II.] ANALYTICAL METHODS 51 



Method of Analysis. 



1. Ten grams of the air-dry fine earth are weighed 

 out into a beaker or basin and treated with 100 c.c. of 

 Nj$ hydrochloric acid ; the soil is well worked up with a 

 rubber pestle (made by fixing a glass rod into a small 

 solid rubber bung) until all the lumps of clay, etc., are 

 broken up. If the soil contains much calcium carbonate, 

 a further addition of acid may be required. 



The object of the acid is to dissolve the carbonates and 

 humates, and thus loosen the particles in any aggre- 

 gates where chalk or humus form the cement. With- 

 out this preliminary treatment the amount of clay 

 found will be largely determined by the proportion 

 of humus present ; the soil of an arable field, for 

 example, will show more clay than the soil of an 

 adjoining pasture, when the sedimentation is made with 

 water alone. But after the preliminary treatment with 

 acid to remove the humus, both fields will show the 

 same proportion of ciay (as they should do, since they 

 are of the same origin), and only differ in the amount 

 of humus they have accumulated — a temporary factor. 



After standing with the acid for an hour, the whole 

 is thrown on a tared filter and well washed until all acid 

 is removed. The filter and its contents are dried and 

 weighed ; the loss the soil has suffered represents the 

 material dissolved and the hygroscopic moisture. 



2. The soil is now washed off the filter with 

 ammoniacal water (about 1 c.c. of strong ammonia 

 solution in half a litre of water) on to a small sieve of 

 100 meshes to the linear inch, the portion passing through 

 being collected in a beaker which is marked on the side 

 at a distance of 8-5 cm. from the bottom. 



The ammonia completes the dissolution of the humates, 

 and also masks the effect of any traces of soluble salts 

 which may be left and would cause aggregation in the 

 manner indicated earlier, p. 38. 



