Taken from
http://www.canine-epilepsy.com/Poison.html
If he got into an acid -- by chewing a battery, for example, or drinking bleach -- Milk of Magnesia will negate the acid. Give one teaspoon for every five pounds of pet. Absorb it with charcoal. Giving your pet activated charcoal, either in tablet form or as a powder mixed with water, will quickly absorb toxins from the stomach before they have a chance to be absorbed into the system. Even after giving charcoal, however, the original poison is still in the gut, so you'll want to see your vet right away