Apropos to the general question behind these threads, J. C. Maxwell writes
in Chapter 1 of his treatise (para 34 and 35):
"The electrification of a body is therefore a physical quantity capable of
measurement . . . We therefore are entitled to use language fitted to deal
with electrification as a quantity as well as a quality, and to speak of
any electrified body as 'charged with a certain quantity of positive or
negative electricity.'
While admitting electricity, as we have now done, to the rank of a
physical quantity, we must not too hastily assume that it is, or is not, a
form of energy, or that it belongs to any known category of physical
quantities. All that we have hitherto proved is that it cannot be created
or annihilated, so that if the total quantity of electricity within a
closed surface is increased or diminished, the increase or diminution must
have passed in or out through the closed surface.
This is true of matter, and is expressed by the equation known as the
Equation of Continuity in Hydrodynamics.
It is not true of heat, for heat may be increased or diminished within a
closed surface, without passing in or out through the surface, by the
transformation of some other form of energy into heat, or of heat into
some other form of energy . . ."
This is only a taste - all physics teachers should have Maxwell's treatise
on their shelves and peruse it. It is available in 2 paperback volumes
from Dover - try Amazon.com.