METALLURGY OF CAST IRON.
aluminum bronze castings. I have seen a pot of aluminum bronze kept for twelve hours in a furnace before tests had proven it to be the grade of metal de-, sired, and the chances were that, had it proven all right, if a second test had been taken a few moments later it would have shown that a great change had taken place in the metal. The author succeeded in obtaining sound castings from some very complex patterns, but he was not able to make any formula or directions for a mixture which would insure like desired results every melting, as far as physical tests were concerned. It must be remembered that at this time pure aluminum was not obtained for commercial purposes, as it is at the present day. Then it was only obtainable by being alloyed with iron or copper containing from about 5 to 20 per cent, of aluminum. To obtain 5 to 20 per cent, of aluminum in any alloy of copper or iron, 80 to 95 per cent, of these latter elements had to be melted in mixture with what was in the pot in order to have a chance of securing the grade wanted. Since the advent of the Pittsburgh Reduction Co., about the year 1890, aluminum is obtainable for commercial purposes in a free state, without being alloyed with any other metal. This has proved more satisfactory in enabling a formula to be utilized to the end of securing like results at all times, but has not re-, moved the difficulty of obtaining perfect castings of aluminum bronze alloys.
The author has tried aluminum in mixture with cast iron. In some cases it would slightly improve the strength, and again it would weaken the iron. The influence of aluminum is similar to that of silicon. the melting of white and gray irons. The contrast is remarkably sharp, and on the whole it shows us that