88 THE EEACTIONS OCCURRING IN SOILS. IV. 



As represented in the ordinary text-book manner the re- 

 actions are : 



In the case of the manure heap 



CaS0 4 +(NH 4 ) 9 C0 8 = CaC0 8 +(NH 4 ) a S0 4 

 and in the case of ammonium sulphate applied to soil 

 CaCO+ (NH 4 ). 2 S0 4 = CaSO 4 + (NH 4 ) a CO. 



Now, in the light of what has been said, it is obvious that 

 neither of the equations really represents what happens in 

 either case, 



In the first place the carbonates involved in the reactions 

 are probably not normal carbonates but acid carbonates, since 

 excess of carbon dioxide is present both in the manure heap 

 and in the soil. 



The reaction might be represented 



CaS0 4 + 2NH 4 HC0 8 Ca (HCO 8 ) a + (NH 4 ) a S0 4 

 equilibrium being attained when the ratio of the ammonium 

 sulphate to the ammonium carbonate attains a certain value if 

 the solutions are so concentrated that separation of CaSO 4 and 

 Ca(HCO s ). 2 in the solid state can occur (as perhaps may happen 

 in a- manure heap); but the conditions of equilibrium will, in 

 dilute solution, be also affected by the quantities of calcium 

 sulphate and calcium bicarbonate present in a dissolved state, 

 for it must be remembered that their influence only becomes 

 constant when they are present in such quantities that they 

 separate partially in the solid state. 



It is only fair to say, however, that the tendency for the soil 

 to absorb and retain ammonium carbonate will also play an 

 important part in the case of the action in the soil, that com- 

 pound being withdrawn from the sphere of action as fast as it 

 is formed, thus diminishing the speed of the reaction repre- 

 sented by the equation read from left to right. 



