332 
BOILING OF LIQUIDS IN GLASS VESSELS. 
a metallic vessel the same liquid would boil precisely at 
212°, and in a glass vessel, in its usual condition, without 
any previous preparation, the boiling-point would be a 
little above 212°. In these cases the boiling-point of the 
liquid appears to have some relation to the condition of the 
surface of the containing vessel, and to be unconnected with 
the presence or absence of air in the liquid. 
There are other cases, as already shown, in which certain 
substances, dissolved or suspended in the liquid, occasion 
variations in the boiling-point as great as those noticed by 
Marcet. Some salts, and especially resins and oils, belong 
to this class ; and it is worthy of remark that the same sub- 
stance, shellac for instance, when spread over the surface 
of the glass, produces an effect the opposite of that which 
occurs when it is merely suspended in the liquid. In the 
one case the boiling point is reduced, while in the other it 
is raised to the extent of seven or eight degrees. But these 
variations, caused by the presence of substances dissolved 
or suspended in the liquid, do not occur in metallic vessels. 
The water containing shellac, which boils at 220° in a glass 
flask, if put into a metallic vessel will boil steadily at 212°, 
without the slightest tendency to bumping. Indeed, I have 
invariably found that liquids, the ebullition of which, in 
glass vessels, is accompanied by even the most violent 
bumping, present no such phenomenon when boiled in 
metallic vessels. 
The effects which I have observed in a great number of 
cases have suggested the probability of their being con- 
nected with the electrical condition of the liquid operated 
upon, and of the vessel containing it. It is not my purpose, 
however, on the present occasion, to enter into any details 
with the view of explaining the cause of these phenomena, 
but to describe the means by which their occurrence may 
be prevented, and, moreover to describe an arrangement of 
