STATE GEOLOGIST. 363 
MeeuiMoOgaic was ZO Uuken per sqiane) cin tor the cements stored” in 
air and 45.3 kg. per square cm. for the cements exposed to pure carbon 
dioxide. The effect of moist air on cement is not as injurious as is 
often supposed. Sewage was found to have practically no effect upon. 
standard cement mortar. Tar and mineral oils do not act upon cement; 
organic oils and the tannic acids form soaps with the lime of the cement 
which tend to soften the latter. This action, however, owing to surface 
incrustation, is of little importance in practical work. Of the materials 
added to cement for coloring purposes, like pyrolusite for black, iron 
or ochre for red and yellow, ultramarines for blue and green, only the 
latter do not decrease the ultimate strength. Ultramarine, in fact, has 
a strong tendency to increase the strength due to pozzuolanic action. 
Owing to the basic character of cements and the content of sulphates and 
alkalies, a number of minor reactions take place with the coloring con- 
stituents. Thus iron ore is in part attacked by the lime and bleached, 
as may be observed on the hollow blocks now used to so large an extent, 
the pyrolusite likewise is attacked and made, in part, soluble, while the 
ultramarine is decomposed in a comparatively short time, since its sulphur 
is removed by the lime of the cement. As the sulphides seem necessary 
for the color,on decomposition of the compound,2( Na,Al,Si,O,,) +Na.Sy,, 
the color must, of course, disappear. The addition of ground white 
marble does not help much in retaining these colors, but the grinding 
together of cement and white quartz, or white anhydrous silicates, would 
result in far greater permanency. Likewise the colors could be made 
permanent in themselves by being prepared as silicates. It seems to the 
writer that the Portland cement manufacturers should cater to this 
demand for prepared cement as well as to the production of white cements. 
The addition of such silicious matter would also tend to increase the 
durability of cement work in a most decided manner and would help 
remove the prejudice, justified in many cases, against architectural cement 
surfaces. 
In the table on page 364, the effects of a number of salts upon the 
streneth of Portland cement are shown: 
It is true that many cements are apparently improved by the addition 
of gypsum in small amounts, but it has also been found that high grade 
cements show practically no improvement. Dr. Erdmenger’s work proves 
quite strikingly that the gypsum is a source of weakness which should 
be kept within the lowest possible limit. 
THE ENDURING QUALITIES OF PORTLAND CEMENT. 
As has already been indicated, Portland cement, like all basic hydrous 
rocks, is subject to rather rapid destruction by atmospheric agencies 
if exposed without the addition of sand. It has also been found that 
