ULMIC ACID. Ulmin. Some trees, and more especially the elm when it is old, secrete a liquid which dries as it exudes : the dry residue consists principally of mucilaginous matter, with some carbonate or acetate of potash, and eventually the mucilaginous matter undergoes a change, and, combining with the potash, forms a substance which was first examined by Vauquolin and Klaproth, and to which Dr. Thomson gave the name of u/min. This name was changed by Berzclins to that of geic acid, because on treating soils with alkalies a considerable quantity of a similar compound is obtained.
Ulmin, or ulmic acid, may be artificially obtained, according to 13mconnot, by the following process :—heat in a silver crucible equal weights of potash and sawdust, with a little water ; the mixture is to be continually stirred : the mass softens and swells rapidly, and is then to be removed from the heat and stirred till cold : during the operation oxygen is absorbed from the air, owing to which, the ulmio acid is formed. When cold, the product, which contains ulmato of potash, is dissolved in water, filtered, and treated with dilute sul phuric acid, which combines with the potash, and precipitates the ulmic acid from combination with it : the acid thus obtained is to bo washed and dried. The properties of this ulmic acid are, that it is of a deep brown colour, very brittle, and breaks in ;angular fragments, and is almost insoluble in water. When precipitated from its solution
in an alkali, it is in the state of hydrate, and it then dissolves in 1500 times its weight of boiling water, in 2500 timer, between 60' and 70' Fehr., and in 6000 times at 32'. The solution in cold water is brownish-yellow ; that in hot is deep brown. Moss rater owes its dark brown colour to the presence of ulmic acid.
It is insoluble in acidulated water or in saline solutions : sulphuric acid dissolves it without apparent alteration, and becomes blackish : water precipitates it from this solution. Ulmic acid reddens tincture of litmus. It is dissolved by alcohol, from which it separates in crystalline scales by spontaneous evaporation.
It has been already mentioned that ulmic acid may be obtained from soils : it may also be procured from rotten leaves, bog-earth, wood-soot, or turf, by digesting them in a weak solution of potash : by this a brown-coloured solution of ulmate of potash is formed, from which acids throw down ulmic acid.
According to Boullay, ulmin consists of ltalaguti and Boullay, by treating sugar with dilute sulphuric 'acid, obtained two substances, which they supposed to be identical with nimbi and ulmic acid ; but, according to Liebig, they are of a different nature, and he has given them the names of sacehulmin and sacchulmic acid.