2 



CEMENTS, LIMES, AND PLASTERS. 



TABLE 2. 

 VALUE OF CEMENTING MATERIALS PRODUCED IN THE UNITED STATES, 1900-1903. 



It will be seen that the value of the entire group has more than 

 doubled in these four years. Examination of the figures for each sub- 

 group will show that this increase was by no means equally distributed. 

 The production of Portland cement almost tripled in value from 1900 

 to 1903; the values of the plaster and slag-cement production about 

 doubled; while lime increased only 50 per cent, and magnesia and the 

 natural cements were practically stationary. 



The great advance in value of the cementing materials, taken as a 

 group, has been steady and natural. Similar increases can therefore be 

 reasonably expected to occur in future years. Individual years, however, 

 may give less encouraging results; because any general business depres- 

 sion reacts sharply upon building industries first of all. 



Classification and Relationships of Cementing Materials. 



It seems desirable, before taking up the various classes of cement 

 materials individually, to devote an introductory section to the con- 

 sideration of the entire group of cementing materials, and to attempt 

 to indicate briefly the relationships that exist between the different 

 classes which compose this group. 



These relationships, as regards both resemblances and differences, 

 seem to be best brought out by the scheme of classification presented 

 below. This classification was fii'st published by the writer in 1902,* 

 in a form differing but slightly from that here given. It is based 

 primarily upon the amount of chemical change caused by the processes 

 of manufacture and use ; and secondarily upon the chemical composi- 

 tion of the cementing material after setting. As regard is paid to both 

 technologic and commercial considerations, it would seem to furnish a 

 fairly satisfactory working classification. 



* Eckel. E. C. The classification of the crystalline cements. American Geol- 

 ogist, vol. 29, pp. 146-154. March, 1902. 



