Probably every reader/viewer of sci-fi/fantasy has at one point encountered the classic bit of trickery: "The poison wasn't in the drink - it was in the cup!" - I am imagining a hypothetical reverse situation.

Suppose I am involved in an official ceremony with a visiting dignitary - one whom I would like to assassinate. The ceremony has me provide a drink (not necessarily wine) of which he will partake - making poison an obvious method of assassination. However, due to hard lessons learned from past misfortunes, the form of the ceremony has been changed in the following ways:

  • I provide the drink, but both the dignitary and I must partake of it.
  • Each of us will provide our own ceremonial cup, so neither of us can tamper with the other's.

This should, it is thought, defeat any attempt of mine to poison the dignitary without also poisoning myself. However, a devious alternative has suggested itself to my mind, and I'm off to see the chemist*.

I ask the chemist to provide me with:

  1. A poison that I can add to the drink, which, in lethal dose, is sufficiently undetectable to smell and taste.
  2. An antidote that I can have in my cup, which is:
  • Preferably something I can smear around inside the cup (or added to something I can smear), as opposed to a liquid or powder which could fall out;
  • Small enough in quantity that the cup appears empty to a cursory glance, yet of sufficient quantity/potency to neutralize the lethal dose of poison I will drink;
  • Guaranteed to dissolve/mix with the drink without too much agitation (no more than 5 seconds of swirling it under my nose and enjoying the bouquet).

What does my chemist (*who is familiar with all the compounds generally known by the early-to-mid 1800s, but knows nothing of modern synthetic chemistry) suggest to me?

Some final freedoms/constraints:

  • The drink need not be alcoholic; I may choose from a selection that includes anything from 0% to 40% alcohol per volume.
  • My cup can be made of metal, wood, glass, pottery, or some artful combination; however, it is only a cup and cannot contain hidden compartments/mechanisms etc.
  • DKNguyen makes the excellent point that if a poison is sufficiently slow-acting, an antidote could be taken after the ceremony. (Or, for a fast-acting poison, perhaps before.) However, my interest is primarily in the combination of chemicals that could be hidden in the drink/cup in this way.
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    $\begingroup$ If it's slow acting can't you just take the antidote afterwards? $\endgroup$ – DKNguyen Apr 20 at 22:12
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    $\begingroup$ Certainly! But so could (hypothetically) the other guy... the setting is a fun illustration; the question is focused on the chemistry. $\endgroup$ – Qami Apr 20 at 22:13
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    $\begingroup$ "The vessel with the pestle has the brew that is true" and now I'll shut-up and get back in my box. $\endgroup$ – A Rogue Ant. Apr 20 at 22:23
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    $\begingroup$ Your poison reminds me of Iocane powder. Watch to the end of the clip to see an alternative to your scenario. $\endgroup$ – JBH Apr 21 at 4:40
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    $\begingroup$ @JBH Without even clicking on the link, I can be certain that I never want to go in against a Sicilian when death is on the line. ;) $\endgroup$ – Qami Apr 21 at 5:01

One of the most famous poisons of all time seems to fit the bill here: Cyanide.

Cyanide is neutralised by B12 vitamins, in particular Hydroxocobalamin, but all are somewhat effective. B12s are found naturally in liver, as well as fermented plant foods like tempeh and in seaweed. The first usage of vitamin B12 (take by eating liver) as a treatment in our world is 1920, but its deficiency had been described in ~1850 as a disease. These are a bit of a stretch for your conditions, but another remedy exists.

Ferric ions are commonly found in rust. They are what's called a competitor for cyanide, meaning that cyanide will try to bind to the iron and to the enzymes, but it won't be able to bind both, so a sufficient concentration of ferric ions will effectively neutralise the cyanide.

The chemist could therefore recommend poisoning the wine with cyanide and use a copper cup to drink. Prior to the ceremony, fill your cup with water containing a high concentration of rust and let it evaporate naturally. The rust in the water will form a reddish coat on the inside of the cup, hidden by the brown copper. This will dissolve into the wine with a few slushes, and neutralize the poison. It will ruin the taste of the wine however

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    $\begingroup$ Brilliant. Only disadvantage is that Cyanide has a very distinctive odor and taste, not easily hidden by any beverage. "Here, have a toast of this bitter almond liqueur?" $\endgroup$ – PcMan Apr 21 at 12:14
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    $\begingroup$ @PcMan Amaretto is a drink at about 25% alcohol that can be made from bitter almonds and was supposedly created in the 16th century. Makers must treat the almonds first to remove the cyanide, so if there is a trace of it in the drink that could harm our esteemed guest's health, the distillers will surely be whipped for their incompetence $\endgroup$ – Whitehot Apr 21 at 12:25
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    $\begingroup$ That's where you don't poison the wine at all, you just blame it. Poison the cake and put the antidote in the cutlery, far more suited to a touch of almond. $\endgroup$ – Separatrix Apr 21 at 13:17
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    $\begingroup$ @Qami Very good point, I had forgotten to check the solubility! Yes rust on its own is insoluble, but combined with a chelating agent, like citric acid, it becomes quite soluble. You would probably need a bit more preparation with your cup beforehand, but it should still be possible, seeing as ferric citrate would be left after evaporation, as it is more stable than ferric ions. It is however stretch the chemical knowledge of the 1850s a bit... As for the cup, a coloured glass goblet should work very well too for this endeavor. $\endgroup$ – Whitehot Apr 21 at 16:05
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    $\begingroup$ @Whitehot - yes, no objections here. Neutralizing in the cup is just a safer way :) $\endgroup$ – Alexander Apr 24 at 21:14

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