OPERA T10NK

23

ton is met by choosing as the flux a substance of opposite
U> that of the refractory sample. That is, if the latter is
icld nature (as silica and polysilicates) the flux should be
and conversely.
Mlity.—No general statement can be made with regard
relative fusibility of various compounds, as based upon
emloal composition of these compounds. It may be noted
refractory silicates are usually made more readily fusible
ueitip; the ratio of silica to metal oxide through the introduc-
f more metals, particularly of the alkali metals. Both of
mints are made by using alkali metal carbonates as fluxes,
the not. result of the reaction at high temperatures is to
»arhon dioxide and to combine the alkali metal oxide with
Fracitory silicate. This will explain why these carbonates
noKt always chosen as fluxes for silicates. A reaction such
following may occur when orthoclase is fused with sodium
i ate:
iSisO8+f)Na8CO8-*KaSiO8+5NaaSi08+2NaAlO2+6CO2,
n or lean complicated mixture of aluminates and silicates
alkali metals being formed.
ic Fluxes."-—Sodium carbonate, potassium carbonate and
u-potassium carbonate arc the most important of the basic
that are used for analytical purposes. These are used
' for fusion with silica and the refractory silicates. Such
as calcium oxide, used for fluxing silicates in the blast
i€* for iron, are of little use for analytical purposes, partly
*e the resulting compounds aro not soluble and partly
^o metals that arc to bo determined in the sample are
need by the use of such materials.
I Fluxes.- -Fluxes of an acid nature are valuable chiefly
ming fusible, soluble compounds when heated with metallic
or waits that are over-saturated with metallic oxides. The
wsf ul of such fluxes are the pyrosulphates and the biborates
him and potassium.
1 HulphatoH are often used instead of pyrosulphates. When
rmer are heated they give off water arid they are completely
rtcd into pyrosulphates by heating to higher temperatures:
2NaH804-* Na2Sa()7 + H«O.