Bram.—On the Building Materials of Otago 128 
considerable quantity in 1868, and tested it against Portland cement in the 
following manner :—Two bricks were laid together with mortars of the two 
cements, and kept a month in water and a fortnight dry. The highest results 
obtained were, with Moeraki mortar, three to one, and Portland, one to one. 
It took 400 pounds in both cases to tear asunder the bricks. Assuming 
they were placed crosswise, this would give a tensile strength of 22 pounds per 
square inch. About the same time Mr. G. M. Barr got an unmixed sample 
that stood 150 pounds in 24 days, against 110 for Portland cement under 
the same conditions. These comparisons are not, however, fair to the im- 
ported article, as the samples tested must have been of a very inferior 
quality. Instead of 25 pounds in the first experiment, ordinary Portland 
cement should have stood 140, and instead of 110 in the second, the resist- 
ance should have been 270 pounds. Mr. John Macgregor also tested the 
Moeraki cement, but the result was less satisfactory than either of the 
above. Two samples of mortar were made with pure cement and salt 
water—one was kept dry for 10 days, and the other in salt water for 87 
days. Neither of them stood any measurable strain. Mr. Macgregor also 
noted that the samples contracted very much in setting, which indicates 
too much carbonate of lime. The irregularity in composition of the Moeraki 
boulders is so great that it would be practically impossible to manufacture 
cement from them of a uniform quality ; one kiln might be equal to the 
best Portland, and the next quite worthless. We may therefore conclude 
that the expense of selection on the one hand, and the risk of failure on 
the other, are insurmountable obstacles in the way of its general utilization. 
Artificial Cements. 
When I began to investigate the subject of native cements and limes, I 
was under the impression that we had no stone capable of furnishing 
hydraulic limes, consequently some little time was devoted to the con- 
sideration of providing an artificial substitute; but the existence of natural 
cementing ingredients of a high character having been fully established, the 
necessity for adopting the latter expedient is removed, the subject will 
therefore be dismissed in a few words. 
As you are probably-aware, English Portland cement is made from two 
of the most common and abundant raw materials in the country—chalk and 
clay—and the manufacture is equally simple. The materials are mixed in 
the proportion of seven of the former to three of the latter, then burned in 
a kiln and pulverized as already described. In Germany, where there is 
no chalk, a substitute is found in hard limestone. This entails extra labour 
in pulverizing the raw material as well as the cement, but the result is 
practically the same. 
Ordinary yellow clay does not make good cement; that in common use 
