348 Reviews. — Licbig^s Organic Chemistry. 



tasteless leaves of the Agave Americana absorb only 0.3 of their vol- 

 ume of oxygen, in the dark, during 24 hours, the leaves of the Ptnus 

 Abies, which contain volatile and resinous oils, absorb 10 tin)es, those 

 of the Quercus Robur containing tannic acid 14 times, and the balmy 

 leaves of the Populus alba 21 times that quantity. This chemical 

 action is shown, very plainly, also in the leaves of the Cotyledon 

 calycinum, the Cacalia jicoides and others ; for they are sour like 

 sorrel in the morning, tasteless at noon, and bitter in the evening. 

 The formation of acids is effected during the night, by a true process 

 of oxidation: these are deprived of their acid properties during the 

 day and evening, and are changed, by separation of a part of their 

 oxygen, into compounds containing oxygen anil hydrogen, either in 

 the same proportions as in water, or even with an excess of hydro- 

 gen, which is the composition of all tasteless and bitter substances. 



The opinion is not new that the carbonic acid of the air serves for 

 the nutriment of plants, and that its carbon is assimilated by them ; 

 it has been admitted, defended, and argued for, by the soundest and 

 most intelligent natural jjhiiosophers, namely, by Priestley, Senne- 

 bier, De Saussure, and even by Ingenhouss himself 



The question whether carbonic acid is the food of plants or not, 

 has been made the subject of experiments with perfect zeal and good 

 faith ; the results have been opposed to that view. But how was 

 the inquiry instituted.'' 



The seeds of balsamines, beans, cresses, and gourds, were sown 

 in pure Carrara marble, and sprinkled with water containing car- 

 bonic acid. The seeds sprang, but the plants did not attain to the 

 development of the third small leaf. In other cases, they allowed 

 the water to penetrate the marble from below, yet, in spite of this, 

 they died. It is worthy of observation, that they lived longer with 

 pure distilled water than with that impregnated with carbonic acid; 

 but still, in this case also, they eventually perished. Other experi- 

 menters sowed seeds of plants in flowers of sulphur and sulphate of 

 baryta, and tried to nourish them with carbonic acid, but without 

 success. 



Such experiments have been considered as positive proofs, that 

 carbonic acid will not nourish plants ; but the manner in which they 

 were instituted is opposed to all rules of philosophical inquiry, and 

 to all the laws of chemistry. 



Again, in chapter III., on this same subject, the introsus- 

 ception of carbonic acid as a nutriment, takes place where, 

 instead of humus., (a substance formerly supposed to act di- 

 rectly as the food of plants,) charcoal is used, we learn that 



Plants thrive in powdered charcoal, and may be brought to blos- 

 som and bear fruit if exposed to the influence of the rain and tho 

 atmosphere ; the charcoal may be previously heated to redness. 

 Charcoal is the most "indifferent" and most unchangeable sub- 

 stance known ; it may be kept for centuries without change, and is 

 therefore not subject to decomposition. The only substances which 

 it can yield to plants arc some salts, which it contains, amongst 

 which ia silicate of potash. It is known, however, to possess the 



