4] 8 M. BECQUEREL ON CHEMICAL DECOMPOSITION AND 



each of the platina wires, the end of a wire of that metal is attached, on 

 which the experiment is to be made. The plate in contact with the al- 

 kali receives the negative electricity which disengages itself in its re- 

 action on the water, or the solution of the nitrate or the chloride, while 

 the plate in the acid receives the positive electricity which escapes dur- 

 ing the same reaction. We thus obtain a permanent pile if we only 

 take care to close the vessels so as to prevent evaporation and the action 

 of the air on the alkali. By plunging several plates of platina into the 

 jars we may act on several sets of apparatus at the same time. 



Water may also be substituted for potash, and a copper wire plunged 

 into each vessel. We then obtain a chemical action, and an electric cur- 

 rent (from the copper to the acid) sufficiently strong to produce decom- 

 positions similar to those already mentioned. 



It cannot be doubted that, in the electro-chemical decompositions 

 produced by means of currents proceeding from an electricity of low 

 tension, the oxygen and the acid take the direction of the positive pole, 

 an they do in the decompositions effected by means of a pile formed of 

 several elements. The wire communicating with the negative pole is 

 visibly covered with metal, but it cannot always be seen that the oxygen 

 and the acid are transferred to the positive pole. In such eases they 

 have formed an insoluble compound. 



We have likewise already shown that when two silver wires, both in 

 communication with the decomposing apparatus, were plunged into a 

 solution of nitrate of copper, the positive end became perceptibly dim- 

 med, while the negative end retained its metallic brilliancy, thoiigh no 

 trace of metallic copper could be perceived on its surface. This is to 

 be explained either by supposing that the copper, as will sometimes hap- 

 pen when an insoluble compound can be formed, has remained in the so- 

 lution, (and in this case there has been no transfer of the elements of the 

 nitrate although it has been decomposed,) or that the deposit on the ne- 

 gative end is so slight as to be imperceptible. 



Let us now take two small glass vessels of a cylindrical form, the one 

 containing a solution of nitrate of barytes, and the other a solution of 

 sulphate of copper. We establish the communication between these 

 solutions by means of a bent tube, small in diameter, and containing pot- 

 ters' clay moistened with a weak solution of sea salt, in order that the 

 transfer of the electricity may be effected with ease. Into the sulphate 

 we plunge the copper wire which corresponds with the negative side of 

 the apparatus, and the other wire, into the nitrate of barytes. It is evi- 

 dent that if the sulphuric acid goes to the positive pole, it will, in pass- 

 ing through the solution of nitrate, combine with the barytes and form 

 a precipitate. 



Now the following is what actually takes place : after the experiment 

 has been continued for four or five hours, the negative end is covered 



