Stewart. — Experiments in Hydraidic Mortar. 103 



of tlie trials of the lime induced tLe writer, as engineer in charge of tlie 

 works, to autliorize tlie employment of tlie abo'^'e lime and pure Arolcanic 

 sand as mortar in tlie 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 u.p 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 omng to 

 the extreme sharpness of the volcanic 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, hydraulic 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 accident 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, volcanic 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 

 volcanic 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 



