CHEMICAL WORK OF THE ATMOSPHERE 37 



The red color of desert sands has frequently hecn remarked 

 upon. It is due to a coating- of iron oxide over the rounded quartz 

 grains. Phillips (76) has determined the total amount of iron 

 oxide of the coating of the sands in the Nefud desert of Arabia to 

 be 0.21 per cent., while the sand itself, after the solution of the 

 coating, still contained 0.28 per cent. of,iron oxide, 0.88 per cent, of 

 clay and 98.53 per cent, of silica. Walther holds that the iron of 

 the crust was also originally in the sand and has found its way to 

 the surface of the grain under the intense heating of these grains 

 from exposure to the sun. Similar conditions are rather wide- 

 spread within the arid belt of the earth, and such coating of quartz 

 sand grains may be considered as typical of desert sands, whether 

 of recent origin or preserved in older formations. 



Oxidation of Organic Compounds. (Ya-n Hise-ioo:^(5/.) In 

 the presence of water and bacteria, cellulose and other organic sub- 

 stances are oxidized with the production of a number of organic 

 acids, such as humic, ulmic, crenic, etc. (See Chapter IV.) Fur- 

 ther oxidation of these acids results in the production of carbon 

 dioxide and water. The artificial oxidation of carbon in the form of 

 coal and other combustibles has become a factor of great impor- 

 tance. It is estimated that at the present time 1,000,000,000 metric 

 tons of coal are oxidized each year, and this, with an average of 

 80 per cent, of carbon, would produce a total of 2,933,333,000 

 metric tons of COo to be passed into the atmosphere each year. 

 This is 0.1233 per cent, of the total amount of CO, at present in 

 the atmosphere. Continuing this rate of consumption of coal for 

 812 years, the amount of CO2 in the atmosphere would be doubled. 

 (Van Hise-ioo r^d^.) The oxidation of nitrogen to ammonium 

 nitrites and nitrates takes place in the presence of water and with 

 the aid of bacteria. It is most marked in the tropics, where the 

 nitrates of the soil sometimes amount to 30 per cent, of the 

 mass. 



Hydration. The chemical union of water with minerals is 

 hydration, and the results are hydroxides. So far as hydration of 

 minerals by atmospheric moisture is concerned, the process is a 

 superficial one, but within the belt of weathering of the lithosphere 

 it is a very extensive process due to the percolation of the ground 

 water. It will be further considered under that heading. A com- 

 paratively low temperature favors hydration of minerals, a temper- 

 ature above 110° C. at ordinary conditions of pressure will stay the 

 process or even reverse it, dehydration being the result. 



Kaolinization. The ordinary effect of the atmospheric mois- 

 ture on the rocks is the attack upon the feldspars producing kaolin 



