552 



Miscellaneous. 



The author arrives at the conclusion, that as the soil cannot be 

 the source from which carbonic acid is derived, it must be the 

 atmosphere. I think he has come to this conclusion too hastily. 

 I venture to affirm, that it is certain that the vegetable matter 

 contained in soil is changed into carbonic acid by the oxygen of the 

 air, by way of combustion. It cannot be questioned, that the car- 

 bonic acid produced in this way is absorbed by the moisture con- 

 tained in soil, and then attracted by the roots. It is therefore very 

 probable that soil contributes much to the nourishment of plants ; and 

 this probability is increased by the observation, that the quantity of 

 carbonic acid does not appear to have increased in forests, which for 

 a thousand years never have been cut, and certainly not in propor- 

 tion to the quantity of vegetable matter produced by the falling of 

 leaves, the breaking of branches, &c. 



Dr. Liebig next inserts (p. 15) a very absurd observation : 

 ** Humus," he says, " is produced, according ,to the opinion of all 

 scientific men, by decomposition and decay. Therefore there cannot 

 be an original humus, as there existed plants before the humus." I 

 answer ; " carbonic acid is produced, according to Dr. Liebig and the 

 opinion of all scientific men, by the process of combustion and res- 

 piration ; therefore there cannot have been an original carbonic acid, 

 as there existed plants before animals and combustion." But of 

 what use are such follies in a scientific work ? What do we know 

 of the nature of that process by which the earth forms her produc- 

 tions ? I think, just nothing. Carbonic acid is a combination of 

 carbon and oxygen; humus is a combination of carbonic acid, 

 oxygen, and hydrogen. Does Dr. Liebig think it more difficult for 

 nature to bring about the combination of the three last mentioned 

 substances, than that of the two first ? 



After Dr. Liebig (p. 17, &c.) has repeated the well-known facts 

 respecting the continued production of carbonic acid, and that never- 

 theless the portion of this matter contained in the atmosphere does 

 apparently* not increase, he briefly asks, " what becomes of the car- 

 bonic acid ?" and he answers as briefly, " it is absorbed by the leaves 



* Mr. A. Dumas, in his Statics of Organic Chemistry, has shown that our 

 eudiometric experiments are much too scanty to prove that the atmosphere is not 

 subject to any change in the proportion of its components. 



