DECAY OF ORGANIC MATTERS. 243 



they attain that stage of their alteration in which they give out hy 

 drogen. 



In pursuing with persevering sagacity the study of putrefaction, 

 M. de Saussure discovered the cause of this condensation ; it con- 

 sists in the fact, that an organic suhstance in course of spontaneous 

 decomposition, acts in some respects like the platina sponge placed 

 in a mixture of oxygen and hydrogen gas ; we know that platina 

 recently heated and introduced into a mixture of these two gases, 

 determines their union in the proportions required to constitute water. 

 Nowr by substituting for the metal some moistened seeds, previously 

 deprived of their germinating faculty, the same effect is produced : 

 the two gases combine until one of the two entirely disappears. 

 When this combustion of hydrogen, proceeding from the decomposi- 

 tion of organic substances, takes place in the body of the atmosphere 

 which contains azote, it is possible that a minute quantity of ammonia 

 may be produced together with water ; nor is it going too far to 

 suppose, that manures very slightly azotized, take up azote from 

 the atmosphere during their fermentation; that during the act of 

 vegetation itself, the hydrogen proceeding from the decomposed 

 water, or yet more, that which makes part of the essential oils form- 

 ed by plants, may, in oxidating afresh, introduce atmospheric azote 

 into their composition. 



Dead organized matter, such as wood, straw, or leaves, exposed 

 to wet, and for a long time to the action of the air, ends by becom- 

 ing transformed into a brown substance, which when damped is al- 

 most black, which falls to powder when dry, and which is commonly 

 known by the name of humus or mould. 



This is, so to speak, the last term of the decomposition of organic 

 matter ; mould appears to belong already to the mineral kingdom ; 

 and whatever may be the diversity of its origin, it presents a suf- 

 ficient number of peculiar characteristics to be considered a distinct 

 substance. In fact, the atmosphere continues to exert its action 

 upon mould ; its inflammable elements are dissipated by a slow and 

 imperceptible combustion, giving place to water and carbonic acid. 

 But in this ulterior decomposition, those fetid products which char- 

 acterize putrid fermentation are no longer observed. 



Wet saw-dust, placed for some weeks in an atmosphere of oxygen, 

 forms a certain quantit}' of carbonic acid, and the volume of the gas 

 does not perceptibly diminish. The wood at the surface acquires a 

 deep-brown color. Several experiments made by Saussure, prove 

 that dead wood does not absorb the oxygen gas of the atmosphere ; 

 it transforms it into carbonic acid, and the action takes place as if 

 the carbon of the organic matter alone experienced the effects of the 

 oxygen ; for the gaseous volume remains the same. The loss, how- 

 ever, undergone by the ligneous fibre, during its exposure to the air, 

 is greater than it ought to be if carbon alone were eliminated : whence 

 Saussure concludes, that while the woody matter loses carbon, it 

 also lets some of its constituent water escape. 



As a consequence of these observations, the relative proportion 

 of carbon ought to augment in the humid wood changed by the ac 



