Dry Ice Baths, the Easy Way I t is sometimes necessary to use small qumtities of dry ice around the laboratory for cooling purposes. When buying commercial dry ice, the minimum order, delivery time, the storage of the dry ice present problems to the irregular user. Therefore, the reel cost of dry ice per time of use can be quite high. By obtaining C 0 2in syphon tube bottles and generating dry ice in the , , , quantities needed on demand, the above problems can be circumvented. There are in fact several devices available commercially t o accomplish this, hut with budgets what they are today, it is sometimes bard t o justify the expense. m,v,mn~wL~c An inexpensive device far making dry ice can be fabricated from a few simple parts, i.e., a bottle fitting, '/.in. pipe to '11 in. tube fitting, a few feet of in. O.D. copper tubing, and aninsulated container for the dry ice (see figure). One end of the tubing is connected to the bottle of Con. The other end is crimped with &pairof pliers to form an orifice and inserted into t.be container. The orifice, as shown in the insert of the figure, will be too small to measure. It is made hv ,trial and error to nrovide sufficient flow that the end frosts readilv a1.d ye, is .sift. I,, hnndlr r;uily. .\ g n l w en!, Lr n d d ~ 1nest l o the buttle to monitor the i,uttlr prey r e . LJrv ice in,,! rr.,dil) fornl~dwlwn the iupply pre...ore is Mo\v sbout 300 p,>g. .\n inerpen.lve injul,t~nllid fur n s i d e rnmn~h up I . i l l f I i . The dry i l r I h w r f l ~c?n 4 l,e mndr from u :I-irr. rhwk piece of polystyrene foam. ' h I will be in the form of snow and is emily used for cooling. The typical cost of Conis $4.50 for a 50-lh bottle. A bottle will yield about lL5-lbs of dry ice in snow form a t a resultant cost of 39$/lh. This compares with a delivered cost of lld/lh for block dry ice. The block dry ice price does not tdce into account the 300400 lb minimum order for deliverv or storaee and handline cost. The snow can be fonnerl :,I ahout T,.: 111.1. lh. If the dry ive I- t o Ije 11-rd in n rool!np Ilnrh, d d mrtllanol t o t h r l)ewsr fln.ck hriorc making the d q i c e Yi4d c m 1w i n c r e s d hy placing the orifire i n the metlwwl. The re-dlanr :I.~II? I.;rs ~ X V C J I C . ~ ~ thermal transfer properties for cooling and cryogenic gas drying.
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This work has been supported by the Department of the Navy under contract N00017-72-C-4401.
H. BRUCE LAND111
78 /Journal of Chemical Education
