108 Observations on Liehig's " Organic Chemistry T 



measures are all Hessian ; the proportions are the same, what- 

 ever standard is taken). He says that the carbonic acid is in the 

 state of an oxide. Carbonic oxide is only absorbable by water 

 sparingly, estimated from -^-^ to j^ of its volume. Solubility 

 in water is, perhaps, not required by the action of the leaves. 

 From the fact of plants generating caoutchouc, wax, fats, and 

 'volatile oils, containing hydrogen in large quantity and no 

 oxygen, we may be certain, he says, that plants decompose 

 water, because from no other body could the hydrogen be 

 obtained ; and, though some parts of plants contain the oxygen 

 and hydrogen in the proportions of water, they cannot exist 

 in the plant in the state of water. He then gives an analysis of 

 various substances produced by plants, showing that most oxy- 

 gen is separated to the air when oils are formed, as less is 

 retained; and in acids the reverse. These vital processes, he 

 says, differ from the chemical formation of salts, being the very 

 reverse ; but carbonic acid, zinc, and water, when brought into 

 contact, act upon one another, and separate the hydrogen, per- 

 haps by electric action ; the zinc acting so far like the plant. 

 The remainder, however, contains carbonic acid, zinc, and the 

 oxygen of the water, in a white pulverulent compound, but not 

 combined into the form of wood, nor with the oxygen and 

 carbon separated. The carbonic acid separated in the process 

 of decay is most from acid substances ; oily have not the same 

 tendency to putrefy, as they want oxygen. The numerous 

 springs which emit carbonic acid in the neighbourhood of 

 extinct volcanoes, he mentions as a great source of carbonic 

 acid. The Eifel, near Coblentz, has been calculated to yield 

 90,000 lb. daily to the atmosphere, corresponding to 64',800 lb. 

 of pure oxygen, when decomposed by plants. 



On the next subject, the Origin and Assimilation of NitrogeJi^ 

 this writer differs from all others, in the prominence he has 

 given to it. Former writers told us that nitrogen existed only 

 in small quantities, most of it in the higher order of plants ; 

 and though its necessity was inferred from its presence, yet 

 little comparatively was said about it. Dr. Liebig, however, 

 says, we cannot suppose a plant would attain maturity, even in 

 the richest vegetable mould, without the presence of nitrogen ; 

 since we know that nitrogen exists in every part of the vegetable 

 structure : if it is not found in the solids themselves, it is to be 

 found in the fluids that surround them. 



On the question, how this nitrogen is obtained, he con- 

 siders it from ammonia solely, which is a compound of hy- 

 drogen and nitrogen. We have not the slightest reason, he 

 says, for believing that the nitrogen of the atmosphere takes 

 part in the processes of assimilation of plants and animals ; 

 on the contrary, he says, many plants emit the nitrogen which 



