Some experiments upon this important subject were made by Mr. Jardine, of the Water Company in Edinburgh. The method of proving was to close one end of a piece of pipe, and then inject water into it by means of a forcing pump attached to the other end, the force or pressure being measured by a gauge belonging to the pump. When the water from the injecting pump begins to press out the pipe, little or no alteration is observed in it tor some time. As the operation proceeds, however, the pipe gradually swells throughout its whole length, until, at last, a small protuberance is observed rising in some weak part, which increases until the substance of the pipe, becoming thinner and thinner, is at last rent asunder. In the first experiment, the pipe was of one and a half inch bore, and the metal, which was remarkably soft and ductile, was one-fifth of an inch in thickness. This sustained a power equivalent to that of a column of water one thousand feet high, equal to thirty atmospheres, or 420 lbs. per square inch of internal surface, without alteration; but with a pressure equal to twelve thousand feet of water it began to swell, and with fourteen thousand feet, or six hundred pounds on the square inch, it burst.

When measured after the experiment it was found to have swelled until of a diameter of 1 inch. The edges of the fracture were not ragged, but smooth like a knife. In a second experiment, the pipe was two inches in diameter, and one-fifth of an inch in thickness. It sustained a pressure equal to that of a column of water eight hundred feet high, with hardly any swelling, but with one thousand feet it burst; the fracture in this was not so fine as in the former instance, the metal being much less ductile.