Discarding copper, it has been proposed to substitute steel or iron.  In the early days of the higher pressures, Mr. Alexander Taylor adopted wrought iron for steam pipes.  One fitted in the Claremont in February, 1882, was recently removed from the vessel for experimental purposes, and was reported upon by Mr. Magnus Sandison in a paper read before the Northeast Coast Institution of Engineers and Shipbuilders.[2] The following is a summary of the facts.  The pipe was 5 inches external diameter, and 0.375 inch thick.  It was lap welded in the works of Messrs. A. & J. Stewart.  The flanges were screwed on and brazed externally.  The pipe was not lagged or protected in any manner.  After eight and a half years’ service the metal measured where cut 0.32 and 0.375 inch in thickness, showing that the wasting during that time had been very slight.  The interior surface of the tube exhibited no signs of pitting or corrosion.  It was covered by a thin crust of black oxide, the maximum thickness of which did not exceed 1/32 inch.  Where the deposit was thickest it was curiously striated by the action of the steam.  On the scale being removed, the original bloom on the surface of the metal was exposed.  It would thus appear that the danger from corrosion of iron steam pipes is not borne out in their actual use; and hence so much of 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 deg.    |    12.34    |     8.38    |    14.64   |
Tin     8  / |            |             |             |            |
Zinc    31/2 \ |            |             |             |            |
Lead    11/2  \|    400 deg.    |    10.83    |     6.30    |    11.79   |
--------------+------------+-------------+-------------+----

--------+
Copper 87   /|     50 deg.    |    13.86    |     8.33    |    20.30   |
Tin     8  { |            |             |             |            |