boys’ department. 
193 
ISogs’ JB^artment. 
AGRICULTURAL CHEMISTRY—No. 3. 
Boys, in my last letter I told you that the essen¬ 
tial constituents of the atmosphere were oxygen, 
nitrogen, carbonic acid, ammonia, and watery vapor. 
These were all particularly described, except the 
last, and this I told you was a compound of oxy¬ 
gen and hydrogen, the two gases that form water. 
Hydrogen derives its name from two Greek words 
which signify generator of water. It is sixteen 
times lighter than oxygen, and fourteen times 
lighter than atmospheric air, and on this account it 
is often used for charging air balloons. These, 
when filled with hydrogen, rise on the same princi¬ 
ple as smoke in air, a cork in water, or a leaden 
bullet in quicksilver. 
Hydrogen is an inflammable gas, and burns with 
a blue flame, as you may observe in the lower part 
of the blaze of a candle. When ignited, it unites 
with a portion of the oxygen of the atmosphere, 
and the parts, thus combined, form water. This 
combination is always in the proportion of one part , 
by weight, of hydrogen, with eight parts of oxygen, 
or two to one by volume, and if these two gases 
were united in any other proportion, they would 
not produce water. It will be well for you to re¬ 
member, that substances composed of the same ele¬ 
ments, but in different proportions, often have quite 
different, and sometimes quite opposite characters. 
The following is an instance of this sort:—Sugar 
and starch, although differing widely in their ap¬ 
pearance and general properties, are composed of 
precisely the same ingredients; namely, oxygen, 
hydrogen, and carbon; and the only difference is, 
that starch contains about one tenth less of hydro¬ 
gen and oxygen, than sugar. 
When hydrogen is burned, the water produced is 
chemically pure ; but it is never thus found in na¬ 
ture. You know that water has the power of dis¬ 
solving common salt, and many other substances, 
when brought in contact with them; and as there 
are always soluble substances in the soil, the water 
of springs and brooks must hold some of them in 
solution ; consequently, the water of every spring, 
or rivulet, will be influenced by the soluble ingre¬ 
dients contained in the earth where it is located. 
But, you wi*ll now ask, is the water which falls 
from the clouds, chemically pure ’? Rain water is, 
indeed, much purer than spring water, and on this 
account, it has a more insipid taste; yet it is not 
chemically pure. You recollect I told you, when 
speaking of the ammonia of the atmosphere, that it 
was very soluble in water; therefore, it is always 
present in rain water. Carbonic acid is also 
brought from the air by every shower, as well as a 
portion of the air itself. You perceive, then, that 
water is capable of dissolving the ingredients of the 
air, as well as those of the soil, and you will here¬ 
after learn in what manner vegetable existence is 
benefited by this solvent action. You are aware 
that spring and well water is sometimes said to be 
hard; that is, when it will not form a lather, or 
swds, with soap. This is owing to its containing a 
portion of sulphate of lime (plaster of Paris), 
which it has extracted from the earth, and which 
forms, with soap, an insoluble chemical compound. 
Another peculiarity of water, is, that it sometimes 
forms incrustations, such as you may have observ¬ 
ed on the inner surface of tea-kettles, which have 
been some time in use. This is formed chiefly by 
carbonate of lime (carbonic acid and lime combin¬ 
ed), and may be accounted for as follows :—The 
more carbonic acid water contains, the greater 
quantity of carbonate of lime it will dissolve. 
When water is heated, carbonic acid is driven from 
it, and consequently, the carbonate of lime, which 
was held in solution by this acid, falls to the bot¬ 
tom, and adheres to the vessel, forming in time, a 
thick scale, of crust. 
You are now sufficiently acquainted with the 
chemical properties of water. I will, however, 
while on this subject, explain a few more properties 
belonging to it, as matters of curiosity, and as use¬ 
ful additions to your stock of general knowledge. 
Steam, produced from water, by heat, fills a space 
about 1,700 times greater than the water from which 
it was formed, and is about half as heavy as the same 
volume, or bulk of air. This wonderful expansion 
has been taken advantage of for propelling ma¬ 
chinery, and you may form some idea of its mighty 
force, from its power of setting steamboats, loco¬ 
motives, &c., in motion. 
Water, at the level of the sea, boils when raised 
to the temperature of 212°, and in an open vessel, 
no additional heat can raise its temperature above 
this point, (a) When passing into a gaseous state 
(that is, steam or vapor), it absorbs a large portion 
of heat, which remains in the vapor until it is again 
condensed into water. You may have noticed, that, 
when the ground is covered with snow, the air al¬ 
ways feels chilly, although the sun may shine very 
pleasantly. This chilliness is caused by the ab¬ 
sorption of heat while the snow is melting and 
evaporating; and in like manner, heat is absorbed 
and given out by all other substances, when pass¬ 
ing from one state, or condition, to another. This 
general property of bodies may be thus explained : 
When a body is passing from a denser (thicker), to a 
rarer (thinner), state , heat is absorbed ; and when 
passing from a rarer to a denser state , heat is evolv¬ 
ed (given out). The reason why the weather 
moderates during a snow storm, is, because the heat 
contained in the vapor is liberated, and given to the 
air, when the vapor condenses into snow. This 
principle also proves (what every sensible and ob¬ 
serving person is well aware of), that there is more 
economy in using dry wood, than green, for fuel. 
The latter usually contains nearly one third its 
weight of water, which, while the wood is burning, 
must be converted into steam. A cord of green 
wood is estimated to contain, generally, about 170 
gallons of water; therefore, when burned in this 
state, as much heat is lost— absolutely lost —as 
would be carried away in the steam from the same 
quantity of water, if it were boiled away in kettles ! 
Were it not for this heat-absorbing power of va¬ 
por the warmth of summer would be insupportable, 
and every change of atmospheric temperature 
would be a source of misery. The following ex¬ 
planation will convince you of the truthfulness of 
this assertion. You know that, when ether, or al¬ 
cohol, is dropped on the hand, a sensation of cold 
