PROSPECTS OF THE NATURAL-CEMENT INDUSTRY. 293 



average brand of Portland cement. The faults charged against the 

 natural cements are not, therefore, universal. 



There remains to be considered the second point: whether, when 

 these faults do occur, they are unavoidable and inherent in the idea 

 of a natural cement, or whether, on the other hand, they can be 

 avoided economically. To the present writer it seems obvious that 

 most brands could, with sufficient care, be freed from both faults, and 

 that this improvement could be carried out without raising the cost of 

 manufacture to a profitless point. 



In regard to chemical control of the raw material and product, it 

 can be said that, with very few exceptions, none is attempted in the 

 American natural-cement industry. The plants of the Lehigh district 

 of Pennsylvania, which are run in connection with Portland-cement 

 plants, are, of course, better off in this respect than the others. Exclud- 

 ing these Pennsylvania plants, there is, to the writer's knowledge, only 

 one American natural-cement plant which employs a chemist. It seems 

 only right that the name of this honorable exception should be published 

 it is the Pembina Cement Company, of North Dakota. 



Careful analyses of the raw material and the product will, as pointed 

 out earlier in this volume, enable the manager to select the proper burn- 

 ing-point for his rock, and to correct any defects in its composition. 

 Few quarries show rock of such uniform character that it can all be 

 burned at the same temperature, yet at most plants this is just what 

 is attempted. 



The product must also be given more careful treatment after burning, 

 both in regard to seasoning and grinding. At the present day there 

 is no reason why a coarsely ground or unsound natural cement should 

 be put on the market. Economical fine-grinding machines are obtain- 

 able and should be installed. They will soon repay their first cost, 

 and their high power consumption per unit is more than made up by 

 the great increase in the amount and quality of the output. 



