398 



REIBLING AND REYES. 



The same experiment was repeated on a larger scale with brand 

 cement. 



In this ease the cement was exposed in a 10-liter, square, coverless can for 

 six months, from September 1, 1909, to January 2, 1910. The can was placed 

 near an open window so as to insure an ample change of fresh air. Table X 

 records the results. 



Table X. — ■Penetration of air into undisturbed cement. 



Sample number. 



Distance 



from 

 surface. 



Loss 

 by igni- 

 tion. 



Carbon- 

 diox- 

 ide. 



Mois- 

 . ture. 



i 

 Condition of 

 cement. 



1. . 



mm. 

 0- 3 

 3- 13 

 13- 25 

 25- 76 

 76-127 



Per ct. 

 12. 72 

 9.28 

 4.12 

 3.66 

 3.60 



Per ct. 

 8.56 

 5.88 

 0.84 

 0.53 

 » 0. 35 



Per ct. 

 1.75 

 1.31 

 0.86 

 0.62 

 0.55 



Caked hard. 

 Caked. 



Slightly caked. 

 Not caked. 

 Do. 



2 -.____ 



3 



4 __ 



5___ 





a The unexposed cement contained 0.35 per cent of carbon-dioxide. 



These figures show that only exposed surfaces of ground Portland 

 cement are subjected to aeration, and consequently the material under- 

 neath this seasoned surface may possess physical characteristics differing 

 entirely from those of the upper layers. While the percentage of carbon- 

 dioxide changes but very little at a distance greater than 13 millimeters 

 below the surface of the cement, water absorbed from the atmosphere 

 may slowly penetrate further. This is shown by Table XL 



Table XI. — Penetration of moisture into undisturbed cement. 



Constituents. 



Loss by ignition 



Carbon dioxide 



Moisture 



Water of combination liberated at a low, red heat 



Cement 

 before 

 being 



aerated. 



Per cent. 

 0.48 

 0.12 

 0.00 

 0.36 



Aerated 

 cement." 



Per cent. 

 1.88 

 0.12 

 0.23 

 1.52 



"■ Cement aerated 4 months and 17 days in open glass cylinders ; samples taken 127 

 millimeters below the surface. 



The absorption of water and carbon-dioxide from the air by small 

 quantities of cement which are frequently remixed, is made clear by 

 Table XII. 



The conditions in this instance were the following: Three brands (O, H, and 

 M) were used. In each case 50 grams of cement placed in 250 cubic centimeter 

 beakers, each of the same diameter, were mixed and weighed daily. An empty 

 beaker of the same size collected so little dust (0.002 gram in 2 months) as to 

 make a correction for dust unnecessary. The first figures in Table XII give the 

 average of three samples. At the intervals stated, one beaker was removed from 

 each set and the percentage of volatile constituents in the cement determined. 



