Page:Miscellaneous Papers on Mechanical Subjects.djvu/114

 width of cut at least three times as great as that ordinarily given in English works.

At Pittsburgh a large casting for a hydraulic press was cooled by the following method:—Water is introduced into the interior of the core by a pipe, which extends to the bottom, and fills it previous to casting. Provision is made for the escape of the air by making the core fluted.

When the metal is poured into the mould it immediately heats the water, which is then drawn off by an escape pipe at the top of the core, and a supply of cold water is continually running in at the bottom.

Heat is thus gradually taken from the mass, and the whole cools uniformly. The casting was 10 inches thick, and weighed 7 tons. It took from three to four days cooling.

The best charcoal pig iron was selling in Pittsburgh at $45 per ton, having risen within a short period from $30 per ton.

Major Wade, of Pittsburgh, has made many experiments on the tensile strength of this iron. He found that it required a force of 45,000 pounds to tear asunder a bar an inch square. Some of the results of his experiments have been published by the United States Government in the "Ordnance Manual."

8. Pickling Castings.—The process of