ORGANIC CHEMISTRY. 



ORGANIC CHEMISTRY. 



nate. Ray tried this in the vacuum of an air- 

 pump with some lettuce seed; they did not 

 germinate in vacuo, but they grew very well 

 when the atmospheric air (which contains 21 

 per cent, of this gas) was admitted. It is for 

 this reason that the farmer is careful not to 

 bury his seed-corn so deep in the ground as to 

 be out of the influence of the oxygen of the 

 atmosphere. Beyond a certain depth, which 

 varies with different plants, no seeds, in fact, 

 will vegetate. Seeds have been buried deep 

 in the earth for centuries, and when, after- 

 wards, they have been accidentally thrown 

 upon the surface, have vegetated. There is 

 reason for believing that it is not the entire at- 

 mospheric air, but only its oxygen, which is 

 essential to germination. In the experiments 

 of M. Saussure, the quantity of oxygen con- 

 sumed by various plants during their germina- 

 tion varied very considerably in amount. 

 Wheat and barley, weight for weight, con- 

 sumed less oxygen than peas ; and peas less 

 than beans and kidney-beans. The oxygen 

 consumed by wheat and barley amounts to be- 

 tween T(J V n th and j^Vnth of their weight, while 

 that consumed by beans and kidney-beans may 

 amount to ,,V,th part of their weight. The 

 oxygen absorbed by the seed is in all proba- 

 bility combined with the carbon of the plant, 

 and emitted during its germination, in the 

 state of carbonic acid gas. This gas is com- 

 posed entirely of carbon and oxygen, in the 

 proportion of 6-12 parts of the former and 16 

 of the latter ; and the quantity of it emitted is 

 exactly equal in amount to the quantity of oxy- 

 ppn ftbaortwd by the seed that should unite 

 with the carbon of the plant, to form the car- 

 bonic acid gas, and a certain quantity of carbon 

 is always lost by the seed during vegetation. 



When once a plant has vegetated, its growth 

 proceeds with more or less rapidity ; none that 

 I am aware of remain stationary; indeed, it 

 cannot remain stationary, and live. They in- 

 crease in size, require a supply of various sub- 

 stances as food, and the examination of the 

 nature of this nutriment constitutes one of the 

 most valuable branches of organic chemistry; 

 for under this head are included the assistance 

 afforded to plants by the gases, the /r/As,and by 

 water. In the examination of the food of plants 

 will also be illustrated the important questions 

 of rotation, of fertilizers, and of various other 

 important questions, which in this work will 

 be found treated of under their respective 

 heads ; and it will be useless to repeat what I 

 have there at some length endeavoured to illus- 

 trate. That the atmosphere yields its carbon 

 and its oxygen ; the soil its silica, alumina, and 

 magnesia, with various saline matters ; and that 

 water yields both hydrogen and oxygen for the 

 service of the plant, is pretty well established 

 by many valuable experiments which I have 

 there <jiven : and it is impossible to observe 

 the results of the analysis of a perfect plant 

 without being struck with the number of its 

 ingredients, and perceiving at once the proba- 

 ble sources from whence it drew its supply,. 

 Take, for instance, the analysis by M. Cadet 

 of the solid matters or ashes of the common 

 garlic. From 172 parts of these he obtain- 

 ed of 



109 



Potash 



Sulphate and muriate of potash 

 Alumina - 

 Phosphate of lime - 

 Oxide of iron - 



Magnesia 



Lime ------ 



Silica- - 



141-1 



All these substances, there is little doubt, 

 were absorbed by the plant from soil in which 

 it grew ; but in the fresh or unburnt garlic 

 these are combined with about eight times 

 their weight of mucilage, albumen, sulphur, 

 vegetable fibre, and water. Now the three 

 first of these must have been formed during 

 the growth of the plant, from either the atmo- 

 sphere or from water : the first (the atmosphere) 

 being composed of oxygen, nitrogen, and car 

 bonic acid ; and the latter (water) of hydrogen 

 and oxygen. Mucilage was found by M. Ber 

 zelius to be composed of 



Parti. 



Oxygen 51 -306 



Carbon 41-906 



Hydrogen ----- 6-788 



100- 



Albumen contains, according to the analysis 

 of MM. Gay Lussac and Thenard, 



Pads. 



Carbon ----.- 52883 



Oxygen ------ 28-872 



Hydrogen 7-540 



Nitrogen 15705 



100- 



The same excellent chemists have shown 

 woody fibre to be composed of 



Oxygen - 



Carbon 



Hydrogen 



Parts. 

 4225 



5-75 



100- 



The chief vegetable matters of the garlic, there- 

 fore, the student will remark (and the same 

 conclusion applies to other vegetables), are 

 composed entirely of two or three principal 

 ingredients. The composition of all plants is, 

 in fact, much more similar than is commonly 

 supposed. For instance, all the vegetable acids, 

 such as vinegar (acetic acid), sugar, gum, 

 starch, woody fibre, &c., are composed of three 

 substances, viz., carbon, oxygen, and hydrogen, 

 arranged in different proportions, as may be 

 seen from the following table : 



The decomposition of vegetable substances. All 

 dead vegetable substances, when left to them- 

 selves, under favourable circumstances, speedi- 

 ly decay, or decompose, and are resolved into 

 their constituents. This is commonly effected 

 in two ways, either by fermentation or by putre- 

 4D 865 



