Chemical Education Today
From Past Issues
Refrigeration—From Ice Man to Ozone Hole by Kathryn R. Williams
Who says history doesn't repeat itself? The From Past Issues column in the March 1999 issue demonstrated the “what-comes-around” nature of scientific units (1). This month’s look back into the 20th century presents another example—the hazards of refrigeration fluids. Journal issues from the 1920s and early 1930s contain numerous short notes relating to refrigeration. For example, readers of Volume 5 learned that “the U.S. Bureau of Standards has issued standard weights and maximum sizes for the chunks of frozen water that the ice man puts into the refrigerator daily” (2). But size regulation was not the only factor affecting the ice business. At the same time, modern cooling devices were beginning to put the ice man in cold storage. As the inconvenience of puddles and the replacement of ice on a daily basis eased, more serious problems emerged. A newsbite in a 1929 JCE issue told of deaths from refrigerant leaks in several parts of the U.S., but added reassurances that “iceless cooling machines do not form a very serious menace to life and health” (3). The report attributed the fatalities to asphyxia by methyl chloride, a common refrigerant at that time. Ammonia and sulfur dioxide were also used for this purpose, as explained in Cooling and Refrigeration, a paper by Associate Editor Otto Reinmuth in the October 1929 issue (4). If you are looking for resource material on refrigeration, you should definitely consult Reinmuth’s paper, but there is a less technical discussion in Ward V. Evans’s later article (5). Evans’s schematic of a compression-based refrigerator is reproduced in Figure 1 with a brief summary of the operation. Figure 2a shows Reinmuth’s diagram of the Icyball, a popular commercial cooling unit based on absorption of the refrigerant vapor rather than compression (4). Earl F. Shumaker fashioned the demonstration absorber unit shown in Figure 2b to convince perplexed students that a “flame can be used to make something cold” (6). In support of the absorber design, Reinmuth states, “Gas, oil, coal, etc., may be employed as a source of heat. The fuel cost for one ‘charging’ is said to be about two cents when gas is used, and one heating provides refrigeration and freezes ice cubes and desserts for twenty-four to forty-eight hours” (4). Reinmuth’s use of the word “charging” points out the Icyball’s main disadvantage—intermittent operation. Continuously operating systems required much more complicated designs, as Reinmuth explained. Like compressor-based refrigerators, automated absorption systems contained multiple components with valves and connections. And with connections came the possibility of leaks of toxic refrigerant vapors. Despite government assurances that “None of the three refrigerants mentioned, ammonia, sulfur dioxide, or methyl chloride… are violent poisons when breathed for a short time in low concentrations” (3), scientists and entrepreneurs sought alternative fluids and compressor designs. By today’s standards many of these remedies posed equally serious safety hazards. 1540
Figure 1. Essential components of a mechanical refrigerator. Refrigerant fluid in the liquid receiver passes through the expansion valve and vaporizes. The heat of vaporization is taken from the refrigerator compartment, which gets cold. The mechanical compressor increases the pressure on the vapor, which condenses back to the liquid and releases heat to the surrounding room air (5, figure showing the elementary refrigeration cycle).
Figure 2a. Sketch of the “Icyball”, an absorber unit with ammonia as the refrigerant. Initially the H2O/NH3 solution in the hot ball is heated by a flame to evaporate the ammonia, which condenses in the cold ball. The temperature in the cold ball decreases as the condensed ammonia evaporates and redissolves in the water left in the hot ball (4, Fig. 1).
Figure 2b. Classroom demonstration apparatus (6 ).
Journal of Chemical Education • Vol. 77 No. 12 December 2000 • JChemEd.chem.wisc.edu
Chemical Education Today
For example, the firm Comstock and West invented a unit utilizing boiling mercury vapor that “is discharged into a venturi tube, sucking water vapor [the refrigerant fluid] from the cooling unit and compressing it” (7). The U.S. Bureau of Mines investigated adding acrolein, “an irritating gas used in the World War”, to methyl chloride to “make it impossible for a person to remain near a leak long enough to be injured” (8). A Science Service report in the September 1930 issue of JCE announced a major breakthrough in refrigerant chemistry, the synthesis of “a new gas [that]… is non-poisonous and non-inflammable, and… very closely approaches the refrigerating engineer’s notion of an ideal substance” (9). The compound was CCl2F2, often called Freon-12, invented by Thomas Midgley and Albert L. Henne, research scientists in the laboratory of a General Motors affiliate. Three decades later Midgley’s personal account of the discovery of the first chlorofluorocarbon was reprinted in JCE as part of Alfred B. Garrett’s “Flash of Genius” collection (10). Midgley’s reflections provide an excellent example of how the chemist fuses information from the literature with chemical insight—and some experimental serendipity—to design a compound with the desired properties. Unfortunately, the desired properties didn’t include protection of the ozone layer, which filters biologically harmful radiation from the solar spectrum. It was about forty years later when scientists realized the dangers of CFC release into the atmosphere. Nearly unreactive in the lower atmosphere, chlorofluorocarbons survive to reach the stratosphere. There, UV radiation initiates photodecomposition to form free chlorine atoms, which abstract oxygen atoms from ozone. Color-coded images of southern-hemispheric ozone distribution, reproduced in Figure 3 from the cover of the May 1987 JCE, clearly indicate the growth of the “ozone hole” between 1979 and 1983. The same issue contains an excellent article,
Figure 3. The cover of the May 1987 Journal shows the growth of the Antarctic ozone hole between 1979 and 1983 (11).
Chlorofluorocarbons and Stratospheric Ozone, that explains the CFC–ozone relationships for readers not familiar with atmospheric chemistry (11). Reflecting the loop of phase changes in the coils of a cooling unit, the status of refrigerant fluids traced a full circle in the years between the ice man and the ozone hole. Twenty-first century chemists are still making important contributions to refrigerant technology—synthesizing viable replacements for CFCs and obtaining crucial physical and toxicological data. References 1. Williams, K. R. J. Chem. Educ. 1999, 76, 313. 2. Science Service. J. Chem. Educ. 1928, 5, 1128. 3. Science Service. J. Chem. Educ. 1929, 6, 1983. 4. Reinmuth, O. J. Chem. Educ. 1929, 6, 1768. 5. Evans, W. V. J. Chem. Educ. 1942, 19, 539. 6. Shumaker, E. F. J. Chem. Educ. 1944, 21, 195. 7. Science Service. J. Chem. Educ. 1931, 8, 42. 8. Science Service. J. Chem. Educ. 1931, 8, 62. 9. Science Service. J. Chem. Educ. 1930, 7, 2164. 10. Garrett, A. B. J. Chem. Educ. 1962, 39, 361. 11. Elliott, S.; Rowland, F. S. J. Chem. Educ. 1987, 64, 387.
Kathryn R. Williams is a member of the Department of Chemistry, University of Florida, P. O. Box 117200, Gainesville, FL 32611-7200;
[email protected].
JChemEd.chem.wisc.edu • Vol. 77 No. 12 December 2000 • Journal of Chemical Education
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