Clay is composed of silica (SiO 2 ) which is finely 

 powdered quartz sand, together with alumina, and iron 

 oxide. In a clay which is best suited for cement the 

 amount of silica should be about three times the 

 quantity of the alumina and ferric oxide combined. 



We have the following approximate proportions of 

 ingredients in every 100 parts of Portland cement: 

 Limestone Lime (CaCO 3 ) ... .60 to 65 parts 



f Silica (Sid) 21 to 24 parts 



Clay 29 to 36 parts { Alumina (Ai 2 O. : ) 6 to 8 parts 



[ Iron Oxide (Te 2 Q,) 2 to 4 parts 



These ^are the principal components. There are also 

 present in proportions stated: 



Magnesia from l / 2 of one part to 2 parts. 



Sulphuric acid from y 2 of one part to i l / 2 parts. 



Carbonic acid and water i part to 3 parts. 



These last three are unimportant except when they 

 are too evident by their presence, and are generally 

 considered as impurities. 



These materials thoroughly mixed, are then burned 

 in a kiln, using either powdered coal, oil or gas flames 

 under pressure. After the fused clinker or burned 

 product is cooled, it is ground very fine, stored in 

 bins for a required time, and is then ready to ship. 



SAND. 



In all our ideas of the use of cement, sand enters as 

 an essential constituent, and an elementary understand- 

 ing of its qualities, good and bad, is necessary. We 

 can apply the term "sand" to any finely divided ma- 

 terial, which will not disintegrate or decay, and which 

 can be used with cement to make this filler. The com- 

 mon term in specifications is that "sand must be clean, 

 sharp and coarse." A rough field test for percentage 

 of loam is to rub the damp sand between your palms, 

 and then see hew much loajn you can scrape off. Put 

 a handful on a piece of glass or a piece of clean writ- 



