12 



CEMENTS, LIMES, AND PLASTERS. 



Chemical compounds. Certain chemical combinations will be 

 mentioned very frequently in the discussion of cementing materials. 

 The more important of these compounds are listed in the following 

 table, with their symbols and also the name by which they are known 

 when they occur as minerals or as commercial products. 



TABLE 4. 

 NAMES AND SYMBOLS OP PRINCIPAL COMPOUNDS. 



Heat-units. Two heat-units are now in common use the British 

 and the metric. 



The British thermal unit ( = B.T.U.) is the quantity of heat required 

 to raise the temperature of 1 Ib. of water one degree Fahrenheit when 

 at the temperature of maximum density ( = 39.1 F. or 4C.). 



The metric unit ( = calorie) is the quantity of heat required to raise 

 the temperature of 1 kilogram of water one degree centigrade when 

 at the temperature of maximum density. 



From these definitions the two units may be converted according 

 to the following equations : 



1 B.T.U.= .252 calorie. 

 1 calorie = 3.968 B.T.U. 

 1 calorie per kilogram =1.8 B.T.U per pound. 



Metric conversion tables. Since much of the literature of cementing 

 materials is published in French and German, metric units are frequently 

 employed. In the present volume such units have been converted 

 into American units throughout, but for convenience a few conversion 

 tables are here inserted to cover the more common cases. 



