I.] ANALYTICAL METHODS 57 



s removed. The filter and its contents are dried and 

 veighed ; the loss the soil has suffered represents the 

 naterial dissolved and the hygroscopic moisture. 



2. The soil is now washed off the filter with 

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

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

 00 meshes to the linear inch, the portion passing through 

 )eing collected in a beaker which is marked on the side 

 it 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. 53. 



The portion which remains on the sieve is dried and 



veighed. It is then divided into "fine gravel" and 



coarse sand " by means of a sieve with round holes of 



: mm. in diameter, the portion retained by the sieve 



>eing designated " fine gravel." 



3. The portion in the beaker is well worked up with 

 he rubber pestle, ammoniacal water is added up to the 

 5-5 cm. mark, and the whole is put aside to stand for 

 wenty-four hours. The turbid, supernatant liquid is 

 hen rapidly poured off into a large jar, and the residue 

 s rubbed up again with the rubber pestle and more 

 immoniacal water, as before. The whole operation of 

 illing to the mark, standing for twenty-four hours, and 

 souring off the turbid liquid is carried through as 

 before, and repeated as long as any matter remains 

 n suspension for twenty-four hours. Generally seven 

 :o ten decantations will be sufficient, after which the 

 jnited turbid liquid is evaporated to dryness in a tared 

 aasin, and weighed. This fraction consists of the " clay " 

 ^articles less than 0-002 mm. in diameter, together with 

 ill the soluble and some of the insoluble humus. The 

 :ontents of the dish are ignited over an Argand burner 



