The text of A. F. Yarrow's paper "Some experiments having reference to the durability of water-tube boilers." read at the summer meeting of the fortieth session of the Institution of Naval Architects, 20th July 1899. A. F. Yarrow had carried out a series of experiments in order to ascertain the comparative merits of nickel steel tubes compared with mild steel tubes in water-tube boilers. The nickel steel that the paper referred to was an alloy containing 20 to 25 percent nickel. In the experiments described, Yarrow tried to reproduce the worst conditions with regard to wear and tear that the tubes in a water-tube could be subjected to. In Yarrow's opinion the deterioration of the tubes in water-tube boilers was probably due to: (1) the action of acids in the water, due to grease, which in spite of every precaution found its way into the boiler; (2) the overheating of the tubes and the oxidation of the outside of the tubes through contact with hot gases; (3) the action of the steam, which, if superheated, decomposed, causing deterioration of the inside of the tubes. Yarrow found that boiler tubes made from a nickel steel alloy containing 20 to 25 percent nickel were at least twice as durable as those made of mild steel. See also Yarrow, A. F., 1899, "Some experiments having reference to durability of water-tube boilers." Transactions of the Institution of Naval Architects, vol. 41, pp. 333-346, for the full text of Yarrow's paper and the discussions that followed.