According to the indications furnished, iodine, bromine, one, or all of the acids, the caustic alkalies, etc., are then detected by means of the methods to be employed in cases where the expert has a clew to the poison present. In this manner, the presence of potassa and soda, and of bromine and iodine, even in mixtures, is easily ascertained. It only remains to mention the course to be pursued when suspicion exists that poisoning has been caused by the administration of a mixture of several acids. The suspected materials are boiled with water, and alcohol added to the solution in order to coagulate the animal matters. The solution is next filtered, the filtrate placed in a retort provided with a receiver and distilled until the residual portion acquires a pasty consistency. In this way, the acids present are separated into two classes: (_a_) those that are sufficiently volatile to have passed into the receiver, such as, acetic, nitric, hydrochloric and sulphuric acids (the latter acid will only be partially volatilized); and (_b_) those that remain in the retort. The former are detected by examining the distillate as previously directed. The residue remaining in the retort is treated with absolute alcohol, the fluid filtered, and a solution of acetate of lead added to the filtrate: sulphuric, phosphoric and oxalic acids, if present, are precipitated. The precipitate is suspended in water and decomposed by means of sulphuretted hydrogen. The acids contained are now set free, and are detected by applying the tests already mentioned. If there be reason to suspect the presence of both sulphuric and oxalic acids, the distillation is discontinued after a short time. The two acids are dissolved by shaking the moderately concentrated fluid remaining in the retort with ether, and, upon evaporating the solution, will be obtained in a state suitable for examination. Oxalic acid is then detected by means of sulphate of lime; sulphuric by means of oxalate of baryta. The above examinations would fail to effect the detection of _phosphorus_, and it is necessary to examine a separate portion of the original substance for this body. IV. MISCELLANEOUS EXAMINATIONS. DETERMINATION OF THE NATURE AND COLOR OF THE HAIR AND BEARD. A criminal, in order to conceal his identity, may change the color of the hair and beard by artificial means; either to a darker shade, in case they were naturally of a light color, or, to a lighter hue, if they were originally dark, and the chemical expert may be called upon to detect this artificial coloration, and restore the original color of the hair. It may also happen, that portions of hair still adhere to the clots of blood sometimes found on an instrument which has been employed in the commission of a crime, and consequently the question may arise as to the nature of the hair, whether it be human or animal. DETERMINATION OF THE COLOR OF THE HAIR AND BEARD.