652 
CHAPTERS FOR STUDENTS. 
I 
3 6 6 
\ 
J 
the apparatus is plunged into boiling water. If each measured in the first in- 
stance 100 millimetres, a scale applied to the tube when it has been thoroughly- 
heated by the water, would indicate something like the following :— 
At Freezing Point. At Boiling Point. 
100 millims. iron become nearly 100$ 
,, „ mercury „ „ 102 
,, ,, air ,, ,, 137 
It is assumed that the containing tube itself undergoes no change ; in reality 
it becomes larger, but not visibly so. 
7. All solid bodies (with one or two exceptions) expand with rise of tempera¬ 
ture, and in growing larger generally do so more in one direction than in another, 
especially if possessed of “ structure,” as in the instances of wood and most 
crystals. 
All liquids, except water, expand upon the application of heat to them. But 
water near the temperature at which 
it crystallizes does not acknowledge the 
rule. This may be shown by having a 
bulb blown upon a tube and filling it 
with water. Upon plunging it into 
water in which some ice is floating, the 
height of liquid in the stem (1) will con¬ 
tinue to fall down (2, 3) to a certain 
point (4), where it will stop, and, as the 
0 temperature of the water continually 
goes down, will rise again steadily to 
another point (7), where it will remain 
fixed so long as the temperature is unaltered. 
If this water were cooled still further, it would freeze. The act of freezing 
or solidifying is accompanied by a still further increase in bulk. Ice is, there¬ 
fore, lighter than the coldest water, and floats in it. 
The great importance of this in nature is obvious :—If ice were heavier than 
water it would sink to the bottom of the sea and rivers, and there would be out 
of reach of the sun’s influence, so that, probably, all but the torrid zone would 
be eternal winter. 
8 . The influence of rise of temperature in gases is remarkable from its pro¬ 
ducing practically equal effects, as to volume, upon all of them. Further, if a 
gas be heated through any given range on a thermometric scale, it will dilate; 
and if, whilst in this state, its temperature is further raised by an accession of 
heat equal to the former, the new increase of volume will be in the same pro¬ 
portion as the former increase. 
If the tube in par. 6 had been plunged not into boiling water, but into a 
mixture of equal parts of ice-cold and boiling water, so that a temperature half¬ 
way between might be obtained, the length of the column of air would have 
increased not to 100 + 36 - 6, but to 100 -f 18‘3. So that by halving the in¬ 
crease of temperature, the proportion of bulk added is also halved. In a similar 
way, if we were to divide the increase of temperature by 100, the increase of 
volume would also be divided by 100. Upon the Centigrade thermometer the 
grange of temperature between the freezing and boiling points of water is di¬ 
vided into 100 equal “ degrees.” Referring again to our experimental tube :— 
Since the 100 millimetres of air at the lowest point become 136‘6 when at the 
highest point, they would become for one of these degrees (that is -pi^th of 
36*6 
the interval), 100 -j- 100'366. 
Generally, if one measure of air be taken at any temperature, it becomes 
^ = j B00366 when at a temperature one degree Centigrade hotter. 
