A NEW METHOD FOR THE DETERMINATION OF 

 FREE LIME, AND ON SO-CALLED DEAD BURNT 

 LIME.* 



Edward H. Keiser and S. W. Forder. 



A great many attempts have been made to devise a quanti- 

 tative method for the determination of free lime in Portland 

 cements, basic phosphate slags, commercial quick lime and 

 similar substances but none of the methods thus far proposed 

 have been satisfactory, nor have any of them come into gen- 

 eral use. The difficulty is that in the substances mentioned, 

 besides the free lime there are basic lime compounds, such as 

 the basic di and tricalcium silicates which are decomposed by 

 water with the formation of calcium hydroxide. When these 

 substances are treated with aqueous solutions, as, for example, 

 sugar solution, for the purpose of dissolving the free lime, 

 the water of the solution at once acts upon the basic lime 

 compounds and forms calcium hydroxide. It is, therefore, 

 impossible to determine how much of the lime that is found 

 was in combination and how much was in free condition. 



The method described below depends upon the fact that 

 uncombined lime, that is, free lime, combines almost instantly 

 with water whereas the basic calcium silicates are acted upon 

 much more slowly by water. The process is carried out as 

 follows: A weighed quantity of the substance, .2 to .5 

 grams in a platinum crucible is first heated to drive off mois- 

 ture, or, in the case of cements, is heated with the blast lamp 

 for a few minutes to expel any carbon dioxide, and after 

 cooling in a desiccator is again weighed. A few drops of 

 distilled water, which has been recently boiled, are then 

 added and the crucible placed in the brass protector Z), shown 

 in the figure, (i) is simply a cylindrical box provided with a 



* Presented to The Academy of Science of St. Louis, October 19^ 1903. 



(165) 



