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clofely heaped together, I was fully fatisfied as to the caiife of the 

 hardnefs or cohefion which Lime acqiiires after being moillcned ; for 

 the falts flioot from it, one among another, in all directions, and 

 being foft when firfl; formed, they muil, as they harden, become 

 clofely coagulated, and fixed to each other, fo that not a tingle fait 

 is formed in the fubllance, but it is united or connefted with others : 

 and I am fully convinced, that the hardnefs or ftrong cohetion we 

 find in Lime when made into Mortar, arifes only from the Inline par- 

 ticles or minute falts produced in it, which are of fuch a nature, 

 that when once formed, and thoroughly hardened and compadled 

 together, they can never afterwards be dillblved, unlefs by the 

 powerful efFe6l of fire. 



In relle6ling on the nature of Lime, as thus defcribed, I began to 

 think that if the Mortar of old buildings were burnt over again, 

 the faline particles formed in it would be fo diflblved that it might 

 be again moiliened with w^ater, and become ferviceable as before. 

 In order to make trial of this, I took fome pieces of dry Mortar 

 from the roof of my houfe, and heated them red hot ; wdien cold 

 I found they were become fo foft, that they might be crumbled to 

 powder between the fingers ; and, upon wetting this powder with 

 water, I found it to poflefs all the properties of new-made Lime. 



Now% fmce we find that the faline particles in Lime or Mortar are 

 the only reafon that Mortar or Cement, when dry, becomes hard or 

 ftony, and that if the fame be again burnt it becomes foft, all thofe 

 faline particles being dilTolved, infomuch that we can crumble it be- 

 tween our fingers, we may be well afi^ured that Lime is unfit to 

 make Mortar or Cement for w^alls of buildings wherein great fires 

 axe to be made, and that the proper fubtlance for fuch kind of work 

 is good Clay, which becomes the harder the more it is expofed to 

 the fire. 



I alfo concluded, that this Ihooting or formation of falts in com- 

 mon Lime, mull alfo take place in that kind of Cement which is 

 called Tras, or Terras, which is of that nature that it acquires a ftony 



