224 MEDICAL JURISPHUDENCE with carbon is found in the barrel of the firearm, if black gunpowder was used. For the first five or six hours this deposit forms a strong alkaline solution with distilled water and emits an offensive odour of sulphuretted hydrogen. If the solution is filtered, and the nitrate is treated with a solution of lead acetate, a black precipitate of lead sulphide is formed. After exposure to air and moisture for a few days potassium sulphide t becomes converted into thiosulphate, thiocyanate and finally into potassium ? sulphate, which forms a neutral solution with distilled water and gives a * white precipitate with lead acetate. At later periods oxides of iron (iron rust) with traces of iron sulphate are formed in the barrel. Smokeless nitro-powders leave a dark grey deposit in the barrel of a recently discharged firearm. It does not change with the lapse of time. It forms a neutral solution with distilled water, and contains nitrites and nitrates, but does not contain sulphides. If the chromate or bichromate powder is used, the residue in the barrel is usually of a greenish tint.10 It should be borne in mind that the composition of the deposit would vary considerably, if the firearm was dirty at the time of its discharge, and the medical practitioner has no means to know its condition prior to dis- charge. Again, the deposit would not be found, if the weapon had been" thoroughly cleansed after discharge. Direction from which the Weapon was fired.—The question regarding the direction from which the weapon was fired may arise in a case where it is alleged that it was fired from a certain point in a quarrel. To ascertain this it is necessary to know the position of the victim at the ffine- of the discharge of the bullet, when a straight line drawn between the entrance and exit wounds and prolonged in front should indicate the line of direction. In some cases it is difficult to determine the direction as the bullet is so often deflected by the tissues that its course is very irregular. 10. For further details of the examination of the weapon and the residue the reader is referred to Sydney Smith and Glaister's Recent Advances in Forensic Medicine, Ed. n, Chapts, HI and IV.