CHEMICAL WOKK. 129 



Carbonic acid is given out in respiration, and is a product of animal and 

 vegetable decay ; and by this means it becomes distributed through the air 

 and waters. The humus acids, among the results of vegetable and animal 

 decay by oxidation, occur in all damp soils in which such decay is going 

 on. The action of these acids has been studied by A. A. Julien.^ They 

 are effective especially through tiieir affinity for iron protoxide, magnesia, 

 lime, soda, potash, and some other protoxide bases. 



a. In water, carbonic acid takes up calcium carbonates from any calcareous material, 

 whether in the state of limestone, or in other conditions, to make calcium bicarbonate 

 for transportation. On evaporation, the bicarbonate again becomes calcium carbonate. 

 The amount taken up is increased by the presence of magnesium or sodium sulphate in the 

 waters (Hunt). The Mammoth Hot Springs contain 0-6254 parts of calcium carbonate 

 in 1000 of water, which is over 4 times as much as pure water saturated with carbonic acid 

 will take up (Russell). 



b. It 'takes the bases — potash, soda, lime — out of a feldspar, thus destroying the 

 miueral to as great a depth in a rock as the carbonated water and air can penetrate, 

 and reduces it to clay. This is true especially of the potash-feldspars, orthoclase, and 

 microcline. The same work is done by the humus acids. The clay results thus : Ortho- 

 clase consists of silica, alumina, and potash. In the change it loses the potash and part of 

 the silica, and becomes silica, alumina, and water. Thus the compound, K2O. AI2O3 . Si60i2 , 

 becomes HoO.Al203.Si20^, and 1 of water. Half of the water (HoO) received replaces 

 the potash (K2O) lost. 



c. Carbonic acid decomposes other minerals in a similar way, taking out the protoxide 

 bases. It may thus form a soluble iron bicarbonate in waters, which streamlets may 

 convey to marshes. But only a trace of this iron salt can be held in waters under the 

 existing atmospheric pressure. The humus acids also make, with iron, soluble salts, and 

 do, at present, the chief part of such transportation for the making of bog ores. On the 

 evaporation of the solvent waters, the iron in each case is usually deposited as hydrous 

 sesquioxide or limonite. 



d. Further : it is supposed that carbonic and humus acids may aid in the oxidation 

 of the protoxide-iron of a mineral by bringing it to the surface of a mass of porous rocks, 

 so as to make the oxidation possible. 



2. Destructive effects. — For the reasons stated carbonated water con- 

 taining humus acids has done a vast amount of eroding work. 



(a) Draining out by infiltrating vmters. — The lightest work is the drain- 

 ing of any soluble ingredient out of a rock. Calcareous grains are thus 

 drained from a porous calcareous sandstone, or quartzyte, increasing its 

 porosity. So also calcareous fossils are removed from rocks that admit infil- 

 trating waters, leaving the rock cellular. When a crystalline limestone or 

 marble, a porous rock, consists of dolomite, but contains mixed calcite, all 

 the calcite grains are drained out because they are the most soluble, and 

 the rest are left to fall to loose sand, an effect exemplified in many places 

 over Canaan, Conn., and Berkshire County, Mass. If the fossils of a lime- 

 stone are made of calcite and aragonite (the latter the prismatic calcium 

 carbonate), the aragonite portion is taken away — a fact first reported by 

 Sorby. Shells of the kind referred to are those of the genera Pinna, Mytihis, 



1 On the reaction of the humus acids see A. A. Julien, Rep. Amer. Assoc, 1879. 

 Dana's manual — 9 



