What is the soil made of? 7 



soil sediment is really a little more gritty than the clay. 

 Although it contains the clay it also contains something 

 else. 



When the experiment is made very carefully in a 

 proper way this material can be separated from the 

 pure clay. It is .called silt, but really there are a 

 number of silts, some almost like clay and some almost 

 like sand ; they shade one into the other. 



If there is enough grit it should be weighed : we 

 obtained 14 decigrams of grit from 10 grams of our top 

 soil and 17 decigrams from 10 grams of bottom soil. 

 We cannot separate the clay from the silt, but when 

 this is done in careful experiments it is found that the 

 subsoil contains more clay than the top soil. We should 

 of course expect this because we have found that the 

 subsoil is more sticky than the top soil. These results 

 are put into the columns as before so that we can now 

 see at once how much of our soil is water, how much 

 can burn away, how much is grit, and how much is clay 

 and other things. 



What would have happened if the sample had been 

 dug out during wetter or drier weather ? The quantity 

 of water would have been different, but in other respects 

 the soil would have remained the same. It is therefore 

 best to avoid the changes in the amount of water by 

 working always with 10 grams of dried soil. The results 

 we obtained were : — 



Top soil Subsoil 

 Weight of dry soil before burning ... 100 100 decigrams 

 „ „ „ after „ ... 92 97 



The part that burned away weighed ... 8 3 „ 



Weight of grit from 10 grams of dried soil 17 19 „ 



The columns are given in Fig. 3, 



