700 



KEW YORK STATE MUSEUM 



Redgrave gives tlie following analyses of English Portland 

 cement mixtures. 



1 Mixture made at Folkestone from gray chalk and gault clay 



2 Forest of Dean limestone and clay 



3 ^Aiixture from Barrow lias quarries 



All dried at 100° C, but 2 and 3 have perhaps also lost some 



1 2 



Sand 2.5 5.57 



Silica 11.83 9.61 



Ferric oxid 1.97 2.42 



Alumina 5.23 3.45 



Iron pyrites tr 



CaCO| 74.18 



MgCO 1.29 



CaSOg 

 K2O. . 

 NagO., 



.18 



.9 



.31 



1.82 



75.89 

 1.5 

 .16 

 .88 

 .39 

 .61 



3 



2.58 

 11.41 



2 . 34 



4.8 

 .43 

 74.00 



2.61 

 .21 

 .93 

 .46 

 .43 



A clay or Medway mud from Gillingham is as follows: 



Sand 



I Hyd. 

 silicates 



SiOs. 38.413 



Al and Fe 1.856 



SiO^ 25.249 



AlsOs 14.244 



F^203 6.744 



CaO 81 



MgO 1.727 



K2O 2.957 



^920 773 



1^2^ _, 3,384 



Pyrite , .214 



The clay used for cement should not contain an excess of sand 

 or iron. Clays low in iron are usually of a gray or blue color 

 and light yellow on weathering. The clay should be fairly sili- 

 cious, and the more amorphous silica present the better. Mi- 

 chaelis^ gives the following typical examples. 



1 Hydraulischer mortel u. Portland-eemente, p. 99. 



