28 
Steam Engme. 
falls on the scale of the theirmometer. Thus on the sum^ 
mit of Mount Blanc, water was found by Saussure to boil 
at 187° Fahrenheit.^ 
The influence of a diminished pressure in facilitating 
ebullition, may be inferred also from the following very 
simple experiment : Place, over a lamp, a Florence flask, 
about three 4ths filled with water ; let it boil briskly 
during a few minutes ; and, immediately on removing it 
from the lamp, cork it tightly, and suddenly invert it. 
The water will now cease to boil ; but, on cooling the 
convex part of the flask by a stream of cold water, the 
boiling will be renewed. Applying boiling water from 
the spout of a tea-kettle to the same part of the flask, the 
water will again cease to boil. This renewal of the ebulli- 
tion, by the application of cold (an apparent paradox,) is 
owing to the formation of an imperfect vacuum, over the 
hot water, by the condensation of steam ; and the suspen- 
sion of the boiling, on re-applying the heat, to the renewed 
pressure on die surface of the hot water, occasioned by the 
formation of fresh steam. 
From these facts, it may be inferred, that the particles 
of caloric are mutually repulsive, and that they commu- 
nicate this repulsive tendency to other bodies in which ca- 
loric is contained. This repulsive power tends to change 
solids into fluids, and liquids into aeriform bodies, and is 
chiefly counteracted by the pressure of the atmosphere. 
Were this counteracting cause removed, many bodies, 
which at present have a liquid form, ivould cease to be 
such, and would be changed into a gaseous state. Pre- 
cisely the same effect, therefore, results from the preva- 
lence of either of these forces. Add to certain liquids a 
quantity of caloric, in other words, place them in a high 
* This furnishes one the means of measuring- the height o£ 
mountains. 
