102 Transactions. 
the ordinary Mahurangi lime, the writer was induced to investigate the 
properties of some limestone from Mahurangi, but obtained on the opposite 
side of the river from whence that commonly used is procured. 
A freshly-burnt sample was obtained, as also a portion of the unburnt 
stone. The latter was analyzed by Mr. Strehy, then in Auckland. The 
result was,— 
Carbonate of lime Tm ec VEO 
» iron n crc MH 
magnesia ... tcn 04 
Silent of alumina E x Po 
Wate ux d x CAE 
100°0 
‘The above analysis indicates a moderately hydraulic lime, and it agrees 
well with the practical tests to which the sample was put. The rock as then 
worked was, however, by no means homogencous, so that neither test could 
be depended on as fairly representing the whole. It will be observed that 
the silicate of alumina, or clay, is 13:5 per cent. of the whole, and it is now 
pretty well agreed that it is this which is the active substance in giving 
hydraulicity to lime. Also, that even in the most highly burnt limes and 
cements, the lime and silicate of alumina are only Piscine combined 
until the formation of a hydrate takes place. 
The practical tests to which the lime was subjected were,— 
(1.) The slaking, by immersing a piece in water for about half a minute, 
and observing the time which elapsed before it became powdery. This was 
generally about ten minutes. 
(2.) A strong paste was formed by the addition of water, and a saucer 
was filled and immersed in water. The hardening process was observable in 
about three weeks, and in two months it required considerable pressure to 
force a penknife into the mass. 
(3.) A portion was made into mortar with common sharp sand, and it 
exhibited middling setting powers under water. 
(4.) Another portion was mixed with sifted volcanic sand, in various 
proportions, and made into mortar. This showed a considerable improve- 
ment in the hardening under water. The best proportions were found to be 
equal parts of sand and lime. 
The above investigations were undertaken about three years ago, and 
were mainly instigated by the scarcity of Portland cement in Auckland, 
£2 to £3 being asked for this per barrel at the time, and some of the 
samples, to the writer's knowledge, were about as much worth as so much 
road dust. The railway was then in progress, and the contractor for the 
first section had failed to rocure a supply of cement in time. The results 
