io PHYSICAL CONSTITUTION OF SOIL 



finger. After ten seconds the turbid water is decanted, and 

 the operation repeated till the water runs off clear and the 

 sand remains clean ; this is then dried and weighed. It is 

 called the 'coarse sand.' The turbid water which has been 

 decanted is then acidified with nitric acid and allowed to stand 

 till all calcium carbonate is dissolved * ; the whole is thrown 

 on a filter, and the residue washed with distilled water till 

 all lime is removed. The fine soil is then washed off the 

 filter with distilled water into a two-litre beaker, and 2, cm. 

 of ammonia added to dissolve humic matter. After three or 

 four hours the whole is diluted with distilled water to two 

 litres, well stirred, and allowed to stand twenty-four hours. 

 The matter still in suspension is then removed by a syphon. 

 The sediment is again treated with 3 cc. of ammonia, and again 

 diffused in a litre of pure water, and after twenty-four hours 

 the water is decanted. If the decanted water is distinctly 

 turbid the treatment must be again repeated. The sediment 

 is finally dried and weighed ; it is reckoned as ' fine sand.' 



The clay left in suspension is precipitated by the addition 

 of an acid l , and collected on a filter. The filter when drained 

 is placed on blotting paper, and by skilful manipulation 

 when half dry the clay is pressed into a single cake, which 

 is dried and weighed ; the paper of the filter is burnt, and 

 the ash added to the mass of clay before weighing. 



By treating the stones and the coarse sand with dilute acid, 

 any calcium carbonate they contain can be determined. The 

 calcium carbonate occurring in the finer portion can be 

 determined in the nitric acid solution mentioned above. By 

 proceeding in this way the siliceous and calcareous matter 



1 The action of these reagents will be understood when we have spoken 

 of the coagulation of clay, see p. 30. 



