Mary Engle Pennington

Mary Engle Pennington

Mary Engle Pennington on top of a box car. Courtesy the Collections of the University of Pennsylvania.

When people called Mary Engle Pennington (1872–1952) “The Ice Lady” it was not because of her personality. Pennington, a bacteriological chemist, spent most of her career studying refrigeration and how best to use it to keep foods fresh and safe to eat. She designed refrigerators for the home and refrigerated cars for railroads, and she set scientific standards for food safety.

Pennington was born in Nashville, Tennessee. Her mother was a Quaker from Philadelphia, and when Mary was a child the family moved to Philadelphia to be closer to her mother’s family. At 12 years old, she discovered a book about medical chemistry and became fascinated by the idea of atoms and molecules—things she could not see but that were very real and important. It dawned on her that if all the invisible and unnoticed oxygen on Earth suddenly disappeared, all living things would die. “Like a flash in a dark place, I got the idea of the realness of the invisible world,” she once recalled. Pondering this, she was instantly hooked on chemistry.

When Pennington was 18, she enrolled at the University of Pennsylvania, which was just a few blocks from her home. After studying science for four years, she was awarded a “certificate of proficiency.” She had completed all the work for a bachelor of science degree, but the university did not grant bachelor’s degrees to women at that time.

Thankfully, Pennington’s teachers felt differently about women’s education, and they encouraged her to stay on at Penn, where she eventually earned her Ph.D. She carried out postdoctoral research in chemical botany at Penn, and then went to Yale University, where she did postdoctoral research in physiological chemistry. After that, she came home to Philadelphia and spent a few years working in medical labs.

In 1904 Pennington took a job with the City of Philadelphia, where she was in charge of ensuring the safety of milk and dairy products sold in the city. Her work was now more bacteriology than chemistry, and this would be true for most of her career. Contaminated food was a big problem in those days, largely due to unsanitary handling. Dairy farms weren’t always sanitary, nor were the food markets. Ice cream sold by street vendors was especially unsafe. Pennington knew that legal regulations were necessary, but she also knew she’d meet resistance if she tried to force the issue. Instead, she met one-on-one with farmers and vendors to explain the problem, actually showing ice cream vendors slides of the bacteria that were found growing in their buckets. She convinced farmers of the need to inspect their milk before shipping it, and vendors of the need to boil their buckets. When she finally pushed for laws requiring such practices, she met little opposition. The Ice Lady would become famous for this warm and personal approach.

Pennington soon caught the eye of the public health crusader Harvey Washington Wiley, who recruited her to work for him at the U.S. Department of Agriculture (USDA). Wiley had lobbied for the 1906 Pure Food and Drug Act, which created the Food and Drug Administration (FDA) to oversee the safety of food and medicines sold in the United States. Pennington became heavily involved in the activities of the FDA and was often called in as an expert witness in court cases involving accusations of food-safety violation.

At the USDA, Pennington did pioneering research on refrigeration and how it could be used to keep food safe from bacteria, which can spoil food. Bacteria grow faster in warmer temperatures, so chilling food prevents bacteria from growing. Pennington researched the ideal temperatures for storing different kinds of food to prevent bacterial growth. She paid particular attention to eggs. (She even invented the modern egg carton to keep eggs from breaking during shipping.) Shipping food was a special problem because of the time it took to transport food from one end of the United States to the other, and food often went bad in transit. Pennington designed refrigerated railroad boxcars that were well insulated so that food stayed cold throughout its trip.

In 1919 Pennington left the USDA to work for a company that made refrigerator insulation, and in 1922 she started her own consulting business in New York City. She lived there until her death in 1952 at the age of 80.

Catalyst Series: Women in Chemistry

Women in Chemistry


Hear It Firsthand


Connect with CHF


Distillations Podcast logo
Listen to the latest episodes of CHF’s award-winning podcast.

Historically Grounded Perspectives
