174 REIBLING AND REYES. 
excessive free lime which caused the steamed pats to warp manifested 
itself very distinctly upon the strength. This is apparent from the figures 
in Table LIII which record the average results obtained from the 12 
samples which warped, together with the average of the other 58 sound 
samples. 
TABLE LIII.—Average tensile and compressive strengths of typical 
American hard-burned Portland cements. 
Strength in pounds per square inch. 
Mortar. Cement. 7 aa a 
4 7 360 * 
days.| days. Gain. days. | days. Gain. 
Per ct. Per ct. 
Sound and unsound-_--_--____- 669 | 696 4.0) 5,009 | 12,028) 138.1 
Neat s2ab ahs eee ed (Unsound asses eee eee seen 709 | 685| 3.4] 5,903 | 12,088} 104.7 
ound).22o2Seuse_ es eee 667 | 698 5.6 | 4,824 | 12,016 | 149.1 
. Sound and unsound_-__-______ 270 | 366] 35.5) 1,117] 3,741) 234.9 
1:3 Ottawa sand_____ (Wn sound Sees enemas 295} 365] 23.7} 1,200) 3,660/| 205 
Wound 2222enss=-- sea enenee 265 | 367] 38.3] 1,103) 3,755 | 240.4 
| 
 Sampies C. T. 18, 17, 14, 68, 24, 9, 5, 10, 11, 28, 39, 53. 
Instances have been noted in which a sound Portland cement 
showed as decided a drop in strength as an unsound product, 
but as the soundness tests often fail to measure or even to detect 
the quantity of free lime or to designate its condition this 
apparent discrepancy is readily accounted for. When the condi- 
tion and quantity of free lime is determined by means of the 
microscopic phenolate test, discrepancies do not occur. We have 
found this effect of free lime so characteristic that no 28-day or 
longer test is needed to determine the fitness of cements for 
use. If an otherwise satisfactory cement hardens in a desirable 
manner for about seven days and the microscopic test shows 
only a very little hard-burned free lime after this cement has 
been reground, then there is no doubt about the ability of the 
material to continue to harden in a satisfactory manner for 
years. Free magnesia is not detected by the microscopic or 
boiling tests, but as the total magnesia is maintained below 
5 per cent and its combination with silica and alumina is 
dependent upon the same conditions of proper burning as lime, 
it is evident that the less the free lime the less also the free 
magnesia. 
In the hands of an expert the microscopic test for free lime 
gives more definite and reliable information regarding the fu- 
ture behavior of hard-burned Portland cements than 28-day or 
