Harris sells similar products. See their 2004 catalogue, page 679.
Remember to wear insulating gloves when handling dry ice.
Arrange good ventilation in the room where it is made and used, and make sure that the gas does not collect at a low point