BY R. GREIG-SMITH. 165 



The set of experiments show that vegetable-mould, oiiginally 

 of ail acid reaction, is made more acid by the action of beat, 

 such as by sterilisation for two hours at 130°. The acid sub- 

 stances are partly soluble in alcohol and in water. They consist 

 of two kinds, one of which is capable of being neutralised by the 

 bicarbonates of the alkaline earths. The other makes itself 

 evident when in contact with the hydrates of the earths. The 

 mould which was examined removed from four to five times more 

 alkali from the hydrate than from the bicarbonate. 



At the close of the baryta- water experiment, the control-soil 

 was rapidly filtered on the pump, washed with a small quantity 

 of water, transferred back to the bottle and shaken with 300 c.c. 

 of water, and tested from time to time. 



3 hours ... ... . . 26*5 



1 day ... ... ... ... 36 



2 days 36 



Of the 433 c.c. removed from 100 grams of dry, organic matter^ 

 36 were given up to water, and we may, therefore, consider the 

 difference of roughly 400 c.c. as being in combination. 



The sterilised leaf-mould was also filtered and shaken with 200 

 c.c. of twentieth-normal hydrochloric acid. This removed the 

 following amounts of normal lime. 



3 hours ... ... ... 328 



1 day ... ... ... ... 343 



2 days 343 



Deducting this from the total baryta absorbed, viz., 464 c.c, 



we have 120 c.c, which is close to the amount absorbed from the 

 bicarbonates. It is evident that the kind of humic acid, which 

 fixes the bulk of the lime from a solution of the hydrate, forms 

 with it a feeble combination. This is destroyed by mineral acids 

 but is not attected to any extent by water. The combination 

 seems to be too detinite in its quantitative relations for a simple 

 case of adsorption. 



From the experiments, it was concluded that the organic 

 matter of the leaf- mould contained humic acids, and, of these, 

 about one-quarter were capable of decomposing the bicarbonates 

 of the earths, while three-fourths were too weak to do this but 



