A woman was arrested yesterday after her three-year-old son drank a colourless toxic chemical, possibly mistaking it for water. The boy, identified only as Shek, was in a critical condition in Prince of Wales Hospital last night after drinking the liquid - suspected to have contained potassium cyanide - from a bottle he took from his mother's handbag at their Sha Tin home. The 30-year-old mother, arrested on suspicion of child neglect, was released on bail with no charge being laid and must report back to police on Sunday. The mishap, which took place at about 11.50pm on Monday, came less than 12 hours after a 20-month-old boy drank kerosene from a soft-drink bottle at his home in Tseung Kwan O. Police said Shek was playing in the living room of the family's flat at Lok Sam House in Lung Hang Estate. His mother, surnamed Leung, was taking a bath and his grandfather was looking after him. Initial investigation indicated he took the bottle from the handbag while the grandfather was not looking. 'When his grandfather returned, the boy shouted, saying that he wanted to drink water, and then he vomited,' a police source said. 'His mother ran out of the bathroom to check. After being told that he had taken the solution from the bottle, she called police immediately.' Ms Leung, a merchandiser for a jewellery company, took Shek to Union Hospital before an ambulance arrived. He was later transferred to Prince of Wales Hospital. The solution is suspected to have contained potassium cyanide, used in electroplating or cleaning silver products, which Ms Leung had brought from her mainland office for tests at her Hong Kong office to see whether her company could use it. 'The solution is colourless. We suspect the boy thought it was water,' a police source said. 'We believe he took only a sip ... If he had taken a lot, he would have lost his life.' Former Medical Association chairman Choi Kin said potassium cyanide was highly toxic and would cause a lack of oxygen in the body's cells. 'Under its influence, cells around the whole body will receive insufficient oxygen at the same time and die,' Dr Choi said. 'Anyone who takes a large dose will die in a very short period.' Police have seized the bottle of solution and taken it to a government laboratory. Detectives from Sha Tin police station are investigating. Meanwhile, the boy who drank kerosene was in a stable condition in United Christian Hospital yesterday. He was accidentally fed the flammable liquid - bought and used by his great-grandmother - by his three-year-old brother. 'Children like to put things into their mouths,' Dr Choi said. 'Dangerous substances like chemicals should not be [left] lying around at home.' Anyone who has ingested poison should be sent to hospital as early as possible, where he or she would be given an antidote or have the stomach pumped, he said.