Pennington, Mary Engle (1872–1952)
Pennington, Mary Engle (1872–1952)
American chemist who developed refrigeration techniques to preserve perishable foods. Name variations: M.E. Pennington; Polly. Born Mary Engle Pennington on October 8, 1872, in Nashville, Tennessee; died of a heart attack in New York, New York, on December 27, 1952; daughter of Henry Pennington (a businessman) and Sarah B. Molony Pennington; University of Pennsylvania, certificate of proficiency, 1892, Ph.D., 1895.
Was a fellow in botany, University of Pennsylvania (1895–97); was a fellow in physiological chemistry, Yale University (1897–98); was a research worker, department of hygiene, University of Pennsylvania (1898–1901); worked as consultant, Philadelphia Clinical Laboratory (1898–1907); was a lecturer, Woman's Medical College of Pennsylvania (1898–1906); was director, Philadelphia Department of Health and Charities' bacteriological laboratory (1901–07); was first chief and bacteriological chemist, United States Department of Agriculture's Food Research Laboratory, Philadelphia, Pennsylvania (1905–19); developed refrigeration techniques to prevent food spoilage and devised standards for refrigerated railroad cars (1907–17); earned the Food Administration's Notable Service Medal (1918); was director of research and development, American Balsa Company, New York City (1919–23); was first female member of the American Society of Refrigerating Engineers (1920); was a private chemical consultant to food industry and developed techniques to freeze food and design commercial and household refrigerators (1922–52); co-authored Eggs (1933); won the Francis P. Garvan Medal for women in chemistry presented by the American Chemical Society (1940); made fellow, American Society of Refrigerating Engineers (1947); was first female member of Poultry Historical Society's Hall of Fame; was vice-president American Institute of Refrigeration at time of death (1952).
(with Georgiana Walter) "A Bacterial Study of Commercial Ice Cream," in New York Medical Journal (November 1907); "Changes Taking Place in Chickens in Cold Storage," in USDA Yearbook (1907, pp. 197–206); (with Howard C. Pierce) "The Effect of the Present Method of Handling Eggs on the Industry and the Product," in USDA Yearbook (1910, pp. 461–476); (with Helen M.P. Betts and Pierce) "How to Kill and Bleed Market Poultry," in USDA Bureau of Chemistry (circular no. 61, 1910); "Studies of Poultry From the Farm to the Consumer," in USDA Bureau of Chemistry (circular no. 64, 1910); (with Evelyn Witmer and Pierce) "The Comparative Rate of Decomposition in Drawn andUndrawn Market Poultry," in USDA Bureau of Chemistry (circular no. 70, 1911); "The Handling of Dressed Poultry a Thousand Miles from the Market," in USDA Yearbook (1912, pp. 285–292); "Practical Suggestions for the Preparation of Frozen and Dried Eggs," in USDA Bureau of Chemistry (circular no. 98, 1912); (with Pierce) "An All-Metal Poultry-Cooling Rack," in U.S. Bureau of Chemistry (circular no. 115, 1913); "Supplementing Our Meat Supply With Fish," in USDA Yearbook (1913, pp. 191–206); (with Arden D. Greenlee) "The Refrigeration of Dressed Poultry in Transit," in USDA Bulletin (no. 17, 1913); (with Minnie K. Jenkins, E.Q. St. John, and William B. Hicks) "A Bacteriological and Chemical Study of Commercial Eggs in the Producing Districts of the Central West," in USDA Bulletin (no. 51, 1914); (with Pierce and Harlan L. Shrader) "The Egg and Poultry Demonstration Car Work in Reducing our $50,000,000 Waste in Eggs," in USDA Yearbook (1914, pp. 363–380); (with Jenkins and Betts) "How to Handle Eggs," in USDA Bulletin (no. 565, 1918); Why We Refrigerate Foods (Chicago: National Association of Ice Industries, 1926); (with Frank L. Platt and Clara Gebhard Snyder) Eggs (Chicago: Institute of American Poultry Industries, 1933); The Care of Perishable Food Aboard Ship (NY: G. Ehlenberger, 1942); The Freezing of Eggs (NY: American Society of Refrigerating Engineers, 1948).
