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PRACTICE 14 



Determination of Loss on Ignition. 



The loss that a soil suffers when it is ignited is often taken as a 

 measure of the organic matter, but it can only be a very rough ap- 

 proximation at best for most soils. For some subsurface and nearly 

 all subsoils, it gives little or no idea of the amount of organic matter. 

 By igniting, the organic matter, volatile salts and water of hydration 

 will be driven off. In heavy clay soils and all fine grained ones, this 

 latter forms a very large part of the loss. Subsoils with little or no 

 organic matter may lose as much as surface soils, due to the larger 

 amount of clay and consequently a larger amount of water of hydra- 

 tion which is driven off by the heat. The more organic matter pres- 

 ent in a soil, the nearer the loss on ignition will correspond to the 

 real amount so that for peat soils, ignition may give a close approxi- 

 mation to the amount of organic matter present. 



Weigh out 5 grams of water-free soil or air-dry soil calculated to a 

 water-free basis and ignite in a small crucible to low red heat for 15 

 to 20 minutes. Cool in a desiccator and weigh. Determine loss for 

 silt, loam, clay and peat. 



Of which of the soils loses most? "Why? 



How do coarse and fine grained soils compare in loss? 



