314 
Monday , 2d April 1860. 
Lord NEAVES, Vice-President, in the Chair. 
The following communications were read : — 
1. On the Solidification of Limes and Cements. By George 
Bohertson, C.E. 
The paper was deduced from a series of experiments, made on the 
London Dock Works with blue lias and Dorking limes ; and at 
Leith Docks with the limes in the neighbourhood of Edinburgh, 
and with cements both natural and artificial. A short account was 
first given of the nature of the experiments at the London Docks, 
with the points investigated. A longer and more professional 
account of these is to be found in the Transactions of the Institu- 
tion of Civil Engineers for 1857-58. 
The solidification of lime was considered under two general 
heads. 
ls^, That of ordinary limes and plasters, in which the action of 
setting was proved to be at first entirely of a mechanical nature, 
when slaked lime is used for mortar ; when quick lime is used, 
though the set is hastened by the chemical act of hydration, it is 
still, in practice, caused by mechanical causes, — the set in both 
cases being due to the absorption into the pores of the lime of a 
great part of the water of mixture, accompanied by a contraction in 
the bulk of the mortar. After the first set, induration increases ; 
at first from the evaporation of some of the water of mixture, and 
afterwards from the absorption of carbonic acid from the atmosphere. 
The author found, that when limestones were cemented together, 
the mortar absorbed carbonic acid from the stones themselves, some- 
what in proportion to the quantity in the limestone. He also found 
that the presence of silica in chemical combination with lime 
deadened the desire of the lime for carbonic acid. In hydraulic 
lime, therefore, which owes the permanence of its set to silica in 
combination with it, the induration due to carbonic acid is less 
than in ordinary and purer limes. 
The second division of the subject comprised all limes and 
cements which set •permanently hard under water. In this case, 
