248 REIBLING AND REYES. 



represent the commercial product from which it is taken. Therefore, 

 and because so many influences must be taken into consideration where 

 the set of a cement is concerned, we have been forced to trace causes 

 and results and reason from them step by step, and this process brought 

 about the somewhat voluminous nature of this paper. For the same 

 reason, a brief summary of all the important conclusions arrived at can 

 not be made, the interdependent nature of such conclusions preventing 

 a brief statement of facts. 



However, with respect to the control of the setting properties of 

 Portland cement we believe that a method has been devised whereby 

 the manufacturer before packing his cement can ascertain whether its 

 setting properties are controllable, and if so, the minimum amount of 

 retarder required to keep the set within normal or desired limits during 

 the process of ordinary storage. 



The manufacturer, especially, should give the subject of partial re- 

 gauging due consideration, as the first effect of seasoning on cements 

 which have this sudden set is to eliminate the regauging, but to quicken 

 the rate of setting in the commercial application of the product and 

 such cements although apparently slow setting when tested at the mill 

 are especially apt to be quick setting when tested at their destination. 

 So far as our experience goes, this is the main cause of the serious dis- 

 crepancies which occasionally occur between the reports of the set from 

 the manufacturer and those from 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 one-half of these could not 

 have produced a slow-setting paste before they were packed, unless during 

 the process of mixing regaiuging had taken place to a considerable extent. 



It has also been noticed that the policy of some manufacturers has 

 been to plaster their cement with between 0.75 and 1.25 per cent of 

 gypsum. This policy, although evidently purely an economic one, has 

 often caused serious financial losses to both manufacturer and consumer, 

 for we have found that the majority of quick-setting cements only re- 

 quired about 0.5 per cent of additional plaster to make them slow setting. 



This work also gives adequate reason for the failure of so many in- 

 vestigators to establish definite facts concerning the effects on the setting 

 properties of various methods of treating the clinker. 



Take, for instance, the explanation of H. Spencer Conover'^ to the question, 

 "Why does cement sometimes become quick-setting?" He likens the reactions of 

 the tempering of cement to that of steel, and states that the stability of cement 

 depends to a large extent upon the proportion of alit and celit to each other. 

 His statements are based upon the results obtained by dividing a sample of clinker 

 into three parts and cooling them in different ways. 



'^Cement Age (1905), 3, 479-86. 



