COMPOSITION OF HUMUS. 5 



received various names according to the different 

 external characters and chemical properties which 

 it presents. Thus, ulmin, humic acid, coal of 

 humus, and humin, are names applied to modifica- 

 tions of humus. They are obtained by treating 

 peat, woody fibre, soot, or brown coal with alkalies ; 

 by decomposing sugar, starch, or sugar-of-milk 

 by means of acids ; or by exposing alkaline solu- 

 tions of tannic and gallic acids to the action of 

 the air. 



The modifications of humus which are soluble 

 in alkalies, are called humic acid ; while those 

 which are insoluble have received the designations 

 of humin and coal of humus. 



The names given to these substances might cause 

 it to be supposed that their composition is identical. 

 But a more erroneous notion could not be enter- 

 tained ; since even sugar, acetic acid, and colophan 

 do not differ more widely in the proportions of 

 their constituent elements, than do the various 

 modifications of humus. 



Humic acid formed by the action of hydrate of 

 potash upon sawdust contains, according to the ac- 

 curate analysis of Peligot, 72 per cent, of carbon, 

 while the humic acid obtained from turf and brown 

 coal contains, according to Sprengel, only 58 per 

 cent.; that produced by the action of dilute sulphuric 

 acid upon sugar, 57 per cent, according to Malaguti ; 

 and that, lastly, which is obtained from sugar or from 

 starch, by means of muriatic acid, according to the 



