Q. _Why does ornamental STEEL (of a purple or LILAC colour) rust more readily than polished WHITE steel?_ A. Because the lilac tinge is produced by _partial oxidation_; and the process which forms rust has, therefore, _already_ commenced. Q. _How can lilac STEEL be kept FREE from RUST?_ A. By keeping it in a very _dry place_; for then no additional oxygen will come in contact with it, to increase its amount of rust. Q. _Do any OTHER metals (besides iron) combine rapidly with oxygen?_ A. Yes; copper, lead, mercury, and even silver to some extent. Q. _Why does COPPER TARNISH?_ A. The tarnish of copper is caused by its _oxidation_; that is, the oxygen of the air combines with the surface of the copper, and instead of _rusting it_, covers it with a _dark tarnish_. Q. _Why does LEAD lose its BRIGHTNESS, and become DULL and of a DARKER hue, by being exposed to the air?_ A. The vapour of the air combines with the lead, and _oxidizes its surface_; but instead of becoming _rusty_, the surface becomes _dull_, and of a _darker colour_. Q. _Why is it difficult to keep SILVER BRIGHT?_ A. Because the vapour of the air oxidizes its surface, and _tarnishes_ it. Q. _Why do silver TEA-POTS and SPOONS tarnish more quickly than silver ore or bullion?_ A. Because alloy (of some _baser_ metal) is used to make it more _hard and lasting_; and this _alloy_ oxidizes more quickly than silver itself. Q. _Why does GERMAN silver turn a dingy yellow in a few hours?_ A. German silver has a great affinity for oxygen, and shows its oxidation by a _sickly yellow tarnish_, instead of rust. Q. _If quicksilver (or mercury) is tarnished like copper and lead,--Why does it preserve its BRILLIANCY in BAROMETERS and THERMOMETERS?_ A. Because _air_ is excluded from it, and no moisture comes in contact with it to _oxidize_ (or _tarnish_ it). Q. _Is GOLD affected by the atmosphere?_ A. Not readily: gold will never combine with oxygen of itself, (or without aid). Q. _Which of the METALS is capable of resisting oxidation altogether?_ A. Plat'inum; in consequence of which, the graduated arcs of delicate instruments for observation are made of plat'inum instead of any _other_ metal. Q. _Why is PLAT'INUM used for the graduated arcs of delicate mathematical instruments, instead of any other metal?_ A. Because it will never oxidize; but retain its _bright surface_ in all weathers free from both _rust and tarnish_. Q. _Before plat'inum was discovered, which of the metals was employed for the same purpose?_ A. Gold. Platinum, (a white metal), so called from "plata," the Spanish word for _silver_. It was first introduced into England by Mr. Wood, (A. D. 1749) from South America. Q. _For what other SCIENTIFIC purposes is PLAT'INUM now used?_ A. For crucibles in which _acids_ are employed, and for galvanic batteries. Q. _Why are CRUCIBLES (in which acids are employed) made of PLAT'INUM?_