A Hong Kong teacher has been arrested after posting instructions online that would allow anyone to create a highly flammable and poisonous gas. Officers from the Cyber Security and Technology Crime Bureau in China noticed the article — the author of which was not named in the press — in an online forum last month, reported the South China Morning Post. According to Chief Inspector Cheng Chak-yan, the instructions provided images and a list of the components needed to make toxic hydrogen sulphide, and detailed how much damage could be done with different ratios. Police found the teacher in question…