These consequences are in perfect accordance with the results already obtained from observing the time necessary to convert a given quantity of water into steam by the application of heat. From the present result it follows, that in the reduction of a given quantity of steam to water it parts with as much heat as is sufficient to raise 5-1/2 cubic inches from 32° to 212°, that is, 5-1/2 times 180° or 990°.
(21.) There is an effect produced in this process to which it is material that we should attend. The steam which filled the space of 1728 cubic inches shrinks when reconverted into water into the dimensions of 1 cubic inch. It therefore leaves 1727 cubic inches of the vessel it contains unoccupied. By this property steam is rendered instrumental in the formation of a vacuum.
By allowing steam to circulate through a vessel, the air may be expelled from it, and its place filled by steam. If the vessel be then closed and cooled the steam will be reduced to water, and, falling in drops on the bottom and sides of the vessel, the space which it filled will become a _vacuum_. This may be easily established by experiment. Let a long glass tube be provided with a hollow ball at one end, and having the other end open.[5] Let a small quantity of spirits be poured in at the open end, and placing the glass ball over the flame of a lamp, let the spirits be boiled. After some time the steam will be observed to issue copiously from the open end of the tube which is presented upwards. When this takes place, let the tube be inverted, and its open end plunged in a basin of cold water. The heat being thus removed, the cool air will reconvert the steam in the tube into liquid, and a vacuum will be produced, into which the pressure of the atmosphere on the surface of the water in the basin will force the water through the tube, and it will rush up with considerable force, and fill the glass ball.
[Footnote 5: A common glass flask with a long neck will answer the purpose.]
In this experiment it is better to use spirits than water, because they boil at a lower heat, and expose the glass to less liability to break, and also the tube may more easily be handled.
Futility of early claims. -- Watt, the real Inventor. -- Hero of Alexandria. -- Blasco Garay. -- Solomon de Caus. -- Giovanni Branca. -- Marquis of Worcester. -- Sir Samuel Morland. -- Denis Papin. -- Thomas Savery.