Chickens played a major role in Mary Engle Pennington's scientific achievements. Considered the greatest refrigeration authority in the early 20th century, she focused on preserving poultry products, and her methods to refrigerate perishable foods drastically changed consumer behavior. Before refrigeration, people bought food fresh from the market and risked being poisoned. Foods such as dairy and poultry products, if improperly stored, often transmitted deadly bacteria. As America urbanized and cities swelled with foreign and rural immigrants, large supplies of safe food became necessary. Pennington provided means to bring food from the farm to the consumer, minimizing food-related illnesses and deaths and farmers' losses from spoiled and wasted foods. She designed refrigerated storage and transportation methods and developed frozen-food research. Her work revolutionized the way Americans eat: fresh foods are now available every day of the year.
Mary Engle Pennington, called Polly, was born in Nashville, Tennessee, on October 8, 1872, the daughter of Henry and Sarah Molony Pennington , but lived in the South only briefly. Maps of Nashville reveal her paternal family's influence; the Cumberland River curves around Pennington Bend northeast of the state capitol. Young Mary moved with her family to Pennsylvania, living in a large three-story, red-brick house. Sarah Pennington's Quaker family, the Engles, lived in West Philadelphia, and Mary's great-grandfather, Joseph Engle, a Pennsylvania judge, had been an escort for General Lafayette when he visited America in 1825. Pennington always considered Philadelphia, not Nashville, to be her hometown, declaring, "I'd never have been born anywhere but Philadelphia if I'd had anything to do with it." Her younger sister, Helen, was born in that city in 1878.
Henry Pennington, an entrepreneur, founded a label manufacturing business in Philadelphia. He was also fond of gardening. Encouraged to assist him, Mary became familiar with vegetables and plants and especially enjoyed examining flowers. In addition to learning about flora, Pennington discovered local fauna, in particular chickens, at Philadelphia markets. Every Saturday morning, she accompanied her mother to market, and occasionally they ventured to farms outside the city to place orders. Stalls that were full of produce in summer stood empty in winter. Pennington became aware that when hens laid fewer eggs and scarcities occurred out of season, prices soared too high for many people to afford fresh eggs. She pondered whether there was any means to store eggs year round.
When she was 12, she discovered a Rand's Medical Chemistry text in the Philadelphia Mercantile Library, and the librarian agreed to let her borrow it. An avid reader, Pennington devoured the tome while sitting on the family porch. She realized that elements, invisible to the naked eye, built everything that surrounded her and were necessary to sustain life. Oxygen was in air, nitrogen was in soil, and hydrogen was in water. "Suddenly, one day, I realized, lickity hoop, that although I couldn't touch, taste, or smell them, they really existed. It was a milestone," Pennington declared. "Like a flash of light in a dark place, I got the idea of the realness of the invisible world."
Intrigued, Pennington asked the head-mistress at her private girls' school if she would offer chemistry lectures. Since science was not a proper subject for young ladies, the headmistress was scandalized and refused. Though somewhat surprised by Mary's sudden enthusiasm, Pennington's family supported her new-found interests. In 1890, she approached the dean and asked to enroll in the Towne Scientific School at the University of Pennsylvania, which was near the Pennington home. Both Dean Horace Jayne and chemistry professor Dr. Edgar F. Smith supported coeducation and allowed her admittance. Pennington completed the required courses, including chemistry, biology, bacteriology, and zoology, in two years. The only woman in her class, Pennington received a certificate of proficiency, not a B.S. like her male peers, because the university refused to grant degrees to women.
