664: NEW YORK STATE MUSEUM 



More than 10^ of magnesia makes tlie lime shorty and 25^ to 

 SO^j it is asserted, renders the stone unfit for burning; " never- 

 theless, such stone is burned in the southeastern part of New 

 York state. 



10^ of silica-, it is maintained, gives the lime hydraulic proper- 

 ties. 



Frasch also states that limestone of 95^ purity yields 59^ 

 burnt lime with 90;^ calcium oxid; of 90^ purity, gives QOfo burnt 

 lime with 80fo CaO; 85^ stone gives 65.5^ with 72^ CaO, and 

 80'^ stone gives 70^ with 64^ CaO. 



Slaking. Lime in its normal condition and when dry is totally 

 ■unaffected by carbonic acid gas but when heated takes it up 

 rather quickly. The addition of water to lime can be done in a 

 variety of ways according to the degree of slaking that is to be 

 brought about. If a lump of quicklime is immersed in water 

 for an instant it saturates itself at once, and this absorption is 

 accompanied by the evolution of heat and a swelling and bursting 

 of the lime, which finally falls to a fine powder, the hydrate of 

 the lime, Ca (0H)2. The chemical action which has taken place 

 is expressed by the formula CaO+H20 = Ca(OH)2. 



This method of hydration is considered to be better than pour- 

 ing the water on the lime. 



The hydrate of lime thus obtained is a fine, white powder of a 

 specific gravity of 2.1. Its water of hydration is pretty firmly 

 combined and is only driven off by reheating to redness. 



Fat limes slake very fast and produce more heat than lean 

 ones, and lime will slake even in the air by the absorption of 

 moisture, so that, if not used immediately, it should be protected 

 from the atmosphere as much as possible. 



lime may also be slaked by putting the lumps in water for a 

 few minutes, then withdraAving and packing away to allow the 

 lime to change to powder. The common method usually em- 

 ployed in building operations is to mix the lime with water in a 

 box. " Too much water makes it thin and injures its cohesive 

 strength. If only a part of the water required is added at first 



