84 
many local purposes where great tensile strength 
may not be required ; but it is of course Far below 
the strength of English -made cement; thus the 
average tensile strength of the cement manufac- 
tured at the Folkestone Works during 1881 was 
497 lbs. per square inch of sectional area, 
The following analyses from the Engiflieer, 
1882, as quoted by Professor \V. N. Hartley in 
article "Cements in Thorpe's Dictionary of 
Applied Chemistry, include an analysis of the clay 
used for cement making, also of the mixture of 
clay and chalk, which, -when mixed in the wet 
way, is called " slurry." The third column &ives 
the analyses of the mixture after being dried and 
burnt, and the fourth column the analysis of the 
cement after it has been treated with water, and 
has had seven days to harden • — 
"Cement manufacture, Cliff, Kent, Me -i 
Francis & Co. — Table showing the percentage 
composition of the materials and products, and 
the changes due to burning, grinding, and mixing 
with water." 
Sand... 
Silica 
Ferric oxide 
Alumina 
Magnesia 
Magnesium carbo- 
nate 
Lime 
Calcium sulphate 
,, carbonate 
Water and carbo- 
nic acid 
Water and organic 
matter 
Clay. 
0-87 
5414 
7-76 
14-68 
4'48 
2-01 
15 03 
98-97 
Slurry, 
1-24 
11-77 
2 is 
4-45 
2-87 
69-97 
5-29 
97-75 
Cement 
0- 98 
20-45 
4-37 
8-05 
1- 48 
1-48 
6213 
213 
101-07 
116 
18-77 
3-08 
7-04 
1-52 
1-52 
54-89 
1-73 
9 45 
98-96 
The following are some other examples of 
analyses of Portland cement, also from the 
Engineer of 1882:— 
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The same authority inform.- us that cement 
is in a proper state of division when not lews than 
80 per cent, passes through a sieve of 2,900 holes 
per square inch. 
Some impure lime.-tones, when calcined, form 
limes which harden under water, in period* »arviu" 
from 20 days in the case of feebly hydraulic 
limes, to as little as 1 day in limes that are 
highly hydraulic. The following is E. 0, Laurie '■ 
table of hydraulic limes :— 
Proportion of day 
to 100 ]>art> of 
calcium carbonate 
in the limestone 
5'3 to 8-2 
B-2 to 14-8 
14 -8 t o 191 
191 to 21-8 
2P8 to 26-7 
Lii 
feebly hydraulic contains 
„ fairly „ „ 
,, hydraulic ,, 
,, highly hydraulic ,, 
Limit of hydraulic lime ,, 
A strong hydraulic lime is made from A bertha.* 
limestone, which has the following OPTO position : 
per cent. 
Calcium carbonate ... ... 86 2 
Clay ... ... ... ... 11-2 
Water alkalies, iVc. ... ... 2-6 
1000 
This lime, when mixed with pozzuolani alone, 
or with sand in addition, forms hydraulic mortals. 
The following example of hydraulic mortars, as 
also the above analyses of limestone, are from 
Thorpe's Dictionary of Applied Chemistry: — 
Composition of Hydraulic Mortars. 
Aberthaw lime 
Slaked powder Pozzuolani. Sand. 
Description of Mortar : — 
(1) 
Eddystone 
o 
2 
(2) 
Stone Mortar 
2 
1 
1 
(3) 
do '2nd quality 
2 
1 
2 
f4) 
Face Mortar 
2 
1 
3 
(5) 
do 2nd quality 
2 
1 
9 
6) 
Backing Mortar 
2 
1 
3 
Concrete. 
When cement is mixed with sand, gravel, or 
broken stone, in such proportion that, in presence 
of water, the mixture solidifies to a hard arti- 
ficial stone such a mixture constitutes what is 
known as concrete, so much used for marine 
buildings, water-works and other purposes. 
Proportions of Stones, Sand, and Cement in 
various Concretes. 
The following are the proportions by volume of 
the materials used for the concrete of the Colombo 
Breakwater, viz., six of stone, two of sand, one 
of cement. 
For the LabUgama and Maligakanda reservoirs, 
the concrete was made by mixing stones and sand 
in equal proportions, and then adding one part 
of cement to six parts of mixed stone and sand. 
The concrete for the floor of the Maligakanda 
reservoir was composed of four parts of sand 
and one of cement. 
For foundations for tea machinery in Ceylon tea 
factories concrete is often employed. The follow- 
ing is an example of the proportions, viz., four of 
stones, two and a half of sand, one of cement. 
These, along with some other concretes men- 
tioned in the article on Cement by Professor 
W. N. Hartley already referred to, are put into 
tabular form for the sake of ready comparison :— * 
