[16] Magnetic iron and pyrites in basic rocks; tin stone in granite and porphyry.
[17] Ancient authors report cases of this kind.
[18] The largest bronze statue of modern times is the "Bavaria" in Munich, which is 20 meters high and weighs 80 tons. It consists of 12 pieces and cost about a quarter of a million dollars.
[19] When a bronze is remelted six times the percentage of tin is reduced to half the original (Dumas). The evaporation of the metal can be shown by holding a cold plate on it while melted. Tin is immediately deposited on it.
[20] They usually made a copper and zinc alloy, but it is possible that they also understood the art of embedding the casting in zinc ore (calamine) and heating strongly, whereby the surface of the metal was "cemented" and colored.
[21] On examining a broken surface of an antique mirror, it will be seen that only the outside is white. It is probable that the finished mirror was embedded in some arsenical substance and heated, which cemented and colored the surface.
[22] Uchatius makes his famous hard bronze by cooling and hydraulic pressure. Bronzes with 8 to 12 per cent. of tin are most benefited by this process. Bronzes with very little tin in them are but little affected by chilling and hammering (Riche). Alloys that are hard already, such as bronzes rich in tin and phosphorus, become too brittle and useless by repeated hammering.
[23] When a cast sheet of inelastic bronze or brass is hammered or rolled, it "feathers."
[24] The Romans preferred to put in some bronze that had been repeatedly cast.
[25] One piece was scarcely scratched by feldspar, another by quartz. The Greek and Roman weapons in the Berlin Museum were tested as to hardness by Dr. Von Dechend at the suggestion of the Director-General, Von Schone. All of them were scratched by fluorspar; there were no hard bronzes among them. If the races of classical antiquity were not acquainted with hard bronze, it is easy to see why they soon began to use iron, in contrast with the Semitic-Hamitic races.