English Chemist and Physician
William Henry was a leading experimental chemist who helped establish the validity of Dalton's atomic theory. Best known for his investigation of gases, he formulated Henry's Law, which describes the relationship between mass and pressure for a gas dissolved in liquid. Henry also wrote the most influential chemistry textbook of his time, which stood as the standard for over thirty years.
Henry was born into a wealthy English family in Manchester. At age 10, he was injured by a falling beam and left with chronic, lifelong pain. This limited his play and led to his becoming an avid student. At age 16, he began his studies in medicine and in 1795 entered the University of Edinburgh, Scotland. A year later, however, he left to work in the family's manufacturing business. During this period, he did original research in chemistry. He returned to school in 1805 and earned his medical degree in 1807.
Henry was fascinated by the work of the French chemist Antoine Lavoisier (1743-1794). A generation earlier, Lavoisier had made chemistry a true scientific discipline, providing basic principles and challenging the existing vestiges of alchemy. Henry delivered lectures on the French chemist's work, and these evolved into Elements of Experimental Chemistry. First published in 1801, this textbook went through 11 editions in 30 years and introduced generations of chemists to Lavoisier's chemical nomenclature and the use of careful experimental measurement.
Henry was a friend of John Dalton (1766-1844), a friendship that was pivotal to both of their careers and to chemistry. Dalton is famous for his atomic theory, which holds that all the elements of matter are made up of indivisible, indestructible atoms. Dalton was brilliant and audacious in his thinking about chemistry, but clumsy and careless in the lab. As a teacher, Dalton also had little time or money for experimentation. Henry, on the other hand, had the time, the money, and the talent. He performed critical experiments that supported Dalton's theory and stimulated Dalton's thinking about atoms. Most of Henry's experiments were done on gases because they provided a simpler chemical model than other forms of matter. During this time, he formulated Henry's Law, his most famous achievement. Simply stated, this law holds that the mass of a gas that dissolves in a liquid is proportional to the pressure exerted by the gas on the liquid if the temperature is kept constant. Henry's Law is limited to less soluble gases and gases that do not react chemically with the liquid. Still, it is useful and continues to be employed to explain carbonation and to make calculations for safe diving.
Thanks in large part to Henry, the atomic theory came to be generally accepted. This led to a deeper and more subtle view of nature. Elements could be identified, ordered, and categorized according to their chemical properties. The monumental result of atomic theory was the creation of the periodic table of elements, which is one of the most important tools for understanding and manipulating materials.
Henry himself was slow to back atomic theory. Many historians believe that, had he become an early proponent, he would share credit with Dalton. While he had taken a leap in accepting Lavoisier as a young man, later in life Henry became cautious and did not take a stand when his experiments pointed to change (as with the composition of hydrochloric acid). He held onto old beliefs, such as insisting heat had mass. For society, Henry's reluctance had important results in medicine.
In 1824 Henry's bad health ended his career as an experimental chemist. Surgery on his hands made further work in the lab impossible. Henry turned his attention to medicine. He theorized that there was a chemical nature to disease, and that using heat to destroy the bad chemicals could alleviate illnesses and reduce the spread of diseases. During the 1831 cholera epidemic, he created an inexpensive and simple device that used heat to disinfect clothing. The device was effective and might have prevented illness and saved many lives, but, again, Henry failed to become an advocate. Heat sterilization was forgotten for another 30 years until Louis Pasteur (1822-1895) developed his germ theory of disease.
Along with chronic pain, Henry suffered from depression. In 1836, after a dozen years of being unable to work in the lab, he took his own life.