ELECTRICAL EXCITEMENT BY STEAM, OIL, ETC. 
27 
boiler positive, but their power appeared to be reduced : increase of the force of steam, 
as in all other cases, would, there is little doubt, have exalted it again. When alkali 
was in the steam-globe, oil and resin lost very much of their power, and oil of turpen- 
tine very little. This fact will be important hereafter (2126.). 
2122. We have seen that the action of such bodies as oil introduced into the jet of 
steam changed its power (2108.), but it was only by experiment we could tell whether 
this change was to such an extent as to alter the electricity for few or many of the 
bodies against which the steam stream rubbed. With olive oil in the box C, all the 
insulated cones before enumerated (2097-) were made positive. With acetic acid in 
the steam-globe all were made neutral (2091.). With resin in the box C (2113.), all 
the substances in the former list (2099.) were made positive, there was not one ex- 
ception. 
2123. The remarkable power of oil, oil of turpentine, resin, &c., when in very small 
quantity, to change the exciting power of water, though as regards some of them 
(2112.) they are inactive without it, will excuse a few theoretical observations upon 
their mode of action. In the first place it appears that steam alone cannot by friction 
excite the electricity, but that the minute globules of water which it carries with it 
being swept over, rubbed upon and torn from the rubbed body (2085.) excite it and 
are excited, just as when the hand is passed over a rod of shell-lac. When olive oil 
or oil of turpentine is present, these globules are, I believe, virtually converted into 
globules of these bodies, and it is no longer water, but the new fluids which are 
rubbing the rubbed bodies. 
2124. The reasons for this view are the following. If a splinter of wood dipped in 
olive oil or oil of turpentine touch the surface of water, a pellicle of the former instantly 
darts and spreads over the surface of the latter. Hence it is pretty certain that 
every globule of water passing through the boxC, containing olive oil or oil of turpen- 
tine. will have a pellicle over it. Again, if a metal, wooden, or other balance-pan be 
well cleaned and wetted with water, and then put on the surface of clean water in a 
dish, and the other pan be loaded until almost, but not quite able to pull the first pan 
from the water, it will give a rough measure of the cohesive force of the water. If 
now the oily splinter of wood touch any part of the clean surface of the water in the 
dish, not only will it spread over the whole surface, but cause the pan to separate 
from the water, and if the pan be put down again, the water in the dish will no longer 
be able to retain it. Hence it is evident that the oil facilitates the separation of the 
water into parts by a mechanical force not otherwise sufficient, and invests these 
parts with a film of its own substance. 
2125. All this must take place to a great extent in the steam passage: the parti- 
cles of water there must be covered each with a film of oil. The tenuity of this film 
is no objection to the supposition, for the action of excitement is without doubt at 
