Tons of old chemicals that have turned toxic and potentially explosive were being removed from two buildings at Hunter College, where they were like "a time bomb" in science laboratories, officials said.

The discovery of the chemicals, some up to 30 years old, forced the college to close Thomas Hunter Hall and the North Building on May 20, city Department of Environmental Protection and school officials said.

Among the chemicals found were 25 canisters of explosive and highly reactive chemicals, including ether and picric acid, and 90 canisters of gases, some of which may be poisonous, said department spokeswoman Joan Paylo.

"Picric acid, when it crystallizes, can be as explosive as dynamite in small quantities. It is feared throughout labs when it is old," Paylo said, calling the chemicals "a time bomb."

College officials learned about the chemicals' presence when the Fire Department discovered ether during an inspection May 11, college spokesman Robin Elliott said.