Four persons died near Baruipur of South 24-Parganas late on Tuesday after they allegedly consumed formalin mixed with liquor, mistaking the former for water while having drinks.

Baruipur police said victims were drinking alcohol at a poultry farm in Rana village when they ran out of water. They picked up a bottle of formalin mistaking it for water.

The deceased were identified as Shankar Mandal, Saheb Halder, Rajat Halder and Munim Yadav, all in their 30s. The first three were residents of Raidighi, while the Yadav hailed from Bhojpur.

Two other persons hailing from Bhojpur who consumed the deadly mix are critically ill and fighting for life at a hospital in Calcutta.

All victims were first taken to Baruipur subdivisional hospital where the four succumbed. Two others were transferred to Chittaranjan Medical College & Hospital in Calcutta.

Baruipur police have begun a probe and recovered the bottle of the suspected chemical (formalin), which is basically a water-based solution of formaldehyde, a pungent gas, which can cause death from swelling of throat or burns in lungs if consumed.

A professor of Kalyani University’s chemistry department said: “Drinking as little as 30ml (two tablespoons) of formalin can cause death.”

Police and local sources said during the intervening hours of Tuesday night six persons, who went to attend a religious event at a relative’s house in Rana village, took a break to drink. They went to a nearby house and began drinking.

“When they ran out of water, they found a bottle and mistook its contents for water. They mixed it with the liquor they were drinking. But as soon as they drank the liquid, they experienced burns. Local residents rushed them to the hospital,” a police officer said.

Police sources said the suspected bottle had been sent for a forensic test. Probe is on how the chemical found its way to the poultry farm.

“We have begun a case of unnatural deaths and detained the owner of the poultry for interrogation,” a police officer said.