84 liUMIC ACID. 



older books, under the names of extractive, vegetable extract, mucilaginous 

 matter, and the like. Saussure, for instance, filled a vessel with turf, and 

 moistened it thoroughly with pure water, when by putting ten thousand 

 parts of it by weight under a heavy press, and filtering and evaporating 

 the fluid, he obtained twenty-six parts of what he termed extract; from 

 ten thousand parts of well dunged and rich kitchen garden mould, he ob- 

 tained ten parts of extract ; and from ten thousand parts of good corn field 

 mould, he obtained four parts of extract. 



"M. Polydore Boullay found that the liquid manure, drained from 

 dunghills, contains a large proportion of humic acid, which accounts for 

 its fertilizing properties so well known in China and on the continent; and 

 he found it also in peat earth, and in varying proportions in all sorts of 

 turf. It appears probable, from Gay-Lussac having found a similar acid 

 (technically azumic acid), on decomposing the prussic acid (technically 

 hydro-cyanic acid), that the humic acid may be found in animal blood, and 

 if so, it will account for its utility as a manure for vines, &c. Dobereiiier 

 found the gallic acid convertible into the humic." 



[When the second edition of this essay was published (in 1835), 

 the above annunciation had but just before been made, showing 

 that there was indeed high scientific authority for the very general 

 existence of a vegetable acid in soils. And since that time, the 

 fact has been admitted by almost all scientific writers, and has 

 been treated of at length in sundry chemical works and reports of 



p geological surveys in this country. The doctrine of the existence 

 of an acid of soil, of vegetable origin, which before had scarcely 



, any other authority for its support than mine, humble and obscure 

 as that was, is now of universal acceptation. Still, notwithstand- 

 ing all that has been written on the subject, very little light has 

 been thrown on it by the chemists who have treated of it. Being 

 myself too little informed to be able to properly digest these 

 different speculations and to balance authorities, and to separate 

 the true and valuable from the erroneous or worthless of what has 

 > been lately published, I deem it best still to rely on my own pre- 

 viously published views and proofs only, as presented in the fore- 

 going pages. Therefore, leaving it to chemists to settle their 

 present differences of opinion in regard to the qualities, and even 

 identity, as well as name of the acid of soil, and to clear away the 

 existing confusion and obscurity of their views, I will, for the 

 present, adopt nothing on their authority in this respect. Still, I 

 earnestly hope that their subsequent investigations may be success- 

 ful in eliciting and determining what is true of this acid and also 

 in applying the truths ascertained to advance the knowledge of the 

 composition and improvement of soils. For the same reason, I 

 shall also decline adopting any of the various terms which have 

 been successively applied by different, and even the same chemists, 

 to designate the acid of soil ; as humic, geic, crenic, and o,pocrenic 

 acid, &c. 1842.] 



[Long after the publication of the latest of the passages of the 

 foregoing chapter, I first learned the existence of good and sufficient 



