twelve months, and two, four, six, ten, and twenty years, some
of the blocks have, or will be, taken up and subjected to
chemical tests, the material being also examined to ascertain
the effect of exposure upon them. The blocks tested at
intervals of less than one year after being placed in position
gave very variable results, and the tests were not of much
value.

The mortar blocks between high and low water mark of the Arctic
Ocean at Vardo suffered the worst, and only those made with the
strongest mixture of cement, 1 to 1, withstood the severe frost
experienced. The best results were obtained when the mortar was
made compact, as such a mixture only allowed diffusion to take
place so slowly that its effect was negligible; but when, on
the other hand, the mortar was loose, the salts rapidly
penetrated to the interior of the mass, where chemical changes
took place, and caused it to disintegrate. The concrete blocks
made with 1 to 3 mortar disintegrated in nearly every case,
while the stronger ones remained in fairly good condition. The
best results were given by concrete containing an excess of
very fine sand. Mixing very finely-ground silica, or trass,
with the cement proved an advantage where a weak mixture was
employed, but in the other cases no benefit was observed.

The Association of German Portland Cement Manufacturers carried
out a series of tests, extending over ten years, at their
testing station at Gross Lichterfeld, near Berlin, the results
of which were tabulated by Mr. C. Schneider and Professor Gary.
In these tests the mortar blocks were made 3 in cube and the
concrete blocks l2 in cube; they were deposited in two tanks,