Congo Red Solution was used to test the purity of Avertin before use. Avertin is a rectal anaesthetic that was used heated which could created dibromacetaldehyde and hydrobomic acid, the former being highly corrosive to rectal mucosa. Once this was known it was recommended that the solution should not be heated above body temperature and should be tested with Congo Red prior to use.Brown cardboard box with pink manufacturer's label adhered to front and text printed in black. The box contains an amber coloured bottle with blue wax seal and pink manufacturer's label with black printed text. There is also a clear glass dropper.avertin, dibromacetaldehyde, hydrobomic acid, rectal anaesthesia, rectal mucosa