By Eamonn Ryan
In the mid-18th century, the concept of refrigeration was largely confined to natural methods – storing ice harvested in winter or utilising cool underground spaces. This is Part 1 of a two-part series.
However, a quiet revolution was brewing in the burgeoning field of chemistry and physics, spearheaded by pioneering minds. Among them was William Cullen, a Scottish physician and chemist, whose groundbreaking experiment in 1756 at the University of Glasgow marked a pivotal moment: the first recorded creation of artificial ice through an evaporative cooling process. This achievement, though not immediately commercialised, laid the fundamental scientific groundwork for the refrigeration industry we know today.
The scientific landscape of cold
To appreciate Cullen’s innovation, it’s important to understand the scientific context of his time. The nature of heat and cold was still a subject of intense debate. While theories like the caloric theory (heat as a fluid) were prevalent, scientists were beginning to grasp the principles of phase change – how substances absorb or release heat when they change state (for instance, from liquid to gas or liquid to solid). It was known that evaporation caused cooling, as evidenced by the chilling effect of alcohol evaporating from the skin. Cullen’s genius lay in his ability to harness and intensify this natural phenomenon to achieve temperatures low enough for freezing.
Cullen’s ingenious experiment
Cullen’s experiment was elegantly simple yet profoundly effective. He demonstrated that by creating a partial vacuum above a volatile liquid, he could significantly accelerate its evaporation, thereby drawing heat rapidly from its surroundings.
The core setup involved:
- A flask of diethyl ether: Cullen chose ether due to its low boiling point and high volatility, meaning it evaporated readily even at room temperature
- A vacuum pump: He placed the flask containing ether inside a larger vessel, which was then connected to a vacuum pump
- A small amount of water: Crucially, he placed a small container of water (often in a dish) within the vessel, alongside the ether flask, but not in direct contact with the ether itself