Deemed eligible by faculty to continue her studies according to a university statute regarding "extraordinary cases," Pennington ignored the discrimination that she had encountered and pursued postgraduate work in chemistry. Her scholarship as a graduate student and her thesis on "Derivatives of Columbium and Tantalum" earned her a doctorate in 1895. Pennington's feat was a rarity: she was honored with a Ph.D. without having a bachelor's degree. She soon discovered that the chemistry profession had the same bias as academia when it came to female practitioners. Though Pennington was the third woman to join the American Chemical Society, it remained staunchly masculine. At that time, most women chemists applied their knowledge and skills to what was then considered the more "feminine" field of home economics, which welcomed them.
But Mary Pennington elected to stick with the pure sciences. Continuing her interest in plants, she was a research fellow in chemical botany at the University of Pennsylvania for two years, teaching graduate students plant physiology. Then she devoted a year to postgraduate study of physiological chemistry at Yale University. Working with Dr. Russell Chittenden, she conducted pioneering research on the effect of color on plant growth, bathing Spirogyra nitida (mermaid's hair) with varicolored lights. Pennington then returned to Philadelphia. Continually aware that well-educated women scientists were not highly in demand or approved of, she contemplated ways to promote her scientific work and unearth opportunities for her imagination. Enterprisingly, she founded the Philadelphia Clinical Laboratory to offer doctors better laboratory resources. She performed accurate bacteriological analyses for approximately 400 physicians who paid an annual minimum of $50 each. At the same time, she was a research worker in the University of Pennsylvania's department of hygiene.
Pennington's expertise won her an appointment at the Woman's Medical College of Pennsylvania, where she lectured and directed the chemistry laboratory until 1906. Teaching physiological chemistry, she co-authored an article with her student and cousin, Georgiana Walter , for the New York Medical Journal.
Pennington's successful independent research resulted in her being named director of the newly created Philadelphia Department of Health and Charities' bacteriological laboratory. At that time, reform was a popular platform for progressives, and Pennington revised her goals, choosing to apply science to improve society instead of focusing on pure science in the laboratory. She quickly became an expert in food chemistry. Her initial work concerned eradicating impure milk that might transmit deadly diseases, including tuberculosis. Without laws to protect food products, Pennington faced an unusual challenge; she wanted to insure that the source of milk was healthy. Since retail milk sellers could not verify whether the milk they bought from dairies was uncontaminated, Pennington established the first systematic dairy and milk inspection standards, including a scientific examination of cattle herds, which were adopted by municipal health boards nationwide. She then urged retailers to handle milk safely, mainly to preserve it at low temperatures. She devised profitable means for dairy producers and dealers who cooperated with her.
Pennington then tackled "hokey-pokey" vendors, whose pushcart ice cream had caused outbreaks of sickness, and even a few fatalities, among city schoolchildren. When she analyzed a slide sample of the ice cream, she discovered millions of bacteria. Inviting the vendors to her laboratory to see the slides, she also showed them slides of ice cream prepared in a sanitary environment and explained that, by simply sterilizing their kettles and ladles in boiling water, they could prevent illness. Upset at the microscopic dangers, many of the ice-cream sellers agreed to adopt preventative steps. Once personnel in dairies and ice-cream factories understood the invisible dangers, most managers agreed to cooperate and adopt her suggestions for food handling. As a result, Pennington improved the quality of life for consumers and formed the basis for her refrigeration research.
In 1907, family friend Dr. Harvey W. Wiley, chief of the Bureau of Chemistry in the U.S. Department of Agriculture (USDA), urged her to research refrigeration as a method of food preservation for the federal government. Previously, she had investigated for Wiley rumors that turkeys had been frozen for a decade and then served at a banquet. By examining the history of slaughtered poultry in warehouses, Pennington determined that birds could be stored for one year at freezing temperatures. Impressed with her findings, Wiley asked Pennington to take a civil service examination. At first, the uninformed Pennington "was mad as wrath," then agreed to be tested. Concerned, however, that government bureaucrats would not approve the appointment of a female bacteriological chemist, Wiley advised her to sign her exam "M.E. Pennington." After that, Pennington published many of her articles the same way, and often her clients did not realize that she was a woman. She humorously recalled how one executive asked his secretary "to get rid of the woman" when Pennington appeared in his office.
