ct experiments with the calorimeter.

EMILY.

And is the result of this combustion, like that of sulphur, an acid?

MRS. B.

Yes; phosphoric acid. And had we duly proportioned the phosphorus and
the oxygen, they would have been completely converted into phosphoric
acid, weighing together, in this new state, exactly the sum of their
weights separately. The water would have ascended into the receiver, on
account of the vacuum formed, and would have filled it entirely. In this
case, as in the combustion of sulphur, the acid vapour formed is
absorbed and condensed in the water of the receiver. But when this
combustion is performed without any water or moisture being present, the
acid then appears in the form of concrete whitish flakes, which are,
however, extremely ready to melt upon the least admission of moisture.

EMILY.

Does phosphorus, in burning in atmospherical air, produce, like sulphur,
a weaker sort of the same acid?

MRS. B.

No: for it burns in atmospherical air, nearly at the same temperature as
in pure oxygen gas; and it is in both cases so strongly disposed to
combine with the oxygen, that the combustion is perfect, and the product
similar; only in atmospherical air, being less rapidly supplied with
oxygen, the process is performed in a slower manner.

CAROLINE.

But is there no method of acidifying phosphorus in a slighter manner, so
as to form _phosphorus_ acid?

MRS. B.

Yes, there is. When simply exposed to the atmosphere, phosphorus
undergoes a kind of slow combustion at any temperature above zero.

EMILY.

But is not the process in this case rather an oxydation than a
combustion? For if the oxygen is too slowly absorbed for a sensible
quantity of light and heat to be disengaged, it is not a true
combustion.

MRS. B.

The case is not as you suppose: a faint light is emitted which is very
discernible in the dark; but the heat evolved is not sufficiently strong
to be sensible: a whitish vapour arises from this combustion, which,
uniting with water, condenses into liquid phosphorus acid.

CAROLINE.

Is it not very singular that phosphorus should burn at so low a
temperature in atmospherical air, whilst it does not burn in pure oxygen
without the application of heat?

MRS. B.

So it at first appears. But this circumstance seems to be owing to the
nitrogen gas of the atmosphere. This gas dissolves small particles of
phosphorus, which being thus minutely divided and diffused in th