220 



On the Decomposition of Water by Zinc. 



[Mar. 14, 







1 



T VJJ.. Ill LUU. ^ClllllliO. 



i 



i. 





ItO U 



9 



1 1 -4- 



93 6 



3,*4. 



10-0 



38-8 (X 2) 



5. 



o O 



zo u 



6. 



108 



21-0 



7. 



9-4 



171 



8. 



7-7 



12-3 



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 experiment 

 was repeated with water as free from oxygen as could be obtained by boil- 

 ing. 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 apparatus 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 boiling-point, when it gave off 93*4 cub. 

 centims. in ten minutes ; after another period of two days it gave 64" I 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 conjunction 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, 

 when 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 ascer- 

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

 tion of this hydrogen gas. Two thin plates of copper were taken, the one 



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

 been working in the same direction. 



