608 



FARMERS' REGISTER, 



[No. II 



Parts. 

 3840 parts ofripe peas afford of starch - 1265 

 Fibrous matter analogous to starch, ? _ q.q 



with the coats of the peas - 5 



A substance analogous to jzluten 

 Mucilage - - ^ - - 249 



Saccharine matter - - - 81 



Albumen - - - - 66 



Volatile matter _ . . 540 



Earthy phosphates - - - 11 



Loss - - - - 229 



1000 parts of dry oak hark, from a small tree 

 deprived of epidermis, contain, 

 Of Woody Fibre - - - 876 



Tannin - - - - 57 



Extract - - - - 31 



Mucilage - - - - 18 



Matter rendered insoluble during J) 



evaporation, probably a mix-^ - 9 



ture of albumen and extract ) 

 Loss, partly saline matter - - 29 



To ascertain the primary elements of the differ- 

 ent vegetable principles, and tlie proportions in 

 which they are combined, different methods of 

 analysis have been adopted. The most simple 

 are their decomposition by heat, or their formation 

 into new products by combustion. 



When any vegetable principle is acted on by a 

 strong red heat, its elements become newly ar- 

 ranged. Such of them as are volatile are expelled 

 in the gaseous form ; and are either condensed as 

 fluids, or remain permanently elastic. The fixed 

 remainder is either carbonaceous, earthy, saline^ 

 alkaline, or metallic matter. 



To make correct experiments on the decompo- 

 sition of vegetable substances by heat, requires a 

 complicated apparatus, much time and labor, and 

 all the resources of the philosophical chemist; but 

 such results as are useful to the agriculturist may 

 be easily obtained. The apparatus necessary, is 

 a iireen glass retort, attached by cement to a re- 

 ceiver, connected with a tube passing under an 

 inverted jar of known capacity, filled with water.* 

 A given weight of the substance is to be heated 

 to redness, in the retort over a charcoal fire; the 

 receiver is to be kept cool, and the process conti- 

 nued as long as any elastic matter is generated. 

 The condensible fluids will collect in the receiver, 

 and the fixed residuum will be found in the retort. 

 The fluid products of the distillation of vegetable 

 substances are principally water, with some ace- 

 tous and mucous acids, and empyreumatic oil, or 

 tar, and in some cases ammonia. The gases 

 are carbonic acid gas, carbonic oxide, and car- 

 buretted hydrogen; sometimes with olefiant gas, 

 and hydrogen; and sometimes, but more rarely, 

 with azote. Carbonic acid is the only one of 

 those gases rapidly absorbed by water; the rest 

 are inflammable; olefiant gas burns with a bright 

 white light; carburet ted hydrogen with a light 

 hke wax; carbonic oxide with a feeble blue flame. 

 The properties of hydrogen and azote have been 

 described in the last lecture. The specific gravi- 

 ty of carbonic acid gas, is to that of air as 20.7, 

 to 13.7, and it consists of one proportion of carbon 

 11.4, and two of oxyget) 30. The specific gravi- 

 ty of gaseous oxide of carbon, is, taking the same 

 standard, 13.2, and it consists of one proportion of 

 carbon, and one of oxygen. 



• See Fig:. 14, 



The specific gravities of carburetted hydrogen 

 and olefiant gas, are respectively 8 and 13; both 

 contain four proportions of hydrogen; the first 

 contains one proportion, the second two propor- 

 tions of carbon. 



If the weight of the carbonaceous residuum be 

 added to the weight of the fluids condensed in the 

 receiver, and they be subtracted from the whole 

 weight of the substance, the remainder will be 

 the weight of the gaseous matter. 



The acetous and mucous acids, and the ammo- 

 nia formed, are usually in very small quantities; 

 and by comparing the proportions of water and 

 charcoal with the quantity of the gases, taking 

 into account their qualities, a general idea may 

 be formed of the composition of the substance. 

 The proportions of the elements in the greater 

 number of the vegetable substances which can be 

 used as food, have been already ascertained by 

 philosophical chemists, and have been stated in 

 the preceding pages; the analysis by distillation, 

 may, however, in some cases, be useful in esti- 

 mating the powers of manures, in a manner that 

 will be explained in a future lecture. 



The statements of the composition of vegetable 

 substances, quoted from MM. Gay Lussac and 

 Thenard, were obtained by these philosophers by 

 exposing the substances to the action of heated 

 chlorate of potassa; a body that consists of potas- 

 sium, chlorine, and oxygen; and which afforded 

 oxygen to the carbon and the hydrogen. Their 

 experiments were made in a peculiar apparatus, 

 and required great caution, and were of a very 

 delicate nature. It will not therefore be necessary 

 to enter upon any details of them. 



It is evident from the whole tenor of the state- 

 ments which have been made, that the most es- 

 sential vegetable substances consist of hydrogen, 

 carbon, and oxygen in difl'erent proportions, gene- 

 rally alone, but in some few cases combined with 

 azote. The acids, alkalies, eanhs, metallic oxides, 

 and saline compounds, though necessary in the 

 vegetable economy, must be considered as of less 

 importance, particularly in their relation to agri- 

 culture, than the other principles; and as it ap- 

 pears from M. de Saussure's table, and from other 

 experiments, they differ in the same species of ve- 

 getable when it is raised on difl'erent soils. 



MM. Gay Lussac and Thenard have deduced 

 three propositions, which they have called laiosy 

 from their experiments on vegetable substances. 

 The first is, "That a vegetable substance is al- 

 ways acid whenever the oxygen it contains is to 

 the hydrogen in a greater proportion than in 

 water." 



The third, '-That a vegetable substance is 

 neither acid nor resinous, but is either saccharine 

 or mucilaginous, or analogous to woody fibre or 

 starch, whenever the oxygen and hydrogen in it 

 are in the same proportions as in water." 



7'he second, "That a vegetable substance is 

 always resinous, or oily or spirituous, whenever it 

 contains oxygen in a smaller proportion to the 

 hydrogen than exists in vvater." 



New experiments upon other vegetable sub- 

 stances, besides those examined by MM. Gay 

 Lussac and Thenard, are required before these in- 

 teresting conclusions can be fully admitted. Their 

 researches establish, however, the close analogy 

 between several vegetable compounds differing in 

 their sensible qualities, and combined with those 



