CEMENT FOR A MODERN STREET. 



153 



Since 1890 great progress has been made in the United States in 

 the application of theoretical and scientific principles to the technology 

 of Portland cements, and the result has been an enormous expansion 

 of the business with an improved quality of the product. 



The original method pursued in England, and largely adopted 

 elsewhere, was to grind the materials very wet, floating off the fine 

 particles to a large tanlv where they were allowed to settle. The settling 

 and drying required a great deal of time. This method was followed 

 by a dry process in which the materials were ground together dry and 

 then moistened sufficiently to be molded into briquettes. The bri- 

 quettes were then dried and stacked in a kiln and burned. The intro- 

 duction of rotary kilns rendered the molding and drying unnecessary 

 as either dry or wet materials, as a dry powder or wet mud are fed 

 directly to the kilns. The composition of the materials, whether it 



Fig. 4. General View of Works of Virginia Portland Cement Company, Craigsville 



Augusta Co., Va. 



be cement rock or mixed materials, must be maintained by constant 

 chemical analysis, as the percentage of carbonate of lime should not 

 vary by more than I/2 per cent, from that found correct for the other 

 materials used. 



From the foregoing statements it will be observed that two quite 

 different methods of manufacture are followed. In the first the cement 

 'mix' is molded into briquettes, which are dried, stacked in a kiln and 

 burned. For the burning by this method three different forms of kiln 



