140 ' ROTATION OF CROPS. 



Every part and constituent of the body is obtained from plants. 

 By the organism of the plants, are formed those compounds which 

 serve for the formation of the blood ; there can be no doubt that 



or malic acid would result. By the separation of 9 equivalents of oxygen, 

 tartaric acid would be produced ; the separation of 12 equivalents would 

 produce malic acid. 



Hydrated oxalic acid C i 2 H 6 O 2 < — 9 =C 1 2 H 6 1 5 =3 Eq. tartaric acid. 

 " " Ci<jH 6 2 4— 0, 2 =Ci 2 H 6 1 2=3Eq. malic acid. 



By the simple separation of water from the elements of malic acid citrio 

 acid is produced ; we know that we can produce, by means of heat, aco- 

 nitic acid from citric acid, and fumaric acid, or maleic acid, from malic 

 acid. 



Malic acid Ci 2 H 6 12 — HO=Ci 2 H 5 Oi i=3 Eq. citric acid. 

 " Ci 2 H 6 Oi 2 — 3 HO=:Ci 2 H 8 9 =3 Eq. fumaric acid. 



Now we can view tartaric, citric, and malic acids as compounds of 

 oxalic acid with sugar, with gum, with woody fibre, or with the elements 

 of these : 



Tartaric Acid. Oxalic Acid. Dry Sugar of Grapes. 



2(C l2 H 6 13 ) = C l2 18 + C 12 H l2 O l2 

 In such a manner, therefore, that the addition of new quantities of hydro- 

 gen would enable all these acids to aid in the formation of sugar, starch, 

 and gum. When this conversion is effected the alkalies in union with 

 the acids must of course be liberated, and they will thus be rendered capa- 

 ble of playing anew the same part. According to this view, it is quite 

 conceivable that one equivalent of an alkali may enable 10, 20, or 100 

 equivalents of carbon to pass into constituents of a plant; but the time 

 necessary to effect the transformation will vary according to the amount 

 of base present. 



If a perennial evergreen, by the help of a certain quantity of alkali, is 

 able to assimilate a certain amount of carbon during the whole year, it will 

 be necessary to convey to a summer plant four times the quantity of alknli, 

 in order to enable it to assimilate the same amount of carbon in one-fourth 

 the time. 



Gay-Lussac first observed that by the contact of an alkali, at a high tem- 

 perature, with tartaric, citric, and oxalic acids, or sugar, woody fibre, &c, 

 these substances were reconverted into carbonic acid. 



This mode of decomposition is quite the reverse of that which takes 

 place in plants In the latter the elements of water unite with the com- 

 pound of carbon (carbonic acid); and oxalic acid, tartaric acid, &c, are 

 thus produced, in consequence of a separation or ox tgen. But in 

 the chemical process referred to, the elements of the water unite with the 

 elements of oxalic and tartaric acids, &c, and they are reconverted into 

 carbonic acid, in consequence of a separation of hydrogen. 



Without the development of any gas, tartaric and citric acids, in contact 

 with alkali, even at a temperature of 400° F., are decomposed into oxalic 



