IX. A, 2 Reibling and Reyes: Portland Cement Materials 129 



kiln products. In the rotary kiln process the clinker is cooled 

 much more rapidly, and if, as in this instance, the prospective 

 manufacturers intend to install rotaries the clinker from the 

 experimental burnings should be cooled accordingly. It was for 

 this reason that we designed a furnace which enables us to dump 

 the clinker and cool it as rapidly or as slowly as desired. 



The necessity of testing the resulting cements in a thorough 

 and comprehensive manner is also imperative. This is especially 

 true of the "time of setting." The extent and manner in which 

 the setting properties of cements may change owing to the 

 influence of slight variations in the quantity of retarder or degree 

 of seasoning, the means whereby it is possible to ascertain if 

 the set is capable of being kept within desirable limits during 

 storage, and the minimum amount of retarder required have 

 been fully described.^ Yet, it is the common practice of many 

 laboratories to add 2 or 2.5 per cent of plaster to the cement 

 and submit the result obtained as characterizing its setting 

 properties. Nothing is apt to be more misleading, as the following 

 incident will serve to show. 



One of the reports submitted to our inspection showed that 

 the tester had added 2 per cent of calcined gypsum and obtained 

 a cement which required an excessively high percentage of water 

 for normal consistency and gained its initial and final sets in 

 about five and one-half and nine hours, respectively. These and 

 other similar results made it appear that the manufacturers 

 would have considerable difficulty in producing Portland cement 

 from these raw materials which would set and harden with 

 sufficient rapidity. 



However, for reasons which we have already thoroughly dis- 

 cussed,^ the opinion was expressed that these cements really set 

 so quickly that they became partially regauged and consequently 

 abnormally slow setting during the mixing process. The com- 

 monness of errors of this kind has been pointed out. In fact, 

 so far as our experience goes, the regauging of extremely 

 quick-setting cements is the main cause of the serious dis- 

 crepancies which occasionally occur between the reports of the set 

 from the manufacturer and those of the consumer. Nine-tenths 

 of the cements which, when tested in the cement laboratory of 

 the Bureau of Science, failed to pass our standard specifications 

 did so only because they set with abnormal quickness. Fully 



' This Journal, Sec. A (1912), 7, 207-252. 

 'Ibid. (1911), 6, 248. 



