During the 18th and 19th centuries in Europe, a single pinch of a white, odorless, and tasteless powder could cause a healthy person to slowly die in agony without leaving a trace. Victims were simply recorded as having "died of illness."

This powder was arsenic. Among lawyers, doctors, and journalists of that era, it earned another chilling moniker: "inheritance powder." This reflected a period when arsenic became an ideal murder tool for acquiring property, a situation that persisted until forensic science revolutionized the legal landscape.

According to historical records, arsenic accounted for a significant proportion of intentional poisonings in the 19th century, making up about one-third of all poison-related criminal cases in England, earning it the title "King of Poisons."

'The perfect weapon'

Arsenic trioxide, the most common form of arsenic, exists as a fine white powder that dissolves easily in food and drinks. It is odorless, tasteless, and does not cause immediate reactions. Victims typically fell ill gradually over several days or weeks before succumbing.

Arsenic trioxide in white powder form. Photo: Klarity Health Library

Symptoms of arsenic poisoning, including vomiting, diarrhea, abdominal pain, and exhaustion, closely resembled common intestinal diseases prevalent in 18th and 19th century Europe, such as cholera, typhoid, and dysentery. Given the rudimentary state of medicine at the time, doctors rarely suspected poisoning.

Crucially, autopsies were not widespread or mandatory then. Most family deaths resulted in quick burials. To secure a poisoning conviction, courts relied almost solely on testimony or catching the perpetrator in the act, which was nearly impossible with a "silent" poison like arsenic.

Arsenic perfectly suited the motive of "silent murder" because it was readily available, inexpensive, and difficult to detect. Perpetrators were often family members, those directly involved in cooking meals or caring for the victim during illness. This intimacy helped arsenic become a "weapon in the kitchen."

19th-century British and French newspapers referred to arsenic as "inheritance powder" or "poudre de succession"—a powder that created "illness-induced" deaths to seize inherited assets.

'King of poisons' dethroned

One of the classic arsenic poisoning cases was that of Marie Lafarge in 1840 in France. Charles Lafarge, a foundry owner, died after several days of suffering from cholera-like symptoms. Before his severe illness, he had consumed cake and food sent to him by his wife, Marie. Marie had previously persuaded her husband to draft a will leaving all his property to her.

His family and the police suspected an unusual death, but how could they prove the presence of poison in Charles’s body?

For the first time in French judicial history, the court summoned chemists. The trial quickly evolved into a scientific debate. Experts fiercely argued over a new method: the Marsh test.

The Marsh test was the first chemical method in history capable of detecting arsenic in a deceased person's body, invented by British chemist James Marsh in 1836.

The principle of the Marsh test involves converting arsenic in a sample (organs, food, vomit) into arsine gas, which is then burned to create a metallic arsenic deposit on a glass surface. This deposit can be observed directly and distinguished from other metals.

After multiple tests, the final results confirmed arsenic in Charles’s body. Marie was sentenced to life imprisonment with hard labor.

Although Marie was later pardoned, the case marked a pivotal turning point: arsenic was no longer an invisible poison before the law. From this point on, forensic science officially became a crucial part of uncovering the truth in criminal cases.

Following the Marsh test, methods for detecting the "King of Poisons" continued to improve. Laws controlling the sale of poisons were enacted. Autopsies gradually became a mandatory standard in cases of unnatural death.

As arsenic ceased to be the "perfect weapon," criminals began to turn to other poisons such as cyanide, thallium, and pesticides, forcing forensic science to keep pace to uphold justice.

Tue Anh

(according to

Britannica

Poisoner's Handbook

PoisonedLives