EXAMINATION OF FIRE-ARMS. (_Proposed by M. Boutigny._) The examination of fire-arms is sometimes useful in determining the date at which a weapon has been discharged or reloaded. The methods used in examinations of this nature vary, as the weapon under inspection is one provided with a flint or an ordinary percussion lock. The value of the tests employed is also affected by the kind of powder used; _i. e._, whether common gunpowder, gun-cotton or white gunpowder (prepared by mixing yellow prussiate of potassa, chlorate of potassa and sugar) has been taken. THE GUN IS PROVIDED WITH A FLINT-LOCK, AND WAS CHARGED WITH ORDINARY POWDER. In case the weapon has been wiped or exposed to moisture subsequent to its seizure, it is impossible to form any conclusion as to the date of its discharge, etc. It is therefore advisable, upon receiving the weapon, to carefully wrap the lock in a woollen cloth, and to close the barrel. The exterior of the gun is at first submitted to a careful examination, and notice taken of the approximate thickness of any existing rust spots. The fire-pan and adjacent portion of the barrel are also examined by aid of a magnifying glass, especial attention being given to the detection of traces of a moist and pulverulent incrustation of a greyish or blackish color, formed by the combustion of the gunpowder, and of crystals of sulphate of iron. If the weapon is loaded, the wad is withdrawn and the color of its cylindrical portion and of the powder, as well as the size of the ball or shot, noted. This preliminary examination ended, the barrel and fire-pan are separately washed with distilled water, and the washings passed through filter paper which has previously been well washed, first with pure hydrochloric acid, then with distilled water. The filtrate is next divided into three portions, and these separately examined for: (1) sulphuric acid, by addition of chloride of barium; (2) for iron, by oxidizing the salts contained in the fluid with a few drops of nitric acid and adding a solution of ferrocyanide of potassium, the presence of iron being indicated by the formation of a blue coloration, or a blue precipitate; and (3) for sulphides, by means of a solution of subacetate of lead. If a bluish-black incrustation is discovered on the fire-pan or on the neighboring portions of the barrel, and both rust and crystals of sulphate of iron are absent, and the washings, which were originally of a light-yellow color, assume a chocolate-brown coloration upon the addition of solution of subacetate of lead, _the gun has been discharged within two hours at the longest_. If the incrustation possesses a lighter color and traces of iron have been detected in the washings, but neither rust nor crystals have been discovered on the barrel or fire-pan, _the weapon has been discharged more than two, but less than twenty-four hours_.