Who Killed Napoleon?

A lock of Napoleon’s hair.

After his defeat at Waterloo in 1815, Napoleon was exiled to St. Helena, a small island in the Atlantic Ocean, where he spent the last six years of his life. In the 1960s, samples of his hair were analyzed and found to contain a high level of arsenic, suggesting that he might have been poisoned. The prime suspects are the governor of St. Helena, with whom Napoleon did not get along, and the French royal family, who wanted to prevent his return to France.

Elemental arsenic is not that harmful. The commonly used poison is actually arsenic(III) oxide, As₂O₃, a white compound that dissolves in water, is tasteless, and if administered over a period of time, is hard to detect. It was once known as the “inheritance powder” because it could be added to grandfather’s wine to hasten his demise so that his grandson could inherit the estate!

In 1832 the English chemist James Marsh devised a procedure for detecting arsenic. This test, which now bears Marsh’s name, combines hydrogen formed by the reaction between zinc and sulfuric acid with a sample of the suspected poison. If As₂O₃ is present, it reacts with hydrogen to form a toxic gas, arsine (AsH₃). When arsine gas is heated, it decomposes to form arsenic, which is recognized by its metallic luster. The Marsh test is an effective deterrent to murder by As₂O₃, but it was invented too late to do Napoleon any good, if, in fact, he was a victim of deliberate arsenic poisoning.

Doubts about the conspiracy theory of Napoleon’s death developed in the early 1990s, when a sample of the wallpaper from his drawing room was found to contain copper arsenate (CuHAsO₄), a green pigment that was commonly used at the time Napoleon lived. It has been suggested that the damp climate on St. Helena promoted the growth of molds on the wallpaper. To rid themselves of arsenic, the molds could have converted it to trimethyl arsine [(CH₃)₃As], which is a volatile and highly poisonous compound. Prolonged exposure to these vapors would have ruined Napoleon’s health and would also account for the presence of arsenic in his body, though it may not have been the primary cause of his death. This provocative theory is supported by the fact that Napoleon’s regular guests suffered from gastrointestinal disturbances and other symptoms of arsenic poisoning and that their health all seemed to improve whenever they spent hours working outdoors in the garden, their main hobby on the island.

We will probably never know whether Napoleon died from arsenic poisoning, intentional or accidental, but this exercise in historical sleuthing provides a fascinating example of the use of chemical analysis. Not only is chemical analysis used in forensic science, but it also plays an essential part in endeavors ranging from pure research to practical applications, such as quality control of commercial products and medical diagnosis.