PROPERTIES OF PORTLAND CEMENT. 



407 



Fig. 14. — Photograph of commercial Portland cement clinkers showing particles of free 

 lime visible to the naked eye. (1) Stationary kiln clinker (brand L) ; (2) 

 stationary kiln clinker (brand O) ; (3) rotary kiln clinker (brand O) ; (4) 

 rotary kiln clinker (brand K). 



The reason for the inactivity of coarse particles -of lime throughout the 

 burning process of Portland cement clinker is especially apparent from 

 the work of Day and Shepherd 3S when we take into consideration the 

 fact that the clinker is a product of incipient fusion, rather than of a 

 melt. These authors say that contrary to Hoffmann's statement that 

 "temperature of formation is above the temperature of fusion," just the 

 reverse is true. Under normal conditions these mineral combinations 



^Joum. Am. Chem. Soc. (1906), 28, 1092. 



