22 An Account of the Soil [pt. i 



(such as farmyard manure, or green crops ploughed in), 

 frost, and good cultivation also have the same effect. 

 On the other hand alkaHne manures such as liquid 

 manure, and manures like nitrate of soda that leave an 

 alkaline residue in the soil, tend to change the crumbly 

 back into the sticky state, and if much clay is present 

 they have a bad effect on the condition of the soil. 



These changes are readily, demonstrated by experi- 

 ment. Stir up some clay in rain or distilled water, pour 

 off the turbid liquid and divide it into three equal parts. 

 To one add 5 to lOc.c. of lime water; to another the 

 same quantity of dilute ammonia solution ; leave the 

 third alone. Flocculation is seen to take place rapidly 

 under the influence of lime ; the untreated portion settles 

 much more slowly; ammonia almost entirety prevents 

 settling. The effect on drainage can be shown by putting 

 a layer of clay supported on a perforated disk into each 

 of three funnels: sprinkle lime on one; pour 10 c.c. of 

 dilute ammonia solution on to another. Then pour 

 water on to all three so that it stands at the same height 

 in each funnel : leave for a time. Percolation begins first 

 on the limed clay : next on the untreated clay ; but pro- 

 ceeds only slowly if at all on the clay treated with 

 ammonia. 



More careful experiments have shown that chemically 

 ptire lime does not flocculate clay but behaves like 

 ammonia: flocculation only goes on in presence of a 

 little carbon dioxide which, however, is always present 

 in the soil. 



Silts. Between the inert sand particles and the re- 

 active clay particles there come a number of others of 

 intermediate grade differing somcAvhat from either. As 

 they are smaller than sand they pack together with 



