Table showing the Colour produced by the Action of the Mineral Acids on the Skin and on Cloth +-------------+----------------------+--------------------------+ | | Skin. | Cloth. | +-------------+----------------------+--------------------------+ |Sulphuric |Brown colour. |Dirty-brown edges becoming| | acid. | | red after a | | | | few days from absorption| | | | of moisture. | | | | | |Nitric acid. |Bright yellow, due to |Yellow, orange-red, or | | | the formation of | brown. | | | picric acid. Colour | | | | heightened by | | | | alkalies. | | | | | | |Hydrochloric |Greyish-white. |Bright red changing | | acid. | | after some days to | | | | reddish-brown. | | | | | +-------------+----------------------+--------------------------+ SULPHATE OF INDIGO A dark blue liquid formed by dissolving indigo in strong sulphuric acid. Used as a dye. The symptoms are much the same as those detailed under sulphuric acid, with the additional bluing of the mouth and lips. It may be detected with the tests given under sulphuric acid, the blue colour being first discharged by boiling it with nitric acid. CARBOLIC ACID Phenol. Phenic Acid. Coal-tar Creosote. Oil of Tar Carbolic acid is obtained in the dry distillation of coal, and forms the acid portion of coal-tar oil, from which it is subsequently extracted by shaking the crude coal-tar oil with a mixture of slaked lime and water. After allowing the mixture to stand for some time, the watery portion is separated from the undissolved oil, the former treated with hydrochloric acid, and the resulting oily fluid purified by careful distillation. Up to the year 1900 no restrictions were put upon the sale of carbolic acid, but owing to the large number of suicidal and accidental deaths from its use, it was by Act of Parliament scheduled as a poison, and all preparations containing more than 3 per cent. of it, cresylic acid, or their homologues, must be sold as poisons.