ORGANIC MATTERS OF THE SOIL. 225 
(besides, perhaps, unaltered vegetable matters) two char- 
acteristic ingredients, which have been designated ulmic 
acid and ulmin, (so named from having been found in a 
brown mass that exuded from an elm tree, wdmus being 
the Latin for elm). These two bodies demand particular 
notice. ’ 
When brown peat is boiled with water, it gives a yel-| 
lowish or pale-brown liquid, being but little soluble in 
pure water. If, however, it be boiled with dilute solution 
of carbonate of soda (sal-soda), a dark-brown liquid is 
obtained, which owes its color to ulmate of soda. The 
alkali dissolves the insoluble ulmic acid by combining 
with it to form a soluble compound. By repeatedly heat- 
ing the same portion of peat with new quantities of sal- 
soda solution, and pouring off the liquids each time, there 
arrives a moment when the peat no longer yields any color 
to the solution. The brown peat is thus separated into 
one portion soluble, and another insoluble, in carbonate of 
soda. Udmic acid has passed into the solution, and ulmin* 
remains undissolved (mixed, it may be, with unaltered 
vegetable matters, recognizable by their form and struc- 
ture, and with sand and mineral substances). 
By adding hydrochloric acid to the brown solution as 
long as it foams or effervesces, the ulmic acid separates in 
brown, bulky flocks, and is insoluble in dilute hydrochloric 
acid, but is a little soluble in pure water. When moist, it 
has an acid reaction, and dissolves readily in alkalies or 
alkali-carbonates. On drying, the ulmic acid shrinks 
greatly and remains as a brown, coherent mass. 
The ulmin* which remains after treatment of brown 
. peat with carbonate of soda is an indifferent, neutral (i. e., 
not acid) body, which has the satne composition as the 
* The above statement is made on the authority of Mulder. The writer has, 
however, found, in several cases, that continued treatment with carbonate of 
soda alone completely dissolves the humus, leaving a residue of cellulose which 
yields nothing to caustic alkali. He is, therefore, inclined to disbelieve in the 
existence of ulmin and humin as distinct from ulmic and humic acids. 
