SMEG Ole Gist: 197 
CHAPTER V. 
ON THE NATURE OF PORTLAND CEMENT. 
Portland cement is an artificial silicate produced by intimately 
blending clayey and calcareous materials, burning them to vitrification, and 
grinding the resultant slag-like mass to a fine powder. ‘This powder, if of 
the proper composition, will hydrate and harden in water to a stone-like 
mass, of practically constant volume, which shows considerable tensile 
and crushing strength and is able to cement together relatively large 
quantities of sand. In composition it varies between the following limits: 
Per cents. 
Ingredients. | i nicest 
Minimum. | Maximum. 
illC acy aner sta ware ward ota se nee et ceune: 19 26 
NUTINI nee Pale ee oe eee eee | + 11 
HeTniGloxi dese een tee se ee 2 5 
HTS eet ARATE a rece rie ure ie fee ne. Sansa 58 67 
IMASTIESI Ate tea eer Semen ee la ae, 0 | 5 
SMMC BOC scoscoveccsosnvans 0 | eo 
INV cea ae ee ee ee | Ones 3.0 
The table on page 195 shows the composition of ten American Port- 
land cements of well established reputations: 
The average American Portland cement calculates to the formula 
T.10CaO, 0.363Si10,, 0.074A1,O,, 0.021Fe,O, al!owing for the presence of 
0.83 per cent. of CaO as sulphate. Calculated to the basis of silica 
equal to unity, we have the general formula: 3.04CaO SiO,, 0.23A1,Os, 
0.058le,O,. For purposes of comparison, especially with reference to 
the study of the clay base of cements, we might calculate still another for- 
mula, making the alumina equivalent equal to unity, obtaining: 14.99CaO, 
4.93510,Al1,O,, 0.284Fe,O,. The reason for making alumina equal to 
