56 EIGHTH REPORT — 1838. 



least does not appear in the distilled fluid until the formation of hypo- 

 nitrous ether has nearly or altogether ceased. 



5. That the production of aldehyd and oxalic acids are nearly si- 

 multaneous ; and that both these ap]:)ear to result from the secondary 

 action of nitric acid upon products formed in the eai-lier stages of the 

 operation. 



6. That the crystals long known as " les cristaux de Hierne" formed 

 when the distillation is protracted until red fumes appear, are oxalic 

 acid, notwithstanding their remarkable micaceous form ; and that the 

 " substance tres facile a charbonner" of Thenard is probably aldehyd, 

 which, from its behaviour witli alkalies, might apparently merit that 

 character. 



Notice respecting the Arlijicial Formation of a Bcmc Chloride of Cop- 

 per hj Voltaic Influence. By Golding Bird, M.D., S)-c. 



Becquerel has proved that a homogeneous metallic surface exposed 

 to the action of a given fluid will assume a state of electric tension, 

 provided that the fluid in Avhich it is immersed is of different degrees 

 of concentration in two different layers, so that the plate may become 

 unequally acted upon at two different points. The crystallization of 

 protoxide of copper by the immersion of a plate of that metal in a so- 

 lution of its nitrate, some of the black oxide being placed in the lower 

 part of the vessel, affords a familiar example of this circumstance. But 

 if the fluid remains homogeneous, quoad its degree of concentration, 

 no action, so far as electricity is concerned, ensues, unless one portion 

 of the metallic surface immersed is in a condition which enables it to be 

 more readily acted on than the other. This may be effected by partial 

 and superficial oxidation, by roughening or burnishing part of the me- 

 tallic surface, or by the induction of that peculiar passive state which 

 Schonbein has shown to exist in some metals under certain circum- 

 stances. 



If a plate of metallic copper is made the negative electrode of a single 

 pair, acting on a solution of copper, crystallization of the latter metal, 

 often in delicate, rosette-like patches, if the current is weak, ensues. 

 This deposition generally takes place at the lower part of the metallic 

 plate, leaving the upper one smooth and free from crystals. A plate 

 thus prepared is in a condition to assume two different electric states 

 on immersion in a homogeneous fluid, in consequence of the delicate 

 crystals of metallic copper undergoing oxidation more readily than the 

 smooth part of the plate. Such a piece of metal was immersed in a so- 

 lution of common salt during three months in a dark closet ; on ex- 

 amining the plate at the end of that time, the smooth portion, on which 

 no metallic crystals had been deposited, was found tarnished and covered 

 with blackish patches, without any perceptible roughening of the sur- 

 face. The lower portion of the same plate on whicli the copper had 

 crystallized had undergone a very interesting change, the metallic 

 crystals having become replaced by an infinite number of hemispheri- 



