436 
Book II. 
EARTHS. 
partly to the combination of part of the water. This 
last circumstance is the reason that if to common mor 
tar one fourth part of lime, reduced to powder without 
being slacked, be added, the mortar when dry acquires 
much greater solidity than it otherwise would do. This 
was first proposed by Loriot*; and a number of ex 
periments were afterwards made by Morveauf. The 
proportions which this philosopher found to answer 
best are the following. 
Fine sand0.3 
Cement of well baked bricks .. 0.3 
Slacked lime  0.2 
Unslacked lime. 0.2 
1.0 
The same advantages may be attained by using as little 
water as possible in slacking the lime. This was first 
pointed out by La Fayef. 
Higgins found that the addition of burnt bones im 
proved mortar by giving it tenacity, and rendering it 
less apt to crack in drylng : but they ought never to 
exceed one fourth of the lime employed. 
When a little manganese is added to mortar, it ac 
quires the important property of hardening under wa 
ter, so that it may be employed in constructing those 
edifices which are constantly exposed to the action of 
water. Limestone is found not unfrequently combined 
with manganese ; and in that case it becomes brown by 
calcination, instead of white. These native limestones 
are employed for making water mortar; but good 
water mortar may be made by the following process, 
first proposed by Morveau: Mix together 4 parts of 
t Ibid. ix. 437. 
Ibid. vi. 311. 
5 Faur dke Phye.i. 25.