Hashish is classified as a Class B controlled substance under the Misuse of Drugs Act 1971. The status of "liquid cannabis" is "currently the subject of legal argument"[24] The Misuse of Drugs Act: A Guide For Forensic Scientists published by the Royal Society of Chemistry suggests that the term "liquid cannabis" is preferable to "hash oil", as it does not involve definition of what exactly constitutes an "oil". The authors also recommend adoption of "purified form" instead of "solvent extract" when describing hash oil, as the former would not require proof of solvent usage by forensic scientists.[25]