13. Natural cement, as its name implies, is made from rock as it occurs in nature. Argillaceous limestones or argillo-magnesian limestones, having the proper proportion of clay, magnesia and lime, may be used for the production of natural cement. The burning is not carried so far as in the manufacture of Portland cement, and the resulting product is of lighter weight and usually quicker setting, though some natural cements are quite slow setting. The properties of these cements, coming from different localities, vary greatly. In fact, it is difficult to distinguish some natural cements from Portland, and they may be considered to grade into the natural Portlands. Light burning in manufacture, light weight per cubic foot, and slower rate of acquiring strength, may be considered the distinguishing characteristics from a physical point of view.

1 For an excellent resume of the qualities and distinguishing character-sties of slag cements, the reader is referred to "Report of Board of Engineers on Steel Portland Cement as used in United States Lock at Plaque-mine, La." Washington, 1900.

Analyses Of Natural Cements

Brand.

Locality.

Silica.

Alumina.

Iron Oxide.

Lime.

Magnesia.

Potash and Soda.

Carbonic Acid, water, and Loss.

Bonneville Improved .

A

30

40

10.36

2

60

52

12

0

21

3.07

Round Top.....

B

28

02

10.20

8

80

44

48

1

00

0

50

7.00

Cumberland.....

C

28

30

10.12

4

42

49

60

3

76

Double Star.....

D

23

32

6.99

5

97

53

96

7

76

2.00

Black Diamond . . .

E

22

54

8.24

2

14

42

31

5

39

2

82

. . .

Fern Leaf .....

F

26

40

6.28

1

00

45

22

9

00

4

24

7.86

Hulme...... .

G

25

28

7.85

1

43

44

65

9

50

4

25

7.04

Star........

H

23

29

5.96

2

16

41

28

15

39

1

98

Norton.......

I

27

98

7.28

1

70

37

59

15

00

7

96

2.49

Rosendale.....

J

26

54

5.

89

45

30

17

06

Brooklyn Bridge . . .

K

30

84

7.75

2

11

34

49

17

77

4

00

3.04

Hoffman......

L

27

30

7.14

1

80

35

98

18

00

6

80

2.98

Lawrence......

M

22

77

10.

43

34

54

21

85

63

4.43

Newark & Rosendale .

N

28

71

5.88

3

60

27

00

30

00

3.52

Clarks Utica ....

0

34

66

5.10

1

00

30

24

18

00

6

16

4.84

Milwaukee.....

P

23

16

6.33

1

71

36

08

20

38

5

27

7.07

Mankato......

Q

27

70

7.06

1

86

37

00

22

63

2.46

James River . . . .

R

49

53

11.

29

25

15

13

77

0.26

Howard.......

S

22

58

7.23

3

35

48

18

15

00

3.66

Union Akron ....

T

17

14

7.61

2

00

36

83

25

09

3

64

Akron Star.....

U

20

40

6.22

2

56

40

64

25

80

1.47

Buffalo.......

V

16

48

4.40

2

00

39

20

26

52

1

85

6.80

The localities indicated by letters are as follows:

A, Siegfried, Pa. ; B, Hancock, Md.; C, Cumberland, Md.; D, Fort Scott, Kan.; E, F, and G, Louisville, Ky.; H, Speeds, Ind.; I, K, L, M, and N, Ulster Co., N. Y.; J, Howes Cove, N. Y.; O, Utica, 111.; P, Milwaukee, Wis.; Q, Mankato, Minn.; R, Locker, Virginia; S, Cement, Ga.; T and U, Akron, N. Y.; V, Buffalo, N. Y.

Comparing these analyses with those given for Portland cement in Table 2, it is seen that natural cements have a higher percentage of silica, about the same amount of alumina, and a much smaller content of lime, than have Portlands. Many natural cements have a large percentage of magnesia, but the magnesia and lime together of natural cements usually do not equal the percentage of lime in Portlands. In other words, the hydraulic index is usually higher than in Portland cements.

14. Analyses

Table 3 gives the results of a number of analyses of natural cement, compiled from various sources.

Table 3.