18

Mr. White’s Design for the New London Bridge,

greater force would have been necessary to break the pipe;—so that this experiment shows the negligence in constructingit, and not the strength of brick and cement. The pipe hadbeen made for years.

At the beginning of February 1812, some pipes were madeof three measures of cement and two measures of sand, 8inches internal diameter, 2 inches thick, and 5 feel long; thethickness was not indeed uniform, owing to accidents in themaking; but this will be noticed in relating each experiment.At the beginning of May following, some of them were burstby the means above mentioned, having the tube of mercuryattached.

The first pipe tried sustained a momentary pressure of 70inches, but it afterwards burst with 56 inches mercury, = 63feet water; it broke from top to bottom, having a very straightcrack on one side only, and there the thickness was T6 inch.

A second pipe burst with 42 inches mercury, and the frac-tured part was 1*75 inch thick.

A third burst with 47 inches mercury, and the thinnestpart was 1‘8 inch thick.

In January 1812, around brick tank was made, 41 inches indiameter and 42 inches deep, of the thickness only of a brickthick, i. e. 2^ inches, with an internal coating of cement halfan inch thick; a brick head was made to it, so that every partwas water-tight. In May following it was tried by the forcing-pump, when the head (which might have been expected togive way first, as the obstacles in putting it on did not admitthe cement to be properly applied) parted from the sides with17 inches mercury.

Specific Gravity, SfC. of Cement .—Specific gravity of Romancement made up a long time was 1T6, which was also thatof mineral cement the same as the bricks were made of.

100 parts of Roman cement stone absorb of water 15.

100 parts of mineral cement absorb of water 17 - 6 to 18 - 5.

A cubic foot of Roman cement forms |rds of a foot ofstone, shrinking ^rd by its being mixed with water, of whichit takes 47 of its own weight.

A bushel of mixture composed of 3 measures of cementand 2 of sand forms 1 cubic foot of stone.

A cubic foot of cement brick-work weighs 105 pounds.

VII. Memorandum of an Experiment made by Mr. Southern,November 12 , 1800, with a close brick box made with Parker’sand Wyatt’s Cement.

The box is 5 inches square within, 17 inches long, and the

brick-