THE NONMETALLIC MINERALS. 



267 



Constituents. 



(Calcium carbonate about. 



Silica do... 



Magnesium carbonate do 



Iron oxide do — 



Alumina do. . . 



Potash and soda do. . . 



Lime do. . . 



Magnesia do. . . 



Carbonic acid do. . . 



Upper chalk. 



97. 90 to 98. 60 



.(•,(. 1.59 



.10 .21 



.35 .74 



Gray chalk. 



87. 35 to 96. 52 



1 . (i7 

 .10 

 .38 



1.14 

 .42 



fi. 84 

 ..50 

 .46 

 .93 



4. 29 



Clay. 



It is stated that the presence of more than very small quantities of 

 sand, iron oxides, or vegetable matter in the clay is detrimental. A 

 good cement mud before burning may contain from 68 to T8 per cent 

 of calcium carbonate, 21 to 15 per cent of silica, and from 10 to 7 per 

 cent of alumina. 



The following analyses from the same source as the above serve to 

 show (I) the composition of the clay; (II) the mixed clay and chalk or 

 "slurry,''' as it is called, and (III) the cement powder prepared from 

 the same: 



Constituents. 



Lime 



Calcium .sulphate 



Calcium carbonate 



Silica (soluble) 



Alumina 



Magnesium carbonate 



Magnesia 



Iron oxide 



Sand 



Water 



I. 

 Clay. 



2.01 

 54.14 

 14.68 



4.48 



7.76 



.87 



15.03 



II. 

 Slurry. 



69.97 

 11.77 

 4.45 



2.87 



2.13 

 1.24 

 7.59 



III. 

 Cement. 



62.13 

 2.13 



20. 45 

 8.05 



1.48 

 4.37 



Several brands of Portland cement are manufactured in America, 

 usually from a mixture of materials, the proportions of which have 

 been worked out by experiment. At the Coplay Cement Works, in 

 Lehigh County, Pennsylvania, a blue-gray crystalline limestone and 

 dark gray more siliceous variety are ground and mixed into the desired 

 proportions, molded into a brick, and burnt to the condition of a 

 slag. The material is then ground to a powder and forms the cement. 

 Through the courtesy of the manager, the Museum collections contain 

 samples of the crude and manufactured materials, as follows: Lime- 

 stone (Specimen No. 535-41, U.S.N.M.); cement rock (No. 53542, 

 U.S.N.M.). Composition formed by admixing the two rocks (No. 

 53513, U.S.N.M.); and the clinker (No. 53514, U.S.N.M.) obtained by 



