708 NEW YOEK STATE MUSEUM 



the quality of tlie manufactured product. These changes are 

 three in number, i. e. driving off of the mechanically combined 

 water; driving off the carbonic acid; fusing together of the silica, 

 alumina, lime and iron. Each of these requires a different tem- 

 perature for its accomplishment, but the attainment of the proper 

 temperature to produce the last change is the most important. 

 If the required temperature is overstepped, the cement is over- 

 burned and has little or no setting power. 



Specific gravity. The specific gravity of the Portland cement 

 is often an indication of the thoroughness of the burning, and is 

 determinable by some form of pycnometer. 



One type consists of a flask with a stopper, and having a long 

 graduated neck. The vessel is filled with benzin or turpentine 

 up to the zero graduation on the tube. A given weight of ce- 

 ment is dropped into the tube, care being taken to allow all the 

 air bubbles to escape, when the rise of the liquid in the tube 

 indicates the volume of cement added. If metric units have been 

 used, then the specific gravity of the cement is equal to the weight 

 of the quantity added in grams divided by the increase in volume 

 in cubic centimeters. 



Well burned Portland cement has a specific gravity of more 

 than 3.05, but should not exceed 3.15 or 3.20. 



In making this test it is necessary to see that there are no 

 lumps, and that the cement is thoroughly dried. 



Kilns. The types of kilns used in the United States are: 

 intermittent or dome kilns; continuous kilns, of Dietzsch or 

 Shof er type ; rotary furnace. 



In the old-fashioned intermittent kiln the bricks of cement and 

 coke are charged in alternate layers. The Dietzsch and Shofer 

 kilns are continuous, as already stated, and possess the great 

 advantages of cheaper fuel, economy of labor, and of burning 

 the dry, powdered material. The rotary furnace effects an enor- 

 mous saving of time and labor, and it is claimed that the tem- 

 perature can be regulated far more exactly than is possible in 



