4.42 M. I5ECQUEREL ON CHEMICAL EFFECTS OF VOLTAIC ACTION. 



copper is substituted. The extremity a', whicli is still the positive pole, 

 attracts the oxygen and the nitric acid : the latter decomposes the sul- 

 phite and takes possession of the base; the sulphurous acid is carried 

 to the oxide of copper, which is formed at the same time, and combines 

 with it : the sulphite of copper itself combines with the sulphite of pot- 

 ash, whence there results a compound that crystallizes in beautiful octa- 

 hedrons; but as the nitric acid still continues to arrive, it decomposes 

 this double sulphite at last : sulphurous acid gas then escapes, and the 

 sulphite of potash is transformed into bisulphite and nitrate of potash. 

 As to the sulphite of copper, it is precipitated in transparent octahedral 

 crystals, of a vivid red, with the brilliancy of garnets. M. Chevreul, 

 a long time since, obtained this sulphite of copper by the ordinary 

 processes of chemistry. We might extend the number of the results yet 

 further, but the object we have had in view, which was to communicate 

 the description of an apparatus of very general applicability, seems to us 

 to be sufficiently attained. 



Notes communicated by Goldlng Bird, Esq. 



Potter's-clay, p. 417, last line but two. 



M. Becquerel invariably uses clay as a medium for forming a connection between two fluids when 

 their mutual reaction is necessary, but he gives a very requisite caution that the clay must be care- 

 fully tempered with water or a saline solution ; for if too dry, it will not allow the transfer of elec- 

 tric currents with sufficient facility ; and if too racist, it admits of the admixture of the two fluids, 

 which (as when the tube curved like the letter U is used) it is intended to separate. Thence it has 

 not unfrequently happened, that many of the experiments described by M. Becquerel have failed in 

 the hands of some who have repeated them, merely from inattention to the clay being in a suffi- 

 ciently moist or dry state. All these difficulties, which although apparently trifling are nevertheless 

 occasionally fatal to the success of experiments, may be obviated by substituting plaster of Paris 

 for the potter's-clay ; for by merely mixing it with water or a saline solution, it may be readily 

 poured into a tube of any required form, where it rapidly solidifies, and while in this state is suffi- 

 ciently porous to admit of a very slow admixture of the two fluids employed, as well as to allow of 

 the ready transfer of the feeblest voltaic current. 



V. *22. Crystallixation qf Protoxide of Copper. 



The crystals obtained by the process here described by M. Becq\ierel are exceedingly distinct, and 

 very closely resemble some of the native forms of the oxide or ruby copper ore. This i)rotoxide is 

 generally found native, mixed with crystals of metallic copper ; and by availing ourselves of a very 

 weak electric current, kept up for some weeks, an exceedingly close imitation of this native com- 

 bination may be obtained. For this purpose take a glass tube open at both ends, about half an inch 

 in diameter and three inches in length : close one end of this tube by means of a plug of pkister of 

 Paris, about one-third of an inch in thickness; fill this tube with a solution of the niirate or chlo- 

 ride of copper moderately diluted, and place it inside a cylindrical glass vessel nearly filled with a 

 weak solution of potassa or soda. These two fluids, very slowly mixing through the plug of plaster 

 of Paris, would, if left to themselves, cause a gradual formation and deposition of hydrated deutoxidc 

 of copper. Make a compound arc of two pieces of metal, one of copper, the other of lead, taking care 

 that their surfaces are quite clean, or even polished ; plunge the leaden leg of the arc into the outer 

 cylinder of the little apparatus, and the copper leg into the smaller one, containing the solution of 

 nitrate or chloride of copper, and leave the apparatus to itself. Slow electric action ensues ; the copper 

 limb of the arc becoming the negative, and the lead (which slowly dissolves in the alkaline solution) 

 the positive electrode ; the electric currents thus set in motion readily traverse the plaster of Paris 

 partition, and cause the reduction of the deutoxide of copper (precipitated by the slow admixture of 

 the alkaline solution with the copper salt) partly to the metallic state and partly to the state of prot- 

 oxide. That portion of the peroxide which is thus reduced to the metallic state yields very fine and 

 tolerably large crystals, which are of course deposited on the surface of the copper negative electrode. 

 Mixed with these crystals, the protoxide is deposited in very delicate, transparent, ruby-red crystals, 

 not isolated and separate, but deposited in rosette-like patches, which present under a lensan exceed- 

 ingly beautiful appearance. So closely do some of the specimens of protoxide and metallic copper 

 thus obtained resemble the native forms, that it would be difficult, if not impossible, even for an ex- 

 perienced eye to distinguish the native from the factitious specimens, if the nature of the substance 

 they are precipitated on did not betray their origin. 



P. 425. Crystallization of Oxide of Zh)e. 



This oxide may be obtained much more conveniently by the use of the apparatus contrived for the 

 crystallization of the ruby oxide of copper (vide la»t note) with the substitution of a solution of oxide 

 of zinc in caustic potassa for the uncombined alkali, in the larger vessel. By this arrangement, the 

 copper leg of the arc becomes, as before, the negative, and the leaden the positive plate of a miniature 

 battery, sufficient however to cause a very elegant deposition of oxide of zinc on the plate of lead 

 or positive electrode in the course of a week or ten days; whilst upon the copper plate or negative 

 electrode a mixed deposit of metallic copper and ruby-coloured protoxide takes place, rivaling in 

 beauty that obtained by the last-described process. By this modification of the appar.itu5, the two 

 oxides (zinc and copper) may be obtained crystallized by one and the same operation. 



