On Hydraulic Cements. 
mixture of the materials, I will detail the precautions requisite in this preliminary 
operation. 
The carbonate of lime being reduced to a fine powder, is mixed up intimately 
with the clay, adding sufficient water to render it a stiff paste, such as bricks would 
be made of ; after this, the composition is moulded into lumps of the shape of 
bricks, 4 inches X 3 x 2, and set to dry. It is then calcined in a lime-kiln, until 
the carbonic acid is thoroughly driven off. 
The composition is now to be ground up, dry, into a very fine powder ; and this 
operation requires attention ; for the same composition which will make a good and 
lasting cement, when well pounded, will not succeed at all, when badly ground up. 
In the state of powder the lime is ready for use, and may be preserved, if kept from 
the contact of air and water. When used, it is merely to be mixed up with water ; 
a greater proportion of liquid being added when the cement is required to harden 
slowly, and less when quick setting is the object : when the quantity of water is very 
small, or barely enough to make a paste of the powder, a very few minutes suffice 
to render it quite hard. 
Col. Pasley employed blue clay, taken from the bed of the Medway, in most of his 
experiments, and found it preferable to the brown clay, apparently from its con- 
taining protoxyd of iron, in lieu of the peroxyd of that metal, which, in all cases, 
proved detrimental to the cement. With the brown clay, indeed, it was found ad- 
vantageous to mix about 2 per cent, of protoxyd, to make it a good alloy for the 
lime ; and to prevent its conversion to the state of peroxyd in the kiln, a further 
addition of some carbonaceous matter, such as coal dust, resin, &c. was in all cases 
found necessary. The superiority of the blue clay may probably be owing to its 
containing a portion of vegetable carbon, diffused through it. The proportion of 
carbonaceous matter added, should form l-15th or l-20th of the mass. 
The following are the results of the various experiments made at Chatham. 
Expt. Blue Clay. Chalk. Coal Dust. Cement. 
1. 
2 7 
66,3 
2. 
27 
67,1 
3. 
27 
65,9 
4. 
The same composition, with 1-1 5th 
very well. 
6,7 very hard and good. 
6,9 equally good. 
7>1 not quite so good, 
of different oils and resins, also answered 
5 Chalk and blue clay, the latter of which had been previously washed, did 
not form a good cement : the composition falling to pieces under water, 
, *" g substances > whc " in the proportion of l-15th of the whole 
bonl K „ e f r !,,d OU reSt ° r r ,0 thC WSShed Cla >' its hydraulic property = viz. car- 
bonate of soda, carbonate of potash, and muriate of soda. 
. Compounds of chalk and pipe clay would not answer alone • but the above 
mentioned saline ingredients add^d „ i • » Dut tae abme 
cements the uronertv n f h j • G ca * cmatlon » at once conferred upon these 
r ng under water - The ***«**, m ju ^ 
cumstances^ " ^ ™ ^ ^ *> ^^th, according to cir- 
when immeTed in^ateT”^^^ 1 - 10 qUalitieS ’ hecomin 8 excessively hard of itself, 
exceeding slowness. Should the 4 clnatlon > but n hardened without heat, and with 
it was thought it might prove preffirableTo 118 ^ 7 f ° rming * Cement be a doIomite ’ 
The foregoing memoranda * , pure hmestone for hydraulic purposes. 
lanas may be formed bv 1 • ° the facility with which artificial puzzo- 
^ ** a very ^ ^ F"*** of 
exist already in the clay employed * where this may not be supposed to 
