CEMENT FOR A MODERN STREET. 157 



is performed qiuckly and is quickly arrested when the process is com- 

 pleted. 



Experience has proved that the burning of cement is an important 

 factor in its manufacture as determining its qualities. A cement that 

 is properly proportioned, thoroughly mixed and well burned and finely 

 ground will set in about two hours after mixing with water, will harden 

 well after setting and will continue to harden through long periods, 

 even to several years. Ground gypsum is frequently added to cement 

 to control the setting. 



Cement should be finely ground. Ninety-two to ninety-three per 

 cent, should pass a sieve of 100 meshes to the linear inch. 



Until within the last decade, the Portland cements manufactured in 

 the United States were generally inferior to the best English, German, 

 Belgian and French brands. While these foreign cements have been 

 maintained with the highest degree of excellence the American brands 

 have been greatly improved until at the present time there are no 

 better cements made anvwhere in the world than in the United States. 



