132 NATURE TEACHING. 



and to this add the various substances whose 

 effects we wish to try. 



To the soil in A. add nothing. This is the 

 control or standard. 



To B. add about 8lbs. of well rotted pen 

 manure, or stable manure. Carefully fork the 

 manure into the sand, or remove the soil and 

 mix the manure with it in a dry place, and 

 then return to the box. 



To C. add 2oz. of finely powdered chalk 

 or marl, scattering it evenly over the surface 

 and stir in lightly with a fork. Then add ^oz. 

 of sulphate of ammonia. 



To D. add about 2oz. of finely powdered 

 chalk or marl, mix well, and then apply Joz. 

 basic slag, Joz. sulphate of potash and Joz. 

 sulphate of ammonia.* Scatter these substan- 

 ces evenly over the surface, stirring each in 

 before the next is added. Dig in the basic 

 slag somewhat deeply. 



Finally, spread an ounce of moist garden 

 soil over each, in order to ensure the presence 

 of the nitrifying organisms which would prob- 

 ably be absent from the washed sand. 



* In accordance with what has been said before it is advisable 

 to add the sulphate of ammonia at least a fortnight after the lime 

 or batic slag has been applied, to prevent the loss of the ammonia, 



