February 13, 1785 - Birth of Pierre Louis Dulong who found the relationship between the specific heat of an element and its atomic weight

At the age of 16, he entered the Ecole Polytechnique in Paris (France), where he was a student of two of the most brilliant chemists of his time: Claude Louis Berthollet and Louis Jacques Thénard.

After completing his higher studies, he qualified as a doctor and began to practise his profession. However, his future was not very promising in this field. Dulong abandoned medicine and began working in the chemistry laboratory owned by the aforementioned Berthollet. Later, Thénard, noticing the young Dulong's great value, offered him a job as an assistant at the polytechnic school where he had studied.

What seemed to be a stroke of good fortune in his fortuitous discovery of nitrogen trichloride (1813) turned into a small tragedy that cost him the sight of one eye and almost one hand.

Dulong's most important work in the field of physics was carried out jointly with Alexis-Thérèse Petit, professor of physics at the Ecole Polytechnique. In 1817 they both showed that Newton's law of refrigeration was true only for small temperature differences. Their work on temperature measurement and heat transfer (1818) was awarded a prize by the French Academy.

A year later, their experiments on the expansion and measurement of temperatures heat transfer and specific heat of gases led them to establish the empirical law on specific heats, known as Dulong and Petit's Law. This law would later be used in the determination of atomic weights.

In 1829, he found that, under the same conditions of pressure and temperature, equal volumes of all gases give off or absorb the same amount of heat when they are rapidly expanded or compressed to the same fraction of their initial volumes. He also deduced that the temperature changes accompanying these changes are inversely proportional to the heat capacities of the gases at constant volume.

With François Arago, he published a study of the elasticity of steam at high temperatures (1830). His last article (1838) describes the experiments he carried out to determine the heat developed in a chemical reaction.

In addition to the discovery of nitrogen trichloride (or azo chloride), Dulong and Petit's Law, and his research on water and steam in collaboration with Arago, Dulong also succeeded in synthesising hypophosphoric acid, published a study on the density of various fluids, and measured the refractive index and speed of sound in different gases.

If you want to know more about this scientist, click on the following link: Pierre Louis Dulong