The following analyses of several cement-stones, and of the cement made with them, is taken from the works of Berthier, Davy, and others— The stories are in this country calcined in kilns, ground, sifted. and packed in casks. The colour of the powder is a dark brown, with a tinge of red. It absorbs very little water when made, into paste, and soon hardens. Immediately before using, it is mixed with sharp sand in various proportions.
This composition is employed in all marine and river embankments, in the footings of walls in damp situations, and in various other purposes to which common mortar is unsuited.
.111ert.r.5R. Mixing, Blending, and Beating of ; M. Felibien observes, that the ancient masons were so very scrupulous in the process of properly mixing and blending the materials in the making of mortar, that the Greeks kept ten men con stantly employed, for a long space of time, to each basin ; this rendered the mortar of such prodigious hardness, that Vitruvitis tells us the pieces of plaster fidling off from old walls. served to make tables. Felibien adds, that it was a maxim among old masons to their labourers, that they should dilute it with the sweat of their brow, i.e., labour at it a long time instead of drowning it with water to have done the sooner.
In modern practice, when the buildings are of conside(able intirnitude, the mortar is usually ground in a mill; hutwhich ever way made, it may be laid down as a fixed rule, that the more labour there is bestowed on the mixing and thoroughly blending the mortar, the harder and better will it he, and, as a necessary consequence also, so much more perfect will be the work in which it is used.
The following excellent observations on the advantages of beating mortar, are taken from Mr. Weale's useful little work, " Dictionary of Terms of Arts." "Mortar contained in a mould may be beaten or rammed in the manner of a mode of building formerly in use, whereby walls were formed by ramming and heating down earth, clay, &c.. between upright planks,' and acquires by that means great compactness ; but an increase of resistance does not always result from it.
"In order that any material be beaten with effect, it is necessary that it should possess a certain degree of consis tency, which is a mean hetween complete pulverulence and that state of ductility which constitutes a firm paste. No
compression is possible, when the material escapes from under the rammer; and this is still practised by the builders in pise, who never employ any but earth slightly moistened. Mortar may always be prepared in this way, leaving it. after it has been worked in the ordinary manner, to undergo desiccation to a proper extent.
"The successive approximation of the particles of the compressed material to one another, necessarily determines a foliated structure, which, though it may not be perceived, is nevertheless real. Analogy will lead to the conclusion, that in every possible case, a body thus f(n.med ought to oppose ;I greater resistance to a tractile force, in proportion as its direction forms a smaller angle with the plane of the lamina?, ; however, experience shows that this in general does not take place. The following has been determined in this respect :— " 1st. Beating has the effect of augmenting the absolute resistance of mortars of rich limes and pure sand in every case, but in an unequal manner. The greatest resistance assumes a direction perpendicular to the planes of the lamina., when the mortars are buried in a damp soil immediately after their fabrication. It remains parallel to these same planes, when the mortars have been exposed to the atmospheric influence.
" •nd. The effect of beating is not constantly useful to mortars of hydraulic or eminently hydraulic limes, and cal ca•eous or quartose sands or powders. except in the case when these mortars are used under a damp soil. The greatest resistance is then in a direction perpendicular to the planes of these as with the mortars of rich limes ; but in the air the superiority of the mortars which have been beaten, over those which have not, is only exhibited in one direction, and that is parallel to the plane of the laminze.
"3rd. Beating becomes injurious in every case, when the hydrates of the hydraulic or eminently hydraulic limes are employed without admixture, and subjected to the influence of a (lamp soil ; and is favourable to it only in the direction parallel to the l•minw, when the stuff dries in the air."