A Simple Apparatus tor Laboratory Dry Ice Producrim I t is advantageous for a small-quantity dry-ice user to have a quick and cost-effective method of producing dry ice in the laboratory. The method could also he used as a backup source for large-quantity users. An apparatus for this purpose has been previously described in THIS JOURNAL by Land.' His system involves the forced flow of liquid COz through an orifice at the end of a lengthy tube. The orifice is constructed by "trial and error" and the COz is collected in aDewar bottle. We describe here an apparatus that is used in our department for the occasional production of pound quantities of dry ice. We have found it to he easier to build, simpler to use, and more time- and cost-effectiveta operate than the orifice system. As shown in the accompanying figure, our apparatus consists of a collection bag assembly that is attached to a liquid COz cylinder equipped with a siphon tube. Since liquid COz cylinders are available either with or without a siphon ear tube, this feature must he s~ecifiedwhen obtainine the tank from thelocal n~ cylinder wppl~rr.The hag-to-cylinder runnrcthm requires only thr prerenrr ofnstandnrd ',-in. hosefmmg. We uspa hlathtrmnwdlr valvethat ha,.wrh a tilting. The collectim bag assemhly consi3ts of n one-hole rubbrr stupper, a hose clamp, part of a sleeve from a worn out lab coat, and either a piece of rope or a large paper clip that can he used to temporarily close off the lower end of the sleeve. Whendry ice is needed, the hag assembly is simply attached to the COz~uurceby slipping the rubber stopper over the hose fitting. The valve is then opened to allow a rapid flow of COz into the hag. One pound of dry ice can be made in less than 2 min. The dry ice made in this way is in a powdery form which may be used directly in cold traps, thus eliminating the need to hreak uo blocks. It is retrieved from the collection hae.. bv. removine.. the naoer clio a t the lower end. Carhun dimide is shipped cc,mmercially in lrquid form under pressure I- 830 psigl at n,om iernpcrature. Dry icr formarmn rrquirei the cool~ng01 C01 hayond the normnl sublimination temperature during the rapid relraw ufpreraurc. The cooling is caused by the rvoporatron of the liquid and thr Joule.Thornpmn efiect ot the expandmg gas. The tfflciency of the dry ice production apparatus depends on the rates of two opposing processes, i.e., the rate of cooling by the rapid release of pressure, and the rate of heat absorption from the surroundings. For this reason,it is necessary to keep the uninsulated path of liquid COz as short as possible in order to minimize the heat conduction orocess. Although there are some commercial apparatuses for laboratory use presently on the market, we have found this apparatus to he quite suitable for occasional needs, including classroom demonstrations of COz phase changes. The authors thank Marycollette Hruskosy for drawing the accompanying sketch. ~
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50,78 (1973). 'Land, Bruce H., 111, J. CHEM.EDUC.,
90
Journal of Chemical Education
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Myong-Ku - Ahn and Richard A. Kionaas Indiana State University Term Haute. IN 47809
