1831 .] 
On Hydraulic Cements. 
55 
In Bengal, where from the low level of the ground, and the humidity of the cli- 
mate, the foundations of all buildings are peculiarly exposed to damp, and in many 
cases, as in bridges, &c. are immersed in water immediately after construction ; it 
would seem more urgently requisite to employ a cement which should have the 
property of hardening under water; and yet, as far as I can learn, this desirable 
quality has not yet been found in any of the mortars of the country. Although, 
therefore, the results of Colonel Pasley’s researches have not yet been published to 
the world, I shall take advantage of my having been present throughout the course 
of his experiments, to communicate the principal facts elicited therefrom, and at 
the time to shew, how successful has been their application towards the formation 
of a hydraulic cement out of materials procurable in Calcutta, and indeed all 
over India. 
The composition of Roman cement, which has been assumed as a model for imita- 
tion, by architects, was found by Guyton Morveau, to be as follows : — 
Lime, 
Carbonic acid, 
Protoxyd of iron, 
Silica, 
Alumina, 
Loss, 
40,3] 
33,0 J 
^ Carbonate of lime, 
73,3 
11,3 
9,9] 
4,4 j 
► Clay, 
14,3 
1,1 
100,0 
A second analysis, by M. Drapier, of the Boulogne stone, which precisely resent-" 
bles that of Sheppey in its properties, yielded the following composition : 
Clay, 
{ 
Carbonate of lime, 
61,6 
Carbonate of iron, 
6,0 
Silica, 
15,0 
Alumina, 
4,8 
Oxyd of iron. 
3,0 
Water, 
6,6 
Loss, 
3,0 
100,0 
} 
22,8 
These analyses prove, that the stone called Sheppey stone, is an argillaceous lime- 
stone, with a large proportion of oxyd of iron, a substance that seems to play an 
important part in the mixture. 
The principal difference between the natural stone, and an artificial compound of 
the same substances, must evidently be in the more intimate commixture of the 
ingredients of the former ; for it is not probable that a thorough chemical combina- 
tion exists between the lime and silex or alumina, since the former earth is rea- 
dily separable by an acid, leaving the clay apparently in its original natural state. 
The principle, then, upon which Colonel Pasley proceeded, was to make as perfect 
a mixture as possible of his materials, that is, an exact imitation of the natural 
stone before calcination ; and to deal with it afterwards just in the same way as 
with the Roman cement. 
The materials, which formed the basis of his artificial puzzolana, were carbonate 
of lime and clay, in the proportion of 5 parts of the former, to 2 of the latter : to 
these it was found necessary to add other substances in particular cases of which 
mention will presently be made. As success mainly depended upon the proper 
