Originally, exactly as much as a volume of water equal to the cube of the hundredth part of the metre, at the temperature of melting ice. I don't find that terribly helpful. Not many did. That's why, in 1889, the mass of the kilogram was redefined as being equal to the IPK.
Boiling water is also an effective poison ivy killer. If the area where you will be killing poison ivy has no other plants you wish to keep, pour boiling water over the poison ivy plant. Boiling water will kill any part of a plant that it comes in contact with, so be careful using this around desirable plants.
Tips Poison ivy, oak and sumac: Tips for managing. A rash from poison ivy, poison oak or poison sumac is caused by an oil found in these plants called urushiol (you-ROO-shee-all). When this oil touches your skin, it often causes an itchy, blistering rash. Most people can safely treat the rash at home.