OF THE ASSIMILATION OF CARBON. 



applied to modifications of humus. They are obtained by treat- 

 ing peat, woody fibre, soot, or brown coal, with alkalies ; by de- 

 composing sugar, starch, or sugar of milk by means of acids ; or 

 by exposing alkaline solutions 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 sup. 

 posed that their composition is identical. But a more erroneous 

 notion could not be entertained ; since even sugar, acetic acid, 

 and resin, 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 accurate 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 muri- 

 atic acid, according to the analysis of Stein, 64 per cent. Mala- 

 guti states, moreover, that humic acid contains an equal number 

 of equivalents of oxygen and hydrogen, that is to say, that these 

 elements exist in it in the proportions for forming water ; while, 

 according to Sprengel, the oxygen is in excess ; and Peligot esti- 

 mates the quantity of hydrogen at 14 equivalents, and the oxygen 

 at only G equivalents, making the deficiency of oxygen as great 

 as 8 equivalents. Mulder and Herrmann have shown that de- 

 cayed willow- wood, peat, or vegetable mould, after being treat- 

 ed with water and alcohol, leave a solid brown substance, which 

 yields to alkalies a peculiar humic acid. This humic acid con- 

 sists of carbon and the elements of water. But besides these 

 usual constituents, it contains a certain quantity of ammonia, in 

 a state of chemical combination. 



It is quite evident, therefore, that chemists have been in the 

 habit of designating by the names of humic acid or humin, all 

 the brown or black-colored products of the decomposition of 

 organic bodies, according as they were soluble or insoluble in 



