668
THE POPULAR SCIENCE MONTHLY.
to illustrate the superiority of Milwaukee cement, shows that the strength of the Milwaukee was three hundred and eighty-two pounds per square inch at thirty days, and only three hundred and fifty pounds per square inch at sixty days. This hardly proves either the superiority of Milwaukee, or that natural
Fig. 2.—Diagram showing the Relative Tensile Strength of English and American Portland and Two Brands of American Natural,
cement increases in strength with age; and, as it is the average of seventy-five specimens, would rather seem to disapprove the points mentioned. It is true that briquettes made of the same cement, at the same time, kept under the same conditions, and broken at the same time, show a great variation in tensile
