54 THE SOIL. III. 



of boiling water, it reddens litmus, and expels carbon dioxide 

 from carbonate, forming humates which are all insoluble with 

 the exception of those of the alkalis. 



The ammonium compourid C (i0 H 4s (NH 4 ) (i O 27 is very soluble 

 in water. With calcium chloride a compound C (;0 H 4(i Ca ;! 

 (NH 4 ) 2 27 is precipitated. Ulmic acid is stated by Detmer to 

 be identical with humic acid. Crenic and apocrenic acids are 

 produced by oxidation of humic acid. The former is said to 

 be found in moist soils, the latter in dry, loose ones. Crenic 

 acid is said to have the composition C^H 24 lc ,-\- 3H 2 0, apocrenic 

 acid C 24 H 12 O 12 -t-H 2 O. :|: The free acids are soluble in water. 



The following gives some of the formulae which have been 

 proposed for the constituents of humus : 



Thenard. Detmer. Mulder. Stockbridge. 



Humic acid C W H 10 10 C (i0 H 54 27 C 40 H 24 O 12 C al H a4 12 

 Humin C 40 H :W 15 C. 21 H 24 12 



Ulmic acid C GO H,, 4 27 C 40 H 2H O 12 C 40 H a ,O la + H 2 0. 



Ulmin C 40 H,A 4 C 40 H 2 ,0 12 + H 2 0. 



Crenic acid C 24 H 24 1(i +3H 2 C 12 H 12 0,. 



Apocrenic acid C. 24 H 12 12 + H 2 C 21 H 24 12 . 



The correctness of any of these formulae is greatly to be 

 doubted, as they leave out of account the nitrogen which is 

 always found in the analyses and which Mulder assumed to be 

 present as ammonia. 



In 1889 a study of the black soils of Eussia was published 

 by Kostytcheff,! in which he found that the humus contained 

 from 4-0 to 6*65% of nitrogen, a quantity greatly in excess of 

 that in the original vegetable matter from which it was pro- 

 duced (1-6 to 2%). He found that when wet vegetable matter 

 (hay) was allowed to decay under a bell jar, air being injected 

 daily, the dry matter considerably diminished, but that no loss 

 of nitrogen occurred, so that the percentage of nitrogen in- 

 creased from 1-27 to 2*04. He concludes that the nitrogen in 

 humus exists mainly as proteid bodies, very little being as 

 amide ; that both bacteria and moulds aid in the conversion of 

 vegetable matter into humus ; that if decay occurs beneath 

 water the vegetable structure is retained and peat results, if in 



* Mulder, A. 36, 243. t r. abst. in Jour. Clieni. Sac. 1891, p. 611. 



