xii. a, 3 Witt and Reyes: Calcium Sulphate on Cement 



141 



are placed in a large Erlenmeyer flask; carbon dioxide, washed 

 in sulphuric acid and in water, is passed into the flask for ten 

 minutes. The contents of the flask are then shaken violently. 

 This process is repeated three times. If the setting time of 

 the cement becomes less than one hour, it is likely to deteriorate 

 during storage. The latter test was applied to a number of 

 samples of brand F chosen at random and to brands A to E for 

 comparison. The results are shown in Table IV. 



Table IV. — Effect of carbon dioxide absorption on the setting times of 

 cements. 



Brand. 



Sul- 

 phu- 

 ric 



anhy- 

 dride. 



Original cement. 



After absorption of CO2 

 for ten minutes. 



After absorption of CO2 

 for twenty minutes. 



Loss 

 on 

 igni- 

 tion. 



Wa- 

 ter 



used. 



Time of 



setting. 



Loss 

 on 

 igni- 

 tion. 



Water 



Time of 

 setting. 



Loss 

 on 

 igni- 

 tion. 



Water 



Time of 



setting. 



Initial. 



Final. 





Initial. 



Final. 





Initial. 



Final. 





P.ct. 



P.ct. 



P.ct. 



H. m. 



H. m. 



P. ct. 



P. ct. 



H. m. 



H. m. 



P. ct. 



P. ct. 



H. m. 



H. m. 



A .... 



0.67 2.67 



24 



5 15 



8 40 



2.85 



24 



5 20 



7 40 



3.28 



24 



3 45 



6 50 



B .... 



0.86 3.07 



23 



5 10 



8 40 



3.10 



23 



5 30 



7 50 



3.75 



25 



3 45 



7 



C 



1.34 1 2.06 



25 



5 30 



8 40 



2.10 



25 



5 15 



8 5 



2.58 



25 



4 40 



8 



D..__ 



1.34 t 1.36 



23 



3 40 



6 40 



1.56 



24 



5 20 



9 50 



.1.59 



24 



5 5 



9 35 



E .... 



1.24 2.11 



23 



4 50 



8 



2.18 



23 



4 35 7 



3.11 1 23 



3 30 



6 45 



F .... 



2.00 



2.60 



22 



1 55 



3 45 



3.06 



22 



7 



3 10 



3.21 



24 



1 20 



4 10 



Fl... 



1.50 



2.13 



22 



2 35 



5 60 



2.30 



23 



1 50 



5 40 



2.37 



25 



3 5 



5 50 



F2... 



1.20 



2.89 



25 



5 5 



7 45 



3.07 



26 



4 25 



8 5 



3.16 



26 



4 35 



8 15 



F3... 



1.41 



3.80 



25 



4 10 



7 20 



4.03 



25 



4 35 10 



4.19 



26 



6 15 



9 45 



a All samples were tested for soundness and found satisfactory. 



In these examples it can be seen that there is no relation be- 

 tween the amount of sulphuric anhydride present and the change 

 in setting time caused by absorption of carbon dioxide. The 

 sample of brand F having the highest percentage of sulphuric 

 anhydride is the only one that becomes quick-setting. 



According to Hentschel 17 the change in setting time of a 

 cement in storage is due to the formation of alkaline carbonates 

 from absorption of carbon dioxide. The cements shown in Table 

 IV were gauged with sodium carbonate solutions of three con- 

 centrations. It can be seen from Table V that the set was but 

 little affected. 



Loc. cit. 



