HUMIC ACID. * 83 



essay, (January 1832.)* But since that time I have first heard of 

 a discovery, and of consequent investigations by men of science, 

 which seem to furnish direct proof of what I have been contending 

 for, viz. the existence of a vegetable acid substance in soils and 

 manures, generally diffused, and often in large proportions, and 

 yet which had not been known or suspected by chemists previously. 

 The first intimation of this discovery which reached me was in an 

 extract in a newspaper from the "Alphabet of Scientific Gar- 

 dening," by Professor Rennie, published in London in 1833, from 

 which the part relative to this subject will be quoted below. 

 Since, I have seen the French version of the late work of Berze- 

 lius, in which his views of humic acid (or, as he names it, the geic 

 acid) are given more at length. ( The facts respecting humic 

 acid, as concisely stated in the following quotation from Professor 

 Rennie, furnish strong confirmation of some of the opinions which 

 I have endeavoured to maintaia. It will however be left, without 

 farther comment, for the reader to observe the accordance, and to 

 make the application. 



" Jlumic acid and humin. In most chemical books the terms ulmic acid 

 and ulmin are used, from ulmus, elm ; but, as its substance occurs in most, 

 if not all plants, the name is bad. I prefer Sprcngel's terms, from humus, 

 soil. 



"This important substance was first discovered by Klaproth, in a sort 

 of gum from an elm ; but it has since been found by Berzelius in all barks ; 

 by M. Braconnot in saw-dust, starch, and sugar; and, what is still more 

 interesting for our present purpose, it has been found by Sprengel and M. 

 Polydore Boullay to constitute a leading principle in soils and manures. 

 Humin appears to be formed of carbon and hydrogen, and the humic acid 

 of humin and oxygen. Pure humin is of a deep blackish brown, without 

 taste or smell, and water dissolves it with great difficulty and in small 

 quantities ; consequently it cannot, when pure, be available as food for 

 plants. 



" Humic acid, however, which, I may remark, is not sour to the taste, 

 readily combines with many of the substances found in soils and manures, 

 and not only renders them, but itself also, easy to be dissolved in water, 

 which in their separate state could not take place. In this way humic acid 

 will combine with lime, potass, and ammonia, in the form of humates, and the 

 smallest portion of these will render it soluble in tvater and fit to be taken up by 

 the spongelets of the root fibres. 



' ' It appears to have been from ignorance of the important action of the 

 humic acid in thus helping to dissolve earthy matters, that the older 

 writers were so puzzled to discover how lime and potass got into plants; 

 and it seems also to be this, chiefly, which is so vaguely treated of in the 



* The general positions and views taken as to acid and neutral soils are 

 also, in substance and purport, just as they appeared in my first publica- 

 tion on this subject, in 1821. 



f A long extract from Berzelius' " Traite de Chimie," embracing these 



views, was translated for and published in the two preceding editions of 



this essay, and also in the Farmer's Register. It is omitted now as un- 

 necessary. 1849. 



