Inheritance Powder

Spoiler Warning: I discuss critical details of the mystery novel The Pale Horse by Agatha Christie, and various iterations including Agatha Christie’s Marple: S06E02

In Cluedo there’s the rope, the revolver and the dagger (though Clue‘s kitchen knife seems more appropriate), and then improvised bludgeons are overly represented (lead pipe, candlestick, spanner). Curiously omitted is poison*, considering that Agatha Christie’s murderers often turn to poison for their dark purposes. It was actually comforting to see belladonna plants harvested for medicinal use early in Greenshaw’s Folly assured they would figure into the imminent mystery developing.


The classic poison of the middle-ages, arsenic is both an agent and a product of industrial smelting. Arsenic became notorious as inheritance powder for its use in Europe, especially among Italian aristocracy, to accelerate magisterial turnover. Arsenic is also a component of green paints and glazes, and has claimed the lives quite by accident of plenty of unknowing, or merely careless, artisans.

Well into the twentieth century arsenic has been sold to the public in insecticides and weed killers, and is relatively easy for the novice murderer to come by.

Don’t worry too much about murder by arsenic, though. Firstly, arsenic poisoning takes a while. You have to slip small doses into your target’s tea. Make it strong tea to disguise the flavor. And not too much, or your victim will puke and eye you — and tea — suspiciously from then on. Arsenic isn’t water soluble, either, so it floats to the top in conspicuous oily blobs that might be concealed by cream. A compulsive stirring habit might help.

Then there’s a matter of pathology. During the Renaissance, Cholera was still a problem, and arsenic poisoning expressed similar symptoms. With the development of forensics, arsenic poisoning reveals itself in hair and nails, much like lead poisoning. Modern pathologists can determine pretty exactly when a victim started his arsenic dietary supplement, and by how much. These days, arsenic poisoning is strongly indicative our murderess doesn’t know what she is doing.

There is the unfortunate matter of arsenic pollution which poisons villages at a time. Arsenic gets nicely absorbed into soils and into vegetables that grow there. Rice is a particular culprit for shortening lifespans en mass. Too much pollution, and it gets into the water table and keeps pathologists and health inspectors really busy.


Skilled murderers use thallium. Indeed, thallium is the sort of poison that, like explosive compounds, provides a self-contained process of sorting out the skilled from the …insufficiently skilled. Thallium is odorless, tasteless, water-soluble and readily absorbed in the skin. Other than hair loss, the symptoms of thallium poisoning are similar to countless other ailments. People try (and sometimes succeed) to murder with thallium to this day, discovered by the authorities less often than we’d like to admit.

The original novel of The Pale Horse is credited for saving at least two lives by alerting readers to the symptoms of thallium poisoning that matched too similarly to a real-life case. It’s also inspired the occasional murderer to resort to thallium. Sometimes a little too much knowledge can lead to temptation. Indeed, in the nineteenth and twentieth centuries, Thallium became notorious as inheritance powder for its use to accelerate… yeah. That.

Thallium was the active ingredient in rat and ant poison until its hazards became fully appreciated. It was also used in treatments for ringworm and other skin infections. Since then, especially with the development of antibiotics, we’ve replaced medicinal thallium with agents safer and more effective.

Thallium is still used in optics and electronics, though. When not used to close the distance between a prodigal heir and his prize, thallium is responsive to infrared light, hence it is used in photoresistors and daylight-reactive lenses. So if looking to poison someone with thallium, you might need a handy specialist.


We tend not to think of Cyanide as a murderer’s weapon, unless the murderer is the state. Gas chambers use hydrogen cyanide, including those used in the Nazi genocide program.

Cyanide has a shorter half-life (that is, biological half-life) than other poisons, so it’s not very useful for gently sloping the health of a targeted individual for the worse. Cyanide is everywhere, including the food we eat. We are cautioned to avoid the seeds of fruits, such as the seeds of apples, but you will have to eat a lot of apples — even an uncomfortable number of apple seeds — to poison yourself.

