the way is cleared for a stronger and more reliable material than copper. So far the source of danger seems to be in the weld, which would be inadmissible in larger pipes; but there is no reason why these should not be lapped and riveted. There seems, however, a more promising way out of the difficulty in the Mannesmann steel tubes which are now being "spun" out of solid bars, so as to form weldless tubes. [Footnote 2: Transactions Northeast Coast Institution of Engineers and Shipbuilders, vol. 7, 1890-91, p. 179.] TABLE I.--TENSILE STRENGTH OF GUN METAL AT HIGH TEMPERATURES. --------------+------------+-------------+-------------+------------+ | | | | | Composition |Temperature | Tensile | Elastic | Elongation | of | of oil | strength | limit | in | gun metal. | bath. | per square | per square | length of | | | inch. | inch. | 2 inches | --------------+------------+-------------+-------------+------------+ Per cent. | Fahr. | Tons | Tons | Per cent. | Copper 87 /| 50° | 12.34 | 8.38 | 14.64 | Tin 8 / | | | | | Zinc 3½ \ | | | | | Lead 1½ \| 400° | 10.83 | 6.30 | 11.79 | --------------+------------+-------------+-------------+------------+ Copper 87 /| 50° | 13.86 | 8.33 | 20.30 | Tin 8 { | | | | | Zinc 5 \| 458° | 10.70 | 7.43 | 12.42 | --------------+------------+-------------+-------------+------------+ Cast steel has been freely used by the writer for bends, junction pieces, etc., of steam pipes, as well as for steam valve chests; and except for the fact that steel makers' promises of delivery are generally better than their performance, the result has thus far been satisfactory in all respects. These were adopted because there existed some doubt as to the strength of gun metal under a high temperature; and as the data respecting its strength appeared of a doubtful character, a series of careful tests were made to determine the tensile strength of gun metal when at atmospheric and higher temperatures. The test bars were all 0.75 in diameter, or 0.4417 square inch sectional area; and those tested at the higher temperatures were broken while immersed in a bath of oil at the temperature here stated, each line being the mean of four experiments. The result of these experiments was to give somewhat greater faith in gun metal as a material to be used under a higher temperature; but as steel is much stronger, it is probably the most advisable material to use, when the time necessary to procure it can be allowed.