Q. _Why are CRUCIBLES (in which acids are employed) made of PLAT'INUM?_

A. Because the acid would act upon _other metals_, or upon _gla.s.s_, and prevent the experimenter's success.

Q. _Which of the METALS have the GREATEST affinity to OXYGEN?_

A. Those called _pota.s.sium_ and _sodium_.

Pota.s.sium and sodium derive their names from potash and soda. Pota.s.sa is the oxide of pota.s.sium; and soda is the oxide of sodium.

Q. _How is the affinity of pota.s.sium and sodium for oxygen shewn?_

A. They _decompose water_ the moment they are brought into contact with it.

Q. _What effect has POTa.s.sIUM on WATER?_

A. It _catches fire_ the moment it is thrown into water, and burns with a vivid flame, which is still further increased by the combustion of _hydrogen_ separated from the water.

(N.B. Water is composed of oxygen and hydrogen; and pota.s.sium separates the two gases.)

Q. _What effect has SODIUM on WATER?_

A. It does _not take fire_ as pota.s.sium does, but undergoes very rapid _oxidation_.

Q. _Is the FURR of KETTLES an oxide?_

A. No; the furr (or deposit of boiling water) is a precipitate of _lime and mineral salt_, separated from the water by the process of boiling.

Q. _Is not this FURR of boiling water often DANGEROUS?_

A. Yes; especially in _tubular boilers_, such as those employed in railways.

Q. _Why is this FURR especially TROUBLESOME in RAILWAY engines?_

A. Because it is a _bad conductor of heat_; in consequence of which, it hinders the evaporating effect of the fire, and prevents the economy of fuel.

Q. _Why is this FURR especially DANGEROUS in RAILWAY engines?_

A. Because when it is deposited in the boilers, they are likely to become _over-heated_; and then _explosion_ will take place from the sudden generation of highly elastic steam.

Q. _Why cannot RAILWAY engines be fed with BRACKISH WATER?_

A. Because brackish water contains _mineral salt_, which makes a much larger deposit of furr, than that which contains _only vegetable matter_.

CHAPTER XIX.

CARBONIC ACID GAS.

Q. _What is CHOKE DAMP?_

A. _Carbonic acid gas_ acc.u.mulated at the bottom of wells and pits, which renders them noxious, and often fatal.

Q. _Why is not this carbonic acid TAKEN UP by the AIR, and DIFFUSED, as it is in cities?_

A. Because (being _heavier than common air_) it cannot _rise from the well or pit_; and no wind can get to it to blow it away.

Q. _Is CARBONIC ACID WHOLESOME?_

A. No; it is _fatal to animal life_, when inhaled through the mouth; acting on the stomach, _as a narcotic poison_ (i. e. a poison which produces death from drowsiness).

Q. _How can any one KNOW, if a place be infested with CARBONIC ACID GAS?_

A. If a pit or well contain carbonic acid, _a candle_ (let down into it) _will be instantly extinguished_. The rule, therefore, is this--Where a _candle will burn, a man can live_; but _what will extinguish a candle_, will _also destroy life_.

Q. _Why does a MINER lower a CANDLE into a mine, before he descends?_

A. Because the _candle will be extinguished_, if the mine contains carbonic acid gas: but if the candle is _not extinguished_, the mine is _safe_, and the man may fearlessly descend.

Q. _Why are PERSONS sometimes KILLED, by leaning over BEER VATS?_

A. Vats (where beer has been made) contain a _large quant.i.ty of carbonic acid gas_, produced by the "vinous fermentation" of the beer; and when a man incautiously _leans over a beer vat_, and inhales the carbonic acid, he is immediately _killed_ thereby.

Q. _Why are PERSONS often KILLED, who enter BEER VATS to clean them?_

A. Carbonic acid (being _heavier than atmospheric air_) often rests upon the _bottom of a vat_: when, therefore, a person enters the vat, and _stoops to clean the bottom_, he inhales the pernicious gas, which _kills_ him.

Q. _Why are the JUNGLES of Jarva and Hindostan so FATAL to life?_