EXPERIMENTS AND PRACTICAL WORK 61 



Expt. 97. Action of Water containing Carbon Di- 

 oxide. Observe that if pure water is poured on lime- 

 stone no change takes place, but that if muriatic acid, 

 vinegar, or limejuice is poured on it it is gradually 

 dissolved. In a similar manner water, after it has 

 travelled through the soil, takes up carbon dioxide, and 

 is then able to dissolve carbonates slowly. 



Expt. 98. Animals play an Important Part in mak- 

 ing' and improving' Soils. 



(a) Observe that remains of animals gradually decom- 

 pose and form part of the humus in the soil. 



(b) Excreta of Animals. Put some cow or other 

 manure on a worn-out plot of land, and observe what 

 beneficial effect it has on the soil. 



(c) Value of Bones. Break up some old bones into as 

 small pieces as possible, and use as manure. 



(d) Work of Earthworms. Collect some earthworm 

 casts, crush, and observe the good texture of the 

 material continually being brought to the surface of 

 the soil. 



Expt. 99. How Vegetation forms and enriches 

 Soil 



(a) Humus. Observe that in undisturbed positions 

 a rich vegetable mould is found under trees from the 

 decay of leaves and branches that have fallen from 

 above. 



(b) Roots occasionally split Bocks. Record any instance 

 that you have seen of the roots of a plant splitting open 

 a rock. 



Expt. 100. How Air aids in the Formation of Soil. 

 Examine the surface of rocks exposed to the action of 

 the air, and observe by scratching that the surface is 

 softer than the inside. 



