370 REIBLING AND REYES. 



D. B. Butler 5 makes the following statement : "Unstable lime compounds, or 

 rather lime compounds which, after a more or less prolonged lapse of time, 

 slake with considerable expansion, there certainly are, and these are doubtless 

 answerable for the unsound cements which are sometimes met with, but anyone 

 with experience in such matters will appreciate the fact that free lime, i. e., 

 calcium oxide, can not exist in contact with argillaceous or acid compounds at 

 ordinary cement kiln temperature." 



W. Michaelis, Sr., 6 writes as follows : "Even by the clinkering process the 

 inside of the coarser grains of calcined lime can never be reached by the fusing 

 silicates surrounding them. The powdered clinker therefore must contain a 

 certain amount of uncombined lime." 



The more direct evidence of chemical, thermochemical and microscopical ex- 

 periments has also led to diverse conclusions. 



W. Richter T believes that all lime in cement is combined. Steuer, 8 Wormser 

 and Spanjer, 9 and Hart, 10 on the contrary, state that they have extracted 44, 

 26.6, and 30.34 per cent, respectively, of calcium oxide free from combination, 

 from Portland cement. 



There is also a diversity of opinion in regard to the physical and chemical 

 properties of free lime and its effect upon the properties of the cement. 



Hart u states that the reason why 30 or 34 per cent of free lime can exist 

 in Portland cement without injury to the product is because this lime is vitrified 

 and crystalline, differing physically from amorphous lime. He believes that on 

 hydrating, this vitrified lime hardens imder water and considers the balance of 

 the cement material as ballast, as slag which does not harden. Others u regard the 

 lack of much free lime in the rotary clinker as detrimental. They believe that the 

 old set-kiln process was best, even though it produced a cement which contained 

 much free lime. They state that under the modern practice of ageing, grinding, 

 and mixing, a considerable amount of free lime is taken care of and that, although 

 the rotary kiln has reduced the percentage of free lime, it has worked an injury 

 because the increase in the silica and alumina ratio has resulted in a cement 

 that fails to maintain its high early strength. 



E. D. Campbell, 13 assumes the opposite to be true and writes as follows : "Free 

 lime in Portland cement will not only not be slaked during the mixing and setting 

 of the cement, but will not become completely hydrated even when the cement 

 is immersed in water until about fourteen days have elapsed. The result of this 

 gradual slaking is to produce abnormal expansion of the cement. The expansion 

 due to free lime slaking in the air may become so great after several months as 

 to cause complete disintegration." 



E. B. McCready's 14 views are similar. He states that: 



"When the amount of uncombined lime is not enough to cause disruption, 

 the strain exerted simply weakens the specimen so that it is more readily broken 



5 Official Correspondence. 



"Cement & Eng. News (1909), 21, 344. 



7 Thonindustrie Ztg. (1883), 46. 



8 Ibid. (1899), 604. 

 °lbid. (1885), 



10 Ibid., 659, 770, 853; (1900), 188. 



11 hoc. clt. See also Blerninger, Albert Victor, The Manufacture of Hydraulic 

 Cements, (1904), 215; Bull. Oeol. Surv., Ohio (1904) IV, No. 3. 

 12 Journ. Amer. Ghem. Soc. Abs. (1908), 2, 2983. 

 13 Journ. Amer. Ghem. Soc. (1906), 6, 1298. 

 14 Amer. Soc. Test. Mat. (1907), 7, 375. 



