VI.] ANALYSES OF TYPICAL SOILS 149 



acid. The bottle is kept in a warm place or an incubator 

 at 25° for twenty-four hours before distilling off the 

 ammonia. 



The table (Appendix I.) shows the analyses by the 

 method above described of a few typical soils. 



It will be seen, as a rule, that the water retained by 

 the soil when air dry, the loss on ignition, and the 

 nitrogen, rise and fall together, because the humus 

 which contains the nitrogen is the most hygroscopic 

 constituent of soils. Clay soils which tend to conserve 

 humus also contain the most constitutional water ; this 

 further tends to increase the loss on ignition in their case. 



The proportion of nitrogen found ranges from 0-5 

 per cent, in very rich pasture soils down to below 01 

 per cent, on light arable soils, it is rarely up to 02 per 

 cent, in arable soils, and the warmer, the more open, 

 and more worked the soil is, the less will be the pro- 

 portion of nitrogen. In the fertile hop-gardens of 

 East Kent the percentage of nitrogen is rarely as much 

 as 02 per cent., despite the great dressings of nitro- 

 genous manure that are annually applied. 



The proportion of phosphoric acid in soils is not so 

 variable as the proportion of nitrogen ; it ranges from 

 about 006 per cent, to 02 per cent. ; the lower amounts 

 occur generally on the sands and clays, the higher on 

 loams and soils well provided with calcium carbonate. 



The proportion of potash shows extreme variations, 

 a clay soil may yield one per cent, of potash to strong 

 hydrochloric acid, a sand only one-tenth as much. It 

 has already been pointed out that "clay" is chiefly 

 the result of the weathering of felspars and kindred 

 minerals containing potash; this weathering is never 

 chemically complete, so that all soils containing any 

 considerable admixture of clay are necessarily rich in 

 potash. The amount dissolved out by hydrochloric 



