310 JRescarche$ on Vegetaiioru 



Extracts of vegetables placed in the air gradually deposit 

 in it pellicles less soluble ; during this alteration the oxvgen 

 of the atmosphere is changed into carbonic acid ; but the 

 volume of the latter undergoes no change, or experiences 

 - that only which arises from the absorption of the carbonic 

 acid which is formed ; at the same time a part of the oxvgen 

 and hydrogen which enter into the composition of the ve- 

 getable substance forms a more intimate combination, and 

 is reduced to water •, so that the extract loses much less of 

 its weight by this production of \Aater than by the carbon 

 separated from it, and there is found a greater proportion 

 of carbon than before this' formation of carbonic acid : we 

 have before remarlced other circumstances in w hich a double 

 effect takes place during vegetation. 



Dead wood produces the same effect on the atmosphere, 

 and undergoes the same production of water : when de- 

 prived, by repeated decoctions, of all its soluble part, and 

 exposed to the air, it changes the oxvgen gas of it into 

 carbonic acid ; its own oxvgen and hydroacn form water; 

 it then gives a new extract in the water in which it is boiled, 

 and by means of its successive Josses acquires a superabun- 

 dance of carbon. It had been observed that in the acctifi- 

 cation of wine there is an absorption of' oxvaeu gas, and 

 this oxygen absorbed had been considered as the cause of 

 the acidity which is developed ; but Saussure has ascer- 

 tained that the oxygen gas is merely changed into carbonic 

 acid, and that there is no other absorption than that of the 

 carbonic acid formed : the production of acidity can there- 

 tore arise only from the excess of oxvgen which becomes 

 prevalent when a part of the hvdrogcn has produced water. 



The ca^-e is not the same with 'he epoch at which, by the 

 progress of alteration, the vegetable substances placed under 

 water disengage inflammablt- gas: thev can then absorb 

 oxygen gas, which in all probability produces water. 



Oils form another exception : they really absorb oxygen : 

 the author was not able to ascertain whether there was a 

 production of oxygen, or whether the oxvgen combined with 

 the oil. He has not yet cleared up what takes place in the 

 transition of oil to the state of resin. 



Azotic ^as is not affected by vegetable substances, except 

 by souje oils which absorb a small quantity of it, but which 

 retain it onlv wcaklv. 



Vegetables exposed to the action of the air and of water 

 are at length reduced to a black substance whi( h Saussure 

 distinguishes by the name of tcrreau (vcffctable mould) : 

 preceding experiments show that this substance is not the 



result 



