1837.] 



On the Induration of Mortar, 



37 



consequently able to afford carbonic acid to assist in the conversion of 

 the hydrate of lime into carbonate, and the property that substance has 

 of, in a peculiar manner, facilitating the solution of the alkaline earths 

 in water. 



With regard to the jaggry supplying carbonic acid to the mortar, I 

 have made the following calculation, shewing that, in order to give 

 sufficient carbon, 48 parts of sugar must be mixed with every 100 of 

 unslaked lime. But, as the quantity used is but one lb. to 288 lbs. of 

 slaked lime, it appears improbable that the jaggry, if useful, is so on 

 this account. 



4.68 parts of hydrate of To which add 1.73 parts There will result 

 lime contain of sugar containing -p 



3.56 Lime 0 3.56 lime. 



.94 Oxygen 801 1.741 oxygen. 



.185 Hydrogen 179 .75 carbon. 



Carbon 75 .364 hydrogen. 



To which, if .259 of oxygen, obtained from the water or air, be added, 

 there will be oxygen and carbon in the due proportion to make 2.74 of 

 carbonic acid ; which, with 3.56 lime, will form 6.30 carbonate of lime. 

 Now 3.56 : 1.73 : : 100 : 48. 



It must be particularly noticed that, in order that the mortar should 

 harden, it is not merely necessary that the lime should be thoroughly 

 carbonated. Common chalk and shells are as completely carbonate of 

 lime, as are the calcaneus spar or marble; yet the hardness of the 

 former substances is very inferior to that of the latter. 



The hardness of the mortar probably depends upon crystallization. 

 A writer, quoted in the Encyclopaedia Britannic a, says, that the lime 

 crystallizes and entangles the sand in its crystals. Now, in order that 

 crystallization may be effected, it is requisite that the crystallizable 

 matter be dissolved, in the first instance — and the jaggry, in assisting 

 the solution, probably assists crystallization. The use of lime water — 

 i. e. a crystallizable solution of lime in water, instead of common 

 water, has, I know, been practised by the Madras engineers at Nag- 

 pore, if not elsewhere, and with good effect. Water dissolves but 

 l-450th part of lime, but the addition of sugar would enable it to dis- 

 solve a larger quantity, in proportion as a larger quantity of sugar was 

 employed. 



It appears to me probable, therefore, that it would be found a good 

 method to use, instead of a solution of jaggry in water, as is the pre- 

 sent practice of the bricklayers in this country, a solution of jaggry 

 in water, which should afterwards be saturated with lime, and then 

 made use of to moisten the mortar, when the brickwork is being 

 built. There would thus be used, in an early stage of the building, 

 water holding a quantity of the lime in a crystallizable state, which, 



J" 



