the Decomposition of Water by Zinc. 75 



The first action, therefore, was about five times as great as in the 

 case of the copper ; and it diminished more rapidly, doubtless through 

 the zinc becoming more quickly protected by oxide. 



Lest it might be contended that the free oxygen, usually present 

 in distilled water, had been the means of starting this action, the ex- 

 periment was repeated with water as free from oxygen as could be 

 obtained by boiling. One metre of the same zinc-foil, covered with 

 copper, was employed ; and the result was nearly as before, 40 cub. 

 centims. of gas being obtained the first day at the mean temperature 

 of 9^ C. This arrangement was taken advantage of to examine the 

 effect of a high temperature. Without removing the delivery-tube, 

 the contents of the flask were heated to near 100° C, when 123*5 

 cub. centims. of hydrogen were given off in ten minutes. The appa- 

 ratus was allowed to cool, with the mouth of the tube under water, 

 when the production of gas became small again ; and after two days 

 -it was again heated nearly to the boihng-point, when it gave off 93-4 

 cub. centims. in ten minutes ; after another period of two days it gave 

 64*1 cub. centims. and after three days more 132*1 cub. centims. in 

 the first thirty minutes, 108*4 in the second thirty minutes, 94*3 in 

 the third, and 89*9 in the fourth. 



Iron and lead, under similar circumstances, also decomposed pure 

 water ; and the action of magnesium was greatly increased by con- 

 junction with copper. The effect of the more negative metal was 

 the same as would have been produced by an increase of heat. 



In a practical point of view this experiment may serve as a ready 

 means of preparing pure hydrogen ; in a theoretical point of view, 

 its interest seems to lie in the fact that the dissociation of a binary 

 compound by means of two metals may take place at infinitesimally 

 short distances, v/hen it would not take place where the layer of 

 liquid is enough to offer resistance to the current — and also in the 

 correlation between this force and heat"^. 



P.S. March 14. — At the suggestion of Prof. Stokes, we tried to 

 ascertain if the well-known influence of points had much to do with 

 the separation of this hydrogen gas. Two thin plates of copper were 

 taken, the one smooth, the other rough with electrolytically-deposited 

 copper ; these were separated from thin plates of zinc merely by pieces 

 of muslin ; and the metals were folded over at each end and hammered 

 together. Each couple v/as placed in water ; and for some days very 

 minute bubbles of gas formed, but only at the junction of the metals, 

 and about equally in each case. 



As might be expected, this zinc in conjunction with copper is capable 

 of decomposing other liquids than water. Chloroform yields readily 

 to its power ; and iodide of ethyl, which Prof. Frankland decomposed 

 by zinc only at a great heat, is split up rapidly at the ordinary tem- 

 perature. 



* Since the above was written we have accidentally heard that Dr. W. Hiissell 

 has been working in the same direction. 



