. 32 QUANTITATIVE AG'RK'WCIfAL J.V.i/.»'/.<
Platinum Substitutes.—The increasing .scarcity of platinum
has made the introduction of substitutes a practical necessity.
While it is true that pure platinum ixxssesses certain prop-
erties that cannot be duplicated by any other metal en-
alloy, yet certain alloys have been found to he suitable for
making into crucibles and dishes that will serve for many
of the operations of the analytical laboratory, in place
of the platinum that has been in use. Two of these will
be mentioned.
"Palau" is a trade name for an alloy containing about SO
per cent gold and 20 per cent palladium. Its melting point IH
about 1370°.
"Rhotanium" is a name given to a series of gold-palladium
alloys whose melting points range front 1150 to l-lalf. Hofh
palau and rhotaniurn may be used in place of platinum exrept.
where much oxidation is to be expected or where very high tem-
peratures are employed.
Unfortunately the manufacturer discourage the IIHI* of thene
substitutes by maintaining the price of manufactured articles .so
close to that of platinum ware that the* purchaser will usually
pay the difference in order to obtain the more satisfactory
platinum.
Burners.—The burner that is to be used by flu* analyst may IN*
anything from the cheapest and simplest burner of the Btmscn
type to the most expensive and complicated burner obtainable.
The purchaser has his choice* and probably certain advantages
are possessed by each burner, The only feature that in really
essential is independent regulation of air ami gas supply. The*
requirements are quite different in different caws and I hi* mmlynt
must have at his disposal all kinds of flume, from f hi* yellow illumi-
nating flame to the most intensely hot and oxidizing flume, and
he requires very small and very large fliiiwH nf iwh Hiuv. In
order to obtain this variety of flame there must I** nome method of
regulating the gas supply without changing the {irfwun* uf the*
gas valve, since this also changes the amount of nir drawn in at
the mixer. The simplest form of Hunwn burner dm** not, fx*rmit
this gas regulation without unscrewing the upper itilw* itml ilmng-
ing the gas jot by the um of pliera, Btieh regulation in w»t fu-
sible in practice.