480 Mr. Grove on some Phcenomena of 
brilliant voltaic arc, while in hydrogen or a vacuum with the 
same power a feeble spark only is perceptible at the moment 
of disruption. Mercury on the other hand gives a tolerably 
brilliant spark in hydrogen, azote, or a vacuum, and one more 
nearly approaching to that which it gives in air. Thus in an 
oxidating medium there are three requisites for a brilliant 
discharge, viz. oxidability, volatility, and looseness of ag- 
gregation : in other media the two latter alone obtain; and the 
brilliant arc given by charcoal appears to depend principally 
upon the last; thus wood charcoal gives a larger and more 
diffuse flame than the carbon from gas retorts. 
In the following list the metals are arranged, as nearly as 
may be, in respect to the length and brilliancy of the arc 
they give in atmospheric air, the discharge being taken be- 
tween two points of the same metal : 
Potassium, 
Antimony, 
Sodium, 
Bismuth, 
Zinc, 
Copper, 
Mercury, 
Silver, 
Iron, 
Gold, 
Tin, 
Platinum. 
Lead, 
It has been noticed by Sir H. Davy, Dr. Hare, and Mr. 
Daniell, that a certain portion of matter is projected from the 
positive to the negative electrode: the quantity thus percepti- 
bly projected is indeed very small ; but I observed that when 
the discharge was taken in a close vessel the whole interior 
was lined with a pulverulent deposit, which if the vessel con- 
tained atmospheric air was an oxide of the metal employed, 
but if it contained azote or hydrogen was a reguline preci- 
pitate of the metal. Faraday’s researches have established, 
that in electrolysis a voltaic current can only pass by a de- 
rangement of the molecules of matter ; that the quantity of 
the current* which passes, is directly proportional to the 
atomic disturbance it occasions : he deduces from this that 
the quantity of electricity united with the atoms of bodies 
is as their equivalent numbers, or in other words, that the 
equivalent numbers of different bodies serve as the exponents 
of the comparative quantities of electricity associated with 
them. Now what takes place in the disruptive discharge? 
When we see the dazzling flame between the terminals of a 
voltaic battery, do we see electricity, or do we not rather see 
matter, detached, as Davy supposed, by the mysterious agency 
* However unpredicable the words quantity, current, &c. may be of an 
agent imponderable, and having no definite relation to space, these words 
express understood functions, and it seems impossible to devise others 
which would not be open to similar objections. 
