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360                        METALLURGY   OF   CAST   IRON.
often showing a " cold shut " or bad union of iron at the point where the streams of metal from the respective ladles meet each other. Aluminum is also alloyed with silver, nickel, tungsten, manganese and silicon, as well as copper, iron and steel.
Pure aluminum is the lightest of all known metals, except magnesium. Its specific gravity is from 2.6 to 2.7 and it melts at about 1500 degrees F. It is white in color, of a soft nature, possessing a strength of about one-third that of wrought iron. While pure aluminum melts at 1500 degrees F., still its reduction in the blast furnace from any ore is such as not to alloy with the iron to any extent. Why the iron will not take up aluminum to any degree in the process of reducing ores is a question still unanswered. It is a test that shows that iron possesses but little affinity for aluminum, so far as proving of any practical value to iron founding is concerned. In all the author's experience with aluminum in cast iron he cannot say that he ever knew it to accomplish anything which could not be obtained by means of silicon, which is much cheaper than aluminum.
* For the specific gravity and weight per cubic inch of other metals, see Table 136, page 593.lity. With soft grades aluminum, can make tiu* metal sluggish, with excessive dross on its surface, just as can be the case by having too much silicon in a mixt lire.