RAW MATERIAL: NATURAL-CEMENT ROCK. 



217 



replacing, advantageously, a good hydraulic lime. Manufacturers, 

 however, will not guarantee it, as it is made of refuse stone not suit- 

 able for the manufacture of Portland cement. It has a natural light- 

 yellow color. Cinders are very often added, changing it to a grayish 

 color resembling Portland cement, and also increasing its resistance in 

 a slight degree. This is the product which is purchased by unscrupu- 

 lous exporters and sold by them marked as Portland cement. This 

 fact is significant and should attract the attention of builders, to avoid 

 disasters such as the unexpected collapse of buildings, where first-class 

 cement has been supposed to have been employed ". 



Fig. 34 shows the results of a series of tests of American Portlands, 

 American natural cements, and Belgian "natural Portlands". These 

 results may be accepted as quite representative of the various types of 

 cements tested, and show clearly that the so-called "natural Portlands" 

 have little in common with true or artificial Portlands. 



Natural-cement materials of England. The materials used by 

 Parker, the first manufacturer of English natural cements, were septaria 

 i.e., nodules of clayey lime carbonate. These occur in certain forma- 

 tions in the south of England, and are still used in the English natural- 

 cement industry. The supply is obtained along the coasts, where the 

 nodules have been washed out of the beds which contain them. 



TABLE 102 

 ANALYSES OF NATURAL-CEMENT ROCKS, ENGLAND. 



1. Sheppey septaria. Redgrave, "Calcareous Cements", p. 49. 



2. Sheppey septaria. Berthier, analyst. Burnell, "Limes, Cements, Mortars, etc.", p. 80. 



3. Sheppey septaria. Knauss, analyst. Zwick, "Hydraulischer Kalk und Portland-Cemente", 



p. 69. 



4. Harwich septaria. Redgrave, "Calcareous Cements", p. 49. 



5. Harwich septaria. Knauss, analyst. Zwick, "Hydraulischer Kalk und Portland-Cemente", 



p. 69 



