AGRICULTURAL CHEMISTRY. 



75 



AGRICULTURAL CHEMISTRY. I 



(Continued from p. 64.) 



* And when one of them is acted on by 

 sealing-wax, and the other by glass that 

 has been rubbed by woolen, they attract 

 each other ; hence it is said, that bodies 

 similarly electrified repel each other, and 

 bodies dissimilarly electrified attract each 

 other : and the electricity of glass is call- 

 ed vitrious or jjositive electricity, and that 

 of sealing-wax resinous or negative elec- 

 tricity. 



When of two bodies made to rub each 

 other one is found positively electrified, 

 the other is always found negatively elec- 

 trified, and, as in the common electrical 

 machine, these states are capable of being 

 communicated to metals placed upon rods 

 or pillars of glass. 



Electricity is produced likewise by the 

 contact of bodies ; thus a piece of zinc 

 and of silver give a slight electrical shock 

 when they are made to touch each other, 

 and to touch the tongue: and when a 

 number of plates of copper and zinc, one 

 hundred for instance, are arranged in a 

 pile with cloths moistened in salt and 

 water, in the order of zinc, copper, mois- 

 tened cloth, zinc, copper, cloth, and so on, 

 they form an electrical battery which will 

 give strong shocks and sparks, and which 

 is possessed of remarkable chemical pow- 

 ers. The luminous phenomena produced 

 by common electricity are well known. 

 It would be improper to dwell upon the^n 

 in this place. They are the most impres- 

 sive effects occasioned by this agent, and 

 they offer illustrations of lightning and 

 thunder. 



Electrical changes are constantly taking 

 place in nature, on the surface of the 

 earth and in the atmosphere ; but as yet 

 the effects of this power in vegetation have 

 not been correctly estimated. It has been 

 shown by experiments made by means of 

 the voltaic battery (the instrument com- 

 posed of zinc, copper and water) that 

 compound bodies in general are capable 

 of being decomposed by electrical powers, 

 and it is probable, that the various elecri- 

 cal phenomena occuring in our system, 

 must influence both the germination of 

 seeds and the growth of plants. I found 

 that corn sprouted much more rapidly in 

 water positively electrified by the voltaic 

 instrument than water negatively electri- 



fied ; and experiments made upon the 

 atmosphere show that clouds arc usually 

 negative ; and as when a cloud is in one 

 state of electricity the surface of the earth 

 beneath is brought into the opposite state, 

 it is probable that in common cases the 

 surface of the earth is positive. 



Different opinions are entertained 

 amongst scientific men respecting the 

 nature of electricity ; by some the phe- 

 nomena are conceived to depend upon a 

 single subtile fluid in excess in bodies said 

 to be positively electrified, in deficiency 

 in the bodies said to be negatively electri- 

 fied. A second class suppose the effects 

 to be produced by two different fluids, 

 called by them the vitrious fluid and the 

 resinous fluid, and others regard them as 

 affections or motions of matter, or an ex- 

 hibition of attractive powers, similar to 

 those which produce chemical combina- 

 tion and decomposition ; but usually ex- 

 erting their action on masses. 



The different powers that have been 

 thus generally described, continually act 

 upon common matter so as to change its 

 form and produce arrangements fitted for 

 the purposes of life. Bodies are either 

 simple or compound. A body is said to 

 be simple when it is capable of being 

 resolved into any other forms of matter. 

 Thus gold, and silver, though they may 

 be melted by heat or dissolved in cor- 

 rosive menstrua, j-et are recovered un- 

 changed in their properties, and they are 

 said to be simple bodies. 



A body is considered as compound, 

 when two or more distinct substances are 

 capable of being produced from it ; thus 

 marble is a compound body for by a strong 

 heat it is converted into lime, and an 

 elastic fluid is disengaged in the process ; 

 and the proof of our knowledge of the 

 true composition of a body is, that it is 

 capable of being reproduced by the same 

 substances as those into which it had been 

 decomposed ; thus by exposing lime for 

 a long while to the elastic fluid, disengag- 

 ed during its calcination, it becomes con- 

 verted into a substance similar to pow- 

 dered marble. The term element has the 

 same meaning as simple or undccom- 

 pounded body ; but it is applied merely 

 with reference to the present state of 

 chemical knowledge. "It is probable that 

 as yet we are not acquainted with any of 



