PROPERTIES OF PORTLAND CEMENT. 



379 



The same cements shown by figures 6 and 8, when seasoned in moist 

 air give crystals (see figure 9) which correspond exactly to those secured 

 with calcium hydroxide (see figure 2). 



An increase in the percentage of water in the test solution also has 

 the effect of producing crystals similar to those shown in the last figure. 



It might be argued that 

 in cement, certain silicates 

 or aluminates of calcium 

 might be decomposed by the 

 test solution to give crystals 

 identical with those pro- 

 duced from free lime. Apart 

 from the fact that such a 

 discussion would be purely 

 academic, were compounds to 

 exist so easily decomposed 

 by phenol, yet it may be 

 stated that perfectly sinter- 

 ed, aerated and nonaerated 

 clinkers, ground to pass a 

 200-mesh sieve, fail to give 

 White's reaction ; so that it 

 appeai-s not to be character- 

 istic of lime which has 

 entered into combination at 

 higher temperatures with 

 other substances in cement. 



Fig. 9. — Characteristic crystals obtained from slaked lime 

 in Portland cement. 



Therefore, White's test offers a positive means for the identification of 

 sintered, nonsintered and hydrated free lime in such materials as Port- 

 land cement; however, only an experienced operator who thoroughly 

 understands the conditions of the reaction in which three different 

 characteristic habits of the same crystal can be produced under given 

 circumstances can do this successfully. 



It is often extremely difficult, if not impossible, to estimate accurately 

 the relative quantities of the different kinds of free lime which are 

 present, but the conclusions to be drawn can often .be rendered more 

 certain by examining several slides in test solutions containing different 

 percentages of water. A study of the material retained on sieves of 

 different sizes may also give valuable information. The test solution is 

 hygroscopic and must be protected from moisture. 



APPLICATIONS OF THE TEST FOR FREE LIME. 



It has been stated that "cement which comes from the kiln, containing 

 more than a trace of free lime, will not pass the boiling test until the 

 free lime has been removed." However, in spite of the fact that all of 

 the cements recorded in Table A were perfectly sound, they each showed 