No, you need concentrated cyanide, and you poison your target with one dose. Look to old fashioned film photography, electroplating and plastics manufacturing which all use the stuff. A little goes a long way. All the way. This, of course, presents the unfortunate problem of an adequately healthy person transforming into a lifeless cadaver rather quickly and conspicuously, which tends to get the constabulary and local coroners all astir. Of course, if there’s twenty other suspects at your party, this might be less of an issue.

Still, cyanide capsules are more notorious for appearing in spy and war fiction as suicide caps when looking to avoid a fate worse than death. At the end of WWII rumors of rape and brutality by the Soviet front terrified Nazi leaders and their families, and many of them used cyanide to take their own lives rather than risk fleeing into the countryside.

When not requiring a modest-paced lingering death, cyanide is a fine means of murder by poison. John Tawell murdered his mistress in 1845 with hydrogen cyanide when their relationship was at risk of being discovered. He’s more known for the telegraph facilitating in his arrest. Then of course Rasputin was offered petit fours laced with cyanide. They didn’t work, and no cyanide was found in his system. Some say he was avoiding sweets at the time, while others say he ate over a dozen. It may have been the cyanide evaporated during the baking of the treats; they were prepared by accomplished chefs, not exactly accomplished murderers. In Agatha Christie’s works, cyanide is used in And Then There Were None and Sparkling Cyanide.

Cyanide poses a threat also due to smoke inhalation. Textile and plastic fires will produce cyanide gas. Warehouse and nightclub fires (nightclubs fitted with polyurethane soundproofing) are known for killing club-goers and workers via cyanide poisoning. Fortunately for the rest of civilization, cyanide gasses are lighter than air, and don’t linger to murder cities at a time, but in fire science, these are notorious situations for hazardous materials turn-out, or just letting the blaze burn.

And Beyond

In Arthur Conan Doyle’s The Sign of Four the use of curare darts proves to be an exotic enough a clue to indicate someone who’s been to South America, or even a native from there. It raises a problem with poisons — or delivery systems — that are not readily available, though a clever murderer might borrow someone else’s supply of hazardous materials to make some hazards of his own.

Ricin and Abrin are extremely deadly, possessing all the dangers of thallium but more so. But they’re products of unique castor oil plants and have no functional purposes in medicine or industry (with the exception of some experimental cancer treatments). This was the toxin of the notorious umbrella murder of Georgi Markov. Not only did the rarity of the toxin implicate a well-funded hit, but the delivery pellet was machine tooled, and required no less than a factory to craft. It was a superfluous display of tradecraft that served as a KGB signature. Opinions differ as to whether or not that was intended. Ricin attacks tend to indicate a professional hit, though Agatha Christie utilizes Ricin in the short story The House of Lurking Death

Then there’s 210Po (polonium-210), probably the deadliest poison to be willfully used to murder a person. Alexander Litvinenko was in political asylum in London when FSB agents Andrey Lugovoy and Dmitry Kovtun slipped 10ccs of 210Po into Litvinenko’s tea. It was two-hundred times the lethal dose.

210Po is thankfully too rare for common murder, and really too hazardous to use as a poison. Lugovoy and Kovt suffered from radiation poisoning just from handling the stuff, and the trails of radioactivity provided Scotland Yard a brilliant path to follow all the way back to the port from which it entered London. There’s also the matter of collateral damage, with poor Litvinenko irradiating everyone he happened to meet before he fell ill and was properly diagnosed.

The rarity of radionuclide polonium-210 was such that it not only was able to implicate a nation, but specific leaders and officials. The attack was assuredly an official FSB operation personally authorized by Premiere Vladimir Putin.

Next time, just shoot him, guys.

* The Cluedo prototype, Murder! featured poison, and a syringe (also bomb, shillelagh, fireplace poker and axe and the more familiar knife, rope and revolver). There’s no clear cause for poison’s removal, except that the official release reduced rooms, weapons and suspects all down to six. Poison was culled with the other weapons.


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