F. S. Mark 



157 



50 c.c. of a 20 7o solution of ammonium chloride were introduced by 

 means of a S-wa}' fumiel, and the distillation was continued for thirty 

 minutes after the contents of the distilling flask reached the boil. The 

 same apparatus as before was used, with the addition of an acid trap 

 containing dilute sulphuric acid and litted with a condenser. This trap 

 was provided to prevent ammonia from reaching the absorbing Reiset 

 tower, as it was found that ammonia interfered with the phenol-phthalein 

 titration rendering it slower and less sharp. The results obtained by 

 this method (expressed as before in milligrams of carbon dioxide per 

 100 grams of air-dried soil) were always lower than those obtained 

 with hydrochloric acid. 



Soil 



1st 30 mins. 



2nd 30 mius. 



Transvaal III 

 Ohio I 



83 

 140 



65 



79 



A series of soils yielded on the average 52 milligrams more carbon 

 dioxide per 100 grams of soil by distillation with hydrochloric acid than 

 with ammonium chloride. The subsoils agreed very closely, a difference 

 of only 12 milligrams carbon dioxide per 100 grams soil being obtained 

 on the average. This points to the organic matter, which is com- 

 paratively speaking absent in the subsoil, as the source of the extra 

 carbon dioxide evolved from the surface soil. 



The next step was to ascertain whether by boiling such soils with 

 water alone any evolution of carbon dioxide took place. This was in- 

 variably found to be the case. The results, calculated as before, are 

 given in the following table. 125 c.c. of water was used and the 

 boilinfr continued for 30 minutes. 



As it was highly improbable that these soils, all of which showed 

 a strong acid reaction to litmus, contained any appreciable amount of 

 carbonate, and as they gave off carbon dioxide on boiling with water 



