simply crossed concrete off their list of available materials when it
comes to marine construction. It is a subject too large in itself to be
discussed as subsidiary to a minor structure like the one herein
described, and though many have rejected concrete under these
conditions, other engineers equally conservative are using it freely and
without fear.

The writer consulted with his partner and others at some length, and,
considering all the advantages to accrue by the use of these concrete
caissons, decided to do so after taking all known precautions.

[Illustration: FIG. 1.]

These precautions consisted in:

First, the use of cement in which the chemical constituents were limited
as follows:

It was specified that the cement should not contain more than 1.75% of
anhydrous sulphuric acid (SO_{3}) nor more than 3% of magnesia (MgO);
also that no addition greater than 3% should have been made to the
ingredients making up the cement subsequent to calcination.

Secondly, to secure by careful inspection the most completely
homogeneous mixture possible, with especial care in the density of the
outer skin of the caissons.

Thirdly, a prolonged seasoning process before the new concrete should be
immersed in the sea water.