326 



OF PORTLAND i KMKNT. 



The clayey mud and the chalk used must be mixed in 

 such proportions that the resulting cement contains no 

 excess either of clay or lime. Too much lime, or incom- 

 plete mixture of the lime and clay, yields a cement which 

 may show great strength soon after setting, but becomes 

 much weaker afterwards owing to the working or swelling 

 of the excess lime. 



Too much clay generally produces a weak, quick- 

 setting cement, which may have a brownish, or " foxey," 

 colour. 



Fio. 163A. MOULD FOR CEMENT 

 BRIQUETTES. 



FIG. 163B. HOLDER FOR CEMENT 

 BRIQUETTES. 



* Butler gives the following composition of Portland 

 cement : 



Lime . . . 

 Silica ... 

 Alumina 

 Iron oxide 



60 to 64 per cent. 

 20 to 24 



6 to 10 



3 to 5 



Portland cement weighs from llOlbs. to 1241bs. per 

 bushel. It should be kept in a dry place which is at the 

 same time cool, and should, if possible, be taken out of 

 the sacks or barrels and allowed to remain for some little 

 time, before being used, exposed to the air until any 

 tendency to heating has left it. 



* B. Butler, "Portland Cement." 



