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PREPARATION OT MORTAR AND CEMENTS. 253

PREPARATION OF MORTAR AND CEMENTS.

Lime forms the principal part of the mortar or cement, usedfor connecting stones and bricks in buildings. It is generallymade of lime, sand, and water. Its hardening is a species ofcrystallization, owing to a slow absorption of carbonic acid andwater. No certain proportion of lime, silex, and water, forforming mortar, is adhered to in this country; we are informedhowever, that in the best mortar one part of lime and two ofsand are generally mixt with so much water as is sufficient togive it a certain consistence. The lime, the sand, and thewater require to be very much beaten together, in order to pro-duce an intimate mixture and combination of them in their mi-nutest particles, without which the mortar cannot possiblyanswer the intended purpose.

IVater cement, or mortar, which has the property of harden-ing under water, may be prepared according to Guyton,* bymixing together four parts of blue clay, six of black oxid ofmanganese, and nine of carbonate of lime. This mixture is tobe heated to a white heat, in order to decompose the carbonateof lime, it is then mixed with 60 parts of sand, and formedinto mortar with a sufficient quantity of water.

Dr. Bryan Higgins has found that burnt bones improve thecommon mortar very much; and as the mortar prepared accordingto his direction is certainly the best that can be proposed, we shallshortly notice the composition of it. Take 56 parts of washedcoarse sand, whose single grains do not exceed T ' 5 part of an inchin diameter, and 42 of fine sand. Mix and wet them with lime-water, add gradually 14 parts of slaked lime, beat it well to-gether, and lastly, add a like quantity of powdered bone-ashes

* Ann. de Chimie xxxvi : , p. 259.