Brarn.— On the Building Materials of Otago. 195 
tion to Pozzuolanas is that, like the Moeraki boulders, uniformity of composi- 
tion cannot be ensured. 
Aggregates. 
Except in the case of the higher hydraulic limes and cements, where the 
maximum strength is obtained by using them in a pure state, as much 
depends on the aggregate as on the cementing material, notwithstanding 
which there is no article used in construction that commands s0 little atten- 
tion. The main essentials of a good aggregate are sharpness and freedom 
from earth or other impurities of a similar nature. The proper size and 
hardness vary with the quality of the cementing material ;—rich lime takes 
a coarse soft sand, and cement a fine hard one. 
As no attempt had been made to determine the relative merits of the 
Otago sands, I collected a number in the vicinity of Dunedin and experi- 
mented on them in the following manner, and with the results given in 
Table V. Each kind of sand was made into mortar with Waihola lime in 
the proportion of one of lime to two of sand. The lime had been air-slaked, 
and was sifted through a gold-dust sieve before being used. The ingredients 
were measured in the most exact manner, and carefully mixed with the 
smallest quantity of water that would give plasticity. The mortar was 
then used to cement ordinary bricks placed crosswise, which gave a bearing 
surface of about 18 square inches. After being kept in the open air for 160 
days the bricks were pulled asunder with weights increased gradually to 
the breaking point. It will be seen from the table that the highest results 
were obtained from’ Anderson Bay sand, which broke with a strain of 226 
pounds. About 1} square inches of the mortar in the inside was not quite 
hard. Assuming that this only supported half as much as the other por- 
tion, we make the cohesive strength 18 pounds on the square inch. Two 
samples of each kind of sand were tested. Taking only the highest in each 
pair, we find that, out of a total of 27, four broke with strains ranging 
from 226 to 150 pounds, nine from 150 to 100, six from 100 to 75, and six 
from 75 to 47, while two did not stand any measurable strain. I regret to 
add that many of the last three classes are constantly used in Dunedin. 
General. 
In conclusion, I shall briefly recapitulate the leading points of my 
subject, and consider its practical bearing. 
Leaving out the materials in Tables II. and IV., which are compara- 
tively valueless, the following will show the various purposes for which the 
Otago limes are suited, each class being eapable of performing the funetions 
of those under it as well as its own :— 
Rich Limes.— 
Nos. 9 to 14. Dea and agricultural and caustic pur- 
poses only. 
