Metallic zinc, with dilute nitric acid, gives protoxide of nitrogen; and by taking one equivalent of this gas and four equivalents of hydrogen, water and ammonia may be formed. NO + 4H = NH³ + HO. The nitric acid, acting gradually and slowly on the zinc, is transformed into ammonia, equivalent for equivalent. When this reaction has ceased, then follows a disengagement of hydrogen gas from the zinc, which is permitted for a few seconds. It now remains to ascertain the percentage of ammonia. The ammonia may be distilled off and then absorbed by a normal or previously ascertained quantitative solution of oxalic acid, and afterwards to ascertain the quantity of oxalic acid not taken up; deduct this from the original quantity contained in the absorbing solution, and the result gives the percentage of oxalic acid neutralized by the absorption of the ammonia; from this the ammonia is calculated. Mohr’s apparatus for the disengagement of ammonia may be used with advantage in this operation. See Mohr’s Traite d’analyse chimique, supplement, p. 402, Paris, 1857. Tilberg[7] analysed the Stockholm Nitro-Glycerin with the following results: C³H⁵(NO²)O³ (the Carbon atoms being estimated as 12, Hydrogen 1, Oxygen 16,) and regarded it as Mono-Nitro-Glycerin. [6] Comptes rendus, V. xxxvii, p. 947. [7] Chemical News, March 1869, p. 151. In proof of the fact of Nitro-Glycerin being explosive by concussion effected at a distance, if proof were needed, I instance a small can containing about 4 lbs. of Nitro-Glycerin left by the blaster about 350 feet from the heading, and partially protected by the rail which was curved upwards to prevent the cars running over the dump, was exploded, when a full charge of 16 holes was fired in the heading at the West End of the Hoosac Tunnel. It will be noted that there could be no heat developed 350 feet from the primary explosion, and being enclosed in an ordinary kerosene can, it appears a striking instance of the possibility of explosion from induced concussion. Again, in April, 1872, a cartridge of Nitro-Glycerin was left in the cartridge chest, containing about 2 lbs. Nitro-Glycerin, whilst 20 charges of blasting powder were fired in the heading, 200 feet distant; the explosion of the powder was unusually heavy, and the Nitro-Glycerin exploded, tearing the chest to pieces, fracturing the air main and disrupting the track. This indubitably proves the explosion of Nitro-Glycerin by concussion, and should warn every operator to be careful to place any surplus explosive away from exploders, and as far distant as possible from where an explosion is intended, and particularly in such position that if it should explode, a contingency possible, there may be no one near the vessel containing such surplus.