Chemical Science. 391 



be rolled round the zinc, or if the latter be studded with pieces of 

 platina, then the quantity of gas evolved principally from the platina 

 is much more than from the zinc alone. 



Now, tlu! action upon the alloyed zinc appears to be quite analo- 

 gous to the action upon the voltaic circle formed above by the zinc and 

 platina. The small chemical action which takes place on pure zinc 

 determines an electric current between each molecule of zinc, and 

 the molecule of other metal in contact with it. These currents de- 

 compose the water which they traverse, according to the well-known 

 laws of voltaic decomposition evolving the hydrogen upon the 

 heterogeneous molecule, which is negative in all the alloys and com- 

 binations mentioned, and carrying the oxygen to the zinc, which is 

 positive, and, combining with it, it forms first an oxide and then a sul- 

 phate, which dissolves. This decomposition of water, and conse- 

 quently the quantity of hydrogen evolved, will be greater as the minute 

 currents of electricity are stronger, and these will be stronger as the 

 acid increases in conducting power. Now it has been found experi- 

 mentally that the acid mixture which conducts best, evolves most gas 

 in a given time. 



The decomposition of water should, in this mode of viewing the 

 question, also increase with the difference between the oxidability 

 of the zinc and the other metal. The iron zinc has, however, in these 

 experiments, surpassed the copper zinc, although the two latter metals 

 form a more powerful voltaic arrangement ; but then two circum- 

 stances affect the result. The energy of the current depends much 

 upon the facility with which it can pass from the negative metal to 

 the fluid in contact ; and it has been ascertained that this passage takes 

 place to the acid from the iron, much more readily than from the cop- 

 per. On the other hand, the copper zinc exerts always a stronger action 

 at first than afterwards stronger, indeed, sometimes than iron zinc ; 

 but then the intensity of its voltaic action causes decomposition of 

 part of the zinc salt in solution, oxide is deposited upon the particles 

 of copper, and, forming the crust before spoken of, diminishes very 

 importantly its voltaic action. The same effect occurs with distilled 

 zinc, furnished with platina wires. 



From all these considerations, there appears to be no reason to 

 doubt that the striking difference between pure zinc and zinc of com- 

 merce, when put into dilute sulphuric acid, is due to the presence of 

 heterogeneous substances in the latter. By analysis, ordinary zinc 

 is usually found to contain traces of copper, tin, lead, and rather 

 more than a hundredth of iron ; and, on extending the experiments 

 with the zinc alloys, it was found that 2 per cent, of iron filings, 

 added to distilled zinc, was sufficient to render it as active in acid as 

 ordinary zinc. 



The elevation of temperature resulting from the chemical action of 

 the liquid upon these zincs, and which increases with the vivacity of 

 the action, is very probably due to the heating power of these nume- 

 rous electric currents. These currents are more powerful when most 

 gas is disengaged ; the heating power of the voltaic current is well 



