/ 
1831.] 
On Water Cements. 
67 
6. A water lime, or an imperfect water cement, treated in the same way, will not 
harden in heating, and will either swell and fall to pieces, or will continue sott in a 
basin of water. 
§ 2. — Of the Pure Limes and Water Limes. 
7. The pure limes, such as chalk and statuary marble, are all white, and are 
quite unfit for building under water, as they never set at all, but remain in a state 
of pulp. 
8. The water limes, such as the aberthaw, blue lyas, &c., are generally coloured 
by the oxides of iron, and consist of the same component parts as the water cements, 
but with more of carbonate of lime, and less of silica and alumina, than the latter. 
These limes, when made into mortar, are good for the body of wharf walls, as they 
set under the level of water : but for the facings of wharf walls, it is common to 
add to them a proportion of puzzolana, or to use the water cements in preference, 
as the latter are better calculated to resist the action of water in mass. 
§ 3. — The Subject of Water Cements continued. 
9. Calcined water cements require to be ground or pounded to a state of impalpable 
powder, before they are used. The best and most powerful natural cements, after 
being burned to the greatest nicety, are not fit for use, when imperfectly pulverized. 
The calcined Harwich cement, which is the hardest of the natural calcined cements, 
is often spoiled or injured from this cause, as the same process that may grind the 
Sheppy cement well, is not capable of reducing this harder substance to the state of 
impalpable powder. I believe that this circumstance, which is not generull} under 
stood, is the chief cause of the Harwich cement being considered inferior to the 
other natural cements. 1 have scarcely ever seen any of it ground so fine as it 
ought to be. ... 
10. Moisture, or even damp air, will soon ruin the best calcined cements in t le 
state of powder. 
11. Dry air does not spoil the calcined cement powder all at once, but by slow 
deo-re'es. When this powder is quite perfect, is does not effervesce in a diluted acid, 
but remains undissolved at the bottom. By exposure to air, it gradually absorbs 
carbonic acid gas, which causes it to effervesce more and more in a diluted acid, 
until by degrees it is acted upon as much as the natural cement stone, previously 
to calcination, would be by the same diluted acid. At this period, it loses all its 
power as a water cement. In the intermediate states, between the absolute non- 
effervescence, and the entire solution of all the calcareous and magnesian parts of 
the cement, in the diluted acid, it will act as a more or less perfect cement, in pro- 
portion to the period of its having been exposed to air. 
12. We found, by experiment, that a small quantity of calcined cement powder, 
exposed to dry air, in a saucer, was very little injured for the first week or two, 
but that it gradually deteriorated, and was nearly spoiled at the end of the sixti 
week of such exposure. At first it set immediately, and with great heat. ter 
each successive week it set slower and slower, and with less heat. Latter } , t e 
warmth was not perceptible. 
§ 4 .—Method of Testing the Quality of the Manufactured Cements. 
The manufactured cements are always put into air-tight casks, after being cal 
cined and pulverized. The following are the means of judging of their quality. 
13. Put a part of the cement powder into the diluted muriatic (or ot ei) aci • 
If little or no effervescence takes place, the cement is sufficiently burned, nit i 
may be overburned. 