At the turn of the 20th century, female government employees, like many women in academia, encountered discrimination. Generally assigned stereotypical female work, they were underpaid and seldom promoted. Women scientists worked in isolated positions or were clustered in areas, such as the Bureau of Plant Industry, where they performed work that male employees refused to do. For the most part, the only women achieving managerial positions accomplished this in the aforementioned field of home economics. Pennington managed to overcome these obstacles and was a pioneering female federal scientist. Officials hired her as a bacteriological chemist, believing she was a man because of her initials; she performed so admirably and indispensably that when they realized she was a woman, they had no grounds to dismiss or demote her.
By 1908, Wiley appointed Pennington as the first chief of the newly established U.S. Food Research Laboratory, a division of the Bureau of Chemistry. At her insistence, Pennington's laboratory was created in Philadelphia so that she could be near her family and professional colleagues and continue her consulting work. Although Wiley wanted her to work in Washington, D.C., the strong-willed Pennington refused, fearing that her work might become entangled in administrative red-tape. She agreed to appear annually in the capitol to ask for appropriations.
Pennington conducted experiments in the laboratory and negotiated on behalf of the government with food agents. The laboratory became a nucleus for research concerning food handling and storage, especially in preventing spoilage of eggs, poultry, and fish. Supervising a staff ranging from four to fifty researchers, she devised techniques that various facets of the food industry, such as warehousing, packaging, and distributing, adopted.
Her goal was to insure enforcement of the first Pure Food and Drug Act, passed in 1906, which fomented bitter legal controversies with food producers. Pennington conducted laboratory analyses for Wiley to use in court to serve as proof that the law had been violated. During this time, she managed to devise successful refrigeration techniques and gain respect for her professional expertise. Many food dealers sought her advice to develop hygienic procedures and avoid prosecution.
Acting as the official American delegate, Pennington attended the First International Congress of Refrigeration in Paris in 1908 (she would participate in these congresses throughout her life). The only female delegate, she delivered an address for Wiley. Refrigeration became her primary research focus. Although she did not invent refrigeration, Pennington developed procedures to insure that refrigerated foods remained fresh and edible, and helped establish the refrigeration industry.
Considered America's foremost authority on the refrigeration of perishable foods, Pennington enabled wide geographical access to healthy fresh foods year round. At that time, the law did not permit government inspectors to enter packing houses and wholesale food buildings. Seeking cooperation between government and dealers, Pennington convinced owners to permit her access to these businesses and explore food handling problems firsthand. Chickens were her primary concern. Along with her laboratory assistants, Pennington focused on problems encountered in killing and storing chickens. They had already examined chickens in retail stores, but only by obtaining access to the poultry processing industry were they able to suggest solutions. Wrapping her brown hair in a towel and wearing gloves and an apron, she assisted in the killing process in the abattoirs and quickly dismissed wringing and axing necks as sanitary killing methods.
Instead of immersing chickens in boiling water to pluck off feathers, which caused deterioration during storage and transportation, she invented a sharp knife to pierce the brains and cut the jugular veins from inside. This method of slaughter resulted in the feathers being easily removed without immersion, while the bodies remained intact during shipping. She also discovered suitable temperatures to remove body heat and freeze-dry the birds for storage, avoiding packing on ice which melted en route and often waterlogged carcasses. During this work, Pennington developed guidelines for poultry storage limits and patented an all-metal poultry-cooling rack in 1912.
