TESTING OF PORTLAND CEMENT. 337 



time of initial set. The setting will be considered as 

 finished when the surface of the cement supports the 

 needle without its penetrating to any appreciable degree." 



The time of initial set varies from one to 20 minutes, 

 and that of complete set from four to 120 minutes. 



The process of setting causes the cement to rise in 

 temperature, the extent of this rise being ascertained by 

 mixing some cement and, water in a small vessel, placing 

 a thermometer in the paste and watching the mercury. 

 Mr. Deacon used this method to ascertain the setting 

 properties of the cement he used on the Vyrnwy dam. 

 According to his own statement, "if within 15 minutes, 

 the rise of the thermometer exceeds 2 Fah., or, within 

 60 minutes, 3 Fah., the cement is further exposed before, 

 use."* 



As examples of the results given by samples of cement 

 subjected to the above tests, the figures on p. 338 may be 

 quoted. These results are given by Mr. D. B. Butler in 

 his paper on " The Finer Grinding of Portland Cement, "f 

 and are illustrative of some experiments on the properties 

 of cement as delivered by the manufacturer, and the same 

 cements after being much more finely ground. The three 

 kinds of cement dealt with are F, from the lias districts 

 of Warwickshire, G, from the Northfleet shore of the 

 Thames, H, from the Grays shore of the Thames, and I, 

 from the Medway. 



I Prof. Unwin quotes the following figures obtained by 

 Bauschinger from crushing tests of neat cement and of 

 cement and sand. JSSUSf. 



Mean crushing strength of neat cement, seven 



days after gauging 1,800 



Do. for cubes of one part cement to three parts 



sand 825 



Do. for cubes of one part cement to five parts 



sand 500 



Where the time of testing is longer than one week, the 

 following has to be added. 

 The general equation is 



y = c -\- d \/x 1 



* Mhi. Proc. I.C.E., vol. cxxvi. f-Min. Proc. I.C.E., vol. cxxxii. 

 J Unwin's Testing. 



