Keiser & Forder — Determination of Free Lime. 169 



nate is used, because the lime at too high temperatures be- 

 comes dead burnt, that is, it becomes incapable of uniting 

 with water. Zulkowski, Chemische Industrie, 1901, page 

 290, maintains that a portion of the lime in Portland cements 

 is in this dead burnt condition. In an article in the Thonin- 

 industrie Zeitung, 1902, the same author suggests the formula 



Ca^ Ca for dead burnt lime. 



For the purpose of determining the behavior of highly 

 heated lime towards water, powdered Iceland spar was placed 

 between the carbon pencils of an electric arc and the current 

 passed for one hour. A number of particles of semi-fused 

 lime were thus obtained. These particles were carefully 

 separated from the powder that had not melted, and weighed 

 quantities were hydrated by the above described method. It 

 was found that this lime that had been heated in the electric 

 arc slaked more slowly than that which had not been heated 

 to so high a temperature, but still it combined slowly with 

 water at ordinary temperatures and on allowing it to stand 

 with water at the ordinary temperature for 24 hours it had 

 slaked completely. When the temperature was raised to 85 de- 

 grees, the slaking was complete in two hours. The following 

 results were obtained : — 



Another specimen of lime that had been heated with the 

 oxy-coal gas blowpipe gave the following result : — 



.3557 .1163 100.5 



These experiments show that pure lime that has been 

 heated to very high temperatures, even semi-fused lime is not 



