A quantity of nitrous gas was procured in a water apparatus, from
the decomposition of nitrous acid by mercury. A portion of it was
transferred to the mercurial trough. After the mercury and the jar
had been dried by bibulous paper, 40 measures of this portion were
agitated in a solution of sulphate of iron. The gas remaining after
the absorption was complete, filled about a measure and half; so that
the nitrous gas contained nearly ¹/₂₆ nitrogene.
Thermometer being 53°, a small piece of well-burnt charcoal, the
weight of which could hardly have equalled a quarter of a grain,
was introduced ignited, into a small cylinder filled with mercury,
graduated to,10 grain measures; to this, 16 measures, equal to 160
grain m. of nitrous gas, were admitted. An absorption of about one
measure and half took place. When the focus of a lens was thrown on the
charcoal, a slight increase of the gas was produced, from the emission
of that which had been absorbed.
After the process had been carried on for about a half an hour, the
charcoal evidently began to fume, and to consume very slowly, though no
alteration in the volume of the gas was observed.
The sun not constantly shining, the progress of the experiment was now
and then stopped: but taking the whole time, the focus could not have
been applied to it for less than four hours. When the process was
finished, the gas was increased in bulk nearly three quarters of a
measure.
A drop of water was introduced into the cylinder, by means of a small
glass tube, on the supposition that the carbonic acid, and nitrogene,
might be capable of holding in solution, more water than that contained
in the nitrous gas decomposed; but no alteration of volume took place.
When 20 grain measures of solution of pale green[100] sulphate of iron
were introduced into the cylinder, they became rather yellower than
before, but not dark at the edges, as is always the case when nitrous
gas is present. On agitation, a diminution of nearly half a measure was
produced, doubtless from the absorption of some of the carbonic acid by
the solution.
[100] That is, sulphate of iron containing oxide of iron, in the first
degree of oxygenation.
A small quantity of caustic potash, much more than was sufficient to
decompose the sulphate of iron, was now introduced. A rapid diminution
took place, and the gas remaining filled about 8 measures. This gas was
agitated for some time over water, but no absorption took place. Two
measures of it were then transferred into a detonating cylinder with
two measures of oxygene. The electric spark was puffed through them,
but no diminution was produced. Hence it was nitrogene, mingled with no
ascertainable quantity of hydrogene: consequently little or no water
could have been decomposed in the process.
Now supposing, for the greater ease of calculation, each of the
measures employed, cubic inches.
16 of nitrous gas—¹/₂₆ = 15,4 were decomposed, and these weigh, making
the necessary corrections, 5,2; but 7,4 nitrogene were produced, and
these weigh about 2,2. So that reasoning from the relative specific
gravities of nitrous gas and nitrogene, 5,2 grains of nitrous gas will
be composed of 3 oxygene, and 2,2 nitrogene.
But 8,7 of carbonic acid were produced, which weigh 4,1 grains, and
consist of 2,9 oxygene, and 1,2 charcoal.[101] Consequently, drawing
conclusions from the quantity of carbonic acid formed, 5,2 grains of
nitrous gas will consist of 2,9 oxygene, and 2,3 nitrogene.
[101] That is, carbon, or oxide of diamond.
The difference in these estimations is much less than could have been
expected; and taking the mean proportions, it would be inferred from
them, that 100 grains of nitrous gas, contain 56,5 oxygene, and 43,5
nitrogene.
I repeated this experiment with results not very different, except that
the increase of volume was rather greater, and that more unabsorbable
gas remained; which probably depended on the decomposition of a minute
quantity of water, that had adhered to the charcoal in passing through
the mercury.
As nitrous gas is decomposable into nitrous acid, and nitrogene, by the
electric spark; it occurred to me, that a certain quantity of nitrous
acid might have been possibly produced, in the experiments on the
decomposition of nitrous gas, by the intensely ignited charcoal. To
ascertain this circumstance, I introduced into 12 measures of nitrous
gas, a small piece of charcoal which had been just reddened. The sun
being very bright, the focus of the lens was kept on it for rather more
than an hour and quarter. In the middle of the process it began to fume
and to sparkle, as if in combustion. In three quarters of an hour, the
gas was increased rather more than half a measure; but no alteration of
volume took place afterwards.
The mercury was not white on the top as is usually the case when
nitrous acid is produced. On introducing into the cylinder a little
pale green sulphate of iron, and then adding prussiate of potash, a
white precipitate only was produced. Now, if the minutest quantity
of nitric acid had been formed, it would have been decomposed by the
pale green oxide of iron, and hence, a visible quantity of prussian
blue[102] produced, as will be fully explained hereafter.
[102] That is, blue prussiate of iron.