Pennington's ideas were also used in the design of refrigerator cars. Concentrating her efforts on the transportation of food, she researched and determined the necessary temperature during cold storage processes to refrigerate foods safely in rail cars (and later in trucks). She focused on humidity control in freezing rooms, because as freezing temperatures occurred, the air in the freight car lost its ability to retain moisture and food became dry. Once the food was thawed, it regained water and became moldy. "At temperatures above freezing," she commented, "one is between the Scylla of excessive drying and the Charybdis of mold." Riding in a caboose outfitted as a laboratory and living quarters, Pennington studied the chickens as they traveled cross-country, monitoring electrical thermometers to record temperatures. Following foodstuffs thousands of miles from producer to market, often working all day in a warehouse and sleeping on the train, Pennington enthused, "That's the way to travel, leisurely jogging along, talking over the crops with the farmers at the crossings, switched into a train yard at night instead of speeding through space and being hustled out of a berth at daybreak."
She gained national publicity for this feat (much of it inaccurately stating that she rode in the refrigerated cars) and ultimately improved transportation conditions with the standardized refrigeration car. Through her work, Pennington enabled poultry producers to kill chickens in prime condition, dry-pluck and freeze-dry them, and sell them to consumers in as edible a state as they were when fresh killed. Next, she decided to achieve similar results with eggs.
Because hens laid the bulk of their eggs in the spring, poultry producers sought improved egg storage in order to supply eggs to consumers at consistently affordable prices throughout the year. Farmers disliked the low prices they received when eggs were plentiful, and consumers often eliminated eggs from their diets during the winter months. Pennington began to explore means to cold-store eggs safely.
The problem required several considerations. First, farmers delivering eggs to warehouses had to make sure that eggs were fresh, especially in the summer; eggs in warehouses would be only as fresh as they were when stored. Then Pennington had to determine the best temperatures and methods to store eggs. Aware that farmers were motivated by financial rewards, she helped create the first egg quality charts which graded eggs scientifically, deciding which eggs were suitable for storage and would retain the nutritious qualities of fresh-laid eggs.
Pennington focused on egg-breaking factories, where cracked and blemished eggs were broken and dried or frozen. The residue was sold to bakers and confectioners who used the powdered product for cooking. However, eggbreaking factories tended to be unsanitary, and USDA Secretary James Wilson threatened to close them. Fearing that farmers would suffer heavy financial losses, Pennington sought a compromise. She convinced egg-breaking plants to refrigerate their products and follow her methods "of near-surgical asepsis," in which buildings were sterilized with steam and workers trained to follow sanitary handling measures. Pennington's work saved millions of dollars worth of eggs from wastage.
Next, she turned her attention to egg transportation problems. Utilizing a branch food research laboratory in Indianapolis, Pennington continued her analyses of temperatures. Her investigations enabled eggs from the Midwest, America's "Egg Basket," to be delivered safely throughout the United States. She also helped design cushioning packaging to eliminate broken eggshells and reduced profits. She wrote about her experiences in the book Eggs.
Simultaneously, Pennington contributed to America's World War I efforts. Women scientists found that the war provided new professional opportunities, though their role was often minimized. President Woodrow Wilson established the U.S. Food Administration in August 1917. Scientists concentrated on increasing domestic food production while decreasing American consumption of food in order to alleviate European food shortages.
Pennington acted as a consultant to the Food Administration's perishable products division. She and her staff, dubbing themselves "the imperishables," secured safe means to export agricultural produce. As demand for transporting perishable foods greatly increased with the need to feed troops, Pennington solidified refrigerator car standards. American railroads contributed 40,000 refrigerator cars to the war effort. After evaluating them in 1917, Pennington declared that only 3,000 cars were suitably insulated and ventilated to transport meat; she assisted the government in establishing official standards for ice-cooled refrigerator cars, which remained current through World War II (mechanically refrigerated cars were introduced in the 1950s). Herbert Hoover, chair of the (U.S.) Commission for Relief in Belgium and a fellow Quaker, presented her with a Notable Service Medal for her wartime work with perishable foods, and Pennington received public accolades. Through her war efforts, food producers, shippers, warehouses, and government agencies were united toward the common goal of preserving food. Calling her "Auntie Sam," the railway and poultry workers considered her "the voice of conscience in the refrigerating world." Both the food industry and consumers accepted the use of refrigerated food, expediting the creation of such facilities.
