54 



AGRICULTURAL 2HEMISTRY. 



those of a later period. The bones of hu- | belong to those which are termed fellow- 



man skulls found at Pompeii contain as 

 much fluoric acid as those of animals of a 

 former world, for if they be placed in a state 

 of powder in glass vessels, and digested 

 with sulphuric acid, the interior of the ves- 

 sel will, after twenty-four hours, be found 

 powerfully corroded (Liebig;) whilst the 

 bones and teeth of animals of the present 

 day contain only traces of it. (Berzelius.) 



De Saussure remarked that plants require 

 quantities of the component parts of soils in 

 different stages of their developement; an 

 observation of much importance in consider- 

 ing the growth of plants. Thus wheat 

 yielded 79-1000 of ashes a month before blos- 

 soming, 54-1000 while in blossom, and 

 33-1000 after the ripening of the seeds. It 

 is therefore evident that wheat, from the 

 time of its flowering, restores a part of its 

 organic constituents to the soil, although the 

 phosphate of magnesia remains in the seeds. 



The fallow-time, as we have already 

 shown, is that period of culture during 

 which land is exposed to a progressive dis- 

 integration by means of the influence of the 

 atmosphere, for the purpose of rendering a 

 certain quantity of alkalies capable of being 

 appropriated by plants. 



NOAV, it is evident, that the careful tilling 

 of fallow-land must increase and accelerate 

 this disintegration. For the purpose of agri- 

 culture, it is quite indifferent, whether the 

 land is covered with weeds, or with a plant 

 which does not abstract the potash inclosed 

 in it. Now many plants in the family of 

 the leguminosce are remarkable on account 

 of the small quantity of alkalies or salts in 

 general which they contain ; the Windsor 

 bean (ViciaFaba,} for example, contains no 

 free alkalies, and not one per cent, of the 

 phosphates of lime and magnesia. (Einhof.) 

 The bean of the kidney-bean (Phascolus 



contains only traces of salts. (Bra- 

 connut.) The stem of lucerne (Medicago 

 sativit) contains only 0.83 per cent., that of 

 the lentil (Ervum Lens) only 0.57 of phos- 

 phate of lime with albumen. (Crome.) 

 Buck- wheat dried in the sun yields only 

 0.681 per cent, of ashes, of which 0.09 parts 

 are soluble salts. (Zenneck.)* These plants 



* The small quantity of phosphates which th( 

 seeds of the lentils, beans, and peas contain, mus 

 be the cause of their small value as articles of nour 

 ishment, since they surpass all other vegetable fooc 

 in the quantity of nitrogen which enters into their 

 composition. " But as the component parts of the 

 bones (phosphate of lime and magnesia) are absent 

 they satisfy the appetite without increasing the 

 strength. The following is an analysis of lentil 

 (Playfair.) 6.092 grammes lost 0.972 grammes oi 

 water at 212. 0.566 grammes, burned with ox 

 ide of copper, gave 0.910 grammes carbonic acic 

 and 0.336 grammes of water. The lentils o: 

 combustion with oxide of copper, yielded a gas 

 in which the proportion of the nitrogen to the car 

 bonic acid was as 1 to 16. 



Carbon 44.45 



Hydro-en 6.59 



Nitrogen 6.42 



Water 15.95 



rops, and the cause wherefore they do not 

 xercise any injurious influence on corn 

 vhich is cultivated immediately after them 



that they do not extract the alkalies of 

 he soil, and only a very small quantity of 

 >hosphates. 



It is evident that two plants growing be- 



ide each other will mutually injure one 



mother, if they withdraw the same food 



rom the -soil. Hence it is riot surprising 



hat the wild chamomile (Matricaria Chamo- 



milla) and Scotch-broom (Spartium Scopa- 



rium) impede the growth of corn, when it 



considered that both yield from 7 to 7.43 

 >er cent, of ashes, which contain ^ of car- 

 >onate of potash. The darnel and the flea- 

 )ane (Erigeron acre) blossom and bear fruit 

 at the same time as com, so that when 

 growing mingled with it, they will partake 

 f the component parts of the soil, and in 

 proportion to the vigour of their growth, 

 hat of the corn must decrease; for what 

 one receives, the others are deprived of. 

 Plants will, on the contrary, thrive beside 

 each other, either when the substances 

 necessary for their growth which they ex- 

 tract from the soil are of different kinds, or 

 when they themselves are not both in the 

 same stages of developement at the same time. 



On a soil, for example, which contains 

 potash, both wheat and tobacco may be 

 reared in succession, because the latter plant 

 does not require phosphates, salts which are 

 invariably present in wheat, but requires 

 only alkalies, and food containing nitrogen. 



According to the analysis of Posselt and 

 Riemann, 10,000 parts of the leaves of the 

 tobacco-plant contain 16 parts of phosphate 

 of lime, 8.8 parts of silica, and no magnesia; 

 whilst an equal quantity of wheat straw 

 contains 47.3 parts, and the same quantity 

 of the grain of wheat 99.45 parts of phos- 

 phates. (De Saussure.) 



Now, if we suppose that the grain of 

 wheat is equal to half the weight of its 

 straw, then the quantity of phosphates ex- 

 tracted from a soil by the same weights of 

 wheat and tobacco must be as 97.7 : 16. 

 This difference is very considerable. The 

 roots of tobacco, as well as those of wheat, 

 extract the phosphates contained in the soil, 

 but they restore them again, because they 

 are not essentially necessary to the deve- 

 lopement of the plant. 



CHAPTER VIII. 



ON THE ALTERNATION OF CROPS. 



T has .ong since been found by experience, 

 that the growth of annual plants is rendered 

 imperfect, and their crops of fruit or herbs 

 less abundant, by cultivating them in suc- 

 cessive years on the same soil, and that, in 

 spite of the loss of time, a greater quantitv 

 of grain is obtained when a field is allowed 



