97 



[April 



III. — On the solidifying, or induration of Chun am. — Com- 

 municated through Lieutenant Braddock. 



Lime or Chunam as it is called by the natives is in chemi- 

 cal terms the oxide of Calcium, supposed by analogy to be a 

 metal combined with one portion of oxygen. It is also de- 

 signated an alkaline-earth, because it has the property of 

 altering the vegetable blues to red, and turmeric, brown, 

 like the mineral and vegetable alkalis. As it is found in 

 nature, it is always combined with a gaseous acid, the car- 

 bonic acid, the sulphuric, phosphoric, and some others. 

 The first combination is the marble of the statuary, — the 

 shell of which the Indian chunam is generally made, — it is 

 the common chalk ; the second is the plaster of Paris, of 

 which casts are made, — it is the alabaster or selenite, of 

 which vases are made and small figures ; — the phosphoric ig 

 that combination with lime, which constitutes the human and 

 other bones : there are other combinations, such as the fluate 

 of lime, or Derbyshire spar. 



Lime in itself and by itself possesses no indurative or 

 binding property ; it must be combined. Lime is not found 

 as an oxide of the metal, calcium, — it must be reduced to 

 that state by the expulsion of the acid with which it is com- 

 bined, — it is then what is called unslaked or caustic lime ; it 

 is by the action of fire that the carbonic acid is driven off. 

 Lime possesses a great affinity for water and is capable of 

 taking up and solidifying a considerable quantity, evolving 

 much caloric at the same time : having gone through this 

 process, it becomes a hydrate, or slaked lime, retaining still 

 its causticity, or capacity for combination with, and power to 

 decompose vegetable and animal matter. 



In this state, it has no indurating or cohesive property, it 

 is friable, it must be in combination ; and its great affinity is 

 to silex or sand, to this substance it mechanically attaches 

 itself with great avidity, and forms what is commonly called 

 mortar or cement ; but it is necessary that water should be 

 the medium by which the minute particles of each should 

 be brought into full and equal contact : there is no doubt 



