Q. _Why is the miner in DANGER, if the gas ignites and burns in the INSIDE of the safety-lamp?_

A. Because the heat of the burning gas will soon _destroy the wire gauze_, and then the flame (being free) will set fire to the mine.

CHAPTER XXI.

PHOSPHURETTED HYDROGEN GAS.

Q. _From what does the very OFFENSIVE EFFLUVIA of CHURCH-YARDS arise?_

A. From a gas called PHOSPHURETTED HYDROGEN; which is _phosphorus_ combined with _hydrogen gas_.

Q. _What is PHOSPHORUS?_

A. A pale amber-coloured substance, resembling wax in appearance. The word is derived from two Greek words, which mean "_to produce or carry light_." ([Greek: phos-pherein]).

Q. _How is PHOSPHORUS OBTAINED?_

A. By heating bones to a white heat; by which means the animal matter and charcoal are _consumed_, and what is left is called "_phosphate of lime_."

Q. _How is PHOSPHATE OF LIME converted into PHOSPHORUS?_

A. It is reduced to _powder_, and mixed with _sulphuric acid_; which (being heated and filtered) is converted into _phosphorus_.

Q. _Of what are LUCIFER MATCHES made?_

A. Of phosphorus; and above 250 thousand lbs. of phosphorus are used every year in London alone, merely for the manufacture of lucifer matches.

Q. _Why does a PUTREFYING dead BODY SMELL so offensively?_

A. From the _phosphuretted hydrogen gas_, which always arises from putrefying animal substances.

The escape of _ammonia_ and _sulphur_ contributes also to this offensive effluvia.

Q. _What is the cause of the IGNIS FATUUS, Jack o'Lantern, or Will o'the Wisp?_

A. This luminous appearance (which haunts meadows, bogs, and marshes) arises from the _gas of putrefying animal and vegetable substances_; especially decaying fish.

Q. _What gases arise from these PUTREFYING substances?_

A. _Phosphuretted hydrogen gas_ from putrefying _animal_ substances: and

_Carburetted hydrogen_, (or inflammable gas) from fermenting _vegetable_ matters.

Some persons erroneously think that the AURORA BOREALIS, or Northern Lights, may be attributed to the same gases, burning in the upper regions of the air.

Q. _How are these gases IGNITED on bogs and meadows?_

A. By the electricity of the air, the rays of the sun, some accidental spark, the lamp of some traveller, or in some similar way.

And sometimes from the spontaneous combustion of some dung-heaps, &c. in the locality.

Q. _Why does an ignis fatuus or Will o'the Wisp FLY from us when we RUN to MEET it?_

A. When we run _towards_ an ignis fatuus, we produce a current of air, which drives the light gas _forwards_.

Q. _Why does an ignis fatuus run AFTER us, when we FLEE from it in fright?_

A. When we run _away_ from the ignis fatuus, we produce a current in the way we run, which _attracts_ the light inflammable gas in the _same course_.

Q. _Is not a kind of Jack o'Lantern sometimes produced by an INSECT?_

A. Yes; a swarm of luminous insects sometimes pa.s.ses over a meadow, and produces an appearance exactly like that of the ignis fatuus.

Q. _May this meteoric appearance be attributed to any OTHER cause, besides those mentioned?_

A. Yes; if many horses, sheep, pigs, or oxen, are pastured on a meadow, the _animal vapour_ arising from them (strongly electrified by the air) _will ignite_, and produce a luminous appearance.

Q. _May not many GHOST stories have risen from some ignis fatuus lurking about church-yards?_

A. Perhaps _all_ the ghost stories (which deserve any credit at all) have arisen from the ignited gas of church-yards lurking about the tombs, to which _fear_ has added its own creations.

CHAPTER XXII.

WIND.