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.
No, the poison ivy blisters are the caused by the body's natural allergic reaction to the plants. If the blisters break and ooze, the fluid does not contain the oil that causes spreading. The rash-causing oil, called urushiol, from the original contact with poison oak and poison ivy will continue spreading (unless removed) for the first one or two days. It is found in in all parts of poison ivy, oak and sumac plants whether dead, dormant or thriving.