PROPERTIES OF PORTLAND CEMENT. 



383 



presence of the latter in unadulterated Portland cement is a positive 

 proof of underburning. 



Free, sintered lime may exist in dense, thoroughly clinkered cement 

 material if the conditions essential for yielding a completely homogeneous 

 product, such as fineness, duration of exposure to high temperature, 

 proper chemical composition, etc., have not been complied with. On 

 the other hand, Portland cement clinker may be burned perfectly so as 

 neither to contain free lime nor have lime liberated in the ordinary process 

 of cooling and grinding. 



The data recorded in Tables IV, V, and VI show the effects of the 

 atmosphere on sintered, nonsintered and slaked lime in Portland cement 

 under different conditions of aeration. 



Conditions of the experiment recorded in Table IV. — Five grams of the cement 

 (Brand 0, Table III) which for the greater part gave plumes on microscopic 

 examination, were exposed to the atmosphere in a 5-millimeter test tube. At 

 regularly increasing intervals of from thirty minutes to one day, the test tube 

 was corked, its contents thoroughly shaken, and a test made from the resulting 

 mixture. 



Table IV. — Microscopic tests of an aerating cement containing uncombined 



sintered lime. 



Sam- 

 ple 



num- 

 ber. 



Time. 



Microscopic test (duplicate samples). 



1 



4 



7 



11 



15 

 21 





An almost immediate formation of plumes, some of which were 

 fully developed in a few minutes. Others developed more slowly, 

 requiring as long as 15 or 20 minutes to complete the reaction. 

 At first no individual needles appeared, but after 10 minutes a 

 few short radiating clusters were discovered. 



Similar to the above, except that a careful comparison of many 

 samples indicated the presence of long needles. 



Many plumes develop almost immediately. In some instances their 

 edges were first surrounded with rather long radiating needles. 

 These were soon pushed aside and so formed an outer smooth edge 

 to the plumes which could not be distinguished from the rest of the 

 crystalline formation. These slides show a marked increase in the 

 relative amount of needles, most of which radiate from central 

 nuclei in the form of rosettes. 



A mass of rosettes and clusters formed of long, needle-shaped crys- 

 tals is shown. A few part feather and part needle rosettes are 

 formed. 



No plumes nor feathery crystals appear. The slide shows clusters 

 of long needles and rosettes in abundance. 



No crystals whatever appear within 1 hour. 



Aerated 2 hours 



Aerated 8 hours 



Aerated 32 hours 



Aerated 80 hours 



Aerated 272 hours___ 



99667- 



