This singular substance was accidentally discovered by _Brandt_, a chemist of Hamburgh, in the year 1669,[340] as he was attempting to extract from human urine a liquid capable of converting silver into gold. It was also subsequently discovered by _Kunkel_ and by _Boyle_, without these latter chemists having, in any way, participated in the researches of each other. Phosphorus, when pure, is semi-transparent and of a yellowish colour; but when kept some time in water, it becomes opaque externally, and then has a great resemblance to white wax. Its consistence is nearly that of wax; it may be cut with a knife. Its mean specific gravity is 1·770. It generally occurs in sticks. When exposed to the air, provided the temperature be not lower than 43°, it emits a white smoke, which has the smell of garlic, and is luminous in the dark. This smoke is more abundant, the higher the temperature is, and is occasioned by the gradual combustion of the phosphorus. When heated to 148° it takes fire, and burns with a very bright flame, and gives out a great quantity of white smoke, which is phosphoric acid. Oils dissolve phosphorus, provided the temperature be a little raised. Water has no effect upon it, unless it be aerated, when it renders the surface of the phosphorus opaque and white, which in a short time becomes red. This change depends upon oxidation. _Symptoms of poisoning by Phosphorus._ This substance, whether introduced into the stomach in its pure form, or dissolved in oil, will occasion the most violent symptoms, from its escharotic action,[341] It has been employed in medicine,[342] in a state of minute division, in the dose of one-fourth of a grain, and is said by _Leroi_ to be very efficacious in restoring and establishing the force[343] of young persons exhausted by sensual indulgence, and of even prolonging the life of the aged.[344] It has also been given as a stimulant in local fevers. We are, however, greatly inclined to question the safety of such a practice, notwithstanding the diminutiveness of the dose. The reader will find some interesting cases of poisoning by phosphorus, translated from the German work of _Weickard_, in _Hooper’s_ Medical Dictionary, under the consideration of that article. Should such a case present itself for the investigation of the forensic physician, he will not find any difficulty in identifying the substance; its external character, its smell, and, above all, its peculiar property of yielding luminous vapour, are too palpable and distinctive, to admit the possibility of error. MECHANICAL POISONS—_Powdered glass_—_Enamel powder_—_Chopped hair, &c. &c._