Srewart.— Experiments in Hydraulic Mortar. 103 
of the trials of the lime induced the writer, as engineer in charge of the 
works, to authorize the employment of the above lime and pure voleanie 
sand as mortar in the construction of the tunnel. The lime was brought to 
the works unslaked, and used as soon as possible. No more water was used 
than sufficed to work the mortar, and the working up of mortar that had 
partially set in the heap was forbidden. The best proportions were found 
in practice to be five parts of lime to four parts of sand. This was owing to 
the extreme sharpness of the voleanie sand, and also to the fact that it was 
often sifted too large. The same cause renders the joints of the brickwork 
too large for sightliness, but the result so far as strength is concerned is 
very satisfactory. If the sand were obtained from volcanic gravel ground 
by edge runners, it is likely that the common proportions of lime and sand 
would suffice. 
It is to be regretted that a regular supply of this lime was not obtained 
after all the trouble about it. It was also often not well burnt, causing 
great waste in slaking and sifting. Hence, common lime was often 
smuggled into the work, and where such was the case it has not failed 
to show itself. , 
During the progress of the works specimens were regularly taken and 
tested. They showed more of the properties of cement than of mortar 
made by lime; and the writer is confident that, with further investigations 
and with due precautions, hydraulie lime equal to the bulk of the imported 
Portland cement may be obtained. 
Most of the foundations of the stone work in the viaduct in Mechanic's 
Bay are laid in the above lime. Often, however, common lime was used with 
a small mixture of cement. "When both these materials are good, this has 
always been found, in the writer's experience, to produce hydraulicity to an 
extent proportional to the quantity of the latter. 
The writer regrets that all the specimens of the test bricks were not 
carefully preserved. They were commonly left on the works in some pool 
of water or running stream, and often broken for examination. One only 
has been retained, and that more by aecident than design. It is now pro- 
duced. The bricks are joined by the mortar used in the foundation of the 
sea abutment of the viaduct. The materials then being used were the 
hydraulic lime two parts, voleanic and common sand each one part. The 
specimen was laid at once in a pool of water, and a short time afterwards 
circumstances caused it to be looked for and preserved. Samples of the 
voleanic sand mentioned are also here shown of the black and red. The 
latter is more abundant in the necessary fineness, but both were used as 
they could be procured. 
It is not believed that this sand possesses properties in the same degree 