After the armistice in 1919, Pennington resigned from the USDA to become director of the research and development department of the American Balsa Company in New York City. A manufacturer of insulating materials, the company was willing to double her government salary. After three years, she, like many women scientists, chose to create her own independent consulting office, in the city's Woolworth Building. She devoted her energy to developing effective means to handle, ship, and store perishable foods for packing houses, shipping firms, and warehouses. Pennington traveled frequently, as much as 50,000 miles per year in America and abroad, to investigate industries, steamers, refrigerator cars, and egg-breaking factories.
She also directed the Household Refrigeration Bureau of the National Association of Ice Industries from 1923 to 1931. Acting as a publicist, she convinced three universities—Columbia, Purdue, and Chicago—to add household refrigeration courses to their curricula. Because no textbooks existed, she wrote pamphlets, which were more popular than scholarly in context, entitled "The Romance of Ice," "Desserts Frozen with Ice and Salt," and "Journeys with Refrigerated Food." Millions of these booklets were circulated; she also dispensed information on radio programs.
Refining her food preservation techniques, Pennington attacked a new problem, that of frozen foods. She realized that canning and smoking were viable preservation methods but insisted that freezing was better because foods remained fresh. She designed and built refrigerated warehouses and coolers as well as refrigerators for both industry and homes. Pennington also conducted original research concerning frozen-food processing, again concentrating on poultry. Writing and editing numerous articles for scholarly journals, popular magazines, and government bulletins, she discussed quality control in the refrigeration industry. She co-authored several works with her sister, Helen M.P. Betts . Having first experimented with freezing sweet corn in Minnesota in 1913, Pennington preceded Clarence Birdseye, who is usually credited with initiating industrial food freezing. Evaluating the best freezing processes for each variety of food, she especially enjoyed telling how she located strawberries in a Pacific Coast cold-storage plant and transported them by rail to Philadelphia. The berries were used to make the first out-of-season, fresh-fruit strawberry ice cream available in America.
Mary Pennington also helped the fish industry develop a standardized process to scale, skin, freeze, and dry-pack fish fillets as soon as the catch was delivered to the factory. Utilizing a government experimental freezer, she studied frozen fish samples to determine chemical changes over several months. She decided that fish which were glazed (frozen into a block of ice, thus sealing the fish from fungus and mold) did not lose nutritional qualities.
During World War II, the Office of the Quartermaster General requested that Pennington serve as a consultant to the Research and Development Branch of the Military Planning Division of the War Shipping Administration. Recognizing the vital role food played in military efforts, she sought new ways to cushion foods because insulating materials were being diverted to wartime usage. Pennington wrote a handbook for troops, The Care of Perishable Food Aboard Ship, and advanced her designs of refrigerated spaces for storing and transporting food.
Throughout her career, Pennington accrued many honors. In 1920, she became the first female member of the American Society of Refrigerating Engineers (also a fellow in 1947 and director). She actively participated on the organization's program, educational, and publications committees and was associate editor of Refrigerating Engineering's application data sections from 1944 through 1948. She was a member of the organization's council for two years beginning in 1946 and in 1952 was associate editor of the Refrigeration Data Book—Applications, having contributed to previous volumes. She was the first woman elected to the Poultry Historical Society's Hall of Fame. In 1910, she was the only woman starred in the second edition of American Men and Women of Science, indicating that she was among the top 1,000 researchers. She won the American Chemical Society's Francis P. Garvan Medal in 1940. Awarded to distinguished female chemists, this golden medallion and its monetary prize were considered, at the time, the most prestigious honor for women scientists. Although the American Chemical Society had gained more female members and established a women's service committee, women were rarely included on programs until the 1940s. Society awards went to men, not women, and the Garvan medal was the primary means through which women chemists received any recognition or publicity.
