ASSIMILATION OF HYDROGEN. 



which have the power to separate them- 

 selves from one another, in innumerable 

 processes, in a manner imperceptible to our 

 senses ; while carbonic acid, on the contrary, 

 is only decomposable by violent chemical 

 action. 



Most vegetable structures contain hydro- 

 gen in the form of water, which can be sepa- 

 rated as such, and replaced by other bodies ; 

 but the hydrogen which is essential to their 

 constitution caunot possibly exist in the state 

 of water. 



All the hydrogen necessary for the forma- 

 tion of an organic compound is supplied to 

 a plant by the decomposition of water. The 

 process of assimilation, in its most simple 

 form, consists in the extraction of hydrogen 

 from water, and carbon from carbonic acid, 

 in consequence of which, either all the oxy- 

 gen of the water and carbonic acid is sepa- 

 rated, as in the formation of caoutchouc, the 

 volatile oils which contain no oxygen, and 

 other similar substances, or only a part of it 

 is exhaled. 



The known composition of the organic 

 compounds most generally present in vege- 

 tables, enables us to state in definite propor- 

 tions the quantity of oxygen separated during 

 their formation. 



36 eq. carbonic acid and") 



22 eq. hydrogen derived >= Woody Fibra, 

 from 22 eq. water. J 



with the separation of 72 eq. oxygen. 

 36 eq. carbonic acid and") 



S6 eq. hydrogen derived >= Sugar, 

 from 36 eq. water 



with the separation of 72 eq. oxygen. 

 36 eq. carbonic acid and") 



30 eq. hydrogen derived >= Starch, 

 from 30 eq. water J 



with the separation of 72 eq. oxygen. 

 36 eq. carbonic acid and^ 



16 eq. hydrogen derived >= Tannic Acid, 

 from 16 eq. water 3 



with the separation of 64 eq. oxygen. 

 36 eq. carbonic acid and") 



18 eq. hydrogen derived >= Tartaric Acid, 

 from 18 eq. water J 



with the separation of 45 eq. oxygen. 

 36 eq. carbonic acid and") 



18 eq. hydrogen derived >= Malic Acid, 

 from 18 eq. water 3 



with the separation of 54 eq. oxygen. 

 36 eq. carbonic acid and} 

 24 eq. hydrogen derived > = Oil of Turpentine. 

 from 24 eq. water ) 



with the separation of 84 eq. oxygen. 



It will readily be perceived that the for- 

 mation of the acids is accompanied with the 

 smallest separation of oxygen ; that the 

 amount of oxygen set free increases with the 

 production of the so-named neutral sub- 

 stances, and reaches its maximum in the 

 formation of the oils. Fruits remain acid 

 in cold summers ; while the most numerous 

 trees under the tropics are those which pro- 

 duce oils, caoutchouc, fcnd other substances 

 containing very little oxygen. The action 

 of sunshine and influence of heat upon the 

 ripening of fruit is thus, in a certain mea- 

 sure, represented by the numbers above 

 cited 



The green resinous principle of the leaf 

 diminishes in quantity, while oxygen is ah* 

 sorbed, when fruits are ripened in the dark ; 

 red and yellow colouring matters are formed ; 

 tartaric, citric, and tannic acids disappear, 

 and are replaced by sugar, amylin, or gum. 

 6 eq. Tartaric Acid, by absorbing 6 eq. 

 oxygen from the air, form Grape Sugar, 

 with the separation of 12 eq. carbonic acid. 

 1 eq. Tannic Acid, by absorbing 8 eq. oxy- 

 gen from the air, and 4 eq. water, form 1 

 eq. of Amylin, or starch, with separation of 

 6 eq. carbonic acid. 



We can explain, in a similar manner, tne 

 formation of all the component substances 

 of plants which contain no nitrogen, whether 

 they are produced from carbonic acid and 

 water, with separation of oxygen, or by the 

 conversion of one substance into the other, 

 by the assimilation of oxygen and separation 

 of carbonic acid. We do not know in what 

 form the production of these constituents 

 takes place ; in this respect, the representa- 

 tion of their formation which we have given 

 must not be received in an absolute sense, 

 it being intended only to render the nature 

 of the process more capable of apprehension ; 

 but it must not be forgotten, that if the con- 

 version of tartaric acid into sugar, in grapes, 

 be considered as a fact, it must take place 

 under all circumstances in the same propor- 

 tions. 



The vital process in plants is, with refer- 

 ence to the point we have been considering, 

 the very reverse of the chemical processes 

 engaged in the formation of salts. Carbonic 

 acid, zinc, and water, when brought into 

 contact, act upon one another, and hydrogen 

 is separated, while a white pulverulent 

 compound is formed, which contains car- 

 bonic acid, zinc, and the oxygen of the 

 water. A living plant represents the zinc 

 in this process : but the process of assimila- 

 tion gives rise to compounds, which contain 

 the elements of carbonic acid and the hydro- 

 gen of water, whilst oxygen is separated. 



Decay has been described above as the 

 great operation of nature, by which that 

 oxygen, which was assimilated by plants 

 during life, is again returned to the atmo- 

 sphere. During the progress of growth, 

 plants appropriate carbon in the form of car- 

 bonic acid, and hydrogen from the decom- 

 position of water, the oxygen of which is 

 set free, together with a part of all that con- 

 tained in the carbonic acid. In the process 

 of putrefaction, a quantity of water, exactly 

 corresponding to that of tb.e hydrogen, is 

 again formed by extraction of oxygen from 

 the air; while all the oxygen of the organic 

 matter is returned to the atmosphere in the 

 form of carbonic acid. Vegetable matters 

 can emit carbonic acid, during their decay, 

 only in proportion to the quantity of oxygen 

 which they contain; acids, therefore, yield 

 more carbonic acid than neutral compounds ; 

 while fatty acids, resin, and wax, do not 

 putrefy ; they remain in the soil without any 

 apparent change. 



B2 



