Part 27 (1/2)
Any liquid which boils at a _lower_ degree can be made to boil if immersed in a liquid which boils at a higher degree. Thus a _cup of ether_ can be made to boil in a saucepan of _water_. A _cup of water_ in a saucepan of _brine or syrup_. But a _cup of water_ will _not_ boil if immersed in _ether_; nor a _cup of syrup_ in _water_.
Q. _Why are CLOUDS HIGHER on a FINE DAY?_
A. 1st--Because the _air_ (expanded by heat) _drives them higher up_: and
2ndly--The _clouds themselves are lighter_, and therefore _more buoyant_.
Q. _Why are the CLOUDS LIGHTER on a FINE DAY?_
A. Because their mists are either _absorbed by the dry air_, or _vapourized_ by the hot sun.
Q. _Why is a CUP PUT topsy-turvy into a FRUIT-PIE?_
A. Its princ.i.p.al use is to _hold the crust up_, and _prevent it from sinking_, when the cooked fruit gives away under it.
Q. _Does not the cup PREVENT the FRUIT of the pie from BOILING OVER?_
A. No, by no means; it would rather tend to _make it boil over_, than otherwise.
Q. _Why would the cup tend rather to MAKE the FRUIT BOIL OVER?_
A. As soon as the pie is put into the oven, the _air_ in the cup will _begin to expand_, and drive every particle of juice from under it; the pie dish, therefore, will have a cup-full _less room_ to hold its fruit, than if the cup were _taken out_.
Q. _If the juice is driven OUT of the cup, why is the CUP always FULL of JUICE, when the pie is cut up?_
A. Immediately the pie is drawn, the _air_ in the cup begins to _condense again_, and _occupy a smaller s.p.a.ce_; in consequence of which, there is no longer _enough air to fill the cup_, and so _juice_ rushes in _to fill up the deficiency_.
Q. _Why does JUICE rush into the cup, because the cup is NOT FULL of AIR?_
A. As the external air _presses upon the surface of the juice_, it rushes into the cup _un.o.bstructed_; as mercury rises through the tube of a barometer through similar pressure.
CHAPTER X.
EXPANSION FROM HEAT.
_(Continued.)_
Q. _Does heat expand every thing ELSE BESIDES air and water?_
A. Yes; _every_ thing (that man is acquainted with) is expanded by heat.