Frustrated that journalists mistakenly described her as "the woman who knows more than anyone else about iceboxes," Pennington summarized her career for The New Yorker reporter Barbara Heggie by noting, "Ye gods and little fishes, I'm an expert in the handling, transportation, and storage of perishables and the application of refrigeration." She worked so hard that her physician ordered her to visit the Caribbean to relax from her busy schedule. Pennington wrote her sister that, in fact, she spent most of her time trying to convince local businessmen of the socioeconomic benefits of refrigeration. Until shortly before her death, she continued to seek solutions and perfect methods concerning perishable foods.
Mary Pennington lived with her Persian cat Bonny in a New York penthouse apartment, over-looking the Hudson River, at 100 Riverside Drive; it was filled with Early American furniture, Quaker samplers, and family mementoes. A dark-eyed, quiet, confident woman, she enjoyed tending her terrace garden, growing the flowers that she loved as a girl. True to her professional achievements, she savored hosting dinner parties, serving primarily frozen foods to her guests. They enjoyed a smorgasbord of produce from a diversity of states—celery from Florida, salmon from Washington, and eggs from Ohio—and such dessert treats as raspberries on ice cream in December. To explain her vision of refrigeration and frozen foods, Pennington quoted poet Alexander Pope: "To take to the poles the products of the sun, And knit the unsocial climates into one."
Pennington promoted science education for women and influenced her niece and namesake, Polly Betts Elderfield , to become a chemist. Devoutly religious, Mary was a lifelong member of the Society of Friends. After falling in her apartment, the 80-year-old Pennington died of a heart attack in New York's St. Luke's Hospital on Saturday, December 27, 1952.
Mary Engle Pennington insured access to safe, nutritious diets. She also abetted the American economy and the modern commercialization of food, ensuring food producers steady prices and reliable markets while reducing losses due to spoiled produce. Grocery stores became a convenient means for farmers to sell their produce and for people to purchase healthy food. Cities swelled, absorbing the farmland that had been used to supply local markets, as long-distance hauling of frozen foods to urban areas altered consumer and demographic patterns. Assuring stability of food sources, despite season, weather, or region, Pennington alleviated scarcity of crucial dietary essentials. She almost singlehandedly guaranteed Americans a way to eat nutritiously and expeditiously as technology revolutionized most lifestyles. Every day, millions of Americans heat frozen food in microwave ovens. Pennington altered the way that food is perceived and handled in our society. Remarking that "food is like a newspaper. Good today, no good tomorrow," she recognized her contribution. "There is a thrill when a scientific idea suddenly strikes home in the form of a practical solution to an industrial problem."
Goff, Alice C. Women CAN Be Engineers. Youngstown, OH: self-published, 1946.
Hartwell, Anne. "Mary E. Pennington, Who Keeps Cold Storage Cold," in Woman's Journal. November 1930, pp. 11, 42–43.
Heggie, Barbara. "Profiles: Ice Woman," in The New Yorker. September 6, 1941, pp. 23–26, 29–30.
"Mary Engle Pennington: October 8, 1872–December 27, 1952," in Refrigerating Engineering. February 1953, p. 184.
Yost, Edna. American Women of Science. Philadelphia, PA: J.B. Lippincott, 1955.
Miles, Wyndham D. American Chemists and Chemical Engineers. Washington, DC: American Chemical Society, 1976.
Mullendore, William C. History of the United States Food Administration, 1917–1919. Stanford, CA: Stanford University Press, 1941.
Rossiter, Margaret W. Women Scientists in America: Struggles and Strategies to 1940. Baltimore, MD: The Johns Hopkins University Press, 1982.
Skolnik, Herman, and Kenneth M. Reese, eds. A Century of Chemistry: The Role of Chemists and the American Chemical Society. Washington, DC: American Chemical Society, 1976.
Correspondence resides in the Bureau of Chemistry files in the USDA Records, National Archives, Washington, D.C.; as well as with the Charles H. Herty Papers, Emory University, Atlanta, Georgia.
Elizabeth D. Schafer , Ph.D., freelance writer in history of technology and science, Loachapoka, Alabama