382 Intelligence and Miscellaneous Articles. 



is proved by the fact of its being totally prevented by the addition of 

 a small quantity of lime-water, or of calcined magnesia. And that it 

 is not an effect of galvanism, is proved by its being prevented or im- 

 mediately arrested by the same means. It is equally certain from the 

 same facts, that the relatively large quantity of metal has no influence 

 upon the result : this is further quite obvious from the fact that the 

 water is decomposed, however small the quantity of the iron, if the 

 agency of carbonic acid be conjoined with that of this metal. 



" The decomposition of water by the contact of iron, has indeed, in 

 every instance, depended upon the concealed agency of carbonic acid 

 contained in the water, or united to a portion of the oxide of the 

 metal. This decomposition has been effected more slowly or more 

 rapidly, according as the quantity of the acid has been smaller or 

 greater. There is a most marked difference in the rapidity with which 

 the water is decomposed, between a portion of distilled water which 

 has been boiled for a short time, and another portion which has been 

 simply charged with air exspired from the lungs, into each of which 

 precisely the same quantity of iron has been put. And in every case 

 the decomposition of the water has been prevented or arrested by 

 withdrawing the influence of the carbonic acid altogether. — In some 

 of my experiments, especially in those in which I had taken the greatest 

 pains to expel the air from the water by long boiling, and to exclude 

 it afterwards, I waited several months before I observed the slightest 

 evolution of hydrogen gas, which however eventually took place in all 

 cases in which the agency of the carbonic acid was not entirely ex- 

 cluded." 



CONDUCTING POWER OF METALS FOR ELECTRICITY. 



The following are the results of M. Pouillet's researches on this sub- 

 ject, and are highly interesting, especially as regards the effects of 

 alloys on the metals ; for even small quantities of foreign substances 

 exert great influence on the conducting power. The purity of the silver 

 is expressed by the proportion of pure silver, per cent., present in the 

 alloy ; the column of figures represents the conducting power. 



Silver of 986 860 Brass 194 



Copper 738 Iron 121 



Silver of 948 656 Gold 18 car. fine ..109 • 



Fine gold 622 Platina 100 



Silver of 80 569 



M. Pouillet finds, 1. That the conducting power is very exactly 

 proportional to the section of the wires from the smallest diameter to 

 that of three lines. 2. That it is in the inverse ratio, not of the length 

 of the wire, but of the length increased by a constant quantity A. This 

 quantity A, unchangeable for various lengths of the same wire, changes 

 with the nature of the metal, and for each metal is in the inverse ratio 

 of the section of the wire. M. Pouillet therefore believes that the con- 

 ductibility is truly in the inverse ratio of the length of the wires, pro- 

 vided that the resistance opposed to the electricity in traversing the 

 fluid in the cells of the trough and different conductors which carry it 

 to the experimental wire, could be taken into account. — Bull. Univ. 

 Institution Journal. 



CONDUCTING 



