SULPHURIC ACID (_Oil of Vitriol_).—This heavy, oily looking liquid is met with in two states, concentrated and diluted; and being extensively employed in commerce and manufactures is much more frequently used as a poison than the other mineral acids. Many infants and young children have been poisoned by it; occasionally also men, under the influence of drink. The acid is not unfrequently thrown over the person, either to disfigure the features or to destroy the clothes. The parts of the body with which it is brought into contact are stained at first of a white, and afterwards of a dark brown or black color. The smallest fatal dose of concentrated acid recorded, in the adult, is one drachm; but recovery has taken place after as much as two ounces. But it must be understood that the acid proves fatal mainly by its power of corrosion, so that a small dose of the concentrated acid is more dangerous than is a much larger dose of it in the dilute form. The average period at which death occurs is from sixteen to twenty-four hours; but on the other hand, death may not occur for months, and may only follow the organic changes induced by cicatrization following the swallowing of the acid, or the malnutrition following its destructive action on the coats of the stomach. _Tests._—It is not within the province of these Memoranda to treat of the various processes by which poisons are to be detected; for to make a trustworthy analysis requires the skill of a professed chemist, whose assistance should be allowed in these medico-legal investigations. Where the character of a dead man or the life of a supposed criminal is at stake there must be no chance of error. The ordinary tests will, however, be briefly described, if only to help the physician to treat the case more satisfactorily than he could do by merely guessing that an irritant or narcotic had been employed: Concentrated sulphuric acid is usually a brownish colored liquid, which chars or corrodes wood or other organic matter brought into contact with it, and when mixed with water gives out heat. When diluted, its presence may be thus detected: 1. The liquid is known to be acid by its action on litmus paper. 2. Add to a portion of the suspected liquid a few drops of nitric acid, and then a solution of nitrate of barium; a white precipitate (sulphate of barium) will fall if sulphuric acid be present. This test is extremely delicate; for although other acids yield a precipitate on the addition of nitrate of barium, yet as such deposits are all soluble in nitric acid the previous addition of this acid will prevent their formation. 3. The precipitate should next be collected, dried, and reduced with charcoal by the blow-pipe flame to the condition of barium sulphide. This, when treated with a drop of hydrochloric acid, gives off sulphuretted hydrogen, known by blackening paper dipped in acetate of lead solution.