Observations 07i Liehig^s " Organic Chemistry ^^ 103 



tracted from the air every second of time, for 8 hours daily 

 for 200 days, he calculates that 1000 lb. of carbon would be 

 produced on 80,000 square feet. This is only half the quantity 

 formerly estimated as produced by corn, &c., the quantity of 

 land being doubled; he adds, in a note, that -lime whitewash 

 has been calculated to absorb, on the surface of walls, nearly 

 three times the quantity. This takes it for granted, however, 

 that the absorption by the leaves is equal to the affinity of lime, 

 deprived of its carbonic acid, for that gas, which is one of the 

 most powerful ; and that the air at every second is deprived of 

 the whole of its carbonic acid, and the plants surrounded with a 

 full volume of new air, with its full proportions. 



He says, next, that the roots, and other parts of the plant, absorb 

 constantly water and carbonic acid, independent of solar light, 

 which is only needed to assimilate and fix the carbon ; and this 

 admission should qualify the declaration of carbonic acid being ex- 

 cliisively absorbed by the leaves. In the tropical climates, he says, 

 where vegetation is most active, the air does not contain near so 

 much carbonic acid as in temperate climates ; the streams of air 

 which are moved from one climate to another serve to equalise the 

 whole, and the air is thus purified, and its proportion of oxygen, 

 the most essential to the life of animals, kept up. The experi- 

 ments of De Saussure, he says, have proved that the upper strata 

 of the air contain more carbonic acid than the lower. It was 

 stated to be the case, (De Saussure, Thomson's Chemistry,) that 

 the air over the Lake of Geneva contained least carbonic acid, 

 that over the plains at Chamboisy more ; in a confined court at 

 Geneva more was contained than on the plain ; and rather more in 

 the air of some mountainous places than in that of the plain. It is 

 not stated whether the air from the mountain was from a confined 

 situation or not, that over the sea would be least from the moist- 

 ure : but, from the specific gravity of the carbonic acid, it must 

 have a base to rest on, whether mountain or plain, and the upper 

 strata of the air cannot generally contain most. 



He next says that no matter can be considered nutritious, or 

 necessary to the growth of plants, which possesses a composition 

 either similar to, or identical with, theirs; and that vegetable 

 physiologists have informed us that aqueous solutions of sugar, 

 starch, and gum are imbibed by the roots of plants, and carried 

 to all parts of their structure, but are not assimilated. Where 

 this admission was made it is not said, nor do I ever recollect 

 of seeing it. Sir H. Davy, p. 270. and 271., says that, having 

 used strong solutions of sugar, mucilage, tannin principle, and 

 jelly, he found the plants that imbibed them died; and he was 

 once of opinion these substances were not fit for nutriment^ until, 

 suspecting it was owing to the solution being too concentrated, 

 he tried the effects of these solutions, very much diluted, on 



H 4 



