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Can a Gold Potassium Cyanide Tablet Really Kill a Car Battery?

Q. I am researching the use of Gold Potassium Cyanide by the French Resistance in WWII. Supposedly, a small tablet of the substance (<500 mcg), when dropped into a car battery will render the battery inoperable, by coating the battery plates (presumably with gold).

Is this possible or likely?

Arthur Turley
amateur historian & writer - London, UK
August 26, 2016

September 2, 2016

A. Hello Arthur, I replied to your question a few days ago but for some reason it didn't post [ed. note: just running a little behind] ...

August 31, 2016
Hello Arthur, I am not an expert on batteries used in WW2 but can tell you modern batteries use a mole percentage of about 49% sulfuric acid. My experience with gold plating is extensive however. As you may know, sulfuric acid in concentrations as low as 10 percent can drop gold out of solution if not added correctly. There is also a severe reaction that takes place when KCN is added to H2SO4. Why would tabs of Potassium Gold Cyanide be used? Why not just KCN? Anyway to answer your question, the plates would not be covered with gold (if that was actually used.) The gold will not stay in the acid solution long enough to coat the plates. Just the addition of KCN will have an explosive reaction inside a battery especially if sealed immediately, and render the battery inoperable. Just curious, what is the basis of this question and how it relates to the French Resistance?

Are you sure the tablet you refer to is potassium gold cyanide and not plain potassium cyanide? Anyway, when cyanide is introduced to sulfuric acid you probably know, creates cyanide gas, and could cause the battery to heat up and explode. Would it ruin the battery? You bet! If for some reason the tablet was potassium gold cyanide, the gold contained in the tablet would drop to the bottom of the battery and not coat the plates. Sulfuric acid as low as 10% can drop gold out of solution if not added correctly. Just curious, what is the full basis of your question? If it were sabotage, wouldn't it be easier for the enemy to take a coil wire out of the vehicle so it wouldn't start?

Mark Baker
Process Engineer - Phoenix Arizona

A. An interesting question and answer!
I like the concept of a battery exploding with the pressure of hydrogen cyanide gas. The expression 'hoist with his own petard' comes to mind!
It seems extremely unlikely to work and there are many far simpler, cheaper and safer ways of disabling a battery

Geoff Smith
Hampshire, England
September 3, 2016

Q. My Dad, a chemist, served in WWII in Algeria as an ordinance expert. One of his duties was packaging material to drop into France in support of the resistance. He told me of these tablets that were included with the dropped material, and told me they contained gold.

No, I am not sure if the tablets are KCN, Au KCN, or something else. A tablet that caused an immediate explosion would have not been effective, as the goal was to sabotage the battery without detection.

Any thoughts on what it could be? Would KCN in small quantities (a few grams) perhaps disable the battery without any explosion?

I am researching for a novel, and want to get the facts right.

Arthur Turley
- London, UK
September 3, 2016

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