Boulogne-sur-Mer, France, has given expression to the following
opinions:--

1. No cement or other hydraulic product has yet been found
which presents absolute security against the decomposing action
of sea-water.

2. The most injurious compound of sea-water is the acid of the
dissolved sulphates, sulphuric acid being the principal agent
in the decomposition of cement.

3. Portland cement for sea-water should be low in aluminium and
as low as possible in lime.

4. Puzzolanic material is a valuable addition to cement for
sea-water construction,

5. As little gypsum as possible should be added for regulating
the time of setting to cements which are to be used in sea-
water.

6. Sand containing a large proportion of fine grains must never
be used in concrete or mortar for sea-water construction.

7. The proportions of the cement and aggregate for sea-water
construction must be such as will produce a dense and
impervious concrete.

On the whole, sea-water has very little chemical effect on good
Portland cements, such as are now easily obtainable, and,