152 



Dr. Andrews on the Properties of Voltaic Circles. 



both attain such a temperature that they dissolve with the greatest possible rapi- 

 dity when the difference will undergo a diminution. 



The effect of the distance of the platina and zinc plates from each other in 

 the acid was next investigated. 



Two couples of platina and zinc, similar in every respect, except that in the 

 one, the zinc plate and platina were in contact, and in the other, at the distance 

 of .1 inch, were introduced into sulphuric acid, at the temperature of 225° cent. 

 The quantity of zinc dissolved in the first couple was to that dissolved in the 

 second as 1.587 : 1. When the distances between the platina and zinc were 

 .1 and .5 inch respectively, the quantities of zinc dissolved were as 1.441 : 1. 

 The temperature in this case was 230°. The galvanometer needle was also 

 more strongly deflected when the metals were near each other. The action of 

 the acid on the zinc therefore increases with the proximity of the platina, as in 

 common voltaic circles. This is further shown by the parts of the surface of 

 the zinc which are nearest the platina dissolving most rapidly. 



Next the distance between the platina and zinc plates being the same, the 

 extent of the platina surface in each couple was varied. The results obtained 

 are exhibited in the following table, in which the second column shows the dis- 

 tance between the platina and zinc in the acid; the third, the extent of the 

 platina surface in each couple referred to that of the zinc as unit ; the fourth, 

 the ratio of the platina surfaces to each other ; the fifth, the ratio of the quan- 

 tities of zinc dissolved with the respective platina surfaces ; and the sixth, the 

 temperature. 



Although the variations in the extent of the platina surfaces, both when 

 compared to each other and to the surface of the zinc, are very considerable, yet 

 the quantities of zinc dissolved present only slight differences, and do not appear 



