44 ESSAYS AND OBSERVATIONS 



were in fome places allowed to remain in 

 contact with one another. 



EX PER. XXVIII. 



Equal parts of quick-lime* and fand 

 were kneaded together and dried. In 

 this ftate, the mafs fuffered no change 

 from water ; but, when properly burnt, 

 it exploded in water with conhderable 

 violence. 



EXPER. XXIX. 



A piece of old mortar, after calcina- 

 tion, fell down immediately in water. 

 This mortar, examined by the acid of 

 fea-falt, appeared to confift of calcarious 

 earth and fand, in equal proportions f. 



Thus 



* I could by no njeans make crude calcarious earth 

 cohere with fand in fuch a manner as to redft either the 

 flighteft touch, or the influence of water. 



f la the fame manner, the proportion of fand in any 

 mortar may be eafily examined ; and confequently, the 

 eompofition of fuch mortars, as have, for many ages, 

 vlthftood the effefls of time, may be thus difcovered. 



