PHYSICAL AND CHEMICAL PROPERTIES. PARTS IV, V. 153 
The soundness of the cements is a fundamental consideration, 
and the fact that our work showed that any tendency toward 
unsoundness developed more slowly in cold than in hot water, 
and still more slowly in air, verified the previous statements 
concerning the properties and influences of free lime. 
Cements so bad as utterly to disintegrate when subjected to 
the boiling test have remained in the air for over a month 
without showing a measurable increase in volume. However, 
any tendency toward unsoundness is eventually very apt to 
become more pronounced in the air because the slaking lime 
increases its volume more in air than in water. 
Our experiments show that the worst results are obtained 
if the hardened mortar is weathered outside and exposed to 
the sun and rain. Plate VII, fig. 1, is from a photograph of 
a cement which remained sound in water and air and almost 
passed the boiling test, but which disintegrated when exposed 
to the sun and rain. As several other cements remained sound 
after similar treatment, the destruction produced by weathering 
the mortar can not be attributed solely to the heat of the sun. 
Generally speaking, Portland cements shrink in the air and 
expand in water, and it is thought that the constantly humid 
and dry conditions of the weathered material tend to produce 
a maximum disrupting effect. Plate VII, fig. 2, shows the 
beneficial results obtained by regrinding the same cement. 
The soundness is improved by the presence of sand and other 
suitable aggregates. The development of changes in volume is 
also largely dependent upon the permeability of the mortar; 
that is, the greater the porosity, the greater the possibility of 
rapid and uniformly distributed changes in volume. 
Portland cements may he classified with respect to their 
soundness as follows: 
(1) Cements which fail to pass all of the standard tests for soundness. 
(2) Cements which fail to pass the accelerated tests, but which remain 
sound in normal air and water for twenty-eight days. 
(3) Cements which pass all tests for soundness. 
No consideration is given to Portland cements which warp, 
erack, or disintegrate so quickly in cold water or in air as 
to place them in class 1. However, it is usually possible greatly 
to improve the quality of such cements by properly seasoning 
them, the first effect of which tends to place them in class 2. 
Some class 2 cements disintegrate sooner or later after the 
specified twenty-eight days have expired, while others remain 
sound and strong for an indefinite number of years; therefore, 
the significance of the hot test is very uncertain. This and 
