ducing no violent and sudden changes. The re- 
sults of its action are various and useful. This 
moderation is highly beneficial to the life of ani- 
mals and plants, which a too great energy of 
action would destroy. Water is a component 
part of the blood, and of milk; and it is an indis- 
pensable agent in both the structures and the 
food of the body. In its capacity of solvent, it 
carries into the animal frame the salts necessary 
for the secretions of living animal matter. It 
serves as a vehicle for the exhalations of the 
lungs and skin; and it is mixed with all the 
animal excretions. It acts the same beneficial 
part for vegetable as for animal life, being the 
vehicle of vegetable excretions and products; 
and is also an agent in the structure of plants. 
By its assistance flint and potash find their way 
into the structure of wheaten straw; by its aid 
the various other salts necessary to the structure 
of plants are absorbed. In vegetable matter, 
| starch exists in mechanical mixture with it, 
| gum and sugar are held in solution by it. In 
| grain, in the potato, in farinaceous plants, wa- 
ter exists in large proportions, as it does in every 
kind of fruit, and in every kind of wood, stalk, 
leaf. and flower. Water, in short, fertilises the 
surface of the earth; in its absence, no vegeta- 
tion could occur, no living thing exist. All 
organised nature requires it to sustain organism 
and life. Inorganic nature cannot do without 
it. Few liquids are free from water. Most of 
the fixed mineral acids contain it more or less; 
and it is a constituent of alcohol, even of ether. 
Solids also contain it. There is no crystallization 
of salts which is not due to water; deprived of 
it, the crystals fall to powder. Water likewise 
exists in almost all our appliances in domestic 
life. Without it we could not manufacture soap, 
nor paper, nor cloth, nor linen, nor leather, nor 
felt, nor china, nor earthenware, nor hardware, 
nor a variety of other matters of indispensable 
utility. Without it we should have neither wine, 
nor beer, nor ale, nor cider; for when not used 
artificially, it exists naturally in the fruits em- 
ployed to produce these beverages. Without it, 
we should often be suffocated; for it absorbs 
noxious gases, and many molecules of matter 
that would strangely affect the lungs of breath- 
ing creatures. 
Water at ordinary temperatures remains a 
liquid; at 32° Fahrenheit it hardens into ice; 
at 212° Fahrenheit it is converted into steam or 
vapour, quite invisible when not condensed by a 
colder medium, but generally visible in ordinary 
domestic boilings, because condensed by the 
colder air into which it emerges from the pot or 
tea-kettle. Although the temperature of water 
from ice just melted be precisely the same as that 
of the ice itself, namely, 32°,an amount of 140° 
more of insensible or specific heat, not indicated 
by the thermometer, must have been absorbed 
_by the water to maintain its liquid condition. 
If this heat could not be absorbed from the sur- 
WATER. 
ice-bound, that the strongest heat of summer 
rounding media, if the temperature of the air 
remained at 32°, no thaw could take place. Thus, 
a lump of ice at 22°, being 10° below the freez- 
ing point, placed in a room at the temperature of 
50°, would require, to melt. it, just fourteen times 
the number of minutes or hours that would raise 
it from 22° to 32°. If, for instance, ten minutes 
were occupied in bringing the lump of ice from 
22° to 32°, two hours and twenty minutes would 
be required to melt it into water at 32°. Thus, 
10° of heat having entered the ice in ten minutes, 
fourteen times that amount was necessary to 
liquify it without raising the temperature, and 
14 X 10=140. Dr Black suspended, side by side, 
two glass globes, of the same dimensions and ca- 
pacity, the one filled with water at 33°, the other 
with ice at 32°. In half an hour, the tempera- 
ture of the water had increased to 40°; but ten 
hours and a half elapsed before the ice was melt- 
ed and the temperature of the water resulting 
from it raised to 40°. Hence, if, in half an hour, 
the water was heated to 40°, and it required 
twenty one half-hours to heat the ice to the same 
temperature, the corollary deducible is that 7° 
of heat entered into the globes every half-hour. 
Thus, 7 X 21 = 147, from which we must sub- 
tract the 7° which the water reached above 33° 
Therefore, 7 X 21 = 147 —7 = 140°. Again, if 
a pound of ice pounded, at 32°, be mixed with a 
pound of water at 172°, the ice is immediately 
melted, and the result is two pounds of water at 
only 32°. Therefore, 140° have disappeared dur- 
ing the melting, being the exact quantity ab- 
sorbed by the melted ice at the expense of the 
heated water. If this absorption of heat had 
not taken place, the result would have been two 
pounds of water at a mean temperature of 102°. 
These facts explain the cause of the slowness 
with which the ice and snow melt when a thaw 
succeeds an intense frost. Days and even weeks 
sometimes intervene before the whole is liqui- 
fied. The same facts also account for the chilli- 
ness of the air during a thaw; the specific heat 
absorbed by the water from the melting ice is 
taken from the atmosphere at the expense of its © 
sensible temperature, to become latent or speci- 
fic; and therefore the air feels more cold and 
raw than before the thaw commenced. 
If water, in the process of cooling and solidify- 
ing, followed the ordinary laws of heat and expan- 
sion of liquids, its surface would contract, and 
become heavy in proportion to its contraction, 
and sink beneath the other layers; and these 
would successively replace it, so that the whole 
body would become gradually cooled to the freez- 
ing point, the lower stratum being always the 
coldest, and therefore the first to solidify or freeze. 
But, were this really the case, the bottom or un- | 
der surface of the fluid would freeze first, which 
is contrary to fact; also, every river would be- 
come so full of ice, each of its banks, as well as 
every sea-coast in our latitudes, would become so 
