26 
&teum Engine* 
5, To a saturated solution of sulphate of potash in wa- 
ter, or of any salt that is insoluble in alcohol, add an equal 
measure of alcohol. The alcohol, attracting the water 
more strongly than the salt retains it, precipitates the salt^ 
and considerable heat is producedi 
Caloric the Cause of Vapour, 
I. Every liquid^ when of the same degree of chemical 
purity^ andunder equal circumstances of atmospheric pres- 
sure^ has one peculiar point of temperature^ at which it 
invariably boils, — -Thus, pure water always boils at 212®, 
alcohol at 176, and ether at 98* Fahrenheit; and, when 
once brought to the boiling point, no liquid can be made 
hotter, however long the application of heat be continued. 
The boiling point of water may be readily ascertained, by 
immersing a thermometer in water boiling over the firCi 
As there is some danger in applying heat directly to a 
vessel containing either ether or alcohol, the ebullition of 
these fluids may be shown, by immersing the vessel con- 
taining them in water, the temperature of which may be 
gradually raised. The appearance of boiling is owing to 
the formation of vapour at the bottom of the vessel, and 
its escape through the heated fluid above it. That the 
steam, which escapes, is actually formed at the bottom, 
and not at the top of the water, may be seen by boiling 
some water in a Florence flask, or other transparent ves- 
sel, over an Argand’s lamp. The bubbles of vapour will 
ali -ascend from the bottom of the vessel. 
II. . Steani has exactly the same temperature as boiling 
wa/er.— Let a tin vessel be provided, having tw^o holes 
in its cover, one of which is just large enough to admit 
the stem of a thermometer. Fill it partly with water, and 
let the bulb of the thermometer be an inch or two above 
the surface of the water, leaving the other aperture open 
