CHEMISTEY OF SOILS 129 



is ultimately resolved into kaolin, potassium carbonate and 

 silica, as shown in the following equation 



2KAlSi 3 8 +C0 2 -f 2H 2 = Si 2 5 Al 2 (OH)4+K 2 C03+4Si0 2 



Orthoclase. Kaolin. 



The silica is liberated in a highly hydrated, and possibly 

 at first in a soluble, condition, but the water with which 

 it is united is not shown in the equation because there is 

 no means of knowing how much is present under different 

 conditions. 



The relation between orthoclase and kaolin is not, per- 

 haps, so readily apparent from the formulae but may be 

 indicated thus 



f SiO.O A10.Si0 2 ( SiO.O A10.0H 2 



1 SiO.OK l SiO.O A10.0H 2 



Orthoclase. Kaolin. 



It will be seen that a silicate of the same type as kaolin 

 would be produced by elimination of the Si0 2 group and 

 hydration of the alumina ; the further replacement of the 

 potash by alumina from another molecule and the break up 

 of the latter would complete the change. This may be 

 illustrated as follows : 



| SiO.OAl 0.(SiO~ 2 



I SiO 



(SiO 



( SiO 



Of the intermediate stages of the reaction it is impos- 

 sible to speak with any certainty. Only a very small 

 proportion of the potash is ever found to be soluble in 

 water, but the fact is probably accounted for by the 

 phenomena of absorption (p. 103). All the potash that 

 is soluble in dilute acids has probably been reduced 



