1.) A substance such as
lemon juice, rain, obviously acid rain, or milk, that have a pH of under 7.0. They conduct
electricity, and have a sour taste. Weak acids (milk & rain) don't have much of an effect on human skin (although they have a horrible effect on teeth). Strong acids such as acid rain & battery acid (especially car) will "eat away" your skin and flesh probably up to the bone.
2.)
Lysergic acid diethylamide, LSD, LSD-25, or acid. A very, very, very, very, very, very, very, very, very, very, very, very to the 9000th power dangerous that a gram of it can kill you many times over.
A few micrograms can make you high for eight to twelve hours. In the late 50's to the early 70's, it was probably the most common deaths among hippies other than random violence.