DECAY OF ORGANIC MATTERS. 245 



m the final result of the decomposition. Peat, which is derived, as 

 we know, from the slow decomposition of submerged plants, does not 

 appear to be formed in the swamps of warm cHmates ; it has, per- 

 haps, never been encountered in the stagnant waters of liie equinoc- 

 tial regions ; there the woody fibre appears to be totally dissipated 

 in carbonic acid gas, and in marsh gas, the probable source of the 

 insalubrity of those countries. Lakes with peat bottoms are not 

 found except on the very high table-lands of the Andes, in localities 

 where the mean temperature does not exceed 49" or 50" V. 



The alkalies are powerful agents in the decomposition of certain 

 organic substances, whether in determining or in accelerating it. 

 There are some, indeed, which experience no change without their 

 intervention, whatever may be the other conditions favorable to de- 

 composition. Thus, according to M. Chevreul, many coloring sub- 

 stances may be preserved in solution almost indefinitely, without 

 change, in contact with gallic acid ; but the presence ot a very small 

 quannty of free alkali suffices for their immediately acquiring the 

 power of absorbing oxygen, and at the same time of acquiring a brown 

 tint, M. Chevreul observed that 3.087 grs. of hematine dissolved 

 in potash will absorb 3.857 grs. of oxygen in forming 0.925 of car- 

 bonic acid. The oxygen which enters into the carbonic acid, there- 

 fore, represents nothing like the quantity which was fixed by the 

 solution, and it is almost certain that this gas likewise reacted upon 

 the hydrogen of the coloring matter. The use of the alkalies for 

 accelerating the destruction of organized matter has been long known 

 to agriculturists. 



Straw, fern, and the ligneous parts of plants are sometimes strat- 

 ified with quick-lime, in order to facilitate their disintegration, and 

 consequently their decomposition. The utility of this old practice 

 cannot be disputed while confined whhin certain limits ; but it is 

 often abused ; for it is beyond doubt that alkalies mingled indiscrim- 

 inately with manure become in reality more injurious than advan- 

 tageous for the end proposed in their introduction. 



The appearance of a certain brown substance, little soluble in 

 water, but easily dissolving in alkalies, is a characteristic proper to 

 all vegetable mailer under decomposition ; a characteristic which 

 becomes more marked as the decomposition advances towards its 

 last stage, namely, the production of humus. This substance is 

 ulmine, which, on account of some acid properties which it pos- 

 sesses, is also named ulmic acid. It forms a part of mould, and M. 

 P. BouUay constantly found it in the water of dunghills. 



In 1797, Vauquelin discovered ulmine united with potash in the 

 matter of the exudation from the ulcer of an elm-tree. 



In 1804, Klaprolh confirmed this observation. M. Braconnot 

 succeeded in obtaining ulmine artificially by subjecting woody fibre 

 to the action of alkalies. This substance is easily procured by 

 carefully heating in a silver capsule, and continually stirring a mix- 

 ture of equal parts of potash and of saw-dust slightly damped. At 

 a certain time the woody matter softens and suddenly dissolves ; the 

 mass then begins to swell up, and the fire is slaked. The product 



21* 



