266 
THE CULTIVATOR. 
Sept, 
become converted into the substance of the plant. The 
leaves of plants have a peculiar function, namely, that 
of separating the carbonic acid from the other constitu¬ 
ents of the atmosphere, of retaining the carbon of this 
carbonic acid, and setting its other ingredient, the 
oxygen, free. After the sap has thus been mixed in the 
leaves, with the carbon which the leaves derive from 
the atmosphere, it goes to increase the growth of the 
plant. The water taken up by the root undergoes a 
somewhat similar decomposition, its hydrogen being 
retained and its oxygen liberated. 
In some of the products of plants, such as turpentine, 
all the oxygen of the water and carbonic acid have been 
liberated. 
Oxygen is chiefly remarkable as a most powerful 
Supporter of combustion; it is the substance which in 
natural operations, consumes and burns up all vegetable 
«imd animal matter. It is this oxygen which, by its action 
upon the carbon and hydrogen of our wood, coal, oil, 
&c., produces that light and heat which we feel to be 
so necessary. It is oxygen which causes this candle to 
burn at the present moment; if deprived of oxygen it 
would be extinguished; but if the supply be augmented 
its brilliancy will be much increased. I will immerse 
the lighted candle in this jar of oxygen. In a moment 
you see the flame becomes brilliant, and burns with so 
much splendor as to dazzle the eyes. 
A similar increase in the intensity of the action is 
seen, when other combustible substances, such as sul¬ 
phur and phosphorus, previously ignited in the air, are 
brought into contact with pure oxygen gas. 
Iron, zinc, and other metals will burn in oxygen 
with great ease, as I shall have occasion to show you 
towards the close of the lecture. It will not be diffi¬ 
cult for you to understand why chemical action or 
combustion should be so much more intense in pure 
oxygen than in air. In the pure oxygen there is 
nothing to prevent the intimate contact of the two 
bodies which are uniting with one another, that is, the 
burning body and the oxygen; and as fast as one portion 
of oxygen has acted on the combustible body, its place 
is supplied by another portion, which in its turn will be 
wholly expended on the burning body. In common 
air this is different. Before the combustible body can 
be acted upon by one cubic inch of oxygen, five cubic 
inches of the atmosphere must be presented to it, which 
of course will take up five times the time. But the 
four cubic inches of nitrogen have also the effect of 
cooling the burning body in passing through the flame 
with the oxygen. The amount of light and heat pro¬ 
duced depends on the quantity of chemical action which 
takes place in a given time. It is quite evident that 
the greatest action in the least time will take place with 
the pure materials. If we, by any artificial means, can 
contrive to make common air pass in large quantities 
through the interstices of combustible bodies, as char¬ 
coal, coal, &c. } previously in a state of ignition, we 
shall in a measure increase the action as if we employed 
pure oxygen, because we shall cause a greater action in 
a given period of time. 
It must now be apparent to all of you that the more 
oxygen we can get through a common fire place, or 
the more that can be brought in contact with the fuel 
in a given time, the greater will be the combustion, and 
the greater the heat. In the open air coals burn dull, 
and do not give out much heat or light in a given time. 
If coals be put in a fire place, more air gets through 
them in a given time, and a great heat will be pro¬ 
duced; but then the coals will burn sooner. If you 
want to get more heat you must enclose the coals in a 
furnace connected with a high chimney, so that all the air 
is obliged to pass into the furnace through the bars at 
the bottom. You will thus have in the chimney a col¬ 
umn of hot air, which is lighter than cold air. The 
cold heavy air will therefore force upwards the light 
air of the chimney and endeavor to supply its place; 
and as the air can only get into the chimney by passing 
through the furnace, a large quantity of oxygen is in 
this way supplied to the fuel in a short time. But 
though you get more heat in a given time, you consume 
more coals. I will give you another instance: The 
common blacksmith’s forge, where, I have no doubt, 
you have often seen the workmen blow the bellows till 
they were almost tired. The object is to send a greater 
amount of air, (that is to say, to send more oxygen) 
among the coals, and by this means to produce a greater 
amount of heat in a given time; but in proportion to 
the rapid production of this heat will be the quantity of 
coals consumed. Now there is one fact in connection 
with this which you will do well to note. A pound of 
charcoal, in uniting with oxygen, gives out always the 
same amount of heat whether burnt quickly or slowly; 
and the same may be said of hydrogen and other combus¬ 
tibles; and whether the union be quick or slow, or whe¬ 
ther a given amount of fuel be consumed in five 
minutes or five hours, the sum total of heat evolved 
will be the same. But it is evident that if the fuel be 
wholly consumed in five minutes, the heat in this case 
will be very intense during its short continuance; but 
if it last five hours, the heat will not be intense, but low 
and continuous. 
Now, wherever oxygen is absorbed, that is, when it 
comes into union with another substance, heat is given 
out. I will give you an instance where common vege¬ 
table matter will ignite spontaneously, merely from the 
fact of its being brought in contact and unioh with oxy¬ 
gen. If we take a pound or two of cotton, and mix it 
with linseed oil or olive oil, (the best is boiled linseed 
oil,) and then lay it in a corner, the mixture will be on 
fire in twenty-four hours. The cotton exposes a great 
surface of the oil to the action of the oxygen of the 
air; and is at the same time from its porous nature, 
a bad conductor of heat. Very well; the oxygen and 
oil begin to act on one another; a little of the car¬ 
bon and hydrogen of the oil is slowly consumed, and 
a small quantity of heat is generated, which slightly 
raises the temperature of the whole mass; for the non¬ 
conducting nature of the cotton will not allow the heat 
to escape as it is produced. More oxygen acts on the 
oil, more heat is given out, and this goes on till the 
whole gets to a red heat; light is evolved, and the mass 
is set fire to. 
In the north of England, where a deal of oil is used 
in machinery, and where it is cleaned by waste cotton, 
many mills were at one time burned down from the 
cause I have mentioned. The dirty oiled cotton waste 
was thrown into a corner on Saturday night, and the 
mill was burned down before Monday; and it was fre¬ 
quently believed to be the work of an incendiary. 
Persons have been blamed for the crime; while the 
real cause was that which I am now telling you. The 
manufacturers are now more cautious, and take care not 
to allow the oily waste cotton to accumulate. 
Agriculturists are liable to accidents of a similar kind. 
How much money has heen lost from the storing of hay 
in a wet state instead of in a dry! Wet operates like 
oil; it enables the oxygen to get hold of the woody 
matter of the hay upon which it does not act in the dry. 
The hay is stacked in a great hurry, without being 
properly dried. Being damp and porous, the oxygen is 
absorbed, and a little heat given out, which cannot 
readily escape; a little more oxygen is absorbed, and a 
little more heat given out, till a red heat is attained, 
and then fire breaks out. Now the difference between 
the oil and the cotton, and the damp hay is only this; 
that in the first case the fire breaks out in a few hours, 
(from twelve to twenty-four will be sufficient,) while 
in the stack four or five days or weeks may sometimes 
be required. 
I can show you another case. When farmers want to 
make manure, they heap up great masses of straw, 
litter, and excx-ements; and what takes place! It be¬ 
gins to smoke and gets heated. And where does the 
heat come from; how is it generated? The mass de¬ 
creases in bulk very much ; in eight or ten months it will 
have diminished at least half. But what is the cause? 
Don’t you see this? The active and energetic oxygen 
is at work. You have vegetable matter moistened with 
water, you have oxygen absorbed, and it consumes the 
dung; but more slowly than in the case of the hav. I 
told you that hay may take fire in four or five weeks; 
