134 
CHEMISTRY OF HORTICULTURE. 
substance so burnt. If ten grains of common charcoal be burnt in a jar containing pure 
oxygen, the product will be gaseous, and to all appearance the destruction will be complete 
(excepting that small portion of ash which results from impurity), but the gas (carbonic acid) 
produced will weigh more than did the pure charcoal in the first instance. Thus, if six 
grains of such charcoal be consumed, fourteen grains of carbonic acid will be formed. 
Again, if the combustible exposed to the action of oxygen gas be a metal — as for example 
a coil of iron wire of known weight, — the result will be an oxide of iron in its lowest or 
first condition of oxydation (a protoxide), and allowance being made for impurities and 
correction, twenty-eight grains of the iron will have acquired eight grains of oxygen, which 
can be collected and weighed. The reader must now recollect that the " combining 
number " of oxygen gas in the atomic theory, is always represented by 8, as that ofx 
hydrogen by 1, it being the unit upon which English chemists base their calculations of 
atomic weights ; and therefore, when one grain or one hundred pounds of hydrogen gas 
combine with eight grains or eight hundred pounds of oxygen gas, the representative 
number of the combined elements will be 9, or, in plainer terms, one of hydrogen and 
eight of oxygen will produce nine of water. The words "combine " and "combination," by no 
means imply a simple mixture of the two substances, but their absolute union by electro- 
chemical energy, effected by a slow, or more rapid and intense, combustion. Now, the former 
process is incessantly proceeding throughout nature, in the gradual combination of oxygen 
with combustible substances : thus, for instance, wood and vegetable substances gradually 
decaying, acquire varying tints, and a change and diminution of substance, till, finally, they 
disappear ; that is, have passed off as invisible vapours. Hence, the air we breathe always 
contains a very considerable quantity of carbonic acid. Iron, unprotected by paint or 
varnish, soon acquires a film of rust, which increases till at length the metal becomes corroded, 
and progressively acquires weight (as a peroxide) in the proportion of twelve parts of oxygen 
to twenty- eight of pure metallic iron. 
All nature abounds with phenomena transcendently and miraculously glorious. Not one 
particle of its entire substance ever is, was, or can be lost ; and the same broad assertion 
will apply to those ceaseless changes which result from attraction and combination 
throughout nature. 
The question now presents itself : What are those two gases, hydrogen and oxygen — 
what their individual, specific nature ? We meet with no satisfactory answer to this 
inquiry, and therefore must appeal to direct experiment. If we can imagine two quantities 
of the two gases to be contained in separate vessels — the hydrogen to be double that of the 
oxygen in volume — we obtain a correct idea of a simple mixture of those elements which, 
when chemically united, produce water. Let us, however, assume a form which may present 
a somewhat natural condition of the two elements, so situated as to permit the perfect 
union of the two to be effected with great facility. Every one knows that a moist film of 
soap can be formed into a spherical bubble at the bowl of a common tobacco-pipe. If two 
such bubbles,— one contaiiling any given quantity of hydrogen gas (say 12 cubical inches), 
and another just half the volume of oxygen gas (say 6 cubical inches) — be cautiously 
made to approach each other, the smallest spark of electricity will instantly ignite the two, 
and produce one volume of watery vapour. If the two gases be previously mixed in a 
bladder, a soap-bubble so formed will, in consequence of its increased levity ascend, and 
explode on contact with a lighted taper. Experiments of a similar character are frequently 
exhibited at public chemical lectures, where also the quantities are exactly measured, so as 
to leave no doubt of the actual results. A voltaic current of electricity decomposes water, 
but with great difficulty if the fluid be perfectly pure, and free from any decomposing 
vegetable or acid matter ; and Dr. Faraday has inferred that the quantity of water so de- 
composed, corresponds exactly with that of the electricity which passes ; he also states, that 
" one grain of water, acidulated to facilitate conduction, will require an electric current to 
be continued for 3| minutes of time to effect its decomposition ; which current must be 
powerful enough to retain a piatina wire, part of an inch in thickness, red hot in the 
air the whole time." — Researches, No. 859. 
Now, though it may be difficult to admit that the electricity which passes as a current, 
