Lime 



A similar process takes place in the mortar. 

 The lime takes back from the atmosphere the 

 gas which was lost through the heat of the 

 kiln, and gradually becomes chalk. It is 

 mixed with sand in order to separate it and 

 thus to enable it more easily to absorb the 

 air that is required for its conversion into 

 chalk. When the mortar is completely 

 restored to the condition of chalk, the courses 

 of a building are so firmly connected that it is 

 sometimes easier to break the stones than to 

 remove them. 



Fat lime or pure lime, in contact with water, 

 becomes very hot, increases considerably in 

 volume and forms a strong adhesive mortar. 

 Greystone lime does not heat readily, cracks 

 slowly and scarcely increases in volume. 

 The former is derived from almost pure chalk ; 

 and may be mixed with much sand, when 

 it provides abundant mortar : the latter 

 comes from chalk containing various foreign 

 matters, takes up less sand and produces less 

 mortar. Both harden in the air by absorbing 

 carbonic acid gas which converts them into 

 chalk. 



There is a third variety of lime, hydraulic 

 lime, which possesses the valuable property of 

 hardening under water. It comes from chalk 



125 



