1.35gm of the powder, 2 capsules is more than enough for a peaceful death. The effect is greatest when the salt reaches the acid environment of the stomach, so one’s stomach should be empty before taking the cyanide.
A noted variation to this methodology was used by computer pioneer Alan Turing, who injected the dissolved salt into an apple before eating it. Alan’s act of suicide was interestingly omitted from the 2014 film, ‘The Imitation Game.’
What about hydrogen cyanide gas?
Potassium cyanide is not the only form of cyanide that is lethal. There is also the gas, hydrogen cyanide.
The process of making hydrogen cyanide gas mimics that used historically in the US gas chamber in acts of capital punishment. There, the solid cyanide salt (sodium, potassium or calcium cyanide) was added to concentrate acid in order create the legal gas. The gas chamber was abandoned in the 1990s by most US states for reasons of being cruel and unusual punishment.
Hydrogen cyanide can be made by placing 500ml of concentrated hydrochloric acid in a plastic bucket and adding a few grams of the solid salt. This will rapidly produce hydrogen cyanide. If this is done in a confined space (a vehicle,or small room with windows shut) the inhalation of this gas will lead to a rapid and inevitable death.
Concentrated hydrochloric acid (>25%) is readily available from hardware stores. The smell of the hydrogen cyanide gas is sometimes reported as similar to that of bitter almonds.