148 
IOWA ACADEMY OP SCIENCE 
chemical activity is neither violent nor rapid. Being continually re- 
plenished from the storehouses of the atmosphere, their work goes on 
unceasngly over a large porton of our globe. The calcium which thej^ 
extract from rocks is carried by rivers to the sea and is finally depos- 
ited in the form of limestones. "" Alkaline waters, espec- 
ially thermal waters of the sodium carbonate class, are also active sol- 
vents of mineral substances. Their tendency, however, is opposite to that 
of the* acid Avaters, for they dissolve silica rather than bases and act 
as precipitants for magnesia and lime.” 
The Portland cement, being calcium silicate and calcium aluminate^ 
is acted upon readily by the carbonate or other acid waters to dissolve 
out the calcium, and is also acted upon by the alkaline Avaters, aa^McIi 
replace the calcium and combine AAuth the silica. In either case the in- 
tegrity of the original silicate has been destroyed and it is no longer a 
bonding material to hold sand and gravel combined in an artificial 
stone. 
Van Ilise’ Treatise on Metamorphism, U. S. Geological Survey, gives 
the factors affecting the alteration of rocks. ‘‘Porosity is favorable to 
rapid change ; to contain minerals Avhich are soluble is favorable ; to 
contain water or gas is favorable for rapid alteration.” The concrete 
tile and seAA^er pipe noAV manufactured are invariably highly porous. 
Their mineral content is readily acted upon and dissolved by the free 
access of solvent acids or alkaline Avaters to all parts of the porous ma- 
terial. The content of Avater is large, as the bonding material has de- 
rived all its bonding power by a rehydration of the ground cement 
clinker. Van Hise says: “The greatest destruction of materials occur 
in the belt of Aveathering. This belt extends from the surface to the 
level of ground- Avater, the greatest destruction occurring at ground-Avater 
level.” Drain tile is ahvays at groundwater level, for they themselves 
determine this level. Van Hise assigns the greatest relative importance 
to C 0^, as it is everyAAdiere at work upon the surface of the earth and 
is ahvays active and is immeasurably the most important in the belt of 
Aveathering. And again: “The one liquid through which the greater 
part of all alteration of rocks occurs is Avater solutions.” Kahlenberg 
and Lincoln, Journal of Physical Chemistry, Vol. 2, p. 1898, holds that 
“When dilute solutions of silicates are made in groundwaters, the silrca 
exists in the form of colloidal silicic acid.” Ostwald divides the bases 
into the strong, moderate and Aveak. In the belt of Aveathering the alka- 
lis, sodium and potassium, are dissolved first, next comes calcium, the 
magnesia, iron and aluminum dissolving last. Van Hise summarizes 
the importance of these studies in a paragraph : 
