PROPERTIES OF PORTLAND CEMENT.- PART III. 



241 



mechanical way and know little of the scientific technical considerations 

 involved. One of us had occasion to work vrith the routine cement tester 

 of this large manufacturing plant. Together we took the setting prop- 

 erties of a number of samples all of which^ apparently, gave satisfactory 

 results. However, by means of the calorimeter test, it was found that 

 one produced a partially regauged cement paste. This cement was 

 exposed to the atmosphere for a few hours and again tested. A normal 

 but extremely quick-setting paste resulted. 



Later, the arrival of another shipment of abnormally quick-setting 

 cement from this same manufacturer gave us an opportunity to test 

 our conclusions regarding the regauging of the cement at the factory. 

 Accordingly, we subjected this material to a careful examination the 

 essential results of which are recorded in Table XXXII : 



Table XXXII. — Setting properties of brand cement tested for request No. 85725. 



Quick setting cement (finene.?s=76. 2 and 

 96. 0; per cent of SO3=0. 89). 



Temper- 

 ature of 

 labora- 

 tory dur- 

 ing the 

 mixing 

 and set- 

 ting. 



Speci- 

 fic 



grav- 

 ity. 



Quantity 

 of water 

 required 

 to pro- 

 duce a 

 paste of 

 normal 

 consist- 

 ency. 



Time 

 of ini- 

 tial set 

 in min- 

 utes. 



As received 



As received but aerated 4 hours, 



°C. 



26-27 



26-27 



26-27 



27-28 



27-28 



28-29 



3.12 

 3.11 

 3.09 

 3.08 

 3.07 

 X 



Per cent. 

 23 

 22 

 20 

 20.5 

 21.0 

 22 



20 

 10 

 70 

 90 

 60 

 60 



As received but aerated 21 hours 



As received but aerated 27 hours 



As received but aerated 40 hours 



As received -f 5 per cent of plaster 





From these figures it is evident that the cement as received had not 

 seasoned sufficiently entirely to eliminate regauging during the process 

 of mixing, and furthermore, that a slow-setting paste could have been 

 obtained at the factory only because less calcium had become slaked and 

 consequently regauging had occurred to some extent. 



Cement L also proved truly characteristic of the general nature of 

 the commercial product which it represents. 



We have never encountered a quick-setting sample of brand L cement even 

 when as little as 0.46 of sulphuric anhydride (SO3) was present. Formerly the 

 manufacturer ground this cement so coarsely that this was thought to account 

 for its slow set. However, during the last year the material from the same 

 mill has been much more finely ground and although the chemical composition 

 and specific gravity have remained practically unchanged the cement as heretofore 

 continued to set very slowly. In fact we reground some to an extremely fine 



